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Debugging with GDB
******************

This file describes GDB, the GNU symbolic debugger.

This is the Ninth Edition, for GDB (GDB) Version 7.2.

Copyright (C) 1988-2010 Free Software Foundation, Inc.

This edition of the GDB manual is dedicated to the memory of Fred
Fish.  Fred was a long-standing contributor to GDB and to Free software
in general.  We will miss him.

* Summary::                     Summary of GDB
* Sample Session::              A sample GDB session

* Invocation::                  Getting in and out of GDB
* Commands::                    GDB commands
* Running::                     Running programs under GDB
* Stopping::                    Stopping and continuing
* Reverse Execution::           Running programs backward
* Process Record and Replay::   Recording inferior's execution and replaying it
* Stack::                       Examining the stack
* Source::                      Examining source files
* Data::                        Examining data
* Optimized Code::              Debugging optimized code
* Macros::                      Preprocessor Macros
* Tracepoints::                 Debugging remote targets non-intrusively
* Overlays::                    Debugging programs that use overlays

* Languages::                   Using GDB with different languages

* Symbols::                     Examining the symbol table
* Altering::                    Altering execution
* GDB Files::                   GDB files
* Targets::                     Specifying a debugging target
* Remote Debugging::            Debugging remote programs
* Configurations::              Configuration-specific information
* Controlling GDB::             Controlling GDB
* Extending GDB::               Extending GDB
* Interpreters::		Command Interpreters
* TUI::                         GDB Text User Interface
* Emacs::                       Using GDB under GNU Emacs
* GDB/MI::                      GDB's Machine Interface.
* Annotations::                 GDB's annotation interface.
* JIT Interface::               Using the JIT debugging interface.

* GDB Bugs::                    Reporting bugs in GDB

* Command Line Editing: (rluserman).       Command Line Editing
* Using History Interactively: (history).  Using History Interactively
* Formatting Documentation::    How to format and print GDB documentation
* Installing GDB::              Installing GDB
* Maintenance Commands::        Maintenance Commands
* Remote Protocol::             GDB Remote Serial Protocol
* Agent Expressions::           The GDB Agent Expression Mechanism
* Target Descriptions::         How targets can describe themselves to
GDB
* Operating System Information:: Getting additional information from
the operating system
* Trace File Format::		GDB trace file format
* Copying::			GNU General Public License says
how you can copy and share GDB
* GNU Free Documentation License::  The license for this documentation
* Index::                       Index

File: gdb.info,  Node: Summary,  Next: Sample Session,  Prev: Top,  Up: Top

Summary of GDB
**************

The purpose of a debugger such as GDB is to allow you to see what is
going on "inside" another program while it executes--or what another
program was doing at the moment it crashed.

GDB can do four main kinds of things (plus other things in support of
these) to help you catch bugs in the act:

* Start your program, specifying anything that might affect its
behavior.

* Make your program stop on specified conditions.

* Examine what has happened, when your program has stopped.

* Change things in your program, so you can experiment with
correcting the effects of one bug and go on to learn about another.

You can use GDB to debug programs written in C and C++.  For more
information, see *note Supported Languages: Supported Languages.  For
more information, see *note C and C++: C.

Support for D is partial.  For information on D, see *note D: D.

Support for Modula-2 is partial.  For information on Modula-2, see
*note Modula-2: Modula-2.

Debugging Pascal programs which use sets, subranges, file variables,
or nested functions does not currently work.  GDB does not support
entering expressions, printing values, or similar features using Pascal
syntax.

GDB can be used to debug programs written in Fortran, although it
may be necessary to refer to some variables with a trailing underscore.

GDB can be used to debug programs written in Objective-C, using
either the Apple/NeXT or the GNU Objective-C runtime.

* Free Software::               Freely redistributable software
* Contributors::                Contributors to GDB

File: gdb.info,  Node: Free Software,  Next: Contributors,  Up: Summary

Free Software
=============

GDB is "free software", protected by the GNU General Public License
(GPL).  The GPL gives you the freedom to copy or adapt a licensed
program--but every person getting a copy also gets with it the freedom
to modify that copy (which means that they must get access to the
source code), and the freedom to distribute further copies.  Typical
software companies use copyrights to limit your freedoms; the Free
Software Foundation uses the GPL to preserve these freedoms.

Fundamentally, the General Public License is a license which says
that you have these freedoms and that you cannot take these freedoms
away from anyone else.

Free Software Needs Free Documentation
======================================

The biggest deficiency in the free software community today is not in
the software--it is the lack of good free documentation that we can
include with the free software.  Many of our most important programs do
not come with free reference manuals and free introductory texts.
Documentation is an essential part of any software package; when an
important free software package does not come with a free manual and a
free tutorial, that is a major gap.  We have many such gaps today.

Consider Perl, for instance.  The tutorial manuals that people
normally use are non-free.  How did this come about?  Because the
authors of those manuals published them with restrictive terms--no
copying, no modification, source files not available--which exclude
them from the free software world.

That wasn't the first time this sort of thing happened, and it was
far from the last.  Many times we have heard a GNU user eagerly
describe a manual that he is writing, his intended contribution to the
community, only to learn that he had ruined everything by signing a
publication contract to make it non-free.

Free documentation, like free software, is a matter of freedom, not
price.  The problem with the non-free manual is not that publishers
charge a price for printed copies--that in itself is fine.  (The Free
Software Foundation sells printed copies of manuals, too.)  The problem
is the restrictions on the use of the manual.  Free manuals are
available in source code form, and give you permission to copy and
modify.  Non-free manuals do not allow this.

The criteria of freedom for a free manual are roughly the same as for
free software.  Redistribution (including the normal kinds of
commercial redistribution) must be permitted, so that the manual can
accompany every copy of the program, both on-line and on paper.

Permission for modification of the technical content is crucial too.
When people modify the software, adding or changing features, if they
are conscientious they will change the manual too--so they can provide
accurate and clear documentation for the modified program.  A manual
that leaves you no choice but to write a new manual to document a
changed version of the program is not really available to our community.

Some kinds of limits on the way modification is handled are
acceptable.  For example, requirements to preserve the original
author's copyright notice, the distribution terms, or the list of
authors, are ok.  It is also no problem to require modified versions to
include notice that they were modified.  Even entire sections that may
not be deleted or changed are acceptable, as long as they deal with
nontechnical topics (like this one).  These kinds of restrictions are
acceptable because they don't obstruct the community's normal use of
the manual.

However, it must be possible to modify all the _technical_ content
of the manual, and then distribute the result in all the usual media,
through all the usual channels.  Otherwise, the restrictions obstruct
the use of the manual, it is not free, and we need another manual to
replace it.

lose manuals to proprietary publishing.  If we spread the word that
free software needs free reference manuals and free tutorials, perhaps
the next person who wants to contribute by writing documentation will
realize, before it is too late, that only free manuals contribute to
the free software community.

If you are writing documentation, please insist on publishing it
under the GNU Free Documentation License or another free documentation
license.  Remember that this decision requires your approval--you don't
have to let the publisher decide.  Some commercial publishers will use
a free license if you insist, but they will not propose the option; it
is up to you to raise the issue and say firmly that this is what you
want.  If the publisher you are dealing with refuses, please try other
publishers.  If you're not sure whether a proposed license is free,
write to <licensingATgnu.org>.

You can encourage commercial publishers to sell more free, copylefted
manuals and tutorials by buying them, and particularly by buying copies
from the publishers that paid for their writing or for major
improvements.  Meanwhile, try to avoid buying non-free documentation at
all.  Check the distribution terms of a manual before you buy it, and
insist that whoever seeks your business must respect your freedom.
Check the history of the book, and try to reward the publishers that
have paid or pay the authors to work on it.

The Free Software Foundation maintains a list of free documentation
http://www.fsf.org/doc/other-free-books.html'.

File: gdb.info,  Node: Contributors,  Prev: Free Software,  Up: Summary

Contributors to GDB
===================

Richard Stallman was the original author of GDB, and of many other GNU
programs.  Many others have contributed to its development.  This
section attempts to credit major contributors.  One of the virtues of
free software is that everyone is free to contribute to it; with
regret, we cannot actually acknowledge everyone here.  The file
ChangeLog' in the GDB distribution approximates a blow-by-blow account.

Changes much prior to version 2.0 are lost in the mists of time.

_Plea:_ Additions to this section are particularly welcome.  If you
or your friends (or enemies, to be evenhanded) have been unfairly
omitted from this list, we would like to add your names!

So that they may not regard their many labors as thankless, we
particularly thank those who shepherded GDB through major releases:
Andrew Cagney (releases 6.3, 6.2, 6.1, 6.0, 5.3, 5.2, 5.1 and 5.0); Jim
Blandy (release 4.18); Jason Molenda (release 4.17); Stan Shebs
(release 4.14); Fred Fish (releases 4.16, 4.15, 4.13, 4.12, 4.11, 4.10,
and 4.9); Stu Grossman and John Gilmore (releases 4.8, 4.7, 4.6, 4.5,
and 4.4); John Gilmore (releases 4.3, 4.2, 4.1, 4.0, and 3.9); Jim
Kingdon (releases 3.5, 3.4, and 3.3); and Randy Smith (releases 3.2,
3.1, and 3.0).

Richard Stallman, assisted at various times by Peter TerMaat, Chris
Hanson, and Richard Mlynarik, handled releases through 2.8.

Michael Tiemann is the author of most of the GNU C++ support in GDB,
with significant additional contributions from Per Bothner and Daniel
Berlin.  James Clark wrote the GNU C++ demangler.  Early work on C++
was by Peter TerMaat (who also did much general update work leading to
release 3.0).

GDB uses the BFD subroutine library to examine multiple object-file
formats; BFD was a joint project of David V.  Henkel-Wallace, Rich
Pixley, Steve Chamberlain, and John Gilmore.

David Johnson wrote the original COFF support; Pace Willison did the
original support for encapsulated COFF.

Brent Benson of Harris Computer Systems contributed DWARF 2 support.

Adam de Boor and Bradley Davis contributed the ISI Optimum V support.
Per Bothner, Noboyuki Hikichi, and Alessandro Forin contributed MIPS
support.  Jean-Daniel Fekete contributed Sun 386i support.  Chris
Hanson improved the HP9000 support.  Noboyuki Hikichi and Tomoyuki
Hasei contributed Sony/News OS 3 support.  David Johnson contributed
Encore Umax support.  Jyrki Kuoppala contributed Altos 3068 support.
Jeff Law contributed HP PA and SOM support.  Keith Packard contributed
NS32K support.  Doug Rabson contributed Acorn Risc Machine support.
Bob Rusk contributed Harris Nighthawk CX-UX support.  Chris Smith
contributed Convex support (and Fortran debugging).  Jonathan Stone
contributed Pyramid support.  Michael Tiemann contributed SPARC support.
Tim Tucker contributed support for the Gould NP1 and Gould Powernode.
Pace Willison contributed Intel 386 support.  Jay Vosburgh contributed
Symmetry support.  Marko Mlinar contributed OpenRISC 1000 support.

Andreas Schwab contributed M68K GNU/Linux support.

Rich Schaefer and Peter Schauer helped with support of SunOS shared
libraries.

Jay Fenlason and Roland McGrath ensured that GDB and GAS agree about
several machine instruction sets.

Patrick Duval, Ted Goldstein, Vikram Koka and Glenn Engel helped
develop remote debugging.  Intel Corporation, Wind River Systems, AMD,
and ARM contributed remote debugging modules for the i960, VxWorks,
A29K UDI, and RDI targets, respectively.

Brian Fox is the author of the readline libraries providing
command-line editing and command history.

Andrew Beers of SUNY Buffalo wrote the language-switching code, the
Modula-2 support, and contributed the Languages chapter of this manual.

Fred Fish wrote most of the support for Unix System Vr4.  He also
enhanced the command-completion support to cover C++ overloaded symbols.

Hitachi America (now Renesas America), Ltd. sponsored the support for
H8/300, H8/500, and Super-H processors.

NEC sponsored the support for the v850, Vr4xxx, and Vr5xxx
processors.

Mitsubishi (now Renesas) sponsored the support for D10V, D30V, and
M32R/D processors.

Toshiba sponsored the support for the TX39 Mips processor.

Matsushita sponsored the support for the MN10200 and MN10300
processors.

Fujitsu sponsored the support for SPARClite and FR30 processors.

Kung Hsu, Jeff Law, and Rick Sladkey added support for hardware
watchpoints.

Michael Snyder added support for tracepoints.

Stu Grossman wrote gdbserver.

Jim Kingdon, Peter Schauer, Ian Taylor, and Stu Grossman made nearly
innumerable bug fixes and cleanups throughout GDB.

The following people at the Hewlett-Packard Company contributed
support for the PA-RISC 2.0 architecture, HP-UX 10.20, 10.30, and 11.0
(narrow mode), HP's implementation of kernel threads, HP's aC++
compiler, and the Text User Interface (nee Terminal User Interface):
Ben Krepp, Richard Title, John Bishop, Susan Macchia, Kathy Mann,
Satish Pai, India Paul, Steve Rehrauer, and Elena Zannoni.  Kim Haase
provided HP-specific information in this manual.

DJ Delorie ported GDB to MS-DOS, for the DJGPP project.  Robert
Hoehne made significant contributions to the DJGPP port.

Cygnus Solutions has sponsored GDB maintenance and much of its
development since 1991.  Cygnus engineers who have worked on GDB
fulltime include Mark Alexander, Jim Blandy, Per Bothner, Kevin
Buettner, Edith Epstein, Chris Faylor, Fred Fish, Martin Hunt, Jim
Ingham, John Gilmore, Stu Grossman, Kung Hsu, Jim Kingdon, John Metzler,
Fernando Nasser, Geoffrey Noer, Dawn Perchik, Rich Pixley, Zdenek
Radouch, Keith Seitz, Stan Shebs, David Taylor, and Elena Zannoni.  In
addition, Dave Brolley, Ian Carmichael, Steve Chamberlain, Nick Clifton,
JT Conklin, Stan Cox, DJ Delorie, Ulrich Drepper, Frank Eigler, Doug
Evans, Sean Fagan, David Henkel-Wallace, Richard Henderson, Jeff
Holcomb, Jeff Law, Jim Lemke, Tom Lord, Bob Manson, Michael Meissner,
Jason Merrill, Catherine Moore, Drew Moseley, Ken Raeburn, Gavin
Romig-Koch, Rob Savoye, Jamie Smith, Mike Stump, Ian Taylor, Angela
Thomas, Michael Tiemann, Tom Tromey, Ron Unrau, Jim Wilson, and David
Zuhn have made contributions both large and small.

Andrew Cagney, Fernando Nasser, and Elena Zannoni, while working for
Cygnus Solutions, implemented the original GDB/MI interface.

Jim Blandy added support for preprocessor macros, while working for
Red Hat.

Andrew Cagney designed GDB's architecture vector.  Many people
including Andrew Cagney, Stephane Carrez, Randolph Chung, Nick Duffek,
Richard Henderson, Mark Kettenis, Grace Sainsbury, Kei Sakamoto,
Yoshinori Sato, Michael Snyder, Andreas Schwab, Jason Thorpe, Corinna
Vinschen, Ulrich Weigand, and Elena Zannoni, helped with the migration
of old architectures to this new framework.

Andrew Cagney completely re-designed and re-implemented GDB's
unwinder framework, this consisting of a fresh new design featuring
frame IDs, independent frame sniffers, and the sentinel frame.  Mark
Kettenis implemented the DWARF 2 unwinder, Jeff Johnston the libunwind
unwinder, and Andrew Cagney the dummy, sentinel, tramp, and trad
unwinders.  The architecture-specific changes, each involving a
complete rewrite of the architecture's frame code, were carried out by
Jim Blandy, Joel Brobecker, Kevin Buettner, Andrew Cagney, Stephane
Carrez, Randolph Chung, Orjan Friberg, Richard Henderson, Daniel
Jacobowitz, Jeff Johnston, Mark Kettenis, Theodore A. Roth, Kei
Sakamoto, Yoshinori Sato, Michael Snyder, Corinna Vinschen, and Ulrich
Weigand.

Christian Zankel, Ross Morley, Bob Wilson, and Maxim Grigoriev from
Tensilica, Inc. contributed support for Xtensa processors.  Others who
have worked on the Xtensa port of GDB in the past include Steve Tjiang,
John Newlin, and Scott Foehner.

Michael Eager and staff of Xilinx, Inc., contributed support for the
Xilinx MicroBlaze architecture.

File: gdb.info,  Node: Sample Session,  Next: Invocation,  Prev: Summary,  Up: Top

1 A Sample GDB Session
**********************

You can use this manual at your leisure to read all about GDB.
However, a handful of commands are enough to get started using the
debugger.  This chapter illustrates those commands.

One of the preliminary versions of GNU m4' (a generic macro
processor) exhibits the following bug: sometimes, when we change its
quote strings from the default, the commands used to capture one macro
definition within another stop working.  In the following short m4'
session, we define a macro foo' which expands to 0000'; we then use
the m4' built-in defn' to define bar' as the same thing.  However,
when we change the open quote string to <QUOTE>' and the close quote
string to <UNQUOTE>', the same procedure fails to define a new synonym
baz':

$cd gnu/m4$ ./m4
define(foo,0000)

foo
0000
define(bar,defn(foo'))

bar
0000
changequote(<QUOTE>,<UNQUOTE>)

define(baz,defn(<QUOTE>foo<UNQUOTE>))
baz
Ctrl-d
m4: End of input: 0: fatal error: EOF in string

Let us use GDB to try to see what is going on.

$gdb m4 GDB is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for GDB; type "show warranty" for details. GDB 7.2, Copyright 1999 Free Software Foundation, Inc... (gdb) GDB reads only enough symbol data to know where to find the rest when needed; as a result, the first prompt comes up very quickly. We now tell GDB to use a narrower display width than usual, so that examples fit in this manual. (gdb) set width 70 We need to see how the m4' built-in changequote' works. Having looked at the source, we know the relevant subroutine is m4_changequote', so we set a breakpoint there with the GDB break' command. (gdb) break m4_changequote Breakpoint 1 at 0x62f4: file builtin.c, line 879. Using the run' command, we start m4' running under GDB control; as long as control does not reach the m4_changequote' subroutine, the program runs as usual: (gdb) run Starting program: /work/Editorial/gdb/gnu/m4/m4 define(foo,0000) foo 0000 To trigger the breakpoint, we call changequote'. GDB suspends execution of m4', displaying information about the context where it stops. changequote(<QUOTE>,<UNQUOTE>) Breakpoint 1, m4_changequote (argc=3, argv=0x33c70) at builtin.c:879 879 if (bad_argc(TOKEN_DATA_TEXT(argv[0]),argc,1,3)) Now we use the command n' (next') to advance execution to the next line of the current function. (gdb) n 882 set_quotes((argc >= 2) ? TOKEN_DATA_TEXT(argv[1])\ : nil, set_quotes' looks like a promising subroutine. We can go into it by using the command s' (step') instead of next'. step' goes to the next line to be executed in _any_ subroutine, so it steps into set_quotes'. (gdb) s set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 530 if (lquote != def_lquote) The display that shows the subroutine where m4' is now suspended (and its arguments) is called a stack frame display. It shows a summary of the stack. We can use the backtrace' command (which can also be spelled bt'), to see where we are in the stack as a whole: the backtrace' command displays a stack frame for each active subroutine. (gdb) bt #0 set_quotes (lq=0x34c78 "<QUOTE>", rq=0x34c88 "<UNQUOTE>") at input.c:530 #1 0x6344 in m4_changequote (argc=3, argv=0x33c70) at builtin.c:882 #2 0x8174 in expand_macro (sym=0x33320) at macro.c:242 #3 0x7a88 in expand_token (obs=0x0, t=209696, td=0xf7fffa30) at macro.c:71 #4 0x79dc in expand_input () at macro.c:40 #5 0x2930 in main (argc=0, argv=0xf7fffb20) at m4.c:195 We step through a few more lines to see what happens. The first two times, we can use s'; the next two times we use n' to avoid falling into the xstrdup' subroutine. (gdb) s 0x3b5c 532 if (rquote != def_rquote) (gdb) s 0x3b80 535 lquote = (lq == nil || *lq == '\0') ? \ def_lquote : xstrdup(lq); (gdb) n 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup(rq); (gdb) n 538 len_lquote = strlen(rquote); The last line displayed looks a little odd; we can examine the variables lquote' and rquote' to see if they are in fact the new left and right quotes we specified. We use the command p' (print') to see their values. (gdb) p lquote$1 = 0x35d40 "<QUOTE>"
(gdb) p rquote
$2 = 0x35d50 "<UNQUOTE>" lquote' and rquote' are indeed the new left and right quotes. To look at some context, we can display ten lines of source surrounding the current line with the l' (list') command. (gdb) l 533 xfree(rquote); 534 535 lquote = (lq == nil || *lq == '\0') ? def_lquote\ : xstrdup (lq); 536 rquote = (rq == nil || *rq == '\0') ? def_rquote\ : xstrdup (rq); 537 538 len_lquote = strlen(rquote); 539 len_rquote = strlen(lquote); 540 } 541 542 void Let us step past the two lines that set len_lquote' and len_rquote', and then examine the values of those variables. (gdb) n 539 len_rquote = strlen(lquote); (gdb) n 540 } (gdb) p len_lquote$3 = 9
(gdb) p len_rquote
$4 = 7 That certainly looks wrong, assuming len_lquote' and len_rquote' are meant to be the lengths of lquote' and rquote' respectively. We can set them to better values using the p' command, since it can print the value of any expression--and that expression can include subroutine calls and assignments. (gdb) p len_lquote=strlen(lquote)$5 = 7
(gdb) p len_rquote=strlen(rquote)
$6 = 9 Is that enough to fix the problem of using the new quotes with the m4' built-in defn'? We can allow m4' to continue executing with the c' (continue') command, and then try the example that caused trouble initially: (gdb) c Continuing. define(baz,defn(<QUOTE>foo<UNQUOTE>)) baz 0000 Success! The new quotes now work just as well as the default ones. The problem seems to have been just the two typos defining the wrong lengths. We allow m4' exit by giving it an EOF as input: Ctrl-d Program exited normally. The message Program exited normally.' is from GDB; it indicates m4' has finished executing. We can end our GDB session with the GDB quit' command. (gdb) quit File: gdb.info, Node: Invocation, Next: Commands, Prev: Sample Session, Up: Top 2 Getting In and Out of GDB *************************** This chapter discusses how to start GDB, and how to get out of it. The essentials are: * type gdb' to start GDB. * type quit' or Ctrl-d' to exit. * Menu: * Invoking GDB:: How to start GDB * Quitting GDB:: How to quit GDB * Shell Commands:: How to use shell commands inside GDB * Logging Output:: How to log GDB's output to a file File: gdb.info, Node: Invoking GDB, Next: Quitting GDB, Up: Invocation 2.1 Invoking GDB ================ Invoke GDB by running the program gdb'. Once started, GDB reads commands from the terminal until you tell it to exit. You can also run gdb' with a variety of arguments and options, to specify more of your debugging environment at the outset. The command-line options described here are designed to cover a variety of situations; in some environments, some of these options may effectively be unavailable. The most usual way to start GDB is with one argument, specifying an executable program: gdb PROGRAM You can also start with both an executable program and a core file specified: gdb PROGRAM CORE You can, instead, specify a process ID as a second argument, if you want to debug a running process: gdb PROGRAM 1234 would attach GDB to process 1234' (unless you also have a file named 1234'; GDB does check for a core file first). Taking advantage of the second command-line argument requires a fairly complete operating system; when you use GDB as a remote debugger attached to a bare board, there may not be any notion of "process", and there is often no way to get a core dump. GDB will warn you if it is unable to attach or to read core dumps. You can optionally have gdb' pass any arguments after the executable file to the inferior using --args'. This option stops option processing. gdb --args gcc -O2 -c foo.c This will cause gdb' to debug gcc', and to set gcc''s command-line arguments (*note Arguments::) to -O2 -c foo.c'. You can run gdb' without printing the front material, which describes GDB's non-warranty, by specifying -silent': gdb -silent You can further control how GDB starts up by using command-line options. GDB itself can remind you of the options available. Type gdb -help to display all available options and briefly describe their use (gdb -h' is a shorter equivalent). All options and command line arguments you give are processed in sequential order. The order makes a difference when the -x' option is used. * Menu: * File Options:: Choosing files * Mode Options:: Choosing modes * Startup:: What GDB does during startup File: gdb.info, Node: File Options, Next: Mode Options, Up: Invoking GDB 2.1.1 Choosing Files -------------------- When GDB starts, it reads any arguments other than options as specifying an executable file and core file (or process ID). This is the same as if the arguments were specified by the -se' and -c' (or -p') options respectively. (GDB reads the first argument that does not have an associated option flag as equivalent to the -se' option followed by that argument; and the second argument that does not have an associated option flag, if any, as equivalent to the -c'/-p' option followed by that argument.) If the second argument begins with a decimal digit, GDB will first attempt to attach to it as a process, and if that fails, attempt to open it as a corefile. If you have a corefile whose name begins with a digit, you can prevent GDB from treating it as a pid by prefixing it with ./', e.g. ./12345'. If GDB has not been configured to included core file support, such as for most embedded targets, then it will complain about a second argument and ignore it. Many options have both long and short forms; both are shown in the following list. GDB also recognizes the long forms if you truncate them, so long as enough of the option is present to be unambiguous. (If you prefer, you can flag option arguments with --' rather than -', though we illustrate the more usual convention.) -symbols FILE' -s FILE' Read symbol table from file FILE. -exec FILE' -e FILE' Use file FILE as the executable file to execute when appropriate, and for examining pure data in conjunction with a core dump. -se FILE' Read symbol table from file FILE and use it as the executable file. -core FILE' -c FILE' Use file FILE as a core dump to examine. -pid NUMBER' -p NUMBER' Connect to process ID NUMBER, as with the attach' command. -command FILE' -x FILE' Execute commands from file FILE. The contents of this file is evaluated exactly as the source' command would. *Note Command files: Command Files. -eval-command COMMAND' -ex COMMAND' Execute a single GDB command. This option may be used multiple times to call multiple commands. It may also be interleaved with -command' as required. gdb -ex 'target sim' -ex 'load' \ -x setbreakpoints -ex 'run' a.out -init-command FILE' -ix FILE' Execute commands from file FILE before loading the inferior (but after loading gdbinit files). *Note Startup::. -init-eval-command COMMAND' -iex COMMAND' Execute a single GDB command before loading the inferior (but after loading gdbinit files). *Note Startup::. -directory DIRECTORY' -d DIRECTORY' Add DIRECTORY to the path to search for source and script files. -r' -readnow' Read each symbol file's entire symbol table immediately, rather than the default, which is to read it incrementally as it is needed. This makes startup slower, but makes future operations faster. --readnever' Do not read each symbol file's symbolic debug information. This makes startup faster but at the expense of not being able to perform symbolic debugging. File: gdb.info, Node: Mode Options, Next: Startup, Prev: File Options, Up: Invoking GDB 2.1.2 Choosing Modes -------------------- You can run GDB in various alternative modes--for example, in batch mode or quiet mode. -nx' -n' Do not execute commands found in any initialization files. Normally, GDB executes the commands in these files after all the command options and arguments have been processed. *Note Command Files: Command Files. -quiet' -silent' -q' "Quiet". Do not print the introductory and copyright messages. These messages are also suppressed in batch mode. -batch' Run in batch mode. Exit with status 0' after processing all the command files specified with -x' (and all commands from initialization files, if not inhibited with -n'). Exit with nonzero status if an error occurs in executing the GDB commands in the command files. Batch mode also disables pagination, sets unlimited terminal width and height *note Screen Size::, and acts as if set confirm off' were in effect (*note Messages/Warnings::). Batch mode may be useful for running GDB as a filter, for example to download and run a program on another computer; in order to make this more useful, the message Program exited normally. (which is ordinarily issued whenever a program running under GDB control terminates) is not issued when running in batch mode. -batch-silent' Run in batch mode exactly like -batch', but totally silently. All GDB output to stdout' is prevented (stderr' is unaffected). This is much quieter than -silent' and would be useless for an interactive session. This is particularly useful when using targets that give Loading section' messages, for example. Note that targets that give their output via GDB, as opposed to writing directly to stdout', will also be made silent. -return-child-result' The return code from GDB will be the return code from the child process (the process being debugged), with the following exceptions: * GDB exits abnormally. E.g., due to an incorrect argument or an internal error. In this case the exit code is the same as it would have been without -return-child-result'. * The user quits with an explicit value. E.g., quit 1'. * The child process never runs, or is not allowed to terminate, in which case the exit code will be -1. This option is useful in conjunction with -batch' or -batch-silent', when GDB is being used as a remote program loader or simulator interface. -nowindows' -nw' "No windows". If GDB comes with a graphical user interface (GUI) built in, then this option tells GDB to only use the command-line interface. If no GUI is available, this option has no effect. -windows' -w' If GDB includes a GUI, then this option requires it to be used if possible. -cd DIRECTORY' Run GDB using DIRECTORY as its working directory, instead of the current directory. -fullname' -f' GNU Emacs sets this option when it runs GDB as a subprocess. It tells GDB to output the full file name and line number in a standard, recognizable fashion each time a stack frame is displayed (which includes each time your program stops). This recognizable format looks like two \032' characters, followed by the file name, line number and character position separated by colons, and a newline. The Emacs-to-GDB interface program uses the two \032' characters as a signal to display the source code for the frame. -epoch' The Epoch Emacs-GDB interface sets this option when it runs GDB as a subprocess. It tells GDB to modify its print routines so as to allow Epoch to display values of expressions in a separate window. -annotate LEVEL' This option sets the "annotation level" inside GDB. Its effect is identical to using set annotate LEVEL' (*note Annotations::). The annotation LEVEL controls how much information GDB prints together with its prompt, values of expressions, source lines, and other types of output. Level 0 is the normal, level 1 is for use when GDB is run as a subprocess of GNU Emacs, level 3 is the maximum annotation suitable for programs that control GDB, and level 2 has been deprecated. The annotation mechanism has largely been superseded by GDB/MI (*note GDB/MI::). --args' Change interpretation of command line so that arguments following the executable file are passed as command line arguments to the inferior. This option stops option processing. -baud BPS' -b BPS' Set the line speed (baud rate or bits per second) of any serial interface used by GDB for remote debugging. -l TIMEOUT' Set the timeout (in seconds) of any communication used by GDB for remote debugging. -tty DEVICE' -t DEVICE' Run using DEVICE for your program's standard input and output. -P' --python' Change interpretation of command line so that the argument immediately following this switch is taken to be the name of a Python script file. This option stops option processing; subsequent options are passed to Python as sys.argv'. This option is only available if Python scripting support was enabled when GDB was configured. -tui' Activate the "Text User Interface" when starting. The Text User Interface manages several text windows on the terminal, showing source, assembly, registers and GDB command outputs (*note GDB Text User Interface: TUI.). Alternatively, the Text User Interface can be enabled by invoking the program gdbtui'. Do not use this option if you run GDB from Emacs (*note Using GDB under GNU Emacs: Emacs.). -interpreter INTERP' Use the interpreter INTERP for interface with the controlling program or device. This option is meant to be set by programs which communicate with GDB using it as a back end. *Note Command Interpreters: Interpreters. --interpreter=mi' (or --interpreter=mi2') causes GDB to use the "GDB/MI interface" (*note The GDB/MI Interface: GDB/MI.) included since GDB version 6.0. The previous GDB/MI interface, included in GDB version 5.3 and selected with --interpreter=mi1', is deprecated. Earlier GDB/MI interfaces are no longer supported. -write' Open the executable and core files for both reading and writing. This is equivalent to the set write on' command inside GDB (*note Patching::). -statistics' This option causes GDB to print statistics about time and memory usage after it completes each command and returns to the prompt. -version' This option causes GDB to print its version number and no-warranty blurb, and exit. File: gdb.info, Node: Startup, Prev: Mode Options, Up: Invoking GDB 2.1.3 What GDB Does During Startup ---------------------------------- Here's the description of what GDB does during session startup: 1. Sets up the command interpreter as specified by the command line (*note interpreter: Mode Options.). 2. Reads the system-wide "init file" (if --with-system-gdbinit' was used when building GDB; *note System-wide configuration and settings: System-wide configuration.) and executes all the commands in that file. 3. Reads the init file (if any) in your home directory(1) and executes all the commands in that file. 4. Executes commands and command files specified by the -iex' and -ix' options in their specified order. Usually you should use the -ex' and -x' options instead, but this way you can apply settings before GDB init files get executed and before inferior gets loaded. 5. Processes command line options and operands. 6. Reads and executes the commands from init file (if any) in the current working directory as long as set auto-load local-gdbinit' is set to on' (*note Init File in the Current Directory::). This is only done if the current directory is different from your home directory. Thus, you can have more than one init file, one generic in your home directory, and another, specific to the program you are debugging, in the directory where you invoke GDB. 7. If the command line specified a program to debug, or a process to attach to, or a core file, GDB loads any auto-loaded scripts provided for the program or for its loaded shared libraries. *Note Auto-loading::. If you wish to disable the auto-loading during startup, you must do something like the following:$ gdb -iex "set auto-load python-scripts off" myprogram

Option -ex' does not work because the auto-loading is then turned
off too late.

8. Reads command files specified by the -x' option.  *Note Command
Files::, for more details about GDB command files.

9. Reads the command history recorded in the "history file".  *Note
Command History::, for more details about the command history and
the files where GDB records it.

Init files use the same syntax as "command files" (*note Command
Files::) and are processed by GDB in the same way.  The init file in
your home directory can set options (such as set complaints') that
affect subsequent processing of command line options and operands.
Init files are not executed if you use the -nx' option (*note Choosing
Modes: Mode Options.).

To display the list of init files loaded by gdb at startup, you can
use gdb --help'.

The GDB init files are normally called .gdbinit'.  The DJGPP port
of GDB uses the name gdb.ini', due to the limitations of file names
imposed by DOS filesystems.  The Windows ports of GDB use the standard
name, but if they find a gdb.ini' file, they warn you about that and
suggest to rename the file to the standard name.

---------- Footnotes ----------

(1) On DOS/Windows systems, the home directory is the one pointed to
by the HOME' environment variable.

File: gdb.info,  Node: Quitting GDB,  Next: Shell Commands,  Prev: Invoking GDB,  Up: Invocation

2.2 Quitting GDB
================

quit [EXPRESSION]'
q'
To exit GDB, use the quit' command (abbreviated q'), or type an
end-of-file character (usually Ctrl-d').  If you do not supply
EXPRESSION, GDB will terminate normally; otherwise it will
terminate using the result of EXPRESSION as the error code.

An interrupt (often Ctrl-c') does not exit from GDB, but rather
terminates the action of any GDB command that is in progress and
returns to GDB command level.  It is safe to type the interrupt
character at any time because GDB does not allow it to take effect
until a time when it is safe.

If you have been using GDB to control an attached process or device,
you can release it with the detach' command (*note Debugging an

File: gdb.info,  Node: Shell Commands,  Next: Logging Output,  Prev: Quitting GDB,  Up: Invocation

2.3 Shell Commands
==================

If you need to execute occasional shell commands during your debugging
session, there is no need to leave or suspend GDB; you can just use the
shell' command.

shell COMMAND STRING'
Invoke a standard shell to execute COMMAND STRING.  If it exists,
the environment variable SHELL' determines which shell to run.
Otherwise GDB uses the default shell (/bin/sh' on Unix systems,
COMMAND.COM' on MS-DOS, etc.).

The utility make' is often needed in development environments.  You
do not have to use the shell' command for this purpose in GDB:

make MAKE-ARGS'
Execute the make' program with the specified arguments.  This is
equivalent to shell make MAKE-ARGS'.

File: gdb.info,  Node: Logging Output,  Prev: Shell Commands,  Up: Invocation

2.4 Logging Output
==================

You may want to save the output of GDB commands to a file.  There are
several commands to control GDB's logging.

set logging on'
Enable logging.

set logging off'
Disable logging.

set logging file FILE'
Change the name of the current logfile.  The default logfile is
gdb.txt'.

set logging overwrite [on|off]'
By default, GDB will append to the logfile.  Set overwrite' if
you want set logging on' to overwrite the logfile instead.

set logging redirect [on|off]'
By default, GDB output will go to both the terminal and the
logfile.  Set redirect' if you want output to go only to the log
file.

show logging'
Show the current values of the logging settings.

File: gdb.info,  Node: Commands,  Next: Running,  Prev: Invocation,  Up: Top

3 GDB Commands
**************

You can abbreviate a GDB command to the first few letters of the command
name, if that abbreviation is unambiguous; and you can repeat certain
GDB commands by typing just <RET>.  You can also use the <TAB> key to
get GDB to fill out the rest of a word in a command (or to show you the
alternatives available, if there is more than one possibility).

* Command Syntax::              How to give commands to GDB
* Completion::                  Command completion
* Help::                        How to ask GDB for help

File: gdb.info,  Node: Command Syntax,  Next: Completion,  Up: Commands

3.1 Command Syntax
==================

A GDB command is a single line of input.  There is no limit on how long
it can be.  It starts with a command name, which is followed by
arguments whose meaning depends on the command name.  For example, the
command step' accepts an argument which is the number of times to
step, as in step 5'.  You can also use the step' command with no
arguments.  Some commands do not allow any arguments.

GDB command names may always be truncated if that abbreviation is
unambiguous.  Other possible command abbreviations are listed in the
documentation for individual commands.  In some cases, even ambiguous
abbreviations are allowed; for example, s' is specially defined as
equivalent to step' even though there are other commands whose names
start with s'.  You can test abbreviations by using them as arguments
to the help' command.

A blank line as input to GDB (typing just <RET>) means to repeat the
previous command.  Certain commands (for example, run') will not
repeat this way; these are commands whose unintentional repetition
might cause trouble and which you are unlikely to want to repeat.
User-defined commands can disable this feature; see *note dont-repeat:
Define.

The list' and x' commands, when you repeat them with <RET>,
construct new arguments rather than repeating exactly as typed.  This
permits easy scanning of source or memory.

GDB can also use <RET> in another way: to partition lengthy output,
in a way similar to the common utility more' (*note Screen Size:
Screen Size.).  Since it is easy to press one <RET> too many in this
situation, GDB disables command repetition after any command that
generates this sort of display.

Any text from a #' to the end of the line is a comment; it does
nothing.  This is useful mainly in command files (*note Command Files:
Command Files.).

The Ctrl-o' binding is useful for repeating a complex sequence of
commands.  This command accepts the current line, like <RET>, and then
fetches the next line relative to the current line from the history for
editing.

File: gdb.info,  Node: Completion,  Next: Help,  Prev: Command Syntax,  Up: Commands

3.2 Command Completion
======================

GDB can fill in the rest of a word in a command for you, if there is
only one possibility; it can also show you what the valid possibilities
are for the next word in a command, at any time.  This works for GDB
commands, GDB subcommands, and the names of symbols in your program.

Press the <TAB> key whenever you want GDB to fill out the rest of a
word.  If there is only one possibility, GDB fills in the word, and
waits for you to finish the command (or press <RET> to enter it).  For
example, if you type

(gdb) info bre <TAB>

GDB fills in the rest of the word breakpoints', since that is the only
info' subcommand beginning with bre':

(gdb) info breakpoints

You can either press <RET> at this point, to run the info breakpoints'
command, or backspace and enter something else, if breakpoints' does
not look like the command you expected.  (If you were sure you wanted
info breakpoints' in the first place, you might as well just type
<RET> immediately after info bre', to exploit command abbreviations
rather than command completion).

If there is more than one possibility for the next word when you
press <TAB>, GDB sounds a bell.  You can either supply more characters
and try again, or just press <TAB> a second time; GDB displays all the
possible completions for that word.  For example, you might want to set
a breakpoint on a subroutine whose name begins with make_', but when
you type b make_<TAB>' GDB just sounds the bell.  Typing <TAB> again
displays all the function names in your program that begin with those
characters, for example:

(gdb) b make_ <TAB>
GDB sounds bell; press <TAB> again, to see:
make_a_section_from_file     make_environ
make_abs_section             make_function_type
make_blockvector             make_pointer_type
make_cleanup                 make_reference_type
make_command                 make_symbol_completion_list
(gdb) b make_

After displaying the available possibilities, GDB copies your partial
input (b make_' in the example) so you can finish the command.

If you just want to see the list of alternatives in the first place,
you can press M-?' rather than pressing <TAB> twice.  M-?' means
<META> ?'.  You can type this either by holding down a key designated
as the <META> shift on your keyboard (if there is one) while typing
?', or as <ESC> followed by ?'.

Sometimes the string you need, while logically a "word", may contain
parentheses or other characters that GDB normally excludes from its
notion of a word.  To permit word completion to work in this situation,
you may enclose words in '' (single quote marks) in GDB commands.

The most likely situation where you might need this is in typing the
name of a C++ function.  This is because C++ allows function
overloading (multiple definitions of the same function, distinguished
by argument type).  For example, when you want to set a breakpoint you
may need to distinguish whether you mean the version of name' that
takes an int' parameter, name(int)', or the version that takes a
float' parameter, name(float)'.  To use the word-completion
facilities in this situation, type a single quote '' at the beginning
of the function name.  This alerts GDB that it may need to consider
more information than usual when you press <TAB> or M-?' to request
word completion:

(gdb) b 'bubble( M-?
bubble(double,double)    bubble(int,int)
(gdb) b 'bubble(

In some cases, GDB can tell that completing a name requires using
quotes.  When this happens, GDB inserts the quote for you (while
completing as much as it can) if you do not type the quote in the first
place:

(gdb) b bub <TAB>
GDB alters your input line to the following, and rings a bell:
(gdb) b 'bubble(

In general, GDB can tell that a quote is needed (and inserts it) if you
have not yet started typing the argument list when you ask for
completion on an overloaded symbol.

Expressions: C Plus Plus Expressions.  You can use the command set
overload-resolution off' to disable overload resolution; see *note GDB
Features for C++: Debugging C Plus Plus.

When completing in an expression which looks up a field in a
structure, GDB also tries(1) to limit completions to the field names
available in the type of the left-hand-side:

(gdb) p gdb_stdout.M-?
magic      to_delete  to_fputs   to_put     to_rewind
to_data    to_flush   to_isatty  to_read    to_write

This is because the gdb_stdout' is a variable of the type struct
ui_file' that is defined in GDB sources as follows:

struct ui_file
{
int *magic;
ui_file_flush_ftype *to_flush;
ui_file_write_ftype *to_write;
ui_file_fputs_ftype *to_fputs;
ui_file_delete_ftype *to_delete;
ui_file_isatty_ftype *to_isatty;
ui_file_rewind_ftype *to_rewind;
ui_file_put_ftype *to_put;
void *to_data;
}

---------- Footnotes ----------

(1) The completer can be confused by certain kinds of invalid
expressions.  Also, it only examines the static type of the expression,
not the dynamic type.

File: gdb.info,  Node: Help,  Prev: Completion,  Up: Commands

3.3 Getting Help
================

You can always ask GDB itself for information on its commands, using
the command help'.

help'
h'
You can use help' (abbreviated h') with no arguments to display
a short list of named classes of commands:

(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without
stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of
commands in that class.
Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

help CLASS'
Using one of the general help classes as an argument, you can get a
list of the individual commands in that class.  For example, here
is the help display for the class status':

(gdb) help status
Status inquiries.

List of commands:

info -- Generic command for showing things
about the program being debugged
show -- Generic command for showing things

Type "help" followed by command name for full
documentation.
Command name abbreviations are allowed if unambiguous.
(gdb)

help COMMAND'
With a command name as help' argument, GDB displays a short
paragraph on how to use that command.

apropos ARGS'
The apropos' command searches through all of the GDB commands,
and their documentation, for the regular expression specified in
ARGS.  It prints out all matches found.  For example:

results in:

multiple times in one run
multiple times in one run

complete ARGS'
The complete ARGS' command lists all the possible completions for
the beginning of a command.  Use ARGS to specify the beginning of
the command you want completed.  For example:

complete i

results in:

if
ignore
info
inspect

This is intended for use by GNU Emacs.

In addition to help', you can use the GDB commands info' and
show' to inquire about the state of your program, or the state of GDB
itself.  Each command supports many topics of inquiry; this manual
introduces each of them in the appropriate context.  The listings under
info' and under show' in the Index point to all the sub-commands.
*Note Index::.

info'
This command (abbreviated i') is for describing the state of your
program.  For example, you can show the arguments passed to a
function with info args', list the registers currently in use
with info registers', or list the breakpoints you have set with
info breakpoints'.  You can get a complete list of the info'
sub-commands with help info'.

set'
You can assign the result of an expression to an environment
variable with set'.  For example, you can set the GDB prompt to a
$-sign with set prompt$'.

show'
In contrast to info', show' is for describing the state of GDB
itself.  You can change most of the things you can show', by
using the related command set'; for example, you can control what
number system is used for displays with set radix', or simply
inquire which is currently in use with show radix'.

To display all the settable parameters and their current values,
you can use show' with no arguments; you may also use info set'.
Both commands produce the same display.

Here are three miscellaneous show' subcommands, all of which are
exceptional in lacking corresponding set' commands:

show version'
Show what version of GDB is running.  You should include this
information in GDB bug-reports.  If multiple versions of GDB are
in use at your site, you may need to determine which version of
GDB you are running; as GDB evolves, new commands are introduced,
and old ones may wither away.  Also, many system vendors ship
variant versions of GDB, and there are variant versions of GDB in
GNU/Linux distributions as well.  The version number is the same
as the one announced when you start GDB.

show copying'
info copying'
Display information about permission for copying GDB.

show warranty'
info warranty'
Display the GNU "NO WARRANTY" statement, or a warranty, if your
version of GDB comes with one.

File: gdb.info,  Node: Running,  Next: Stopping,  Prev: Commands,  Up: Top

4 Running Programs Under GDB
****************************

When you run a program under GDB, you must first generate debugging
information when you compile it.

You may start GDB with its arguments, if any, in an environment of
your choice.  If you are doing native debugging, you may redirect your
program's input and output, debug an already running process, or kill a
child process.

* Compilation::                 Compiling for debugging
* Starting::                    Starting your program
* Arguments::                   Your program's arguments
* Environment::                 Your program's environment

* Working Directory::           Your program's working directory
* Input/Output::                Your program's input and output
* Attach::                      Debugging an already-running process
* Kill Process::                Killing the child process

* Inferiors and Programs::      Debugging multiple inferiors and programs
* Threads::                     Debugging programs with multiple threads
* Forks::                       Debugging forks
* Checkpoint/Restart::          Setting a _bookmark_ to return to later

File: gdb.info,  Node: Compilation,  Next: Starting,  Up: Running

4.1 Compiling for Debugging
===========================

In order to debug a program effectively, you need to generate debugging
information when you compile it.  This debugging information is stored
in the object file; it describes the data type of each variable or
function and the correspondence between source line numbers and
addresses in the executable code.

To request debugging information, specify the -g' option when you
run the compiler.

Programs that are to be shipped to your customers are compiled with
optimizations, using the -O' compiler option.  However, some compilers
are unable to handle the -g' and -O' options together.  Using those
compilers, you cannot generate optimized executables containing
debugging information.

GCC, the GNU C/C++ compiler, supports -g' with or without -O',
making it possible to debug optimized code.  We recommend that you
_always_ use -g' whenever you compile a program.  You may think your
program is correct, but there is no sense in pushing your luck.  For

Older versions of the GNU C compiler permitted a variant option
-gg' for debugging information.  GDB no longer supports this format;
if your GNU C compiler has this option, do not use it.

GDB knows about preprocessor macros and can show you their expansion
(*note Macros::).  Most compilers do not include information about
preprocessor macros in the debugging information if you specify the
-g' flag alone, because this information is rather large.  Version 3.1
and later of GCC, the GNU C compiler, provides macro information if you
specify the options -gdwarf-2' and -g3'; the former option requests
debugging information in the Dwarf 2 format, and the latter requests
"extra information".  In the future, we hope to find more compact ways
to represent macro information, so that it can be included with -g'
alone.

File: gdb.info,  Node: Starting,  Next: Arguments,  Prev: Compilation,  Up: Running

4.2 Starting your Program
=========================

run'
r'
Use the run' command to start your program under GDB.  You must
first specify the program name (except on VxWorks) with an
argument to GDB (*note Getting In and Out of GDB: Invocation.), or
by using the file' or exec-file' command (*note Commands to
Specify Files: Files.).

If you are running your program in an execution environment that
supports processes, run' creates an inferior process and makes that
process run your program.  In some environments without processes,
run' jumps to the start of your program.  Other targets, like
remote', are always running.  If you get an error message like this
one:

The "remote" target does not support "run".
Try "help target" or "continue".

then use continue' to run your program.  You may need load' first

The execution of a program is affected by certain information it
receives from its superior.  GDB provides ways to specify this
information, which you must do _before_ starting your program.  (You
can change it after starting your program, but such changes only affect
your program the next time you start it.)  This information may be
divided into four categories:

The _arguments._
Specify the arguments to give your program as the arguments of the
run' command.  If a shell is available on your target, the shell
is used to pass the arguments, so that you may use normal
conventions (such as wildcard expansion or variable substitution)
in describing the arguments.  In Unix systems, you can control
which shell is used with the SHELL' environment variable.  *Note
Your Program's Arguments: Arguments.

The _environment._
Your program normally inherits its environment from GDB, but you
can use the GDB commands set environment' and unset environment'
to change parts of the environment that affect your program.
*Note Your Program's Environment: Environment.

The _working directory._
Your program inherits its working directory from GDB.  You can set
the GDB working directory with the cd' command in GDB.  *Note
Your Program's Working Directory: Working Directory.

The _standard input and output._
Your program normally uses the same device for standard input and
standard output as GDB is using.  You can redirect input and output
in the run' command line, or you can use the tty' command to set
a different device for your program.  *Note Your Program's Input
and Output: Input/Output.

_Warning:_ While input and output redirection work, you cannot use
pipes to pass the output of the program you are debugging to
another program; if you attempt this, GDB is likely to wind up
debugging the wrong program.

When you issue the run' command, your program begins to execute
immediately.  *Note Stopping and Continuing: Stopping, for discussion
of how to arrange for your program to stop.  Once your program has
stopped, you may call functions in your program, using the print' or
call' commands.  *Note Examining Data: Data.

If the modification time of your symbol file has changed since the
last time GDB read its symbols, GDB discards its symbol table, and
reads it again.  When it does this, GDB tries to retain your current
breakpoints.

start'
The name of the main procedure can vary from language to language.
With C or C++, the main procedure name is always main', but other
languages such as Ada do not require a specific name for their
main procedure.  The debugger provides a convenient way to start
the execution of the program and to stop at the beginning of the
main procedure, depending on the language used.

The start' command does the equivalent of setting a temporary
breakpoint at the beginning of the main procedure and then invoking
the run' command.

Some programs contain an "elaboration" phase where some startup
code is executed before the main procedure is called.  This
depends on the languages used to write your program.  In C++, for
instance, constructors for static and global objects are executed
before main' is called.  It is therefore possible that the
debugger stops before reaching the main procedure.  However, the
temporary breakpoint will remain to halt execution.

Specify the arguments to give to your program as arguments to the
start' command.  These arguments will be given verbatim to the
underlying run' command.  Note that the same arguments will be
reused if no argument is provided during subsequent calls to
start' or run'.

It is sometimes necessary to debug the program during elaboration.
In these cases, using the start' command would stop the execution
of your program too late, as the program would have already
completed the elaboration phase.  Under these circumstances,
insert breakpoints in your elaboration code before running your
program.

set exec-wrapper WRAPPER'
show exec-wrapper'
unset exec-wrapper'
When exec-wrapper' is set, the specified wrapper is used to
launch programs for debugging.  GDB starts your program with a
shell command of the form exec WRAPPER PROGRAM'.  Quoting is
added to PROGRAM and its arguments, but not to WRAPPER, so you
should add quotes if appropriate for your shell.  The wrapper runs
until it executes your program, and then GDB takes control.

You can use any program that eventually calls execve' with its
arguments as a wrapper.  Several standard Unix utilities do this,
e.g. env' and nohup'.  Any Unix shell script ending with exec
"$@"' will also work. For example, you can use env' to pass an environment variable to the debugged program, without setting the variable in your shell's environment: (gdb) set exec-wrapper env 'LD_PRELOAD=libtest.so' (gdb) run This command is available when debugging locally on most targets, excluding DJGPP, Cygwin, MS Windows, and QNX Neutrino. set disable-randomization' set disable-randomization on' This option (enabled by default in GDB) will turn off the native randomization of the virtual address space of the started program. This option is useful for multiple debugging sessions to make the execution better reproducible and memory addresses reusable across debugging sessions. This feature is implemented only on GNU/Linux. You can get the same behavior using (gdb) set exec-wrapper setarch uname -m -R set disable-randomization off' Leave the behavior of the started executable unchanged. Some bugs rear their ugly heads only when the program is loaded at certain addresses. If your bug disappears when you run the program under GDB, that might be because GDB by default disables the address randomization on platforms, such as GNU/Linux, which do that for stand-alone programs. Use set disable-randomization off' to try to reproduce such elusive bugs. The virtual address space randomization is implemented only on GNU/Linux. It protects the programs against some kinds of security attacks. In these cases the attacker needs to know the exact location of a concrete executable code. Randomizing its location makes it impossible to inject jumps misusing a code at its expected addresses. Prelinking shared libraries provides a startup performance advantage but it makes addresses in these libraries predictable for privileged processes by having just unprivileged access at the target system. Reading the shared library binary gives enough information for assembling the malicious code misusing it. Still even a prelinked shared library can get loaded at a new random address just requiring the regular relocation process during the startup. Shared libraries not already prelinked are always loaded at a randomly chosen address. Position independent executables (PIE) contain position independent code similar to the shared libraries and therefore such executables get loaded at a randomly chosen address upon startup. PIE executables always load even already prelinked shared libraries at a random address. You can build such executable using gcc -fPIE -pie'. Heap (malloc storage), stack and custom mmap areas are always placed randomly (as long as the randomization is enabled). show disable-randomization' Show the current setting of the explicit disable of the native randomization of the virtual address space of the started program. File: gdb.info, Node: Arguments, Next: Environment, Prev: Starting, Up: Running 4.3 Your Program's Arguments ============================ The arguments to your program can be specified by the arguments of the run' command. They are passed to a shell, which expands wildcard characters and performs redirection of I/O, and thence to your program. Your SHELL' environment variable (if it exists) specifies what shell GDB uses. If you do not define SHELL', GDB uses the default shell (/bin/sh' on Unix). On non-Unix systems, the program is usually invoked directly by GDB, which emulates I/O redirection via the appropriate system calls, and the wildcard characters are expanded by the startup code of the program, not by the shell. run' with no arguments uses the same arguments used by the previous run', or those set by the set args' command. set args' Specify the arguments to be used the next time your program is run. If set args' has no arguments, run' executes your program with no arguments. Once you have run your program with arguments, using set args' before the next run' is the only way to run it again without arguments. show args' Show the arguments to give your program when it is started. File: gdb.info, Node: Environment, Next: Working Directory, Prev: Arguments, Up: Running 4.4 Your Program's Environment ============================== The "environment" consists of a set of environment variables and their values. Environment variables conventionally record such things as your user name, your home directory, your terminal type, and your search path for programs to run. Usually you set up environment variables with the shell and they are inherited by all the other programs you run. When debugging, it can be useful to try running your program with a modified environment without having to start GDB over again. path DIRECTORY' Add DIRECTORY to the front of the PATH' environment variable (the search path for executables) that will be passed to your program. The value of PATH' used by GDB does not change. You may specify several directory names, separated by whitespace or by a system-dependent separator character (:' on Unix, ;' on MS-DOS and MS-Windows). If DIRECTORY is already in the path, it is moved to the front, so it is searched sooner. You can use the string $cwd' to refer to whatever is the current
working directory at the time GDB searches the path.  If you use
.' instead, it refers to the directory where you executed the
path' command.  GDB replaces .' in the DIRECTORY argument (with
the current path) before adding DIRECTORY to the search path.

show paths'
Display the list of search paths for executables (the PATH'
environment variable).

show environment [VARNAME]'
Print the value of environment variable VARNAME to be given to
your program when it starts.  If you do not supply VARNAME, print
the names and values of all environment variables to be given to
your program.  You can abbreviate environment' as env'.

set environment VARNAME [=VALUE]'
Set environment variable VARNAME to VALUE.  The value changes for
your program only, not for GDB itself.  VALUE may be any string;
the values of environment variables are just strings, and any
interpretation is supplied by your program itself.  The VALUE
parameter is optional; if it is eliminated, the variable is set to
a null value.

For example, this command:

set env USER = foo

tells the debugged program, when subsequently run, that its user
is named foo'.  (The spaces around =' are used for clarity here;
they are not actually required.)

unset environment VARNAME'
Remove variable VARNAME from the environment to be passed to your
program.  This is different from set env VARNAME ='; unset
environment' removes the variable from the environment, rather
than assigning it an empty value.

_Warning:_ On Unix systems, GDB runs your program using the shell
indicated by your SHELL' environment variable if it exists (or
/bin/sh' if not).  If your SHELL' variable names a shell that runs an
initialization file--such as .cshrc' for C-shell, or .bashrc' for
BASH--any variables you set in that file affect your program.  You may
wish to move setting of environment variables to files that are only
run when you sign on, such as .login' or .profile'.

File: gdb.info,  Node: Working Directory,  Next: Input/Output,  Prev: Environment,  Up: Running

4.5 Your Program's Working Directory
====================================

Each time you start your program with run', it inherits its working
directory from the current working directory of GDB.  The GDB working
directory is initially whatever it inherited from its parent process
(typically the shell), but you can specify a new working directory in
GDB with the cd' command.

The GDB working directory also serves as a default for the commands
that specify files for GDB to operate on.  *Note Commands to Specify
Files: Files.

cd DIRECTORY'
Set the GDB working directory to DIRECTORY.

pwd'
Print the GDB working directory.

It is generally impossible to find the current working directory of
the process being debugged (since a program can change its directory
during its run).  If you work on a system where GDB is configured with
the /proc' support, you can use the info proc' command (*note SVR4
Process Information::) to find out the current working directory of the
debuggee.

File: gdb.info,  Node: Input/Output,  Next: Attach,  Prev: Working Directory,  Up: Running

4.6 Your Program's Input and Output
===================================

By default, the program you run under GDB does input and output to the
same terminal that GDB uses.  GDB switches the terminal to its own
terminal modes to interact with you, but it records the terminal modes
your program was using and switches back to them when you continue

info terminal'
Displays information recorded by GDB about the terminal modes your
program is using.

You can redirect your program's input and/or output using shell
redirection with the run' command.  For example,

run > outfile

starts your program, diverting its output to the file outfile'.

Another way to specify where your program should do input and output
is with the tty' command.  This command accepts a file name as
argument, and causes this file to be the default for future run'
commands.  It also resets the controlling terminal for the child
process, for future run' commands.  For example,

tty /dev/ttyb

directs that processes started with subsequent run' commands default
to do input and output on the terminal /dev/ttyb' and have that as
their controlling terminal.

An explicit redirection in run' overrides the tty' command's
effect on the input/output device, but not its effect on the controlling
terminal.

When you use the tty' command or redirect input in the run'
command, only the input _for your program_ is affected.  The input for
GDB still comes from your terminal.  tty' is an alias for set
inferior-tty'.

You can use the show inferior-tty' command to tell GDB to display
the name of the terminal that will be used for future runs of your
program.

set inferior-tty /dev/ttyb'
Set the tty for the program being debugged to /dev/ttyb.

show inferior-tty'
Show the current tty for the program being debugged.

File: gdb.info,  Node: Attach,  Next: Kill Process,  Prev: Input/Output,  Up: Running

4.7 Debugging an Already-running Process
========================================

attach PROCESS-ID'
This command attaches to a running process--one that was started
outside GDB.  (info files' shows your active targets.)  The
command takes as argument a process ID.  The usual way to find out
the PROCESS-ID of a Unix process is with the ps' utility, or with
the jobs -l' shell command.

attach' does not repeat if you press <RET> a second time after
executing the command.

To use attach', your program must be running in an environment
which supports processes; for example, attach' does not work for
programs on bare-board targets that lack an operating system.  You must
also have permission to send the process a signal.

When you use attach', the debugger finds the program running in the
process first by looking in the current working directory, then (if the
program is not found) by using the source file search path (*note
Specifying Source Directories: Source Path.).  You can also use the
file' command to load the program.  *Note Commands to Specify Files:
Files.

The first thing GDB does after arranging to debug the specified
process is to stop it.  You can examine and modify an attached process
with all the GDB commands that are ordinarily available when you start
processes with run'.  You can insert breakpoints; you can step and
continue; you can modify storage.  If you would rather the process
continue running, you may use the continue' command after attaching
GDB to the process.

detach'
When you have finished debugging the attached process, you can use
the detach' command to release it from GDB control.  Detaching
the process continues its execution.  After the detach' command,
that process and GDB become completely independent once more, and
you are ready to attach' another process or start one with run'.
detach' does not repeat if you press <RET> again after executing
the command.

If you exit GDB while you have an attached process, you detach that
process.  If you use the run' command, you kill that process.  By
default, GDB asks for confirmation if you try to do either of these
things; you can control whether or not you need to confirm by using the
set confirm' command (*note Optional Warnings and Messages:
Messages/Warnings.).

File: gdb.info,  Node: Kill Process,  Next: Inferiors and Programs,  Prev: Attach,  Up: Running

4.8 Killing the Child Process
=============================

kill'
Kill the child process in which your program is running under GDB.

This command is useful if you wish to debug a core dump instead of a
running process.  GDB ignores any core dump file while your program is
running.

On some operating systems, a program cannot be executed outside GDB
while you have breakpoints set on it inside GDB.  You can use the
kill' command in this situation to permit running your program outside
the debugger.

The kill' command is also useful if you wish to recompile and
relink your program, since on many systems it is impossible to modify an
executable file while it is running in a process.  In this case, when
you next type run', GDB notices that the file has changed, and reads
the symbol table again (while trying to preserve your current
breakpoint settings).

File: gdb.info,  Node: Inferiors and Programs,  Next: Threads,  Prev: Kill Process,  Up: Running

4.9 Debugging Multiple Inferiors and Programs
=============================================

GDB lets you run and debug multiple programs in a single session.  In
addition, GDB on some systems may let you run several programs
simultaneously (otherwise you have to exit from one before starting
another).  In the most general case, you can have multiple threads of
execution in each of multiple processes, launched from multiple
executables.

GDB represents the state of each program execution with an object
called an "inferior".  An inferior typically corresponds to a process,
but is more general and applies also to targets that do not have
processes.  Inferiors may be created before a process runs, and may be
retained after a process exits.  Inferiors have unique identifiers that
are different from process ids.  Usually each inferior will also have
its own distinct address space, although some embedded targets may have
several inferiors running in different parts of a single address space.
Each inferior may in turn have multiple threads running in it.

To find out what inferiors exist at any moment, use info inferiors':

info inferiors'
Print a list of all inferiors currently being managed by GDB.

GDB displays for each inferior (in this order):

1. the inferior number assigned by GDB

2. the target system's inferior identifier

3. the name of the executable the inferior is running.

An asterisk *' preceding the GDB inferior number indicates the
current inferior.

For example,

(gdb) info inferiors
Num  Description       Executable
2    process 2307      hello
* 1    process 3401      goodbye

To switch focus between inferiors, use the inferior' command:

inferior INFNO'
Make inferior number INFNO the current inferior.  The argument
INFNO is the inferior number assigned by GDB, as shown in the
first field of the info inferiors' display.

You can get multiple executables into a debugging session via the
add-inferior' and clone-inferior' commands.  On some systems GDB can
add inferiors to the debug session automatically by following calls to
fork' and exec'.  To remove inferiors from the debugging session use
the remove-inferior' command.

add-inferior [ -copies N ] [ -exec EXECUTABLE ]'
Adds N inferiors to be run using EXECUTABLE as the executable.  N
defaults to 1.  If no executable is specified, the inferiors
begins empty, with no program.  You can still assign or change the
program assigned to the inferior at any time by using the file'
command with the executable name as its argument.

clone-inferior [ -copies N ] [ INFNO ]'
Adds N inferiors ready to execute the same program as inferior
INFNO.  N defaults to 1.  INFNO defaults to the number of the
current inferior.  This is a convenient command when you want to
run another instance of the inferior you are debugging.

(gdb) info inferiors
Num  Description       Executable
* 1    process 29964     helloworld
(gdb) clone-inferior
(gdb) info inferiors
Num  Description       Executable
2    <null>            helloworld
* 1    process 29964     helloworld

You can now simply switch focus to inferior 2 and run it.

remove-inferior INFNO'
Removes the inferior INFNO.  It is not possible to remove an
inferior that is running with this command.  For those, use the
kill' or detach' command first.

To quit debugging one of the running inferiors that is not the
current inferior, you can either detach from it by using the
detach inferior' command (allowing it to run independently), or kill it
using the kill inferior' command:

detach inferior INFNO'
Detach from the inferior identified by GDB inferior number INFNO.
Note that the inferior's entry still stays on the list of
inferiors shown by info inferiors', but its Description will show
<null>'.

kill inferior INFNO'
Kill the inferior identified by GDB inferior number INFNO.  Note
that the inferior's entry still stays on the list of inferiors
shown by info inferiors', but its Description will show <null>'.

After the successful completion of a command such as detach',
detach inferior', kill' or kill inferior', or after a normal process
exit, the inferior is still valid and listed with info inferiors',
ready to be restarted.

To be notified when inferiors are started or exit under GDB's
control use set print inferior-events':

set print inferior-events'
set print inferior-events on'
set print inferior-events off'
The set print inferior-events' command allows you to enable or
disable printing of messages when GDB notices that new inferiors
have started or that inferiors have exited or have been detached.
By default, these messages will not be printed.

show print inferior-events'
Show whether messages will be printed when GDB detects that
inferiors have started, exited or have been detached.

Many commands will work the same with multiple programs as with a
single program: e.g., print myglobal' will simply display the value of
myglobal' in the current inferior.

Occasionaly, when debugging GDB itself, it may be useful to get more
info about the relationship of inferiors, programs, address spaces in a
debug session.  You can do that with the maint info program-spaces'
command.

maint info program-spaces'
Print a list of all program spaces currently being managed by GDB.

GDB displays for each program space (in this order):

1. the program space number assigned by GDB

2. the name of the executable loaded into the program space,
with e.g., the file' command.

An asterisk *' preceding the GDB program space number indicates
the current program space.

In addition, below each program space line, GDB prints extra
information that isn't suitable to display in tabular form.  For
example, the list of inferiors bound to the program space.

(gdb) maint info program-spaces
Id   Executable
2    goodbye
Bound inferiors: ID 1 (process 21561)
* 1    hello

Here we can see that no inferior is running the program hello',
while process 21561' is running the program goodbye'.  On some
targets, it is possible that multiple inferiors are bound to the
same program space.  The most common example is that of debugging
both the parent and child processes of a vfork' call.  For
example,

(gdb) maint info program-spaces
Id   Executable
* 1    vfork-test
Bound inferiors: ID 2 (process 18050), ID 1 (process 18045)

Here, both inferior 2 and inferior 1 are running in the same
program space as a result of inferior 1 having executed a vfork'
call.

File: gdb.info,  Node: Threads,  Next: Forks,  Prev: Inferiors and Programs,  Up: Running

4.10 Debugging Programs with Multiple Threads
=============================================

In some operating systems, such as HP-UX and Solaris, a single program
may have more than one "thread" of execution.  The precise semantics of
threads differ from one operating system to another, but in general the
threads of a single program are akin to multiple processes--except that
they share one address space (that is, they can all examine and modify
the same variables).  On the other hand, each thread has its own
registers and execution stack, and perhaps private memory.

GDB provides these facilities for debugging multi-thread programs:

* thread THREADNO', a command to switch among threads

* info threads', a command to inquire about existing threads

* thread apply [THREADNO] [ALL] ARGS', a command to apply a command
to a list of threads

* set print thread-events', which controls printing of messages on
thread start and exit.

* set libthread-db-search-path PATH', which lets the user specify
which libthread_db' to use if the default choice isn't compatible
with the program.

_Warning:_ These facilities are not yet available on every GDB
configuration where the operating system supports threads.  If
your GDB does not support threads, these commands have no effect.
For example, a system without thread support shows no output from
info threads', and always rejects the thread' command, like this:

Thread ID 1 not known.  Use the "info threads" command to
see the IDs of currently known threads.

The GDB thread debugging facility allows you to observe all threads
while your program runs--but whenever GDB takes control, one thread in
particular is always the focus of debugging.  This thread is called the
"current thread".  Debugging commands show program information from the
perspective of the current thread.

Whenever GDB detects a new thread in your program, it displays the
target system's identification for the thread with a message in the
form [New SYSTAG]'.  SYSTAG is a thread identifier whose form varies
depending on the particular system.  For example, on GNU/Linux, you
might see

[New Thread 46912507313328 (LWP 25582)]

when GDB notices a new thread.  In contrast, on an SGI system, the
SYSTAG is simply something like process 368', with no further
qualifier.

For debugging purposes, GDB associates its own thread number--always
a single integer--with each thread in your program.

info threads'
Display a summary of all threads currently in your program.  GDB
displays for each thread (in this order):

1. the thread number assigned by GDB

2. the target system's thread identifier (SYSTAG)

3. the current stack frame summary for that thread

An asterisk *' to the left of the GDB thread number indicates the

For example,

3 process 35 thread 27  0x34e5 in sigpause ()
2 process 35 thread 23  0x34e5 in sigpause ()
* 1 process 35 thread 13  main (argc=1, argv=0x7ffffff8)

On HP-UX systems:

For debugging purposes, GDB associates its own thread number--a
small integer assigned in thread-creation order--with each thread in

Whenever GDB detects a new thread in your program, it displays both
GDB's thread number and the target system's identification for the
thread with a message in the form [New SYSTAG]'.  SYSTAG is a thread
identifier whose form varies depending on the particular system.  For
example, on HP-UX, you see

when GDB notices a new thread.

Display a summary of all threads currently in your program.  GDB
displays for each thread (in this order):

1. the thread number assigned by GDB

2. the target system's thread identifier (SYSTAG)

3. the current stack frame summary for that thread

An asterisk *' to the left of the GDB thread number indicates the

For example,

* 3 system thread 26607  worker (wptr=0x7b09c318 "@") \

at quicksort.c:137
2 system thread 26606  0x7b0030d8 in __ksleep () \

from /usr/lib/libc.2
1 system thread 27905  0x7b003498 in _brk () \

from /usr/lib/libc.2

a Solaris-specific command:

Display info on Solaris user threads.

thread THREADNO'
argument THREADNO is the internal GDB thread number, as shown in
the first field of the info threads' display.  GDB responds by
displaying the system identifier of the thread you selected, and
its current stack frame summary:

[Switching to process 35 thread 23]
0x34e5 in sigpause ()

As with the [New ...]' message, the form of the text after
Switching to' depends on your system's conventions for identifying

The debugger convenience variable $_thread' contains the number of the current thread. You may find this useful in writing breakpoint conditional expressions, command scripts, and so forth. See *Note Convenience Variables: Convenience Vars, for general information on convenience variables. thread apply [THREADNO] [ALL] COMMAND' The thread apply' command allows you to apply the named COMMAND to one or more threads. Specify the numbers of the threads that you want affected with the command argument THREADNO. It can be a single thread number, one of the numbers shown in the first field of the info threads' display; or it could be a range of thread numbers, as in 2-4'. To apply a command to all threads, type thread apply all COMMAND'. set print thread-events' set print thread-events on' set print thread-events off' The set print thread-events' command allows you to enable or disable printing of messages when GDB notices that new threads have started or that threads have exited. By default, these messages will be printed if detection of these events is supported by the target. Note that these messages cannot be disabled on all targets. show print thread-events' Show whether messages will be printed when GDB detects that threads have started and exited. *Note Stopping and Starting Multi-thread Programs: Thread Stops, for more information about how GDB behaves when you stop and start programs with multiple threads. *Note Setting Watchpoints: Set Watchpoints, for information about watchpoints in programs with multiple threads. set libthread-db-search-path [PATH]' If this variable is set, PATH is a colon-separated list of directories GDB will use to search for libthread_db'. If you omit PATH, libthread-db-search-path' will be reset to an empty list. On GNU/Linux and Solaris systems, GDB uses a "helper" libthread_db' library to obtain information about threads in the inferior process. GDB will use libthread-db-search-path' to find libthread_db'. If that fails, GDB will continue with default system shared library directories, and finally the directory from which libpthread' was loaded in the inferior process. GDB also consults first if inferior specific thread debugging library loading is enabled by set auto-load libthread-db' (*note libthread_db.so.1 file::). The default system shared library directory is the only kind not needing to be enabled by set auto-load libthread-db' (*note libthread_db.so.1 file::). For any libthread_db' library GDB finds in above directories, GDB attempts to initialize it with the current inferior process. If this initialization fails (which could happen because of a version mismatch between libthread_db' and libpthread'), GDB will unload libthread_db', and continue with the next directory. If none of libthread_db' libraries initialize successfully, GDB will issue a warning and thread debugging will be disabled. Setting libthread-db-search-path' is currently implemented only on some platforms. show libthread-db-search-path' Display current libthread_db search path. File: gdb.info, Node: Forks, Next: Checkpoint/Restart, Prev: Threads, Up: Running 4.11 Debugging Forks ==================== On most systems, GDB has no special support for debugging programs which create additional processes using the fork' function. When a program forks, GDB will continue to debug the parent process and the child process will run unimpeded. If you have set a breakpoint in any code which the child then executes, the child will get a SIGTRAP' signal which (unless it catches the signal) will cause it to terminate. However, if you want to debug the child process there is a workaround which isn't too painful. Put a call to sleep' in the code which the child process executes after the fork. It may be useful to sleep only if a certain environment variable is set, or a certain file exists, so that the delay need not occur when you don't want to run GDB on the child. While the child is sleeping, use the ps' program to get its process ID. Then tell GDB (a new invocation of GDB if you are also debugging the parent process) to attach to the child process (*note Attach::). From that point on you can debug the child process just like any other process which you attached to. On some systems, GDB provides support for debugging programs that create additional processes using the fork' or vfork' functions. Currently, the only platforms with this feature are HP-UX (11.x and later only?) and GNU/Linux (kernel version 2.5.60 and later). By default, when a program forks, GDB will continue to debug the parent process and the child process will run unimpeded. If you want to follow the child process instead of the parent process, use the command set follow-fork-mode'. set follow-fork-mode MODE' Set the debugger response to a program call of fork' or vfork'. A call to fork' or vfork' creates a new process. The MODE argument can be: parent' The original process is debugged after a fork. The child process runs unimpeded. This is the default. child' The new process is debugged after a fork. The parent process runs unimpeded. show follow-fork-mode' Display the current debugger response to a fork' or vfork' call. On Linux, if you want to debug both the parent and child processes, use the command set detach-on-fork'. set detach-on-fork MODE' Tells gdb whether to detach one of the processes after a fork, or retain debugger control over them both. on' The child process (or parent process, depending on the value of follow-fork-mode') will be detached and allowed to run independently. This is the default. off' Both processes will be held under the control of GDB. One process (child or parent, depending on the value of follow-fork-mode') is debugged as usual, while the other is held suspended. show detach-on-fork' Show whether detach-on-fork mode is on/off. If you choose to set detach-on-fork' mode off, then GDB will retain control of all forked processes (including nested forks). You can list the forked processes under the control of GDB by using the info inferiors' command, and switch from one fork to another by using the inferior' command (*note Debugging Multiple Inferiors and Programs: Inferiors and Programs.). To quit debugging one of the forked processes, you can either detach from it by using the detach inferior' command (allowing it to run independently), or kill it using the kill inferior' command. *Note Debugging Multiple Inferiors and Programs: Inferiors and Programs. If you ask to debug a child process and a vfork' is followed by an exec', GDB executes the new target up to the first breakpoint in the new target. If you have a breakpoint set on main' in your original program, the breakpoint will also be set on the child process's main'. On some systems, when a child process is spawned by vfork', you cannot debug the child or parent until an exec' call completes. If you issue a run' command to GDB after an exec' call executes, the new target restarts. To restart the parent process, use the file' command with the parent executable name as its argument. By default, after an exec' call executes, GDB discards the symbols of the previous executable image. You can change this behaviour with the set follow-exec-mode' command. set follow-exec-mode MODE' Set debugger response to a program call of exec'. An exec' call replaces the program image of a process. follow-exec-mode' can be: new' GDB creates a new inferior and rebinds the process to this new inferior. The program the process was running before the exec' call can be restarted afterwards by restarting the original inferior. For example: (gdb) info inferiors (gdb) info inferior Id Description Executable * 1 <null> prog1 (gdb) run process 12020 is executing new program: prog2 Program exited normally. (gdb) info inferiors Id Description Executable * 2 <null> prog2 1 <null> prog1 same' GDB keeps the process bound to the same inferior. The new executable image replaces the previous executable loaded in the inferior. Restarting the inferior after the exec' call, with e.g., the run' command, restarts the executable the process was running after the exec' call. This is the default mode. For example: (gdb) info inferiors Id Description Executable * 1 <null> prog1 (gdb) run process 12020 is executing new program: prog2 Program exited normally. (gdb) info inferiors Id Description Executable * 1 <null> prog2 You can use the catch' command to make GDB stop whenever a fork', vfork', or exec' call is made. *Note Setting Catchpoints: Set Catchpoints. File: gdb.info, Node: Checkpoint/Restart, Prev: Forks, Up: Running 4.12 Setting a _Bookmark_ to Return to Later ============================================ On certain operating systems(1), GDB is able to save a "snapshot" of a program's state, called a "checkpoint", and come back to it later. Returning to a checkpoint effectively undoes everything that has happened in the program since the checkpoint' was saved. This includes changes in memory, registers, and even (within some limits) system state. Effectively, it is like going back in time to the moment when the checkpoint was saved. Thus, if you're stepping thru a program and you think you're getting close to the point where things go wrong, you can save a checkpoint. Then, if you accidentally go too far and miss the critical statement, instead of having to restart your program from the beginning, you can just go back to the checkpoint and start again from there. This can be especially useful if it takes a lot of time or steps to reach the point where you think the bug occurs. To use the checkpoint'/restart' method of debugging: checkpoint' Save a snapshot of the debugged program's current execution state. The checkpoint' command takes no arguments, but each checkpoint is assigned a small integer id, similar to a breakpoint id. info checkpoints' List the checkpoints that have been saved in the current debugging session. For each checkpoint, the following information will be listed: Checkpoint ID' Process ID' Code Address' Source line, or label' restart CHECKPOINT-ID' Restore the program state that was saved as checkpoint number CHECKPOINT-ID. All program variables, registers, stack frames etc. will be returned to the values that they had when the checkpoint was saved. In essence, gdb will "wind back the clock" to the point in time when the checkpoint was saved. Note that breakpoints, GDB variables, command history etc. are not affected by restoring a checkpoint. In general, a checkpoint only restores things that reside in the program being debugged, not in the debugger. delete checkpoint CHECKPOINT-ID' Delete the previously-saved checkpoint identified by CHECKPOINT-ID. Returning to a previously saved checkpoint will restore the user state of the program being debugged, plus a significant subset of the system (OS) state, including file pointers. It won't "un-write" data from a file, but it will rewind the file pointer to the previous location, so that the previously written data can be overwritten. For files opened in read mode, the pointer will also be restored so that the previously read data can be read again. Of course, characters that have been sent to a printer (or other external device) cannot be "snatched back", and characters received from eg. a serial device can be removed from internal program buffers, but they cannot be "pushed back" into the serial pipeline, ready to be received again. Similarly, the actual contents of files that have been changed cannot be restored (at this time). However, within those constraints, you actually can "rewind" your program to a previously saved point in time, and begin debugging it again -- and you can change the course of events so as to debug a different execution path this time. Finally, there is one bit of internal program state that will be different when you return to a checkpoint -- the program's process id. Each checkpoint will have a unique process id (or PID), and each will be different from the program's original PID. If your program has saved a local copy of its process id, this could potentially pose a problem. 4.12.1 A Non-obvious Benefit of Using Checkpoints ------------------------------------------------- On some systems such as GNU/Linux, address space randomization is performed on new processes for security reasons. This makes it difficult or impossible to set a breakpoint, or watchpoint, on an absolute address if you have to restart the program, since the absolute location of a symbol will change from one execution to the next. A checkpoint, however, is an _identical_ copy of a process. Therefore if you create a checkpoint at (eg.) the start of main, and simply return to that checkpoint instead of restarting the process, you can avoid the effects of address randomization and your symbols will all stay in the same place. ---------- Footnotes ---------- (1) Currently, only GNU/Linux. File: gdb.info, Node: Stopping, Next: Reverse Execution, Prev: Running, Up: Top 5 Stopping and Continuing ************************* The principal purposes of using a debugger are so that you can stop your program before it terminates; or so that, if your program runs into trouble, you can investigate and find out why. Inside GDB, your program may stop for any of several reasons, such as a signal, a breakpoint, or reaching a new line after a GDB command such as step'. You may then examine and change variables, set new breakpoints or remove old ones, and then continue execution. Usually, the messages shown by GDB provide ample explanation of the status of your program--but you can also explicitly request this information at any time. info program' Display information about the status of your program: whether it is running or not, what process it is, and why it stopped. * Menu: * Breakpoints:: Breakpoints, watchpoints, and catchpoints * Continuing and Stepping:: Resuming execution * Signals:: Signals * Thread Stops:: Stopping and starting multi-thread programs File: gdb.info, Node: Breakpoints, Next: Continuing and Stepping, Up: Stopping 5.1 Breakpoints, Watchpoints, and Catchpoints ============================================= A "breakpoint" makes your program stop whenever a certain point in the program is reached. For each breakpoint, you can add conditions to control in finer detail whether your program stops. You can set breakpoints with the break' command and its variants (*note Setting Breakpoints: Set Breaks.), to specify the place where your program should stop by line number, function name or exact address in the program. On some systems, you can set breakpoints in shared libraries before the executable is run. There is a minor limitation on HP-UX systems: you must wait until the executable is run in order to set breakpoints in shared library routines that are not called directly by the program (for example, routines that are arguments in a pthread_create' call). A "watchpoint" is a special breakpoint that stops your program when the value of an expression changes. The expression may be a value of a variable, or it could involve values of one or more variables combined by operators, such as a + b'. This is sometimes called "data breakpoints". You must use a different command to set watchpoints (*note Setting Watchpoints: Set Watchpoints.), but aside from that, you can manage a watchpoint like any other breakpoint: you enable, disable, and delete both breakpoints and watchpoints using the same commands. You can arrange to have values from your program displayed automatically whenever GDB stops at a breakpoint. *Note Automatic Display: Auto Display. A "catchpoint" is another special breakpoint that stops your program when a certain kind of event occurs, such as the throwing of a C++ exception or the loading of a library. As with watchpoints, you use a different command to set a catchpoint (*note Setting Catchpoints: Set Catchpoints.), but aside from that, you can manage a catchpoint like any other breakpoint. (To stop when your program receives a signal, use the handle' command; see *note Signals: Signals.) GDB assigns a number to each breakpoint, watchpoint, or catchpoint when you create it; these numbers are successive integers starting with one. In many of the commands for controlling various features of breakpoints you use the breakpoint number to say which breakpoint you want to change. Each breakpoint may be "enabled" or "disabled"; if disabled, it has no effect on your program until you enable it again. Some GDB commands accept a range of breakpoints on which to operate. A breakpoint range is either a single breakpoint number, like 5', or two such numbers, in increasing order, separated by a hyphen, like 5-7'. When a breakpoint range is given to a command, all breakpoints in that range are operated on. * Menu: * Set Breaks:: Setting breakpoints * Set Watchpoints:: Setting watchpoints * Set Catchpoints:: Setting catchpoints * Delete Breaks:: Deleting breakpoints * Disabling:: Disabling breakpoints * Conditions:: Break conditions * Break Commands:: Breakpoint command lists * Save Breakpoints:: How to save breakpoints in a file * Static Probe Points:: Listing static probe points * Error in Breakpoints:: Cannot insert breakpoints'' * Breakpoint-related Warnings:: Breakpoint address adjusted...'' File: gdb.info, Node: Set Breaks, Next: Set Watchpoints, Up: Breakpoints 5.1.1 Setting Breakpoints ------------------------- Breakpoints are set with the break' command (abbreviated b'). The debugger convenience variable $bpnum' records the number of the
breakpoint you've set most recently; see *note Convenience Variables:
Convenience Vars, for a discussion of what you can do with convenience
variables.

break LOCATION'
Set a breakpoint at the given LOCATION, which can specify a
function name, a line number, or an address of an instruction.
(*Note Specify Location::, for a list of all the possible ways to
specify a LOCATION.)  The breakpoint will stop your program just
before it executes any of the code in the specified LOCATION.

When using source languages that permit overloading of symbols,
such as C++, a function name may refer to more than one possible
place to break.  *Note Ambiguous Expressions: Ambiguous
Expressions, for a discussion of that situation.

It is also possible to insert a breakpoint that will stop the
program only if a specific thread (*note Thread-Specific
Breakpoints::) or a specific task (*note Ada Tasks::) hits that
breakpoint.

break'
When called without any arguments, break' sets a breakpoint at
the next instruction to be executed in the selected stack frame
(*note Examining the Stack: Stack.).  In any selected frame but the
innermost, this makes your program stop as soon as control returns
to that frame.  This is similar to the effect of a finish'
command in the frame inside the selected frame--except that
finish' does not leave an active breakpoint.  If you use break'
without an argument in the innermost frame, GDB stops the next
time it reaches the current location; this may be useful inside
loops.

GDB normally ignores breakpoints when it resumes execution, until
at least one instruction has been executed.  If it did not do
this, you would be unable to proceed past a breakpoint without
first disabling the breakpoint.  This rule applies whether or not
the breakpoint already existed when your program stopped.

break ... if COND'
Set a breakpoint with condition COND; evaluate the expression COND
each time the breakpoint is reached, and stop only if the value is
nonzero--that is, if COND evaluates as true.  ...' stands for one
of the possible arguments described above (or no argument)
specifying where to break.  *Note Break Conditions: Conditions,

tbreak ARGS'
Set a breakpoint enabled only for one stop.  ARGS are the same as
for the break' command, and the breakpoint is set in the same
way, but the breakpoint is automatically deleted after the first
time your program stops there.  *Note Disabling Breakpoints:
Disabling.

hbreak ARGS'
Set a hardware-assisted breakpoint.  ARGS are the same as for the
break' command and the breakpoint is set in the same way, but the
breakpoint requires hardware support and some target hardware may
not have this support.  The main purpose of this is EPROM/ROM code
debugging, so you can set a breakpoint at an instruction without
changing the instruction.  This can be used with the new
trap-generation provided by SPARClite DSU and most x86-based
targets.  These targets will generate traps when a program
accesses some data or instruction address that is assigned to the
debug registers.  However the hardware breakpoint registers can
take a limited number of breakpoints.  For example, on the DSU,
only two data breakpoints can be set at a time, and GDB will
reject this command if more than two are used.  Delete or disable
unused hardware breakpoints before setting new ones (*note
Disabling Breakpoints: Disabling.).  *Note Break Conditions:
Conditions.  For remote targets, you can restrict the number of
hardware breakpoints GDB will use, see *note set remote
hardware-breakpoint-limit::.

thbreak ARGS'
Set a hardware-assisted breakpoint enabled only for one stop.  ARGS
are the same as for the hbreak' command and the breakpoint is set
in the same way.  However, like the tbreak' command, the
breakpoint is automatically deleted after the first time your
program stops there.  Also, like the hbreak' command, the
breakpoint requires hardware support and some target hardware may
not have this support.  *Note Disabling Breakpoints: Disabling.

rbreak REGEX'
Set breakpoints on all functions matching the regular expression
REGEX.  This command sets an unconditional breakpoint on all
matches, printing a list of all breakpoints it set.  Once these
breakpoints are set, they are treated just like the breakpoints
set with the break' command.  You can delete them, disable them,
or make them conditional the same way as any other breakpoint.

The syntax of the regular expression is the standard one used with
tools like grep'.  Note that this is different from the syntax
used by shells, so for instance foo*' matches all functions that
include an fo' followed by zero or more o's.  There is an
implicit .*' leading and trailing the regular expression you
supply, so to match only functions that begin with foo', use
^foo'.

When debugging C++ programs, rbreak' is useful for setting
breakpoints on overloaded functions that are not members of any
special classes.

The rbreak' command can be used to set breakpoints in *all* the
functions in a program, like this:

(gdb) rbreak .

rbreak FILE:REGEX'
If rbreak' is called with a filename qualification, it limits the
search for functions matching the given regular expression to the
specified FILE.  This can be used, for example, to set breakpoints
on every function in a given file:

(gdb) rbreak file.c:.

The colon separating the filename qualifier from the regex may
optionally be surrounded by spaces.

info breakpoints [N]'
info break [N]'
Print a table of all breakpoints, watchpoints, and catchpoints set
and not deleted.  Optional argument N means print information only
about the specified breakpoint (or watchpoint or catchpoint).  For
each breakpoint, following columns are printed:

_Breakpoint Numbers_

_Type_
Breakpoint, watchpoint, or catchpoint.

_Disposition_
Whether the breakpoint is marked to be disabled or deleted
when hit.

_Enabled or Disabled_
Enabled breakpoints are marked with y'.  n' marks
breakpoints that are not enabled.

Where the breakpoint is in your program, as a memory address.
For a pending breakpoint whose address is not yet known, this
field will contain <PENDING>'.  Such breakpoint won't fire
until a shared library that has the symbol or line referred
by breakpoint is loaded.  See below for details.  A
breakpoint with several locations will have <MULTIPLE>' in
this field--see below for details.

_What_
Where the breakpoint is in the source for your program, as a
file and line number.  For a pending breakpoint, the original
string passed to the breakpoint command will be listed as it
cannot be resolved until the appropriate shared library is
loaded in the future.

If a breakpoint is conditional, info break' shows the condition on
the line following the affected breakpoint; breakpoint commands,
if any, are listed after that.  A pending breakpoint is allowed to
have a condition specified for it.  The condition is not parsed
for validity until a shared library is loaded that allows the
pending breakpoint to resolve to a valid location.

info break' with a breakpoint number N as argument lists only
that breakpoint.  The convenience variable $_' and the default examining-address for the x' command are set to the address of the last breakpoint listed (*note Examining Memory: Memory.). info break' displays a count of the number of times the breakpoint has been hit. This is especially useful in conjunction with the ignore' command. You can ignore a large number of breakpoint hits, look at the breakpoint info to see how many times the breakpoint was hit, and then run again, ignoring one less than that number. This will get you quickly to the last hit of that breakpoint. GDB allows you to set any number of breakpoints at the same place in your program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (*note Break Conditions: Conditions.). It is possible that a breakpoint corresponds to several locations in your program. Examples of this situation are: * For a C++ constructor, the GCC compiler generates several instances of the function body, used in different cases. * For a C++ template function, a given line in the function can correspond to any number of instantiations. * For an inlined function, a given source line can correspond to several places where that function is inlined. In all those cases, GDB will insert a breakpoint at all the relevant locations(1). A breakpoint with multiple locations is displayed in the breakpoint table using several rows--one header row, followed by one row for each breakpoint location. The header row has <MULTIPLE>' in the address column. The rows for individual locations contain the actual addresses for locations, and show the functions to which those locations belong. The number column for a location is of the form BREAKPOINT-NUMBER.LOCATION-NUMBER. For example: Num Type Disp Enb Address What 1 breakpoint keep y <MULTIPLE> stop only if i==1 breakpoint already hit 1 time 1.1 y 0x080486a2 in void foo<int>() at t.cc:8 1.2 y 0x080486ca in void foo<double>() at t.cc:8 Each location can be individually enabled or disabled by passing BREAKPOINT-NUMBER.LOCATION-NUMBER as argument to the enable' and disable' commands. Note that you cannot delete the individual locations from the list, you can only delete the entire list of locations that belong to their parent breakpoint (with the delete NUM' command, where NUM is the number of the parent breakpoint, 1 in the above example). Disabling or enabling the parent breakpoint (*note Disabling::) affects all of the locations that belong to that breakpoint. It's quite common to have a breakpoint inside a shared library. Shared libraries can be loaded and unloaded explicitly, and possibly repeatedly, as the program is executed. To support this use case, GDB updates breakpoint locations whenever any shared library is loaded or unloaded. Typically, you would set a breakpoint in a shared library at the beginning of your debugging session, when the library is not loaded, and when the symbols from the library are not available. When you try to set breakpoint, GDB will ask you if you want to set a so called "pending breakpoint"--breakpoint whose address is not yet resolved. After the program is run, whenever a new shared library is loaded, GDB reevaluates all the breakpoints. When a newly loaded shared library contains the symbol or line referred to by some pending breakpoint, that breakpoint is resolved and becomes an ordinary breakpoint. When a library is unloaded, all breakpoints that refer to its symbols or source lines become pending again. This logic works for breakpoints with multiple locations, too. For example, if you have a breakpoint in a C++ template function, and a newly loaded shared library has an instantiation of that template, a new location is added to the list of locations for the breakpoint. Except for having unresolved address, pending breakpoints do not differ from regular breakpoints. You can set conditions or commands, enable and disable them and perform other breakpoint operations. GDB provides some additional commands for controlling what happens when the break' command cannot resolve breakpoint address specification to an address: set breakpoint pending auto' This is the default behavior. When GDB cannot find the breakpoint location, it queries you whether a pending breakpoint should be created. set breakpoint pending on' This indicates that an unrecognized breakpoint location should automatically result in a pending breakpoint being created. set breakpoint pending off' This indicates that pending breakpoints are not to be created. Any unrecognized breakpoint location results in an error. This setting does not affect any pending breakpoints previously created. show breakpoint pending' Show the current behavior setting for creating pending breakpoints. The settings above only affect the break' command and its variants. Once breakpoint is set, it will be automatically updated as shared libraries are loaded and unloaded. For some targets, GDB can automatically decide if hardware or software breakpoints should be used, depending on whether the breakpoint address is read-only or read-write. This applies to breakpoints set with the break' command as well as to internal breakpoints set by commands like next' and finish'. For breakpoints set with hbreak', GDB will always use hardware breakpoints. You can control this automatic behaviour with the following commands:: set breakpoint auto-hw on' This is the default behavior. When GDB sets a breakpoint, it will try to use the target memory map to decide if software or hardware breakpoint must be used. set breakpoint auto-hw off' This indicates GDB should not automatically select breakpoint type. If the target provides a memory map, GDB will warn when trying to set software breakpoint at a read-only address. GDB normally implements breakpoints by replacing the program code at the breakpoint address with a special instruction, which, when executed, given control to the debugger. By default, the program code is so modified only when the program is resumed. As soon as the program stops, GDB restores the original instructions. This behaviour guards against leaving breakpoints inserted in the target should gdb abrubptly disconnect. However, with slow remote targets, inserting and removing breakpoint can reduce the performance. This behavior can be controlled with the following commands:: set breakpoint always-inserted off' All breakpoints, including newly added by the user, are inserted in the target only when the target is resumed. All breakpoints are removed from the target when it stops. set breakpoint always-inserted on' Causes all breakpoints to be inserted in the target at all times. If the user adds a new breakpoint, or changes an existing breakpoint, the breakpoints in the target are updated immediately. A breakpoint is removed from the target only when breakpoint itself is removed. set breakpoint always-inserted auto' This is the default mode. If GDB is controlling the inferior in non-stop mode (*note Non-Stop Mode::), gdb behaves as if breakpoint always-inserted' mode is on. If GDB is controlling the inferior in all-stop mode, GDB behaves as if breakpoint always-inserted' mode is off. GDB itself sometimes sets breakpoints in your program for special purposes, such as proper handling of longjmp' (in C programs). These internal breakpoints are assigned negative numbers, starting with -1'; info breakpoints' does not display them. You can see these breakpoints with the GDB maintenance command maint info breakpoints' (*note maint info breakpoints::). ---------- Footnotes ---------- (1) As of this writing, multiple-location breakpoints work only if there's line number information for all the locations. This means that they will generally not work in system libraries, unless you have debug info with line numbers for them. File: gdb.info, Node: Set Watchpoints, Next: Set Catchpoints, Prev: Set Breaks, Up: Breakpoints 5.1.2 Setting Watchpoints ------------------------- You can use a watchpoint to stop execution whenever the value of an expression changes, without having to predict a particular place where this may happen. (This is sometimes called a "data breakpoint".) The expression may be as simple as the value of a single variable, or as complex as many variables combined by operators. Examples include: * A reference to the value of a single variable. * An address cast to an appropriate data type. For example, *(int *)0x12345678' will watch a 4-byte region at the specified address (assuming an int' occupies 4 bytes). * An arbitrarily complex expression, such as a*b + c/d'. The expression can use any operators valid in the program's native language (*note Languages::). You can set a watchpoint on an expression even if the expression can not be evaluated yet. For instance, you can set a watchpoint on *global_ptr' before global_ptr' is initialized. GDB will stop when your program sets global_ptr' and the expression produces a valid value. If the expression becomes valid in some other way than changing a variable (e.g. if the memory pointed to by *global_ptr' becomes readable as the result of a malloc' call), GDB may not stop until the next time the expression changes. Depending on your system, watchpoints may be implemented in software or hardware. GDB does software watchpointing by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.) On some systems, such as HP-UX, PowerPC, GNU/Linux and most other x86-based targets, GDB includes support for hardware watchpoints, which do not slow down the running of your program. watch EXPR [thread THREADNUM]' Set a watchpoint for an expression. GDB will break when the expression EXPR is written into by the program and its value changes. The simplest (and the most popular) use of this command is to watch the value of a single variable: (gdb) watch foo If the command includes a [thread THREADNUM]' clause, GDB breaks only when the thread identified by THREADNUM changes the value of EXPR. If any other threads change the value of EXPR, GDB will not break. Note that watchpoints restricted to a single thread in this way only work with Hardware Watchpoints. rwatch EXPR [thread THREADNUM]' Set a watchpoint that will break when the value of EXPR is read by the program. awatch EXPR [thread THREADNUM]' Set a watchpoint that will break when EXPR is either read from or written into by the program. info watchpoints' This command prints a list of watchpoints, using the same format as info break' (*note Set Breaks::). If you watch for a change in a numerically entered address you need to dereference it, as the address itself is just a constant number which will never change. GDB refuses to create a watchpoint that watches a never-changing value: (gdb) watch 0x600850 Cannot watch constant value 0x600850. (gdb) watch *(int *) 0x600850 Watchpoint 1: *(int *) 6293584 GDB sets a "hardware watchpoint" if possible. Hardware watchpoints execute very quickly, and the debugger reports a change in value at the exact instruction where the change occurs. If GDB cannot set a hardware watchpoint, it sets a software watchpoint, which executes more slowly and reports the change in value at the next _statement_, not the instruction, after the change occurs. You can force GDB to use only software watchpoints with the set can-use-hw-watchpoints 0' command. With this variable set to zero, GDB will never try to use hardware watchpoints, even if the underlying system supports them. (Note that hardware-assisted watchpoints that were set _before_ setting can-use-hw-watchpoints' to zero will still use the hardware mechanism of watching expression values.) set can-use-hw-watchpoints' Set whether or not to use hardware watchpoints. show can-use-hw-watchpoints' Show the current mode of using hardware watchpoints. For remote targets, you can restrict the number of hardware watchpoints GDB will use, see *note set remote hardware-breakpoint-limit::. When you issue the watch' command, GDB reports Hardware watchpoint NUM: EXPR if it was able to set a hardware watchpoint. Currently, the awatch' and rwatch' commands can only set hardware watchpoints, because accesses to data that don't change the value of the watched expression cannot be detected without examining every instruction as it is being executed, and GDB does not do that currently. If GDB finds that it is unable to set a hardware breakpoint with the awatch' or rwatch' command, it will print a message like this: Expression cannot be implemented with read/access watchpoint. Sometimes, GDB cannot set a hardware watchpoint because the data type of the watched expression is wider than what a hardware watchpoint on the target machine can handle. For example, some systems can only watch regions that are up to 4 bytes wide; on such systems you cannot set hardware watchpoints for an expression that yields a double-precision floating-point number (which is typically 8 bytes wide). As a work-around, it might be possible to break the large region into a series of smaller ones and watch them with separate watchpoints. If you set too many hardware watchpoints, GDB might be unable to insert all of them when you resume the execution of your program. Since the precise number of active watchpoints is unknown until such time as the program is about to be resumed, GDB might not be able to warn you about this when you set the watchpoints, and the warning will be printed only when the program is resumed: Hardware watchpoint NUM: Could not insert watchpoint If this happens, delete or disable some of the watchpoints. Watching complex expressions that reference many variables can also exhaust the resources available for hardware-assisted watchpoints. That's because GDB needs to watch every variable in the expression with separately allocated resources. If you call a function interactively using print' or call', any watchpoints you have set will be inactive until GDB reaches another kind of breakpoint or the call completes. GDB automatically deletes watchpoints that watch local (automatic) variables, or expressions that involve such variables, when they go out of scope, that is, when the execution leaves the block in which these variables were defined. In particular, when the program being debugged terminates, _all_ local variables go out of scope, and so only watchpoints that watch global variables remain set. If you rerun the program, you will need to set all such watchpoints again. One way of doing that would be to set a code breakpoint at the entry to the main' function and when it breaks, set all the watchpoints. In multi-threaded programs, watchpoints will detect changes to the watched expression from every thread. _Warning:_ In multi-threaded programs, software watchpoints have only limited usefulness. If GDB creates a software watchpoint, it can only watch the value of an expression _in a single thread_. If you are confident that the expression can only change due to the current thread's activity (and if you are also confident that no other thread can become current), then you can use software watchpoints as usual. However, GDB may not notice when a non-current thread's activity changes the expression. (Hardware watchpoints, in contrast, watch an expression in all threads.) *Note set remote hardware-watchpoint-limit::. File: gdb.info, Node: Set Catchpoints, Next: Delete Breaks, Prev: Set Watchpoints, Up: Breakpoints 5.1.3 Setting Catchpoints ------------------------- You can use "catchpoints" to cause the debugger to stop for certain kinds of program events, such as C++ exceptions or the loading of a shared library. Use the catch' command to set a catchpoint. catch EVENT' Stop when EVENT occurs. EVENT can be any of the following: throw' The throwing of a C++ exception. catch' The catching of a C++ exception. exception' An Ada exception being raised. If an exception name is specified at the end of the command (eg catch exception Program_Error'), the debugger will stop only when this specific exception is raised. Otherwise, the debugger stops execution when any Ada exception is raised. When inserting an exception catchpoint on a user-defined exception whose name is identical to one of the exceptions defined by the language, the fully qualified name must be used as the exception name. Otherwise, GDB will assume that it should stop on the pre-defined exception rather than the user-defined one. For instance, assuming an exception called Constraint_Error' is defined in package Pck', then the command to use to catch such exceptions is catch exception Pck.Constraint_Error'. exception unhandled' An exception that was raised but is not handled by the program. assert' A failed Ada assertion. exec' A call to exec'. This is currently only available for HP-UX and GNU/Linux. syscall' syscall [NAME | NUMBER] ...' A call to or return from a system call, a.k.a. "syscall". A syscall is a mechanism for application programs to request a service from the operating system (OS) or one of the OS system services. GDB can catch some or all of the syscalls issued by the debuggee, and show the related information for each syscall. If no argument is specified, calls to and returns from all system calls will be caught. NAME can be any system call name that is valid for the underlying OS. Just what syscalls are valid depends on the OS. On GNU and Unix systems, you can find the full list of valid syscall names on /usr/include/asm/unistd.h'. Normally, GDB knows in advance which syscalls are valid for each OS, so you can use the GDB command-line completion facilities (*note command completion: Completion.) to list the available choices. You may also specify the system call numerically. A syscall's number is the value passed to the OS's syscall dispatcher to identify the requested service. When you specify the syscall by its name, GDB uses its database of syscalls to convert the name into the corresponding numeric code, but using the number directly may be useful if GDB's database does not have the complete list of syscalls on your system (e.g., because GDB lags behind the OS upgrades). The example below illustrates how this command works if you don't provide arguments to it: (gdb) catch syscall Catchpoint 1 (syscall) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Catchpoint 1 (returned from syscall 'close'), \ 0xffffe424 in __kernel_vsyscall () (gdb) Here is an example of catching a system call by name: (gdb) catch syscall chroot Catchpoint 1 (syscall 'chroot' [61]) (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Catchpoint 1 (returned from syscall 'chroot'), \ 0xffffe424 in __kernel_vsyscall () (gdb) An example of specifying a system call numerically. In the case below, the syscall number has a corresponding entry in the XML file, so GDB finds its name and prints it: (gdb) catch syscall 252 Catchpoint 1 (syscall(s) 'exit_group') (gdb) r Starting program: /tmp/catch-syscall Catchpoint 1 (call to syscall 'exit_group'), \ 0xffffe424 in __kernel_vsyscall () (gdb) c Continuing. Program exited normally. (gdb) However, there can be situations when there is no corresponding name in XML file for that syscall number. In this case, GDB prints a warning message saying that it was not able to find the syscall name, but the catchpoint will be set anyway. See the example below: (gdb) catch syscall 764 warning: The number '764' does not represent a known syscall. Catchpoint 2 (syscall 764) (gdb) If you configure GDB using the --without-expat' option, it will not be able to display syscall names. Also, if your architecture does not have an XML file describing its system calls, you will not be able to see the syscall names. It is important to notice that these two features are used for accessing the syscall name database. In either case, you will see a warning like this: (gdb) catch syscall warning: Could not open "syscalls/i386-linux.xml" warning: Could not load the syscall XML file 'syscalls/i386-linux.xml'. GDB will not be able to display syscall names. Catchpoint 1 (syscall) (gdb) Of course, the file name will change depending on your architecture and system. Still using the example above, you can also try to catch a syscall by its number. In this case, you would see something like: (gdb) catch syscall 252 Catchpoint 1 (syscall(s) 252) Again, in this case GDB would not be able to display syscall's names. fork' A call to fork'. This is currently only available for HP-UX and GNU/Linux. vfork' A call to vfork'. This is currently only available for HP-UX and GNU/Linux. tcatch EVENT' Set a catchpoint that is enabled only for one stop. The catchpoint is automatically deleted after the first time the event is caught. Use the info break' command to list the current catchpoints. There are currently some limitations to C++ exception handling (catch throw' and catch catch') in GDB: * If you call a function interactively, GDB normally returns control to you when the function has finished executing. If the call raises an exception, however, the call may bypass the mechanism that returns control to you and cause your program either to abort or to simply continue running until it hits a breakpoint, catches a signal that GDB is listening for, or exits. This is the case even if you set a catchpoint for the exception; catchpoints on exceptions are disabled within interactive calls. * You cannot raise an exception interactively. * You cannot install an exception handler interactively. Sometimes catch' is not the best way to debug exception handling: if you need to know exactly where an exception is raised, it is better to stop _before_ the exception handler is called, since that way you can see the stack before any unwinding takes place. If you set a breakpoint in an exception handler instead, it may not be easy to find out where the exception was raised. To stop just before an exception handler is called, you need some knowledge of the implementation. In the case of GNU C++, exceptions are raised by calling a library function named __raise_exception' which has the following ANSI C interface: /* ADDR is where the exception identifier is stored. ID is the exception identifier. */ void __raise_exception (void **addr, void *id); To make the debugger catch all exceptions before any stack unwinding takes place, set a breakpoint on __raise_exception' (*note Breakpoints; Watchpoints; and Exceptions: Breakpoints.). With a conditional breakpoint (*note Break Conditions: Conditions.) that depends on the value of ID, you can stop your program when a specific exception is raised. You can use multiple conditional breakpoints to stop your program when any of a number of exceptions are raised. File: gdb.info, Node: Delete Breaks, Next: Disabling, Prev: Set Catchpoints, Up: Breakpoints 5.1.4 Deleting Breakpoints -------------------------- It is often necessary to eliminate a breakpoint, watchpoint, or catchpoint once it has done its job and you no longer want your program to stop there. This is called "deleting" the breakpoint. A breakpoint that has been deleted no longer exists; it is forgotten. With the clear' command you can delete breakpoints according to where they are in your program. With the delete' command you can delete individual breakpoints, watchpoints, or catchpoints by specifying their breakpoint numbers. It is not necessary to delete a breakpoint to proceed past it. GDB automatically ignores breakpoints on the first instruction to be executed when you continue execution without changing the execution address. clear' Delete any breakpoints at the next instruction to be executed in the selected stack frame (*note Selecting a Frame: Selection.). When the innermost frame is selected, this is a good way to delete a breakpoint where your program just stopped. clear LOCATION' Delete any breakpoints set at the specified LOCATION. *Note Specify Location::, for the various forms of LOCATION; the most useful ones are listed below: clear FUNCTION' clear FILENAME:FUNCTION' Delete any breakpoints set at entry to the named FUNCTION. clear LINENUM' clear FILENAME:LINENUM' Delete any breakpoints set at or within the code of the specified LINENUM of the specified FILENAME. delete [breakpoints] [RANGE...]' Delete the breakpoints, watchpoints, or catchpoints of the breakpoint ranges specified as arguments. If no argument is specified, delete all breakpoints (GDB asks confirmation, unless you have set confirm off'). You can abbreviate this command as d'. File: gdb.info, Node: Disabling, Next: Conditions, Prev: Delete Breaks, Up: Breakpoints 5.1.5 Disabling Breakpoints --------------------------- Rather than deleting a breakpoint, watchpoint, or catchpoint, you might prefer to "disable" it. This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can "enable" it again later. You disable and enable breakpoints, watchpoints, and catchpoints with the enable' and disable' commands, optionally specifying one or more breakpoint numbers as arguments. Use info break' to print a list of all breakpoints, watchpoints, and catchpoints if you do not know which numbers to use. Disabling and enabling a breakpoint that has multiple locations affects all of its locations. A breakpoint, watchpoint, or catchpoint can have any of four different states of enablement: * Enabled. The breakpoint stops your program. A breakpoint set with the break' command starts out in this state. * Disabled. The breakpoint has no effect on your program. * Enabled once. The breakpoint stops your program, but then becomes disabled. * Enabled for deletion. The breakpoint stops your program, but immediately after it does so it is deleted permanently. A breakpoint set with the tbreak' command starts out in this state. You can use the following commands to enable or disable breakpoints, watchpoints, and catchpoints: disable [breakpoints] [RANGE...]' Disable the specified breakpoints--or all breakpoints, if none are listed. A disabled breakpoint has no effect but is not forgotten. All options such as ignore-counts, conditions and commands are remembered in case the breakpoint is enabled again later. You may abbreviate disable' as dis'. enable [breakpoints] [RANGE...]' Enable the specified breakpoints (or all defined breakpoints). They become effective once again in stopping your program. enable [breakpoints] once RANGE...' Enable the specified breakpoints temporarily. GDB disables any of these breakpoints immediately after stopping your program. enable [breakpoints] delete RANGE...' Enable the specified breakpoints to work once, then die. GDB deletes any of these breakpoints as soon as your program stops there. Breakpoints set by the tbreak' command start out in this state. Except for a breakpoint set with tbreak' (*note Setting Breakpoints: Set Breaks.), breakpoints that you set are initially enabled; subsequently, they become disabled or enabled only when you use one of the commands above. (The command until' can set and delete a breakpoint of its own, but it does not change the state of your other breakpoints; see *note Continuing and Stepping: Continuing and Stepping.) File: gdb.info, Node: Conditions, Next: Break Commands, Prev: Disabling, Up: Breakpoints 5.1.6 Break Conditions ---------------------- The simplest sort of breakpoint breaks every time your program reaches a specified place. You can also specify a "condition" for a breakpoint. A condition is just a Boolean expression in your programming language (*note Expressions: Expressions.). A breakpoint with a condition evaluates the expression each time your program reaches it, and your program stops only if the condition is _true_. This is the converse of using assertions for program validation; in that situation, you want to stop when the assertion is violated--that is, when the condition is false. In C, if you want to test an assertion expressed by the condition ASSERT, you should set the condition ! ASSERT' on the appropriate breakpoint. Conditions are also accepted for watchpoints; you may not need them, since a watchpoint is inspecting the value of an expression anyhow--but it might be simpler, say, to just set a watchpoint on a variable name, and specify a condition that tests whether the new value is an interesting one. Break conditions can have side effects, and may even call functions in your program. This can be useful, for example, to activate functions that log program progress, or to use your own print functions to format special data structures. The effects are completely predictable unless there is another enabled breakpoint at the same address. (In that case, GDB might see the other breakpoint first and stop your program without checking the condition of this one.) Note that breakpoint commands are usually more convenient and flexible than break conditions for the purpose of performing side effects when a breakpoint is reached (*note Breakpoint Command Lists: Break Commands.). Break conditions can be specified when a breakpoint is set, by using if' in the arguments to the break' command. *Note Setting Breakpoints: Set Breaks. They can also be changed at any time with the condition' command. You can also use the if' keyword with the watch' command. The catch' command does not recognize the if' keyword; condition' is the only way to impose a further condition on a catchpoint. condition BNUM EXPRESSION' Specify EXPRESSION as the break condition for breakpoint, watchpoint, or catchpoint number BNUM. After you set a condition, breakpoint BNUM stops your program only if the value of EXPRESSION is true (nonzero, in C). When you use condition', GDB checks EXPRESSION immediately for syntactic correctness, and to determine whether symbols in it have referents in the context of your breakpoint. If EXPRESSION uses symbols not referenced in the context of the breakpoint, GDB prints an error message: No symbol "foo" in current context. GDB does not actually evaluate EXPRESSION at the time the condition' command (or a command that sets a breakpoint with a condition, like break if ...') is given, however. *Note Expressions: Expressions. condition BNUM' Remove the condition from breakpoint number BNUM. It becomes an ordinary unconditional breakpoint. A special case of a breakpoint condition is to stop only when the breakpoint has been reached a certain number of times. This is so useful that there is a special way to do it, using the "ignore count" of the breakpoint. Every breakpoint has an ignore count, which is an integer. Most of the time, the ignore count is zero, and therefore has no effect. But if your program reaches a breakpoint whose ignore count is positive, then instead of stopping, it just decrements the ignore count by one and continues. As a result, if the ignore count value is N, the breakpoint does not stop the next N times your program reaches it. ignore BNUM COUNT' Set the ignore count of breakpoint number BNUM to COUNT. The next COUNT times the breakpoint is reached, your program's execution does not stop; other than to decrement the ignore count, GDB takes no action. To make the breakpoint stop the next time it is reached, specify a count of zero. When you use continue' to resume execution of your program from a breakpoint, you can specify an ignore count directly as an argument to continue', rather than using ignore'. *Note Continuing and Stepping: Continuing and Stepping. If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, GDB resumes checking the condition. You could achieve the effect of the ignore count with a condition such as $foo-- <= 0' using a debugger convenience variable that
is decremented each time.  *Note Convenience Variables:
Convenience Vars.

Ignore counts apply to breakpoints, watchpoints, and catchpoints.

File: gdb.info,  Node: Break Commands,  Next: Save Breakpoints,  Prev: Conditions,  Up: Breakpoints

5.1.7 Breakpoint Command Lists
------------------------------

You can give any breakpoint (or watchpoint or catchpoint) a series of
commands to execute when your program stops due to that breakpoint.  For
example, you might want to print the values of certain expressions, or
enable other breakpoints.

commands [RANGE...]'
... COMMAND-LIST ...'
end'
Specify a list of commands for the given breakpoints.  The commands
themselves appear on the following lines.  Type a line containing
just end' to terminate the commands.

To remove all commands from a breakpoint, type commands' and
follow it immediately with end'; that is, give no commands.

With no argument, commands' refers to the last breakpoint,
watchpoint, or catchpoint set (not to the breakpoint most recently
encountered).  If the most recent breakpoints were set with a
single command, then the commands' will apply to all the
breakpoints set by that command.  This applies to breakpoints set
by rbreak', and also applies when a single break' command
creates multiple breakpoints (*note Ambiguous Expressions:
Ambiguous Expressions.).

Pressing <RET> as a means of repeating the last GDB command is
disabled within a COMMAND-LIST.

You can use breakpoint commands to start your program up again.
Simply use the continue' command, or step', or any other command that
resumes execution.

Any other commands in the command list, after a command that resumes
execution, are ignored.  This is because any time you resume execution
(even with a simple next' or step'), you may encounter another
breakpoint--which could have its own command list, leading to
ambiguities about which list to execute.

If the first command you specify in a command list is silent', the
usual message about stopping at a breakpoint is not printed.  This may
be desirable for breakpoints that are to print a specific message and
then continue.  If none of the remaining commands print anything, you
see no sign that the breakpoint was reached.  silent' is meaningful
only at the beginning of a breakpoint command list.

The commands echo', output', and printf' allow you to print
precisely controlled output, and are often useful in silent
breakpoints.  *Note Commands for Controlled Output: Output.

For example, here is how you could use breakpoint commands to print
the value of x' at entry to foo' whenever x' is positive.

break foo if x>0
commands
silent
printf "x is %d\n",x
cont
end

One application for breakpoint commands is to compensate for one bug
so you can test for another.  Put a breakpoint just after the erroneous
line of code, give it a condition to detect the case in which something
erroneous has been done, and give it commands to assign correct values
to any variables that need them.  End with the continue' command so
that your program does not stop, and start with the silent' command so
that no output is produced.  Here is an example:

break 403
commands
silent
set x = y + 4
cont
end

File: gdb.info,  Node: Save Breakpoints,  Next: Static Probe Points,  Prev: Break Commands,  Up: Breakpoints

5.1.8 How to save breakpoints to a file
---------------------------------------

To save breakpoint definitions to a file use the save breakpoints'
command.

save breakpoints [FILENAME]'
This command saves all current breakpoint definitions together with
their commands and ignore counts, into a file FILENAME' suitable
for use in a later debugging session.  This includes all types of
breakpoints (breakpoints, watchpoints, catchpoints, tracepoints).
To read the saved breakpoint definitions, use the source' command
(*note Command Files::).  Note that watchpoints with expressions
involving local variables may fail to be recreated because it may
not be possible to access the context where the watchpoint is
valid anymore.  Because the saved breakpoint definitions are
simply a sequence of GDB commands that recreate the breakpoints,
you can edit the file in your favorite editing program, and remove
the breakpoint definitions you're not interested in, or that can
no longer be recreated.

File: gdb.info,  Node: Static Probe Points,  Next: Error in Breakpoints,  Prev: Save Breakpoints,  Up: Breakpoints

5.1.9 Static Probe Points
-------------------------

The GNU/Linux tool SystemTap' provides a way for applications to embed
static probes, using sys/sdt.h'.  GDB can list the available probes,
and you can put breakpoints at the probe points (*note Specify
Location::).

You can examine the available SystemTap' static probes using info
probes':

info probes [PROVIDER [NAME [OBJFILE]]]'
List the available SystemTap' static probes.

If given, PROVIDER is a regular expression used to select which
providers to list.  If omitted, all providers are listed.

If given, NAME is a regular expression used to select which probes
to list.  If omitted, all probes are listed.

If given, OBJFILE is a regular expression used to select which
object files (executable or shared libraries) to examine.  If not
given, all object files are considered.

A probe may specify up to ten arguments.  These are available at the
point at which the probe is defined--that is, when the current PC is at
the probe's location.  The arguments are available using the
convenience variables (*note Convenience Vars::)
$_probe_arg0'...$_probe_arg9'.  Each probe argument is an integer of
the appropriate size; types are not preserved.  The convenience
variable $_probe_argc' holds the number of arguments at the current probe point. These variables are always available, but attempts to access them at any location other than a probe point will cause GDB to give an error. File: gdb.info, Node: Error in Breakpoints, Next: Breakpoint-related Warnings, Prev: Static Probe Points, Up: Breakpoints 5.1.10 "Cannot insert breakpoints" ---------------------------------- If you request too many active hardware-assisted breakpoints and watchpoints, you will see this error message: Stopped; cannot insert breakpoints. You may have requested too many hardware breakpoints and watchpoints. This message is printed when you attempt to resume the program, since only then GDB knows exactly how many hardware breakpoints and watchpoints it needs to insert. When this message is printed, you need to disable or remove some of the hardware-assisted breakpoints and watchpoints, and then continue. File: gdb.info, Node: Breakpoint-related Warnings, Prev: Error in Breakpoints, Up: Breakpoints 5.1.11 "Breakpoint address adjusted..." --------------------------------------- Some processor architectures place constraints on the addresses at which breakpoints may be placed. For architectures thus constrained, GDB will attempt to adjust the breakpoint's address to comply with the constraints dictated by the architecture. One example of such an architecture is the Fujitsu FR-V. The FR-V is a VLIW architecture in which a number of RISC-like instructions may be bundled together for parallel execution. The FR-V architecture constrains the location of a breakpoint instruction within such a bundle to the instruction with the lowest address. GDB honors this constraint by adjusting a breakpoint's address to the first in the bundle. It is not uncommon for optimized code to have bundles which contain instructions from different source statements, thus it may happen that a breakpoint's address will be adjusted from one source statement to another. Since this adjustment may significantly alter GDB's breakpoint related behavior from what the user expects, a warning is printed when the breakpoint is first set and also when the breakpoint is hit. A warning like the one below is printed when setting a breakpoint that's been subject to address adjustment: warning: Breakpoint address adjusted from 0x00010414 to 0x00010410. Such warnings are printed both for user settable and GDB's internal breakpoints. If you see one of these warnings, you should verify that a breakpoint set at the adjusted address will have the desired affect. If not, the breakpoint in question may be removed and other breakpoints may be set which will have the desired behavior. E.g., it may be sufficient to place the breakpoint at a later instruction. A conditional breakpoint may also be useful in some cases to prevent the breakpoint from triggering too often. GDB will also issue a warning when stopping at one of these adjusted breakpoints: warning: Breakpoint 1 address previously adjusted from 0x00010414 to 0x00010410. When this warning is encountered, it may be too late to take remedial action except in cases where the breakpoint is hit earlier or more frequently than expected. File: gdb.info, Node: Continuing and Stepping, Next: Signals, Prev: Breakpoints, Up: Stopping 5.2 Continuing and Stepping =========================== "Continuing" means resuming program execution until your program completes normally. In contrast, "stepping" means executing just one more "step" of your program, where "step" may mean either one line of source code, or one machine instruction (depending on what particular command you use). Either when continuing or when stepping, your program may stop even sooner, due to a breakpoint or a signal. (If it stops due to a signal, you may want to use handle', or use signal 0' to resume execution. *Note Signals: Signals.) continue [IGNORE-COUNT]' c [IGNORE-COUNT]' fg [IGNORE-COUNT]' Resume program execution, at the address where your program last stopped; any breakpoints set at that address are bypassed. The optional argument IGNORE-COUNT allows you to specify a further number of times to ignore a breakpoint at this location; its effect is like that of ignore' (*note Break Conditions: Conditions.). The argument IGNORE-COUNT is meaningful only when your program stopped due to a breakpoint. At other times, the argument to continue' is ignored. The synonyms c' and fg' (for "foreground", as the debugged program is deemed to be the foreground program) are provided purely for convenience, and have exactly the same behavior as continue'. To resume execution at a different place, you can use return' (*note Returning from a Function: Returning.) to go back to the calling function; or jump' (*note Continuing at a Different Address: Jumping.) to go to an arbitrary location in your program. A typical technique for using stepping is to set a breakpoint (*note Breakpoints; Watchpoints; and Catchpoints: Breakpoints.) at the beginning of the function or the section of your program where a problem is believed to lie, run your program until it stops at that breakpoint, and then step through the suspect area, examining the variables that are interesting, until you see the problem happen. step' Continue running your program until control reaches a different source line, then stop it and return control to GDB. This command is abbreviated s'. _Warning:_ If you use the step' command while control is within a function that was compiled without debugging information, execution proceeds until control reaches a function that does have debugging information. Likewise, it will not step into a function which is compiled without debugging information. To step through functions without debugging information, use the stepi' command, described below. The step' command only stops at the first instruction of a source line. This prevents the multiple stops that could otherwise occur in switch' statements, for' loops, etc. step' continues to stop if a function that has debugging information is called within the line. In other words, step' _steps inside_ any functions called within the line. Also, the step' command only enters a function if there is line number information for the function. Otherwise it acts like the next' command. This avoids problems when using cc -gl' on MIPS machines. Previously, step' entered subroutines if there was any debugging information about the routine. step COUNT' Continue running as in step', but do so COUNT times. If a breakpoint is reached, or a signal not related to stepping occurs before COUNT steps, stepping stops right away. next [COUNT]' Continue to the next source line in the current (innermost) stack frame. This is similar to step', but function calls that appear within the line of code are executed without stopping. Execution stops when control reaches a different line of code at the original stack level that was executing when you gave the next' command. This command is abbreviated n'. An argument COUNT is a repeat count, as for step'. The next' command only stops at the first instruction of a source line. This prevents multiple stops that could otherwise occur in switch' statements, for' loops, etc. set step-mode' set step-mode on' The set step-mode on' command causes the step' command to stop at the first instruction of a function which contains no debug line information rather than stepping over it. This is useful in cases where you may be interested in inspecting the machine instructions of a function which has no symbolic info and do not want GDB to automatically skip over this function. set step-mode off' Causes the step' command to step over any functions which contains no debug information. This is the default. show step-mode' Show whether GDB will stop in or step over functions without source line debug information. finish' Continue running until just after function in the selected stack frame returns. Print the returned value (if any). This command can be abbreviated as fin'. Contrast this with the return' command (*note Returning from a Function: Returning.). until' u' Continue running until a source line past the current line, in the current stack frame, is reached. This command is used to avoid single stepping through a loop more than once. It is like the next' command, except that when until' encounters a jump, it automatically continues execution until the program counter is greater than the address of the jump. This means that when you reach the end of a loop after single stepping though it, until' makes your program continue execution until it exits the loop. In contrast, a next' command at the end of a loop simply steps back to the beginning of the loop, which forces you to step through the next iteration. until' always stops your program if it attempts to exit the current stack frame. until' may produce somewhat counterintuitive results if the order of machine code does not match the order of the source lines. For example, in the following excerpt from a debugging session, the f' (frame') command shows that execution is stopped at line 206'; yet when we use until', we get to line 195': (gdb) f #0 main (argc=4, argv=0xf7fffae8) at m4.c:206 206 expand_input(); (gdb) until 195 for ( ; argc > 0; NEXTARG) { This happened because, for execution efficiency, the compiler had generated code for the loop closure test at the end, rather than the start, of the loop--even though the test in a C for'-loop is written before the body of the loop. The until' command appeared to step back to the beginning of the loop when it advanced to this expression; however, it has not really gone to an earlier statement--not in terms of the actual machine code. until' with no argument works by means of single instruction stepping, and hence is slower than until' with an argument. until LOCATION' u LOCATION' Continue running your program until either the specified location is reached, or the current stack frame returns. LOCATION is any of the forms described in *note Specify Location::. This form of the command uses temporary breakpoints, and hence is quicker than until' without an argument. The specified location is actually reached only if it is in the current frame. This implies that until' can be used to skip over recursive function invocations. For instance in the code below, if the current location is line 96', issuing until 99' will execute the program up to line 99' in the same invocation of factorial, i.e., after the inner invocations have returned. 94 int factorial (int value) 95 { 96 if (value > 1) { 97 value *= factorial (value - 1); 98 } 99 return (value); 100 } advance LOCATION' Continue running the program up to the given LOCATION. An argument is required, which should be of one of the forms described in *note Specify Location::. Execution will also stop upon exit from the current stack frame. This command is similar to until', but advance' will not skip over recursive function calls, and the target location doesn't have to be in the same frame as the current one. stepi' stepi ARG' si' Execute one machine instruction, then stop and return to the debugger. It is often useful to do display/i$pc' when stepping by machine
instructions.  This makes GDB automatically display the next
instruction to be executed, each time your program stops.  *Note
Automatic Display: Auto Display.

An argument is a repeat count, as in step'.

nexti'
nexti ARG'
ni'
Execute one machine instruction, but if it is a function call,
proceed until the function returns.

An argument is a repeat count, as in next'.

File: gdb.info,  Node: Signals,  Next: Thread Stops,  Prev: Continuing and Stepping,  Up: Stopping

5.3 Signals
===========

A signal is an asynchronous event that can happen in a program.  The
operating system defines the possible kinds of signals, and gives each
kind a name and a number.  For example, in Unix SIGINT' is the signal
a program gets when you type an interrupt character (often Ctrl-c');
SIGSEGV' is the signal a program gets from referencing a place in
memory far away from all the areas in use; SIGALRM' occurs when the
alarm clock timer goes off (which happens only if your program has
requested an alarm).

Some signals, including SIGALRM', are a normal part of the
functioning of your program.  Others, such as SIGSEGV', indicate
errors; these signals are "fatal" (they kill your program immediately)
if the program has not specified in advance some other way to handle
the signal.  SIGINT' does not indicate an error in your program, but
it is normally fatal so it can carry out the purpose of the interrupt:
to kill the program.

GDB has the ability to detect any occurrence of a signal in your
program.  You can tell GDB in advance what to do for each kind of
signal.

Normally, GDB is set up to let the non-erroneous signals like
SIGALRM' be silently passed to your program (so as not to interfere
with their role in the program's functioning) but to stop your program
immediately whenever an error signal happens.  You can change these
settings with the handle' command.

info signals'
info handle'
Print a table of all the kinds of signals and how GDB has been
told to handle each one.  You can use this to see the signal
numbers of all the defined types of signals.

info signals SIG'
Similar, but print information only about the specified signal
number.

info handle' is an alias for info signals'.

handle SIGNAL [KEYWORDS...]'
Change the way GDB handles signal SIGNAL.  SIGNAL can be the
number of a signal or its name (with or without the SIG' at the
beginning); a list of signal numbers of the form LOW-HIGH'; or
the word all', meaning all the known signals.  Optional arguments
KEYWORDS, described below, say what change to make.

The keywords allowed by the handle' command can be abbreviated.
Their full names are:

nostop'
GDB should not stop your program when this signal happens.  It may
still print a message telling you that the signal has come in.

stop'
GDB should stop your program when this signal happens.  This
implies the print' keyword as well.

print'
GDB should print a message when this signal happens.

noprint'
GDB should not mention the occurrence of the signal at all.  This
implies the nostop' keyword as well.

pass'
noignore'
GDB should allow your program to see this signal; your program can
handle the signal, or else it may terminate if the signal is fatal
and not handled.  pass' and noignore' are synonyms.

nopass'
ignore'
GDB should not allow your program to see this signal.  nopass'
and ignore' are synonyms.

When a signal stops your program, the signal is not visible to the
program until you continue.  Your program sees the signal then, if
pass' is in effect for the signal in question _at that time_.  In
other words, after GDB reports a signal, you can use the handle'
command with pass' or nopass' to control whether your program sees
that signal when you continue.

The default is set to nostop', noprint', pass' for non-erroneous
signals such as SIGALRM', SIGWINCH' and SIGCHLD', and to stop',
print', pass' for the erroneous signals.

You can also use the signal' command to prevent your program from
seeing a signal, or cause it to see a signal it normally would not see,
or to give it any signal at any time.  For example, if your program
stopped due to some sort of memory reference error, you might store
correct values into the erroneous variables and continue, hoping to see
more execution; but your program would probably terminate immediately as
a result of the fatal signal once it saw the signal.  To prevent this,
you can continue with signal 0'.  *Note Giving your Program a Signal:
Signaling.

On some targets, GDB can inspect extra signal information associated
with the intercepted signal, before it is actually delivered to the
program being debugged.  This information is exported by the
convenience variable $_siginfo', and consists of data that is passed by the kernel to the signal handler at the time of the receipt of a signal. The data type of the information itself is target dependent. You can see the data type using the ptype$_siginfo' command.  On Unix
systems, it typically corresponds to the standard siginfo_t' type, as
defined in the signal.h' system header.

Here's an example, on a GNU/Linux system, printing the stray
referenced address that raised a segmentation fault.

(gdb) continue
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400766 in main ()
69        *(int *)p = 0;
(gdb) ptype $_siginfo type = struct { int si_signo; int si_errno; int si_code; union { int _pad[28]; struct {...} _kill; struct {...} _timer; struct {...} _rt; struct {...} _sigchld; struct {...} _sigfault; struct {...} _sigpoll; } _sifields; } (gdb) ptype$_siginfo._sifields._sigfault
type = struct {
}
(gdb) p $_siginfo._sifields._sigfault.si_addr$1 = (void *) 0x7ffff7ff7000

Depending on target support, $_siginfo' may also be writable. File: gdb.info, Node: Thread Stops, Prev: Signals, Up: Stopping 5.4 Stopping and Starting Multi-thread Programs =============================================== GDB supports debugging programs with multiple threads (*note Debugging Programs with Multiple Threads: Threads.). There are two modes of controlling execution of your program within the debugger. In the default mode, referred to as "all-stop mode", when any thread in your program stops (for example, at a breakpoint or while being stepped), all other threads in the program are also stopped by GDB. On some targets, GDB also supports "non-stop mode", in which other threads can continue to run freely while you examine the stopped thread in the debugger. * Menu: * All-Stop Mode:: All threads stop when GDB takes control * Non-Stop Mode:: Other threads continue to execute * Background Execution:: Running your program asynchronously * Thread-Specific Breakpoints:: Controlling breakpoints * Interrupted System Calls:: GDB may interfere with system calls * Observer Mode:: GDB does not alter program behavior File: gdb.info, Node: All-Stop Mode, Next: Non-Stop Mode, Up: Thread Stops 5.4.1 All-Stop Mode ------------------- In all-stop mode, whenever your program stops under GDB for any reason, _all_ threads of execution stop, not just the current thread. This allows you to examine the overall state of the program, including switching between threads, without worrying that things may change underfoot. Conversely, whenever you restart the program, _all_ threads start executing. _This is true even when single-stepping_ with commands like step' or next'. In particular, GDB cannot single-step all threads in lockstep. Since thread scheduling is up to your debugging target's operating system (not controlled by GDB), other threads may execute more than one statement while the current thread completes a single step. Moreover, in general other threads stop in the middle of a statement, rather than at a clean statement boundary, when the program stops. You might even find your program stopped in another thread after continuing or even single-stepping. This happens whenever some other thread runs into a breakpoint, a signal, or an exception before the first thread completes whatever you requested. Whenever GDB stops your program, due to a breakpoint or a signal, it automatically selects the thread where that breakpoint or signal happened. GDB alerts you to the context switch with a message such as [Switching to Thread N]' to identify the thread. On some OSes, you can modify GDB's default behavior by locking the OS scheduler to allow only a single thread to run. set scheduler-locking MODE' Set the scheduler locking mode. If it is off', then there is no locking and any thread may run at any time. If on', then only the current thread may run when the inferior is resumed. The step' mode optimizes for single-stepping; it prevents other threads from preempting the current thread while you are stepping, so that the focus of debugging does not change unexpectedly. Other threads only rarely (or never) get a chance to run when you step. They are more likely to run when you next' over a function call, and they are completely free to run when you use commands like continue', until', or finish'. However, unless another thread hits a breakpoint during its timeslice, GDB does not change the current thread away from the thread that you are debugging. show scheduler-locking' Display the current scheduler locking mode. By default, when you issue one of the execution commands such as continue', next' or step', GDB allows only threads of the current inferior to run. For example, if GDB is attached to two inferiors, each with two threads, the continue' command resumes only the two threads of the current inferior. This is useful, for example, when you debug a program that forks and you want to hold the parent stopped (so that, for instance, it doesn't run to exit), while you debug the child. In other situations, you may not be interested in inspecting the current state of any of the processes GDB is attached to, and you may want to resume them all until some breakpoint is hit. In the latter case, you can instruct GDB to allow all threads of all the inferiors to run with the set schedule-multiple' command. set schedule-multiple' Set the mode for allowing threads of multiple processes to be resumed when an execution command is issued. When on', all threads of all processes are allowed to run. When off', only the threads of the current process are resumed. The default is off'. The scheduler-locking' mode takes precedence when set to on', or while you are stepping and set to step'. show schedule-multiple' Display the current mode for resuming the execution of threads of multiple processes. File: gdb.info, Node: Non-Stop Mode, Next: Background Execution, Prev: All-Stop Mode, Up: Thread Stops 5.4.2 Non-Stop Mode ------------------- For some multi-threaded targets, GDB supports an optional mode of operation in which you can examine stopped program threads in the debugger while other threads continue to execute freely. This minimizes intrusion when debugging live systems, such as programs where some threads have real-time constraints or must continue to respond to external events. This is referred to as "non-stop" mode. In non-stop mode, when a thread stops to report a debugging event, _only_ that thread is stopped; GDB does not stop other threads as well, in contrast to the all-stop mode behavior. Additionally, execution commands such as continue' and step' apply by default only to the current thread in non-stop mode, rather than all threads as in all-stop mode. This allows you to control threads explicitly in ways that are not possible in all-stop mode -- for example, stepping one thread while allowing others to run freely, stepping one thread while holding all others stopped, or stepping several threads independently and simultaneously. To enter non-stop mode, use this sequence of commands before you run or attach to your program: # Enable the async interface. set target-async 1 # If using the CLI, pagination breaks non-stop. set pagination off # Finally, turn it on! set non-stop on You can use these commands to manipulate the non-stop mode setting: set non-stop on' Enable selection of non-stop mode. set non-stop off' Disable selection of non-stop mode. show non-stop' Show the current non-stop enablement setting. Note these commands only reflect whether non-stop mode is enabled, not whether the currently-executing program is being run in non-stop mode. In particular, the set non-stop' preference is only consulted when GDB starts or connects to the target program, and it is generally not possible to switch modes once debugging has started. Furthermore, since not all targets support non-stop mode, even when you have enabled non-stop mode, GDB may still fall back to all-stop operation by default. In non-stop mode, all execution commands apply only to the current thread by default. That is, continue' only continues one thread. To continue all threads, issue continue -a' or c -a'. You can use GDB's background execution commands (*note Background Execution::) to run some threads in the background while you continue to examine or step others from GDB. The MI execution commands (*note GDB/MI Program Execution::) are always executed asynchronously in non-stop mode. Suspending execution is done with the interrupt' command when running in the background, or Ctrl-c' during foreground execution. In all-stop mode, this stops the whole process; but in non-stop mode the interrupt applies only to the current thread. To stop the whole program, use interrupt -a'. Other execution commands do not currently support the -a' option. In non-stop mode, when a thread stops, GDB doesn't automatically make that thread current, as it does in all-stop mode. This is because the thread stop notifications are asynchronous with respect to GDB's command interpreter, and it would be confusing if GDB unexpectedly changed to a different thread just as you entered a command to operate on the previously current thread. File: gdb.info, Node: Background Execution, Next: Thread-Specific Breakpoints, Prev: Non-Stop Mode, Up: Thread Stops 5.4.3 Background Execution -------------------------- GDB's execution commands have two variants: the normal foreground (synchronous) behavior, and a background (asynchronous) behavior. In foreground execution, GDB waits for the program to report that some thread has stopped before prompting for another command. In background execution, GDB immediately gives a command prompt so that you can issue other commands while your program runs. You need to explicitly enable asynchronous mode before you can use background execution commands. You can use these commands to manipulate the asynchronous mode setting: set target-async on' Enable asynchronous mode. set target-async off' Disable asynchronous mode. show target-async' Show the current target-async setting. If the target doesn't support async mode, GDB issues an error message if you attempt to use the background execution commands. To specify background execution, add a &' to the command. For example, the background form of the continue' command is continue&', or just c&'. The execution commands that accept background execution are: run' *Note Starting your Program: Starting. attach' *Note Debugging an Already-running Process: Attach. step' *Note step: Continuing and Stepping. stepi' *Note stepi: Continuing and Stepping. next' *Note next: Continuing and Stepping. nexti' *Note nexti: Continuing and Stepping. continue' *Note continue: Continuing and Stepping. finish' *Note finish: Continuing and Stepping. until' *Note until: Continuing and Stepping. Background execution is especially useful in conjunction with non-stop mode for debugging programs with multiple threads; see *note Non-Stop Mode::. However, you can also use these commands in the normal all-stop mode with the restriction that you cannot issue another execution command until the previous one finishes. Examples of commands that are valid in all-stop mode while the program is running include help' and info break'. You can interrupt your program while it is running in the background by using the interrupt' command. interrupt' interrupt -a' Suspend execution of the running program. In all-stop mode, interrupt' stops the whole process, but in non-stop mode, it stops only the current thread. To stop the whole program in non-stop mode, use interrupt -a'. File: gdb.info, Node: Thread-Specific Breakpoints, Next: Interrupted System Calls, Prev: Background Execution, Up: Thread Stops 5.4.4 Thread-Specific Breakpoints --------------------------------- When your program has multiple threads (*note Debugging Programs with Multiple Threads: Threads.), you can choose whether to set breakpoints on all threads, or on a particular thread. break LINESPEC thread THREADNO' break LINESPEC thread THREADNO if ...' LINESPEC specifies source lines; there are several ways of writing them (*note Specify Location::), but the effect is always to specify some source line. Use the qualifier thread THREADNO' with a breakpoint command to specify that you only want GDB to stop the program when a particular thread reaches this breakpoint. THREADNO is one of the numeric thread identifiers assigned by GDB, shown in the first column of the info threads' display. If you do not specify thread THREADNO' when you set a breakpoint, the breakpoint applies to _all_ threads of your program. You can use the thread' qualifier on conditional breakpoints as well; in this case, place thread THREADNO' before or after the breakpoint condition, like this: (gdb) break frik.c:13 thread 28 if bartab > lim File: gdb.info, Node: Interrupted System Calls, Next: Observer Mode, Prev: Thread-Specific Breakpoints, Up: Thread Stops 5.4.5 Interrupted System Calls ------------------------------ There is an unfortunate side effect when using GDB to debug multi-threaded programs. If one thread stops for a breakpoint, or for some other reason, and another thread is blocked in a system call, then the system call may return prematurely. This is a consequence of the interaction between multiple threads and the signals that GDB uses to implement breakpoints and other events that stop execution. To handle this problem, your program should check the return value of each system call and react appropriately. This is good programming style anyways. For example, do not write code like this: sleep (10); The call to sleep' will return early if a different thread stops at a breakpoint or for some other reason. Instead, write this: int unslept = 10; while (unslept > 0) unslept = sleep (unslept); A system call is allowed to return early, so the system is still conforming to its specification. But GDB does cause your multi-threaded program to behave differently than it would without GDB. Also, GDB uses internal breakpoints in the thread library to monitor certain events such as thread creation and thread destruction. When such an event happens, a system call in another thread may return prematurely, even though your program does not appear to stop. File: gdb.info, Node: Observer Mode, Prev: Interrupted System Calls, Up: Thread Stops 5.4.6 Observer Mode ------------------- If you want to build on non-stop mode and observe program behavior without any chance of disruption by GDB, you can set variables to disable all of the debugger's attempts to modify state, whether by writing memory, inserting breakpoints, etc. These operate at a low level, intercepting operations from all commands. When all of these are set to off', then GDB is said to be "observer mode". As a convenience, the variable observer' can be set to disable these, plus enable non-stop mode. Note that GDB will not prevent you from making nonsensical combinations of these settings. For instance, if you have enabled may-insert-breakpoints' but disabled may-write-memory', then breakpoints that work by writing trap instructions into the code stream will still not be able to be placed. set observer on' set observer off' When set to on', this disables all the permission variables below (except for insert-fast-tracepoints'), plus enables non-stop debugging. Setting this to off' switches back to normal debugging, though remaining in non-stop mode. show observer' Show whether observer mode is on or off. set may-write-registers on' set may-write-registers off' This controls whether GDB will attempt to alter the values of registers, such as with assignment expressions in print', or the jump' command. It defaults to on'. show may-write-registers' Show the current permission to write registers. set may-write-memory on' set may-write-memory off' This controls whether GDB will attempt to alter the contents of memory, such as with assignment expressions in print'. It defaults to on'. show may-write-memory' Show the current permission to write memory. set may-insert-breakpoints on' set may-insert-breakpoints off' This controls whether GDB will attempt to insert breakpoints. This affects all breakpoints, including internal breakpoints defined by GDB. It defaults to on'. show may-insert-breakpoints' Show the current permission to insert breakpoints. set may-insert-tracepoints on' set may-insert-tracepoints off' This controls whether GDB will attempt to insert (regular) tracepoints at the beginning of a tracing experiment. It affects only non-fast tracepoints, fast tracepoints being under the control of may-insert-fast-tracepoints'. It defaults to on'. show may-insert-tracepoints' Show the current permission to insert tracepoints. set may-insert-fast-tracepoints on' set may-insert-fast-tracepoints off' This controls whether GDB will attempt to insert fast tracepoints at the beginning of a tracing experiment. It affects only fast tracepoints, regular (non-fast) tracepoints being under the control of may-insert-tracepoints'. It defaults to on'. show may-insert-fast-tracepoints' Show the current permission to insert fast tracepoints. set may-interrupt on' set may-interrupt off' This controls whether GDB will attempt to interrupt or stop program execution. When this variable is off', the interrupt' command will have no effect, nor will Ctrl-c'. It defaults to on'. show may-interrupt' Show the current permission to interrupt or stop the program. File: gdb.info, Node: Reverse Execution, Next: Process Record and Replay, Prev: Stopping, Up: Top 6 Running programs backward *************************** When you are debugging a program, it is not unusual to realize that you have gone too far, and some event of interest has already happened. If the target environment supports it, GDB can allow you to "rewind" the program by running it backward. A target environment that supports reverse execution should be able to "undo" the changes in machine state that have taken place as the program was executing normally. Variables, registers etc. should revert to their previous values. Obviously this requires a great deal of sophistication on the part of the target environment; not all target environments can support reverse execution. When a program is executed in reverse, the instructions that have most recently been executed are "un-executed", in reverse order. The program counter runs backward, following the previous thread of execution in reverse. As each instruction is "un-executed", the values of memory and/or registers that were changed by that instruction are reverted to their previous states. After executing a piece of source code in reverse, all side effects of that code should be "undone", and all variables should be returned to their prior values(1). If you are debugging in a target environment that supports reverse execution, GDB provides the following commands. reverse-continue [IGNORE-COUNT]' rc [IGNORE-COUNT]' Beginning at the point where your program last stopped, start executing in reverse. Reverse execution will stop for breakpoints and synchronous exceptions (signals), just like normal execution. Behavior of asynchronous signals depends on the target environment. reverse-step [COUNT]' Run the program backward until control reaches the start of a different source line; then stop it, and return control to GDB. Like the step' command, reverse-step' will only stop at the beginning of a source line. It "un-executes" the previously executed source line. If the previous source line included calls to debuggable functions, reverse-step' will step (backward) into the called function, stopping at the beginning of the _last_ statement in the called function (typically a return statement). Also, as with the step' command, if non-debuggable functions are called, reverse-step' will run thru them backward without stopping. reverse-stepi [COUNT]' Reverse-execute one machine instruction. Note that the instruction to be reverse-executed is _not_ the one pointed to by the program counter, but the instruction executed prior to that one. For instance, if the last instruction was a jump, reverse-stepi' will take you back from the destination of the jump to the jump instruction itself. reverse-next [COUNT]' Run backward to the beginning of the previous line executed in the current (innermost) stack frame. If the line contains function calls, they will be "un-executed" without stopping. Starting from the first line of a function, reverse-next' will take you back to the caller of that function, _before_ the function was called, just as the normal next' command would take you from the last line of a function back to its return to its caller (2). reverse-nexti [COUNT]' Like nexti', reverse-nexti' executes a single instruction in reverse, except that called functions are "un-executed" atomically. That is, if the previously executed instruction was a return from another function, reverse-nexti' will continue to execute in reverse until the call to that function (from the current stack frame) is reached. reverse-finish' Just as the finish' command takes you to the point where the current function returns, reverse-finish' takes you to the point where it was called. Instead of ending up at the end of the current function invocation, you end up at the beginning. set exec-direction' Set the direction of target execution. set exec-direction reverse' GDB will perform all execution commands in reverse, until the exec-direction mode is changed to "forward". Affected commands include step, stepi, next, nexti, continue, and finish'. The return' command cannot be used in reverse mode. set exec-direction forward' GDB will perform all execution commands in the normal fashion. This is the default. ---------- Footnotes ---------- (1) Note that some side effects are easier to undo than others. For instance, memory and registers are relatively easy, but device I/O is hard. Some targets may be able undo things like device I/O, and some may not. The contract between GDB and the reverse executing target requires only that the target do something reasonable when GDB tells it to execute backwards, and then report the results back to GDB. Whatever the target reports back to GDB, GDB will report back to the user. GDB assumes that the memory and registers that the target reports are in a consistant state, but GDB accepts whatever it is given. (2) Unless the code is too heavily optimized. File: gdb.info, Node: Process Record and Replay, Next: Stack, Prev: Reverse Execution, Up: Top 7 Recording Inferior's Execution and Replaying It ************************************************* On some platforms, GDB provides a special "process record and replay" target that can record a log of the process execution, and replay it later with both forward and reverse execution commands. When this target is in use, if the execution log includes the record for the next instruction, GDB will debug in "replay mode". In the replay mode, the inferior does not really execute code instructions. Instead, all the events that normally happen during code execution are taken from the execution log. While code is not really executed in replay mode, the values of registers (including the program counter register) and the memory of the inferior are still changed as they normally would. Their contents are taken from the execution log. If the record for the next instruction is not in the execution log, GDB will debug in "record mode". In this mode, the inferior executes normally, and GDB records the execution log for future replay. The process record and replay target supports reverse execution (*note Reverse Execution::), even if the platform on which the inferior runs does not. However, the reverse execution is limited in this case by the range of the instructions recorded in the execution log. In other words, reverse execution on platforms that don't support it directly can only be done in the replay mode. When debugging in the reverse direction, GDB will work in replay mode as long as the execution log includes the record for the previous instruction; otherwise, it will work in record mode, if the platform supports reverse execution, or stop if not. For architecture environments that support process record and replay, GDB provides the following commands: target record' This command starts the process record and replay target. The process record and replay target can only debug a process that is already running. Therefore, you need first to start the process with the run' or start' commands, and then start the recording with the target record' command. Both record' and rec' are aliases of target record'. Displaced stepping (*note displaced stepping: Maintenance Commands.) will be automatically disabled when process record and replay target is started. That's because the process record and replay target doesn't support displaced stepping. If the inferior is in the non-stop mode (*note Non-Stop Mode::) or in the asynchronous execution mode (*note Background Execution::), the process record and replay target cannot be started because it doesn't support these two modes. record stop' Stop the process record and replay target. When process record and replay target stops, the entire execution log will be deleted and the inferior will either be terminated, or will remain in its final state. When you stop the process record and replay target in record mode (at the end of the execution log), the inferior will be stopped at the next instruction that would have been recorded. In other words, if you record for a while and then stop recording, the inferior process will be left in the same state as if the recording never happened. On the other hand, if the process record and replay target is stopped while in replay mode (that is, not at the end of the execution log, but at some earlier point), the inferior process will become "live" at that earlier state, and it will then be possible to continue the usual "live" debugging of the process from that state. When the inferior process exits, or GDB detaches from it, process record and replay target will automatically stop itself. record save FILENAME' Save the execution log to a file FILENAME'. Default filename is gdb_record.PROCESS_ID', where PROCESS_ID is the process ID of the inferior. record restore FILENAME' Restore the execution log from a file FILENAME'. File must have been created with record save'. set record insn-number-max LIMIT' Set the limit of instructions to be recorded. Default value is 200000. If LIMIT is a positive number, then GDB will start deleting instructions from the log once the number of the record instructions becomes greater than LIMIT. For every new recorded instruction, GDB will delete the earliest recorded instruction to keep the number of recorded instructions at the limit. (Since deleting recorded instructions loses information, GDB lets you control what happens when the limit is reached, by means of the stop-at-limit' option, described below.) If LIMIT is zero, GDB will never delete recorded instructions from the execution log. The number of recorded instructions is unlimited in this case. show record insn-number-max' Show the limit of instructions to be recorded. set record stop-at-limit' Control the behavior when the number of recorded instructions reaches the limit. If ON (the default), GDB will stop when the limit is reached for the first time and ask you whether you want to stop the inferior or continue running it and recording the execution log. If you decide to continue recording, each new recorded instruction will cause the oldest one to be deleted. If this option is OFF, GDB will automatically delete the oldest record to make room for each new one, without asking. show record stop-at-limit' Show the current setting of stop-at-limit'. set record memory-query' Control the behavior when GDB is unable to record memory changes caused by an instruction. If ON, GDB will query whether to stop the inferior in that case. If this option is OFF (the default), GDB will automatically ignore the effect of such instructions on memory. Later, when GDB replays this execution log, it will mark the log of this instruction as not accessible, and it will not affect the replay results. show record memory-query' Show the current setting of memory-query'. info record' Show various statistics about the state of process record and its in-memory execution log buffer, including: * Whether in record mode or replay mode. * Lowest recorded instruction number (counting from when the current execution log started recording instructions). * Highest recorded instruction number. * Current instruction about to be replayed (if in replay mode). * Number of instructions contained in the execution log. * Maximum number of instructions that may be contained in the execution log. record delete' When record target runs in replay mode ("in the past"), delete the subsequent execution log and begin to record a new execution log starting from the current address. This means you will abandon the previously recorded "future" and begin recording a new "future". File: gdb.info, Node: Stack, Next: Source, Prev: Process Record and Replay, Up: Top 8 Examining the Stack ********************* When your program has stopped, the first thing you need to know is where it stopped and how it got there. Each time your program performs a function call, information about the call is generated. That information includes the location of the call in your program, the arguments of the call, and the local variables of the function being called. The information is saved in a block of data called a "stack frame". The stack frames are allocated in a region of memory called the "call stack". When your program stops, the GDB commands for examining the stack allow you to see all of this information. One of the stack frames is "selected" by GDB and many GDB commands refer implicitly to the selected frame. In particular, whenever you ask GDB for the value of a variable in your program, the value is found in the selected frame. There are special GDB commands to select whichever frame you are interested in. *Note Selecting a Frame: Selection. When your program stops, GDB automatically selects the currently executing frame and describes it briefly, similar to the frame' command (*note Information about a Frame: Frame Info.). * Menu: * Frames:: Stack frames * Backtrace:: Backtraces * Selection:: Selecting a frame * Frame Info:: Information on a frame File: gdb.info, Node: Frames, Next: Backtrace, Up: Stack 8.1 Stack Frames ================ The call stack is divided up into contiguous pieces called "stack frames", or "frames" for short; each frame is the data associated with one call to one function. The frame contains the arguments given to the function, the function's local variables, and the address at which the function is executing. When your program is started, the stack has only one frame, that of the function main'. This is called the "initial" frame or the "outermost" frame. Each time a function is called, a new frame is made. Each time a function returns, the frame for that function invocation is eliminated. If a function is recursive, there can be many frames for the same function. The frame for the function in which execution is actually occurring is called the "innermost" frame. This is the most recently created of all the stack frames that still exist. Inside your program, stack frames are identified by their addresses. A stack frame consists of many bytes, each of which has its own address; each kind of computer has a convention for choosing one byte whose address serves as the address of the frame. Usually this address is kept in a register called the "frame pointer register" (*note$fp:
Registers.) while execution is going on in that frame.

GDB assigns numbers to all existing stack frames, starting with zero
for the innermost frame, one for the frame that called it, and so on
upward.  These numbers do not really exist in your program; they are
assigned by GDB to give you a way of designating stack frames in GDB
commands.

Some compilers provide a way to compile functions so that they
operate without stack frames.  (For example, the GCC option
-fomit-frame-pointer'
generates functions without a frame.)  This is occasionally done
with heavily used library functions to save the frame setup time.  GDB
has limited facilities for dealing with these function invocations.  If
the innermost function invocation has no stack frame, GDB nevertheless
regards it as though it had a separate frame, which is numbered zero as
usual, allowing correct tracing of the function call chain.  However,
GDB has no provision for frameless functions elsewhere in the stack.

frame ARGS'
The frame' command allows you to move from one stack frame to
another, and to print the stack frame you select.  ARGS may be
either the address of the frame or the stack frame number.
Without an argument, frame' prints the current stack frame.

select-frame'
The select-frame' command allows you to move from one stack frame
to another without printing the frame.  This is the silent version
of frame'.

File: gdb.info,  Node: Backtrace,  Next: Selection,  Prev: Frames,  Up: Stack

8.2 Backtraces
==============

A backtrace is a summary of how your program got where it is.  It shows
one line per frame, for many frames, starting with the currently
executing frame (frame zero), followed by its caller (frame one), and
on up the stack.

backtrace'
bt'
Print a backtrace of the entire stack: one line per frame for all
frames in the stack.

You can stop the backtrace at any time by typing the system
interrupt character, normally Ctrl-c'.

backtrace N'
bt N'
Similar, but print only the innermost N frames.

backtrace -N'
bt -N'
Similar, but print only the outermost N frames.

backtrace full'
bt full'
bt full N'
bt full -N'
Print the values of the local variables also.  N specifies the
number of frames to print, as described above.

The names where' and info stack' (abbreviated info s') are
additional aliases for backtrace'.

In a multi-threaded program, GDB by default shows the backtrace only
for the current thread.  To display the backtrace for several or all of
the threads, use the command thread apply' (*note thread apply:
Threads.).  For example, if you type thread apply all backtrace', GDB
will display the backtrace for all the threads; this is handy when you
debug a core dump of a multi-threaded program.

Each line in the backtrace shows the frame number and the function
name.  The program counter value is also shown--unless you use set
print address off'.  The backtrace also shows the source file name and
line number, as well as the arguments to the function.  The program
counter value is omitted if it is at the beginning of the code for that
line number.

Here is an example of a backtrace.  It was made with the command bt
3', so it shows the innermost three frames.

#0  m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993
#1  0x6e38 in expand_macro (sym=0x2b600, data=...) at macro.c:242
#2  0x6840 in expand_token (obs=0x0, t=177664, td=0xf7fffb08)
at macro.c:71
(More stack frames follow...)

The display for frame zero does not begin with a program counter value,
indicating that your program has stopped at the beginning of the code
for line 993' of builtin.c'.

The value of parameter data' in frame 1 has been replaced by ...'.
By default, GDB prints the value of a parameter only if it is a scalar
(integer, pointer, enumeration, etc).  See command set print
frame-arguments' in *note Print Settings:: for more details on how to
configure the way function parameter values are printed.

If your program was compiled with optimizations, some compilers will
optimize away arguments passed to functions if those arguments are
never used after the call.  Such optimizations generate code that
passes arguments through registers, but doesn't store those arguments
in the stack frame.  GDB has no way of displaying such arguments in
stack frames other than the innermost one.  Here's what such a
backtrace might look like:

#0  m4_traceon (obs=0x24eb0, argc=1, argv=0x2b8c8)
at builtin.c:993
#1  0x6e38 in expand_macro (sym=<value optimized out>) at macro.c:242
#2  0x6840 in expand_token (obs=0x0, t=<value optimized out>, td=0xf7fffb08)
at macro.c:71
(More stack frames follow...)

The values of arguments that were not saved in their stack frames are
shown as <value optimized out>'.

If you need to display the values of such optimized-out arguments,
either deduce that from other variables whose values depend on the one
you are interested in, or recompile without optimizations.

Most programs have a standard user entry point--a place where system
libraries and startup code transition into user code.  For C this is
main'(1).  When GDB finds the entry function in a backtrace it will
terminate the backtrace, to avoid tracing into highly system-specific
(and generally uninteresting) code.

If you need to examine the startup code, or limit the number of
levels in a backtrace, you can change this behavior:

set backtrace past-main'
set backtrace past-main on'
Backtraces will continue past the user entry point.

set backtrace past-main off'
Backtraces will stop when they encounter the user entry point.
This is the default.

show backtrace past-main'
Display the current user entry point backtrace policy.

set backtrace past-entry'
set backtrace past-entry on'
Backtraces will continue past the internal entry point of an
application.  This entry point is encoded by the linker when the
application is built, and is likely before the user entry point
main' (or equivalent) is called.

set backtrace past-entry off'
Backtraces will stop when they encounter the internal entry point
of an application.  This is the default.

show backtrace past-entry'
Display the current internal entry point backtrace policy.

set backtrace limit N'
set backtrace limit 0'
Limit the backtrace to N levels.  A value of zero means unlimited.

show backtrace limit'
Display the current limit on backtrace levels.

---------- Footnotes ----------

(1) Note that embedded programs (the so-called "free-standing"
environment) are not required to have a main' function as the entry
point.  They could even have multiple entry points.

File: gdb.info,  Node: Selection,  Next: Frame Info,  Prev: Backtrace,  Up: Stack

8.3 Selecting a Frame
=====================

Most commands for examining the stack and other data in your program
work on whichever stack frame is selected at the moment.  Here are the
commands for selecting a stack frame; all of them finish by printing a
brief description of the stack frame just selected.

frame N'
f N'
Select frame number N.  Recall that frame zero is the innermost
(currently executing) frame, frame one is the frame that called the
innermost one, and so on.  The highest-numbered frame is the one
for main'.

f ADDR'
Select the frame at address ADDR.  This is useful mainly if the
chaining of stack frames has been damaged by a bug, making it
impossible for GDB to assign numbers properly to all frames.  In
addition, this can be useful when your program has multiple stacks
and switches between them.

On the SPARC architecture, frame' needs two addresses to select
an arbitrary frame: a frame pointer and a stack pointer.

On the MIPS and Alpha architecture, it needs two addresses: a stack
pointer and a program counter.

On the 29k architecture, it needs three addresses: a register stack
pointer, a program counter, and a memory stack pointer.

up N'
Move N frames up the stack.  For positive numbers N, this advances
toward the outermost frame, to higher frame numbers, to frames
that have existed longer.  N defaults to one.

down N'
Move N frames down the stack.  For positive numbers N, this
advances toward the innermost frame, to lower frame numbers, to
frames that were created more recently.  N defaults to one.  You
may abbreviate down' as do'.

All of these commands end by printing two lines of output describing
the frame.  The first line shows the frame number, the function name,
the arguments, and the source file and line number of execution in that
frame.  The second line shows the text of that source line.

For example:

(gdb) up
#1  0x22f0 in main (argc=1, argv=0xf7fffbf4, env=0xf7fffbfc)
at env.c:10

After such a printout, the list' command with no arguments prints
ten lines centered on the point of execution in the frame.  You can
also edit the program at the point of execution with your favorite
editing program by typing edit'.  *Note Printing Source Lines: List,
for details.

up-silently N'
down-silently N'
These two commands are variants of up' and down', respectively;
they differ in that they do their work silently, without causing
display of the new frame.  They are intended primarily for use in
GDB command scripts, where the output might be unnecessary and
distracting.

File: gdb.info,  Node: Frame Info,  Prev: Selection,  Up: Stack

8.4 Information About a Frame
=============================

There are several other commands to print information about the selected
stack frame.

frame'
f'
When used without any argument, this command does not change which
frame is selected, but prints a brief description of the currently
selected stack frame.  It can be abbreviated f'.  With an
argument, this command is used to select a stack frame.  *Note
Selecting a Frame: Selection.

info frame'
info f'
This command prints a verbose description of the selected stack
frame, including:

* the address of the frame

* the address of the next frame down (called by this frame)

* the address of the next frame up (caller of this frame)

* the language in which the source code corresponding to this
frame is written

* the address of the frame's arguments

* the address of the frame's local variables

* the program counter saved in it (the address of execution in
the caller frame)

* which registers were saved in the frame

The verbose description is useful when something has gone wrong
that has made the stack format fail to fit the usual conventions.

info f ADDR'
Print a verbose description of the frame at address ADDR, without
selecting that frame.  The selected frame remains unchanged by this
command.  This requires the same kind of address (more than one
for some architectures) that you specify in the frame' command.
*Note Selecting a Frame: Selection.

info args'
Print the arguments of the selected frame, each on a separate line.

info locals'
Print the local variables of the selected frame, each on a separate
line.  These are all variables (declared either static or
automatic) accessible at the point of execution of the selected
frame.

info catch'
Print a list of all the exception handlers that are active in the
current stack frame at the current point of execution.  To see
other exception handlers, visit the associated frame (using the
up', down', or frame' commands); then type info catch'.  *Note
Setting Catchpoints: Set Catchpoints.

File: gdb.info,  Node: Source,  Next: Data,  Prev: Stack,  Up: Top

9 Examining Source Files
************************

GDB can print parts of your program's source, since the debugging
information recorded in the program tells GDB what source files were
used to build it.  When your program stops, GDB spontaneously prints
the line where it stopped.  Likewise, when you select a stack frame
(*note Selecting a Frame: Selection.), GDB prints the line where
execution in that frame has stopped.  You can print other portions of
source files by explicit command.

If you use GDB through its GNU Emacs interface, you may prefer to
use Emacs facilities to view source; see *note Using GDB under GNU
Emacs: Emacs.

* List::                        Printing source lines
* Specify Location::            How to specify code locations
* Edit::                        Editing source files
* Search::                      Searching source files
* Source Path::                 Specifying source directories
* Machine Code::                Source and machine code

File: gdb.info,  Node: List,  Next: Specify Location,  Up: Source

9.1 Printing Source Lines
=========================

To print lines from a source file, use the list' command (abbreviated
l').  By default, ten lines are printed.  There are several ways to
specify what part of the file you want to print; see *note Specify
Location::, for the full list.

Here are the forms of the list' command most commonly used:

list LINENUM'
Print lines centered around line number LINENUM in the current
source file.

list FUNCTION'
Print lines centered around the beginning of function FUNCTION.

list'
Print more lines.  If the last lines printed were printed with a
list' command, this prints lines following the last lines
printed; however, if the last line printed was a solitary line
printed as part of displaying a stack frame (*note Examining the
Stack: Stack.), this prints lines centered around that line.

list -'
Print lines just before the lines last printed.

By default, GDB prints ten source lines with any of these forms of
the list' command.  You can change this using set listsize':

set listsize COUNT'
Make the list' command display COUNT source lines (unless the
list' argument explicitly specifies some other number).

show listsize'
Display the number of lines that list' prints.

Repeating a list' command with <RET> discards the argument, so it
is equivalent to typing just list'.  This is more useful than listing
the same lines again.  An exception is made for an argument of -';
that argument is preserved in repetition so that each repetition moves
up in the source file.

In general, the list' command expects you to supply zero, one or two
"linespecs".  Linespecs specify source lines; there are several ways of
writing them (*note Specify Location::), but the effect is always to
specify some source line.

Here is a complete description of the possible arguments for list':

list LINESPEC'
Print lines centered around the line specified by LINESPEC.

list FIRST,LAST'
Print lines from FIRST to LAST.  Both arguments are linespecs.
When a list' command has two linespecs, and the source file of
the second linespec is omitted, this refers to the same source
file as the first linespec.

list ,LAST'
Print lines ending with LAST.

list FIRST,'
Print lines starting with FIRST.

list +'
Print lines just after the lines last printed.

list -'
Print lines just before the lines last printed.

list'
As described in the preceding table.

File: gdb.info,  Node: Specify Location,  Next: Edit,  Prev: List,  Up: Source

9.2 Specifying a Location
=========================

Several GDB commands accept arguments that specify a location of your
program's code.  Since GDB is a source-level debugger, a location
usually specifies some line in the source code; for that reason,
locations are also known as "linespecs".

Here are all the different ways of specifying a code location that
GDB understands:

LINENUM'
Specifies the line number LINENUM of the current source file.

-OFFSET'
+OFFSET'
Specifies the line OFFSET lines before or after the "current
line".  For the list' command, the current line is the last one
printed; for the breakpoint commands, this is the line at which
execution stopped in the currently selected "stack frame" (*note
Frames: Frames, for a description of stack frames.)  When used as
the second of the two linespecs in a list' command, this
specifies the line OFFSET lines up or down from the first linespec.

FILENAME:LINENUM'
Specifies the line LINENUM in the source file FILENAME.

FUNCTION'
Specifies the line that begins the body of the function FUNCTION.
For example, in C, this is the line with the open brace.

FILENAME:FUNCTION'
Specifies the line that begins the body of the function FUNCTION
in the file FILENAME.  You only need the file name with a function
name to avoid ambiguity when there are identically named functions
in different source files.

Specifies the program address ADDRESS.  For line-oriented
commands, such as list' and edit', this specifies a source line
that contains ADDRESS.  For break' and other breakpoint oriented
commands, this can be used to set breakpoints in parts of your
program which do not have debugging information or source files.

Here ADDRESS may be any expression valid in the current working
language (*note working language: Languages.) that specifies a code
address.  In addition, as a convenience, GDB extends the semantics
of expressions used in locations to cover the situations that
frequently happen during debugging.  Here are the various forms of

EXPRESSION'
Any expression valid in the current working language.

FUNCADDR'
An address of a function or procedure derived from its name.
In C, C++, Java, Objective-C, Fortran, minimal, and assembly,
this is simply the function's name FUNCTION (and actually a
special case of a valid expression).  In Pascal and Modula-2,
this is &FUNCTION'.  In Ada, this is FUNCTION'Address'
(although the Pascal form also works).

This form specifies the address of the function's first
instruction, before the stack frame and arguments have been
set up.

Like FUNCADDR above, but also specifies the name of the source
file explicitly.  This is useful if the name of the function
does not specify the function unambiguously, e.g., if there
are several functions with identical names in different
source files.

probe:[OBJFILE:][PROVIDER:]NAME'
The GNU/Linux tool SystemTap' provides a way for applications to
embed static probes.  This form of linespec specifies the location
of such a static probe.  See
http://sourceware.org/systemtap/wiki/AddingUserSpaceProbingToApps'

If OBJFILE is given, only probes coming from that shared library
or executable are considered.  If PROVIDER is given, then only
probes from that provider are considered.

*Note Static Probe Points::, for more information on finding and
using static probes.

Some probes have an associated semaphore variable; for instance,
this happens automatically if you defined your probe using a
DTrace-style .d' file.  If your probe has a semaphore, GDB will
automatically enable it when you specify a breakpoint using the
probe:' notation.  But, if you put a breakpoint at a probe's
location by some other method (e.g., break file:line'), then GDB
will not automatically set the semaphore.

File: gdb.info,  Node: Edit,  Next: Search,  Prev: Specify Location,  Up: Source

9.3 Editing Source Files
========================

To edit the lines in a source file, use the edit' command.  The
editing program of your choice is invoked with the current line set to
the active line in the program.  Alternatively, there are several ways
to specify what part of the file you want to print if you want to see
other parts of the program:

edit LOCATION'
Edit the source file specified by location'.  Editing starts at
that LOCATION, e.g., at the specified source line of the specified
file.  *Note Specify Location::, for all the possible forms of the
LOCATION argument; here are the forms of the edit' command most
commonly used:

edit NUMBER'
Edit the current source file with NUMBER as the active line
number.

edit FUNCTION'
Edit the file containing FUNCTION at the beginning of its
definition.

9.3.1 Choosing your Editor
--------------------------

You can customize GDB to use any editor you want (1).  By default, it
is /bin/ex', but you can change this by setting the environment
variable EDITOR' before using GDB.  For example, to configure GDB to
use the vi' editor, you could use these commands with the sh' shell:
EDITOR=/usr/bin/vi
export EDITOR
gdb ...
or in the csh' shell,
setenv EDITOR /usr/bin/vi
gdb ...

---------- Footnotes ----------

(1) The only restriction is that your editor (say ex'), recognizes
the following command-line syntax:
ex +NUMBER file
The optional numeric value +NUMBER specifies the number of the line
in the file where to start editing.

File: gdb.info,  Node: Search,  Next: Source Path,  Prev: Edit,  Up: Source

9.4 Searching Source Files
==========================

There are two commands for searching through the current source file
for a regular expression.

forward-search REGEXP'
search REGEXP'
The command forward-search REGEXP' checks each line, starting
with the one following the last line listed, for a match for
REGEXP.  It lists the line that is found.  You can use the synonym
search REGEXP' or abbreviate the command name as fo'.

reverse-search REGEXP'
The command reverse-search REGEXP' checks each line, starting
with the one before the last line listed and going backward, for a
match for REGEXP.  It lists the line that is found.  You can
abbreviate this command as rev'.

File: gdb.info,  Node: Source Path,  Next: Machine Code,  Prev: Search,  Up: Source

9.5 Specifying Source Directories
=================================

Executable programs sometimes do not record the directories of the
source files from which they were compiled, just the names.  Even when
they do, the directories could be moved between the compilation and
your debugging session.  GDB has a list of directories to search for
source files; this is called the "source path".  Each time GDB wants a
source file, it tries all the directories in the list, in the order
they are present in the list, until it finds a file with the desired
name.

For example, suppose an executable references the file
/usr/src/foo-1.0/lib/foo.c', and our source path is /mnt/cross'.  The
file is first looked up literally; if this fails,
/mnt/cross/usr/src/foo-1.0/lib/foo.c' is tried; if this fails,
/mnt/cross/foo.c' is opened; if this fails, an error message is
printed.  GDB does not look up the parts of the source file name, such
as /mnt/cross/src/foo-1.0/lib/foo.c'.  Likewise, the subdirectories of
the source path are not searched: if the source path is /mnt/cross',
and the binary refers to foo.c', GDB would not find it under
/mnt/cross/usr/src/foo-1.0/lib'.

Plain file names, relative file names with leading directories, file
names containing dots, etc. are all treated as described above; for
instance, if the source path is /mnt/cross', and the source file is
recorded as ../lib/foo.c', GDB would first try ../lib/foo.c', then
/mnt/cross/../lib/foo.c', and after that--/mnt/cross/foo.c'.

Note that the executable search path is _not_ used to locate the
source files.

Whenever you reset or rearrange the source path, GDB clears out any
information it has cached about where source files are found and where
each line is in the file.

When you start GDB, its source path includes only cdir' and cwd',
in that order.  To add other directories, use the directory' command.

The search path is used to find both program source files and GDB
script files (read using the -command' option and source' command).

In addition to the source path, GDB provides a set of commands that
manage a list of source path substitution rules.  A "substitution rule"
specifies how to rewrite source directories stored in the program's
debug information in case the sources were moved to a different
directory between compilation and debugging.  A rule is made of two
strings, the first specifying what needs to be rewritten in the path,
and the second specifying how it should be rewritten.  In *note set
substitute-path::, we name these two parts FROM and TO respectively.
GDB does a simple string replacement of FROM with TO at the start of
the directory part of the source file name, and uses that result
instead of the original file name to look up the sources.

Using the previous example, suppose the foo-1.0' tree has been
moved from /usr/src' to /mnt/cross', then you can tell GDB to replace
/usr/src' in all source path names with /mnt/cross'.  The first
lookup will then be /mnt/cross/foo-1.0/lib/foo.c' in place of the
original location of /usr/src/foo-1.0/lib/foo.c'.  To define a source
path substitution rule, use the set substitute-path' command (*note
set substitute-path::).

To avoid unexpected substitution results, a rule is applied only if
the FROM part of the directory name ends at a directory separator.  For
instance, a rule substituting  /usr/source' into /mnt/cross' will be
applied to /usr/source/foo-1.0' but not to /usr/sourceware/foo-2.0'.
And because the substitution is applied only at the beginning of the
directory name, this rule will not be applied to
/root/usr/source/baz.c' either.

In many cases, you can achieve the same result using the directory'
command.  However, set substitute-path' can be more efficient in the
case where the sources are organized in a complex tree with multiple
subdirectories.  With the directory' command, you need to add each
subdirectory of your project.  If you moved the entire tree while
preserving its internal organization, then set substitute-path' allows
you to direct the debugger to all the sources with one single command.

set substitute-path' is also more than just a shortcut command.
The source path is only used if the file at the original location no
longer exists.  On the other hand, set substitute-path' modifies the
debugger behavior to look at the rewritten location instead.  So, if
for any reason a source file that is not relevant to your executable is
located at the original location, a substitution rule is the only
method available to point GDB at the new location.

You can configure a default source path substitution rule by
configuring GDB with the --with-relocated-sources=DIR' option.  The DIR
should be the name of a directory under GDB's configured prefix (set
with --prefix' or --exec-prefix'), and directory names in debug
information under DIR will be adjusted automatically if the installed
GDB is moved to a new location.  This is useful if GDB, libraries or
executables with debug information and corresponding source code are
being moved together.

directory DIRNAME ...'

dir DIRNAME ...'
Add directory DIRNAME to the front of the source path.  Several
directory names may be given to this command, separated by :'
(;' on MS-DOS and MS-Windows, where :' usually appears as part
of absolute file names) or whitespace.  You may specify a
directory that is already in the source path; this moves it
forward, so GDB searches it sooner.

You can use the string $cdir' to refer to the compilation directory (if one is recorded), and $cwd' to refer to the current
working directory.  $cwd' is not the same as .'--the former tracks the current working directory as it changes during your GDB session, while the latter is immediately expanded to the current directory at the time you add an entry to the source path. directory' Reset the source path to its default value ($cdir:$cwd' on Unix systems). This requires confirmation. show directories' Print the source path: show which directories it contains. set substitute-path FROM TO' Define a source path substitution rule, and add it at the end of the current list of existing substitution rules. If a rule with the same FROM was already defined, then the old rule is also deleted. For example, if the file /foo/bar/baz.c' was moved to /mnt/cross/baz.c', then the command (gdb) set substitute-path /usr/src /mnt/cross will tell GDB to replace /usr/src' with /mnt/cross', which will allow GDB to find the file baz.c' even though it was moved. In the case when more than one substitution rule have been defined, the rules are evaluated one by one in the order where they have been defined. The first one matching, if any, is selected to perform the substitution. For instance, if we had entered the following commands: (gdb) set substitute-path /usr/src/include /mnt/include (gdb) set substitute-path /usr/src /mnt/src GDB would then rewrite /usr/src/include/defs.h' into /mnt/include/defs.h' by using the first rule. However, it would use the second rule to rewrite /usr/src/lib/foo.c' into /mnt/src/lib/foo.c'. unset substitute-path [path]' If a path is specified, search the current list of substitution rules for a rule that would rewrite that path. Delete that rule if found. A warning is emitted by the debugger if no rule could be found. If no path is specified, then all substitution rules are deleted. show substitute-path [path]' If a path is specified, then print the source path substitution rule which would rewrite that path, if any. If no path is specified, then print all existing source path substitution rules. If your source path is cluttered with directories that are no longer of interest, GDB may sometimes cause confusion by finding the wrong versions of source. You can correct the situation as follows: 1. Use directory' with no argument to reset the source path to its default value. 2. Use directory' with suitable arguments to reinstall the directories you want in the source path. You can add all the directories in one command. File: gdb.info, Node: Machine Code, Prev: Source Path, Up: Source 9.6 Source and Machine Code =========================== You can use the command info line' to map source lines to program addresses (and vice versa), and the command disassemble' to display a range of addresses as machine instructions. You can use the command set disassemble-next-line' to set whether to disassemble next source line when execution stops. When run under GNU Emacs mode, the info line' command causes the arrow to point to the line specified. Also, info line' prints addresses in symbolic form as well as hex. info line LINESPEC' Print the starting and ending addresses of the compiled code for source line LINESPEC. You can specify source lines in any of the ways documented in *note Specify Location::. For example, we can use info line' to discover the location of the object code for the first line of function m4_changequote': (gdb) info line m4_changequote Line 895 of "builtin.c" starts at pc 0x634c and ends at 0x6350. We can also inquire (using *ADDR' as the form for LINESPEC) what source line covers a particular address: (gdb) info line *0x63ff Line 926 of "builtin.c" starts at pc 0x63e4 and ends at 0x6404. After info line', the default address for the x' command is changed to the starting address of the line, so that x/i' is sufficient to begin examining the machine code (*note Examining Memory: Memory.). Also, this address is saved as the value of the convenience variable $_' (*note Convenience Variables: Convenience Vars.).

disassemble'
disassemble /m'
disassemble /r'
This specialized command dumps a range of memory as machine
instructions.  It can also print mixed source+disassembly by
specifying the /m' modifier and print the raw instructions in hex
as well as in symbolic form by specifying the /r'.  The default
memory range is the function surrounding the program counter of
the selected frame.  A single argument to this command is a
program counter value; GDB dumps the function surrounding this
value.  When two arguments are given, they should be separated by
a comma, possibly surrounded by whitespace.  The arguments specify
a range of addresses to dump, in one of two forms:

START,END'
the addresses from START (inclusive) to END (exclusive)

START,+LENGTH'
the addresses from START (inclusive) to START+LENGTH'
(exclusive).

When 2 arguments are specified, the name of the function is also
printed (since there could be several functions in the given
range).

The argument(s) can be any expression yielding a numeric value,
such as 0x32c4', &main+10' or $pc - 8'. If the range of memory being disassembled contains current program counter, the instruction at that location is shown with a =>' marker. The following example shows the disassembly of a range of addresses of HP PA-RISC 2.0 code: (gdb) disas 0x32c4, 0x32e4 Dump of assembler code from 0x32c4 to 0x32e4: 0x32c4 <main+204>: addil 0,dp 0x32c8 <main+208>: ldw 0x22c(sr0,r1),r26 0x32cc <main+212>: ldil 0x3000,r31 0x32d0 <main+216>: ble 0x3f8(sr4,r31) 0x32d4 <main+220>: ldo 0(r31),rp 0x32d8 <main+224>: addil -0x800,dp 0x32dc <main+228>: ldo 0x588(r1),r26 0x32e0 <main+232>: ldil 0x3000,r31 End of assembler dump. Here is an example showing mixed source+assembly for Intel x86, when the program is stopped just after function prologue: (gdb) disas /m main Dump of assembler code for function main: 5 { 0x08048330 <+0>: push %ebp 0x08048331 <+1>: mov %esp,%ebp 0x08048333 <+3>: sub$0x8,%esp
0x08048336 <+6>:    and    $0xfffffff0,%esp 0x08048339 <+9>: sub$0x10,%esp

6         printf ("Hello.\n");
=> 0x0804833c <+12>:   movl   $0x8048440,(%esp) 0x08048343 <+19>: call 0x8048284 <puts@plt> 7 return 0; 8 } 0x08048348 <+24>: mov$0x0,%eax
0x0804834d <+29>:   leave
0x0804834e <+30>:   ret

End of assembler dump.

Here is another example showing raw instructions in hex for AMD
x86-64,

(gdb) disas /r 0x400281,+10
Dump of assembler code from 0x400281 to 0x40028b:
0x0000000000400281:  38 36  cmp    %dh,(%rsi)
0x0000000000400283:  2d 36 34 2e 73 sub    $0x732e3436,%eax 0x0000000000400288: 6f outsl %ds:(%rsi),(%dx) 0x0000000000400289: 2e 32 00 xor %cs:(%rax),%al End of assembler dump. Some architectures have more than one commonly-used set of instruction mnemonics or other syntax. For programs that were dynamically linked and use shared libraries, instructions that call functions or branch to locations in the shared libraries might show a seemingly bogus location--it's actually a location of the relocation table. On some architectures, GDB might be able to resolve these to actual function names. set disassembly-flavor INSTRUCTION-SET' Select the instruction set to use when disassembling the program via the disassemble' or x/i' commands. Currently this command is only defined for the Intel x86 family. You can set INSTRUCTION-SET to either intel' or att'. The default is att', the AT&T flavor used by default by Unix assemblers for x86-based targets. show disassembly-flavor' Show the current setting of the disassembly flavor. set disassemble-next-line' show disassemble-next-line' Control whether or not GDB will disassemble the next source line or instruction when execution stops. If ON, GDB will display disassembly of the next source line when execution of the program being debugged stops. This is _in addition_ to displaying the source line itself, which GDB always does if possible. If the next source line cannot be displayed for some reason (e.g., if GDB cannot find the source file, or there's no line info in the debug info), GDB will display disassembly of the next _instruction_ instead of showing the next source line. If AUTO, GDB will display disassembly of next instruction only if the source line cannot be displayed. This setting causes GDB to display some feedback when you step through a function with no line info or whose source file is unavailable. The default is OFF, which means never display the disassembly of the next line or instruction. File: gdb.info, Node: Data, Next: Optimized Code, Prev: Source, Up: Top 10 Examining Data ***************** The usual way to examine data in your program is with the print' command (abbreviated p'), or its synonym inspect'. It evaluates and prints the value of an expression of the language your program is written in (*note Using GDB with Different Languages: Languages.). It may also print the expression using a Python-based pretty-printer (*note Pretty Printing::). print EXPR' print /F EXPR' EXPR is an expression (in the source language). By default the value of EXPR is printed in a format appropriate to its data type; you can choose a different format by specifying /F', where F is a letter specifying the format; see *note Output Formats: Output Formats. print' print /F' If you omit EXPR, GDB displays the last value again (from the "value history"; *note Value History: Value History.). This allows you to conveniently inspect the same value in an alternative format. A more low-level way of examining data is with the x' command. It examines data in memory at a specified address and prints it in a specified format. *Note Examining Memory: Memory. If you are interested in information about types, or about how the fields of a struct or a class are declared, use the ptype EXP' command rather than print'. *Note Examining the Symbol Table: Symbols. * Menu: * Expressions:: Expressions * Ambiguous Expressions:: Ambiguous Expressions * Variables:: Program variables * Arrays:: Artificial arrays * Output Formats:: Output formats * Memory:: Examining memory * Auto Display:: Automatic display * Print Settings:: Print settings * Pretty Printing:: Python pretty printing * Value History:: Value history * Convenience Vars:: Convenience variables * Convenience Funs:: Convenience Functions * Registers:: Registers * Floating Point Hardware:: Floating point hardware * Vector Unit:: Vector Unit * OS Information:: Auxiliary data provided by operating system * Memory Region Attributes:: Memory region attributes * Dump/Restore Files:: Copy between memory and a file * Core File Generation:: Cause a program dump its core * Character Sets:: Debugging programs that use a different character set than GDB does * Caching Remote Data:: Data caching for remote targets * Searching Memory:: Searching memory for a sequence of bytes File: gdb.info, Node: Expressions, Next: Ambiguous Expressions, Up: Data 10.1 Expressions ================ print' and many other GDB commands accept an expression and compute its value. Any kind of constant, variable or operator defined by the programming language you are using is valid in an expression in GDB. This includes conditional expressions, function calls, casts, and string constants. It also includes preprocessor macros, if you compiled your program to include this information; see *note Compilation::. GDB supports array constants in expressions input by the user. The syntax is {ELEMENT, ELEMENT...}. For example, you can use the command print {1, 2, 3}' to create an array of three integers. If you pass an array to a function or assign it to a program variable, GDB copies the array to memory that is malloc'ed in the target program. Because C is so widespread, most of the expressions shown in examples in this manual are in C. *Note Using GDB with Different Languages: Languages, for information on how to use expressions in other languages. In this section, we discuss operators that you can use in GDB expressions regardless of your programming language. Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer in order to examine a structure at that address in memory. GDB supports these operators, in addition to those common to programming languages: @' @' is a binary operator for treating parts of memory as arrays. *Note Artificial Arrays: Arrays, for more information. ::' ::' allows you to specify a variable in terms of the file or function where it is defined. *Note Program Variables: Variables. {TYPE} ADDR' Refers to an object of type TYPE stored at address ADDR in memory. ADDR may be any expression whose value is an integer or pointer (but parentheses are required around binary operators, just as in a cast). This construct is allowed regardless of what kind of data is normally supposed to reside at ADDR. File: gdb.info, Node: Ambiguous Expressions, Next: Variables, Prev: Expressions, Up: Data 10.2 Ambiguous Expressions ========================== Expressions can sometimes contain some ambiguous elements. For instance, some programming languages (notably Ada, C++ and Objective-C) permit a single function name to be defined several times, for application in different contexts. This is called "overloading". Another example involving Ada is generics. A "generic package" is similar to C++ templates and is typically instantiated several times, resulting in the same function name being defined in different contexts. In some cases and depending on the language, it is possible to adjust the expression to remove the ambiguity. For instance in C++, you can specify the signature of the function you want to break on, as in break FUNCTION(TYPES)'. In Ada, using the fully qualified name of your function often makes the expression unambiguous as well. When an ambiguity that needs to be resolved is detected, the debugger has the capability to display a menu of numbered choices for each possibility, and then waits for the selection with the prompt >'. The first option is always [0] cancel', and typing 0 <RET>' aborts the current command. If the command in which the expression was used allows more than one choice to be selected, the next option in the menu is [1] all', and typing 1 <RET>' selects all possible choices. For example, the following session excerpt shows an attempt to set a breakpoint at the overloaded symbol String::after'. We choose three particular definitions of that function name: (gdb) b String::after [0] cancel [1] all [2] file:String.cc; line number:867 [3] file:String.cc; line number:860 [4] file:String.cc; line number:875 [5] file:String.cc; line number:853 [6] file:String.cc; line number:846 [7] file:String.cc; line number:735 > 2 4 6 Breakpoint 1 at 0xb26c: file String.cc, line 867. Breakpoint 2 at 0xb344: file String.cc, line 875. Breakpoint 3 at 0xafcc: file String.cc, line 846. Multiple breakpoints were set. Use the "delete" command to delete unwanted breakpoints. (gdb) set multiple-symbols MODE' This option allows you to adjust the debugger behavior when an expression is ambiguous. By default, MODE is set to all'. If the command with which the expression is used allows more than one choice, then GDB automatically selects all possible choices. For instance, inserting a breakpoint on a function using an ambiguous name results in a breakpoint inserted on each possible match. However, if a unique choice must be made, then GDB uses the menu to help you disambiguate the expression. For instance, printing the address of an overloaded function will result in the use of the menu. When MODE is set to ask', the debugger always uses the menu when an ambiguity is detected. Finally, when MODE is set to cancel', the debugger reports an error due to the ambiguity and the command is aborted. show multiple-symbols' Show the current value of the multiple-symbols' setting. File: gdb.info, Node: Variables, Next: Arrays, Prev: Ambiguous Expressions, Up: Data 10.3 Program Variables ====================== The most common kind of expression to use is the name of a variable in your program. Variables in expressions are understood in the selected stack frame (*note Selecting a Frame: Selection.); they must be either: * global (or file-static) or * visible according to the scope rules of the programming language from the point of execution in that frame This means that in the function foo (a) int a; { bar (a); { int b = test (); bar (b); } } you can examine and use the variable a' whenever your program is executing within the function foo', but you can only use or examine the variable b' while your program is executing inside the block where b' is declared. There is an exception: you can refer to a variable or function whose scope is a single source file even if the current execution point is not in this file. But it is possible to have more than one such variable or function with the same name (in different source files). If that happens, referring to that name has unpredictable effects. If you wish, you can specify a static variable in a particular function or file, using the colon-colon (::') notation: FILE::VARIABLE FUNCTION::VARIABLE Here FILE or FUNCTION is the name of the context for the static VARIABLE. In the case of file names, you can use quotes to make sure GDB parses the file name as a single word--for example, to print a global value of x' defined in f2.c': (gdb) p 'f2.c'::x This use of ::' is very rarely in conflict with the very similar use of the same notation in C++. GDB also supports use of the C++ scope resolution operator in GDB expressions. _Warning:_ Occasionally, a local variable may appear to have the wrong value at certain points in a function--just after entry to a new scope, and just before exit. You may see this problem when you are stepping by machine instructions. This is because, on most machines, it takes more than one instruction to set up a stack frame (including local variable definitions); if you are stepping by machine instructions, variables may appear to have the wrong values until the stack frame is completely built. On exit, it usually also takes more than one machine instruction to destroy a stack frame; after you begin stepping through that group of instructions, local variable definitions may be gone. This may also happen when the compiler does significant optimizations. To be sure of always seeing accurate values, turn off all optimization when compiling. Another possible effect of compiler optimizations is to optimize unused variables out of existence, or assign variables to registers (as opposed to memory addresses). Depending on the support for such cases offered by the debug info format used by the compiler, GDB might not be able to display values for such local variables. If that happens, GDB will print a message like this: No symbol "foo" in current context. To solve such problems, either recompile without optimizations, or use a different debug info format, if the compiler supports several such formats. For example, GCC, the GNU C/C++ compiler, usually supports the -gstabs+' option. -gstabs+' produces debug info in a format that is superior to formats such as COFF. You may be able to use DWARF 2 (-gdwarf-2'), which is also an effective form for debug info. *Note Options for Debugging Your Program or GCC: (gcc.info)Debugging Options. *Note C and C++: C, for more information about debug info formats that are best suited to C++ programs. If you ask to print an object whose contents are unknown to GDB, e.g., because its data type is not completely specified by the debug information, GDB will say <incomplete type>'. *Note incomplete type: Symbols, for more about this. Strings are identified as arrays of char' values without specified signedness. Arrays of either signed char' or unsigned char' get printed as arrays of 1 byte sized integers. -fsigned-char' or -funsigned-char' GCC options have no effect as GDB defines literal string type "char"' as char' without a sign. For program code char var0[] = "A"; signed char var1[] = "A"; You get during debugging (gdb) print var0$1 = "A"
(gdb) print var1
$2 = {65 'A', 0 '\0'} File: gdb.info, Node: Arrays, Next: Output Formats, Prev: Variables, Up: Data 10.4 Artificial Arrays ====================== It is often useful to print out several successive objects of the same type in memory; a section of an array, or an array of dynamically determined size for which only a pointer exists in the program. You can do this by referring to a contiguous span of memory as an "artificial array", using the binary operator @'. The left operand of @' should be the first element of the desired array and be an individual object. The right operand should be the desired length of the array. The result is an array value whose elements are all of the type of the left argument. The first element is actually the left argument; the second element comes from bytes of memory immediately following those that hold the first element, and so on. Here is an example. If a program says int *array = (int *) malloc (len * sizeof (int)); you can print the contents of array' with p *array@len The left operand of @' must reside in memory. Array values made with @' in this way behave just like other arrays in terms of subscripting, and are coerced to pointers when used in expressions. Artificial arrays most often appear in expressions via the value history (*note Value History: Value History.), after printing one out. Another way to create an artificial array is to use a cast. This re-interprets a value as if it were an array. The value need not be in memory: (gdb) p/x (short[2])0x12345678$1 = {0x1234, 0x5678}

As a convenience, if you leave the array length out (as in
(TYPE[])VALUE') GDB calculates the size to fill the value (as
sizeof(VALUE)/sizeof(TYPE)':
(gdb) p/x (short[])0x12345678
$2 = {0x1234, 0x5678} Sometimes the artificial array mechanism is not quite enough; in moderately complex data structures, the elements of interest may not actually be adjacent--for example, if you are interested in the values of pointers in an array. One useful work-around in this situation is to use a convenience variable (*note Convenience Variables: Convenience Vars.) as a counter in an expression that prints the first interesting value, and then repeat that expression via <RET>. For instance, suppose you have an array dtab' of pointers to structures, and you are interested in the values of a field fv' in each structure. Here is an example of what you might type: set$i = 0
p dtab[$i++]->fv <RET> <RET> ... File: gdb.info, Node: Output Formats, Next: Memory, Prev: Arrays, Up: Data 10.5 Output Formats =================== By default, GDB prints a value according to its data type. Sometimes this is not what you want. For example, you might want to print a number in hex, or a pointer in decimal. Or you might want to view data in memory at a certain address as a character string or as an instruction. To do these things, specify an "output format" when you print a value. The simplest use of output formats is to say how to print a value already computed. This is done by starting the arguments of the print' command with a slash and a format letter. The format letters supported are: x' Regard the bits of the value as an integer, and print the integer in hexadecimal. d' Print as integer in signed decimal. u' Print as integer in unsigned decimal. o' Print as integer in octal. t' Print as integer in binary. The letter t' stands for "two". (1) a' Print as an address, both absolute in hexadecimal and as an offset from the nearest preceding symbol. You can use this format used to discover where (in what function) an unknown address is located: (gdb) p/a 0x54320$3 = 0x54320 <_initialize_vx+396>

The command info symbol 0x54320' yields similar results.  *Note
info symbol: Symbols.

c'
Regard as an integer and print it as a character constant.  This
prints both the numerical value and its character representation.
The character representation is replaced with the octal escape
\nnn' for characters outside the 7-bit ASCII range.

Without this format, GDB displays char', unsigned char', and
signed char' data as character constants.  Single-byte members of
vectors are displayed as integer data.

f'
Regard the bits of the value as a floating point number and print
using typical floating point syntax.

s'
Regard as a string, if possible.  With this format, pointers to
single-byte data are displayed as null-terminated strings and
arrays of single-byte data are displayed as fixed-length strings.
Other values are displayed in their natural types.

Without this format, GDB displays pointers to and arrays of
char', unsigned char', and signed char' as strings.
Single-byte members of a vector are displayed as an integer array.

r'
Print using the raw' formatting.  By default, GDB will use a
Python-based pretty-printer, if one is available (*note Pretty
Printing::).  This typically results in a higher-level display of
the value's contents.  The r' format bypasses any Python
pretty-printer which might exist.

For example, to print the program counter in hex (*note
Registers::), type

p/x $pc Note that no space is required before the slash; this is because command names in GDB cannot contain a slash. To reprint the last value in the value history with a different format, you can use the print' command with just a format and no expression. For example, p/x' reprints the last value in hex. ---------- Footnotes ---------- (1) b' cannot be used because these format letters are also used with the x' command, where b' stands for "byte"; see *note Examining Memory: Memory. File: gdb.info, Node: Memory, Next: Auto Display, Prev: Output Formats, Up: Data 10.6 Examining Memory ===================== You can use the command x' (for "examine") to examine memory in any of several formats, independently of your program's data types. x/NFU ADDR' x ADDR' x' Use the x' command to examine memory. N, F, and U are all optional parameters that specify how much memory to display and how to format it; ADDR is an expression giving the address where you want to start displaying memory. If you use defaults for NFU, you need not type the slash /'. Several commands set convenient defaults for ADDR. N, the repeat count The repeat count is a decimal integer; the default is 1. It specifies how much memory (counting by units U) to display. F, the display format The display format is one of the formats used by print' (x', d', u', o', t', a', c', f', s'), and in addition i' (for machine instructions). The default is x' (hexadecimal) initially. The default changes each time you use either x' or print'. U, the unit size The unit size is any of b' Bytes. h' Halfwords (two bytes). w' Words (four bytes). This is the initial default. g' Giant words (eight bytes). Each time you specify a unit size with x', that size becomes the default unit the next time you use x'. For the i' format, the unit size is ignored and is normally not written. For the s' format, the unit size defaults to b', unless it is explicitly given. Use x /hs' to display 16-bit char strings and x /ws' to display 32-bit strings. The next use of x /s' will again display 8-bit strings. Note that the results depend on the programming language of the current compilation unit. If the language is C, the s' modifier will use the UTF-16 encoding while w' will use UTF-32. The encoding is set by the programming language and cannot be altered. ADDR, starting display address ADDR is the address where you want GDB to begin displaying memory. The expression need not have a pointer value (though it may); it is always interpreted as an integer address of a byte of memory. *Note Expressions: Expressions, for more information on expressions. The default for ADDR is usually just after the last address examined--but several other commands also set the default address: info breakpoints' (to the address of the last breakpoint listed), info line' (to the starting address of a line), and print' (if you use it to display a value from memory). For example, x/3uh 0x54320' is a request to display three halfwords (h') of memory, formatted as unsigned decimal integers (u'), starting at address 0x54320'. x/4xw$sp' prints the four words (w') of
memory above the stack pointer (here, $sp'; *note Registers: Registers.) in hexadecimal (x'). Since the letters indicating unit sizes are all distinct from the letters specifying output formats, you do not have to remember whether unit size or format comes first; either order works. The output specifications 4xw' and 4wx' mean exactly the same thing. (However, the count N must come first; wx4' does not work.) Even though the unit size U is ignored for the formats s' and i', you might still want to use a count N; for example, 3i' specifies that you want to see three machine instructions, including any operands. For convenience, especially when used with the display' command, the i' format also prints branch delay slot instructions, if any, beyond the count specified, which immediately follow the last instruction that is within the count. The command disassemble' gives an alternative way of inspecting machine instructions; see *note Source and Machine Code: Machine Code. All the defaults for the arguments to x' are designed to make it easy to continue scanning memory with minimal specifications each time you use x'. For example, after you have inspected three machine instructions with x/3i ADDR', you can inspect the next seven with just x/7'. If you use <RET> to repeat the x' command, the repeat count N is used again; the other arguments default as for successive uses of x'. When examining machine instructions, the instruction at current program counter is shown with a =>' marker. For example: (gdb) x/5i$pc-6
0x804837f <main+11>: mov    %esp,%ebp
0x8048381 <main+13>: push   %ecx
0x8048382 <main+14>: sub    $0x4,%esp => 0x8048385 <main+17>: movl$0x8048460,(%esp)
0x804838c <main+24>: call   0x80482d4 <puts@plt>

The addresses and contents printed by the x' command are not saved
in the value history because there is often too much of them and they
would get in the way.  Instead, GDB makes these values available for
subsequent use in expressions as values of the convenience variables
$_' and $__'.  After an x' command, the last address examined is
available for use in expressions in the convenience variable $_'. The contents of that address, as examined, are available in the convenience variable $__'.

If the x' command has a repeat count, the address and contents saved
are from the last memory unit printed; this is not the same as the last
address printed if several units were printed on the last line of
output.

When you are debugging a program running on a remote target machine
(*note Remote Debugging::), you may wish to verify the program's image
in the remote machine's memory against the executable file you
downloaded to the target.  The compare-sections' command is provided
for such situations.

compare-sections [SECTION-NAME]'
Compare the data of a loadable section SECTION-NAME in the
executable file of the program being debugged with the same
section in the remote machine's memory, and report any mismatches.
With no arguments, compares all loadable sections.  This command's
availability depends on the target's support for the "qCRC"'
remote request.

File: gdb.info,  Node: Auto Display,  Next: Print Settings,  Prev: Memory,  Up: Data

10.7 Automatic Display
======================

If you find that you want to print the value of an expression frequently
(to see how it changes), you might want to add it to the "automatic
display list" so that GDB prints its value each time your program stops.
Each expression added to the list is given a number to identify it; to
remove an expression from the list, you specify that number.  The
automatic display looks like this:

2: foo = 38
3: bar[5] = (struct hack *) 0x3804

This display shows item numbers, expressions and their current values.
As with displays you request manually using x' or print', you can
specify the output format you prefer; in fact, display' decides
whether to use print' or x' depending your format specification--it
uses x' if you specify either the i' or s' format, or a unit size;
otherwise it uses print'.

display EXPR'
Add the expression EXPR to the list of expressions to display each
time your program stops.  *Note Expressions: Expressions.

display' does not repeat if you press <RET> again after using it.

display/FMT EXPR'
For FMT specifying only a display format and not a size or count,
add the expression EXPR to the auto-display list but arrange to
display it each time in the specified format FMT.  *Note Output
Formats: Output Formats.

display/FMT ADDR'
For FMT i' or s', or including a unit-size or a number of units,
add the expression ADDR as a memory address to be examined each
time your program stops.  Examining means in effect doing x/FMT
ADDR'.  *Note Examining Memory: Memory.

For example, display/i $pc' can be helpful, to see the machine instruction about to be executed each time execution stops ($pc' is a
common name for the program counter; *note Registers: Registers.).

undisplay DNUMS...'
delete display DNUMS...'
Remove item numbers DNUMS from the list of expressions to display.

undisplay' does not repeat if you press <RET> after using it.
(Otherwise you would just get the error No display number ...'.)

disable display DNUMS...'
Disable the display of item numbers DNUMS.  A disabled display
item is not printed automatically, but is not forgotten.  It may be
enabled again later.

enable display DNUMS...'
Enable display of item numbers DNUMS.  It becomes effective once
again in auto display of its expression, until you specify
otherwise.

display'
Display the current values of the expressions on the list, just as
is done when your program stops.

info display'
Print the list of expressions previously set up to display
automatically, each one with its item number, but without showing
the values.  This includes disabled expressions, which are marked
as such.  It also includes expressions which would not be
displayed right now because they refer to automatic variables not
currently available.

If a display expression refers to local variables, then it does not
make sense outside the lexical context for which it was set up.  Such an
expression is disabled when execution enters a context where one of its
variables is not defined.  For example, if you give the command
display last_char' while inside a function with an argument
last_char', GDB displays this argument while your program continues to
stop inside that function.  When it stops elsewhere--where there is no
variable last_char'--the display is disabled automatically.  The next
time your program stops where last_char' is meaningful, you can enable
the display expression once again.

File: gdb.info,  Node: Print Settings,  Next: Pretty Printing,  Prev: Auto Display,  Up: Data

10.8 Print Settings
===================

GDB provides the following ways to control how arrays, structures, and
symbols are printed.

These settings are useful for debugging programs in any language:

set print address'
set print address on'
GDB prints memory addresses showing the location of stack traces,
structure values, pointer values, breakpoints, and so forth, even
when it also displays the contents of those addresses.  The default
is on'.  For example, this is what a stack frame display looks
like with set print address on':

(gdb) f
#0  set_quotes (lq=0x34c78 "<<", rq=0x34c88 ">>")
at input.c:530
530         if (lquote != def_lquote)

set print address off'
Do not print addresses when displaying their contents.  For
example, this is the same stack frame displayed with set print

(gdb) set print addr off
(gdb) f
#0  set_quotes (lq="<<", rq=">>") at input.c:530
530         if (lquote != def_lquote)

You can use set print address off' to eliminate all machine
dependent displays from the GDB interface.  For example, with
print address off', you should get the same text for backtraces on
all machines--whether or not they involve pointer arguments.

show print address'
Show whether or not addresses are to be printed.

When GDB prints a symbolic address, it normally prints the closest
earlier symbol plus an offset.  If that symbol does not uniquely
identify the address (for example, it is a name whose scope is a single
source file), you may need to clarify.  One way to do this is with
info line', for example info line *0x4537'.  Alternately, you can set
GDB to print the source file and line number when it prints a symbolic

set print symbol-filename on'
Tell GDB to print the source file name and line number of a symbol
in the symbolic form of an address.

set print symbol-filename off'
Do not print source file name and line number of a symbol.  This
is the default.

show print symbol-filename'
Show whether or not GDB will print the source file name and line
number of a symbol in the symbolic form of an address.

Another situation where it is helpful to show symbol filenames and
line numbers is when disassembling code; GDB shows you the line number
and source file that corresponds to each instruction.

Also, you may wish to see the symbolic form only if the address being
printed is reasonably close to the closest earlier symbol:

set print max-symbolic-offset MAX-OFFSET'
Tell GDB to only display the symbolic form of an address if the
offset between the closest earlier symbol and the address is less
than MAX-OFFSET.  The default is 0, which tells GDB to always
print the symbolic form of an address if any symbol precedes it.

show print max-symbolic-offset'
Ask how large the maximum offset is that GDB prints in a symbolic

If you have a pointer and you are not sure where it points, try set
print symbol-filename on'.  Then you can determine the name and source
file location of the variable where it points, using p/a POINTER'.
This interprets the address in symbolic form.  For example, here GDB
shows that a variable ptt' points at another variable t', defined in
hi2.c':

(gdb) set print symbol-filename on
(gdb) p/a ptt
$4 = 0xe008 <t in hi2.c> _Warning:_ For pointers that point to a local variable, p/a' does not show the symbol name and filename of the referent, even with the appropriate set print' options turned on. Other settings control how different kinds of objects are printed: set print array' set print array on' Pretty print arrays. This format is more convenient to read, but uses more space. The default is off. set print array off' Return to compressed format for arrays. show print array' Show whether compressed or pretty format is selected for displaying arrays. set print array-indexes' set print array-indexes on' Print the index of each element when displaying arrays. May be more convenient to locate a given element in the array or quickly find the index of a given element in that printed array. The default is off. set print array-indexes off' Stop printing element indexes when displaying arrays. show print array-indexes' Show whether the index of each element is printed when displaying arrays. set print elements NUMBER-OF-ELEMENTS' Set a limit on how many elements of an array GDB will print. If GDB is printing a large array, it stops printing after it has printed the number of elements set by the set print elements' command. This limit also applies to the display of strings. When GDB starts, this limit is set to 200. Setting NUMBER-OF-ELEMENTS to zero means that the printing is unlimited. show print elements' Display the number of elements of a large array that GDB will print. If the number is 0, then the printing is unlimited. set print frame-arguments VALUE' This command allows to control how the values of arguments are printed when the debugger prints a frame (*note Frames::). The possible values are: all' The values of all arguments are printed. scalars' Print the value of an argument only if it is a scalar. The value of more complex arguments such as arrays, structures, unions, etc, is replaced by ...'. This is the default. Here is an example where only scalar arguments are shown: #1 0x08048361 in call_me (i=3, s=..., ss=0xbf8d508c, u=..., e=green) at frame-args.c:23 none' None of the argument values are printed. Instead, the value of each argument is replaced by ...'. In this case, the example above now becomes: #1 0x08048361 in call_me (i=..., s=..., ss=..., u=..., e=...) at frame-args.c:23 By default, only scalar arguments are printed. This command can be used to configure the debugger to print the value of all arguments, regardless of their type. However, it is often advantageous to not print the value of more complex parameters. For instance, it reduces the amount of information printed in each frame, making the backtrace more readable. Also, it improves performance when displaying Ada frames, because the computation of large arguments can sometimes be CPU-intensive, especially in large applications. Setting print frame-arguments' to scalars' (the default) or none' avoids this computation, thus speeding up the display of each Ada frame. show print frame-arguments' Show how the value of arguments should be displayed when printing a frame. set print repeats' Set the threshold for suppressing display of repeated array elements. When the number of consecutive identical elements of an array exceeds the threshold, GDB prints the string "<repeats N times>"', where N is the number of identical repetitions, instead of displaying the identical elements themselves. Setting the threshold to zero will cause all elements to be individually printed. The default threshold is 10. show print repeats' Display the current threshold for printing repeated identical elements. set print null-stop' Cause GDB to stop printing the characters of an array when the first NULL is encountered. This is useful when large arrays actually contain only short strings. The default is off. show print null-stop' Show whether GDB stops printing an array on the first NULL character. set print pretty on' Cause GDB to print structures in an indented format with one member per line, like this:$1 = {
next = 0x0,
flags = {
sweet = 1,
sour = 1
},
meat = 0x54 "Pork"
}

set print pretty off'
Cause GDB to print structures in a compact format, like this:

$1 = {next = 0x0, flags = {sweet = 1, sour = 1}, \ meat = 0x54 "Pork"} This is the default format. show print pretty' Show which format GDB is using to print structures. set print sevenbit-strings on' Print using only seven-bit characters; if this option is set, GDB displays any eight-bit characters (in strings or character values) using the notation \'NNN. This setting is best if you are working in English (ASCII) and you use the high-order bit of characters as a marker or "meta" bit. set print sevenbit-strings off' Print full eight-bit characters. This allows the use of more international character sets, and is the default. show print sevenbit-strings' Show whether or not GDB is printing only seven-bit characters. set print union on' Tell GDB to print unions which are contained in structures and other unions. This is the default setting. set print union off' Tell GDB not to print unions which are contained in structures and other unions. GDB will print "{...}"' instead. show print union' Ask GDB whether or not it will print unions which are contained in structures and other unions. For example, given the declarations typedef enum {Tree, Bug} Species; typedef enum {Big_tree, Acorn, Seedling} Tree_forms; typedef enum {Caterpillar, Cocoon, Butterfly} Bug_forms; struct thing { Species it; union { Tree_forms tree; Bug_forms bug; } form; }; struct thing foo = {Tree, {Acorn}}; with set print union on' in effect p foo' would print$1 = {it = Tree, form = {tree = Acorn, bug = Cocoon}}

and with set print union off' in effect it would print

$1 = {it = Tree, form = {...}} set print union' affects programs written in C-like languages and in Pascal. These settings are of interest when debugging C++ programs: set print demangle' set print demangle on' Print C++ names in their source form rather than in the encoded ("mangled") form passed to the assembler and linker for type-safe linkage. The default is on. show print demangle' Show whether C++ names are printed in mangled or demangled form. set print asm-demangle' set print asm-demangle on' Print C++ names in their source form rather than their mangled form, even in assembler code printouts such as instruction disassemblies. The default is off. show print asm-demangle' Show whether C++ names in assembly listings are printed in mangled or demangled form. set demangle-style STYLE' Choose among several encoding schemes used by different compilers to represent C++ names. The choices for STYLE are currently: auto' Allow GDB to choose a decoding style by inspecting your program. gnu' Decode based on the GNU C++ compiler (g++') encoding algorithm. This is the default. hp' Decode based on the HP ANSI C++ (aCC') encoding algorithm. lucid' Decode based on the Lucid C++ compiler (lcc') encoding algorithm. arm' Decode using the algorithm in the C++ Annotated Reference Manual'. *Warning:* this setting alone is not sufficient to allow debugging cfront'-generated executables. GDB would require further enhancement to permit that. If you omit STYLE, you will see a list of possible formats. show demangle-style' Display the encoding style currently in use for decoding C++ symbols. set print object' set print object on' When displaying a pointer to an object, identify the _actual_ (derived) type of the object rather than the _declared_ type, using the virtual function table. set print object off' Display only the declared type of objects, without reference to the virtual function table. This is the default setting. show print object' Show whether actual, or declared, object types are displayed. set print static-members' set print static-members on' Print static members when displaying a C++ object. The default is on. set print static-members off' Do not print static members when displaying a C++ object. show print static-members' Show whether C++ static members are printed or not. set print pascal_static-members' set print pascal_static-members on' Print static members when displaying a Pascal object. The default is on. set print pascal_static-members off' Do not print static members when displaying a Pascal object. show print pascal_static-members' Show whether Pascal static members are printed or not. set print vtbl' set print vtbl on' Pretty print C++ virtual function tables. The default is off. (The vtbl' commands do not work on programs compiled with the HP ANSI C++ compiler (aCC').) set print vtbl off' Do not pretty print C++ virtual function tables. show print vtbl' Show whether C++ virtual function tables are pretty printed, or not. File: gdb.info, Node: Pretty Printing, Next: Value History, Prev: Print Settings, Up: Data 10.9 Pretty Printing ==================== GDB provides a mechanism to allow pretty-printing of values using Python code. It greatly simplifies the display of complex objects. This mechanism works for both MI and the CLI. For example, here is how a C++ std::string' looks without a pretty-printer: (gdb) print s$1 = {
static npos = 4294967295,
_M_dataplus = {
<std::allocator<char>> = {
<__gnu_cxx::new_allocator<char>> = {
<No data fields>}, <No data fields>
},
members of std::basic_string<char, std::char_traits<char>,
std::allocator<char> >::_Alloc_hider:
_M_p = 0x804a014 "abcd"
}
}

With a pretty-printer for std::string' only the contents are
printed:

(gdb) print s
$2 = "abcd" For implementing pretty printers for new types you should read the Python API details (*note Pretty Printing API::). File: gdb.info, Node: Value History, Next: Convenience Vars, Prev: Pretty Printing, Up: Data 10.10 Value History =================== Values printed by the print' command are saved in the GDB "value history". This allows you to refer to them in other expressions. Values are kept until the symbol table is re-read or discarded (for example with the file' or symbol-file' commands). When the symbol table changes, the value history is discarded, since the values may contain pointers back to the types defined in the symbol table. The values printed are given "history numbers" by which you can refer to them. These are successive integers starting with one. print' shows you the history number assigned to a value by printing $NUM = ' before the value; here NUM is the history number.

To refer to any previous value, use $' followed by the value's history number. The way print' labels its output is designed to remind you of this. Just $' refers to the most recent value in the
history, and $$' refers to the value before that. $$N' refers to the
Nth value from the end; $$2' is the value just prior to $$', $$1' is equivalent to $$', and $$0' is equivalent to '. For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type p * If you have a chain of structures where the component next' points to the next one, you can print the contents of the next one with this: p *.next You can print successive links in the chain by repeating this command--which you can do by just typing <RET>. Note that the history records values, not expressions. If the value of x' is 4 and you type these commands: print x set x=5 then the value recorded in the value history by the print' command remains 4 even though the value of x' has changed. show values' Print the last ten values in the value history, with their item numbers. This is like p$$9' repeated ten times, except that
show values' does not change the history.

show values N'
Print ten history values centered on history item number N.

show values +'
Print ten history values just after the values last printed.  If
no more values are available, show values +' produces no display.

Pressing <RET> to repeat show values N' has exactly the same effect
as show values +'.

File: gdb.info,  Node: Convenience Vars,  Next: Convenience Funs,  Prev: Value History,  Up: Data

10.11 Convenience Variables
===========================

GDB provides "convenience variables" that you can use within GDB to
hold on to a value and refer to it later.  These variables exist
entirely within GDB; they are not part of your program, and setting a
convenience variable has no direct effect on further execution of your
program.  That is why you can use them freely.

Convenience variables are prefixed with $'. Any name preceded by $' can be used for a convenience variable, unless it is one of the
predefined machine-specific register names (*note Registers:
Registers.).  (Value history references, in contrast, are _numbers_
preceded by $'. *Note Value History: Value History.) You can save a value in a convenience variable with an assignment expression, just as you would set a variable in your program. For example: set$foo = *object_ptr

would save in $foo' the value contained in the object pointed to by object_ptr'. Using a convenience variable for the first time creates it, but its value is void' until you assign a new value. You can alter the value with another assignment at any time. Convenience variables have no fixed types. You can assign a convenience variable any type of value, including structures and arrays, even if that variable already has a value of a different type. The convenience variable, when used as an expression, has the type of its current value. show convenience' Print a list of convenience variables used so far, and their values. Abbreviated show conv'. init-if-undefined$VARIABLE = EXPRESSION'
Set a convenience variable if it has not already been set.  This
is useful for user-defined commands that keep some state.  It is
similar, in concept, to using local static variables with
initializers in C (except that convenience variables are global).
It can also be used to allow users to override default values used
in a command script.

If the variable is already defined then the expression is not
evaluated so any side-effects do not occur.

One of the ways to use a convenience variable is as a counter to be
incremented or a pointer to be advanced.  For example, to print a field
from successive elements of an array of structures:

set $i = 0 print bar[$i++]->contents

Repeat that command by typing <RET>.

Some convenience variables are created automatically by GDB and given
values likely to be useful.

$_' The variable $_' is automatically set by the x' command to the
last address examined (*note Examining Memory: Memory.).  Other
commands which provide a default address for x' to examine also
set $_' to that address; these commands include info line' and info breakpoint'. The type of $_' is void *' except when set
by the x' command, in which case it is a pointer to the type of
$__'. $__'
The variable $__' is automatically set by the x' command to the value found in the last address examined. Its type is chosen to match the format in which the data was printed. $_exitcode'
When the program being debugged terminates normally, GDB
automatically sets this variable to the exit code of the program,
and resets $_exitsignal' to void'. $_exitsignal'
When the program being debugged dies due to an uncaught signal,
GDB automatically sets this variable to that signal's number, and
resets $_exitcode' to void'. To distinguish between whether the program being debugged has exited (i.e., $_exitcode' is not void') or signalled (i.e.,
$_exitsignal' is not void'), the convenience function $_isvoid'
can be used (*note Convenience Functions: Convenience Funs.).  For
example, considering the following source code:

#include <signal.h>

int
main (int argc, char *argv[])
{
raise (SIGALRM);
return 0;
}

A valid way of telling whether the program being debugged has
exited or signalled would be:

(gdb) define has_exited_or_signalled
Type commands for definition of has_exited_or_signalled''.
End with a line saying just end''.
>if $_isvoid ($_exitsignal)
>echo The program has exited\n
>else
>echo The program has signalled\n
>end
>end
(gdb) run
Starting program:

Program terminated with signal SIGALRM, Alarm clock.
The program no longer exists.
(gdb) has_exited_or_signalled
The program has signalled

As can be seen, GDB correctly informs that the program being
debugged has signalled, since it calls raise' and raises a
SIGALRM' signal.  If the program being debugged had not called
raise', then GDB would report a normal exit:

(gdb) has_exited_or_signalled
The program has exited

$_probe_argc' $_probe_arg0...$_probe_arg9' Arguments to a SystemTap static probe. *Note Static Probe Points::. $_sdata'
The variable $_sdata' contains extra collected static tracepoint data. *Note Tracepoint Action Lists: Tracepoint Actions. Note that $_sdata' could be empty, if not inspecting a trace buffer, or
if extra static tracepoint data has not been collected.

$_siginfo' The variable $_siginfo' contains extra signal information (*note
extra signal information::).  Note that $_siginfo' could be empty, if the application has not yet received any signals. For example, it will be empty before you execute the run' command. $_tlb'
The variable $_tlb' is automatically set when debugging applications running on MS-Windows in native mode or connected to gdbserver that supports the qGetTIBAddr' request. *Note General Query Packets::. This variable contains the address of the thread information block. On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, GDB searches for a user or system name first, before it searches for a convenience variable. File: gdb.info, Node: Convenience Funs, Next: Registers, Prev: Convenience Vars, Up: Data 10.12 Convenience Functions =========================== GDB also supplies some "convenience functions". These have a syntax similar to convenience variables. A convenience function can be used in an expression just like an ordinary function; however, a convenience function is implemented internally to GDB. $_isvoid (EXPR)'
Return one if the expression EXPR is void'.  Otherwise it returns
zero.

A void' expression is an expression where the type of the result
is void'.  For example, you can examine a convenience variable
(see *note Convenience Variables: Convenience Vars.) to check
whether it is void':

(gdb) print $_exitcode$1 = void
(gdb) print $_isvoid ($_exitcode)
$2 = 1 (gdb) run Starting program: ./a.out [Inferior 1 (process 29572) exited normally] (gdb) print$_exitcode
$3 = 0 (gdb) print$_isvoid ($_exitcode)$4 = 0

In the example above, we used $_isvoid' to check whether $_exitcode' is void' before and after the execution of the
program being debugged.  Before the execution there is no exit
code to be examined, therefore $_exitcode' is void'. After the execution the program being debugged returned zero, therefore $_exitcode' is zero, which means that it is not void' anymore.

The void' expression can also be a call of a function from the
program being debugged.  For example, given the following function:

void
foo (void)
{
}

The result of calling it inside GDB is void':

(gdb) print foo ()
$1 = void (gdb) print$_isvoid (foo ())
$2 = 1 (gdb) set$v = foo ()
(gdb) print $v$3 = void
(gdb) print $_isvoid ($v)
$4 = 1 help function' Print a list of all convenience functions. File: gdb.info, Node: Registers, Next: Floating Point Hardware, Prev: Convenience Funs, Up: Data 10.13 Registers =============== You can refer to machine register contents, in expressions, as variables with names starting with $'.  The names of registers are different for
each machine; use info registers' to see the names used on your
machine.

info registers'
Print the names and values of all registers except floating-point
and vector registers (in the selected stack frame).

info all-registers'
Print the names and values of all registers, including
floating-point and vector registers (in the selected stack frame).

info registers REGNAME ...'
Print the "relativized" value of each specified register REGNAME.
As discussed in detail below, register values are normally
relative to the selected stack frame.  REGNAME may be any register
name valid on the machine you are using, with or without the
initial $'. GDB has four "standard" register names that are available (in expressions) on most machines--whenever they do not conflict with an architecture's canonical mnemonics for registers. The register names $pc' and $sp' are used for the program counter register and the stack pointer. $fp' is used for a register that contains a pointer to the
current stack frame, and $ps' is used for a register that contains the processor status. For example, you could print the program counter in hex with p/x$pc

or print the instruction to be executed next with

x/i $pc or add four to the stack pointer(1) with set$sp += 4

Whenever possible, these four standard register names are available
on your machine even though the machine has different canonical
mnemonics, so long as there is no conflict.  The info registers'
command shows the canonical names.  For example, on the SPARC, info
registers' displays the processor status register as $psr' but you can also refer to it as $ps'; and on x86-based machines $ps' is an alias for the EFLAGS register. GDB always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special registers which can hold nothing but floating point; these registers are considered to have floating point values. There is no way to refer to the contents of an ordinary register as floating point value (although you can _print_ it as a floating point value with print/f$REGNAME').

Some registers have distinct "raw" and "virtual" data formats.  This
means that the data format in which the register contents are saved by
the operating system is not the same one that your program normally
sees.  For example, the registers of the 68881 floating point
coprocessor are always saved in "extended" (raw) format, but all C
programs expect to work with "double" (virtual) format.  In such cases,
GDB normally works with the virtual format only (the format that makes
sense for your program), but the info registers' command prints the
data in both formats.

Some machines have special registers whose contents can be
interpreted in several different ways.  For example, modern x86-based
machines have SSE and MMX registers that can hold several values packed
together in several different formats.  GDB refers to such registers in
struct' notation:

(gdb) print $xmm1$1 = {
v4_float = {0, 3.43859137e-038, 1.54142831e-044, 1.821688e-044},
v2_double = {9.92129282474342e-303, 2.7585945287983262e-313},
v16_int8 = "\000\000\000\000\3706;\001\v\000\000\000\r\000\000",
v8_int16 = {0, 0, 14072, 315, 11, 0, 13, 0},
v4_int32 = {0, 20657912, 11, 13},
v2_int64 = {88725056443645952, 55834574859},
uint128 = 0x0000000d0000000b013b36f800000000
}

To set values of such registers, you need to tell GDB which view of the
register you wish to change, as if you were assigning value to a
struct' member:

(gdb) set $xmm1.uint128 = 0x000000000000000000000000FFFFFFFF Normally, register values are relative to the selected stack frame (*note Selecting a Frame: Selection.). This means that you get the value that the register would contain if all stack frames farther in were exited and their saved registers restored. In order to see the true contents of hardware registers, you must select the innermost frame (with frame 0'). However, GDB must deduce where registers are saved, from the machine code generated by your compiler. If some registers are not saved, or if GDB is unable to locate the saved registers, the selected stack frame makes no difference. ---------- Footnotes ---------- (1) This is a way of removing one word from the stack, on machines where stacks grow downward in memory (most machines, nowadays). This assumes that the innermost stack frame is selected; setting $sp' is
not allowed when other stack frames are selected.  To pop entire frames
off the stack, regardless of machine architecture, use return'; see
*note Returning from a Function: Returning.

File: gdb.info,  Node: Floating Point Hardware,  Next: Vector Unit,  Prev: Registers,  Up: Data

10.14 Floating Point Hardware
=============================

Depending on the configuration, GDB may be able to give you more
information about the status of the floating point hardware.

info float'
Display hardware-dependent information about the floating point
unit.  The exact contents and layout vary depending on the
floating point chip.  Currently, info float' is supported on the
ARM and x86 machines.

File: gdb.info,  Node: Vector Unit,  Next: OS Information,  Prev: Floating Point Hardware,  Up: Data

10.15 Vector Unit
=================

Depending on the configuration, GDB may be able to give you more
information about the status of the vector unit.

info vector'
Display information about the vector unit.  The exact contents and
layout vary depending on the hardware.

File: gdb.info,  Node: OS Information,  Next: Memory Region Attributes,  Prev: Vector Unit,  Up: Data

10.16 Operating System Auxiliary Information
============================================

GDB provides interfaces to useful OS facilities that can help you debug

When GDB runs on a "Posix system" (such as GNU or Unix machines), it
interfaces with the inferior via the ptrace' system call.  The
operating system creates a special sata structure, called struct
user', for this interface.  You can use the command info udot' to
display the contents of this data structure.

info udot'
Display the contents of the struct user' maintained by the OS
kernel for the program being debugged.  GDB displays the contents
of struct user' as a list of hex numbers, similar to the
examine' command.

Some operating systems supply an "auxiliary vector" to programs at
startup.  This is akin to the arguments and environment that you
specify for a program, but contains a system-dependent variety of
binary values that tell system libraries important details about the
hardware, operating system, and process.  Each value's purpose is
identified by an integer tag; the meanings are well-known but
system-specific.  Depending on the configuration and operating system
facilities, GDB may be able to show you this information.  For remote
targets, this functionality may further depend on the remote stub's
support of the qXfer:auxv:read' packet, see *note qXfer auxiliary

info auxv'
Display the auxiliary vector of the inferior, which can be either a
live process or a core dump file.  GDB prints each tag value
numerically, and also shows names and text descriptions for
recognized tags.  Some values in the vector are numbers, some bit
masks, and some pointers to strings or other data.  GDB displays
each value in the most appropriate form for a recognized tag, and
in hexadecimal for an unrecognized tag.

On some targets, GDB can access operating-system-specific information
and display it to user, without interpretation.  For remote targets,
this functionality depends on the remote stub's support of the
qXfer:osdata:read' packet, see *note qXfer osdata read::.

info os'
List the types of OS information available for the target.  If the
target does not return a list of possible types, this command will
report an error.

info os processes'
Display the list of processes on the target.  For each process,
GDB prints the process identifier, the name of the user, and the
command corresponding to the process.

File: gdb.info,  Node: Memory Region Attributes,  Next: Dump/Restore Files,  Prev: OS Information,  Up: Data

10.17 Memory Region Attributes
==============================

"Memory region attributes" allow you to describe special handling
required by regions of your target's memory.  GDB uses attributes to
determine whether to allow certain types of memory accesses; whether to
use specific width accesses; and whether to cache target memory.  By
default the description of memory regions is fetched from the target
(if the current target supports this), but the user can override the
fetched regions.

Defined memory regions can be individually enabled and disabled.
When a memory region is disabled, GDB uses the default attributes when
accessing memory in that region.  Similarly, if no memory regions have
been defined, GDB uses the default attributes when accessing all memory.

When a memory region is defined, it is given a number to identify it;
to enable, disable, or remove a memory region, you specify that number.

mem LOWER UPPER ATTRIBUTES...'
Define a memory region bounded by LOWER and UPPER with attributes
ATTRIBUTES..., and add it to the list of regions monitored by GDB.
Note that UPPER == 0 is a special case: it is treated as the
target's maximum memory address.  (0xffff on 16 bit targets,
0xffffffff on 32 bit targets, etc.)

mem auto'
Discard any user changes to the memory regions and use
target-supplied regions, if available, or no regions if the target
does not support.

delete mem NUMS...'
Remove memory regions NUMS... from the list of regions monitored
by GDB.

disable mem NUMS...'
Disable monitoring of memory regions NUMS....  A disabled memory
region is not forgotten.  It may be enabled again later.

enable mem NUMS...'
Enable monitoring of memory regions NUMS....

info mem'
Print a table of all defined memory regions, with the following
columns for each region:

_Memory Region Number_

_Enabled or Disabled._
Enabled memory regions are marked with y'.  Disabled memory
regions are marked with n'.

The address defining the inclusive lower bound of the memory
region.

The address defining the exclusive upper bound of the memory
region.

_Attributes_
The list of attributes set for this memory region.

10.17.1 Attributes
------------------

10.17.1.1 Memory Access Mode
............................

The access mode attributes set whether GDB may make read or write
accesses to a memory region.

While these attributes prevent GDB from performing invalid memory
accesses, they do nothing to prevent the target system, I/O DMA, etc.
from accessing memory.

ro'
Memory is read only.

wo'
Memory is write only.

rw'
Memory is read/write.  This is the default.

10.17.1.2 Memory Access Size
............................

The access size attribute tells GDB to use specific sized accesses in
the memory region.  Often memory mapped device registers require
specific sized accesses.  If no access size attribute is specified, GDB
may use accesses of any size.

8'
Use 8 bit memory accesses.

16'
Use 16 bit memory accesses.

32'
Use 32 bit memory accesses.

64'
Use 64 bit memory accesses.

10.17.1.3 Data Cache
....................

The data cache attributes set whether GDB will cache target memory.
While this generally improves performance by reducing debug protocol
overhead, it can lead to incorrect results because GDB does not know
about volatile variables or memory mapped device registers.

cache'
Enable GDB to cache target memory.

nocache'
Disable GDB from caching target memory.  This is the default.

10.17.2 Memory Access Checking
------------------------------

GDB can be instructed to refuse accesses to memory that is not
explicitly described.  This can be useful if accessing such regions has
undesired effects for a specific target, or to provide better error
checking.  The following commands control this behaviour.

set mem inaccessible-by-default [on|off]'
If on' is specified, make  GDB treat memory not explicitly
described by the memory ranges as non-existent and refuse accesses
to such memory.  The checks are only performed if there's at least
one memory range defined.  If off' is specified, make GDB treat
the memory not explicitly described by the memory ranges as RAM.
The default value is on'.

show mem inaccessible-by-default'
Show the current handling of accesses to unknown memory.

File: gdb.info,  Node: Dump/Restore Files,  Next: Core File Generation,  Prev: Memory Region Attributes,  Up: Data

10.18 Copy Between Memory and a File
====================================

You can use the commands dump', append', and restore' to copy data
between target memory and a file.  The dump' and append' commands
write data to a file, and the restore' command reads data from a file
back into the inferior's memory.  Files may be in binary, Motorola
S-record, Intel hex, or Tektronix Hex format; however, GDB can only
append to binary files.

dump [FORMAT] value FILENAME EXPR'
Dump the contents of memory from START_ADDR to END_ADDR, or the
value of EXPR, to FILENAME in the given format.

The FORMAT parameter may be any one of:
binary'
Raw binary form.

ihex'
Intel hex format.

srec'
Motorola S-record format.

tekhex'
Tektronix Hex format.

GDB uses the same definitions of these formats as the GNU binary
utilities, like objdump' and objcopy'.  If FORMAT is omitted,
GDB dumps the data in raw binary form.

append [binary] value FILENAME EXPR'
Append the contents of memory from START_ADDR to END_ADDR, or the
value of EXPR, to the file FILENAME, in raw binary form.  (GDB can
only append data to files in raw binary form.)

restore FILENAME [binary] BIAS START END'
Restore the contents of file FILENAME into memory.  The restore'
command can automatically recognize any known BFD file format,
except for raw binary.  To restore a raw binary file you must
specify the optional keyword binary' after the filename.

If BIAS is non-zero, its value will be added to the addresses
contained in the file.  Binary files always start at address zero,
so they will be restored at address BIAS.  Other bfd files have a
built-in location; they will be restored at offset BIAS from that
location.

If START and/or END are non-zero, then only data between file
offset START and file offset END will be restored.  These offsets
are relative to the addresses in the file, before the BIAS
argument is applied.

File: gdb.info,  Node: Core File Generation,  Next: Character Sets,  Prev: Dump/Restore Files,  Up: Data

10.19 How to Produce a Core File from Your Program
==================================================

A "core file" or "core dump" is a file that records the memory image of
a running process and its process status (register values etc.).  Its
primary use is post-mortem debugging of a program that crashed while it
ran outside a debugger.  A program that crashes automatically produces
a core file, unless this feature is disabled by the user.  *Note
Files::, for information on invoking GDB in the post-mortem debugging
mode.

Occasionally, you may wish to produce a core file of the program you
are debugging in order to preserve a snapshot of its state.  GDB has a
special command for that.

generate-core-file [FILE]'
gcore [FILE]'
Produce a core dump of the inferior process.  The optional argument
FILE specifies the file name where to put the core dump.  If not
specified, the file name defaults to core.PID', where PID is the
inferior process ID.

Note that this command is implemented only for some systems (as of
this writing, GNU/Linux, FreeBSD, Solaris, Unixware, and S390).

On GNU/Linux, this command can take into account the value of the
file /proc/PID/coredump_filter' when generating the core dump
(*note set use-coredump-filter::).

set use-coredump-filter on'
set use-coredump-filter off'
Enable or disable the use of the file /proc/PID/coredump_filter'
when generating core dump files.  This file is used by the Linux
kernel to decide what types of memory mappings will be dumped or
ignored when generating a core dump file.  PID is the process ID
of a currently running process.

To make use of this feature, you have to write in the
/proc/PID/coredump_filter' file a value, in hexadecimal, which is
a bit mask representing the memory mapping types.  If a bit is set
in the bit mask, then the memory mappings of the corresponding
types will be dumped; otherwise, they will be ignored.  This
configuration is inherited by child processes.  For more
information about the bits that can be set in the
/proc/PID/coredump_filter' file, please refer to the manpage of
core(5)'.

By default, this option is on'.  If this option is turned off',
GDB does not read the coredump_filter' file and instead uses the
same default value as the Linux kernel in order to decide which
pages will be dumped in the core dump file.  This value is
currently 0x33', which means that bits 0' (anonymous private
mappings), 1' (anonymous shared mappings), 4' (ELF headers) and
5' (private huge pages) are active.  This will cause these memory
mappings to be dumped automatically.

File: gdb.info,  Node: Character Sets,  Next: Caching Remote Data,  Prev: Core File Generation,  Up: Data

10.20 Character Sets
====================

If the program you are debugging uses a different character set to
represent characters and strings than the one GDB uses itself, GDB can
automatically translate between the character sets for you.  The
character set GDB uses we call the "host character set"; the one the
inferior program uses we call the "target character set".

For example, if you are running GDB on a GNU/Linux system, which
uses the ISO Latin 1 character set, but you are using GDB's remote
protocol (*note Remote Debugging::) to debug a program running on an
IBM mainframe, which uses the EBCDIC character set, then the host
character set is Latin-1, and the target character set is EBCDIC.  If
you give GDB the command set target-charset EBCDIC-US', then GDB
translates between EBCDIC and Latin 1 as you print character or string
values, or use character and string literals in expressions.

GDB has no way to automatically recognize which character set the
inferior program uses; you must tell it, using the set target-charset'
command, described below.

Here are the commands for controlling GDB's character set support:

set target-charset CHARSET'
Set the current target character set to CHARSET.  To display the
list of supported target character sets, type
set target-charset <TAB><TAB>'.

set host-charset CHARSET'
Set the current host character set to CHARSET.

By default, GDB uses a host character set appropriate to the
system it is running on; you can override that default using the
set host-charset' command.  On some systems, GDB cannot
automatically determine the appropriate host character set.  In
this case, GDB uses UTF-8'.

GDB can only use certain character sets as its host character set.
If you type set target-charset <TAB><TAB>', GDB will list the
host character sets it supports.

set charset CHARSET'
Set the current host and target character sets to CHARSET.  As
above, if you type set charset <TAB><TAB>', GDB will list the
names of the character sets that can be used for both host and
target.

show charset'
Show the names of the current host and target character sets.

show host-charset'
Show the name of the current host character set.

show target-charset'
Show the name of the current target character set.

set target-wide-charset CHARSET'
Set the current target's wide character set to CHARSET.  This is
the character set used by the target's wchar_t' type.  To display
the list of supported wide character sets, type
set target-wide-charset <TAB><TAB>'.

show target-wide-charset'
Show the name of the current target's wide character set.

Here is an example of GDB's character set support in action.  Assume
that the following source code has been placed in the file
charset-test.c':

#include <stdio.h>

char ascii_hello[]
= {72, 101, 108, 108, 111, 44, 32, 119,
111, 114, 108, 100, 33, 10, 0};
char ibm1047_hello[]
= {200, 133, 147, 147, 150, 107, 64, 166,
150, 153, 147, 132, 90, 37, 0};

main ()
{
printf ("Hello, world!\n");
}

In this program, ascii_hello' and ibm1047_hello' are arrays
containing the string Hello, world!' followed by a newline, encoded in
the ASCII and IBM1047 character sets.

We compile the program, and invoke the debugger on it:

$gcc -g charset-test.c -o charset-test$ gdb -nw charset-test
GNU gdb 2001-12-19-cvs
Copyright 2001 Free Software Foundation, Inc.
...
(gdb)

We can use the show charset' command to see what character sets GDB
is currently using to interpret and display characters and strings:

(gdb) show charset
The current host and target character set is ISO-8859-1'.
(gdb)

For the sake of printing this manual, let's use ASCII as our initial
character set:
(gdb) set charset ASCII
(gdb) show charset
The current host and target character set is ASCII'.
(gdb)

Let's assume that ASCII is indeed the correct character set for our
host system -- in other words, let's assume that if GDB prints
characters using the ASCII character set, our terminal will display
them properly.  Since our current target character set is also ASCII,
the contents of ascii_hello' print legibly:

(gdb) print ascii_hello
$1 = 0x401698 "Hello, world!\n" (gdb) print ascii_hello[0]$2 = 72 'H'
(gdb)

GDB uses the target character set for character and string literals
you use in expressions:

(gdb) print '+'
$3 = 43 '+' (gdb) The ASCII character set uses the number 43 to encode the +' character. GDB relies on the user to tell it which character set the target program uses. If we print ibm1047_hello' while our target character set is still ASCII, we get jibberish: (gdb) print ibm1047_hello$4 = 0x4016a8 "\310\205\223\223\226k@\246\226\231\223\204Z%"
(gdb) print ibm1047_hello[0]
$5 = 200 '\310' (gdb) If we invoke the set target-charset' followed by <TAB><TAB>, GDB tells us the character sets it supports: (gdb) set target-charset ASCII EBCDIC-US IBM1047 ISO-8859-1 (gdb) set target-charset We can select IBM1047 as our target character set, and examine the program's strings again. Now the ASCII string is wrong, but GDB translates the contents of ibm1047_hello' from the target character set, IBM1047, to the host character set, ASCII, and they display correctly: (gdb) set target-charset IBM1047 (gdb) show charset The current host character set is ASCII'. The current target character set is IBM1047'. (gdb) print ascii_hello$6 = 0x401698 "\110\145%%?\054\040\167?\162%\144\041\012"
(gdb) print ascii_hello[0]
$7 = 72 '\110' (gdb) print ibm1047_hello$8 = 0x4016a8 "Hello, world!\n"
(gdb) print ibm1047_hello[0]
$9 = 200 'H' (gdb) As above, GDB uses the target character set for character and string literals you use in expressions: (gdb) print '+'$10 = 78 '+'
(gdb)

The IBM1047 character set uses the number 78 to encode the +'
character.

File: gdb.info,  Node: Caching Remote Data,  Next: Searching Memory,  Prev: Character Sets,  Up: Data

10.21 Caching Data of Remote Targets
====================================

GDB caches data exchanged between the debugger and a remote target
(*note Remote Debugging::).  Such caching generally improves
performance, because it reduces the overhead of the remote protocol by
bundling memory reads and writes into large chunks.  Unfortunately,
simply caching everything would lead to incorrect results, since GDB
does not necessarily know anything about volatile values, memory-mapped
I/O addresses, etc.  Furthermore, in non-stop mode (*note Non-Stop
Mode::) memory can be changed _while_ a gdb command is executing.
Therefore, by default, GDB only caches data known to be on the stack(1).
Other regions of memory can be explicitly marked as cacheable; see
*note Memory Region Attributes::.

set remotecache on'
set remotecache off'
This option no longer does anything; it exists for compatibility
with old scripts.

show remotecache'
Show the current state of the obsolete remotecache flag.

set stack-cache on'
set stack-cache off'
Enable or disable caching of stack accesses.  When ON', use
caching.  By default, this option is ON'.

show stack-cache'
Show the current state of data caching for memory accesses.

info dcache [line]'
Print the information about the data cache performance.  The
information displayed includes the dcache width and depth, and for
each cache line, its number, address, and how many times it was
referenced.  This command is useful for debugging the data cache
operation.

If a line number is specified, the contents of that line will be
printed in hex.

---------- Footnotes ----------

(1) In non-stop mode, it is moderately rare for a running thread to
modify the stack of a stopped thread in a way that would interfere with
a backtrace, and caching of stack reads provides a significant speed up
of remote backtraces.

File: gdb.info,  Node: Searching Memory,  Prev: Caching Remote Data,  Up: Data

10.22 Search Memory
===================

Memory can be searched for a particular sequence of bytes with the
find' command.

find [/SN] START_ADDR, +LEN, VAL1 [, VAL2, ...]'
find [/SN] START_ADDR, END_ADDR, VAL1 [, VAL2, ...]'
Search memory for the sequence of bytes specified by VAL1, VAL2,
etc.  The search begins at address START_ADDR and continues for
either LEN bytes or through to END_ADDR inclusive.

S and N are optional parameters.  They may be specified in either
order, apart or together.

S, search query size
The size of each search query value.

b'
bytes

h'
halfwords (two bytes)

w'
words (four bytes)

g'
giant words (eight bytes)

All values are interpreted in the current language.  This means,
for example, that if the current source language is C/C++ then
searching for the string "hello" includes the trailing '\0'.

If the value size is not specified, it is taken from the value's
type in the current language.  This is useful when one wants to
specify the search pattern as a mixture of types.  Note that this
means, for example, that in the case of C-like languages a search
for an untyped 0x42 will search for (int) 0x42' which is
typically four bytes.

N, maximum number of finds
The maximum number of matches to print.  The default is to print
all finds.

You can use strings as search values.  Quote them with double-quotes
("').  The string value is copied into the search pattern byte by byte,
regardless of the endianness of the target and the size specification.

The address of each match found is printed as well as a count of the
number of matches found.

The address of the last value found is stored in convenience variable
$_'. A count of the number of matches is stored in $numfound'.

For example, if stopped at the printf' in this function:

void
hello ()
{
static char hello[] = "hello-hello";
static struct { char c; short s; int i; }
__attribute__ ((packed)) mixed
= { 'c', 0x1234, 0x87654321 };
printf ("%s\n", hello);
}

you get during debugging:

(gdb) find &hello[0], +sizeof(hello), "hello"
0x804956d <hello.1620+6>
1 pattern found
(gdb) find &hello[0], +sizeof(hello), 'h', 'e', 'l', 'l', 'o'
0x8049567 <hello.1620>
0x804956d <hello.1620+6>
2 patterns found
(gdb) find /b1 &hello[0], +sizeof(hello), 'h', 0x65, 'l'
0x8049567 <hello.1620>
1 pattern found
(gdb) find &mixed, +sizeof(mixed), (char) 'c', (short) 0x1234, (int) 0x87654321
0x8049560 <mixed.1625>
1 pattern found
(gdb) print $numfound$1 = 1
(gdb) print $_$2 = (void *) 0x8049560

File: gdb.info,  Node: Optimized Code,  Next: Macros,  Prev: Data,  Up: Top

11 Debugging Optimized Code
***************************

Almost all compilers support optimization.  With optimization disabled,
the compiler generates assembly code that corresponds directly to your
source code, in a simplistic way.  As the compiler applies more
powerful optimizations, the generated assembly code diverges from your
original source code.  With help from debugging information generated
by the compiler, GDB can map from the running program back to
constructs from your original source.

GDB is more accurate with optimization disabled.  If you can
recompile without optimization, it is easier to follow the progress of
your program during debugging.  But, there are many cases where you may
need to debug an optimized version.

When you debug a program compiled with -g -O', remember that the
optimizer has rearranged your code; the debugger shows you what is
really there.  Do not be too surprised when the execution path does not
exactly match your source file!  An extreme example: if you define a
variable, but never use it, GDB never sees that variable--because the
compiler optimizes it out of existence.

Some things do not work as well with -g -O' as with just -g',
particularly on machines with instruction scheduling.  If in doubt,
recompile with -g' alone, and if this fixes the problem, please report
it to us as a bug (including a test case!).  *Note Variables::, for

* Inline Functions::            How GDB presents inlining

File: gdb.info,  Node: Inline Functions,  Up: Optimized Code

11.1 Inline Functions
=====================

"Inlining" is an optimization that inserts a copy of the function body
directly at each call site, instead of jumping to a shared routine.
GDB displays inlined functions just like non-inlined functions.  They
appear in backtraces.  You can view their arguments and local
variables, step into them with step', skip them with next', and
escape from them with finish'.  You can check whether a function was
inlined by using the info frame' command.

For GDB to support inlined functions, the compiler must record
information about inlining in the debug information -- GCC using the
DWARF 2 format does this, and several other compilers do also.  GDB
only supports inlined functions when using DWARF 2.  Versions of GCC
before 4.1 do not emit two required attributes (DW_AT_call_file' and
DW_AT_call_line'); GDB does not display inlined function calls with
earlier versions of GCC.  It instead displays the arguments and local
variables of inlined functions as local variables in the caller.

The body of an inlined function is directly included at its call
site; unlike a non-inlined function, there are no instructions devoted
to the call.  GDB still pretends that the call site and the start of
the inlined function are different instructions.  Stepping to the call
site shows the call site, and then stepping again shows the first line
of the inlined function, even though no additional instructions are
executed.

This makes source-level debugging much clearer; you can see both the
context of the call and then the effect of the call.  Only stepping by
a single instruction using stepi' or nexti' does not do this; single
instruction steps always show the inlined body.

There are some ways that GDB does not pretend that inlined function
calls are the same as normal calls:

* You cannot set breakpoints on inlined functions.  GDB either
reports that there is no symbol with that name, or else sets the
breakpoint only on non-inlined copies of the function.  This
limitation will be removed in a future version of GDB; until then,
set a breakpoint by line number on the first line of the inlined

* Setting breakpoints at the call site of an inlined function may not
work, because the call site does not contain any code.  GDB may
incorrectly move the breakpoint to the next line of the enclosing
function, after the call.  This limitation will be removed in a
future version of GDB; until then, set a breakpoint on an earlier
line or inside the inlined function instead.

* GDB cannot locate the return value of inlined calls after using
the finish' command.  This is a limitation of compiler-generated
debugging information; after finish', you can step to the next
line and print a variable where your program stored the return
value.

File: gdb.info,  Node: Macros,  Next: Tracepoints,  Prev: Optimized Code,  Up: Top

12 C Preprocessor Macros
************************

Some languages, such as C and C++, provide a way to define and invoke
"preprocessor macros" which expand into strings of tokens.  GDB can
evaluate expressions containing macro invocations, show the result of
macro expansion, and show a macro's definition, including where it was
defined.

You may need to compile your program specially to provide GDB with
information about preprocessor macros.  Most compilers do not include
macros in their debugging information, even when you compile with the
-g' flag.  *Note Compilation::.

A program may define a macro at one point, remove that definition
later, and then provide a different definition after that.  Thus, at
different points in the program, a macro may have different
definitions, or have no definition at all.  If there is a current stack
frame, GDB uses the macros in scope at that frame's source code line.
Otherwise, GDB uses the macros in scope at the current listing location;
see *note List::.

Whenever GDB evaluates an expression, it always expands any macro
invocations present in the expression.  GDB also provides the following
commands for working with macros explicitly.

macro expand EXPRESSION'
macro exp EXPRESSION'
Show the results of expanding all preprocessor macro invocations in
EXPRESSION.  Since GDB simply expands macros, but does not parse
the result, EXPRESSION need not be a valid expression; it can be
any string of tokens.

macro expand-once EXPRESSION'
macro exp1 EXPRESSION'
(This command is not yet implemented.)  Show the results of
expanding those preprocessor macro invocations that appear
explicitly in EXPRESSION.  Macro invocations appearing in that
expansion are left unchanged.  This command allows you to see the
effect of a particular macro more clearly, without being confused
by further expansions.  Since GDB simply expands macros, but does
not parse the result, EXPRESSION need not be a valid expression; it
can be any string of tokens.

info macro MACRO'
Show the definition of the macro named MACRO, and describe the
source location or compiler command-line where that definition was
established.

macro define MACRO REPLACEMENT-LIST'
macro define MACRO(ARGLIST) REPLACEMENT-LIST'
Introduce a definition for a preprocessor macro named MACRO,
invocations of which are replaced by the tokens given in
REPLACEMENT-LIST.  The first form of this command defines an
"object-like" macro, which takes no arguments; the second form
defines a "function-like" macro, which takes the arguments given in
ARGLIST.

A definition introduced by this command is in scope in every
expression evaluated in GDB, until it is removed with the macro
undef' command, described below.  The definition overrides all
definitions for MACRO present in the program being debugged, as
well as any previous user-supplied definition.

macro undef MACRO'
Remove any user-supplied definition for the macro named MACRO.
This command only affects definitions provided with the macro
define' command, described above; it cannot remove definitions
present in the program being debugged.

macro list'
List all the macros defined using the macro define' command.

Here is a transcript showing the above commands in action.  First, we
show our source files:

$cat sample.c #include <stdio.h> #include "sample.h" #define M 42 #define ADD(x) (M + x) main () { #define N 28 printf ("Hello, world!\n"); #undef N printf ("We're so creative.\n"); #define N 1729 printf ("Goodbye, world!\n"); }$ cat sample.h
#define Q <
$Now, we compile the program using the GNU C compiler, GCC. We pass the -gdwarf-2' and -g3' flags to ensure the compiler includes information about preprocessor macros in the debugging information.$ gcc -gdwarf-2 -g3 sample.c -o sample
$Now, we start GDB on our sample program:$ gdb -nw sample
GNU gdb 2002-05-06-cvs
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, ...
(gdb)

We can expand macros and examine their definitions, even when the
program is not running.  GDB uses the current listing position to
decide which macro definitions are in scope:

(gdb) list main
3
4       #define M 42
5       #define ADD(x) (M + x)
6
7       main ()
8       {
9       #define N 28
10        printf ("Hello, world!\n");
11      #undef N
12        printf ("We're so creative.\n");
(gdb) info macro ADD
Defined at /home/jimb/gdb/macros/play/sample.c:5
#define ADD(x) (M + x)
(gdb) info macro Q
Defined at /home/jimb/gdb/macros/play/sample.h:1
included at /home/jimb/gdb/macros/play/sample.c:2
#define Q <
(gdb) macro expand ADD(1)
expands to: (42 + 1)
(gdb) macro expand-once ADD(1)
expands to: once (M + 1)
(gdb)

In the example above, note that macro expand-once' expands only the
macro invocation explicit in the original text -- the invocation of
ADD' -- but does not expand the invocation of the macro M', which was

Once the program is running, GDB uses the macro definitions in force
at the source line of the current stack frame:

(gdb) break main
Breakpoint 1 at 0x8048370: file sample.c, line 10.
(gdb) run
Starting program: /home/jimb/gdb/macros/play/sample

Breakpoint 1, main () at sample.c:10
10        printf ("Hello, world!\n");
(gdb)

At line 10, the definition of the macro N' at line 9 is in force:

(gdb) info macro N
Defined at /home/jimb/gdb/macros/play/sample.c:9
#define N 28
(gdb) macro expand N Q M
expands to: 28 < 42
(gdb) print N Q M
$1 = 1 (gdb) As we step over directives that remove N''s definition, and then give it a new definition, GDB finds the definition (or lack thereof) in force at each point: (gdb) next Hello, world! 12 printf ("We're so creative.\n"); (gdb) info macro N The symbol N' has no definition as a C/C++ preprocessor macro at /home/jimb/gdb/macros/play/sample.c:12 (gdb) next We're so creative. 14 printf ("Goodbye, world!\n"); (gdb) info macro N Defined at /home/jimb/gdb/macros/play/sample.c:13 #define N 1729 (gdb) macro expand N Q M expands to: 1729 < 42 (gdb) print N Q M$2 = 0
(gdb)

In addition to source files, macros can be defined on the
compilation command line using the -DNAME=VALUE' syntax.  For macros
defined in such a way, GDB displays the location of their definition as
line zero of the source file submitted to the compiler.

(gdb) info macro __STDC__
Defined at /home/jimb/gdb/macros/play/sample.c:0
-D__STDC__=1
(gdb)

File: gdb.info,  Node: Tracepoints,  Next: Overlays,  Prev: Macros,  Up: Top

13 Tracepoints
**************

In some applications, it is not feasible for the debugger to interrupt
the program's execution long enough for the developer to learn anything
helpful about its behavior.  If the program's correctness depends on
its real-time behavior, delays introduced by a debugger might cause the
program to change its behavior drastically, or perhaps fail, even when
the code itself is correct.  It is useful to be able to observe the
program's behavior without interrupting it.

Using GDB's trace' and collect' commands, you can specify
locations in the program, called "tracepoints", and arbitrary
expressions to evaluate when those tracepoints are reached.  Later,
using the tfind' command, you can examine the values those expressions
had when the program hit the tracepoints.  The expressions may also
denote objects in memory--structures or arrays, for example--whose
values GDB should record; while visiting a particular tracepoint, you
may inspect those objects as if they were in memory at that moment.
However, because GDB records these values without interacting with you,
it can do so quickly and unobtrusively, hopefully not disturbing the
program's behavior.

The tracepoint facility is currently available only for remote
targets.  *Note Targets::.  In addition, your remote target must know
how to collect trace data.  This functionality is implemented in the
remote stub; however, none of the stubs distributed with GDB support
tracepoints as of this writing.  The format of the remote packets used
to implement tracepoints are described in *note Tracepoint Packets::.

It is also possible to get trace data from a file, in a manner
reminiscent of corefiles; you specify the filename, and use tfind' to
search through the file.  *Note Trace Files::, for more details.

This chapter describes the tracepoint commands and features.

* Set Tracepoints::
* Analyze Collected Data::
* Tracepoint Variables::
* Trace Files::

File: gdb.info,  Node: Set Tracepoints,  Next: Analyze Collected Data,  Up: Tracepoints

13.1 Commands to Set Tracepoints
================================

Before running such a "trace experiment", an arbitrary number of
tracepoints can be set.  A tracepoint is actually a special type of
breakpoint (*note Set Breaks::), so you can manipulate it using
standard breakpoint commands.  For instance, as with breakpoints,
tracepoint numbers are successive integers starting from one, and many
of the commands associated with tracepoints take the tracepoint number
as their argument, to identify which tracepoint to work on.

For each tracepoint, you can specify, in advance, some arbitrary set
of data that you want the target to collect in the trace buffer when it
hits that tracepoint.  The collected data can include registers, local
variables, or global data.  Later, you can use GDB commands to examine
the values these data had at the time the tracepoint was hit.

Tracepoints do not support every breakpoint feature.  Ignore counts
on tracepoints have no effect, and tracepoints cannot run GDB commands
when they are hit.  Tracepoints may not be thread-specific either.

Some targets may support "fast tracepoints", which are inserted in a
different way (such as with a jump instead of a trap), that is faster
but possibly restricted in where they may be installed.

Regular and fast tracepoints are dynamic tracing facilities, meaning
that they can be used to insert tracepoints at (almost) any location in
the target.  Some targets may also support controlling "static
tracepoints" from GDB.  With static tracing, a set of instrumentation
points, also known as "markers", are embedded in the target program,
and can be activated or deactivated by name or address.  These are
usually placed at locations which facilitate investigating what the
target is actually doing.  GDB's support for static tracing includes
being able to list instrumentation points, and attach them with GDB
defined high level tracepoints that expose the whole range of
convenience of GDB's tracepoints support.  Namelly, support for
collecting registers values and values of global or local (to the
instrumentation point) variables; tracepoint conditions and trace state
variables.  The act of installing a GDB static tracepoint on an
instrumentation point, or marker, is referred to as "probing" a static
tracepoint marker.

gdbserver' supports tracepoints on some target systems.  *Note
Tracepoints support in gdbserver': Server.

This section describes commands to set tracepoints and associated
conditions and actions.

* Create and Delete Tracepoints::
* Enable and Disable Tracepoints::
* Tracepoint Passcounts::
* Tracepoint Conditions::
* Trace State Variables::
* Tracepoint Actions::
* Listing Tracepoints::
* Listing Static Tracepoint Markers::
* Starting and Stopping Trace Experiments::
* Tracepoint Restrictions::

File: gdb.info,  Node: Create and Delete Tracepoints,  Next: Enable and Disable Tracepoints,  Up: Set Tracepoints

13.1.1 Create and Delete Tracepoints
------------------------------------

trace LOCATION'
The trace' command is very similar to the break' command.  Its
argument LOCATION can be a source line, a function name, or an
address in the target program.  *Note Specify Location::.  The
trace' command defines a tracepoint, which is a point in the
target program where the debugger will briefly stop, collect some
data, and then allow the program to continue.  Setting a
tracepoint or changing its actions doesn't take effect until the
next tstart' command, and once a trace experiment is running,
further changes will not have any effect until the next trace
experiment starts.

Here are some examples of using the trace' command:

(gdb) trace foo.c:121    // a source file and line number

(gdb) trace +2           // 2 lines forward

(gdb) trace my_function  // first source line of function

(gdb) trace *my_function // EXACT start address of function

(gdb) trace *0x2117c4    // an address

You can abbreviate trace' as tr'.

trace LOCATION if COND'
Set a tracepoint with condition COND; evaluate the expression COND
each time the tracepoint is reached, and collect data only if the
value is nonzero--that is, if COND evaluates as true.  *Note
Tracepoint Conditions: Tracepoint Conditions, for more information
on tracepoint conditions.

ftrace LOCATION [ if COND ]'
The ftrace' command sets a fast tracepoint.  For targets that
support them, fast tracepoints will use a more efficient but
possibly less general technique to trigger data collection, such
as a jump instruction instead of a trap, or some sort of hardware
support.  It may not be possible to create a fast tracepoint at
the desired location, in which case the command will exit with an
explanatory message.

GDB handles arguments to ftrace' exactly as for trace'.

strace LOCATION [ if COND ]'
The strace' command sets a static tracepoint.  For targets that
support it, setting a static tracepoint probes a static
instrumentation point, or marker, found at LOCATION.  It may not
be possible to set a static tracepoint at the desired location, in
which case the command will exit with an explanatory message.

GDB handles arguments to strace' exactly as for trace', with the
addition that the user can also specify -m MARKER' as LOCATION.
This probes the marker identified by the MARKER string identifier.
This identifier depends on the static tracepoint backend library
your program is using.  You can find all the marker identifiers in
the ID' field of the info static-tracepoint-markers' command
output.  *Note Listing Static Tracepoint Markers: Listing Static
Tracepoint Markers.  For example, in the following small program
using the UST tracing engine:

main ()
{
trace_mark(ust, bar33, "str %s", "FOOBAZ");
}

the marker id is composed of joining the first two arguments to the
trace_mark' call with a slash, which translates to:

(gdb) info static-tracepoint-markers
Cnt Enb ID         Address            What
1   n   ust/bar33  0x0000000000400ddc in main at stexample.c:22
Data: "str %s"
[etc...]

so you may probe the marker above with:

(gdb) strace -m ust/bar33

Static tracepoints accept an extra collect action -- collect
$_sdata'. This collects arbitrary user data passed in the probe point call to the tracing library. In the UST example above, you'll see that the third argument to trace_mark' is a printf-like format string. The user data is then the result of running that formating string against the following arguments. Note that info static-tracepoint-markers' command output lists that format string in the Data:' field. You can inspect this data when analyzing the trace buffer, by printing the$_sdata variable like any other variable available to
GDB.  *Note Tracepoint Action Lists: Tracepoint Actions.

The convenience variable $tpnum' records the tracepoint number of the most recently set tracepoint. delete tracepoint [NUM]' Permanently delete one or more tracepoints. With no argument, the default is to delete all tracepoints. Note that the regular delete' command can remove tracepoints also. Examples: (gdb) delete trace 1 2 3 // remove three tracepoints (gdb) delete trace // remove all tracepoints You can abbreviate this command as del tr'. File: gdb.info, Node: Enable and Disable Tracepoints, Next: Tracepoint Passcounts, Prev: Create and Delete Tracepoints, Up: Set Tracepoints 13.1.2 Enable and Disable Tracepoints ------------------------------------- These commands are deprecated; they are equivalent to plain disable' and enable'. disable tracepoint [NUM]' Disable tracepoint NUM, or all tracepoints if no argument NUM is given. A disabled tracepoint will have no effect during the next trace experiment, but it is not forgotten. You can re-enable a disabled tracepoint using the enable tracepoint' command. enable tracepoint [NUM]' Enable tracepoint NUM, or all tracepoints. The enabled tracepoints will become effective the next time a trace experiment is run. File: gdb.info, Node: Tracepoint Passcounts, Next: Tracepoint Conditions, Prev: Enable and Disable Tracepoints, Up: Set Tracepoints 13.1.3 Tracepoint Passcounts ---------------------------- passcount [N [NUM]]' Set the "passcount" of a tracepoint. The passcount is a way to automatically stop a trace experiment. If a tracepoint's passcount is N, then the trace experiment will be automatically stopped on the N'th time that tracepoint is hit. If the tracepoint number NUM is not specified, the passcount' command sets the passcount of the most recently defined tracepoint. If no passcount is given, the trace experiment will run until stopped explicitly by the user. Examples: (gdb) passcount 5 2 // Stop on the 5th execution of // tracepoint 2' (gdb) passcount 12 // Stop on the 12th execution of the // most recently defined tracepoint.' (gdb) trace foo (gdb) pass 3 (gdb) trace bar (gdb) pass 2 (gdb) trace baz (gdb) pass 1 // Stop tracing when foo has been // executed 3 times OR when bar has' // been executed 2 times' // OR when baz has been executed 1 time.' File: gdb.info, Node: Tracepoint Conditions, Next: Trace State Variables, Prev: Tracepoint Passcounts, Up: Set Tracepoints 13.1.4 Tracepoint Conditions ---------------------------- The simplest sort of tracepoint collects data every time your program reaches a specified place. You can also specify a "condition" for a tracepoint. A condition is just a Boolean expression in your programming language (*note Expressions: Expressions.). A tracepoint with a condition evaluates the expression each time your program reaches it, and data collection happens only if the condition is true. Tracepoint conditions can be specified when a tracepoint is set, by using if' in the arguments to the trace' command. *Note Setting Tracepoints: Create and Delete Tracepoints. They can also be set or changed at any time with the condition' command, just as with breakpoints. Unlike breakpoint conditions, GDB does not actually evaluate the conditional expression itself. Instead, GDB encodes the expression into an agent expression (*note Agent Expressions:: suitable for execution on the target, independently of GDB. Global variables become raw memory locations, locals become stack accesses, and so forth. For instance, suppose you have a function that is usually called frequently, but should not be called after an error has occurred. You could use the following tracepoint command to collect data about calls of that function that happen while the error code is propagating through the program; an unconditional tracepoint could end up collecting thousands of useless trace frames that you would have to search through. (gdb) trace normal_operation if errcode > 0 File: gdb.info, Node: Trace State Variables, Next: Tracepoint Actions, Prev: Tracepoint Conditions, Up: Set Tracepoints 13.1.5 Trace State Variables ---------------------------- A "trace state variable" is a special type of variable that is created and managed by target-side code. The syntax is the same as that for GDB's convenience variables (a string prefixed with "$"), but they are
stored on the target.  They must be created explicitly, using a
tvariable' command.  They are always 64-bit signed integers.

Trace state variables are remembered by GDB, and downloaded to the
target along with tracepoint information when the trace experiment
starts.  There are no intrinsic limits on the number of trace state
variables, beyond memory limitations of the target.

Although trace state variables are managed by the target, you can use
them in print commands and expressions as if they were convenience
variables; GDB will get the current value from the target while the
trace experiment is running.  Trace state variables share the same
namespace as other "$" variables, which means that you cannot have trace state variables with names like $23' or $pc', nor can you have a trace state variable and a convenience variable with the same name. tvariable$NAME [ = EXPRESSION ]'
The tvariable' command creates a new trace state variable named
$NAME', and optionally gives it an initial value of EXPRESSION. EXPRESSION is evaluated when this command is entered; the result will be converted to an integer if possible, otherwise GDB will report an error. A subsequent tvariable' command specifying the same name does not create a variable, but instead assigns the supplied initial value to the existing variable of that name, overwriting any previous initial value. The default initial value is 0. info tvariables' List all the trace state variables along with their initial values. Their current values may also be displayed, if the trace experiment is currently running. delete tvariable [$NAME ... ]'
Delete the given trace state variables, or all of them if no
arguments are specified.

File: gdb.info,  Node: Tracepoint Actions,  Next: Listing Tracepoints,  Prev: Trace State Variables,  Up: Set Tracepoints

13.1.6 Tracepoint Action Lists
------------------------------

actions [NUM]'
This command will prompt for a list of actions to be taken when the
tracepoint is hit.  If the tracepoint number NUM is not specified,
this command sets the actions for the one that was most recently
defined (so that you can define a tracepoint and then say
actions' without bothering about its number).  You specify the
actions themselves on the following lines, one action at a time,
and terminate the actions list with a line containing just end'.
So far, the only defined actions are collect', teval', and
while-stepping'.

actions' is actually equivalent to commands' (*note Breakpoint
Command Lists: Break Commands.), except that only the defined
actions are allowed; any other GDB command is rejected.

To remove all actions from a tracepoint, type actions NUM' and
follow it immediately with end'.

(gdb) collect DATA // collect some data

(gdb) while-stepping 5 // single-step 5 times, collect data

(gdb) end              // signals the end of actions.

In the following example, the action list begins with collect'
commands indicating the things to be collected when the tracepoint
is hit.  Then, in order to single-step and collect additional data
following the tracepoint, a while-stepping' command is used,
followed by the list of things to be collected after each step in a
sequence of single steps.  The while-stepping' command is
terminated by its own separate end' command.  Lastly, the action
list is terminated by an end' command.

(gdb) trace foo
(gdb) actions
Enter actions for tracepoint 1, one per line:
> collect bar,baz
> collect $regs > while-stepping 12 > collect$pc, arr[i]
> end
end

collect EXPR1, EXPR2, ...'
Collect values of the given expressions when the tracepoint is hit.
This command accepts a comma-separated list of any valid
expressions.  In addition to global, static, or local variables,
the following special arguments are supported:

$regs' Collect all registers. $args'
Collect all function arguments.

$locals' Collect all local variables. $_probe_argc'
Collects the number of arguments from the SystemTap' probe at
which the tracepoint is located.  *Note Static Probe Points:
Static Probe Points

$_probe_argN' Where N varies from 0 to 9. Collects the Nth argument from the SystemTap' probe at which the tracepoint is located. *Note Static Probe Points: Static Probe Points $_sdata'
Collect static tracepoint marker specific data.  Only
available for static tracepoints.  *Note Tracepoint Action
Lists: Tracepoint Actions.  On the UST static tracepoints
library backend, an instrumentation point resembles a
printf' function call.  The tracing library is able to
collect user specified data formatted to a character string
using the format provided by the programmer that instrumented
the program.  Other backends have similar mechanisms.  Here's
an example of a UST marker call:

const char master_name[] = "$your_name"; trace_mark(channel1, marker1, "hello %s", master_name) In this case, collecting $_sdata' collects the string hello
$yourname'. When analyzing the trace buffer, you can inspect $_sdata' like any other variable available to GDB.

You can give several consecutive collect' commands, each one with
a single argument, or one collect' command with several arguments
separated by commas; the effect is the same.

The command info scope' (*note info scope: Symbols.) is
particularly useful for figuring out what data to collect.

teval EXPR1, EXPR2, ...'
Evaluate the given expressions when the tracepoint is hit.  This
command accepts a comma-separated list of expressions.  The results
are discarded, so this is mainly useful for assigning values to
trace state variables (*note Trace State Variables::) without
adding those values to the trace buffer, as would be the case if
the collect' action were used.

while-stepping N'
Perform N single-step instruction traces after the tracepoint,
collecting new data after each step.  The while-stepping' command
is followed by the list of what to collect while stepping
(followed by its own end' command):

> while-stepping 12
> collect $regs, myglobal > end > Note that $pc' is not automatically collected by
while-stepping'; you need to explicitly collect that register if
you need it.  You may abbreviate while-stepping' as ws' or
stepping'.

set default-collect EXPR1, EXPR2, ...'
This variable is a list of expressions to collect at each
tracepoint hit.  It is effectively an additional collect' action
prepended to every tracepoint action list.  The expressions are
parsed individually for each tracepoint, so for instance a
variable named xyz' may be interpreted as a global for one
tracepoint, and a local for another, as appropriate to the
tracepoint's location.

show default-collect'
Show the list of expressions that are collected by default at each
tracepoint hit.

File: gdb.info,  Node: Listing Tracepoints,  Next: Listing Static Tracepoint Markers,  Prev: Tracepoint Actions,  Up: Set Tracepoints

13.1.7 Listing Tracepoints
--------------------------

info tracepoints [NUM]'
Display information about the tracepoint NUM.  If you don't
specify a tracepoint number, displays information about all the
tracepoints defined so far.  The format is similar to that used for
info breakpoints'; in fact, info tracepoints' is the same
command, simply restricting itself to tracepoints.

A tracepoint's listing may include additional information specific
to tracing:

* its passcount as given by the passcount N' command

(gdb) info trace
Num     Type           Disp Enb Address    What
1       tracepoint     keep y   0x0804ab57 in foo() at main.cxx:7
while-stepping 20
collect globfoo, $regs end collect globfoo2 end pass count 1200 (gdb) This command can be abbreviated info tp'. File: gdb.info, Node: Listing Static Tracepoint Markers, Next: Starting and Stopping Trace Experiments, Prev: Listing Tracepoints, Up: Set Tracepoints 13.1.8 Listing Static Tracepoint Markers ---------------------------------------- info static-tracepoint-markers' Display information about all static tracepoint markers defined in the program. For each marker, the following columns are printed: _Count_ An incrementing counter, output to help readability. This is not a stable identifier. _ID_ The marker ID, as reported by the target. _Enabled or Disabled_ Probed markers are tagged with y'. n' identifies marks that are not enabled. _Address_ Where the marker is in your program, as a memory address. _What_ Where the marker is in the source for your program, as a file and line number. If the debug information included in the program does not allow GDB to locate the source of the marker, this column will be left blank. In addition, the following information may be printed for each marker: _Data_ User data passed to the tracing library by the marker call. In the UST backend, this is the format string passed as argument to the marker call. _Static tracepoints probing the marker_ The list of static tracepoints attached to the marker. (gdb) info static-tracepoint-markers Cnt ID Enb Address What 1 ust/bar2 y 0x0000000000400e1a in main at stexample.c:25 Data: number1 %d number2 %d Probed by static tracepoints: #2 2 ust/bar33 n 0x0000000000400c87 in main at stexample.c:24 Data: str %s (gdb) File: gdb.info, Node: Starting and Stopping Trace Experiments, Next: Tracepoint Restrictions, Prev: Listing Static Tracepoint Markers, Up: Set Tracepoints 13.1.9 Starting and Stopping Trace Experiments ---------------------------------------------- tstart' This command takes no arguments. It starts the trace experiment, and begins collecting data. This has the side effect of discarding all the data collected in the trace buffer during the previous trace experiment. tstop' This command takes no arguments. It ends the trace experiment, and stops collecting data. *Note*: a trace experiment and data collection may stop automatically if any tracepoint's passcount is reached (*note Tracepoint Passcounts::), or if the trace buffer becomes full. tstatus' This command displays the status of the current trace data collection. Here is an example of the commands we described so far: (gdb) trace gdb_c_test (gdb) actions Enter actions for tracepoint #1, one per line. > collect$regs,$locals,$args
> while-stepping 11
> collect $regs > end > end (gdb) tstart [time passes ...] (gdb) tstop You can choose to continue running the trace experiment even if GDB disconnects from the target, voluntarily or involuntarily. For commands such as detach', the debugger will ask what you want to do with the trace. But for unexpected terminations (GDB crash, network outage), it would be unfortunate to lose hard-won trace data, so the variable disconnected-tracing' lets you decide whether the trace should continue running without GDB. set disconnected-tracing on' set disconnected-tracing off' Choose whether a tracing run should continue to run if GDB has disconnected from the target. Note that detach' or quit' will ask you directly what to do about a running trace no matter what this variable's setting, so the variable is mainly useful for handling unexpected situations, such as loss of the network. show disconnected-tracing' Show the current choice for disconnected tracing. When you reconnect to the target, the trace experiment may or may not still be running; it might have filled the trace buffer in the meantime, or stopped for one of the other reasons. If it is running, it will continue after reconnection. Upon reconnection, the target will upload information about the tracepoints in effect. GDB will then compare that information to the set of tracepoints currently defined, and attempt to match them up, allowing for the possibility that the numbers may have changed due to creation and deletion in the meantime. If one of the target's tracepoints does not match any in GDB, the debugger will create a new tracepoint, so that you have a number with which to specify that tracepoint. This matching-up process is necessarily heuristic, and it may result in useless tracepoints being created; you may simply delete them if they are of no use. If your target agent supports a "circular trace buffer", then you can run a trace experiment indefinitely without filling the trace buffer; when space runs out, the agent deletes already-collected trace frames, oldest first, until there is enough room to continue collecting. This is especially useful if your tracepoints are being hit too often, and your trace gets terminated prematurely because the buffer is full. To ask for a circular trace buffer, simply set circular_trace_buffer' to on. You can set this at any time, including during tracing; if the agent can do it, it will change buffer handling on the fly, otherwise it will not take effect until the next run. set circular-trace-buffer on' set circular-trace-buffer off' Choose whether a tracing run should use a linear or circular buffer for trace data. A linear buffer will not lose any trace data, but may fill up prematurely, while a circular buffer will discard old trace data, but it will have always room for the latest tracepoint hits. show circular-trace-buffer' Show the current choice for the trace buffer. Note that this may not match the agent's current buffer handling, nor is it guaranteed to match the setting that might have been in effect during a past run, for instance if you are looking at frames from a trace file. File: gdb.info, Node: Tracepoint Restrictions, Prev: Starting and Stopping Trace Experiments, Up: Set Tracepoints 13.1.10 Tracepoint Restrictions ------------------------------- There are a number of restrictions on the use of tracepoints. As described above, tracepoint data gathering occurs on the target without interaction from GDB. Thus the full capabilities of the debugger are not available during data gathering, and then at data examination time, you will be limited by only having what was collected. The following items describe some common problems, but it is not exhaustive, and you may run into additional difficulties not mentioned here. * Tracepoint expressions are intended to gather objects (lvalues). Thus the full flexibility of GDB's expression evaluator is not available. You cannot call functions, cast objects to aggregate types, access convenience variables or modify values (except by assignment to trace state variables). Some language features may implicitly call functions (for instance Objective-C fields with accessors), and therefore cannot be collected either. * Collection of local variables, either individually or in bulk with $locals' or $args', during while-stepping' may behave erratically. The stepping action may enter a new scope (for instance by stepping into a function), or the location of the variable may change (for instance it is loaded into a register). The tracepoint data recorded uses the location information for the variables that is correct for the tracepoint location. When the tracepoint is created, it is not possible, in general, to determine where the steps of a while-stepping' sequence will advance the program--particularly if a conditional branch is stepped. * Collection of an incompletely-initialized or partially-destroyed object may result in something that GDB cannot display, or displays in a misleading way. * When GDB displays a pointer to character it automatically dereferences the pointer to also display characters of the string being pointed to. However, collecting the pointer during tracing does not automatically collect the string. You need to explicitly dereference the pointer and provide size information if you want to collect not only the pointer, but the memory pointed to. For example, *ptr@50' can be used to collect the 50 element array pointed to by ptr'. * It is not possible to collect a complete stack backtrace at a tracepoint. Instead, you may collect the registers and a few hundred bytes from the stack pointer with something like *$esp@300' (adjust to use the name of the actual stack pointer
register on your target architecture, and the amount of stack you
wish to capture).  Then the backtrace' command will show a
partial backtrace when using a trace frame.  The number of stack
frames that can be examined depends on the sizes of the frames in
the collected stack.  Note that if you ask for a block so large
that it goes past the bottom of the stack, the target agent may
report an error trying to read from an invalid address.

* If you do not collect registers at a tracepoint, GDB can infer
that the value of $pc' must be the same as the address of the tracepoint and use that when you are looking at a trace frame for that tracepoint. However, this cannot work if the tracepoint has multiple locations (for instance if it was set in a function that was inlined), or if it has a while-stepping' loop. In those cases GDB will warn you that it can't infer $pc', and default it to
zero.

File: gdb.info,  Node: Analyze Collected Data,  Next: Tracepoint Variables,  Prev: Set Tracepoints,  Up: Tracepoints

13.2 Using the Collected Data
=============================

After the tracepoint experiment ends, you use GDB commands for
examining the trace data.  The basic idea is that each tracepoint
collects a trace "snapshot" every time it is hit and another snapshot
every time it single-steps.  All these snapshots are consecutively
numbered from zero and go into a buffer, and you can examine them
later.  The way you examine them is to "focus" on a specific trace
snapshot.  When the remote stub is focused on a trace snapshot, it will
respond to all GDB requests for memory and registers by reading from
the buffer which belongs to that snapshot, rather than from _real_
memory or registers of the program being debugged.  This means that
*all* GDB commands (print', info registers', backtrace', etc.) will
behave as if we were currently debugging the program state as it was
when the tracepoint occurred.  Any requests for data that are not in
the buffer will fail.

* tfind::                       How to select a trace snapshot
* tdump::                       How to display all data for a snapshot
* save tracepoints::            How to save tracepoints for a future run

File: gdb.info,  Node: tfind,  Next: tdump,  Up: Analyze Collected Data

13.2.1 tfind N'
----------------

The basic command for selecting a trace snapshot from the buffer is
tfind N', which finds trace snapshot number N, counting from zero.  If
no argument N is given, the next snapshot is selected.

Here are the various forms of using the tfind' command.

tfind start'
Find the first snapshot in the buffer.  This is a synonym for
tfind 0' (since 0 is the number of the first snapshot).

tfind none'
Stop debugging trace snapshots, resume _live_ debugging.

tfind end'
Same as tfind none'.

tfind'
No argument means find the next trace snapshot.

tfind -'
Find the previous trace snapshot before the current one.  This
permits retracing earlier steps.

tfind tracepoint NUM'
Find the next snapshot associated with tracepoint NUM.  Search
proceeds forward from the last examined trace snapshot.  If no
argument NUM is given, it means find the next snapshot collected
for the same tracepoint as the current snapshot.

Find the next snapshot associated with the value ADDR of the
program counter.  Search proceeds forward from the last examined
trace snapshot.  If no argument ADDR is given, it means find the
next snapshot with the same value of PC as the current snapshot.

tfind outside ADDR1, ADDR2'
Find the next snapshot whose PC is outside the given range of

Find the next snapshot whose PC is between ADDR1 and ADDR2
(inclusive).

tfind line [FILE:]N'
Find the next snapshot associated with the source line N.  If the
optional argument FILE is given, refer to line N in that source
file.  Search proceeds forward from the last examined trace
snapshot.  If no argument N is given, it means find the next line
other than the one currently being examined; thus saying tfind
line' repeatedly can appear to have the same effect as stepping
from line to line in a _live_ debugging session.

The default arguments for the tfind' commands are specifically
designed to make it easy to scan through the trace buffer.  For
instance, tfind' with no argument selects the next trace snapshot, and
tfind -' with no argument selects the previous trace snapshot.  So, by
giving one tfind' command, and then simply hitting <RET> repeatedly
you can examine all the trace snapshots in order.  Or, by saying tfind
-' and then hitting <RET> repeatedly you can examine the snapshots in
reverse order.  The tfind line' command with no argument selects the
snapshot for the next source line executed.  The tfind pc' command with
no argument selects the next snapshot with the same program counter
(PC) as the current frame.  The tfind tracepoint' command with no
argument selects the next trace snapshot collected by the same
tracepoint as the current one.

In addition to letting you scan through the trace buffer manually,
these commands make it easy to construct GDB scripts that scan through
the trace buffer and print out whatever collected data you are
interested in.  Thus, if we want to examine the PC, FP, and SP
registers from each trace frame in the buffer, we can say this:

(gdb) tfind start
(gdb) while ($trace_frame != -1) > printf "Frame %d, PC = %08X, SP = %08X, FP = %08X\n", \$trace_frame, $pc,$sp, $fp > tfind > end Frame 0, PC = 0020DC64, SP = 0030BF3C, FP = 0030BF44 Frame 1, PC = 0020DC6C, SP = 0030BF38, FP = 0030BF44 Frame 2, PC = 0020DC70, SP = 0030BF34, FP = 0030BF44 Frame 3, PC = 0020DC74, SP = 0030BF30, FP = 0030BF44 Frame 4, PC = 0020DC78, SP = 0030BF2C, FP = 0030BF44 Frame 5, PC = 0020DC7C, SP = 0030BF28, FP = 0030BF44 Frame 6, PC = 0020DC80, SP = 0030BF24, FP = 0030BF44 Frame 7, PC = 0020DC84, SP = 0030BF20, FP = 0030BF44 Frame 8, PC = 0020DC88, SP = 0030BF1C, FP = 0030BF44 Frame 9, PC = 0020DC8E, SP = 0030BF18, FP = 0030BF44 Frame 10, PC = 00203F6C, SP = 0030BE3C, FP = 0030BF14 Or, if we want to examine the variable X' at each source line in the buffer: (gdb) tfind start (gdb) while ($trace_frame != -1)
> printf "Frame %d, X == %d\n", $trace_frame, X > tfind line > end Frame 0, X = 1 Frame 7, X = 2 Frame 13, X = 255 File: gdb.info, Node: tdump, Next: save tracepoints, Prev: tfind, Up: Analyze Collected Data 13.2.2 tdump' -------------- This command takes no arguments. It prints all the data collected at the current trace snapshot. (gdb) trace 444 (gdb) actions Enter actions for tracepoint #2, one per line: > collect$regs, $locals,$args, gdb_long_test
> end

(gdb) tstart

(gdb) tfind line 444
#0  gdb_test (p1=0x11, p2=0x22, p3=0x33, p4=0x44, p5=0x55, p6=0x66)
at gdb_test.c:444
444        printp( "%s: arguments = 0x%X 0x%X 0x%X 0x%X 0x%X 0x%X\n", )

(gdb) tdump
Data collected at tracepoint 2, trace frame 1:
d0             0xc4aa0085       -995491707
d1             0x18     24
d2             0x80     128
d3             0x33     51
d4             0x71aea3d        119204413
d5             0x22     34
d6             0xe0     224
d7             0x380035 3670069
a0             0x19e24a 1696330
a1             0x3000668        50333288
a2             0x100    256
a3             0x322000 3284992
a4             0x3000698        50333336
fp             0x30bf3c 0x30bf3c
sp             0x30bf34 0x30bf34
ps             0x0      0
pc             0x20b2c8 0x20b2c8
fpcontrol      0x0      0
fpstatus       0x0      0
p = 0x20e5b4 "gdb-test"
p1 = (void *) 0x11
p2 = (void *) 0x22
p3 = (void *) 0x33
p4 = (void *) 0x44
p5 = (void *) 0x55
p6 = (void *) 0x66
gdb_long_test = 17 '\021'

(gdb)

tdump' works by scanning the tracepoint's current collection
actions and printing the value of each expression listed.  So tdump'
can fail, if after a run, you change the tracepoint's actions to
mention variables that were not collected during the run.

Also, for tracepoints with while-stepping' loops, tdump' uses the
collected value of $pc' to distinguish between trace frames that were collected at the tracepoint hit, and frames that were collected while stepping. This allows it to correctly choose whether to display the basic list of collections, or the collections from the body of the while-stepping loop. However, if $pc' was not collected, then tdump'
will always attempt to dump using the basic collection list, and may
fail if a while-stepping frame does not include all the same data that
is collected at the tracepoint hit.

File: gdb.info,  Node: save tracepoints,  Prev: tdump,  Up: Analyze Collected Data

13.2.3 save tracepoints FILENAME'
----------------------------------

This command saves all current tracepoint definitions together with
their actions and passcounts, into a file FILENAME' suitable for use
in a later debugging session.  To read the saved tracepoint
definitions, use the source' command (*note Command Files::).  The
save-tracepoints' command is a deprecated alias for save tracepoints'

File: gdb.info,  Node: Tracepoint Variables,  Next: Trace Files,  Prev: Analyze Collected Data,  Up: Tracepoints

13.3 Convenience Variables for Tracepoints
==========================================

(int) $trace_frame' The current trace snapshot (a.k.a. "frame") number, or -1 if no snapshot is selected. (int)$tracepoint'
The tracepoint for the current trace snapshot.

(int) $trace_line' The line number for the current trace snapshot. (char [])$trace_file'
The source file for the current trace snapshot.

(char []) $trace_func' The name of the function containing $tracepoint'.

Note: $trace_file' is not suitable for use in printf', use output' instead. Here's a simple example of using these convenience variables for stepping through all the trace snapshots and printing some of their data. Note that these are not the same as trace state variables, which are managed by the target. (gdb) tfind start (gdb) while$trace_frame != -1
> output $trace_file > printf ", line %d (tracepoint #%d)\n",$trace_line, $tracepoint > tfind > end File: gdb.info, Node: Trace Files, Prev: Tracepoint Variables, Up: Tracepoints 13.4 Using Trace Files ====================== In some situations, the target running a trace experiment may no longer be available; perhaps it crashed, or the hardware was needed for a different activity. To handle these cases, you can arrange to dump the trace data into a file, and later use that file as a source of trace data, via the target tfile' command. tsave [ -r ] FILENAME' Save the trace data to FILENAME. By default, this command assumes that FILENAME refers to the host filesystem, so if necessary GDB will copy raw trace data up from the target and then save it. If the target supports it, you can also supply the optional argument -r' ("remote") to direct the target to save the data directly into FILENAME in its own filesystem, which may be more efficient if the trace buffer is very large. (Note, however, that target tfile' can only read from files accessible to the host.) target tfile FILENAME' Use the file named FILENAME as a source of trace data. Commands that examine data work as they do with a live target, but it is not possible to run any new trace experiments. tstatus' will report the state of the trace run at the moment the data was saved, as well as the current trace frame you are examining. FILENAME must be on a filesystem accessible to the host. File: gdb.info, Node: Overlays, Next: Languages, Prev: Tracepoints, Up: Top 14 Debugging Programs That Use Overlays *************************************** If your program is too large to fit completely in your target system's memory, you can sometimes use "overlays" to work around this problem. GDB provides some support for debugging programs that use overlays. * Menu: * How Overlays Work:: A general explanation of overlays. * Overlay Commands:: Managing overlays in GDB. * Automatic Overlay Debugging:: GDB can find out which overlays are mapped by asking the inferior. * Overlay Sample Program:: A sample program using overlays. File: gdb.info, Node: How Overlays Work, Next: Overlay Commands, Up: Overlays 14.1 How Overlays Work ====================== Suppose you have a computer whose instruction address space is only 64 kilobytes long, but which has much more memory which can be accessed by other means: special instructions, segment registers, or memory management hardware, for example. Suppose further that you want to adapt a program which is larger than 64 kilobytes to run on this system. One solution is to identify modules of your program which are relatively independent, and need not call each other directly; call these modules "overlays". Separate the overlays from the main program, and place their machine code in the larger memory. Place your main program in instruction memory, but leave at least enough space there to hold the largest overlay as well. Now, to call a function located in an overlay, you must first copy that overlay's machine code from the large memory into the space set aside for it in the instruction memory, and then jump to its entry point there. Data Instruction Larger Address Space Address Space Address Space +-----------+ +-----------+ +-----------+ | | | | | | +-----------+ +-----------+ +-----------+<-- overlay 1 | program | | main | .----| overlay 1 | load address | variables | | program | | +-----------+ | and heap | | | | | | +-----------+ | | | +-----------+<-- overlay 2 | | +-----------+ | | | load address +-----------+ | | | .-| overlay 2 | | | | | | | mapped --->+-----------+ | | +-----------+ address | | | | | | | overlay | <-' | | | | area | <---' +-----------+<-- overlay 3 | | <---. | | load address +-----------+ --| overlay 3 | | | | | +-----------+ | | +-----------+ | | +-----------+ A code overlay The diagram (*note A code overlay::) shows a system with separate data and instruction address spaces. To map an overlay, the program copies its code from the larger address space to the instruction address space. Since the overlays shown here all use the same mapped address, only one may be mapped at a time. For a system with a single address space for data and instructions, the diagram would be similar, except that the program variables and heap would share an address space with the main program and the overlay area. An overlay loaded into instruction memory and ready for use is called a "mapped" overlay; its "mapped address" is its address in the instruction memory. An overlay not present (or only partially present) in instruction memory is called "unmapped"; its "load address" is its address in the larger memory. The mapped address is also called the "virtual memory address", or "VMA"; the load address is also called the "load memory address", or "LMA". Unfortunately, overlays are not a completely transparent way to adapt a program to limited instruction memory. They introduce a new set of global constraints you must keep in mind as you design your program: * Before calling or returning to a function in an overlay, your program must make sure that overlay is actually mapped. Otherwise, the call or return will transfer control to the right address, but in the wrong overlay, and your program will probably crash. * If the process of mapping an overlay is expensive on your system, you will need to choose your overlays carefully to minimize their effect on your program's performance. * The executable file you load onto your system must contain each overlay's instructions, appearing at the overlay's load address, not its mapped address. However, each overlay's instructions must be relocated and its symbols defined as if the overlay were at its mapped address. You can use GNU linker scripts to specify different load and relocation addresses for pieces of your program; see *note Overlay Description: (ld.info)Overlay Description. * The procedure for loading executable files onto your system must be able to load their contents into the larger address space as well as the instruction and data spaces. The overlay system described above is rather simple, and could be improved in many ways: * If your system has suitable bank switch registers or memory management hardware, you could use those facilities to make an overlay's load area contents simply appear at their mapped address in instruction space. This would probably be faster than copying the overlay to its mapped area in the usual way. * If your overlays are small enough, you could set aside more than one overlay area, and have more than one overlay mapped at a time. * You can use overlays to manage data, as well as instructions. In general, data overlays are even less transparent to your design than code overlays: whereas code overlays only require care when you call or return to functions, data overlays require care every time you access the data. Also, if you change the contents of a data overlay, you must copy its contents back out to its load address before you can copy a different data overlay into the same mapped area. File: gdb.info, Node: Overlay Commands, Next: Automatic Overlay Debugging, Prev: How Overlays Work, Up: Overlays 14.2 Overlay Commands ===================== To use GDB's overlay support, each overlay in your program must correspond to a separate section of the executable file. The section's virtual memory address and load memory address must be the overlay's mapped and load addresses. Identifying overlays with sections allows GDB to determine the appropriate address of a function or variable, depending on whether the overlay is mapped or not. GDB's overlay commands all start with the word overlay'; you can abbreviate this as ov' or ovly'. The commands are: overlay off' Disable GDB's overlay support. When overlay support is disabled, GDB assumes that all functions and variables are always present at their mapped addresses. By default, GDB's overlay support is disabled. overlay manual' Enable "manual" overlay debugging. In this mode, GDB relies on you to tell it which overlays are mapped, and which are not, using the overlay map-overlay' and overlay unmap-overlay' commands described below. overlay map-overlay OVERLAY' overlay map OVERLAY' Tell GDB that OVERLAY is now mapped; OVERLAY must be the name of the object file section containing the overlay. When an overlay is mapped, GDB assumes it can find the overlay's functions and variables at their mapped addresses. GDB assumes that any other overlays whose mapped ranges overlap that of OVERLAY are now unmapped. overlay unmap-overlay OVERLAY' overlay unmap OVERLAY' Tell GDB that OVERLAY is no longer mapped; OVERLAY must be the name of the object file section containing the overlay. When an overlay is unmapped, GDB assumes it can find the overlay's functions and variables at their load addresses. overlay auto' Enable "automatic" overlay debugging. In this mode, GDB consults a data structure the overlay manager maintains in the inferior to see which overlays are mapped. For details, see *note Automatic Overlay Debugging::. overlay load-target' overlay load' Re-read the overlay table from the inferior. Normally, GDB re-reads the table GDB automatically each time the inferior stops, so this command should only be necessary if you have changed the overlay mapping yourself using GDB. This command is only useful when using automatic overlay debugging. overlay list-overlays' overlay list' Display a list of the overlays currently mapped, along with their mapped addresses, load addresses, and sizes. Normally, when GDB prints a code address, it includes the name of the function the address falls in: (gdb) print main$3 = {int ()} 0x11a0 <main>
When overlay debugging is enabled, GDB recognizes code in unmapped
overlays, and prints the names of unmapped functions with asterisks
around them.  For example, if foo' is a function in an unmapped
overlay, GDB prints it this way:

(gdb) overlay list
No sections are mapped.
(gdb) print foo
$5 = {int (int)} 0x100000 <*foo*> When foo''s overlay is mapped, GDB prints the function's name normally: (gdb) overlay list Section .ov.foo.text, loaded at 0x100000 - 0x100034, mapped at 0x1016 - 0x104a (gdb) print foo$6 = {int (int)} 0x1016 <foo>

When overlay debugging is enabled, GDB can find the correct address
for functions and variables in an overlay, whether or not the overlay
is mapped.  This allows most GDB commands, like break' and
disassemble', to work normally, even on unmapped code.  However, GDB's
breakpoint support has some limitations:

* You can set breakpoints in functions in unmapped overlays, as long
as GDB can write to the overlay at its load address.

* GDB can not set hardware or simulator-based breakpoints in
unmapped overlays.  However, if you set a breakpoint at the end of
your overlay manager (and tell GDB which overlays are now mapped,
if you are using manual overlay management), GDB will re-set its
breakpoints properly.

File: gdb.info,  Node: Automatic Overlay Debugging,  Next: Overlay Sample Program,  Prev: Overlay Commands,  Up: Overlays

14.3 Automatic Overlay Debugging
================================

GDB can automatically track which overlays are mapped and which are
not, given some simple co-operation from the overlay manager in the
inferior.  If you enable automatic overlay debugging with the overlay
auto' command (*note Overlay Commands::), GDB looks in the inferior's
memory for certain variables describing the current state of the
overlays.

Here are the variables your overlay manager must define to support
GDB's automatic overlay debugging:

_ovly_table':
This variable must be an array of the following structures:

struct
{
/* The overlay's mapped address.  */
unsigned long vma;

/* The size of the overlay, in bytes.  */
unsigned long size;

unsigned long lma;

/* Non-zero if the overlay is currently mapped;
zero otherwise.  */
unsigned long mapped;
}

_novlys':
This variable must be a four-byte signed integer, holding the total
number of elements in _ovly_table'.

To decide whether a particular overlay is mapped or not, GDB looks
for an entry in _ovly_table' whose vma' and lma' members equal the
VMA and LMA of the overlay's section in the executable file.  When GDB
finds a matching entry, it consults the entry's mapped' member to
determine whether the overlay is currently mapped.

In addition, your overlay manager may define a function called
_ovly_debug_event'.  If this function is defined, GDB will silently
set a breakpoint there.  If the overlay manager then calls this
function whenever it has changed the overlay table, this will enable
GDB to accurately keep track of which overlays are in program memory,
and update any breakpoints that may be set in overlays.  This will
allow breakpoints to work even if the overlays are kept in ROM or other
non-writable memory while they are not being executed.

File: gdb.info,  Node: Overlay Sample Program,  Prev: Automatic Overlay Debugging,  Up: Overlays

14.4 Overlay Sample Program
===========================

When linking a program which uses overlays, you must place the overlays
at their load addresses, while relocating them to run at their mapped
addresses.  To do this, you must write a linker script (*note Overlay
Description: (ld.info)Overlay Description.).  Unfortunately, since
linker scripts are specific to a particular host system, target
architecture, and target memory layout, this manual cannot provide
portable sample code demonstrating GDB's overlay support.

However, the GDB source distribution does contain an overlaid
program, with linker scripts for a few systems, as part of its test
suite.  The program consists of the following files from
gdb/testsuite/gdb.base':

overlays.c'
The main program file.

ovlymgr.c'
A simple overlay manager, used by overlays.c'.

foo.c'
bar.c'
baz.c'
grbx.c'
Overlay modules, loaded and used by overlays.c'.

d10v.ld'
m32r.ld'
Linker scripts for linking the test program on the d10v-elf' and
m32r-elf' targets.

You can build the test program using the d10v-elf' GCC
cross-compiler like this:

$d10v-elf-gcc -g -c overlays.c$ d10v-elf-gcc -g -c ovlymgr.c
$d10v-elf-gcc -g -c foo.c$ d10v-elf-gcc -g -c bar.c
$d10v-elf-gcc -g -c baz.c$ d10v-elf-gcc -g -c grbx.c
$d10v-elf-gcc -g overlays.o ovlymgr.o foo.o bar.o \ baz.o grbx.o -Wl,-Td10v.ld -o overlays The build process is identical for any other architecture, except that you must substitute the appropriate compiler and linker script for the target system for d10v-elf-gcc' and d10v.ld'. File: gdb.info, Node: Languages, Next: Symbols, Prev: Overlays, Up: Top 15 Using GDB with Different Languages ************************************* Although programming languages generally have common aspects, they are rarely expressed in the same manner. For instance, in ANSI C, dereferencing a pointer p' is accomplished by *p', but in Modula-2, it is accomplished by p^'. Values can also be represented (and displayed) differently. Hex numbers in C appear as 0x1ae', while in Modula-2 they appear as 1AEH'. Language-specific information is built into GDB for some languages, allowing you to express operations like the above in your program's native language, and allowing GDB to output values in a manner consistent with the syntax of your program's native language. The language you use to build expressions is called the "working language". * Menu: * Setting:: Switching between source languages * Show:: Displaying the language * Checks:: Type and range checks * Supported Languages:: Supported languages * Unsupported Languages:: Unsupported languages File: gdb.info, Node: Setting, Next: Show, Up: Languages 15.1 Switching Between Source Languages ======================================= There are two ways to control the working language--either have GDB set it automatically, or select it manually yourself. You can use the set language' command for either purpose. On startup, GDB defaults to setting the language automatically. The working language is used to determine how expressions you type are interpreted, how values are printed, etc. In addition to the working language, every source file that GDB knows about has its own working language. For some object file formats, the compiler might indicate which language a particular source file is in. However, most of the time GDB infers the language from the name of the file. The language of a source file controls whether C++ names are demangled--this way backtrace' can show each frame appropriately for its own language. There is no way to set the language of a source file from within GDB, but you can set the language associated with a filename extension. *Note Displaying the Language: Show. This is most commonly a problem when you use a program, such as cfront' or f2c', that generates C but is written in another language. In that case, make the program use #line' directives in its C output; that way GDB will know the correct language of the source code of the original program, and will display that source code, not the generated C code. * Menu: * Filenames:: Filename extensions and languages. * Manually:: Setting the working language manually * Automatically:: Having GDB infer the source language File: gdb.info, Node: Filenames, Next: Manually, Up: Setting 15.1.1 List of Filename Extensions and Languages ------------------------------------------------ If a source file name ends in one of the following extensions, then GDB infers that its language is the one indicated. .ada' .ads' .adb' .a' Ada source file. .c' C source file .C' .cc' .cp' .cpp' .cxx' .c++' C++ source file .d' D source file .m' Objective-C source file .f' .F' Fortran source file .mod' Modula-2 source file .s' .S' Assembler source file. This actually behaves almost like C, but GDB does not skip over function prologues when stepping. In addition, you may set the language associated with a filename extension. *Note Displaying the Language: Show. File: gdb.info, Node: Manually, Next: Automatically, Prev: Filenames, Up: Setting 15.1.2 Setting the Working Language ----------------------------------- If you allow GDB to set the language automatically, expressions are interpreted the same way in your debugging session and your program. If you wish, you may set the language manually. To do this, issue the command set language LANG', where LANG is the name of a language, such as c' or modula-2'. For a list of the supported languages, type set language'. Setting the language manually prevents GDB from updating the working language automatically. This can lead to confusion if you try to debug a program when the working language is not the same as the source language, when an expression is acceptable to both languages--but means different things. For instance, if the current source file were written in C, and GDB was parsing Modula-2, a command such as: print a = b + c might not have the effect you intended. In C, this means to add b' and c' and place the result in a'. The result printed would be the value of a'. In Modula-2, this means to compare a' to the result of b+c', yielding a BOOLEAN' value. File: gdb.info, Node: Automatically, Prev: Manually, Up: Setting 15.1.3 Having GDB Infer the Source Language ------------------------------------------- To have GDB set the working language automatically, use set language local' or set language auto'. GDB then infers the working language. That is, when your program stops in a frame (usually by encountering a breakpoint), GDB sets the working language to the language recorded for the function in that frame. If the language for a frame is unknown (that is, if the function or block corresponding to the frame was defined in a source file that does not have a recognized extension), the current working language is not changed, and GDB issues a warning. This may not seem necessary for most programs, which are written entirely in one source language. However, program modules and libraries written in one source language can be used by a main program written in a different source language. Using set language auto' in this case frees you from having to set the working language manually. File: gdb.info, Node: Show, Next: Checks, Prev: Setting, Up: Languages 15.2 Displaying the Language ============================ The following commands help you find out which language is the working language, and also what language source files were written in. show language' Display the current working language. This is the language you can use with commands such as print' to build and compute expressions that may involve variables in your program. info frame' Display the source language for this frame. This language becomes the working language if you use an identifier from this frame. *Note Information about a Frame: Frame Info, to identify the other information listed here. info source' Display the source language of this source file. *Note Examining the Symbol Table: Symbols, to identify the other information listed here. In unusual circumstances, you may have source files with extensions not in the standard list. You can then set the extension associated with a language explicitly: set extension-language EXT LANGUAGE' Tell GDB that source files with extension EXT are to be assumed as written in the source language LANGUAGE. info extensions' List all the filename extensions and the associated languages. File: gdb.info, Node: Checks, Next: Supported Languages, Prev: Show, Up: Languages 15.3 Type and Range Checking ============================ _Warning:_ In this release, the GDB commands for type and range checking are included, but they do not yet have any effect. This section documents the intended facilities. Some languages are designed to guard you against making seemingly common errors through a series of compile- and run-time checks. These include checking the type of arguments to functions and operators, and making sure mathematical overflows are caught at run time. Checks such as these help to ensure a program's correctness once it has been compiled by eliminating type mismatches, and providing active checks for range errors when your program is running. GDB can check for conditions like the above if you wish. Although GDB does not check the statements in your program, it can check expressions entered directly into GDB for evaluation via the print' command, for example. As with the working language, GDB can also decide whether or not to check automatically based on your program's source language. *Note Supported Languages: Supported Languages, for the default settings of supported languages. * Menu: * Type Checking:: An overview of type checking * Range Checking:: An overview of range checking File: gdb.info, Node: Type Checking, Next: Range Checking, Up: Checks 15.3.1 An Overview of Type Checking ----------------------------------- Some languages, such as Modula-2, are strongly typed, meaning that the arguments to operators and functions have to be of the correct type, otherwise an error occurs. These checks prevent type mismatch errors from ever causing any run-time problems. For example, 1 + 2 => 3 but error--> 1 + 2.3 The second example fails because the CARDINAL' 1 is not type-compatible with the REAL' 2.3. For the expressions you use in GDB commands, you can tell the GDB type checker to skip checking; to treat any mismatches as errors and abandon the expression; or to only issue warnings when type mismatches occur, but evaluate the expression anyway. When you choose the last of these, GDB evaluates expressions like the second example above, but also issues a warning. Even if you turn type checking off, there may be other reasons related to type that prevent GDB from evaluating an expression. For instance, GDB does not know how to add an int' and a struct foo'. These particular type errors have nothing to do with the language in use, and usually arise from expressions, such as the one described above, which make little sense to evaluate anyway. Each language defines to what degree it is strict about type. For instance, both Modula-2 and C require the arguments to arithmetical operators to be numbers. In C, enumerated types and pointers can be represented as numbers, so that they are valid arguments to mathematical operators. *Note Supported Languages: Supported Languages, for further details on specific languages. GDB provides some additional commands for controlling the type checker: set check type auto' Set type checking on or off based on the current working language. *Note Supported Languages: Supported Languages, for the default settings for each language. set check type on' set check type off' Set type checking on or off, overriding the default setting for the current working language. Issue a warning if the setting does not match the language default. If any type mismatches occur in evaluating an expression while type checking is on, GDB prints a message and aborts evaluation of the expression. set check type warn' Cause the type checker to issue warnings, but to always attempt to evaluate the expression. Evaluating the expression may still be impossible for other reasons. For example, GDB cannot add numbers and structures. show type' Show the current setting of the type checker, and whether or not GDB is setting it automatically. File: gdb.info, Node: Range Checking, Prev: Type Checking, Up: Checks 15.3.2 An Overview of Range Checking ------------------------------------ In some languages (such as Modula-2), it is an error to exceed the bounds of a type; this is enforced with run-time checks. Such range checking is meant to ensure program correctness by making sure computations do not overflow, or indices on an array element access do not exceed the bounds of the array. For expressions you use in GDB commands, you can tell GDB to treat range errors in one of three ways: ignore them, always treat them as errors and abandon the expression, or issue warnings but evaluate the expression anyway. A range error can result from numerical overflow, from exceeding an array index bound, or when you type a constant that is not a member of any type. Some languages, however, do not treat overflows as an error. In many implementations of C, mathematical overflow causes the result to "wrap around" to lower values--for example, if M is the largest integer value, and S is the smallest, then M + 1 => S This, too, is specific to individual languages, and in some cases specific to individual compilers or machines. *Note Supported Languages: Supported Languages, for further details on specific languages. GDB provides some additional commands for controlling the range checker: set check range auto' Set range checking on or off based on the current working language. *Note Supported Languages: Supported Languages, for the default settings for each language. set check range on' set check range off' Set range checking on or off, overriding the default setting for the current working language. A warning is issued if the setting does not match the language default. If a range error occurs and range checking is on, then a message is printed and evaluation of the expression is aborted. set check range warn' Output messages when the GDB range checker detects a range error, but attempt to evaluate the expression anyway. Evaluating the expression may still be impossible for other reasons, such as accessing memory that the process does not own (a typical example from many Unix systems). show range' Show the current setting of the range checker, and whether or not it is being set automatically by GDB. File: gdb.info, Node: Supported Languages, Next: Unsupported Languages, Prev: Checks, Up: Languages 15.4 Supported Languages ======================== GDB supports C, C++, D, Objective-C, Fortran, Java, Pascal, assembly, Modula-2, and Ada. Some GDB features may be used in expressions regardless of the language you use: the GDB @' and ::' operators, and the {type}addr' construct (*note Expressions: Expressions.) can be used with the constructs of any supported language. The following sections detail to what degree each source language is supported by GDB. These sections are not meant to be language tutorials or references, but serve only as a reference guide to what the GDB expression parser accepts, and what input and output formats should look like for different languages. There are many good books written on each of these languages; please look to these for a language reference or tutorial. * Menu: * C:: C and C++ * D:: D * Objective-C:: Objective-C * Fortran:: Fortran * Pascal:: Pascal * Modula-2:: Modula-2 * Ada:: Ada File: gdb.info, Node: C, Next: D, Up: Supported Languages 15.4.1 C and C++ ---------------- Since C and C++ are so closely related, many features of GDB apply to both languages. Whenever this is the case, we discuss those languages together. The C++ debugging facilities are jointly implemented by the C++ compiler and GDB. Therefore, to debug your C++ code effectively, you must compile your C++ programs with a supported C++ compiler, such as GNU g++', or the HP ANSI C++ compiler (aCC'). For best results when using GNU C++, use the DWARF 2 debugging format; if it doesn't work on your system, try the stabs+ debugging format. You can select those formats explicitly with the g++' command-line options -gdwarf-2' and -gstabs+'. *Note Options for Debugging Your Program or GCC: (gcc.info)Debugging Options. * Menu: * C Operators:: C and C++ operators * C Constants:: C and C++ constants * C Plus Plus Expressions:: C++ expressions * C Defaults:: Default settings for C and C++ * C Checks:: C and C++ type and range checks * Debugging C:: GDB and C * Debugging C Plus Plus:: GDB features for C++ * Decimal Floating Point:: Numbers in Decimal Floating Point format File: gdb.info, Node: C Operators, Next: C Constants, Up: C 15.4.1.1 C and C++ Operators ............................ Operators must be defined on values of specific types. For instance, +' is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of C and C++, the following definitions hold: * _Integral types_ include int' with any of its storage-class specifiers; char'; enum'; and, for C++, bool'. * _Floating-point types_ include float', double', and long double' (if supported by the target platform). * _Pointer types_ include all types defined as (TYPE *)'. * _Scalar types_ include all of the above. The following operators are supported. They are listed here in order of increasing precedence: ,' The comma or sequencing operator. Expressions in a comma-separated list are evaluated from left to right, with the result of the entire expression being the last expression evaluated. =' Assignment. The value of an assignment expression is the value assigned. Defined on scalar types. OP=' Used in an expression of the form A OP= B', and translated to A = A OP B'. OP=' and =' have the same precedence. OP is any one of the operators |', ^', &', <<', >>', +', -', *', /', %'. ?:' The ternary operator. A ? B : C' can be thought of as: if A then B else C. A should be of an integral type. ||' Logical OR. Defined on integral types. &&' Logical AND. Defined on integral types. |' Bitwise OR. Defined on integral types. ^' Bitwise exclusive-OR. Defined on integral types. &' Bitwise AND. Defined on integral types. ==, !=' Equality and inequality. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true. <, >, <=, >=' Less than, greater than, less than or equal, greater than or equal. Defined on scalar types. The value of these expressions is 0 for false and non-zero for true. <<, >>' left shift, and right shift. Defined on integral types. @' The GDB "artificial array" operator (*note Expressions: Expressions.). +, -' Addition and subtraction. Defined on integral types, floating-point types and pointer types. *, /, %' Multiplication, division, and modulus. Multiplication and division are defined on integral and floating-point types. Modulus is defined on integral types. ++, --' Increment and decrement. When appearing before a variable, the operation is performed before the variable is used in an expression; when appearing after it, the variable's value is used before the operation takes place. *' Pointer dereferencing. Defined on pointer types. Same precedence as ++'. &' Address operator. Defined on variables. Same precedence as ++'. For debugging C++, GDB implements a use of &' beyond what is allowed in the C++ language itself: you can use &(&REF)' to examine the address where a C++ reference variable (declared with &REF') is stored. -' Negative. Defined on integral and floating-point types. Same precedence as ++'. !' Logical negation. Defined on integral types. Same precedence as ++'. ~' Bitwise complement operator. Defined on integral types. Same precedence as ++'. ., ->' Structure member, and pointer-to-structure member. For convenience, GDB regards the two as equivalent, choosing whether to dereference a pointer based on the stored type information. Defined on struct' and union' data. .*, ->*' Dereferences of pointers to members. []' Array indexing. A[I]' is defined as *(A+I)'. Same precedence as ->'. ()' Function parameter list. Same precedence as ->'. ::' C++ scope resolution operator. Defined on struct', union', and class' types. ::' Doubled colons also represent the GDB scope operator (*note Expressions: Expressions.). Same precedence as ::', above. If an operator is redefined in the user code, GDB usually attempts to invoke the redefined version instead of using the operator's predefined meaning. File: gdb.info, Node: C Constants, Next: C Plus Plus Expressions, Prev: C Operators, Up: C 15.4.1.2 C and C++ Constants ............................ GDB allows you to express the constants of C and C++ in the following ways: * Integer constants are a sequence of digits. Octal constants are specified by a leading 0' (i.e. zero), and hexadecimal constants by a leading 0x' or 0X'. Constants may also end with a letter l', specifying that the constant should be treated as a long' value. * Floating point constants are a sequence of digits, followed by a decimal point, followed by a sequence of digits, and optionally followed by an exponent. An exponent is of the form: e[[+]|-]NNN', where NNN is another sequence of digits. The +' is optional for positive exponents. A floating-point constant may also end with a letter f' or F', specifying that the constant should be treated as being of the float' (as opposed to the default double') type; or with a letter l' or L', which specifies a long double' constant. * Enumerated constants consist of enumerated identifiers, or their integral equivalents. * Character constants are a single character surrounded by single quotes (''), or a number--the ordinal value of the corresponding character (usually its ASCII value). Within quotes, the single character may be represented by a letter or by "escape sequences", which are of the form \NNN', where NNN is the octal representation of the character's ordinal value; or of the form \X', where X' is a predefined special character--for example, \n' for newline. * String constants are a sequence of character constants surrounded by double quotes ("'). Any valid character constant (as described above) may appear. Double quotes within the string must be preceded by a backslash, so for instance "a\"b'c"' is a string of five characters. * Pointer constants are an integral value. You can also write pointers to constants using the C operator &'. * Array constants are comma-separated lists surrounded by braces {' and }'; for example, {1,2,3}' is a three-element array of integers, {{1,2}, {3,4}, {5,6}}' is a three-by-two array, and {&"hi", &"there", &"fred"}' is a three-element array of pointers. File: gdb.info, Node: C Plus Plus Expressions, Next: C Defaults, Prev: C Constants, Up: C 15.4.1.3 C++ Expressions ........................ GDB expression handling can interpret most C++ expressions. _Warning:_ GDB can only debug C++ code if you use the proper compiler and the proper debug format. Currently, GDB works best when debugging C++ code that is compiled with GCC 2.95.3 or with GCC 3.1 or newer, using the options -gdwarf-2' or -gstabs+'. DWARF 2 is preferred over stabs+. Most configurations of GCC emit either DWARF 2 or stabs+ as their default debug format, so you usually don't need to specify a debug format explicitly. Other compilers and/or debug formats are likely to work badly or not at all when using GDB to debug C++ code. 1. Member function calls are allowed; you can use expressions like count = aml->GetOriginal(x, y) 2. While a member function is active (in the selected stack frame), your expressions have the same namespace available as the member function; that is, GDB allows implicit references to the class instance pointer this' following the same rules as C++. 3. You can call overloaded functions; GDB resolves the function call to the right definition, with some restrictions. GDB does not perform overload resolution involving user-defined type conversions, calls to constructors, or instantiations of templates that do not exist in the program. It also cannot handle ellipsis argument lists or default arguments. It does perform integral conversions and promotions, floating-point promotions, arithmetic conversions, pointer conversions, conversions of class objects to base classes, and standard conversions such as those of functions or arrays to pointers; it requires an exact match on the number of function arguments. Overload resolution is always performed, unless you have specified set overload-resolution off'. *Note GDB Features for C++: Debugging C Plus Plus. You must specify set overload-resolution off' in order to use an explicit function signature to call an overloaded function, as in p 'foo(char,int)'('x', 13) The GDB command-completion facility can simplify this; see *note Command Completion: Completion. 4. GDB understands variables declared as C++ references; you can use them in expressions just as you do in C++ source--they are automatically dereferenced. In the parameter list shown when GDB displays a frame, the values of reference variables are not displayed (unlike other variables); this avoids clutter, since references are often used for large structures. The _address_ of a reference variable is always shown, unless you have specified set print address off'. 5. GDB supports the C++ name resolution operator ::'--your expressions can use it just as expressions in your program do. Since one scope may be defined in another, you can use ::' repeatedly if necessary, for example in an expression like SCOPE1::SCOPE2::NAME'. GDB also allows resolving name scope by reference to source files, in both C and C++ debugging (*note Program Variables: Variables.). In addition, when used with HP's C++ compiler, GDB supports calling virtual functions correctly, printing out virtual bases of objects, calling functions in a base subobject, casting objects, and invoking user-defined operators. File: gdb.info, Node: C Defaults, Next: C Checks, Prev: C Plus Plus Expressions, Up: C 15.4.1.4 C and C++ Defaults ........................... If you allow GDB to set type and range checking automatically, they both default to off' whenever the working language changes to C or C++. This happens regardless of whether you or GDB selects the working language. If you allow GDB to set the language automatically, it recognizes source files whose names end with .c', .C', or .cc', etc, and when GDB enters code compiled from one of these files, it sets the working language to C or C++. *Note Having GDB Infer the Source Language: Automatically, for further details. File: gdb.info, Node: C Checks, Next: Debugging C, Prev: C Defaults, Up: C 15.4.1.5 C and C++ Type and Range Checks ........................................ By default, when GDB parses C or C++ expressions, type checking is not used. However, if you turn type checking on, GDB considers two variables type equivalent if: * The two variables are structured and have the same structure, union, or enumerated tag. * The two variables have the same type name, or types that have been declared equivalent through typedef'. Range checking, if turned on, is done on mathematical operations. Array indices are not checked, since they are often used to index a pointer that is not itself an array. File: gdb.info, Node: Debugging C, Next: Debugging C Plus Plus, Prev: C Checks, Up: C 15.4.1.6 GDB and C .................. The set print union' and show print union' commands apply to the union' type. When set to on', any union' that is inside a struct' or class' is also printed. Otherwise, it appears as {...}'. The @' operator aids in the debugging of dynamic arrays, formed with pointers and a memory allocation function. *Note Expressions: Expressions. File: gdb.info, Node: Debugging C Plus Plus, Next: Decimal Floating Point, Prev: Debugging C, Up: C 15.4.1.7 GDB Features for C++ ............................. Some GDB commands are particularly useful with C++, and some are designed specifically for use with C++. Here is a summary: breakpoint menus' When you want a breakpoint in a function whose name is overloaded, GDB has the capability to display a menu of possible breakpoint locations to help you specify which function definition you want. *Note Ambiguous Expressions: Ambiguous Expressions. rbreak REGEX' Setting breakpoints using regular expressions is helpful for setting breakpoints on overloaded functions that are not members of any special classes. *Note Setting Breakpoints: Set Breaks. catch throw' catch catch' Debug C++ exception handling using these commands. *Note Setting Catchpoints: Set Catchpoints. ptype TYPENAME' Print inheritance relationships as well as other information for type TYPENAME. *Note Examining the Symbol Table: Symbols. set print demangle' show print demangle' set print asm-demangle' show print asm-demangle' Control whether C++ symbols display in their source form, both when displaying code as C++ source and when displaying disassemblies. *Note Print Settings: Print Settings. set print object' show print object' Choose whether to print derived (actual) or declared types of objects. *Note Print Settings: Print Settings. set print vtbl' show print vtbl' Control the format for printing virtual function tables. *Note Print Settings: Print Settings. (The vtbl' commands do not work on programs compiled with the HP ANSI C++ compiler (aCC').) set overload-resolution on' Enable overload resolution for C++ expression evaluation. The default is on. For overloaded functions, GDB evaluates the arguments and searches for a function whose signature matches the argument types, using the standard C++ conversion rules (see *note C++ Expressions: C Plus Plus Expressions, for details). If it cannot find a match, it emits a message. set overload-resolution off' Disable overload resolution for C++ expression evaluation. For overloaded functions that are not class member functions, GDB chooses the first function of the specified name that it finds in the symbol table, whether or not its arguments are of the correct type. For overloaded functions that are class member functions, GDB searches for a function whose signature _exactly_ matches the argument types. show overload-resolution' Show the current setting of overload resolution. Overloaded symbol names' You can specify a particular definition of an overloaded symbol, using the same notation that is used to declare such symbols in C++: type SYMBOL(TYPES)' rather than just SYMBOL. You can also use the GDB command-line word completion facilities to list the available choices, or to finish the type list for you. *Note Command Completion: Completion, for details on how to do this. File: gdb.info, Node: Decimal Floating Point, Prev: Debugging C Plus Plus, Up: C 15.4.1.8 Decimal Floating Point format ...................................... GDB can examine, set and perform computations with numbers in decimal floating point format, which in the C language correspond to the _Decimal32', _Decimal64' and _Decimal128' types as specified by the extension to support decimal floating-point arithmetic. There are two encodings in use, depending on the architecture: BID (Binary Integer Decimal) for x86 and x86-64, and DPD (Densely Packed Decimal) for PowerPC. GDB will use the appropriate encoding for the configured target. Because of a limitation in libdecnumber', the library used by GDB to manipulate decimal floating point numbers, it is not possible to convert (using a cast, for example) integers wider than 32-bit to decimal float. In addition, in order to imitate GDB's behaviour with binary floating point computations, error checking in decimal float operations ignores underflow, overflow and divide by zero exceptions. In the PowerPC architecture, GDB provides a set of pseudo-registers to inspect _Decimal128' values stored in floating point registers. See *note PowerPC: PowerPC. for more details. File: gdb.info, Node: D, Next: Objective-C, Prev: C, Up: Supported Languages 15.4.2 D -------- GDB can be used to debug programs written in D and compiled with GDC, LDC or DMD compilers. Currently GDB supports only one D specific feature -- dynamic arrays. File: gdb.info, Node: Objective-C, Next: Fortran, Prev: D, Up: Supported Languages 15.4.3 Objective-C ------------------ This section provides information about some commands and command options that are useful for debugging Objective-C code. See also *note info classes: Symbols, and *note info selectors: Symbols, for a few more commands specific to Objective-C support. * Menu: * Method Names in Commands:: * The Print Command with Objective-C:: File: gdb.info, Node: Method Names in Commands, Next: The Print Command with Objective-C, Up: Objective-C 15.4.3.1 Method Names in Commands ................................. The following commands have been extended to accept Objective-C method names as line specifications: * clear' * break' * info line' * jump' * list' A fully qualified Objective-C method name is specified as -[CLASS METHODNAME] where the minus sign is used to indicate an instance method and a plus sign (not shown) is used to indicate a class method. The class name CLASS and method name METHODNAME are enclosed in brackets, similar to the way messages are specified in Objective-C source code. For example, to set a breakpoint at the create' instance method of class Fruit' in the program currently being debugged, enter: break -[Fruit create] To list ten program lines around the initialize' class method, enter: list +[NSText initialize] In the current version of GDB, the plus or minus sign is required. In future versions of GDB, the plus or minus sign will be optional, but you can use it to narrow the search. It is also possible to specify just a method name: break create You must specify the complete method name, including any colons. If your program's source files contain more than one create' method, you'll be presented with a numbered list of classes that implement that method. Indicate your choice by number, or type 0' to exit if none apply. As another example, to clear a breakpoint established at the makeKeyAndOrderFront:' method of the NSWindow' class, enter: clear -[NSWindow makeKeyAndOrderFront:] File: gdb.info, Node: The Print Command with Objective-C, Prev: Method Names in Commands, Up: Objective-C 15.4.3.2 The Print Command With Objective-C ........................................... The print command has also been extended to accept methods. For example: print -[OBJECT hash] will tell GDB to send the hash' message to OBJECT and print the result. Also, an additional command has been added, print-object' or po' for short, which is meant to print the description of an object. However, this command may only work with certain Objective-C libraries that have a particular hook function, _NSPrintForDebugger', defined. File: gdb.info, Node: Fortran, Next: Pascal, Prev: Objective-C, Up: Supported Languages 15.4.4 Fortran -------------- GDB can be used to debug programs written in Fortran, but it currently supports only the features of Fortran 77 language. Some Fortran compilers (GNU Fortran 77 and Fortran 95 compilers among them) append an underscore to the names of variables and functions. When you debug programs compiled by those compilers, you will need to refer to variables and functions with a trailing underscore. * Menu: * Fortran Operators:: Fortran operators and expressions * Fortran Defaults:: Default settings for Fortran * Special Fortran Commands:: Special GDB commands for Fortran File: gdb.info, Node: Fortran Operators, Next: Fortran Defaults, Up: Fortran 15.4.4.1 Fortran Operators and Expressions .......................................... Operators must be defined on values of specific types. For instance, +' is defined on numbers, but not on characters or other non- arithmetic types. Operators are often defined on groups of types. **' The exponentiation operator. It raises the first operand to the power of the second one. :' The range operator. Normally used in the form of array(low:high) to represent a section of array. %' The access component operator. Normally used to access elements in derived types. Also suitable for unions. As unions aren't part of regular Fortran, this can only happen when accessing a register that uses a gdbarch-defined union type. File: gdb.info, Node: Fortran Defaults, Next: Special Fortran Commands, Prev: Fortran Operators, Up: Fortran 15.4.4.2 Fortran Defaults ......................... Fortran symbols are usually case-insensitive, so GDB by default uses case-insensitive matches for Fortran symbols. You can change that with the set case-insensitive' command, see *note Symbols::, for the details. File: gdb.info, Node: Special Fortran Commands, Prev: Fortran Defaults, Up: Fortran 15.4.4.3 Special Fortran Commands ................................. GDB has some commands to support Fortran-specific features, such as displaying common blocks. info common [COMMON-NAME]' This command prints the values contained in the Fortran COMMON' block whose name is COMMON-NAME. With no argument, the names of all COMMON' blocks visible at the current program location are printed. File: gdb.info, Node: Pascal, Next: Modula-2, Prev: Fortran, Up: Supported Languages 15.4.5 Pascal ------------- Debugging Pascal programs which use sets, subranges, file variables, or nested functions does not currently work. GDB does not support entering expressions, printing values, or similar features using Pascal syntax. The Pascal-specific command set print pascal_static-members' controls whether static members of Pascal objects are displayed. *Note pascal_static-members: Print Settings. File: gdb.info, Node: Modula-2, Next: Ada, Prev: Pascal, Up: Supported Languages 15.4.6 Modula-2 --------------- The extensions made to GDB to support Modula-2 only support output from the GNU Modula-2 compiler (which is currently being developed). Other Modula-2 compilers are not currently supported, and attempting to debug executables produced by them is most likely to give an error as GDB reads in the executable's symbol table. * Menu: * M2 Operators:: Built-in operators * Built-In Func/Proc:: Built-in functions and procedures * M2 Constants:: Modula-2 constants * M2 Types:: Modula-2 types * M2 Defaults:: Default settings for Modula-2 * Deviations:: Deviations from standard Modula-2 * M2 Checks:: Modula-2 type and range checks * M2 Scope:: The scope operators ::' and .' * GDB/M2:: GDB and Modula-2 File: gdb.info, Node: M2 Operators, Next: Built-In Func/Proc, Up: Modula-2 15.4.6.1 Operators .................. Operators must be defined on values of specific types. For instance, +' is defined on numbers, but not on structures. Operators are often defined on groups of types. For the purposes of Modula-2, the following definitions hold: * _Integral types_ consist of INTEGER', CARDINAL', and their subranges. * _Character types_ consist of CHAR' and its subranges. * _Floating-point types_ consist of REAL'. * _Pointer types_ consist of anything declared as POINTER TO TYPE'. * _Scalar types_ consist of all of the above. * _Set types_ consist of SET' and BITSET' types. * _Boolean types_ consist of BOOLEAN'. The following operators are supported, and appear in order of increasing precedence: ,' Function argument or array index separator. :=' Assignment. The value of VAR :=' VALUE is VALUE. <, >' Less than, greater than on integral, floating-point, or enumerated types. <=, >=' Less than or equal to, greater than or equal to on integral, floating-point and enumerated types, or set inclusion on set types. Same precedence as <'. =, <>, #' Equality and two ways of expressing inequality, valid on scalar types. Same precedence as <'. In GDB scripts, only <>' is available for inequality, since #' conflicts with the script comment character. IN' Set membership. Defined on set types and the types of their members. Same precedence as <'. OR' Boolean disjunction. Defined on boolean types. AND, &' Boolean conjunction. Defined on boolean types. @' The GDB "artificial array" operator (*note Expressions: Expressions.). +, -' Addition and subtraction on integral and floating-point types, or union and difference on set types. *' Multiplication on integral and floating-point types, or set intersection on set types. /' Division on floating-point types, or symmetric set difference on set types. Same precedence as *'. DIV, MOD' Integer division and remainder. Defined on integral types. Same precedence as *'. -' Negative. Defined on INTEGER' and REAL' data. ^' Pointer dereferencing. Defined on pointer types. NOT' Boolean negation. Defined on boolean types. Same precedence as ^'. .' RECORD' field selector. Defined on RECORD' data. Same precedence as ^'. []' Array indexing. Defined on ARRAY' data. Same precedence as ^'. ()' Procedure argument list. Defined on PROCEDURE' objects. Same precedence as ^'. ::, .' GDB and Modula-2 scope operators. _Warning:_ Set expressions and their operations are not yet supported, so GDB treats the use of the operator IN', or the use of operators +', -', *', /', =', , <>', #', <=', and >=' on sets as an error. File: gdb.info, Node: Built-In Func/Proc, Next: M2 Constants, Prev: M2 Operators, Up: Modula-2 15.4.6.2 Built-in Functions and Procedures .......................................... Modula-2 also makes available several built-in procedures and functions. In describing these, the following metavariables are used: A represents an ARRAY' variable. C represents a CHAR' constant or variable. I represents a variable or constant of integral type. M represents an identifier that belongs to a set. Generally used in the same function with the metavariable S. The type of S should be SET OF MTYPE' (where MTYPE is the type of M). N represents a variable or constant of integral or floating-point type. R represents a variable or constant of floating-point type. T represents a type. V represents a variable. X represents a variable or constant of one of many types. See the explanation of the function for details. All Modula-2 built-in procedures also return a result, described below. ABS(N)' Returns the absolute value of N. CAP(C)' If C is a lower case letter, it returns its upper case equivalent, otherwise it returns its argument. CHR(I)' Returns the character whose ordinal value is I. DEC(V)' Decrements the value in the variable V by one. Returns the new value. DEC(V,I)' Decrements the value in the variable V by I. Returns the new value. EXCL(M,S)' Removes the element M from the set S. Returns the new set. FLOAT(I)' Returns the floating point equivalent of the integer I. HIGH(A)' Returns the index of the last member of A. INC(V)' Increments the value in the variable V by one. Returns the new value. INC(V,I)' Increments the value in the variable V by I. Returns the new value. INCL(M,S)' Adds the element M to the set S if it is not already there. Returns the new set. MAX(T)' Returns the maximum value of the type T. MIN(T)' Returns the minimum value of the type T. ODD(I)' Returns boolean TRUE if I is an odd number. ORD(X)' Returns the ordinal value of its argument. For example, the ordinal value of a character is its ASCII value (on machines supporting the ASCII character set). X must be of an ordered type, which include integral, character and enumerated types. SIZE(X)' Returns the size of its argument. X can be a variable or a type. TRUNC(R)' Returns the integral part of R. TSIZE(X)' Returns the size of its argument. X can be a variable or a type. VAL(T,I)' Returns the member of the type T whose ordinal value is I. _Warning:_ Sets and their operations are not yet supported, so GDB treats the use of procedures INCL' and EXCL' as an error. File: gdb.info, Node: M2 Constants, Next: M2 Types, Prev: Built-In Func/Proc, Up: Modula-2 15.4.6.3 Constants .................. GDB allows you to express the constants of Modula-2 in the following ways: * Integer constants are simply a sequence of digits. When used in an expression, a constant is interpreted to be type-compatible with the rest of the expression. Hexadecimal integers are specified by a trailing H', and octal integers by a trailing B'. * Floating point constants appear as a sequence of digits, followed by a decimal point and another sequence of digits. An optional exponent can then be specified, in the form E[+|-]NNN', where [+|-]NNN' is the desired exponent. All of the digits of the floating point constant must be valid decimal (base 10) digits. * Character constants consist of a single character enclosed by a pair of like quotes, either single ('') or double ("'). They may also be expressed by their ordinal value (their ASCII value, usually) followed by a C'. * String constants consist of a sequence of characters enclosed by a pair of like quotes, either single ('') or double ("'). Escape sequences in the style of C are also allowed. *Note C and C++ Constants: C Constants, for a brief explanation of escape sequences. * Enumerated constants consist of an enumerated identifier. * Boolean constants consist of the identifiers TRUE' and FALSE'. * Pointer constants consist of integral values only. * Set constants are not yet supported. File: gdb.info, Node: M2 Types, Next: M2 Defaults, Prev: M2 Constants, Up: Modula-2 15.4.6.4 Modula-2 Types ....................... Currently GDB can print the following data types in Modula-2 syntax: array types, record types, set types, pointer types, procedure types, enumerated types, subrange types and base types. You can also print the contents of variables declared using these type. This section gives a number of simple source code examples together with sample GDB sessions. The first example contains the following section of code: VAR s: SET OF CHAR ; r: [20..40] ; and you can request GDB to interrogate the type and value of r' and s'. (gdb) print s {'A'..'C', 'Z'} (gdb) ptype s SET OF CHAR (gdb) print r 21 (gdb) ptype r [20..40] Likewise if your source code declares s' as: VAR s: SET ['A'..'Z'] ; then you may query the type of s' by: (gdb) ptype s type = SET ['A'..'Z'] Note that at present you cannot interactively manipulate set expressions using the debugger. The following example shows how you might declare an array in Modula-2 and how you can interact with GDB to print its type and contents: VAR s: ARRAY [-10..10] OF CHAR ; (gdb) ptype s ARRAY [-10..10] OF CHAR Note that the array handling is not yet complete and although the type is printed correctly, expression handling still assumes that all arrays have a lower bound of zero and not -10' as in the example above. Here are some more type related Modula-2 examples: TYPE colour = (blue, red, yellow, green) ; t = [blue..yellow] ; VAR s: t ; BEGIN s := blue ; The GDB interaction shows how you can query the data type and value of a variable. (gdb) print s$1 = blue
(gdb) ptype t
type = [blue..yellow]

In this example a Modula-2 array is declared and its contents
displayed.  Observe that the contents are written in the same way as
their C' counterparts.

VAR
s: ARRAY [1..5] OF CARDINAL ;
BEGIN
s[1] := 1 ;

(gdb) print s
$1 = {1, 0, 0, 0, 0} (gdb) ptype s type = ARRAY [1..5] OF CARDINAL The Modula-2 language interface to GDB also understands pointer types as shown in this example: VAR s: POINTER TO ARRAY [1..5] OF CARDINAL ; BEGIN NEW(s) ; s^[1] := 1 ; and you can request that GDB describes the type of s'. (gdb) ptype s type = POINTER TO ARRAY [1..5] OF CARDINAL GDB handles compound types as we can see in this example. Here we combine array types, record types, pointer types and subrange types: TYPE foo = RECORD f1: CARDINAL ; f2: CHAR ; f3: myarray ; END ; myarray = ARRAY myrange OF CARDINAL ; myrange = [-2..2] ; VAR s: POINTER TO ARRAY myrange OF foo ; and you can ask GDB to describe the type of s' as shown below. (gdb) ptype s type = POINTER TO ARRAY [-2..2] OF foo = RECORD f1 : CARDINAL; f2 : CHAR; f3 : ARRAY [-2..2] OF CARDINAL; END File: gdb.info, Node: M2 Defaults, Next: Deviations, Prev: M2 Types, Up: Modula-2 15.4.6.5 Modula-2 Defaults .......................... If type and range checking are set automatically by GDB, they both default to on' whenever the working language changes to Modula-2. This happens regardless of whether you or GDB selected the working language. If you allow GDB to set the language automatically, then entering code compiled from a file whose name ends with .mod' sets the working language to Modula-2. *Note Having GDB Infer the Source Language: Automatically, for further details. File: gdb.info, Node: Deviations, Next: M2 Checks, Prev: M2 Defaults, Up: Modula-2 15.4.6.6 Deviations from Standard Modula-2 .......................................... A few changes have been made to make Modula-2 programs easier to debug. This is done primarily via loosening its type strictness: * Unlike in standard Modula-2, pointer constants can be formed by integers. This allows you to modify pointer variables during debugging. (In standard Modula-2, the actual address contained in a pointer variable is hidden from you; it can only be modified through direct assignment to another pointer variable or expression that returned a pointer.) * C escape sequences can be used in strings and characters to represent non-printable characters. GDB prints out strings with these escape sequences embedded. Single non-printable characters are printed using the CHR(NNN)' format. * The assignment operator (:=') returns the value of its right-hand argument. * All built-in procedures both modify _and_ return their argument. File: gdb.info, Node: M2 Checks, Next: M2 Scope, Prev: Deviations, Up: Modula-2 15.4.6.7 Modula-2 Type and Range Checks ....................................... _Warning:_ in this release, GDB does not yet perform type or range checking. GDB considers two Modula-2 variables type equivalent if: * They are of types that have been declared equivalent via a TYPE T1 = T2' statement * They have been declared on the same line. (Note: This is true of the GNU Modula-2 compiler, but it may not be true of other compilers.) As long as type checking is enabled, any attempt to combine variables whose types are not equivalent is an error. Range checking is done on all mathematical operations, assignment, array index bounds, and all built-in functions and procedures. File: gdb.info, Node: M2 Scope, Next: GDB/M2, Prev: M2 Checks, Up: Modula-2 15.4.6.8 The Scope Operators ::' and .' ......................................... There are a few subtle differences between the Modula-2 scope operator (.') and the GDB scope operator (::'). The two have similar syntax: MODULE . ID SCOPE :: ID where SCOPE is the name of a module or a procedure, MODULE the name of a module, and ID is any declared identifier within your program, except another module. Using the ::' operator makes GDB search the scope specified by SCOPE for the identifier ID. If it is not found in the specified scope, then GDB searches all scopes enclosing the one specified by SCOPE. Using the .' operator makes GDB search the current scope for the identifier specified by ID that was imported from the definition module specified by MODULE. With this operator, it is an error if the identifier ID was not imported from definition module MODULE, or if ID is not an identifier in MODULE. File: gdb.info, Node: GDB/M2, Prev: M2 Scope, Up: Modula-2 15.4.6.9 GDB and Modula-2 ......................... Some GDB commands have little use when debugging Modula-2 programs. Five subcommands of set print' and show print' apply specifically to C and C++: vtbl', demangle', asm-demangle', object', and union'. The first four apply to C++, and the last to the C union' type, which has no direct analogue in Modula-2. The @' operator (*note Expressions: Expressions.), while available with any language, is not useful with Modula-2. Its intent is to aid the debugging of "dynamic arrays", which cannot be created in Modula-2 as they can in C or C++. However, because an address can be specified by an integral constant, the construct {TYPE}ADREXP' is still useful. In GDB scripts, the Modula-2 inequality operator #' is interpreted as the beginning of a comment. Use <>' instead. File: gdb.info, Node: Ada, Prev: Modula-2, Up: Supported Languages 15.4.7 Ada ---------- The extensions made to GDB for Ada only support output from the GNU Ada (GNAT) compiler. Other Ada compilers are not currently supported, and attempting to debug executables produced by them is most likely to be difficult. * Menu: * Ada Mode Intro:: General remarks on the Ada syntax and semantics supported by Ada mode in GDB. * Omissions from Ada:: Restrictions on the Ada expression syntax. * Additions to Ada:: Extensions of the Ada expression syntax. * Stopping Before Main Program:: Debugging the program during elaboration. * Ada Tasks:: Listing and setting breakpoints in tasks. * Ada Tasks and Core Files:: Tasking Support when Debugging Core Files * Ada Glitches:: Known peculiarities of Ada mode. File: gdb.info, Node: Ada Mode Intro, Next: Omissions from Ada, Up: Ada 15.4.7.1 Introduction ..................... The Ada mode of GDB supports a fairly large subset of Ada expression syntax, with some extensions. The philosophy behind the design of this subset is * That GDB should provide basic literals and access to operations for arithmetic, dereferencing, field selection, indexing, and subprogram calls, leaving more sophisticated computations to subprograms written into the program (which therefore may be called from GDB). * That type safety and strict adherence to Ada language restrictions are not particularly important to the GDB user. * That brevity is important to the GDB user. Thus, for brevity, the debugger acts as if all names declared in user-written packages are directly visible, even if they are not visible according to Ada rules, thus making it unnecessary to fully qualify most names with their packages, regardless of context. Where this causes ambiguity, GDB asks the user's intent. The debugger will start in Ada mode if it detects an Ada main program. As for other languages, it will enter Ada mode when stopped in a program that was translated from an Ada source file. While in Ada mode, you may use -' for comments. This is useful mostly for documenting command files. The standard GDB comment (#') still works at the beginning of a line in Ada mode, but not in the middle (to allow based literals). The debugger supports limited overloading. Given a subprogram call in which the function symbol has multiple definitions, it will use the number of actual parameters and some information about their types to attempt to narrow the set of definitions. It also makes very limited use of context, preferring procedures to functions in the context of the call' command, and functions to procedures elsewhere. File: gdb.info, Node: Omissions from Ada, Next: Additions to Ada, Prev: Ada Mode Intro, Up: Ada 15.4.7.2 Omissions from Ada ........................... Here are the notable omissions from the subset: * Only a subset of the attributes are supported: - 'First, 'Last, and 'Length on array objects (not on types and subtypes). - 'Min and 'Max. - 'Pos and 'Val. - 'Tag. - 'Range on array objects (not subtypes), but only as the right operand of the membership (in') operator. - 'Access, 'Unchecked_Access, and 'Unrestricted_Access (a GNAT extension). - 'Address. * The names in Characters.Latin_1' are not available and concatenation is not implemented. Thus, escape characters in strings are not currently available. * Equality tests (=' and /=') on arrays test for bitwise equality of representations. They will generally work correctly for strings and arrays whose elements have integer or enumeration types. They may not work correctly for arrays whose element types have user-defined equality, for arrays of real values (in particular, IEEE-conformant floating point, because of negative zeroes and NaNs), and for arrays whose elements contain unused bits with indeterminate values. * The other component-by-component array operations (and', or', xor', not', and relational tests other than equality) are not implemented. * There is limited support for array and record aggregates. They are permitted only on the right sides of assignments, as in these examples: (gdb) set An_Array := (1, 2, 3, 4, 5, 6) (gdb) set An_Array := (1, others => 0) (gdb) set An_Array := (0|4 => 1, 1..3 => 2, 5 => 6) (gdb) set A_2D_Array := ((1, 2, 3), (4, 5, 6), (7, 8, 9)) (gdb) set A_Record := (1, "Peter", True); (gdb) set A_Record := (Name => "Peter", Id => 1, Alive => True) Changing a discriminant's value by assigning an aggregate has an undefined effect if that discriminant is used within the record. However, you can first modify discriminants by directly assigning to them (which normally would not be allowed in Ada), and then performing an aggregate assignment. For example, given a variable A_Rec' declared to have a type such as: type Rec (Len : Small_Integer := 0) is record Id : Integer; Vals : IntArray (1 .. Len); end record; you can assign a value with a different size of Vals' with two assignments: (gdb) set A_Rec.Len := 4 (gdb) set A_Rec := (Id => 42, Vals => (1, 2, 3, 4)) As this example also illustrates, GDB is very loose about the usual rules concerning aggregates. You may leave out some of the components of an array or record aggregate (such as the Len' component in the assignment to A_Rec' above); they will retain their original values upon assignment. You may freely use dynamic values as indices in component associations. You may even use overlapping or redundant component associations, although which component values are assigned in such cases is not defined. * Calls to dispatching subprograms are not implemented. * The overloading algorithm is much more limited (i.e., less selective) than that of real Ada. It makes only limited use of the context in which a subexpression appears to resolve its meaning, and it is much looser in its rules for allowing type matches. As a result, some function calls will be ambiguous, and the user will be asked to choose the proper resolution. * The new' operator is not implemented. * Entry calls are not implemented. * Aside from printing, arithmetic operations on the native VAX floating-point formats are not supported. * It is not possible to slice a packed array. * The names True' and False', when not part of a qualified name, are interpreted as if implicitly prefixed by Standard', regardless of context. Should your program redefine these names in a package or procedure (at best a dubious practice), you will have to use fully qualified names to access their new definitions. File: gdb.info, Node: Additions to Ada, Next: Stopping Before Main Program, Prev: Omissions from Ada, Up: Ada 15.4.7.3 Additions to Ada ......................... As it does for other languages, GDB makes certain generic extensions to Ada (*note Expressions::): * If the expression E is a variable residing in memory (typically a local variable or array element) and N is a positive integer, then E@N' displays the values of E and the N-1 adjacent variables following it in memory as an array. In Ada, this operator is generally not necessary, since its prime use is in displaying parts of an array, and slicing will usually do this in Ada. However, there are occasional uses when debugging programs in which certain debugging information has been optimized away. * B::VAR' means "the variable named VAR that appears in function or file B." When B is a file name, you must typically surround it in single quotes. * The expression {TYPE} ADDR' means "the variable of type TYPE that appears at address ADDR." * A name starting with $' is a convenience variable (*note
Convenience Vars::) or a machine register (*note Registers::).

In addition, GDB provides a few other shortcuts and outright

* The assignment statement is allowed as an expression, returning
its right-hand operand as its value.  Thus, you may enter

(gdb) set x := y + 3
(gdb) print A(tmp := y + 1)

* The semicolon is allowed as an "operator,"  returning as its value
the value of its right-hand operand.  This allows, for example,
complex conditional breaks:

(gdb) break f
(gdb) condition 1 (report(i); k += 1; A(k) > 100)

* Rather than use catenation and symbolic character names to
introduce special characters into strings, one may instead use a
special bracket notation, which is also used to print strings.  A
sequence of characters of the form ["XX"]' within a string or
character literal denotes the (single) character whose numeric
encoding is XX in hexadecimal.  The sequence of characters ["""]'
also denotes a single quotation mark in strings.   For example,
"One line.["0a"]Next line.["0a"]"
contains an ASCII newline character (Ada.Characters.Latin_1.LF')
after each period.

* The subtype used as a prefix for the attributes 'Pos, 'Min, and
'Max is optional (and is ignored in any case).  For example, it is
valid to write

(gdb) print 'max(x, y)

* When printing arrays, GDB uses positional notation when the array
has a lower bound of 1, and uses a modified named notation
otherwise.  For example, a one-dimensional array of three integers
with a lower bound of 3 might print as

(3 => 10, 17, 1)

That is, in contrast to valid Ada, only the first component has a
=>' clause.

* You may abbreviate attributes in expressions with any unique,
multi-character subsequence of their names (an exact match gets
preference).  For example, you may use a'len, a'gth, or a'lh in
place of  a'length.

* Since Ada is case-insensitive, the debugger normally maps
identifiers you type to lower case.  The GNAT compiler uses
upper-case characters for some of its internal identifiers, which
are normally of no interest to users.  For the rare occasions when
you actually have to look at them, enclose them in angle brackets
to avoid the lower-case mapping.  For example,
(gdb) print <JMPBUF_SAVE>[0]

* Printing an object of class-wide type or dereferencing an
access-to-class-wide value will display all the components of the
object's specific type (as indicated by its run-time tag).
Likewise, component selection on such a value will operate on the
specific type of the object.

15.4.7.4 Stopping at the Very Beginning
.......................................

It is sometimes necessary to debug the program during elaboration, and
before reaching the main procedure.  As defined in the Ada Reference
Manual, the elaboration code is invoked from a procedure called
adainit'.  To run your program up to the beginning of elaboration,
simply use the following two commands: tbreak adainit' and run'.

File: gdb.info,  Node: Ada Tasks,  Next: Ada Tasks and Core Files,  Prev: Stopping Before Main Program,  Up: Ada

.................................

Support for Ada tasks is analogous to that for threads (*note
Threads::).  GDB provides the following task-related commands:

info tasks'
This command shows a list of current Ada tasks, as in the
following example:

ID       TID P-ID Pri State                 Name
1   8088000   0   15 Child Activation Wait main_task
2   80a4000   1   15 Accept Statement      b
3   809a800   1   15 Child Activation Wait a
*  4   80ae800   3   15 Runnable              c

In this listing, the asterisk before the last task indicates it to
be the task currently being inspected.

ID
Represents GDB's internal task number.

TID

P-ID
The parent's task ID (GDB's internal task number).

Pri
The base priority of the task.

State
Current state of the task.

Unactivated'
The task has been created but has not been activated.
It cannot be executing.

Runnable'
The task is not blocked for any reason known to Ada.
(It may be waiting for a mutex, though.) It is
conceptually "executing" in normal mode.

Terminated'
The task is terminated, in the sense of ARM 9.3 (5).
Any dependents that were waiting on terminate
alternatives have been awakened and have terminated
themselves.

Child Activation Wait'
The task is waiting for created tasks to complete
activation.

Accept Statement'
The task is waiting on an accept or selective wait
statement.

Waiting on entry call'
The task is waiting on an entry call.

Async Select Wait'
The task is waiting to start the abortable part of an
asynchronous select statement.

Delay Sleep'
The task is waiting on a select statement with only a
delay alternative open.

Child Termination Wait'
The task is sleeping having completed a master within
itself, and is waiting for the tasks dependent on that
master to become terminated or waiting on a terminate
Phase.

Wait Child in Term Alt'
The task is sleeping waiting for tasks on terminate
alternatives to finish terminating.

Accepting RV with TASKNO'
The task is accepting a rendez-vous with the task TASKNO.

Name
Name of the task in the program.

info task TASKNO'
This command shows detailled informations on the specified task,
as in the following example:
ID       TID P-ID Pri State                  Name
1   8077880    0  15 Child Activation Wait  main_task
*  2   807c468    1  15 Runnable               task_1
(gdb) info task 2
Base Priority: 15
State: Runnable

This command prints the ID of the current task.

ID       TID P-ID Pri State                  Name
1   8077870    0  15 Child Activation Wait  main_task
*  2   807c458    1  15 Runnable               t
[Current task is 2]

task TASKNO'
This command is like the thread THREADNO' command (*note
Threads::).  It switches the context of debugging from the current

ID       TID P-ID Pri State                  Name
1   8077870    0  15 Child Activation Wait  main_task
*  2   807c458    1  15 Runnable               t
[Switching to task 1]
#0  0x8067726 in pthread_cond_wait ()
(gdb) bt
#0  0x8067726 in pthread_cond_wait ()
#1  0x8056714 in system.os_interface.pthread_cond_wait ()
#2  0x805cb63 in system.task_primitives.operations.sleep ()
#4  0x804aacc in un () at un.adb:5

break LINESPEC task TASKNO'
These commands are like the break ... thread ...' command (*note
Thread Stops::).  LINESPEC specifies source lines, as described in
*note Specify Location::.

Use the qualifier task TASKNO' with a breakpoint command to
specify that you only want GDB to stop the program when a
particular Ada task reaches this breakpoint.  TASKNO is one of the
numeric task identifiers assigned by GDB, shown in the first
column of the info tasks' display.

If you do not specify task TASKNO' when you set a breakpoint, the
breakpoint applies to _all_ tasks of your program.

You can use the task' qualifier on conditional breakpoints as
well; in this case, place task TASKNO' before the breakpoint
condition (before the if').

For example,

ID       TID P-ID Pri State                 Name
1 140022020   0   15 Child Activation Wait main_task
2 140045060   1   15 Accept/Select Wait    t2
3 140044840   1   15 Runnable              t1
*  4 140056040   1   15 Runnable              t3
(gdb) b 15 task 2
Breakpoint 5 at 0x120044cb0: file test_task_debug.adb, line 15.
(gdb) cont
Continuing.
task # 1 running
task # 2 running

15               flush;
ID       TID P-ID Pri State                 Name
1 140022020   0   15 Child Activation Wait main_task
*  2 140045060   1   15 Runnable              t2
3 140044840   1   15 Runnable              t1
4 140056040   1   15 Delay Sleep           t3

15.4.7.6 Tasking Support when Debugging Core Files
..................................................

When inspecting a core file, as opposed to debugging a live program,
tasking support may be limited or even unavailable, depending on the
platform being used.  For instance, on x86-linux, the list of tasks is
available, but task switching is not supported.  On Tru64, however,
task switching will work as usual.

On certain platforms, including Tru64, the debugger needs to perform
some memory writes in order to provide Ada tasking support.  When
inspecting a core file, this means that the core file must be opened
with read-write privileges, using the command "set write on"' (*note
Patching::).  Under these circumstances, you should make a backup copy
of the core file before inspecting it with GDB.

15.4.7.7 Known Peculiarities of Ada Mode
........................................

Besides the omissions listed previously (*note Omissions from Ada::),
we know of several problems with and limitations of Ada mode in GDB,
some of which will be fixed with planned future releases of the debugger
and the GNU Ada compiler.

* Currently, the debugger has insufficient information to determine
whether certain pointers represent pointers to objects or the
objects themselves.  Thus, the user may have to tack an extra
.all' after an expression to get it printed properly.

* Static constants that the compiler chooses not to materialize as
objects in storage are invisible to the debugger.

* Named parameter associations in function argument lists are
ignored (the argument lists are treated as positional).

* Many useful library packages are currently invisible to the
debugger.

* Fixed-point arithmetic, conversions, input, and output is carried
out using floating-point arithmetic, and may give results that
only approximate those on the host machine.

* The GNAT compiler never generates the prefix Standard' for any of
the standard symbols defined by the Ada language.  GDB knows about
this: it will strip the prefix from names when you use it, and
will never look for a name you have so qualified among local
symbols, nor match against symbols in other packages or
subprograms.  If you have defined entities anywhere in your
program other than parameters and local variables whose simple
names match names in Standard', GNAT's lack of qualification here
can cause confusion.  When this happens, you can usually resolve
the confusion by qualifying the problematic names with package
Standard' explicitly.

Older versions of the compiler sometimes generate erroneous debugging
information, resulting in the debugger incorrectly printing the value
of affected entities.  In some cases, the debugger is able to work
around an issue automatically. In other cases, the debugger is able to
work around the issue, but the work-around has to be specifically
enabled.

set ada trust-PAD-over-XVS on'
Configure GDB to strictly follow the GNAT encoding when computing
the value of Ada entities, particularly when PAD' and PAD___XVS'
types are involved (see ada/exp_dbug.ads' in the GCC sources for
a complete description of the encoding used by the GNAT compiler).
This is the default.

set ada trust-PAD-over-XVS off'
This is related to the encoding using by the GNAT compiler.  If
GDB sometimes prints the wrong value for certain entities,
changing ada trust-PAD-over-XVS' to off' activates a work-around
which may fix the issue.  It is always safe to set ada
trust-PAD-over-XVS' to off', but this incurs a slight performance
penalty, so it is recommended to leave this setting to on' unless
necessary.

File: gdb.info,  Node: Unsupported Languages,  Prev: Supported Languages,  Up: Languages

15.5 Unsupported Languages
==========================

In addition to the other fully-supported programming languages, GDB
also provides a pseudo-language, called minimal'.  It does not
represent a real programming language, but provides a set of
capabilities close to what the C or assembly languages provide.  This
should allow most simple operations to be performed while debugging an
application that uses a language currently not supported by GDB.

If the language is set to auto', GDB will automatically select this
language if the current frame corresponds to an unsupported language.

File: gdb.info,  Node: Symbols,  Next: Altering,  Prev: Languages,  Up: Top

16 Examining the Symbol Table
*****************************

The commands described in this chapter allow you to inquire about the
symbols (names of variables, functions and types) defined in your
program.  This information is inherent in the text of your program and
does not change as your program executes.  GDB finds it in your
program's symbol table, in the file indicated when you started GDB
(*note Choosing Files: File Options.), or by one of the file-management
commands (*note Commands to Specify Files: Files.).

Occasionally, you may need to refer to symbols that contain unusual
characters, which GDB ordinarily treats as word delimiters.  The most
frequent case is in referring to static variables in other source files
(*note Program Variables: Variables.).  File names are recorded in
object files as debugging symbols, but GDB would ordinarily parse a
typical file name, like foo.c', as the three words foo' .' c'.  To
allow GDB to recognize foo.c' as a single symbol, enclose it in single
quotes; for example,

p 'foo.c'::x

looks up the value of x' in the scope of the file foo.c'.

set case-sensitive on'
set case-sensitive off'
set case-sensitive auto'
Normally, when GDB looks up symbols, it matches their names with
case sensitivity determined by the current source language.
Occasionally, you may wish to control that.  The command set
case-sensitive' lets you do that by specifying on' for
case-sensitive matches or off' for case-insensitive ones.  If you
specify auto', case sensitivity is reset to the default suitable
for the source language.  The default is case-sensitive matches
for all languages except for Fortran, for which the default is
case-insensitive matches.

show case-sensitive'
This command shows the current setting of case sensitivity for
symbols lookups.

Describe where the data for SYMBOL is stored.  For a register
variable, this says which register it is kept in.  For a
non-register local variable, this prints the stack-frame offset at
which the variable is always stored.

Note the contrast with print &SYMBOL', which does not work at all
for a register variable, and for a stack local variable prints the
exact address of the current instantiation of the variable.

Print the name of a symbol which is stored at the address ADDR.
If no symbol is stored exactly at ADDR, GDB prints the nearest
symbol and an offset from it:

(gdb) info symbol 0x54320
_initialize_vx + 396 in section .text

This is the opposite of the info address' command.  You can use
it to find out the name of a variable or a function given its

For dynamically linked executables, the name of executable or
shared library containing the symbol is also printed:

(gdb) info symbol 0x400225
_start + 5 in section .text of /tmp/a.out
(gdb) info symbol 0x2aaaac2811cf
__read_nocancel + 6 in section .text of /usr/lib64/libc.so.6

whatis [ARG]'
Print the data type of ARG, which can be either an expression or a
name of a data type.  With no argument, print the data type of
$', the last value in the value history. If ARG is an expression (*note Expressions: Expressions.), it is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place. If ARG is a variable or an expression, whatis' prints its literal type as it is used in the source code. If the type was defined using a typedef', whatis' will _not_ print the data type underlying the typedef'. If the type of the variable or the expression is a compound data type, such as struct' or class', whatis' never prints their fields or methods. It just prints the struct'/class' name (a.k.a. its "tag"). If you want to see the members of such a compound data type, use ptype'. If ARG is a type name that was defined using typedef', whatis' "unrolls" only one level of that typedef'. Unrolling means that whatis' will show the underlying type used in the typedef' declaration of ARG. However, if that underlying type is also a typedef', whatis' will not unroll it. For C code, the type names may also have the form class CLASS-NAME', struct STRUCT-TAG', union UNION-TAG' or enum ENUM-TAG'. ptype [ARG]' ptype' accepts the same arguments as whatis', but prints a detailed description of the type, instead of just the name of the type. *Note Expressions: Expressions. Contrary to whatis', ptype' always unrolls any typedef's in its argument declaration, whether the argument is a variable, expression, or a data type. This means that ptype' of a variable or an expression will not print literally its type as present in the source code--use whatis' for that. typedef's at the pointer or reference targets are also unrolled. Only typedef's of fields, methods and inner class typedef's of struct's, class'es and union's are not unrolled even with ptype'. For example, for this variable declaration: typedef double real_t; struct complex { real_t real; double imag; }; typedef struct complex complex_t; complex_t var; real_t *real_pointer_var; the two commands give this output: (gdb) whatis var type = complex_t (gdb) ptype var type = struct complex { real_t real; double imag; } (gdb) whatis complex_t type = struct complex (gdb) whatis struct complex type = struct complex (gdb) ptype struct complex type = struct complex { real_t real; double imag; } (gdb) whatis real_pointer_var type = real_t * (gdb) ptype real_pointer_var type = double * As with whatis', using ptype' without an argument refers to the type of $', the last value in the value history.

Sometimes, programs use opaque data types or incomplete
specifications of complex data structure.  If the debug
information included in the program does not allow GDB to display
a full declaration of the data type, it will say <incomplete
type>'.  For example, given these declarations:

struct foo;
struct foo *fooptr;

but no definition for struct foo' itself, GDB will say:

(gdb) ptype foo
$1 = <incomplete type> "Incomplete type" is C terminology for data types that are not completely specified. info types REGEXP' info types' Print a brief description of all types whose names match the regular expression REGEXP (or all types in your program, if you supply no argument). Each complete typename is matched as though it were a complete line; thus, i type value' gives information on all types in your program whose names include the string value', but i type ^value$' gives information only on types whose complete
name is value'.

This command differs from ptype' in two ways: first, like
whatis', it does not print a detailed description; second, it
lists all source files where a type is defined.

info scope LOCATION'
List all the variables local to a particular scope.  This command
accepts a LOCATION argument--a function name, a source line, or an
address preceded by a *', and prints all the variables local to
the scope defined by that location.  (*Note Specify Location::, for
details about supported forms of LOCATION.)  For example:

(gdb) info scope command_line_handler
Scope for command_line_handler:
Symbol rl is an argument at stack/frame offset 8, length 4.
Symbol linebuffer is in static storage at address 0x150a18, length 4.
Symbol linelength is in static storage at address 0x150a1c, length 4.
Symbol p is a local variable in register $esi, length 4. Symbol p1 is a local variable in register$ebx, length 4.
Symbol nline is a local variable in register $edx, length 4. Symbol repeat is a local variable at frame offset -8, length 4. This command is especially useful for determining what data to collect during a "trace experiment", see *note collect: Tracepoint Actions. info source' Show information about the current source file--that is, the source file for the function containing the current point of execution: * the name of the source file, and the directory containing it, * the directory it was compiled in, * its length, in lines, * which programming language it is written in, * whether the executable includes debugging information for that file, and if so, what format the information is in (e.g., STABS, Dwarf 2, etc.), and * whether the debugging information includes information about preprocessor macros. info sources' Print the names of all source files in your program for which there is debugging information, organized into two lists: files whose symbols have already been read, and files whose symbols will be read when needed. info functions' Print the names and data types of all defined functions. info functions REGEXP' Print the names and data types of all defined functions whose names contain a match for regular expression REGEXP. Thus, info fun step' finds all functions whose names include step'; info fun ^step' finds those whose names start with step'. If a function name contains characters that conflict with the regular expression language (e.g. operator*()'), they may be quoted with a backslash. info variables' Print the names and data types of all variables that are defined outside of functions (i.e. excluding local variables). info variables REGEXP' Print the names and data types of all variables (except for local variables) whose names contain a match for regular expression REGEXP. info classes' info classes REGEXP' Display all Objective-C classes in your program, or (with the REGEXP argument) all those matching a particular regular expression. info selectors' info selectors REGEXP' Display all Objective-C selectors in your program, or (with the REGEXP argument) all those matching a particular regular expression. Some systems allow individual object files that make up your program to be replaced without stopping and restarting your program. For example, in VxWorks you can simply recompile a defective object file and keep on running. If you are running on one of these systems, you can allow GDB to reload the symbols for automatically relinked modules: set symbol-reloading on' Replace symbol definitions for the corresponding source file when an object file with a particular name is seen again. set symbol-reloading off' Do not replace symbol definitions when encountering object files of the same name more than once. This is the default state; if you are not running on a system that permits automatic relinking of modules, you should leave symbol-reloading' off, since otherwise GDB may discard symbols when linking large programs, that may contain several modules (from different directories or libraries) with the same name. show symbol-reloading' Show the current on' or off' setting. set opaque-type-resolution on' Tell GDB to resolve opaque types. An opaque type is a type declared as a pointer to a struct', class', or union'--for example, struct MyType *'--that is used in one source file although the full declaration of struct MyType' is in another source file. The default is on. A change in the setting of this subcommand will not take effect until the next time symbols for a file are loaded. set opaque-type-resolution off' Tell GDB not to resolve opaque types. In this case, the type is printed as follows: {<no data fields>} show opaque-type-resolution' Show whether opaque types are resolved or not. maint print symbols FILENAME' maint print psymbols FILENAME' maint print msymbols FILENAME' Write a dump of debugging symbol data into the file FILENAME. These commands are used to debug the GDB symbol-reading code. Only symbols with debugging data are included. If you use maint print symbols', GDB includes all the symbols for which it has already collected full details: that is, FILENAME reflects symbols for only those files whose symbols GDB has read. You can use the command info sources' to find out which files these are. If you use maint print psymbols' instead, the dump shows information about symbols that GDB only knows partially--that is, symbols defined in files that GDB has skimmed, but not yet read completely. Finally, maint print msymbols' dumps just the minimal symbol information required for each object file from which GDB has read some symbols. *Note Commands to Specify Files: Files, for a discussion of how GDB reads symbols (in the description of symbol-file'). maint info symtabs [ REGEXP ]' maint info psymtabs [ REGEXP ]' List the struct symtab' or struct partial_symtab' structures whose names match REGEXP. If REGEXP is not given, list them all. The output includes expressions which you can copy into a GDB debugging this one to examine a particular structure in more detail. For example: (gdb) maint info psymtabs dwarf2read { objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) { psymtab /home/gnu/src/gdb/dwarf2read.c ((struct partial_symtab *) 0x8474b10) readin no fullname (null) text addresses 0x814d3c8 -- 0x8158074 globals (* (struct partial_symbol **) 0x8507a08 @ 9) statics (* (struct partial_symbol **) 0x40e95b78 @ 2882) dependencies (none) } } (gdb) maint info symtabs (gdb) We see that there is one partial symbol table whose filename contains the string dwarf2read', belonging to the gdb' executable; and we see that GDB has not read in any symtabs yet at all. If we set a breakpoint on a function, that will cause GDB to read the symtab for the compilation unit containing that function: (gdb) break dwarf2_psymtab_to_symtab Breakpoint 1 at 0x814e5da: file /home/gnu/src/gdb/dwarf2read.c, line 1574. (gdb) maint info symtabs { objfile /home/gnu/build/gdb/gdb ((struct objfile *) 0x82e69d0) { symtab /home/gnu/src/gdb/dwarf2read.c ((struct symtab *) 0x86c1f38) dirname (null) fullname (null) blockvector ((struct blockvector *) 0x86c1bd0) (primary) linetable ((struct linetable *) 0x8370fa0) debugformat DWARF 2 } } (gdb) File: gdb.info, Node: Altering, Next: GDB Files, Prev: Symbols, Up: Top 17 Altering Execution ********************* Once you think you have found an error in your program, you might want to find out for certain whether correcting the apparent error would lead to correct results in the rest of the run. You can find the answer by experiment, using the GDB features for altering execution of the program. For example, you can store new values into variables or memory locations, give your program a signal, restart it at a different address, or even return prematurely from a function. * Menu: * Assignment:: Assignment to variables * Jumping:: Continuing at a different address * Signaling:: Giving your program a signal * Returning:: Returning from a function * Calling:: Calling your program's functions * Patching:: Patching your program File: gdb.info, Node: Assignment, Next: Jumping, Up: Altering 17.1 Assignment to Variables ============================ To alter the value of a variable, evaluate an assignment expression. *Note Expressions: Expressions. For example, print x=4 stores the value 4 into the variable x', and then prints the value of the assignment expression (which is 4). *Note Using GDB with Different Languages: Languages, for more information on operators in supported languages. If you are not interested in seeing the value of the assignment, use the set' command instead of the print' command. set' is really the same as print' except that the expression's value is not printed and is not put in the value history (*note Value History: Value History.). The expression is evaluated only for its effects. If the beginning of the argument string of the set' command appears identical to a set' subcommand, use the set variable' command instead of just set'. This command is identical to set' except for its lack of subcommands. For example, if your program has a variable width', you get an error if you try to set a new value with just set width=13', because GDB has the command set width': (gdb) whatis width type = double (gdb) p width$4 = 13
(gdb) set width=47
Invalid syntax in expression.

The invalid expression, of course, is =47'.  In order to actually set
the program's variable width', use

(gdb) set var width=47

Because the set' command has many subcommands that can conflict
with the names of program variables, it is a good idea to use the set
variable' command instead of just set'.  For example, if your program
has a variable g', you run into problems if you try to set a new value
with just set g=4', because GDB has the command set gnutarget',
abbreviated set g':

(gdb) whatis g
type = double
(gdb) p g
$1 = 1 (gdb) set g=4 (gdb) p g$2 = 1
(gdb) r
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: /home/smith/cc_progs/a.out
"/home/smith/cc_progs/a.out": can't open to read symbols:
Invalid bfd target.
(gdb) show g
The current BFD target is "=4".

The program variable g' did not change, and you silently set the
gnutarget' to an invalid value.  In order to set the variable g', use

(gdb) set var g=4

GDB allows more implicit conversions in assignments than C; you can
freely store an integer value into a pointer variable or vice versa,
and you can convert any structure to any other structure that is the
same length or shorter.

To store values into arbitrary places in memory, use the {...}'
construct to generate a value of specified type at a specified address
(*note Expressions: Expressions.).  For example, {int}0x83040' refers
to memory location 0x83040' as an integer (which implies a certain size
and representation in memory), and

set {int}0x83040 = 4

stores the value 4 into that memory location.

File: gdb.info,  Node: Jumping,  Next: Signaling,  Prev: Assignment,  Up: Altering

17.2 Continuing at a Different Address
======================================

Ordinarily, when you continue your program, you do so at the place where
it stopped, with the continue' command.  You can instead continue at
an address of your own choosing, with the following commands:

jump LINESPEC'
jump LOCATION'
Resume execution at line LINESPEC or at address given by LOCATION.
Execution stops again immediately if there is a breakpoint there.
*Note Specify Location::, for a description of the different forms
of LINESPEC and LOCATION.  It is common practice to use the
tbreak' command in conjunction with jump'.  *Note Setting
Breakpoints: Set Breaks.

The jump' command does not change the current stack frame, or the
stack pointer, or the contents of any memory location or any
register other than the program counter.  If line LINESPEC is in a
different function from the one currently executing, the results
may be bizarre if the two functions expect different patterns of
arguments or of local variables.  For this reason, the jump'
command requests confirmation if the specified line is not in the
function currently executing.  However, even bizarre results are
predictable if you are well acquainted with the machine-language
code of your program.

On many systems, you can get much the same effect as the jump'
command by storing a new value into the register $pc'. The difference is that this does not start your program running; it only changes the address of where it _will_ run when you continue. For example, set$pc = 0x485

makes the next continue' command or stepping command execute at
address 0x485', rather than at the address where your program stopped.
*Note Continuing and Stepping: Continuing and Stepping.

The most common occasion to use the jump' command is to back
up--perhaps with more breakpoints set--over a portion of a program that
has already executed, in order to examine its execution in more detail.

File: gdb.info,  Node: Signaling,  Next: Returning,  Prev: Jumping,  Up: Altering

17.3 Giving your Program a Signal
=================================

signal SIGNAL'
Resume execution where your program stopped, but immediately give
it the signal SIGNAL.  SIGNAL can be the name or the number of a
signal.  For example, on many systems signal 2' and signal
SIGINT' are both ways of sending an interrupt signal.

Alternatively, if SIGNAL is zero, continue execution without
giving a signal.  This is useful when your program stopped on
account of a signal and would ordinary see the signal when resumed
with the continue' command; signal 0' causes it to resume
without a signal.

signal' does not repeat when you press <RET> a second time after
executing the command.

Invoking the signal' command is not the same as invoking the kill'
utility from the shell.  Sending a signal with kill' causes GDB to
decide what to do with the signal depending on the signal handling
tables (*note Signals::).  The signal' command passes the signal
directly to your program.

File: gdb.info,  Node: Returning,  Next: Calling,  Prev: Signaling,  Up: Altering

17.4 Returning from a Function
==============================

return'
return EXPRESSION'
You can cancel execution of a function call with the return'
command.  If you give an EXPRESSION argument, its value is used as
the function's return value.

When you use return', GDB discards the selected stack frame (and
all frames within it).  You can think of this as making the discarded
frame return prematurely.  If you wish to specify a value to be
returned, give that value as the argument to return'.

This pops the selected stack frame (*note Selecting a Frame:
Selection.), and any other frames inside of it, leaving its caller as
the innermost remaining frame.  That frame becomes selected.  The
specified value is stored in the registers used for returning values of
functions.

The return' command does not resume execution; it leaves the
program stopped in the state that would exist if the function had just
returned.  In contrast, the finish' command (*note Continuing and
Stepping: Continuing and Stepping.) resumes execution until the
selected stack frame returns naturally.

GDB needs to know how the EXPRESSION argument should be set for the
inferior.  The concrete registers assignment depends on the OS ABI and
the type being returned by the selected stack frame.  For example it is
common for OS ABI to return floating point values in FPU registers
while integer values in CPU registers.  Still some ABIs return even
floating point values in CPU registers.  Larger integer widths (such as
long long int') also have specific placement rules.  GDB already knows
the OS ABI from its current target so it needs to find out also the
type being returned to make the assignment into the right register(s).

Normally, the selected stack frame has debug info.  GDB will always
use the debug info instead of the implicit type of EXPRESSION when the
debug info is available.  For example, if you type return -1', and the
function in the current stack frame is declared to return a long long
int', GDB transparently converts the implicit int' value of -1 into a
long long int':

Breakpoint 1, func () at gdb.base/return-nodebug.c:29
29        return 31;
(gdb) return -1
Make func return now? (y or n) y
#0  0x004004f6 in main () at gdb.base/return-nodebug.c:43
43        printf ("result=%lld\n", func ());
(gdb)

However, if the selected stack frame does not have a debug info,
e.g., if the function was compiled without debug info, GDB has to find
out the type to return from user.  Specifying a different type by
mistake may set the value in different inferior registers than the
caller code expects.  For example, typing return -1' with its implicit
type int' would set only a part of a long long int' result for a
debug info less function (on 32-bit architectures).  Therefore the user
is required to specify the return type by an appropriate cast
explicitly:

Breakpoint 2, 0x0040050b in func ()
(gdb) return -1
Return value type not available for selected stack frame.
Please use an explicit cast of the value to return.
(gdb) return (long long int) -1
Make selected stack frame return now? (y or n) y
#0  0x00400526 in main ()
(gdb)

File: gdb.info,  Node: Calling,  Next: Patching,  Prev: Returning,  Up: Altering

17.5 Calling Program Functions
==============================

print EXPR'
Evaluate the expression EXPR and display the resulting value.
EXPR may include calls to functions in the program being debugged.

call EXPR'
Evaluate the expression EXPR without displaying void' returned
values.

You can use this variant of the print' command if you want to
execute a function from your program that does not return anything
(a.k.a. "a void function"), but without cluttering the output with
void' returned values that GDB will otherwise print.  If the
result is not void, it is printed and saved in the value history.

It is possible for the function you call via the print' or call'
command to generate a signal (e.g., if there's a bug in the function,
or if you passed it incorrect arguments).  What happens in that case is
controlled by the set unwindonsignal' command.

Similarly, with a C++ program it is possible for the function you
call via the print' or call' command to generate an exception that is
not handled due to the constraints of the dummy frame.  In this case,
any exception that is raised in the frame, but has an out-of-frame
exception handler will not be found.  GDB builds a dummy-frame for the
inferior function call, and the unwinder cannot seek for exception
handlers outside of this dummy-frame.  What happens in that case is
controlled by the set unwind-on-terminating-exception' command.

set unwindonsignal'
Set unwinding of the stack if a signal is received while in a
function that GDB called in the program being debugged.  If set to
on, GDB unwinds the stack it created for the call and restores the
context to what it was before the call.  If set to off (the
default), GDB stops in the frame where the signal was received.

show unwindonsignal'
Show the current setting of stack unwinding in the functions
called by GDB.

set unwind-on-terminating-exception'
Set unwinding of the stack if a C++ exception is raised, but left
unhandled while in a function that GDB called in the program being
debugged.  If set to on (the default), GDB unwinds the stack it
created for the call and restores the context to what it was before
the call.  If set to off, GDB the exception is delivered to the
default C++ exception handler and the inferior terminated.

show unwind-on-terminating-exception'
Show the current setting of stack unwinding in the functions
called by GDB.

Sometimes, a function you wish to call is actually a "weak alias"
for another function.  In such case, GDB might not pick up the type
information, including the types of the function arguments, which
causes GDB to call the inferior function incorrectly.  As a result, the
called function will function erroneously and may even crash.  A
solution to that is to use the name of the aliased function instead.

File: gdb.info,  Node: Patching,  Prev: Calling,  Up: Altering

17.6 Patching Programs
======================

By default, GDB opens the file containing your program's executable
code (or the corefile) read-only.  This prevents accidental alterations
to machine code; but it also prevents you from intentionally patching

If you'd like to be able to patch the binary, you can specify that
explicitly with the set write' command.  For example, you might want
to turn on internal debugging flags, or even to make emergency repairs.

set write on'
set write off'
If you specify set write on', GDB opens executable and core files
for both reading and writing; if you specify set write off' (the
default), GDB opens them read-only.

If you have already loaded a file, you must load it again (using
the exec-file' or core-file' command) after changing set
write', for your new setting to take effect.

show write'
Display whether executable files and core files are opened for
writing as well as reading.

File: gdb.info,  Node: GDB Files,  Next: Targets,  Prev: Altering,  Up: Top

18 GDB Files
************

GDB needs to know the file name of the program to be debugged, both in
order to read its symbol table and in order to start your program.  To
debug a core dump of a previous run, you must also tell GDB the name of
the core dump file.

* Files::                       Commands to specify files
* Separate Debug Files::        Debugging information in separate files
* Index Files::                 Index files speed up GDB
* Symbol Errors::               Errors reading symbol files
* Data Files::                  GDB data files

File: gdb.info,  Node: Files,  Next: Separate Debug Files,  Up: GDB Files

18.1 Commands to Specify Files
==============================

You may want to specify executable and core dump file names.  The usual
way to do this is at start-up time, using the arguments to GDB's
start-up commands (*note Getting In and Out of GDB: Invocation.).

Occasionally it is necessary to change to a different file during a
GDB session.  Or you may run GDB and forget to specify a file you want
to use.  Or you are debugging a remote target via gdbserver' (*note
file: Server.).  In these situations the GDB commands to specify new
files are useful.

file FILENAME'
Use FILENAME as the program to be debugged.  It is read for its
symbols and for the contents of pure memory.  It is also the
program executed when you use the run' command.  If you do not
specify a directory and the file is not found in the GDB working
directory, GDB uses the environment variable PATH' as a list of
directories to search, just as the shell does when looking for a
program to run.  You can change the value of this variable, for
both GDB and your program, using the path' command.

You can load unlinked object .o' files into GDB using the file'
command.  You will not be able to "run" an object file, but you
can disassemble functions and inspect variables.  Also, if the
underlying BFD functionality supports it, you could use gdb
-write' to patch object files using this technique.  Note that GDB
can neither interpret nor modify relocations in this case, so
branches and some initialized variables will appear to go to the
wrong place.  But this feature is still handy from time to time.

file'
file' with no argument makes GDB discard any information it has
on both executable file and the symbol table.

exec-file [ FILENAME ]'
Specify that the program to be run (but not the symbol table) is
found in FILENAME.  GDB searches the environment variable PATH'
if necessary to locate your program.  Omitting FILENAME means to
discard information on the executable file.

symbol-file [ FILENAME ]'
Read symbol table information from file FILENAME.  PATH' is
searched when necessary.  Use the file' command to get both symbol
table and program to run from the same file.

symbol-file' with no argument clears out GDB information on your
program's symbol table.

The symbol-file' command causes GDB to forget the contents of
some breakpoints and auto-display expressions.  This is because
they may contain pointers to the internal data recording symbols
and data types, which are part of the old symbol table data being

symbol-file' does not repeat if you press <RET> again after
executing it once.

When GDB is configured for a particular environment, it
understands debugging information in whatever format is the
standard generated for that environment; you may use either a GNU
compiler, or other compilers that adhere to the local conventions.
Best results are usually obtained from GNU compilers; for example,
using GCC' you can generate debugging information for optimized
code.

For most kinds of object files, with the exception of old SVR3
systems using COFF, the symbol-file' command does not normally
read the symbol table in full right away.  Instead, it scans the
symbol table quickly to find which source files and which symbols
are present.  The details are read later, one source file at a
time, as they are needed.

The purpose of this two-stage reading strategy is to make GDB
start up faster.  For the most part, it is invisible except for
occasional pauses while the symbol table details for a particular
source file are being read.  (The set verbose' command can turn
these pauses into messages if desired.  *Note Optional Warnings
and Messages: Messages/Warnings.)

We have not implemented the two-stage strategy for COFF yet.  When
the symbol table is stored in COFF format, symbol-file' reads the
symbol table data in full right away.  Note that "stabs-in-COFF"
still does the two-stage strategy, since the debug info is actually
in stabs format.

symbol-file [ -readnow ] FILENAME'
file [ -readnow ] FILENAME'
You can override the GDB two-stage strategy for reading symbol
tables by using the -readnow' option with any of the commands that
load symbol table information, if you want to be sure GDB has the
entire symbol table available.

core-file [FILENAME]'
core'
Specify the whereabouts of a core dump file to be used as the
"contents of memory".  Traditionally, core files contain only some
parts of the address space of the process that generated them; GDB
can access the executable file itself for other parts.

core-file' with no argument specifies that no core file is to be
used.

Note that the core file is ignored when your program is actually
running under GDB.  So, if you have been running your program and
you wish to debug a core file instead, you must kill the
subprocess in which the program is running.  To do this, use the
kill' command (*note Killing the Child Process: Kill Process.).

add-symbol-file FILENAME ADDRESS [ -readnow ]'
The add-symbol-file' command reads additional symbol table
information from the file FILENAME.  You would use this command
when FILENAME has been dynamically loaded (by some other means)
into the program that is running.  ADDRESS should be the memory
address at which the file has been loaded; GDB cannot figure this
out for itself.  You can additionally specify an arbitrary number
of -sSECTION ADDRESS' pairs, to give an explicit section name and
base address for that section.  You can specify any ADDRESS as an
expression.

The symbol table of the file FILENAME is added to the symbol table
originally read with the symbol-file' command.  You can use the
add-symbol-file' command any number of times; the new symbol data
thus read keeps adding to the old.  To discard all old symbol data
instead, use the symbol-file' command without any arguments.

Although FILENAME is typically a shared library file, an
executable file, or some other object file which has been fully
relocated for loading into a process, you can also load symbolic
information from relocatable .o' files, as long as:

* the file's symbolic information refers only to linker symbols
defined in that file, not to symbols defined by other object
files,

* every section the file's symbolic information refers to has
actually been loaded into the inferior, as it appears in the
file, and

* you can determine the address at which every section was
loaded, and provide these to the add-symbol-file' command.

Some embedded operating systems, like Sun Chorus and VxWorks, can
load relocatable files into an already running program; such
systems typically make the requirements above easy to meet.
However, it's important to recognize that many native systems use
complex link procedures (.linkonce' section factoring and C++
constructor table assembly, for example) that make the
requirements difficult to meet.  In general, one cannot assume
that using add-symbol-file' to read a relocatable object file's
symbolic information will have the same effect as linking the
relocatable object file into the program in the normal way.

add-symbol-file' does not repeat if you press <RET> after using
it.

add-symbol-file-from-memory ADDRESS'
Load symbols from the given ADDRESS in a dynamically loaded object
file whose image is mapped directly into the inferior's memory.
For example, the Linux kernel maps a syscall DSO' into each
process's address space; this DSO provides kernel-specific code for
some system calls.  The argument can be any expression whose
evaluation yields the address of the file's shared object file
header.  For this command to work, you must have used
symbol-file' or exec-file' commands in advance.

add-shared-symbol-files LIBRARY-FILE'
assf LIBRARY-FILE'
The add-shared-symbol-files' command can currently be used only
in the Cygwin build of GDB on MS-Windows OS, where it is an alias
for the dll-symbols' command (*note Cygwin Native::).  GDB
automatically looks for shared libraries, however if GDB does not
find yours, you can invoke add-shared-symbol-files'.  It takes
one argument: the shared library's file name.  assf' is a
shorthand alias for add-shared-symbol-files'.

The section' command changes the base address of the named
SECTION of the exec file to ADDR.  This can be used if the exec
file does not contain section addresses, (such as in the a.out'
format), or when the addresses specified in the file itself are
wrong.  Each section must be changed separately.  The info files'
command, described below, lists all the sections and their

info files'
info target'
info files' and info target' are synonymous; both print the
current target (*note Specifying a Debugging Target: Targets.),
including the names of the executable and core dump files
currently in use by GDB, and the files from which symbols were
loaded.  The command help target' lists all possible targets
rather than current ones.

maint info sections'
Another command that can give you extra information about program
sections is maint info sections'.  In addition to the section
information displayed by info files', this command displays the
flags and file offset of each section in the executable and core
dump files.  In addition, maint info sections' provides the
following command options (which may be arbitrarily combined):

ALLOBJ'
Display sections for all loaded object files, including
shared libraries.

SECTIONS'
Display info only for named SECTIONS.

SECTION-FLAGS'
Display info only for sections for which SECTION-FLAGS are
true.  The section flags that GDB currently knows about are:
ALLOC'
Section will have space allocated in the process when
loaded.  Set for all sections except those containing
debug information.

LOAD'
Section will be loaded from the file into the child
process memory.  Set for pre-initialized code and data,
clear for .bss' sections.

RELOC'
Section needs to be relocated before loading.

Section cannot be modified by the child process.

CODE'
Section contains executable code only.

DATA'
Section contains data only (no executable code).

ROM'
Section will reside in ROM.

CONSTRUCTOR'
Section contains data for constructor/destructor lists.

HAS_CONTENTS'
Section is not empty.

An instruction to the linker to not output the section.

COFF_SHARED_LIBRARY'
A notification to the linker that the section contains
COFF shared library information.

IS_COMMON'
Section contains common symbols.

set trust-readonly-sections on'
Tell GDB that readonly sections in your object file really are
read-only (i.e. that their contents will not change).  In that
case, GDB can fetch values from these sections out of the object
file, rather than from the target program.  For some targets
(notably embedded ones), this can be a significant enhancement to
debugging performance.

The default is off.

Tell GDB not to trust readonly sections.  This means that the
contents of the section might change while the program is running,
and must therefore be fetched from the target when needed.

show trust-readonly-sections'
Show the current setting of trusting readonly sections.

All file-specifying commands allow both absolute and relative file
names as arguments.  GDB always converts the file name to an absolute
file name and remembers it that way.

GDB supports GNU/Linux, MS-Windows, HP-UX, SunOS, SVr4, Irix, and
IBM RS/6000 AIX shared libraries.

On MS-Windows GDB must be linked with the Expat library to support
shared libraries.  *Note Expat::.

GDB automatically loads symbol definitions from shared libraries
when you use the run' command, or when you examine a core file.
(Before you issue the run' command, GDB does not understand references
to a function in a shared library, however--unless you are debugging a
core file).

On HP-UX, if the program loads a library explicitly, GDB
automatically loads the symbols at the time of the shl_load' call.

There are times, however, when you may wish to not automatically load
symbol definitions from shared libraries, such as when they are
particularly large or there are many of them.

To control the automatic loading of shared library symbols, use the
commands:

set auto-solib-add MODE'
If MODE is on', symbols from all shared object libraries will be
loaded automatically when the inferior begins execution, you
attach to an independently started inferior, or when the dynamic
linker informs GDB that a new library has been loaded.  If MODE is
off', symbols must be loaded manually, using the sharedlibrary'
command.  The default value is on'.

If your program uses lots of shared libraries with debug info that
takes large amounts of memory, you can decrease the GDB memory
footprint by preventing it from automatically loading the symbols
from shared libraries.  To that end, type set auto-solib-add off'
before running the inferior, then load each library whose debug
symbols you do need with sharedlibrary REGEXP', where REGEXP is a
regular expression that matches the libraries whose symbols you
want to be loaded.

To explicitly load shared library symbols, use the sharedlibrary'
command:

info share REGEX'
info sharedlibrary REGEX'
Print the names of the shared libraries which are currently loaded
that match REGEX.  If REGEX is omitted then print all shared
libraries that are loaded.

sharedlibrary REGEX'
share REGEX'
Load shared object library symbols for files matching a Unix
regular expression.  As with files loaded automatically, it only
loads shared libraries required by your program for a core file or
after typing run'.  If REGEX is omitted all shared libraries

nosharedlibrary'
Unload all shared object library symbols.  This discards all
symbols that have been loaded from all shared libraries.  Symbols
from shared libraries that were loaded by explicit user requests

Sometimes you may wish that GDB stops and gives you control when any
of shared library events happen.  Use the set stop-on-solib-events'
command for this:

set stop-on-solib-events'
This command controls whether GDB should give you control when the
dynamic linker notifies it about some shared library event.  The
shared library.

show stop-on-solib-events'
Show whether GDB stops and gives you control when shared library
events happen.

Shared libraries are also supported in many cross or remote debugging
configurations.  GDB needs to have access to the target's libraries;
this can be accomplished either by providing copies of the libraries on
the host system, or by asking GDB to automatically retrieve the
libraries from the target.  If copies of the target libraries are
provided, they need to be the same as the target libraries, although the
copies on the target can be stripped as long as the copies on the host
are not.

For remote debugging, you need to tell GDB where the target
libraries are, so that it can load the correct copies--otherwise, it
may try to load the host's libraries.  GDB has two variables to specify
the search directories for target libraries.

set sysroot PATH'
Use PATH as the system root for the program being debugged.  Any
absolute shared library paths will be prefixed with PATH; many
runtime loaders store the absolute paths to the shared library in
the target program's memory.  If you use set sysroot' to find
shared libraries, they need to be laid out in the same way that
they are on the target, with e.g. a /lib' and /usr/lib' hierarchy
under PATH.

If PATH starts with the sequence remote:', GDB will retrieve the
target libraries from the remote system.  This is only supported
when using a remote target that supports the remote get' command
(*note Sending files to a remote system: File Transfer.).  The
part of PATH following the initial remote:' (if present) is used
as system root prefix on the remote file system.  (1)

For targets with an MS-DOS based filesystem, such as MS-Windows and
SymbianOS, GDB tries prefixing a few variants of the target
absolute file name with PATH.  But first, on Unix hosts, GDB
converts all backslash directory separators into forward slashes,
because the backslash is not a directory separator on Unix:

c:\foo\bar.dll => c:/foo/bar.dll

Then, GDB attempts prefixing the target file name with PATH, and
looks for the resulting file name in the host file system:

c:/foo/bar.dll => /path/to/sysroot/c:/foo/bar.dll

If that does not find the shared library, GDB tries removing the
:' character from the drive spec, both for convenience, and, for
the case of the host file system not supporting file names with
colons:

c:/foo/bar.dll => /path/to/sysroot/c/foo/bar.dll

This makes it possible to have a system root that mirrors a target
with more than one drive.  E.g., you may want to setup your local
copies of the target system shared libraries like so (note c' vs
z'):

/path/to/sysroot/c/sys/bin/foo.dll'
/path/to/sysroot/c/sys/bin/bar.dll'
/path/to/sysroot/z/sys/bin/bar.dll'

and point the system root at /path/to/sysroot', so that GDB can
find the correct copies of both c:\sys\bin\foo.dll', and
z:\sys\bin\bar.dll'.

If that still does not find the shared library, GDB tries removing
the whole drive spec from the target file name:

c:/foo/bar.dll => /path/to/sysroot/foo/bar.dll

This last lookup makes it possible to not care about the drive
name, if you don't want or need to.

The set solib-absolute-prefix' command is an alias for set
sysroot'.

You can set the default system root by using the configure-time
--with-sysroot' option.  If the system root is inside GDB's
configured binary prefix (set with --prefix' or --exec-prefix'),
then the default system root will be updated automatically if the
installed GDB is moved to a new location.

show sysroot'
Display the current shared library prefix.

set solib-search-path PATH'
If this variable is set, PATH is a colon-separated list of
directories to search for shared libraries.  solib-search-path'
is used after sysroot' fails to locate the library, or if the
path to the library is relative instead of absolute.  If you want
to use solib-search-path' instead of sysroot', be sure to set
sysroot' to a nonexistent directory to prevent GDB from finding
your host's libraries.  sysroot' is preferred; setting it to a
nonexistent directory may interfere with automatic loading of
shared library symbols.

show solib-search-path'
Display the current shared library search path.

set target-file-system-kind KIND'
Set assumed file system kind for target reported file names.

Shared library file names as reported by the target system may not
make sense as is on the system GDB is running on.  For example,
when remote debugging a target that has MS-DOS based file system
semantics, from a Unix host, the target may be reporting to GDB a
list of loaded shared libraries with file names such as
c:\Windows\kernel32.dll'.  On Unix hosts, there's no concept of
drive letters, so the c:\' prefix is not normally understood as
indicating an absolute file name, and neither is the backslash
normally considered a directory separator character.  In that case,
the native file system would interpret this whole absolute file
name as a relative file name with no directory components.  This
would make it impossible to point GDB at a copy of the remote
target's shared libraries on the host using set sysroot', and
impractical with set solib-search-path'.  Setting
target-file-system-kind' to dos-based' tells GDB to interpret
such file names similarly to how the target would, and to map them
to file names valid on GDB's native file system semantics.  The
value of KIND can be "auto"', in addition to one of the supported
file system kinds.  In that case, GDB tries to determine the
appropriate file system variant based on the current target's
operating system (*note Configuring the Current ABI: ABI.).  The
supported file system settings are:

unix'
Instruct GDB to assume the target file system is of Unix
kind.  Only file names starting the forward slash (/')
character are considered absolute, and the directory
separator character is also the forward slash.

dos-based'
Instruct GDB to assume the target file system is DOS based.
File names starting with either a forward slash, or a drive
letter followed by a colon (e.g., c:'), are considered
absolute, and both the slash (/') and the backslash (\\')
characters are considered directory separators.

auto'
Instruct GDB to use the file system kind associated with the
target operating system (*note Configuring the Current ABI:
ABI.).  This is the default.

---------- Footnotes ----------

(1) If you want to specify a local system root using a directory
that happens to be named remote:', you need to use some equivalent
variant of the name like ./remote:'.

File: gdb.info,  Node: Separate Debug Files,  Next: Index Files,  Prev: Files,  Up: GDB Files

18.2 Debugging Information in Separate Files
============================================

GDB allows you to put a program's debugging information in a file
separate from the executable itself, in a way that allows GDB to find
and load the debugging information automatically.  Since debugging
information can be very large--sometimes larger than the executable
code itself--some systems distribute debugging information for their
executables in separate files, which users can install only when they
need to debug a problem.

GDB supports two ways of specifying the separate debug info file:

* The executable contains a "debug link" that specifies the name of
the separate debug info file.  The separate debug file's name is
usually EXECUTABLE.debug', where EXECUTABLE is the name of the
corresponding executable file without leading directories (e.g.,
ls.debug' for /usr/bin/ls').  In addition, the debug link
specifies a 32-bit "Cyclic Redundancy Check" (CRC) checksum for
the debug file, which GDB uses to validate that the executable and
the debug file came from the same build.

* The executable contains a "build ID", a unique bit string that is
also present in the corresponding debug info file.  (This is
supported only on some operating systems, notably those which use
the ELF format for binary files and the GNU Binutils.)  For more
details about this feature, see the description of the --build-id'
command-line option in *note Command Line Options:
(ld.info)Options.  The debug info file's name is not specified
explicitly by the build ID, but can be computed from the build ID,
see below.

Depending on the way the debug info file is specified, GDB uses two
different methods of looking for the debug file:

* For the "debug link" method, GDB looks up the named file in the
directory of the executable file, then in a subdirectory of that
directory named .debug', and finally under each one of the global
debug directories, in a subdirectory whose name is identical to
the leading directories of the executable's absolute file name.

* For the "build ID" method, GDB looks in the .build-id'
subdirectory of each one of the global debug directories for a
file named NN/NNNNNNNN.debug', where NN are the first 2 hex
characters of the build ID bit string, and NNNNNNNN are the rest
of the bit string.  (Real build ID strings are 32 or more hex
characters, not 10.)

So, for example, suppose you ask GDB to debug /usr/bin/ls', which
has a debug link that specifies the file ls.debug', and a build ID
whose value in hex is abcdef1234'.  If the list of the global debug
directories includes /usr/lib/debug', then GDB will look for the
following debug information files, in the indicated order:

- /usr/lib/debug/.build-id/ab/cdef1234.debug'

- /usr/bin/ls.debug'

- /usr/bin/.debug/ls.debug'

- /usr/lib/debug/usr/bin/ls.debug'.

Global debugging info directories default to what is set by GDB
configure option --with-separate-debug-dir'.  During GDB run you can
also set the global debugging info directories, and view the list GDB
is currently using.

set debug-file-directory DIRECTORIES'
Set the directories which GDB searches for separate debugging
information files to DIRECTORY.  Multiple path components can be
set concatenating them by a path separator.

show debug-file-directory'
Show the directories GDB searches for separate debugging
information files.

You can also adjust the current verbosity of the "build id" locating.

set build-id-verbose 0'
No additional messages are printed.

set build-id-verbose 1'
Missing separate debug filenames are printed.

set build-id-verbose 2'
Missing separate debug filenames are printed and also all the
parsing of the binaries to find their "build id" content is
printed.

show build-id-verbose'
Show the current verbosity value for the "build id" content
locating.

A debug link is a special section of the executable file named
.gnu_debuglink'.  The section must contain:

* A filename, with any leading directory components removed,
followed by a zero byte,

* zero to three bytes of padding, as needed to reach the next
four-byte boundary within the section, and

* a four-byte CRC checksum, stored in the same endianness used for
the executable file itself.  The checksum is computed on the
debugging information file's full contents by the function given
below, passing zero as the CRC argument.

Any executable file format can carry a debug link, as long as it can
contain a section named .gnu_debuglink' with the contents described
above.

The build ID is a special section in the executable file (and in
other ELF binary files that GDB may consider).  This section is often
named .note.gnu.build-id', but that name is not mandatory.  It
contains unique identification for the built files--the ID remains the
same across multiple builds of the same build tree.  The default
algorithm SHA1 produces 160 bits (40 hexadecimal characters) of the
content for the build ID string.  The same section with an identical
value is present in the original built binary with symbols, in its
stripped variant, and in the separate debugging information file.

The debugging information file itself should be an ordinary
executable, containing a full set of linker symbols, sections, and
debugging information.  The sections of the debugging information file
should have the same names, addresses, and sizes as the original file,
but they need not contain any data--much like a .bss' section in an
ordinary executable.

The GNU binary utilities (Binutils) package includes the objcopy'
utility that can produce the separated executable / debugging
information file pairs using the following commands:

objcopy --only-keep-debug foo foo.debug
strip -g foo

These commands remove the debugging information from the executable
file foo' and place it in the file foo.debug'.  You can use the
first, second or both methods to link the two files:

* The debug link method needs the following additional command to
also leave behind a debug link in foo':

Ulrich Drepper's elfutils' package, starting with version 0.53,
contains a version of the strip' command such that the command
strip foo -f foo.debug' has the same functionality as the two
objcopy' commands and the ln -s' command above, together.

* Build ID gets embedded into the main executable using ld
--build-id' or the GCC counterpart gcc -Wl,--build-id'.  Build ID
support plus compatibility fixes for debug files separation are
present in GNU binary utilities (Binutils) package since version
2.18.

The CRC used in .gnu_debuglink' is the CRC-32 defined in IEEE 802.3
using the polynomial:

x^32 + x^26 + x^23 + x^22 + x^16 + x^12 + x^11
+ x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x + 1

The function is computed byte at a time, taking the least
significant bit of each byte first.  The initial pattern 0xffffffff'
is used, to ensure leading zeros affect the CRC and the final result is
inverted to ensure trailing zeros also affect the CRC.

_Note:_ This is the same CRC polynomial as used in handling the
"Remote Serial Protocol" qCRC' packet (*note GDB Remote Serial
Protocol: Remote Protocol.).  However in the case of the Remote Serial
Protocol, the CRC is computed _most_ significant bit first, and the
result is not inverted, so trailing zeros have no effect on the CRC
value.

To complete the description, we show below the code of the function
which produces the CRC used in .gnu_debuglink'.  Inverting the
initially supplied crc' argument means that an initial call to this
function passing in zero will start computing the CRC using
0xffffffff'.

unsigned long
gnu_debuglink_crc32 (unsigned long crc,
unsigned char *buf, size_t len)
{
static const unsigned long crc32_table[256] =
{
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419,
0x706af48f, 0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4,
0xe0d5e91e, 0x97d2d988, 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07,
0x90bf1d91, 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4,
0xa2677172, 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, 0x32d86ce3,
0x45df5c75, 0xdcd60dcf, 0xabd13d59, 0x26d930ac, 0x51de003a,
0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423, 0xcfba9599,
0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190,
0x01db7106, 0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f,
0x9fbfe4a5, 0xe8b8d433, 0x7807c9a2, 0x0f00f934, 0x9609a88e,
0xe10e9818, 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, 0x6c0695ed,
0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3,
0xfbd44c65, 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a,
0x346ed9fc, 0xad678846, 0xda60b8d0, 0x44042d73, 0x33031de5,
0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa, 0xbe0b1010,
0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17,
0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6,
0x03b6e20c, 0x74b1d29a, 0xead54739, 0x9dd277af, 0x04db2615,
0x73dc1683, 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, 0xf00f9344,
0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a,
0x67dd4acc, 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, 0xd1bb67f1,
0xa6bc5767, 0x3fb506dd, 0x48b2364b, 0xd80d2bda, 0xaf0a1b4c,
0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55, 0x316e8eef,
0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe,
0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31,
0x2cd99e8b, 0x5bdeae1d, 0x9b64c2b0, 0xec63f226, 0x756aa39c,
0x026d930a, 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, 0x92d28e9b,
0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1,
0x18b74777, 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, 0xa00ae278,
0xd70dd2ee, 0x4e048354, 0x3903b3c2, 0xa7672661, 0xd06016f7,
0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc, 0x40df0b66,
0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605,
0xcdd70693, 0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8,
0x5d681b02, 0x2a6f2b94, 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b,
0x2d02ef8d
};
unsigned char *end;

crc = ~crc & 0xffffffff;
for (end = buf + len; buf < end; ++buf)
crc = crc32_table[(crc ^ *buf) & 0xff] ^ (crc >> 8);
return ~crc & 0xffffffff;
}

This computation does not apply to the "build ID" method.

File: gdb.info,  Node: Index Files,  Next: Symbol Errors,  Prev: Separate Debug Files,  Up: GDB Files

18.3 Index Files Speed Up GDB
=============================

When GDB finds a symbol file, it scans the symbols in the file in order
to construct an internal symbol table.  This lets most GDB operations
work quickly--at the cost of a delay early on.  For large programs,
this delay can be quite lengthy, so GDB provides a way to build an
index, which speeds up startup.

The index is stored as a section in the symbol file.  GDB can write
the index to a file, then you can put it into the symbol file using
objcopy'.

To create an index file, use the save gdb-index' command:

save gdb-index DIRECTORY'
Create an index file for each symbol file currently known by GDB.
Each file is named after its corresponding symbol file, with
.gdb-index' appended, and is written into the given DIRECTORY.

Once you have created an index file you can merge it into your symbol
file, here named symfile', using objcopy':

$objcopy --add-section .gdb_index=symfile.gdb-index \ --set-section-flags .gdb_index=readonly symfile symfile There are currently some limitation on indices. They only work when for DWARF debugging information, not stabs. And, they do not currently work for programs using Ada. GDB comes with a program, gdb-add-index', which can be used to add the index to a symbol file. It takes the symbol file as its only argument:$ gdb-add-index symfile

File: gdb.info,  Node: Symbol Errors,  Next: Data Files,  Prev: Index Files,  Up: GDB Files

18.4 Errors Reading Symbol Files
================================

While reading a symbol file, GDB occasionally encounters problems, such
as symbol types it does not recognize, or known bugs in compiler
output.  By default, GDB does not notify you of such problems, since
they are relatively common and primarily of interest to people
debugging compilers.  If you are interested in seeing information about
ill-constructed symbol tables, you can either ask GDB to print only one
message about each such type of problem, no matter how many times the
problem occurs; or you can ask GDB to print more messages, to see how
many times the problems occur, with the set complaints' command (*note
Optional Warnings and Messages: Messages/Warnings.).

The messages currently printed, and their meanings, include:

inner block not inside outer block in SYMBOL'
The symbol information shows where symbol scopes begin and end
(such as at the start of a function or a block of statements).
This error indicates that an inner scope block is not fully
contained in its outer scope blocks.

GDB circumvents the problem by treating the inner block as if it
had the same scope as the outer block.  In the error message,
SYMBOL may be shown as "(don't know)'" if the outer block is not a
function.

block at ADDRESS out of order'
The symbol information for symbol scope blocks should occur in
order of increasing addresses.  This error indicates that it does
not do so.

GDB does not circumvent this problem, and has trouble locating
symbols in the source file whose symbols it is reading.  (You can
often determine what source file is affected by specifying set
verbose on'.  *Note Optional Warnings and Messages:
Messages/Warnings.)

bad block start address patched'
The symbol information for a symbol scope block has a start address
smaller than the address of the preceding source line.  This is
known to occur in the SunOS 4.1.1 (and earlier) C compiler.

GDB circumvents the problem by treating the symbol scope block as
starting on the previous source line.

bad string table offset in symbol N'
Symbol number N contains a pointer into the string table which is
larger than the size of the string table.

GDB circumvents the problem by considering the symbol to have the
name foo', which may cause other problems if many symbols end up
with this name.

unknown symbol type 0xNN''
The symbol information contains new data types that GDB does not
yet know how to read.  0xNN' is the symbol type of the
uncomprehended information, in hexadecimal.

GDB circumvents the error by ignoring this symbol information.
This usually allows you to debug your program, though certain
symbols are not accessible.  If you encounter such a problem and
feel like debugging it, you can debug gdb' with itself, breakpoint
on complain', then go up to the function read_dbx_symtab' and
examine *bufp' to see the symbol.

stub type has NULL name'
GDB could not find the full definition for a struct or class.

const/volatile indicator missing (ok if using g++ v1.x), got...'
The symbol information for a C++ member function is missing some
information that recent versions of the compiler should have
output for it.

info mismatch between compiler and debugger'
GDB could not parse a type specification output by the compiler.

File: gdb.info,  Node: Data Files,  Prev: Symbol Errors,  Up: GDB Files

18.5 GDB Data Files
===================

GDB will sometimes read an auxiliary data file.  These files are kept
in a directory known as the "data directory".

You can set the data directory's name, and view the name GDB is
currently using.

set data-directory DIRECTORY'
Set the directory which GDB searches for auxiliary data files to
DIRECTORY.

show data-directory'
Show the directory GDB searches for auxiliary data files.

You can set the default data directory by using the configure-time
--with-gdb-datadir' option.  If the data directory is inside GDB's
configured binary prefix (set with --prefix' or --exec-prefix'), then
the default data directory will be updated automatically if the
installed GDB is moved to a new location.

File: gdb.info,  Node: Targets,  Next: Remote Debugging,  Prev: GDB Files,  Up: Top

19 Specifying a Debugging Target
********************************

A "target" is the execution environment occupied by your program.

Often, GDB runs in the same host environment as your program; in
that case, the debugging target is specified as a side effect when you
use the file' or core' commands.  When you need more flexibility--for
example, running GDB on a physically separate host, or controlling a
standalone system over a serial port or a realtime system over a TCP/IP
connection--you can use the target' command to specify one of the
target types configured for GDB (*note Commands for Managing Targets:
Target Commands.).

It is possible to build GDB for several different "target
architectures".  When GDB is built like that, you can choose one of the
available architectures with the set architecture' command.

set architecture ARCH'
This command sets the current target architecture to ARCH.  The
value of ARCH can be "auto"', in addition to one of the supported
architectures.

show architecture'
Show the current target architecture.

set processor'
processor'
These are alias commands for, respectively, set architecture' and
show architecture'.

* Active Targets::              Active targets
* Target Commands::             Commands for managing targets
* Byte Order::                  Choosing target byte order

File: gdb.info,  Node: Active Targets,  Next: Target Commands,  Up: Targets

19.1 Active Targets
===================

There are multiple classes of targets such as: processes, executable
files or recording sessions.  Core files belong to the process class,
there can be active only one of a core or a running process.  Otherwise
GDB can work concurrently on multiple active targets, one in each
class.  This allows you to (for example) start a process and inspect
its activity while still having access to the executable file after the
process finishes.  Or if you start process recording (*note Reverse
Execution::) and reverse-step' there you are presented a virtual layer
of the recording target while the process target remains stopped at the
chronologically last point of the process execution.

Use the core-file' and exec-file' commands to select a new core
file or executable target (*note Commands to Specify Files: Files.).  To
specify as a target a process that is already running, use the attach'
command (*note Debugging an Already-running Process: Attach.).

File: gdb.info,  Node: Target Commands,  Next: Byte Order,  Prev: Active Targets,  Up: Targets

19.2 Commands for Managing Targets
==================================

target TYPE PARAMETERS'
Connects the GDB host environment to a target machine or process.
A target is typically a protocol for talking to debugging
facilities.  You use the argument TYPE to specify the type or
protocol of the target machine.

Further PARAMETERS are interpreted by the target protocol, but
typically include things like device names or host names to connect
with, process numbers, and baud rates.

The target' command does not repeat if you press <RET> again
after executing the command.

help target'
Displays the names of all targets available.  To display targets
currently selected, use either info target' or info files'
(*note Commands to Specify Files: Files.).

help target NAME'
Describe a particular target, including any parameters necessary to
select it.

set gnutarget ARGS'
GDB uses its own library BFD to read your files.  GDB knows
whether it is reading an "executable", a "core", or a ".o" file;
however, you can specify the file format with the set gnutarget'
command.  Unlike most target' commands, with gnutarget' the
target' refers to a program, not a machine.

_Warning:_ To specify a file format with set gnutarget', you
must know the actual BFD name.

*Note Commands to Specify Files: Files.

show gnutarget'
Use the show gnutarget' command to display what file format
gnutarget' is set to read.  If you have not set gnutarget', GDB
will determine the file format for each file automatically, and
show gnutarget' displays The current BDF target is "auto"'.

Here are some common targets (available, or not, depending on the GDB
configuration):

target exec PROGRAM'
An executable file.  target exec PROGRAM' is the same as
exec-file PROGRAM'.

target core FILENAME'
A core dump file.  target core FILENAME' is the same as
core-file FILENAME'.

target remote MEDIUM'
A remote system connected to GDB via a serial line or network
connection.  This command tells GDB to use its own remote protocol
over MEDIUM for debugging.  *Note Remote Debugging::.

For example, if you have a board connected to /dev/ttya' on the
machine running GDB, you could say:

target remote /dev/ttya

target remote' supports the load' command.  This is only useful
if you have some other way of getting the stub to the target
system, and you can put it somewhere in memory where it won't get

target sim [SIMARGS] ...'
Builtin CPU simulator.  GDB includes simulators for most
architectures.  In general,
target sim
run
works; however, you cannot assume that a specific memory map,
device drivers, or even basic I/O is available, although some
simulators do provide these.  For info about any
processor-specific simulator details, see the appropriate section
in *note Embedded Processors: Embedded Processors.

Some configurations may include these targets as well:

target nrom DEV'

Different targets are available on different configurations of GDB;
your configuration may have more or fewer targets.

Many remote targets require you to download the executable's code
once you've successfully established a connection.  You may wish to
control various aspects of this process.

set hash'
This command controls whether a hash mark #' is displayed while
downloading a file to the remote monitor.  If on, a hash mark is
displayed after each S-record is successfully downloaded to the
monitor.

show hash'
Show the current status of displaying the hash mark.

set debug monitor'
Enable or disable display of communications messages between GDB
and the remote monitor.

show debug monitor'
Show the current status of displaying communications between GDB
and the remote monitor.

load FILENAME'
Depending on what remote debugging facilities are configured into
GDB, the load' command may be available.  Where it exists, it is
meant to make FILENAME (an executable) available for debugging on
load' also records the FILENAME symbol table in GDB, like the

If your GDB does not have a load' command, attempting to execute
it gets the error message "You can't do that when your target is
...'"

The file is loaded at whatever address is specified in the
executable.  For some object file formats, you can specify the
load address when you link the program; for other formats, like
a.out, the object file format specifies a fixed address.

Depending on the remote side capabilities, GDB may be able to load
programs into flash memory.

load' does not repeat if you press <RET> again after using it.

File: gdb.info,  Node: Byte Order,  Prev: Target Commands,  Up: Targets

19.3 Choosing Target Byte Order
===============================

Some types of processors, such as the MIPS, PowerPC, and Renesas SH,
offer the ability to run either big-endian or little-endian byte
orders.  Usually the executable or symbol will include a bit to
designate the endian-ness, and you will not need to worry about which
to use.  However, you may still find it useful to adjust GDB's idea of
processor endian-ness manually.

set endian big'
Instruct GDB to assume the target is big-endian.

set endian little'
Instruct GDB to assume the target is little-endian.

set endian auto'
Instruct GDB to use the byte order associated with the executable.

show endian'
Display GDB's current idea of the target byte order.

Note that these commands merely adjust interpretation of symbolic
data on the host, and that they have absolutely no effect on the target
system.

File: gdb.info,  Node: Remote Debugging,  Next: Configurations,  Prev: Targets,  Up: Top

20 Debugging Remote Programs
****************************

If you are trying to debug a program running on a machine that cannot
run GDB in the usual way, it is often useful to use remote debugging.
For example, you might use remote debugging on an operating system
kernel, or on a small system which does not have a general purpose
operating system powerful enough to run a full-featured debugger.

Some configurations of GDB have special serial or TCP/IP interfaces
to make this work with particular debugging targets.  In addition, GDB
comes with a generic serial protocol (specific to GDB, but not specific
to any particular target system) which you can use if you write the
remote stubs--the code that runs on the remote system to communicate
with GDB.

Other remote targets may be available in your configuration of GDB;
use help target' to list them.

* Connecting::                  Connecting to a remote target
* File Transfer::               Sending files to a remote system
* Server::	                Using the gdbserver program
* Remote Configuration::        Remote configuration
* Remote Stub::                 Implementing a remote stub

File: gdb.info,  Node: Connecting,  Next: File Transfer,  Up: Remote Debugging

20.1 Connecting to a Remote Target
==================================

On the GDB host machine, you will need an unstripped copy of your
program, since GDB needs symbol and debugging information.  Start up
GDB as usual, using the name of the local copy of your program as the
first argument.

GDB can communicate with the target over a serial line, or over an
IP network using TCP or UDP.  In each case, GDB uses the same protocol
for debugging your program; only the medium carrying the debugging
packets varies.  The target remote' command establishes a connection
to the target.  Its arguments indicate which medium to use:

target remote SERIAL-DEVICE'
Use SERIAL-DEVICE to communicate with the target.  For example, to
use a serial line connected to the device named /dev/ttyb':

target remote /dev/ttyb

If you're using a serial line, you may want to give GDB the
--baud' option, or use the set remotebaud' command (*note set
remotebaud: Remote Configuration.) before the target' command.

target remote HOST:PORT''
target remote tcp:HOST:PORT''
Debug using a TCP connection to PORT on HOST.  The HOST may be
either a host name or a numeric IP address; PORT must be a decimal
number.  The HOST could be the target machine itself, if it is
directly connected to the net, or it might be a terminal server
which in turn has a serial line to the target.

For example, to connect to port 2828 on a terminal server named
manyfarms':

target remote manyfarms:2828

If your remote target is actually running on the same machine as
your debugger session (e.g. a simulator for your target running on
the same host), you can omit the hostname.  For example, to
connect to port 1234 on your local machine:

target remote :1234
Note that the colon is still required here.

target remote udp:HOST:PORT''
Debug using UDP packets to PORT on HOST.  For example, to connect
to UDP port 2828 on a terminal server named manyfarms':

target remote udp:manyfarms:2828

When using a UDP connection for remote debugging, you should keep
in mind that the U' stands for "Unreliable".  UDP can silently
drop packets on busy or unreliable networks, which will cause
havoc with your debugging session.

target remote | COMMAND'
Run COMMAND in the background and communicate with it using a
pipe.  The COMMAND is a shell command, to be parsed and expanded
by the system's command shell, /bin/sh'; it should expect remote
protocol packets on its standard input, and send replies on its
standard output.  You could use this to run a stand-alone simulator
that speaks the remote debugging protocol, to make net connections
using programs like ssh', or for other similar tricks.

If COMMAND closes its standard output (perhaps by exiting), GDB
will try to send it a SIGTERM' signal.  (If the program has
already exited, this will have no effect.)

Once the connection has been established, you can use all the usual
commands to examine and change data.  The remote program is already
running; you can use step' and continue', and you do not need to use
run'.

Whenever GDB is waiting for the remote program, if you type the
interrupt character (often Ctrl-c'), GDB attempts to stop the program.
This may or may not succeed, depending in part on the hardware and the
serial drivers the remote system uses.  If you type the interrupt
character once again, GDB displays this prompt:

Interrupted while waiting for the program.
Give up (and stop debugging it)?  (y or n)

If you type y', GDB abandons the remote debugging session.  (If you
decide you want to try again later, you can use target remote' again
to connect once more.)  If you type n', GDB goes back to waiting.

detach'
When you have finished debugging the remote program, you can use
the detach' command to release it from GDB control.  Detaching
from the target normally resumes its execution, but the results
will depend on your particular remote stub.  After the detach'
command, GDB is free to connect to another target.

disconnect'
The disconnect' command behaves like detach', except that the
target is generally not resumed.  It will wait for GDB (this
instance or another one) to connect and continue debugging.  After
the disconnect' command, GDB is again free to connect to another
target.

monitor CMD'
This command allows you to send arbitrary commands directly to the
remote monitor.  Since GDB doesn't care about the commands it
sends like this, this command is the way to extend GDB--you can
add new commands that only the external monitor will understand
and implement.

File: gdb.info,  Node: File Transfer,  Next: Server,  Prev: Connecting,  Up: Remote Debugging

20.2 Sending files to a remote system
=====================================

Some remote targets offer the ability to transfer files over the same
connection used to communicate with GDB.  This is convenient for
targets accessible through other means, e.g. GNU/Linux systems running
gdbserver' over a network interface.  For other targets, e.g. embedded
devices with only a single serial port, this may be the only way to

Not all remote targets support these commands.

remote put HOSTFILE TARGETFILE'
Copy file HOSTFILE from the host system (the machine running GDB)
to TARGETFILE on the target system.

remote get TARGETFILE HOSTFILE'
Copy file TARGETFILE from the target system to HOSTFILE on the
host system.

remote delete TARGETFILE'
Delete TARGETFILE from the target system.

File: gdb.info,  Node: Server,  Next: Remote Configuration,  Prev: File Transfer,  Up: Remote Debugging

20.3 Using the gdbserver' Program
==================================

gdbserver' is a control program for Unix-like systems, which allows
you to connect your program with a remote GDB via target remote'--but
without linking in the usual debugging stub.

gdbserver' is not a complete replacement for the debugging stubs,
because it requires essentially the same operating-system facilities
that GDB itself does.  In fact, a system that can run gdbserver' to
connect to a remote GDB could also run GDB locally!  gdbserver' is
sometimes useful nevertheless, because it is a much smaller program
than GDB itself.  It is also easier to port than all of GDB, so you may
be able to get started more quickly on a new system by using
gdbserver'.  Finally, if you develop code for real-time systems, you
may find that the tradeoffs involved in real-time operation make it
more convenient to do as much development work as possible on another
system, for example by cross-compiling.  You can use gdbserver' to
make a similar choice for debugging.

GDB and gdbserver' communicate via either a serial line or a TCP
connection, using the standard GDB remote serial protocol.

_Warning:_ gdbserver' does not have any built-in security.  Do
not run gdbserver' connected to any public network; a GDB
connection to gdbserver' provides access to the target system
with the same privileges as the user running gdbserver'.

20.3.1 Running gdbserver'
--------------------------

Run gdbserver' on the target system.  You need a copy of the program
you want to debug, including any libraries it requires.  gdbserver'
does not need your program's symbol table, so you can strip the program
if necessary to save space.  GDB on the host system does all the symbol
handling.

To use the server, you must tell it how to communicate with GDB; the
name of your program; and the arguments for your program.  The usual
syntax is:

target> gdbserver COMM PROGRAM [ ARGS ... ]

COMM is either a device name (to use a serial line), or a TCP
hostname and portnumber, or -' or stdio' to use stdin/stdout of
gdbserver'.  For example, to debug Emacs with the argument foo.txt'
and communicate with GDB over the serial port /dev/com1':

target> gdbserver /dev/com1 emacs foo.txt

gdbserver' waits passively for the host GDB to communicate with it.

To use a TCP connection instead of a serial line:

target> gdbserver host:2345 emacs foo.txt

The only difference from the previous example is the first argument,
specifying that you are communicating with the host GDB via TCP.  The
host:2345' argument means that gdbserver' is to expect a TCP
connection from machine host' to local TCP port 2345.  (Currently, the
host' part is ignored.)  You can choose any number you want for the
port number as long as it does not conflict with any TCP ports already
in use on the target system (for example, 23' is reserved for
telnet').(1)  You must use the same port number with the host GDB
target remote' command.

The stdio' connection is useful when starting gdbserver' with ssh:

(gdb) target remote | ssh -T hostname gdbserver - hello

The -T' option to ssh is provided because we don't need a remote
pty, and we don't want escape-character handling.  Ssh does this by
default when a command is provided, the flag is provided to make it
explicit.  You could elide it if you want to.

Programs started with stdio-connected gdbserver have /dev/null' for
stdin', and stdout',stderr' are sent back to gdb for display through
a pipe connected to gdbserver.  Both stdout' and stderr' use the same
pipe.

20.3.1.1 Attaching to a Running Program
.......................................

On some targets, gdbserver' can also attach to running programs.  This
is accomplished via the --attach' argument.  The syntax is:

target> gdbserver --attach COMM PID

PID is the process ID of a currently running process.  It isn't
necessary to point gdbserver' at a binary for the running process.

You can debug processes by name instead of process ID if your target
has the pidof' utility:

target> gdbserver --attach COMM pidof PROGRAM

In case more than one copy of PROGRAM is running, or PROGRAM has
multiple threads, most versions of pidof' support the -s' option to
only return the first process ID.

20.3.1.2 Multi-Process Mode for gdbserver'
...........................................

When you connect to gdbserver' using target remote', gdbserver'
debugs the specified program only once.  When the program exits, or you
detach from it, GDB closes the connection and gdbserver' exits.

If you connect using target extended-remote', gdbserver' enters
multi-process mode.  When the debugged program exits, or you detach
from it, GDB stays connected to gdbserver' even though no program is
running.  The run' and attach' commands instruct gdbserver' to run
or attach to a new program.  The run' command uses set remote
exec-file' (*note set remote exec-file::) to select the program to run.
Command line arguments are supported, except for wildcard expansion and
I/O redirection (*note Arguments::).

To start gdbserver' without supplying an initial command to run or
process ID to attach, use the --multi' command line option.  Then you
can connect using target extended-remote' and start the program you
want to debug.

gdbserver' does not automatically exit in multi-process mode.  You
can terminate it by using monitor exit' (*note Monitor Commands for
gdbserver::).

20.3.1.3 Other Command-Line Arguments for gdbserver'
.....................................................

The --debug' option tells gdbserver' to display extra status
information about the debugging process.  The --remote-debug' option
tells gdbserver' to display remote protocol debug output.  These
options are intended for gdbserver' development and for bug reports to
the developers.

The --wrapper' option specifies a wrapper to launch programs for
debugging.  The option should be followed by the name of the wrapper,
then any command-line arguments to pass to the wrapper, then --'
indicating the end of the wrapper arguments.

gdbserver' runs the specified wrapper program with a combined
command line including the wrapper arguments, then the name of the
program to debug, then any arguments to the program.  The wrapper runs
until it executes your program, and then GDB gains control.

You can use any program that eventually calls execve' with its
arguments as a wrapper.  Several standard Unix utilities do this, e.g.
env' and nohup'.  Any Unix shell script ending with exec "$@"' will also work. For example, you can use env' to pass an environment variable to the debugged program, without setting the variable in gdbserver''s environment:$ gdbserver --wrapper env LD_PRELOAD=libtest.so -- :2222 ./testprog

20.3.2 Connecting to gdbserver'
--------------------------------

Run GDB on the host system.

First make sure you have the necessary symbol files.  Load symbols
for your application using the file' command before you connect.  Use
set sysroot' to locate target libraries (unless your GDB was compiled
with the correct sysroot using --with-sysroot').

The symbol file and target libraries must exactly match the
executable and libraries on the target, with one exception: the files
on the host system should not be stripped, even if the files on the
target system are.  Mismatched or missing files will lead to confusing
results during debugging.  On GNU/Linux targets, mismatched or missing
files may also prevent gdbserver' from debugging multi-threaded
programs.

Connect to your target (*note Connecting to a Remote Target:
Connecting.).  For TCP connections, you must start up gdbserver' prior
to using the target remote' command.  Otherwise you may get an error
whose text depends on the host system, but which usually looks
something like Connection refused'.  Don't use the load' command in
GDB when using gdbserver', since the program is already on the target.

20.3.3 Monitor Commands for gdbserver'
---------------------------------------

During a GDB session using gdbserver', you can use the monitor'
command to send special requests to gdbserver'.  Here are the
available commands.

monitor help'
List the available monitor commands.

monitor set debug 0'
monitor set debug 1'
Disable or enable general debugging messages.

monitor set remote-debug 0'
monitor set remote-debug 1'
Disable or enable specific debugging messages associated with the
remote protocol (*note Remote Protocol::).

monitor set libthread-db-search-path [PATH]'
When this command is issued, PATH is a colon-separated list of
directories to search for libthread_db' (*note set
libthread-db-search-path' will be reset to an empty list.

monitor exit'
Tell gdbserver to exit immediately.  This command should be
followed by disconnect' to close the debugging session.
gdbserver' will detach from any attached processes and kill any
processes it created.  Use monitor exit' to terminate gdbserver'
at the end of a multi-process mode debug session.

20.3.4 Tracepoints support in gdbserver'
-----------------------------------------

On some targets, gdbserver' supports tracepoints, fast tracepoints and
static tracepoints.

For fast or static tracepoints to work, a special library called the
"in-process agent" (IPA), must be loaded in the inferior process.  This
library is built and distributed as an integral part of gdbserver'.
In addition, support for static tracepoints requires building the
in-process agent library with static tracepoints support.  At present,
the UST (LTTng Userspace Tracer, http://lttng.org/ust') tracing engine
is supported.  This support is automatically available if UST
development headers are found in the standard include path when
gdbserver' is built, or if gdbserver' was explicitly configured using
--with-ust' to point at such headers.  You can explicitly disable the
support using --with-ust=no'.

There are several ways to load the in-process agent in your program:

Specifying it as dependency at link time'
You can link your program dynamically with the in-process agent
library.  On most systems, this is accomplished by adding
-linproctrace' to the link command.

Using the system's preloading mechanisms'
You can force loading the in-process agent at startup time by using
support the concept of preloading user defined libraries.  In most
cases, you do that by specifying LD_PRELOAD=libinproctrace.so' in
the environment.  See also the description of gdbserver''s
--wrapper' command line option.

Using GDB to force loading the agent at run time'
On some systems, you can force the inferior to load a shared
library, by calling a dynamic loader function in the inferior that
takes care of dynamically looking up and loading a shared library.
On most Unix systems, the function is dlopen'.  You'll use the
call' command for that.  For example:

(gdb) call dlopen ("libinproctrace.so", ...)

Note that on most Unix systems, for the dlopen' function to be
available, the program needs to be linked with -ldl'.

On systems that have a userspace dynamic loader, like most Unix
systems, when you connect to gdbserver' using target remote', you'll
find that the program is stopped at the dynamic loader's entry point,
and no shared library has been loaded in the program's address space
yet, including the in-process agent.  In that case, before being able
to use any of the fast or static tracepoints features, you need to let
the loader run and load the shared libraries.  The simplest way to do
that is to run the program to the main procedure.  E.g., if debugging a
C or C++ program, start gdbserver' like so:

$gdbserver :9999 myprogram Start GDB and connect to gdbserver' like so, and run to main:$ gdb myprogram
(gdb) target remote myhost:9999
0x00007f215893ba60 in ?? () from /lib64/ld-linux-x86-64.so.2
(gdb) b main
(gdb) continue

The in-process tracing agent library should now be loaded into the
process; you can confirm it with the info sharedlibrary' command,
which will list libinproctrace.so' as loaded in the process.  You are
now ready to install fast tracepoints, list static tracepoint markers,
probe static tracepoints markers, and start tracing.

---------- Footnotes ----------

(1) If you choose a port number that conflicts with another service,
gdbserver' prints an error message and exits.

File: gdb.info,  Node: Remote Configuration,  Next: Remote Stub,  Prev: Server,  Up: Remote Debugging

20.4 Remote Configuration
=========================

This section documents the configuration options available when
debugging remote programs.  For the options related to the File I/O
extensions of the remote protocol, see *note system-call-allowed:
system.

set remoteaddresssize BITS'
Set the maximum size of address in a memory packet to the specified
number of bits.  GDB will mask off the address bits above that
number, when it passes addresses to the remote target.  The
default value is the number of bits in the target's address.

Show the current value of remote address size in bits.

set remotebaud N'
Set the baud rate for the remote serial I/O to N baud.  The value
is used to set the speed of the serial port used for debugging
remote targets.

show remotebaud'
Show the current speed of the remote connection.

set remotebreak'
If set to on, GDB sends a BREAK' signal to the remote when you
type Ctrl-c' to interrupt the program running on the remote.  If
set to off, GDB sends the Ctrl-C' character instead.  The default
is off, since most remote systems expect to see Ctrl-C' as the
interrupt signal.

show remotebreak'
Show whether GDB sends BREAK' or Ctrl-C' to interrupt the remote
program.

set remoteflow on'
set remoteflow off'
Enable or disable hardware flow control (RTS'/CTS') on the
serial port used to communicate to the remote target.

show remoteflow'
Show the current setting of hardware flow control.

set remotelogbase BASE'
Set the base (a.k.a. radix) of logging serial protocol
communications to BASE.  Supported values of BASE are: ascii',
octal', and hex'.  The default is ascii'.

show remotelogbase'
Show the current setting of the radix for logging remote serial
protocol.

set remotelogfile FILE'
Record remote serial communications on the named FILE.  The
default is not to record at all.

show remotelogfile.'
Show the current setting  of the file name on which to record the
serial communications.

set remotetimeout NUM'
Set the timeout limit to wait for the remote target to respond to
NUM seconds.  The default is 2 seconds.

show remotetimeout'
Show the current number of seconds to wait for the remote target
responses.

set remote hardware-watchpoint-limit LIMIT'
set remote hardware-breakpoint-limit LIMIT'
Restrict GDB to using LIMIT remote hardware breakpoint or
watchpoints.  A limit of -1, the default, is treated as unlimited.

set remote exec-file FILENAME'
show remote exec-file'
Select the file used for run' with target extended-remote'.
This should be set to a filename valid on the target system.  If
it is not set, the target will use a default filename (e.g. the
last program run).

set remote interrupt-sequence'
Allow the user to select one of Ctrl-C', a BREAK' or BREAK-g'
as the sequence to the remote target in order to interrupt the
execution.  Ctrl-C' is a default.  Some system prefers BREAK'
which is high level of serial line for some certain time.  Linux
kernel prefers BREAK-g', a.k.a Magic SysRq g.  It is BREAK'
signal followed by character g'.

show interrupt-sequence'
Show which of Ctrl-C', BREAK' or BREAK-g' is sent by GDB to
interrupt the remote program.  BREAK-g' is BREAK signal followed
by g' and also known as Magic SysRq g.

set remote interrupt-on-connect'
Specify whether interrupt-sequence is sent to remote target when
GDB connects to it.  This is mostly needed when you debug Linux
kernel.  Linux kernel expects BREAK' followed by g' which is
known as Magic SysRq g in order to connect GDB.

show interrupt-on-connect'
Show whether interrupt-sequence is sent to remote target when GDB
connects to it.

set tcp auto-retry on'
Enable auto-retry for remote TCP connections.  This is useful if
the remote debugging agent is launched in parallel with GDB; there
is a race condition because the agent may not become ready to
accept the connection before GDB attempts to connect.  When
auto-retry is enabled, if the initial attempt to connect fails,
GDB reattempts to establish the connection using the timeout
specified by set tcp connect-timeout'.

set tcp auto-retry off'
Do not auto-retry failed TCP connections.

show tcp auto-retry'
Show the current auto-retry setting.

set tcp connect-timeout SECONDS'
Set the timeout for establishing a TCP connection to the remote
target to SECONDS.  The timeout affects both polling to retry
failed connections (enabled by set tcp auto-retry on') and
waiting for connections that are merely slow to complete, and
represents an approximate cumulative value.

show tcp connect-timeout'
Show the current connection timeout setting.

The GDB remote protocol autodetects the packets supported by your
debugging stub.  If you need to override the autodetection, you can use
these commands to enable or disable individual packets.  Each packet
can be set to on' (the remote target supports this packet), off' (the
remote target does not support this packet), or auto' (detect remote
target support for this packet).  They all default to auto'.  For more
information about each packet, see *note Remote Protocol::.

During normal use, you should not have to use any of these commands.
If you do, that may be a bug in your remote debugging stub, or a bug in
GDB.  You may want to report the problem to the GDB developers.

For each packet NAME, the command to enable or disable the packet is
set remote NAME-packet'.  The available settings are:

Command Name         Remote Packet           Related Features
fetch-register'     p'                     info registers'
set-register'       P'                     set'
binary-download'    X'                     load', set'
read-aux-vector'    qXfer:auxv:read'       info auxv'
symbol-lookup'      qSymbol'               Detecting
attach'             vAttach'               attach'
verbose-resume'     vCont'                 Stepping or
resuming multiple
run'                vRun'                  run'
software-breakpoint'Z0'                    break'
hardware-breakpoint'Z1'                    hbreak'
write-watchpoint'   Z2'                    watch'
read-watchpoint'    Z3'                    rwatch'
access-watchpoint'  Z4'                    awatch'
target-features'    qXfer:features:read'   set architecture'
library-info'       qXfer:libraries:read'  info
sharedlibrary'
memory-map'         qXfer:memory-map:read' info mem'
read-sdata-object'  qXfer:sdata:read'      print $_sdata' read-spu-object' qXfer:spu:read' info spu' write-spu-object' qXfer:spu:write' info spu' read-siginfo-object'qXfer:siginfo:read' print$_siginfo'
write-siginfo-object'qXfer:siginfo:write'   set _siginfo' threads' qXfer:threads:read' info threads' get-thread-local- qGetTLSAddr' Displaying storage-address' __thread' variables get-thread-information-block-address'qGetTIBAddr' Display MS-Windows Thread Information Block. search-memory' qSearch:memory' find' supported-packets' qSupported' Remote communications parameters pass-signals' QPassSignals' handle SIGNAL' hostio-close-packet'vFile:close' remote get', remote put' hostio-open-packet' vFile:open' remote get', remote put' hostio-pread-packet'vFile:pread' remote get', remote put' hostio-pwrite-packet'vFile:pwrite' remote get', remote put' hostio-unlink-packet'vFile:unlink' remote delete' noack-packet' QStartNoAckMode' Packet acknowledgment osdata' qXfer:osdata:read' info os' query-attached' qAttached' Querying remote process attach state. File: gdb.info, Node: Remote Stub, Prev: Remote Configuration, Up: Remote Debugging 20.5 Implementing a Remote Stub =============================== The stub files provided with GDB implement the target side of the communication protocol, and the GDB side is implemented in the GDB source file remote.c'. Normally, you can simply allow these subroutines to communicate, and ignore the details. (If you're implementing your own stub file, you can still ignore the details: start with one of the existing stub files. sparc-stub.c' is the best organized, and therefore the easiest to read.) To debug a program running on another machine (the debugging "target" machine), you must first arrange for all the usual prerequisites for the program to run by itself. For example, for a C program, you need: 1. A startup routine to set up the C runtime environment; these usually have a name like crt0'. The startup routine may be supplied by your hardware supplier, or you may have to write your own. 2. A C subroutine library to support your program's subroutine calls, notably managing input and output. 3. A way of getting your program to the other machine--for example, a download program. These are often supplied by the hardware manufacturer, but you may have to write your own from hardware documentation. The next step is to arrange for your program to use a serial port to communicate with the machine where GDB is running (the "host" machine). In general terms, the scheme looks like this: _On the host,_ GDB already understands how to use this protocol; when everything else is set up, you can simply use the target remote' command (*note Specifying a Debugging Target: Targets.). _On the target,_ you must link with your program a few special-purpose subroutines that implement the GDB remote serial protocol. The file containing these subroutines is called a "debugging stub". On certain remote targets, you can use an auxiliary program gdbserver' instead of linking a stub into your program. *Note Using the gdbserver' Program: Server, for details. The debugging stub is specific to the architecture of the remote machine; for example, use sparc-stub.c' to debug programs on SPARC boards. These working remote stubs are distributed with GDB: i386-stub.c' For Intel 386 and compatible architectures. m68k-stub.c' For Motorola 680x0 architectures. sh-stub.c' For Renesas SH architectures. sparc-stub.c' For SPARC architectures. sparcl-stub.c' For Fujitsu SPARCLITE architectures. The README' file in the GDB distribution may list other recently added stubs. * Menu: * Stub Contents:: What the stub can do for you * Bootstrapping:: What you must do for the stub * Debug Session:: Putting it all together File: gdb.info, Node: Stub Contents, Next: Bootstrapping, Up: Remote Stub 20.5.1 What the Stub Can Do for You ----------------------------------- The debugging stub for your architecture supplies these three subroutines: set_debug_traps' This routine arranges for handle_exception' to run when your program stops. You must call this subroutine explicitly near the beginning of your program. handle_exception' This is the central workhorse, but your program never calls it explicitly--the setup code arranges for handle_exception' to run when a trap is triggered. handle_exception' takes control when your program stops during execution (for example, on a breakpoint), and mediates communications with GDB on the host machine. This is where the communications protocol is implemented; handle_exception' acts as the GDB representative on the target machine. It begins by sending summary information on the state of your program, then continues to execute, retrieving and transmitting any information GDB needs, until you execute a GDB command that makes your program resume; at that point, handle_exception' returns control to your own code on the target machine. breakpoint' Use this auxiliary subroutine to make your program contain a breakpoint. Depending on the particular situation, this may be the only way for GDB to get control. For instance, if your target machine has some sort of interrupt button, you won't need to call this; pressing the interrupt button transfers control to handle_exception'--in effect, to GDB. On some machines, simply receiving characters on the serial port may also trigger a trap; again, in that situation, you don't need to call breakpoint' from your own program--simply running target remote' from the host GDB session gets control. Call breakpoint' if none of these is true, or if you simply want to make certain your program stops at a predetermined point for the start of your debugging session. File: gdb.info, Node: Bootstrapping, Next: Debug Session, Prev: Stub Contents, Up: Remote Stub 20.5.2 What You Must Do for the Stub ------------------------------------ The debugging stubs that come with GDB are set up for a particular chip architecture, but they have no information about the rest of your debugging target machine. First of all you need to tell the stub how to communicate with the serial port. int getDebugChar()' Write this subroutine to read a single character from the serial port. It may be identical to getchar' for your target system; a different name is used to allow you to distinguish the two if you wish. void putDebugChar(int)' Write this subroutine to write a single character to the serial port. It may be identical to putchar' for your target system; a different name is used to allow you to distinguish the two if you wish. If you want GDB to be able to stop your program while it is running, you need to use an interrupt-driven serial driver, and arrange for it to stop when it receives a ^C' (\003', the control-C character). That is the character which GDB uses to tell the remote system to stop. Getting the debugging target to return the proper status to GDB probably requires changes to the standard stub; one quick and dirty way is to just execute a breakpoint instruction (the "dirty" part is that GDB reports a SIGTRAP' instead of a SIGINT'). Other routines you need to supply are: void exceptionHandler (int EXCEPTION_NUMBER, void *EXCEPTION_ADDRESS)' Write this function to install EXCEPTION_ADDRESS in the exception handling tables. You need to do this because the stub does not have any way of knowing what the exception handling tables on your target system are like (for example, the processor's table might be in ROM, containing entries which point to a table in RAM). EXCEPTION_NUMBER is the exception number which should be changed; its meaning is architecture-dependent (for example, different numbers might represent divide by zero, misaligned access, etc). When this exception occurs, control should be transferred directly to EXCEPTION_ADDRESS, and the processor state (stack, registers, and so on) should be just as it is when a processor exception occurs. So if you want to use a jump instruction to reach EXCEPTION_ADDRESS, it should be a simple jump, not a jump to subroutine. For the 386, EXCEPTION_ADDRESS should be installed as an interrupt gate so that interrupts are masked while the handler runs. The gate should be at privilege level 0 (the most privileged level). The SPARC and 68k stubs are able to mask interrupts themselves without help from exceptionHandler'. void flush_i_cache()' On SPARC and SPARCLITE only, write this subroutine to flush the instruction cache, if any, on your target machine. If there is no instruction cache, this subroutine may be a no-op. On target machines that have instruction caches, GDB requires this function to make certain that the state of your program is stable. You must also make sure this library routine is available: void *memset(void *, int, int)' This is the standard library function memset' that sets an area of memory to a known value. If you have one of the free versions of libc.a', memset' can be found there; otherwise, you must either obtain it from your hardware manufacturer, or write your own. If you do not use the GNU C compiler, you may need other standard library subroutines as well; this varies from one stub to another, but in general the stubs are likely to use any of the common library subroutines which GCC' generates as inline code. File: gdb.info, Node: Debug Session, Prev: Bootstrapping, Up: Remote Stub 20.5.3 Putting it All Together ------------------------------ In summary, when your program is ready to debug, you must follow these steps. 1. Make sure you have defined the supporting low-level routines (*note What You Must Do for the Stub: Bootstrapping.): getDebugChar', putDebugChar', flush_i_cache', memset', exceptionHandler'. 2. Insert these lines near the top of your program: set_debug_traps(); breakpoint(); 3. For the 680x0 stub only, you need to provide a variable called exceptionHook'. Normally you just use: void (*exceptionHook)() = 0; but if before calling set_debug_traps', you set it to point to a function in your program, that function is called when GDB' continues after stopping on a trap (for example, bus error). The function indicated by exceptionHook' is called with one parameter: an int' which is the exception number. 4. Compile and link together: your program, the GDB debugging stub for your target architecture, and the supporting subroutines. 5. Make sure you have a serial connection between your target machine and the GDB host, and identify the serial port on the host. 6. Download your program to your target machine (or get it there by whatever means the manufacturer provides), and start it. 7. Start GDB on the host, and connect to the target (*note Connecting to a Remote Target: Connecting.). File: gdb.info, Node: Configurations, Next: Controlling GDB, Prev: Remote Debugging, Up: Top 21 Configuration-Specific Information ************************************* While nearly all GDB commands are available for all native and cross versions of the debugger, there are some exceptions. This chapter describes things that are only available in certain configurations. There are three major categories of configurations: native configurations, where the host and target are the same, embedded operating system configurations, which are usually the same for several different processor architectures, and bare embedded processors, which are quite different from each other. * Menu: * Native:: * Embedded OS:: * Embedded Processors:: * Architectures:: File: gdb.info, Node: Native, Next: Embedded OS, Up: Configurations 21.1 Native =========== This section describes details specific to particular native configurations. * Menu: * HP-UX:: HP-UX * BSD libkvm Interface:: Debugging BSD kernel memory images * SVR4 Process Information:: SVR4 process information * DJGPP Native:: Features specific to the DJGPP port * Cygwin Native:: Features specific to the Cygwin port * Hurd Native:: Features specific to GNU Hurd * Neutrino:: Features specific to QNX Neutrino * Darwin:: Features specific to Darwin File: gdb.info, Node: HP-UX, Next: BSD libkvm Interface, Up: Native 21.1.1 HP-UX ------------ On HP-UX systems, if you refer to a function or variable name that begins with a dollar sign, GDB searches for a user or system name first, before it searches for a convenience variable. File: gdb.info, Node: BSD libkvm Interface, Next: SVR4 Process Information, Prev: HP-UX, Up: Native 21.1.2 BSD libkvm Interface --------------------------- BSD-derived systems (FreeBSD/NetBSD/OpenBSD) have a kernel memory interface that provides a uniform interface for accessing kernel virtual memory images, including live systems and crash dumps. GDB uses this interface to allow you to debug live kernels and kernel crash dumps on many native BSD configurations. This is implemented as a special kvm' debugging target. For debugging a live system, load the currently running kernel into GDB and connect to the kvm' target: (gdb) target kvm For debugging crash dumps, provide the file name of the crash dump as an argument: (gdb) target kvm /var/crash/bsd.0 Once connected to the kvm' target, the following commands are available: kvm pcb' Set current context from the "Process Control Block" (PCB) address. kvm proc' Set current context from proc address. This command isn't available on modern FreeBSD systems. File: gdb.info, Node: SVR4 Process Information, Next: DJGPP Native, Prev: BSD libkvm Interface, Up: Native 21.1.3 SVR4 Process Information ------------------------------- Many versions of SVR4 and compatible systems provide a facility called /proc' that can be used to examine the image of a running process using file-system subroutines. If GDB is configured for an operating system with this facility, the command info proc' is available to report information about the process running your program, or about any process running on your system. info proc' works only on SVR4 systems that include the procfs' code. This includes, as of this writing, GNU/Linux, OSF/1 (Digital Unix), Solaris, Irix, and Unixware, but not HP-UX, for example. info proc' info proc PROCESS-ID' Summarize available information about any running process. If a process ID is specified by PROCESS-ID, display information about that process; otherwise display information about the program being debugged. The summary includes the debugged process ID, the command line used to invoke it, its current working directory, and its executable file's absolute file name. On some systems, PROCESS-ID can be of the form [PID]/TID' which specifies a certain thread ID within a process. If the optional PID part is missing, it means a thread from the process being debugged (the leading /' still needs to be present, or else GDB will interpret the number as a process ID rather than a thread ID). info proc mappings' Report the memory address space ranges accessible in the program, with information on whether the process has read, write, or execute access rights to each range. On GNU/Linux systems, each memory range includes the object file which is mapped to that range, instead of the memory access rights to that range. info proc stat' info proc status' These subcommands are specific to GNU/Linux systems. They show the process-related information, including the user ID and group ID; how many threads are there in the process; its virtual memory usage; the signals that are pending, blocked, and ignored; its TTY; its consumption of system and user time; its stack size; its nice' value; etc. For more information, see the proc' man page (type man 5 proc' from your shell prompt). info proc all' Show all the information about the process described under all of the above info proc' subcommands. set procfs-trace' This command enables and disables tracing of procfs' API calls. show procfs-trace' Show the current state of procfs' API call tracing. set procfs-file FILE' Tell GDB to write procfs' API trace to the named FILE. GDB appends the trace info to the previous contents of the file. The default is to display the trace on the standard output. show procfs-file' Show the file to which procfs' API trace is written. proc-trace-entry' proc-trace-exit' proc-untrace-entry' proc-untrace-exit' These commands enable and disable tracing of entries into and exits from the syscall' interface. info pidlist' For QNX Neutrino only, this command displays the list of all the processes and all the threads within each process. info meminfo' For QNX Neutrino only, this command displays the list of all mapinfos. File: gdb.info, Node: DJGPP Native, Next: Cygwin Native, Prev: SVR4 Process Information, Up: Native 21.1.4 Features for Debugging DJGPP Programs -------------------------------------------- DJGPP is a port of the GNU development tools to MS-DOS and MS-Windows. DJGPP programs are 32-bit protected-mode programs that use the "DPMI" (DOS Protected-Mode Interface) API to run on top of real-mode DOS systems and their emulations. GDB supports native debugging of DJGPP programs, and defines a few commands specific to the DJGPP port. This subsection describes those commands. info dos' This is a prefix of DJGPP-specific commands which print information about the target system and important OS structures. info dos sysinfo' This command displays assorted information about the underlying platform: the CPU type and features, the OS version and flavor, the DPMI version, and the available conventional and DPMI memory. info dos gdt' info dos ldt' info dos idt' These 3 commands display entries from, respectively, Global, Local, and Interrupt Descriptor Tables (GDT, LDT, and IDT). The descriptor tables are data structures which store a descriptor for each segment that is currently in use. The segment's selector is an index into a descriptor table; the table entry for that index holds the descriptor's base address and limit, and its attributes and access rights. A typical DJGPP program uses 3 segments: a code segment, a data segment (used for both data and the stack), and a DOS segment (which allows access to DOS/BIOS data structures and absolute addresses in conventional memory). However, the DPMI host will usually define additional segments in order to support the DPMI environment. These commands allow to display entries from the descriptor tables. Without an argument, all entries from the specified table are displayed. An argument, which should be an integer expression, means display a single entry whose index is given by the argument. For example, here's a convenient way to display information about the debugged program's data segment: (gdb) info dos ldtds'
0x13f: base=0x11970000 limit=0x0009ffff 32-Bit Data (Read/Write, Exp-up)'

This comes in handy when you want to see whether a pointer is
outside the data segment's limit (i.e. "garbled").

info dos pde'
info dos pte'
These two commands display entries from, respectively, the Page
Directory and the Page Tables.  Page Directories and Page Tables
are data structures which control how virtual memory addresses are
mapped into physical addresses.  A Page Table includes an entry
for every page of memory that is mapped into the program's address
space; there may be several Page Tables, each one holding up to
4096 entries.  A Page Directory has up to 4096 entries, one each
for every Page Table that is currently in use.

Without an argument, info dos pde' displays the entire Page
Directory, and info dos pte' displays all the entries in all of
the Page Tables.  An argument, an integer expression, given to the
info dos pde' command means display only that entry from the Page
Directory table.  An argument given to the info dos pte' command
means display entries from a single Page Table, the one pointed to
by the specified entry in the Page Directory.

These commands are useful when your program uses "DMA" (Direct
Memory Access), which needs physical addresses to program the DMA
controller.

These commands are supported only with some DPMI servers.

info dos address-pte ADDR'
This command displays the Page Table entry for a specified linear
address.  The argument ADDR is a linear address which should
already have the appropriate segment's base address added to it,
because this command accepts addresses which may belong to _any_
segment.  For example, here's how to display the Page Table entry
for the page where a variable i' is stored:

(gdb) info dos address-pte __djgpp_base_address + (char *)&i'
Page Table entry for address 0x11a00d30:'
Base=0x02698000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0xd30'

This says that i' is stored at offset 0xd30' from the page whose
physical base address is 0x02698000', and shows all the
attributes of that page.

Note that you must cast the addresses of variables to a char *',
since otherwise the value of __djgpp_base_address', the base
address of all variables and functions in a DJGPP program, will be
added using the rules of C pointer arithmetics: if i' is declared
an int', GDB will add 4 times the value of __djgpp_base_address'
to the address of i'.

Here's another example, it displays the Page Table entry for the
transfer buffer:

(gdb) info dos address-pte *((unsigned *)&_go32_info_block + 3)'
Page Table entry for address 0x29110:'
Base=0x00029000 Dirty Acc. Not-Cached Write-Back Usr Read-Write +0x110'

(The + 3' offset is because the transfer buffer's address is the
3rd member of the _go32_info_block' structure.)  The output
clearly shows that this DPMI server maps the addresses in
conventional memory 1:1, i.e. the physical (0x00029000' +
0x110') and linear (0x29110') addresses are identical.

This command is supported only with some DPMI servers.

In addition to native debugging, the DJGPP port supports remote
debugging via a serial data link.  The following commands are specific
to remote serial debugging in the DJGPP port of GDB.

set com1base ADDR'
This command sets the base I/O port address of the COM1' serial
port.

set com1irq IRQ'
This command sets the "Interrupt Request" (IRQ') line to use for
the COM1' serial port.

There are similar commands set com2base', set com3irq', etc. for
setting the port address and the IRQ' lines for the other 3 COM
ports.

The related commands show com1base', show com1irq' etc.  display
the current settings of the base address and the IRQ' lines used
by the COM ports.

info serial'
This command prints the status of the 4 DOS serial ports.  For each
port, it prints whether it's active or not, its I/O base address
and IRQ number, whether it uses a 16550-style FIFO, its baudrate,
and the counts of various errors encountered so far.

File: gdb.info,  Node: Cygwin Native,  Next: Hurd Native,  Prev: DJGPP Native,  Up: Native

21.1.5 Features for Debugging MS Windows PE Executables
-------------------------------------------------------

GDB supports native debugging of MS Windows programs, including DLLs
with and without symbolic debugging information.

MS-Windows programs that call SetConsoleMode' to switch off the
special meaning of the Ctrl-C' keystroke cannot be interrupted by
typing C-c'.  For this reason, GDB on MS-Windows supports C-<BREAK>'
as an alternative interrupt key sequence, which can be used to
interrupt the debuggee even if it ignores C-c'.

There are various additional Cygwin-specific commands, described in
this section.  Working with DLLs that have no debugging symbols is
described in *note Non-debug DLL Symbols::.

info w32'
This is a prefix of MS Windows-specific commands which print
information about the target system and important OS structures.

info w32 selector'
This command displays information returned by the Win32 API
GetThreadSelectorEntry' function.  It takes an optional argument
that is evaluated to a long value to give the information about
this given selector.  Without argument, this command displays
information about the six segment registers.

info w32 thread-information-block'
This command displays thread specific information stored in the
Thread Information Block (readable on the X86 CPU family using
$fs' selector for 32-bit programs and $gs' for 64-bit programs).

info dll'
This is a Cygwin-specific alias of info shared'.

dll-symbols'
This command loads symbols from a dll similarly to add-sym command
but without the need to specify a base address.

set cygwin-exceptions MODE'
If MODE is on', GDB will break on exceptions that happen inside
the Cygwin DLL.  If MODE is off', GDB will delay recognition of
exceptions, and may ignore some exceptions which seem to be caused
by internal Cygwin DLL "bookkeeping".  This option is meant
primarily for debugging the Cygwin DLL itself; the default value
is off' to avoid annoying GDB users with false SIGSEGV' signals.

show cygwin-exceptions'
Displays whether GDB will break on exceptions that happen inside
the Cygwin DLL itself.

set new-console MODE'
If MODE is on' the debuggee will be started in a new console on
next start.  If MODE is off', the debuggee will be started in the
same console as the debugger.

show new-console'
Displays whether a new console is used when the debuggee is
started.

set new-group MODE'
This boolean value controls whether the debuggee should start a
new group or stay in the same group as the debugger.  This affects
the way the Windows OS handles Ctrl-C'.

show new-group'
Displays current value of new-group boolean.

set debugevents'
This boolean value adds debug output concerning kernel events
related to the debuggee seen by the debugger.  This includes
events that signal thread and process creation and exit, DLL
produced by the Windows OutputDebugString' API call.

set debugexec'
This boolean value adds debug output concerning execute events
(such as resume thread) seen by the debugger.

set debugexceptions'
This boolean value adds debug output concerning exceptions in the
debuggee seen by the debugger.

set debugmemory'
This boolean value adds debug output concerning debuggee memory
reads and writes by the debugger.

set shell'
This boolean values specifies whether the debuggee is called via a
shell or directly (default value is on).

show shell'
Displays if the debuggee will be started with a shell.

* Non-debug DLL Symbols::  Support for DLLs without debugging symbols

File: gdb.info,  Node: Non-debug DLL Symbols,  Up: Cygwin Native

21.1.5.1 Support for DLLs without Debugging Symbols
...................................................

Very often on windows, some of the DLLs that your program relies on do
not include symbolic debugging information (for example,
kernel32.dll').  When GDB doesn't recognize any debugging symbols in a
DLL, it relies on the minimal amount of symbolic information contained
in the DLL's export table.  This section describes working with such
symbols, known internally to GDB as "minimal symbols".

Note that before the debugged program has started execution, no DLLs
will have been loaded.  The easiest way around this problem is simply to
start the program -- either by setting a breakpoint or letting the
program run once to completion.  It is also possible to force GDB to
load a particular DLL before starting the executable -- see the shared
library information in *note Files::, or the dll-symbols' command in
*note Cygwin Native::.  Currently, explicitly loading symbols from a
DLL with no debugging information will cause the symbol names to be
duplicated in GDB's lookup table, which may adversely affect symbol
lookup performance.

21.1.5.2 DLL Name Prefixes
..........................

In keeping with the naming conventions used by the Microsoft debugging
tools, DLL export symbols are made available with a prefix based on the
DLL name, for instance KERNEL32!CreateFileA'.  The plain name is also
entered into the symbol table, so CreateFileA' is often sufficient.
In some cases there will be name clashes within a program (particularly
if the executable itself includes full debugging symbols) necessitating
the use of the fully qualified name when referring to the contents of
the DLL.  Use single-quotes around the name to avoid the exclamation
mark ("!")  being interpreted as a language operator.

Note that the internal name of the DLL may be all upper-case, even
though the file name of the DLL is lower-case, or vice-versa.  Since
symbols within GDB are _case-sensitive_ this may cause some confusion.
If in doubt, try the info functions' and info variables' commands or
even maint print msymbols' (*note Symbols::). Here's an example:

(gdb) info function CreateFileA
All functions matching regular expression "CreateFileA":

Non-debugging symbols:
0x77e885f4  CreateFileA
0x77e885f4  KERNEL32!CreateFileA

(gdb) info function !
All functions matching regular expression "!":

Non-debugging symbols:
0x6100114c  cygwin1!__assert
0x61004034  cygwin1!_dll_crt0@0
0x61004240  cygwin1!dll_crt0(per_process *)
[etc...]

21.1.5.3 Working with Minimal Symbols
.....................................

Symbols extracted from a DLL's export table do not contain very much
type information. All that GDB can do is guess whether a symbol refers
to a function or variable depending on the linker section that contains
the symbol. Also note that the actual contents of the memory contained
in a DLL are not available unless the program is running. This means
that you cannot examine the contents of a variable or disassemble a
function within a DLL without a running program.

Variables are generally treated as pointers and dereferenced
automatically. For this reason, it is often necessary to prefix a
variable name with the address-of operator ("&") and provide explicit
type information in the command. Here's an example of the type of
problem:

(gdb) print 'cygwin1!__argv'
$1 = 268572168 (gdb) x 'cygwin1!__argv' 0x10021610: "\230y\"" And two possible solutions: (gdb) print ((char **)'cygwin1!__argv')[0]$2 = 0x22fd98 "/cygdrive/c/mydirectory/myprogram"

(gdb) x/2x &'cygwin1!__argv'
0x610c0aa8 <cygwin1!__argv>:    0x10021608      0x00000000
(gdb) x/x 0x10021608
0x10021608:     0x0022fd98
(gdb) x/s 0x0022fd98
0x22fd98:        "/cygdrive/c/mydirectory/myprogram"

Setting a break point within a DLL is possible even before the
program starts execution. However, under these circumstances, GDB can't
examine the initial instructions of the function in order to skip the
function's frame set-up code. You can work around this by using "*&" to
set the breakpoint at a raw memory address:

Breakpoint 1 at 0x1e04eff0

The author of these extensions is not entirely convinced that
setting a break point within a shared DLL like kernel32.dll' is
completely safe.

File: gdb.info,  Node: Hurd Native,  Next: Neutrino,  Prev: Cygwin Native,  Up: Native

21.1.6 Commands Specific to GNU Hurd Systems
--------------------------------------------

This subsection describes GDB commands specific to the GNU Hurd native
debugging.

set signals'
set sigs'
This command toggles the state of inferior signal interception by
GDB.  Mach exceptions, such as breakpoint traps, are not affected
by this command.  sigs' is a shorthand alias for signals'.

show signals'
show sigs'
Show the current state of intercepting inferior's signals.

set signal-thread'
This command tells GDB which thread is the libc' signal thread.
That thread is run when a signal is delivered to a running
process.  set sigthread' is the shorthand alias of set

show sigthread'
These two commands show which thread will run when the inferior is
delivered a signal.

set stopped'
This commands tells GDB that the inferior process is stopped, as
with the SIGSTOP' signal.  The stopped process can be continued
by delivering a signal to it.

show stopped'
This command shows whether GDB thinks the debuggee is stopped.

set exceptions'
Use this command to turn off trapping of exceptions in the
inferior.  When exception trapping is off, neither breakpoints nor
single-stepping will work.  To restore the default, set exception
trapping on.

show exceptions'
Show the current state of trapping exceptions in the inferior.

set task pause'
This command toggles task suspension when GDB has control.
Setting it to on takes effect immediately, and the task is
suspended whenever GDB gets control.  Setting it to off will take
effect the next time the inferior is continued.  If this option is
set to off, you can use set thread default pause on' or set
thread pause on' (see below) to pause individual threads.

Show the current state of task suspension.

set task detach-suspend-count'
This command sets the suspend count the task will be left with when
GDB detaches from it.

Show the suspend count the task will be left with when detaching.

set task exception-port'
This command sets the task exception port to which GDB will
forward exceptions.  The argument should be the value of the "send
rights" of the task.  set task excp' is a shorthand alias.

set noninvasive'
This command switches GDB to a mode that is the least invasive as
far as interfering with the inferior is concerned.  This is the
same as using set task pause', set exceptions', and set
signals' to values opposite to the defaults.

info send-rights'
info receive-rights'
info port-rights'
info port-sets'
info ports'
info psets'
These commands display information about, respectively, send
rights, receive rights, port rights, port sets, and dead names of
a task.  There are also shorthand aliases: info ports' for info
port-rights' and info psets' for info port-sets'.

set thread pause'
This command toggles current thread suspension when GDB has
control.  Setting it to on takes effect immediately, and the
current thread is suspended whenever GDB gets control.  Setting it
to off will take effect the next time the inferior is continued.
Normally, this command has no effect, since when GDB has control,
the whole task is suspended.  However, if you used set task pause
off' (see above), this command comes in handy to suspend only the

show thread pause'
This command shows the state of current thread suspension.

This command sets whether the current thread is allowed to run.

show thread run'
Show whether the current thread is allowed to run.

This command sets the suspend count GDB will leave on a thread
when detaching.  This number is relative to the suspend count
found by GDB when it notices the thread; use set thread
takeover-suspend-count' to force it to an absolute value.

Show the suspend count GDB will leave on the thread when detaching.

set thread exception-port'
Set the thread exception port to which to forward exceptions.  This
overrides the port set by set task exception-port' (see above).
set thread excp' is the shorthand alias.

set thread takeover-suspend-count'
Normally, GDB's thread suspend counts are relative to the value
GDB finds when it notices each thread.  This command changes the
suspend counts to be absolute instead.

show thread default'
Each of the above set thread' commands has a set thread default'
counterpart (e.g., set thread default pause', set thread default
exception-port', etc.).  The thread default' variety of commands
sets the default thread properties for all threads; you can then
change the properties of individual threads with the non-default
commands.

File: gdb.info,  Node: Neutrino,  Next: Darwin,  Prev: Hurd Native,  Up: Native

21.1.7 QNX Neutrino
-------------------

GDB provides the following commands specific to the QNX Neutrino target:

set debug nto-debug'
When set to on, enables debugging messages specific to the QNX
Neutrino support.

show debug nto-debug'
Show the current state of QNX Neutrino messages.

File: gdb.info,  Node: Darwin,  Prev: Neutrino,  Up: Native

21.1.8 Darwin
-------------

GDB provides the following commands specific to the Darwin target:

set debug darwin NUM'
When set to a non zero value, enables debugging messages specific
to the Darwin support.  Higher values produce more verbose output.

show debug darwin'
Show the current state of Darwin messages.

set debug mach-o NUM'
When set to a non zero value, enables debugging messages while GDB
is reading Darwin object files.  ("Mach-O" is the file format used
on Darwin for object and executable files.)  Higher values produce
more verbose output.  This is a command to diagnose problems
internal to GDB and should not be needed in normal usage.

show debug mach-o'
Show the current state of Mach-O file messages.

set mach-exceptions on'
set mach-exceptions off'
On Darwin, faults are first reported as a Mach exception and are
then mapped to a Posix signal.  Use this command to turn on
trapping of Mach exceptions in the inferior.  This might be
sometimes useful to better understand the cause of a fault.  The
default is off.

show mach-exceptions'
Show the current state of exceptions trapping.

File: gdb.info,  Node: Embedded OS,  Next: Embedded Processors,  Prev: Native,  Up: Configurations

21.2 Embedded Operating Systems
===============================

This section describes configurations involving the debugging of
embedded operating systems that are available for several different
architectures.

* VxWorks::                     Using GDB with VxWorks

GDB includes the ability to debug programs running on various
real-time operating systems.

File: gdb.info,  Node: VxWorks,  Up: Embedded OS

21.2.1 Using GDB with VxWorks
-----------------------------

target vxworks MACHINENAME'
A VxWorks system, attached via TCP/IP.  The argument MACHINENAME
is the target system's machine name or IP address.

On VxWorks, load' links FILENAME dynamically on the current target
system as well as adding its symbols in GDB.

GDB enables developers to spawn and debug tasks running on networked
VxWorks targets from a Unix host.  Already-running tasks spawned from
the VxWorks shell can also be debugged.  GDB uses code that runs on
both the Unix host and on the VxWorks target.  The program gdb' is
installed and executed on the Unix host.  (It may be installed with the
name vxgdb', to distinguish it from a GDB for debugging programs on
the host itself.)

VxWorks-timeout ARGS'
All VxWorks-based targets now support the option vxworks-timeout'.
This option is set by the user, and  ARGS represents the number of
seconds GDB waits for responses to rpc's.  You might use this if
your VxWorks target is a slow software simulator or is on the far
side of a thin network line.

The following information on connecting to VxWorks was current when
this manual was produced; newer releases of VxWorks may use revised
procedures.

To use GDB with VxWorks, you must rebuild your VxWorks kernel to
include the remote debugging interface routines in the VxWorks library
rdb.a'.  To do this, define INCLUDE_RDB' in the VxWorks configuration
file configAll.h' and rebuild your VxWorks kernel.  The resulting
kernel contains rdb.a', and spawns the source debugging task
tRdbTask' when VxWorks is booted.  For more information on configuring
and remaking VxWorks, see the manufacturer's manual.

Once you have included rdb.a' in your VxWorks system image and set
your Unix execution search path to find GDB, you are ready to run GDB.
From your Unix host, run gdb' (or vxgdb', depending on your
installation).

GDB comes up showing the prompt:

(vxgdb)

* VxWorks Connection::          Connecting to VxWorks
* VxWorks Attach::              Running tasks

File: gdb.info,  Node: VxWorks Connection,  Next: VxWorks Download,  Up: VxWorks

21.2.1.1 Connecting to VxWorks
..............................

The GDB command target' lets you connect to a VxWorks target on the
network.  To connect to a target whose host name is "tt'", type:

(vxgdb) target vxworks tt

GDB displays messages like these:

Attaching remote machine across net...
Connected to tt.

GDB then attempts to read the symbol tables of any object modules
loaded into the VxWorks target since it was last booted.  GDB locates
these files by searching the directories listed in the command search
path (*note Your Program's Environment: Environment.); if it fails to
find an object file, it displays a message such as:

prog.o: No such file or directory.

When this happens, add the appropriate directory to the search path
with the GDB command path', and execute the target' command again.

File: gdb.info,  Node: VxWorks Download,  Next: VxWorks Attach,  Prev: VxWorks Connection,  Up: VxWorks

.........................

If you have connected to the VxWorks target and you want to debug an
object that has not yet been loaded, you can use the GDB load' command
to download a file from Unix to VxWorks incrementally.  The object file
given as an argument to the load' command is actually opened twice:
first by the VxWorks target in order to download the code, then by GDB
in order to read the symbol table.  This can lead to problems if the
current working directories on the two systems differ.  If both systems
have NFS mounted the same filesystems, you can avoid these problems by
using absolute paths.  Otherwise, it is simplest to set the working
directory on both systems to the directory in which the object file
resides, and then to reference the file by its name, without any path.
For instance, a program prog.o' may reside in VXPATH/vw/demo/rdb' in
VxWorks and in HOSTPATH/vw/demo/rdb' on the host.  To load this
program, type this on VxWorks:

-> cd "VXPATH/vw/demo/rdb"

Then, in GDB, type:

(vxgdb) cd HOSTPATH/vw/demo/rdb

GDB displays a response similar to this:

Reading symbol data from wherever/vw/demo/rdb/prog.o... done.

You can also use the load' command to reload an object module after
editing and recompiling the corresponding source file.  Note that this
makes GDB delete all currently-defined breakpoints, auto-displays, and
convenience variables, and to clear the value history.  (This is
necessary in order to preserve the integrity of debugger's data
structures that reference the target system's symbol table.)

File: gdb.info,  Node: VxWorks Attach,  Prev: VxWorks Download,  Up: VxWorks

......................

You can also attach to an existing task using the attach' command as
follows:

or suspended when you attach to it.  Running tasks are suspended at the
time of attachment.

File: gdb.info,  Node: Embedded Processors,  Next: Architectures,  Prev: Embedded OS,  Up: Configurations

21.3 Embedded Processors
========================

This section goes into details specific to particular embedded
configurations.

Whenever a specific embedded processor has a simulator, GDB allows
to send an arbitrary command to the simulator.

sim COMMAND'
Send an arbitrary COMMAND string to the simulator.  Consult the
documentation for the specific simulator in use for information

* ARM::                         ARM RDI
* M32R/D::                      Renesas M32R/D
* M68K::                        Motorola M68K
* MicroBlaze::			Xilinx MicroBlaze
* MIPS Embedded::               MIPS Embedded
* OpenRISC 1000::               OpenRisc 1000
* PA::                          HP PA Embedded
* PowerPC Embedded::            PowerPC Embedded
* Sparclet::                    Tsqware Sparclet
* Sparclite::                   Fujitsu Sparclite
* Z8000::                       Zilog Z8000
* AVR::                         Atmel AVR
* CRIS::                        CRIS
* Super-H::                     Renesas Super-H

File: gdb.info,  Node: ARM,  Next: M32R/D,  Up: Embedded Processors

21.3.1 ARM
----------

target rdi DEV'
ARM Angel monitor, via RDI library interface to ADP protocol.  You
may use this target to communicate with both boards running the
Angel monitor, or with the EmbeddedICE JTAG debug device.

target rdp DEV'
ARM Demon monitor.

GDB provides the following ARM-specific commands:

set arm disassembler'
This commands selects from a list of disassembly styles.  The
"std"' style is the standard style.

show arm disassembler'
Show the current disassembly style.

set arm apcs32'
This command toggles ARM operation mode between 32-bit and 26-bit.

show arm apcs32'
Display the current usage of the ARM 32-bit mode.

set arm fpu FPUTYPE'
This command sets the ARM floating-point unit (FPU) type.  The
argument FPUTYPE can be one of these:

auto'
Determine the FPU type by querying the OS ABI.

softfpa'
Software FPU, with mixed-endian doubles on little-endian ARM
processors.

fpa'
GCC-compiled FPA co-processor.

softvfp'
Software FPU with pure-endian doubles.

vfp'
VFP co-processor.

show arm fpu'
Show the current type of the FPU.

set arm abi'
This command forces GDB to use the specified ABI.

show arm abi'
Show the currently used ABI.

set arm fallback-mode (arm|thumb|auto)'
GDB uses the symbol table, when available, to determine whether
instructions are ARM or Thumb.  This command controls GDB's
default behavior when the symbol table is not available.  The
default is auto', which causes GDB to use the current execution
mode (from the T' bit in the CPSR' register).

show arm fallback-mode'
Show the current fallback instruction mode.

set arm force-mode (arm|thumb|auto)'
This command overrides use of the symbol table to determine whether
instructions are ARM or Thumb.  The default is auto', which
causes GDB to use the symbol table and then the setting of set
arm fallback-mode'.

show arm force-mode'
Show the current forced instruction mode.

set debug arm'
Toggle whether to display ARM-specific debugging messages from the
ARM target support subsystem.

show debug arm'
Show whether ARM-specific debugging messages are enabled.

The following commands are available when an ARM target is debugged
using the RDI interface:

rdilogfile [FILE]'
Set the filename for the ADP (Angel Debugger Protocol) packet log.
With an argument, sets the log file to the specified FILE.  With
no argument, show the current log file name.  The default log file
is rdi.log'.

rdilogenable [ARG]'
Control logging of ADP packets.  With an argument of 1 or "yes"'
enables logging, with an argument 0 or "no"' disables it.  With
no arguments displays the current setting.  When logging is
enabled, ADP packets exchanged between GDB and the RDI target
device are logged to a file.

set rdiromatzero'
Tell GDB whether the target has ROM at address 0.  If on, vector
catching is disabled, so that zero address can be used.  If off
(the default), vector catching is enabled.  For this command to
take effect, it needs to be invoked prior to the target rdi'
command.

show rdiromatzero'
Show the current setting of ROM at zero address.

set rdiheartbeat'
Enable or disable RDI heartbeat packets.  It is not recommended to
turn on this option, since it confuses ARM and EPI JTAG interface,
as well as the Angel monitor.

show rdiheartbeat'
Show the setting of RDI heartbeat packets.

target sim [SIMARGS] ...'
The GDB ARM simulator accepts the following optional arguments.

--swi-support=TYPE'
Tell the simulator which SWI interfaces to support.  TYPE may
be a comma separated list of the following values.  The
default value is all'.

none'

demon'

angel'

redboot'

all'

File: gdb.info,  Node: M32R/D,  Next: M68K,  Prev: ARM,  Up: Embedded Processors

21.3.2 Renesas M32R/D and M32R/SDI
----------------------------------

target m32r DEV'
Renesas M32R/D ROM monitor.

target m32rsdi DEV'
Renesas M32R SDI server, connected via parallel port to the board.

The following GDB commands are specific to the M32R monitor:

set download-path PATH'
Set the default path for finding downloadable SREC files.

Show the default path for downloadable SREC files.

set board-address ADDR'
Set the IP address for the M32R-EVA target board.

Show the current IP address of the target board.

set server-address ADDR'
Set the IP address for the download server, which is the GDB's
host machine.

upload [FILE]'
Upload the specified SREC FILE via the monitor's Ethernet upload
capability.  If no FILE argument is given, the current executable

Test the upload' command.

The following commands are available for M32R/SDI:

sdireset'
This command resets the SDI connection.

sdistatus'
This command shows the SDI connection status.

debug_chaos'
Instructs the remote that M32R/Chaos debugging is to be used.

use_debug_dma'
Instructs the remote to use the DEBUG_DMA method of accessing
memory.

use_mon_code'
Instructs the remote to use the MON_CODE method of accessing
memory.

use_ib_break'
Instructs the remote to set breakpoints by IB break.

use_dbt_break'
Instructs the remote to set breakpoints by DBT.

File: gdb.info,  Node: M68K,  Next: MicroBlaze,  Prev: M32R/D,  Up: Embedded Processors

21.3.3 M68k
-----------

The Motorola m68k configuration includes ColdFire support, and a target
command for the following ROM monitor.

target dbug DEV'
dBUG ROM monitor for Motorola ColdFire.

File: gdb.info,  Node: MicroBlaze,  Next: MIPS Embedded,  Prev: M68K,  Up: Embedded Processors

21.3.4 MicroBlaze
-----------------

The MicroBlaze is a soft-core processor supported on various Xilinx
FPGAs, such as Spartan or Virtex series.  Boards with these processors
usually have JTAG ports which connect to a host system running the
Xilinx Embedded Development Kit (EDK) or Software Development Kit (SDK).
This host system is used to download the configuration bitstream to the
target FPGA.  The Xilinx Microprocessor Debugger (XMD) program
communicates with the target board using the JTAG interface and
presents a gdbserver' interface to the board.  By default xmd' uses
port 1234'.  (While it is possible to change this default port, it
requires the use of undocumented xmd' commands.  Contact Xilinx
support if you need to do this.)

Use these GDB commands to connect to the MicroBlaze target processor.

target remote :1234'
Use this command to connect to the target if you are running GDB
on the same system as xmd'.

target remote XMD-HOST:1234'
Use this command to connect to the target if it is connected to
xmd' running on a different system named XMD-HOST.

Use this command to download a program to the MicroBlaze target.

set debug microblaze N'
Enable MicroBlaze-specific debugging messages if non-zero.

show debug microblaze N'
Show MicroBlaze-specific debugging level.

File: gdb.info,  Node: MIPS Embedded,  Next: OpenRISC 1000,  Prev: MicroBlaze,  Up: Embedded Processors

21.3.5 MIPS Embedded
--------------------

GDB can use the MIPS remote debugging protocol to talk to a MIPS board
attached to a serial line.  This is available when you configure GDB
with --target=mips-idt-ecoff'.

Use these GDB commands to specify the connection to your target
board:

target mips PORT'
To run a program on the board, start up gdb' with the name of
your program as the argument.  To connect to the board, use the
command target mips PORT', where PORT is the name of the serial
port connected to the board.  If the program has not already been
downloaded to the board, you may use the load' command to
download it.  You can then use all the usual GDB commands.

For example, this sequence connects to the target board through a
serial port, and loads and runs a program called PROG through the
debugger:

host$gdb PROG GDB is free software and ... (gdb) target mips /dev/ttyb (gdb) load PROG (gdb) run target mips HOSTNAME:PORTNUMBER' On some GDB host configurations, you can specify a TCP connection (for instance, to a serial line managed by a terminal concentrator) instead of a serial port, using the syntax HOSTNAME:PORTNUMBER'. target pmon PORT' PMON ROM monitor. target ddb PORT' NEC's DDB variant of PMON for Vr4300. target lsi PORT' LSI variant of PMON. target r3900 DEV' Densan DVE-R3900 ROM monitor for Toshiba R3900 Mips. target array DEV' Array Tech LSI33K RAID controller board. GDB also supports these special commands for MIPS targets: set mipsfpu double' set mipsfpu single' set mipsfpu none' set mipsfpu auto' show mipsfpu' If your target board does not support the MIPS floating point coprocessor, you should use the command set mipsfpu none' (if you need this, you may wish to put the command in your GDB init file). This tells GDB how to find the return value of functions which return floating point values. It also allows GDB to avoid saving the floating point registers when calling functions on the board. If you are using a floating point coprocessor with only single precision floating point support, as on the R4650 processor, use the command set mipsfpu single'. The default double precision floating point coprocessor may be selected using set mipsfpu double'. In previous versions the only choices were double precision or no floating point, so set mipsfpu on' will select double precision and set mipsfpu off' will select no floating point. As usual, you can inquire about the mipsfpu' variable with show mipsfpu'. set timeout SECONDS' set retransmit-timeout SECONDS' show timeout' show retransmit-timeout' You can control the timeout used while waiting for a packet, in the MIPS remote protocol, with the set timeout SECONDS' command. The default is 5 seconds. Similarly, you can control the timeout used while waiting for an acknowledgment of a packet with the set retransmit-timeout SECONDS' command. The default is 3 seconds. You can inspect both values with show timeout' and show retransmit-timeout'. (These commands are _only_ available when GDB is configured for --target=mips-idt-ecoff'.) The timeout set by set timeout' does not apply when GDB is waiting for your program to stop. In that case, GDB waits forever because it has no way of knowing how long the program is going to run before stopping. set syn-garbage-limit NUM' Limit the maximum number of characters GDB should ignore when it tries to synchronize with the remote target. The default is 10 characters. Setting the limit to -1 means there's no limit. show syn-garbage-limit' Show the current limit on the number of characters to ignore when trying to synchronize with the remote system. set monitor-prompt PROMPT' Tell GDB to expect the specified PROMPT string from the remote monitor. The default depends on the target: pmon target PMON' ddb target NEC010' lsi target PMON>' show monitor-prompt' Show the current strings GDB expects as the prompt from the remote monitor. set monitor-warnings' Enable or disable monitor warnings about hardware breakpoints. This has effect only for the lsi' target. When on, GDB will display warning messages whose codes are returned by the lsi' PMON monitor for breakpoint commands. show monitor-warnings' Show the current setting of printing monitor warnings. pmon COMMAND' This command allows sending an arbitrary COMMAND string to the monitor. The monitor must be in debug mode for this to work. File: gdb.info, Node: OpenRISC 1000, Next: PA, Prev: MIPS Embedded, Up: Embedded Processors 21.3.6 OpenRISC 1000 -------------------- See OR1k Architecture document (www.opencores.org') for more information about platform and commands. target jtag jtag://HOST:PORT' Connects to remote JTAG server. JTAG remote server can be either an or1ksim or JTAG server, connected via parallel port to the board. Example: target jtag jtag://localhost:9999' or1ksim COMMAND' If connected to or1ksim' OpenRISC 1000 Architectural Simulator, proprietary commands can be executed. info or1k spr' Displays spr groups. info or1k spr GROUP' info or1k spr GROUPNO' Displays register names in selected group. info or1k spr GROUP REGISTER' info or1k spr REGISTER' info or1k spr GROUPNO REGISTERNO' info or1k spr REGISTERNO' Shows information about specified spr register. spr GROUP REGISTER VALUE' spr REGISTER VALUE' spr GROUPNO REGISTERNO VALUE' spr REGISTERNO VALUE' Writes VALUE to specified spr register. Some implementations of OpenRISC 1000 Architecture also have hardware trace. It is very similar to GDB trace, except it does not interfere with normal program execution and is thus much faster. Hardware breakpoints/watchpoint triggers can be set using: $LEA/$LDATA' Load effective address/data $SEA/$SDATA' Store effective address/data $AEA/$ADATA' Access effective address ($SEA or $LEA) or data ($SDATA/$LDATA) $FETCH'
Fetch data

When triggered, it can capture low level data, like: PC', LSEA',
LDATA', SDATA', READSPR', WRITESPR', INSTR'.

htrace' commands:
hwatch CONDITIONAL'
Set hardware watchpoint on combination of Load/Store Effective
Address(es) or Data.  For example:

hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)'

hwatch ($LEA == my_var) && ($LDATA < 50) || ($SEA == my_var) && ($SDATA >= 50)'

htrace info'
Display information about current HW trace configuration.

htrace trigger CONDITIONAL'
Set starting criteria for HW trace.

htrace qualifier CONDITIONAL'
Set acquisition qualifier for HW trace.

htrace stop CONDITIONAL'
Set HW trace stopping criteria.

htrace record [DATA]*'
Selects the data to be recorded, when qualifier is met and HW
trace was triggered.

htrace enable'
htrace disable'
Enables/disables the HW trace.

htrace rewind [FILENAME]'
Clears currently recorded trace data.

If filename is specified, new trace file is made and any newly
collected data will be written there.

htrace print [START [LEN]]'
Prints trace buffer, using current record configuration.

htrace mode continuous'
Set continuous trace mode.

htrace mode suspend'
Set suspend trace mode.

File: gdb.info,  Node: PA,  Next: PowerPC Embedded,  Prev: OpenRISC 1000,  Up: Embedded Processors

21.3.8 HP PA Embedded
---------------------

target op50n DEV'
OP50N monitor, running on an OKI HPPA board.

target w89k DEV'
W89K monitor, running on a Winbond HPPA board.

File: gdb.info,  Node: PowerPC Embedded,  Next: Sparclet,  Prev: PA,  Up: Embedded Processors

21.3.7 PowerPC Embedded
-----------------------

GDB supports using the DVC (Data Value Compare) register to implement
in hardware simple hardware watchpoint conditions of the form:

(gdb) watch ADDRESS|VARIABLE \
if  ADDRESS|VARIABLE == CONSTANT EXPRESSION

The DVC register will be automatically used whenever GDB detects
such pattern in a condition expression.  This feature is available in
native GDB running on a Linux kernel version 2.6.34 or newer.

GDB provides the following PowerPC-specific commands:

set powerpc soft-float'
show powerpc soft-float'
Force GDB to use (or not use) a software floating point calling
convention.  By default, GDB selects the calling convention based
on the selected architecture and the provided executable file.

set powerpc vector-abi'
show powerpc vector-abi'
Force GDB to use the specified calling convention for vector
arguments and return values.  The valid options are auto';
generic', to avoid vector registers even if they are present;
altivec', to use AltiVec registers; and spe' to use SPE
registers.  By default, GDB selects the calling convention based
on the selected architecture and the provided executable file.

target dink32 DEV'
DINK32 ROM monitor.

target ppcbug DEV'

target ppcbug1 DEV'
PPCBUG ROM monitor for PowerPC.

target sds DEV'
SDS monitor, running on a PowerPC board (such as Motorola's ADS).

The following commands specific to the SDS protocol are supported by
GDB:

set sdstimeout NSEC'
Set the timeout for SDS protocol reads to be NSEC seconds.  The
default is 2 seconds.

show sdstimeout'
Show the current value of the SDS timeout.

sds COMMAND'
Send the specified COMMAND string to the SDS monitor.

File: gdb.info,  Node: Sparclet,  Next: Sparclite,  Prev: PowerPC Embedded,  Up: Embedded Processors

21.3.9 Tsqware Sparclet
-----------------------

GDB enables developers to debug tasks running on Sparclet targets from
a Unix host.  GDB uses code that runs on both the Unix host and on the
Sparclet target.  The program gdb' is installed and executed on the
Unix host.

remotetimeout ARGS'
GDB supports the option remotetimeout'.  This option is set by
the user, and  ARGS represents the number of seconds GDB waits for
responses.

When compiling for debugging, include the options -g' to get debug
information and -Ttext' to relocate the program to where you wish to
load it on the target.  You may also want to add the options -n' or
-N' in order to reduce the size of the sections.  Example:

sparclet-aout-gcc prog.c -Ttext 0x12010000 -g -o prog -N

You can use objdump' to verify that the addresses are what you
intended:

sparclet-aout-objdump --headers --syms prog

Once you have set your Unix execution search path to find GDB, you
are ready to run GDB.  From your Unix host, run gdb' (or
sparclet-aout-gdb', depending on your installation).

GDB comes up showing the prompt:

(gdbslet)

* Sparclet File::                Setting the file to debug
* Sparclet Connection::          Connecting to Sparclet
* Sparclet Execution::           Running and debugging

File: gdb.info,  Node: Sparclet File,  Next: Sparclet Connection,  Up: Sparclet

21.3.9.1 Setting File to Debug
..............................

The GDB command file' lets you choose with program to debug.

(gdbslet) file prog

GDB then attempts to read the symbol table of prog'.  GDB locates
the file by searching the directories listed in the command search path.
If the file was compiled with debug information (option -g'), source
files will be searched as well.  GDB locates the source files by
searching the directories listed in the directory search path (*note
Your Program's Environment: Environment.).  If it fails to find a file,
it displays a message such as:

prog: No such file or directory.

When this happens, add the appropriate directories to the search
paths with the GDB commands path' and dir', and execute the target'
command again.

File: gdb.info,  Node: Sparclet Connection,  Next: Sparclet Download,  Prev: Sparclet File,  Up: Sparclet

21.3.9.2 Connecting to Sparclet
...............................

The GDB command target' lets you connect to a Sparclet target.  To
connect to a target on serial port "ttya'", type:

(gdbslet) target sparclet /dev/ttya
Remote target sparclet connected to /dev/ttya
main () at ../prog.c:3

GDB displays messages like these:

Connected to ttya.

File: gdb.info,  Node: Sparclet Download,  Next: Sparclet Execution,  Prev: Sparclet Connection,  Up: Sparclet

..........................

Once connected to the Sparclet target, you can use the GDB load'
command to download the file from the host to the target.  The file
name and load offset should be given as arguments to the load' command.
Since the file format is aout, the program must be loaded to the
starting address.  You can use objdump' to find out what this value
is.  The load offset is an offset which is added to the VMA (virtual
memory address) of each of the file's sections.  For instance, if the
program prog' was linked to text address 0x1201000, with data at
0x12010160 and bss at 0x12010170, in GDB, type:

(gdbslet) load prog 0x12010000
Loading section .text, size 0xdb0 vma 0x12010000

If the code is loaded at a different address then what the program
was linked to, you may need to use the section' and add-symbol-file'
commands to tell GDB where to map the symbol table.

File: gdb.info,  Node: Sparclet Execution,  Prev: Sparclet Download,  Up: Sparclet

21.3.9.4 Running and Debugging
..............................

You can now begin debugging the task using GDB's execution control
commands, b', step', run', etc.  See the GDB manual for the list of
commands.

(gdbslet) b main
Breakpoint 1 at 0x12010000: file prog.c, line 3.
(gdbslet) run
Starting program: prog
Breakpoint 1, main (argc=1, argv=0xeffff21c) at prog.c:3
3        char *symarg = 0;
(gdbslet) step
4        char *execarg = "hello!";
(gdbslet)

File: gdb.info,  Node: Sparclite,  Next: Z8000,  Prev: Sparclet,  Up: Embedded Processors

21.3.10 Fujitsu Sparclite
-------------------------

target sparclite DEV'
Fujitsu sparclite boards, used only for the purpose of loading.
You must use an additional command to debug the program.  For
example: target remote DEV using GDB standard remote protocol.

File: gdb.info,  Node: Z8000,  Next: AVR,  Prev: Sparclite,  Up: Embedded Processors

21.3.11 Zilog Z8000
-------------------

When configured for debugging Zilog Z8000 targets, GDB includes a Z8000
simulator.

For the Z8000 family, target sim' simulates either the Z8002 (the
unsegmented variant of the Z8000 architecture) or the Z8001 (the
segmented variant).  The simulator recognizes which architecture is
appropriate by inspecting the object code.

target sim ARGS'
Debug programs on a simulated CPU.  If the simulator supports setup
options, specify them via ARGS.

After specifying this target, you can debug programs for the simulated
CPU in the same style as programs for your host computer; use the
file' command to load a new program image, the run' command to run
your program, and so on.

As well as making available all the usual machine registers (*note
Registers: Registers.), the Z8000 simulator provides three additional
items of information as specially named registers:

cycles'
Counts clock-ticks in the simulator.

insts'
Counts instructions run in the simulator.

time'
Execution time in 60ths of a second.

You can refer to these values in GDB expressions with the usual
conventions; for example, b fputc if $cycles>5000' sets a conditional breakpoint that suspends only after at least 5000 simulated clock ticks. File: gdb.info, Node: AVR, Next: CRIS, Prev: Z8000, Up: Embedded Processors 21.3.12 Atmel AVR ----------------- When configured for debugging the Atmel AVR, GDB supports the following AVR-specific commands: info io_registers' This command displays information about the AVR I/O registers. For each register, GDB prints its number and value. File: gdb.info, Node: CRIS, Next: Super-H, Prev: AVR, Up: Embedded Processors 21.3.13 CRIS ------------ When configured for debugging CRIS, GDB provides the following CRIS-specific commands: set cris-version VER' Set the current CRIS version to VER, either 10' or 32'. The CRIS version affects register names and sizes. This command is useful in case autodetection of the CRIS version fails. show cris-version' Show the current CRIS version. set cris-dwarf2-cfi' Set the usage of DWARF-2 CFI for CRIS debugging. The default is on'. Change to off' when using gcc-cris' whose version is below R59'. show cris-dwarf2-cfi' Show the current state of using DWARF-2 CFI. set cris-mode MODE' Set the current CRIS mode to MODE. It should only be changed when debugging in guru mode, in which case it should be set to guru' (the default is normal'). show cris-mode' Show the current CRIS mode. File: gdb.info, Node: Super-H, Prev: CRIS, Up: Embedded Processors 21.3.14 Renesas Super-H ----------------------- For the Renesas Super-H processor, GDB provides these commands: regs' Show the values of all Super-H registers. set sh calling-convention CONVENTION' Set the calling-convention used when calling functions from GDB. Allowed values are gcc', which is the default setting, and renesas'. With the gcc' setting, functions are called using the GCC calling convention. If the DWARF-2 information of the called function specifies that the function follows the Renesas calling convention, the function is called using the Renesas calling convention. If the calling convention is set to renesas', the Renesas calling convention is always used, regardless of the DWARF-2 information. This can be used to override the default of gcc' if debug information is missing, or the compiler does not emit the DWARF-2 calling convention entry for a function. show sh calling-convention' Show the current calling convention setting. File: gdb.info, Node: Architectures, Prev: Embedded Processors, Up: Configurations 21.4 Architectures ================== This section describes characteristics of architectures that affect all uses of GDB with the architecture, both native and cross. * Menu: * i386:: * A29K:: * Alpha:: * MIPS:: * HPPA:: HP PA architecture * SPU:: Cell Broadband Engine SPU architecture * PowerPC:: File: gdb.info, Node: i386, Next: A29K, Up: Architectures 21.4.1 x86 Architecture-specific Issues --------------------------------------- set struct-convention MODE' Set the convention used by the inferior to return struct's and union's from functions to MODE. Possible values of MODE are "pcc"', "reg"', and "default"' (the default). "default"' or "pcc"' means that struct's are returned on the stack, while "reg"' means that a struct' or a union' whose size is 1, 2, 4, or 8 bytes will be returned in a register. show struct-convention' Show the current setting of the convention to return struct's from functions. File: gdb.info, Node: A29K, Next: Alpha, Prev: i386, Up: Architectures 21.4.2 A29K ----------- set rstack_high_address ADDRESS' On AMD 29000 family processors, registers are saved in a separate "register stack". There is no way for GDB to determine the extent of this stack. Normally, GDB just assumes that the stack is "large enough". This may result in GDB referencing memory locations that do not exist. If necessary, you can get around this problem by specifying the ending address of the register stack with the set rstack_high_address' command. The argument should be an address, which you probably want to precede with 0x' to specify in hexadecimal. show rstack_high_address' Display the current limit of the register stack, on AMD 29000 family processors. File: gdb.info, Node: Alpha, Next: MIPS, Prev: A29K, Up: Architectures 21.4.3 Alpha ------------ See the following section. File: gdb.info, Node: MIPS, Next: HPPA, Prev: Alpha, Up: Architectures 21.4.4 MIPS ----------- Alpha- and MIPS-based computers use an unusual stack frame, which sometimes requires GDB to search backward in the object code to find the beginning of a function. To improve response time (especially for embedded applications, where GDB may be restricted to a slow serial line for this search) you may want to limit the size of this search, using one of these commands: set heuristic-fence-post LIMIT' Restrict GDB to examining at most LIMIT bytes in its search for the beginning of a function. A value of 0 (the default) means there is no limit. However, except for 0, the larger the limit the more bytes heuristic-fence-post' must search and therefore the longer it takes to run. You should only need to use this command when debugging a stripped executable. show heuristic-fence-post' Display the current limit. These commands are available _only_ when GDB is configured for debugging programs on Alpha or MIPS processors. Several MIPS-specific commands are available when debugging MIPS programs: set mips abi ARG' Tell GDB which MIPS ABI is used by the inferior. Possible values of ARG are: auto' The default ABI associated with the current binary (this is the default). o32' o64' n32' n64' eabi32' eabi64' auto' show mips abi' Show the MIPS ABI used by GDB to debug the inferior. set mipsfpu' show mipsfpu' *Note set mipsfpu: MIPS Embedded. set mips mask-address ARG' This command determines whether the most-significant 32 bits of 64-bit MIPS addresses are masked off. The argument ARG can be on', off', or auto'. The latter is the default setting, which lets GDB determine the correct value. show mips mask-address' Show whether the upper 32 bits of MIPS addresses are masked off or not. set remote-mips64-transfers-32bit-regs' This command controls compatibility with 64-bit MIPS targets that transfer data in 32-bit quantities. If you have an old MIPS 64 target that transfers 32 bits for some registers, like SR and FSR, and 64 bits for other registers, set this option to on'. show remote-mips64-transfers-32bit-regs' Show the current setting of compatibility with older MIPS 64 targets. set debug mips' This command turns on and off debugging messages for the MIPS-specific target code in GDB. show debug mips' Show the current setting of MIPS debugging messages. File: gdb.info, Node: HPPA, Next: SPU, Prev: MIPS, Up: Architectures 21.4.5 HPPA ----------- When GDB is debugging the HP PA architecture, it provides the following special commands: set debug hppa' This command determines whether HPPA architecture-specific debugging messages are to be displayed. show debug hppa' Show whether HPPA debugging messages are displayed. maint print unwind ADDRESS' This command displays the contents of the unwind table entry at the given ADDRESS. File: gdb.info, Node: SPU, Next: PowerPC, Prev: HPPA, Up: Architectures 21.4.6 Cell Broadband Engine SPU architecture --------------------------------------------- When GDB is debugging the Cell Broadband Engine SPU architecture, it provides the following special commands: info spu event' Display SPU event facility status. Shows current event mask and pending event status. info spu signal' Display SPU signal notification facility status. Shows pending signal-control word and signal notification mode of both signal notification channels. info spu mailbox' Display SPU mailbox facility status. Shows all pending entries, in order of processing, in each of the SPU Write Outbound, SPU Write Outbound Interrupt, and SPU Read Inbound mailboxes. info spu dma' Display MFC DMA status. Shows all pending commands in the MFC DMA queue. For each entry, opcode, tag, class IDs, effective and local store addresses and transfer size are shown. info spu proxydma' Display MFC Proxy-DMA status. Shows all pending commands in the MFC Proxy-DMA queue. For each entry, opcode, tag, class IDs, effective and local store addresses and transfer size are shown. When GDB is debugging a combined PowerPC/SPU application on the Cell Broadband Engine, it provides in addition the following special commands: set spu stop-on-load ARG' Set whether to stop for new SPE threads. When set to on', GDB will give control to the user when a new SPE thread enters its main' function. The default is off'. show spu stop-on-load' Show whether to stop for new SPE threads. set spu auto-flush-cache ARG' Set whether to automatically flush the software-managed cache. When set to on', GDB will automatically cause the SPE software-managed cache to be flushed whenever SPE execution stops. This provides a consistent view of PowerPC memory that is accessed via the cache. If an application does not use the software-managed cache, this option has no effect. show spu auto-flush-cache' Show whether to automatically flush the software-managed cache. File: gdb.info, Node: PowerPC, Prev: SPU, Up: Architectures 21.4.7 PowerPC -------------- When GDB is debugging the PowerPC architecture, it provides a set of pseudo-registers to enable inspection of 128-bit wide Decimal Floating Point numbers stored in the floating point registers. These values must be stored in two consecutive registers, always starting at an even register like f0' or f2'. The pseudo-registers go from $dl0' through $dl15', and are formed by joining the even/odd register pairs f0' and f1' for $dl0', f2'
and f3' for $dl1' and so on. For POWER7 processors, GDB provides a set of pseudo-registers, the 64-bit wide Extended Floating Point Registers (f32' through f63'). File: gdb.info, Node: Controlling GDB, Next: Extending GDB, Prev: Configurations, Up: Top 22 Controlling GDB ****************** You can alter the way GDB interacts with you by using the set' command. For commands controlling how GDB displays data, see *note Print Settings: Print Settings. Other settings are described here. * Menu: * Prompt:: Prompt * Editing:: Command editing * Command History:: Command history * Screen Size:: Screen size * Numbers:: Numbers * ABI:: Configuring the current ABI * Auto-loading:: Automatically loading associated files * Messages/Warnings:: Optional warnings and messages * Debugging Output:: Optional messages about internal happenings * Other Misc Settings:: Other Miscellaneous Settings File: gdb.info, Node: Prompt, Next: Editing, Up: Controlling GDB 22.1 Prompt =========== GDB indicates its readiness to read a command by printing a string called the "prompt". This string is normally (gdb)'. You can change the prompt string with the set prompt' command. For instance, when debugging GDB with GDB, it is useful to change the prompt in one of the GDB sessions so that you can always tell which one you are talking to. _Note:_ set prompt' does not add a space for you after the prompt you set. This allows you to set a prompt which ends in a space or a prompt that does not. set prompt NEWPROMPT' Directs GDB to use NEWPROMPT as its prompt string henceforth. show prompt' Prints a line of the form: Gdb's prompt is: YOUR-PROMPT' File: gdb.info, Node: Editing, Next: Command History, Prev: Prompt, Up: Controlling GDB 22.2 Command Editing ==================== GDB reads its input commands via the "Readline" interface. This GNU library provides consistent behavior for programs which provide a command line interface to the user. Advantages are GNU Emacs-style or "vi"-style inline editing of commands, csh'-like history substitution, and a storage and recall of command history across debugging sessions. You may control the behavior of command line editing in GDB with the command set'. set editing' set editing on' Enable command line editing (enabled by default). set editing off' Disable command line editing. show editing' Show whether command line editing is enabled. *Note Command Line Editing: (rluserman)Command Line Editing, for more details about the Readline interface. Users unfamiliar with GNU Emacs or vi' are encouraged to read that chapter. File: gdb.info, Node: Command History, Next: Screen Size, Prev: Editing, Up: Controlling GDB 22.3 Command History ==================== GDB can keep track of the commands you type during your debugging sessions, so that you can be certain of precisely what happened. Use these commands to manage the GDB command history facility. GDB uses the GNU History library, a part of the Readline package, to provide the history facility. *Note Using History Interactively: (history)Using History Interactively, for the detailed description of the History library. To issue a command to GDB without affecting certain aspects of the state which is seen by users, prefix it with server ' (*note Server Prefix::). This means that this command will not affect the command history, nor will it affect GDB's notion of which command to repeat if <RET> is pressed on a line by itself. The server prefix does not affect the recording of values into the value history; to print a value without recording it into the value history, use the output' command instead of the print' command. Here is the description of GDB commands related to command history. set history filename FNAME' Set the name of the GDB command history file to FNAME. This is the file where GDB reads an initial command history list, and where it writes the command history from this session when it exits. You can access this list through history expansion or through the history command editing characters listed below. This file defaults to the value of the environment variable GDBHISTFILE', or to ./.gdb_history' (./_gdb_history' on MS-DOS) if this variable is not set. set history save' set history save on' Record command history in a file, whose name may be specified with the set history filename' command. By default, this option is disabled. set history save off' Stop recording command history in a file. set history size SIZE' Set the number of commands which GDB keeps in its history list. This defaults to the value of the environment variable HISTSIZE', or to 256 if this variable is not set. History expansion assigns special meaning to the character !'. *Note Event Designators: (history)Event Designators, for more details. Since !' is also the logical not operator in C, history expansion is off by default. If you decide to enable history expansion with the set history expansion on' command, you may sometimes need to follow !' (when it is used as logical not, in an expression) with a space or a tab to prevent it from being expanded. The readline history facilities do not attempt substitution on the strings !=' and !(', even when history expansion is enabled. The commands to control history expansion are: set history expansion on' set history expansion' Enable history expansion. History expansion is off by default. set history expansion off' Disable history expansion. show history' show history filename' show history save' show history size' show history expansion' These commands display the state of the GDB history parameters. show history' by itself displays all four states. show commands' Display the last ten commands in the command history. show commands N' Print ten commands centered on command number N. show commands +' Print ten commands just after the commands last printed. File: gdb.info, Node: Screen Size, Next: Numbers, Prev: Command History, Up: Controlling GDB 22.4 Screen Size ================ Certain commands to GDB may produce large amounts of information output to the screen. To help you read all of it, GDB pauses and asks you for input at the end of each page of output. Type <RET> when you want to continue the output, or q' to discard the remaining output. Also, the screen width setting determines when to wrap lines of output. Depending on what is being printed, GDB tries to break the line at a readable place, rather than simply letting it overflow onto the following line. Normally GDB knows the size of the screen from the terminal driver software. For example, on Unix GDB uses the termcap data base together with the value of the TERM' environment variable and the stty rows' and stty cols' settings. If this is not correct, you can override it with the set height' and set width' commands: set height LPP' show height' set width CPL' show width' These set' commands specify a screen height of LPP lines and a screen width of CPL characters. The associated show' commands display the current settings. If you specify a height of zero lines, GDB does not pause during output no matter how long the output is. This is useful if output is to a file or to an editor buffer. Likewise, you can specify set width 0' to prevent GDB from wrapping its output. set pagination on' set pagination off' Turn the output pagination on or off; the default is on. Turning pagination off is the alternative to set height 0'. Note that running GDB with the --batch' option (*note -batch: Mode Options.) also automatically disables pagination. show pagination' Show the current pagination mode. File: gdb.info, Node: Numbers, Next: ABI, Prev: Screen Size, Up: Controlling GDB 22.5 Numbers ============ You can always enter numbers in octal, decimal, or hexadecimal in GDB by the usual conventions: octal numbers begin with 0', decimal numbers end with .', and hexadecimal numbers begin with 0x'. Numbers that neither begin with 0' or 0x', nor end with a .' are, by default, entered in base 10; likewise, the default display for numbers--when no particular format is specified--is base 10. You can change the default base for both input and output with the commands described below. set input-radix BASE' Set the default base for numeric input. Supported choices for BASE are decimal 8, 10, or 16. BASE must itself be specified either unambiguously or using the current input radix; for example, any of set input-radix 012 set input-radix 10. set input-radix 0xa sets the input base to decimal. On the other hand, set input-radix 10' leaves the input radix unchanged, no matter what it was, since 10', being without any leading or trailing signs of its base, is interpreted in the current radix. Thus, if the current radix is 16, 10' is interpreted in hex, i.e. as 16 decimal, which doesn't change the radix. set output-radix BASE' Set the default base for numeric display. Supported choices for BASE are decimal 8, 10, or 16. BASE must itself be specified either unambiguously or using the current input radix. show input-radix' Display the current default base for numeric input. show output-radix' Display the current default base for numeric display. set radix [BASE]' show radix' These commands set and show the default base for both input and output of numbers. set radix' sets the radix of input and output to the same base; without an argument, it resets the radix back to its default value of 10. File: gdb.info, Node: ABI, Next: Auto-loading, Prev: Numbers, Up: Controlling GDB 22.6 Configuring the Current ABI ================================ GDB can determine the "ABI" (Application Binary Interface) of your application automatically. However, sometimes you need to override its conclusions. Use these commands to manage GDB's view of the current ABI. One GDB configuration can debug binaries for multiple operating system targets, either via remote debugging or native emulation. GDB will autodetect the "OS ABI" (Operating System ABI) in use, but you can override its conclusion using the set osabi' command. One example where this is useful is in debugging of binaries which use an alternate C library (e.g. UCLIBC for GNU/Linux) which does not have the same identifying marks that the standard C library for your platform provides. show osabi' Show the OS ABI currently in use. set osabi' With no argument, show the list of registered available OS ABI's. set osabi ABI' Set the current OS ABI to ABI. Generally, the way that an argument of type float' is passed to a function depends on whether the function is prototyped. For a prototyped (i.e. ANSI/ISO style) function, float' arguments are passed unchanged, according to the architecture's convention for float'. For unprototyped (i.e. K&R style) functions, float' arguments are first promoted to type double' and then passed. Unfortunately, some forms of debug information do not reliably indicate whether a function is prototyped. If GDB calls a function that is not marked as prototyped, it consults set coerce-float-to-double'. set coerce-float-to-double' set coerce-float-to-double on' Arguments of type float' will be promoted to double' when passed to an unprototyped function. This is the default setting. set coerce-float-to-double off' Arguments of type float' will be passed directly to unprototyped functions. show coerce-float-to-double' Show the current setting of promoting float' to double'. GDB needs to know the ABI used for your program's C++ objects. The correct C++ ABI depends on which C++ compiler was used to build your application. GDB only fully supports programs with a single C++ ABI; if your program contains code using multiple C++ ABI's or if GDB can not identify your program's ABI correctly, you can tell GDB which ABI to use. Currently supported ABI's include "gnu-v2", for g++' versions before 3.0, "gnu-v3", for g++' versions 3.0 and later, and "hpaCC" for the HP ANSI C++ compiler. Other C++ compilers may use the "gnu-v2" or "gnu-v3" ABI's as well. The default setting is "auto". show cp-abi' Show the C++ ABI currently in use. set cp-abi' With no argument, show the list of supported C++ ABI's. set cp-abi ABI' set cp-abi auto' Set the current C++ ABI to ABI, or return to automatic detection. File: gdb.info, Node: Auto-loading, Next: Messages/Warnings, Prev: ABI, Up: Controlling GDB 22.7 Automatically loading associated files =========================================== GDB sometimes reads files with commands and settings automatically, without being explicitly told so by the user. We call this feature "auto-loading". While auto-loading is useful for automatically adapting GDB to the needs of your project, it can sometimes produce unexpected results or introduce security risks (e.g., if the file comes from untrusted sources). Note that loading of these associated files (including the local .gdbinit' file) requires accordingly configured auto-load safe-path' (*note Auto-loading safe path::). For these reasons, GDB includes commands and options to let you control when to auto-load files and which files should be auto-loaded. set auto-load off' Globally disable loading of all auto-loaded files. You may want to use this command with the -iex' option (*note Option -init-eval-command::) such as:$ gdb -iex "set auto-load off" untrusted-executable corefile

Be aware that system init file (*note System-wide configuration::)
and init files from your home directory (*note Home Directory Init
File::) still get read (as they come from generally trusted
directories).  To prevent GDB from auto-loading even those init
files, use the -nx' option (*note Mode Options::), in addition to
set auto-load no'.

Show whether auto-loading of each specific auto-load' file(s) is
enabled or disabled.

gdb-scripts:  Auto-loading of canned sequences of commands scripts is on.
local-gdbinit:  Auto-loading of .gdbinit script from current directory
is on.
python-scripts:  Auto-loading of Python scripts is on.
safe-path:  List of directories from which it is safe to auto-load files
is $debugdir:$datadir/auto-load.
scripts-directory:  List of directories from which to load auto-loaded scripts
is $debugdir:$datadir/auto-load.

Print whether each specific auto-load' file(s) have been

gdb-scripts:
Yes     /home/user/gdb/gdb-gdb.gdb
local-gdbinit:  Local .gdbinit file "/home/user/gdb/.gdbinit" has been
python-scripts:
Yes     /home/user/gdb/gdb-gdb.py

These are various kinds of files GDB can automatically load:

* *Note objfile-gdb.py file::, controlled by *note set auto-load
python-scripts::.

* *Note objfile-gdb.gdb file::, controlled by *note set auto-load
gdb-scripts::.

* *Note dotdebug_gdb_scripts section::, controlled by *note set

* *Note Init File in the Current Directory::, controlled by *note

* *Note libthread_db.so.1 file::, controlled by *note set auto-load

These are GDB control commands for the auto-loading:

*Note show auto-load::.              Show setting of all kinds of files.
*Note info auto-load::.              Show state of all kinds of files.
*Note set auto-load gdb-scripts::.   Control for GDB command scripts.
*Note show auto-load gdb-scripts::.  Show setting of GDB command scripts.
*Note info auto-load gdb-scripts::.  Show state of GDB command scripts.
*Note set auto-load                  Control for GDB Python scripts.
python-scripts::.
*Note show auto-load                 Show setting of GDB Python scripts.
python-scripts::.
*Note info auto-load                 Show state of GDB Python scripts.
python-scripts::.
*Note set auto-load                  Control for GDB auto-loaded scripts
scripts-directory::.                 location.
*Note show auto-load                 Show GDB auto-loaded scripts
scripts-directory::.                 location.
*Note set auto-load local-gdbinit::. Control for init file in the
current directory.
*Note show auto-load                 Show setting of init file in the
local-gdbinit::.                     current directory.
*Note info auto-load                 Show state of init file in the
local-gdbinit::.                     current directory.
library.
library.
library.
*Note set auto-load safe-path::.     Control directories trusted for
*Note show auto-load safe-path::.    Show directories trusted for

* Init File in the Current Directory:: set/show/info auto-load local-gdbinit'
* libthread_db.so.1 file::             set/show/info auto-load libthread-db'
* objfile-gdb.gdb file::               set/show/info auto-load gdb-script'
* Auto-loading safe path::             set/show/info auto-load safe-path'

File: gdb.info,  Node: Init File in the Current Directory,  Next: libthread_db.so.1 file,  Up: Auto-loading

22.7.1 Automatically loading init file in the current directory
---------------------------------------------------------------

By default, GDB reads and executes the canned sequences of commands
from init file (if any) in the current working directory, see *note
Init File in the Current Directory during Startup::.

Note that loading of this local .gdbinit' file also requires
path::).

set auto-load local-gdbinit [on|off]'
Enable or disable the auto-loading of canned sequences of commands
(*note Sequences::) found in init file in the current directory.

Show whether auto-loading of canned sequences of commands from
init file in the current directory is enabled or disabled.

info auto-load local-gdbinit'
Print whether canned sequences of commands from init file in the
current directory have been auto-loaded.

File: gdb.info,  Node: libthread_db.so.1 file,  Next: objfile-gdb.gdb file,  Prev: Init File in the Current Directory,  Up: Auto-loading

-----------------------------------------------------

This feature is currently present only on GNU/Linux native hosts.

GDB reads in some cases thread debugging library from places specific
to the inferior (*note set libthread-db-search-path::).

The special libthread-db-search-path' entry $sdir' is processed without checking this set auto-load libthread-db' switch as system libraries have to be trusted in general. In all other cases of libthread-db-search-path' entries GDB checks first if set auto-load libthread-db' is enabled before trying to open such thread debugging library. Note that loading of this debugging library also requires accordingly configured auto-load safe-path' (*note Auto-loading safe path::). set auto-load libthread-db [on|off]' Enable or disable the auto-loading of inferior specific thread debugging library. show auto-load libthread-db' Show whether auto-loading of inferior specific thread debugging library is enabled or disabled. info auto-load libthread-db' Print the list of all loaded inferior specific thread debugging libraries and for each such library print list of inferior PIDs using it. File: gdb.info, Node: objfile-gdb.gdb file, Next: Auto-loading safe path, Prev: libthread_db.so.1 file, Up: Auto-loading 22.7.3 The OBJFILE-gdb.gdb' file --------------------------------- GDB tries to load an OBJFILE-gdb.gdb' file containing canned sequences of commands (*note Sequences::), as long as set auto-load gdb-scripts' is set to on'. Note that loading of this script file also requires accordingly configured auto-load safe-path' (*note Auto-loading safe path::). For more background refer to the similar Python scripts auto-loading description (*note objfile-gdb.py file::). set auto-load gdb-scripts [on|off]' Enable or disable the auto-loading of canned sequences of commands scripts. show auto-load gdb-scripts' Show whether auto-loading of canned sequences of commands scripts is enabled or disabled. info auto-load gdb-scripts [REGEXP]' Print the list of all canned sequences of commands scripts that GDB auto-loaded. If REGEXP is supplied only canned sequences of commands scripts with matching names are printed. File: gdb.info, Node: Auto-loading safe path, Next: Auto-loading verbose mode, Prev: objfile-gdb.gdb file, Up: Auto-loading 22.7.4 Security restriction for auto-loading -------------------------------------------- As the files of inferior can come from untrusted source (such as submitted by an application user) GDB does not always load any files automatically. GDB provides the set auto-load safe-path' setting to list directories trusted for loading files not explicitly requested by user. Each directory can also be a shell wildcard pattern. If the path is not set properly you will see a warning and the file will not get loaded:$ ./gdb -q ./gdb
Reading symbols from /home/user/gdb/gdb...done.
to "$debugdir:$datadir/auto-load".
declined by your auto-load safe-path' set
to "$debugdir:$datadir/auto-load".

The list of trusted directories is controlled by the following
commands:

set auto-load safe-path [DIRECTORIES]'
Set the list of directories (and their subdirectories) trusted for
automatic loading and execution of scripts.  You can also enter a
specific trusted file.  Each directory can also be a shell
wildcard pattern; wildcards do not match directory separator - see
FNM_PATHNAME' for system function fnmatch' (*note fnmatch:
(libc)Wildcard Matching.).  If you omit DIRECTORIES, auto-load
safe-path' will be reset to its default value as specified during
GDB compilation.

The list of directories uses path separator (:' on GNU and Unix
systems, ;' on MS-Windows and MS-DOS) to separate directories,
similarly to the PATH' environment variable.

show auto-load safe-path'
Show the list of directories trusted for automatic loading and
execution of scripts.

Add an entry (or list of entries) the list of directories trusted
for automatic loading and execution of scripts.  Multiple entries
may be delimited by the host platform path separator in use.

This variable defaults to what --with-auto-load-dir' has been
configured to (*note with-auto-load-dir::).  $debugdir' and $datadir'
substitution applies the same as for *note set auto-load
scripts-directory::.  The default set auto-load safe-path' value can
be also overriden by GDB configuration option
--with-auto-load-safe-path'.

Setting this variable to /' disables this security protection,
corresponding GDB configuration option is
--without-auto-load-safe-path'.  This variable is supposed to be set
to the system directories writable by the system superuser only.  Users
can add their source directories in init files in their home
directories (*note Home Directory Init File::).  See also deprecated
init file in the current directory (*note Init File in the Current
Directory during Startup::).

To force GDB to load the files it declined to load in the previous
example, you could use one of the following ways:

~/.gdbinit': add-auto-load-safe-path ~/src/gdb'
Specify this trusted directory (or a file) as additional component
of the list.  You have to specify also any existing directories
displayed by by show auto-load safe-path' (such as /usr:/bin' in
this example).

gdb -iex "set auto-load safe-path /usr:/bin:~/src/gdb" ...'
Specify this directory as in the previous case but just for a
single GDB session.

gdb -iex "set auto-load safe-path /" ...'
Disable auto-loading safety for a single GDB session.  This
assumes all the files you debug during this GDB session will come
from trusted sources.

During compilation of GDB you may disable any auto-loading safety.
This assumes all the files you will ever debug with this GDB come
from trusted sources.

On the other hand you can also explicitly forbid automatic files
loading which also suppresses any such warning messages:

gdb -iex "set auto-load no" ...'
You can use GDB command-line option for a single GDB session.

~/.gdbinit': set auto-load no'
Disable auto-loading globally for the user (*note Home Directory
Init File::).  While it is improbable, you could also use system
init file instead (*note System-wide configuration::).

This setting applies to the file names as entered by user.  If no
entry matches GDB tries as a last resort to also resolve all the file
names into their canonical form (typically resolving symbolic links)
and compare the entries again.  GDB already canonicalizes most of the
filenames on its own before starting the comparison so a canonical form
of directories is recommended to be entered.

22.7.5 Displaying files tried for auto-load
-------------------------------------------

For better visibility of all the file locations where you can place
scripts to be auto-loaded with inferior -- or to protect yourself
against accidental execution of untrusted scripts -- GDB provides a
feature for printing all the files attempted to be loaded.  Both
existing and non-existing files may be printed.

For example the list of directories from which it is safe to
canonicalized filenames which may not be too obvious while setting it
up.

(gdb) set debug auto-load on
(gdb) file ~/src/t/true
for objfile "/tmp/true".
auto-load: Updating directories of "/usr:/opt".
auto-load: Using directory "/usr".
auto-load: Using directory "/opt".
warning: File "/tmp/true-gdb.gdb" auto-loading has been declined
by your auto-load safe-path' set to "/usr:/opt".

set debug auto-load [on|off]'
Set whether to print the filenames attempted to be auto-loaded.

Show whether printing of the filenames attempted to be auto-loaded
is turned on or off.

File: gdb.info,  Node: Messages/Warnings,  Next: Debugging Output,  Prev: Auto-loading,  Up: Controlling GDB

22.8 Optional Warnings and Messages
===================================

By default, GDB is silent about its inner workings.  If you are running
on a slow machine, you may want to use the set verbose' command.  This
makes GDB tell you when it does a lengthy internal operation, so you
will not think it has crashed.

Currently, the messages controlled by set verbose' are those which
announce that the symbol table for a source file is being read; see
symbol-file' in *note Commands to Specify Files: Files.

set verbose on'
Enables GDB output of certain informational messages.

set verbose off'
Disables GDB output of certain informational messages.

show verbose'
Displays whether set verbose' is on or off.

By default, if GDB encounters bugs in the symbol table of an object
file, it is silent; but if you are debugging a compiler, you may find
this information useful (*note Errors Reading Symbol Files: Symbol
Errors.).

set complaints LIMIT'
Permits GDB to output LIMIT complaints about each type of unusual
symbols before becoming silent about the problem.  Set LIMIT to
zero to suppress all complaints; set it to a large number to
prevent complaints from being suppressed.

show complaints'
Displays how many symbol complaints GDB is permitted to produce.

By default, GDB is cautious, and asks what sometimes seems to be a
lot of stupid questions to confirm certain commands.  For example, if
you try to run a program which is already running:

(gdb) run
The program being debugged has been started already.
Start it from the beginning? (y or n)

If you are willing to unflinchingly face the consequences of your own
commands, you can disable this "feature":

set confirm off'
Disables confirmation requests.  Note that running GDB with the
--batch' option (*note -batch: Mode Options.) also automatically
disables confirmation requests.

set confirm on'
Enables confirmation requests (the default).

show confirm'
Displays state of confirmation requests.

If you need to debug user-defined commands or sourced files you may
find it useful to enable "command tracing".  In this mode each command
will be printed as it is executed, prefixed with one or more +'
symbols, the quantity denoting the call depth of each command.

set trace-commands on'
Enable command tracing.

set trace-commands off'
Disable command tracing.

show trace-commands'
Display the current state of command tracing.

File: gdb.info,  Node: Debugging Output,  Next: Other Misc Settings,  Prev: Messages/Warnings,  Up: Controlling GDB

22.9 Optional Messages about Internal Happenings
================================================

GDB has commands that enable optional debugging messages from various
GDB subsystems; normally these commands are of interest to GDB
maintainers, or when reporting a bug.  This section documents those
commands.

set exec-done-display'
Turns on or off the notification of asynchronous commands'
completion.  When on, GDB will print a message when an
asynchronous command finishes its execution.  The default is off.

show exec-done-display'
Displays the current setting of asynchronous command completion

set debug arch'
Turns on or off display of gdbarch debugging info.  The default is
off

show debug arch'
Displays the current state of displaying gdbarch debugging info.

Display debugging messages about inner workings of the AIX thread
module.

show debug aix-thread'
Show the current state of AIX thread debugging info display.

set debug dwarf2-die'
Dump DWARF2 DIEs after they are read in.  The value is the number
of nesting levels to print.  A value of zero turns off the display.

show debug dwarf2-die'
Show the current state of DWARF2 DIE debugging.

set debug displaced'
Turns on or off display of GDB debugging info for the displaced
stepping support.  The default is off.

show debug displaced'
Displays the current state of displaying GDB debugging info
related to displaced stepping.

set debug event'
Turns on or off display of GDB event debugging info.  The default
is off.

show debug event'
Displays the current state of displaying GDB event debugging info.

set debug expression'
Turns on or off display of debugging info about GDB expression
parsing.  The default is off.

show debug expression'
Displays the current state of displaying debugging info about GDB
expression parsing.

set debug frame'
Turns on or off display of GDB frame debugging info.  The default
is off.

show debug frame'
Displays the current state of displaying GDB frame debugging info.

set debug gnu-nat'
Turns on or off debugging messages from the GNU/Hurd debug support.

show debug gnu-nat'
Show the current state of GNU/Hurd debugging messages.

set debug infrun'
Turns on or off display of GDB debugging info for running the
inferior.  The default is off.  infrun.c' contains GDB's runtime
state machine used for implementing operations such as
single-stepping the inferior.

show debug infrun'
Displays the current state of GDB inferior debugging.

set debug lin-lwp'
Turns on or off debugging messages from the Linux LWP debug
support.

show debug lin-lwp'
Show the current state of Linux LWP debugging messages.

set debug lin-lwp-async'
Turns on or off debugging messages from the Linux LWP async debug
support.

show debug lin-lwp-async'
Show the current state of Linux LWP async debugging messages.

set debug observer'
Turns on or off display of GDB observer debugging.  This includes
info such as the notification of observable events.

show debug observer'
Displays the current state of observer debugging.

set debug overload'
Turns on or off display of GDB C++ overload debugging info. This
includes info such as ranking of functions, etc.  The default is
off.

Displays the current state of displaying GDB C++ overload
debugging info.

set debug parser'
Turns on or off the display of expression parser debugging output.
Internally, this sets the yydebug' variable in the expression
parser.  *Note Tracing Your Parser: (bison)Tracing, for details.
The default is off.

show debug parser'
Show the current state of expression parser debugging.

set debug remote'
Turns on or off display of reports on all packets sent back and
forth across the serial line to the remote machine.  The info is
printed on the GDB standard output stream. The default is off.

show debug remote'
Displays the state of display of remote packets.

set debug serial'
Turns on or off display of GDB serial debugging info. The default
is off.

show debug serial'
Displays the current state of displaying GDB serial debugging info.

set debug solib-frv'
Turns on or off debugging messages for FR-V shared-library code.

show debug solib-frv'
Display the current state of FR-V shared-library code debugging
messages.

set debug target'
Turns on or off display of GDB target debugging info. This info
includes what is going on at the target level of GDB, as it
happens. The default is 0.  Set it to 1 to track events, and to 2
to also track the value of large memory transfers.  Changes to
this flag do not take effect until the next time you connect to a
target or use the run' command.

show debug target'
Displays the current state of displaying GDB target debugging info.

set debug timestamp'
Turns on or off display of timestamps with GDB debugging info.
When enabled, seconds and microseconds are displayed before each
debugging message.

show debug timestamp'
Displays the current state of displaying timestamps with GDB
debugging info.

set debugvarobj'
Turns on or off display of GDB variable object debugging info. The
default is off.

show debugvarobj'
Displays the current state of displaying GDB variable object
debugging info.

set debug xml'
Turns on or off debugging messages for built-in XML parsers.

show debug xml'
Displays the current state of XML debugging messages.

File: gdb.info,  Node: Other Misc Settings,  Prev: Debugging Output,  Up: Controlling GDB

22.10 Other Miscellaneous Settings
==================================

set interactive-mode'
If on', forces GDB to operate interactively.  If off', forces
GDB to operate non-interactively, If auto' (the default), GDB
guesses which mode to use, based on whether the debugger was
started in a terminal or not.

In the vast majority of cases, the debugger should be able to guess
correctly which mode should be used.  But this setting can be
useful in certain specific cases, such as running a MinGW GDB
inside a cygwin window.

show interactive-mode'
Displays whether the debugger is operating in interactive mode or
not.

File: gdb.info,  Node: Extending GDB,  Next: Interpreters,  Prev: Controlling GDB,  Up: Top

23 Extending GDB
****************

GDB provides two mechanisms for extension.  The first is based on
composition of GDB commands, and the second is based on the Python
scripting language.

To facilitate the use of these extensions, GDB is capable of
evaluating the contents of a file.  When doing so, GDB can recognize
which scripting language is being used by looking at the filename
extension.  Files with an unrecognized filename extension are always
treated as a GDB Command Files.  *Note Command files: Command Files.

You can control how GDB evaluates these files with the following
setting:

set script-extension off'
All scripts are always evaluated as GDB Command Files.

set script-extension soft'
The debugger determines the scripting language based on filename
extension.  If this scripting language is supported, GDB evaluates
the script using that language.  Otherwise, it evaluates the file
as a GDB Command File.

set script-extension strict'
The debugger determines the scripting language based on filename
extension, and evaluates the script using that language.  If the
language is not supported, then the evaluation fails.

show script-extension'
Display the current value of the script-extension' option.

* Sequences::          Canned Sequences of Commands
* Python::             Scripting GDB using Python

File: gdb.info,  Node: Sequences,  Next: Python,  Up: Extending GDB

23.1 Canned Sequences of Commands
=================================

Aside from breakpoint commands (*note Breakpoint Command Lists: Break
Commands.), GDB provides two ways to store sequences of commands for
execution as a unit: user-defined commands and command files.

* Define::             How to define your own commands
* Hooks::              Hooks for user-defined commands
* Command Files::      How to write scripts of commands to be stored in a file
* Output::             Commands for controlled output

File: gdb.info,  Node: Define,  Next: Hooks,  Up: Sequences

23.1.1 User-defined Commands
----------------------------

A "user-defined command" is a sequence of GDB commands to which you
assign a new name as a command.  This is done with the define'
command.  User commands may accept up to 10 arguments separated by
whitespace.  Arguments are accessed within the user command via
$arg0...$arg9'.  A trivial example:

print $arg0 +$arg1 + $arg2 end To execute the command use: adder 1 2 3 This defines the command adder', which prints the sum of its three arguments. Note the arguments are text substitutions, so they may reference variables, use complex expressions, or even perform inferior functions calls. In addition, $argc' may be used to find out how many arguments have
been passed.  This expands to a number in the range 0...10.

if $argc == 2 print$arg0 + $arg1 end if$argc == 3
print $arg0 +$arg1 + $arg2 end end define COMMANDNAME' Define a command named COMMANDNAME. If there is already a command by that name, you are asked to confirm that you want to redefine it. COMMANDNAME may be a bare command name consisting of letters, numbers, dashes, and underscores. It may also start with any predefined prefix command. For example, define target my-target' creates a user-defined target my-target' command. The definition of the command is made up of other GDB command lines, which are given following the define' command. The end of these commands is marked by a line containing end'. document COMMANDNAME' Document the user-defined command COMMANDNAME, so that it can be accessed by help'. The command COMMANDNAME must already be defined. This command reads lines of documentation just as define' reads the lines of the command definition, ending with end'. After the document' command is finished, help' on command COMMANDNAME displays the documentation you have written. You may use the document' command again to change the documentation of a command. Redefining the command with define' does not change the documentation. dont-repeat' Used inside a user-defined command, this tells GDB that this command should not be repeated when the user hits <RET> (*note repeat last command: Command Syntax.). help user-defined' List all user-defined commands, with the first line of the documentation (if any) for each. show user' show user COMMANDNAME' Display the GDB commands used to define COMMANDNAME (but not its documentation). If no COMMANDNAME is given, display the definitions for all user-defined commands. show max-user-call-depth' set max-user-call-depth' The value of max-user-call-depth' controls how many recursion levels are allowed in user-defined commands before GDB suspects an infinite recursion and aborts the command. In addition to the above commands, user-defined commands frequently use control flow commands, described in *note Command Files::. When user-defined commands are executed, the commands of the definition are not printed. An error in any command stops execution of the user-defined command. If used interactively, commands that would ask for confirmation proceed without asking when used inside a user-defined command. Many GDB commands that normally print messages to say what they are doing omit the messages when used in a user-defined command. File: gdb.info, Node: Hooks, Next: Command Files, Prev: Define, Up: Sequences 23.1.2 User-defined Command Hooks --------------------------------- You may define "hooks", which are a special kind of user-defined command. Whenever you run the command foo', if the user-defined command hook-foo' exists, it is executed (with no arguments) before that command. A hook may also be defined which is run after the command you executed. Whenever you run the command foo', if the user-defined command hookpost-foo' exists, it is executed (with no arguments) after that command. Post-execution hooks may exist simultaneously with pre-execution hooks, for the same command. It is valid for a hook to call the command which it hooks. If this occurs, the hook is not re-executed, thereby avoiding infinite recursion. In addition, a pseudo-command, stop' exists. Defining (hook-stop') makes the associated commands execute every time execution stops in your program: before breakpoint commands are run, displays are printed, or the stack frame is printed. For example, to ignore SIGALRM' signals while single-stepping, but treat them normally during normal execution, you could define: define hook-stop handle SIGALRM nopass end define hook-run handle SIGALRM pass end define hook-continue handle SIGALRM pass end As a further example, to hook at the beginning and end of the echo' command, and to add extra text to the beginning and end of the message, you could define: define hook-echo echo <<<--- end define hookpost-echo echo --->>>\n end (gdb) echo Hello World <<<---Hello World--->>> (gdb) You can define a hook for any single-word command in GDB, but not for command aliases; you should define a hook for the basic command name, e.g. backtrace' rather than bt'. You can hook a multi-word command by adding hook-' or hookpost-' to the last word of the command, e.g. define target hook-remote' to add a hook to target remote'. If an error occurs during the execution of your hook, execution of GDB commands stops and GDB issues a prompt (before the command that you actually typed had a chance to run). If you try to define a hook which does not match any known command, you get a warning from the define' command. File: gdb.info, Node: Command Files, Next: Output, Prev: Hooks, Up: Sequences 23.1.3 Command Files -------------------- A command file for GDB is a text file made of lines that are GDB commands. Comments (lines starting with #') may also be included. An empty line in a command file does nothing; it does not mean to repeat the last command, as it would from the terminal. You can request the execution of a command file with the source' command. Note that the source' command is also used to evaluate scripts that are not Command Files. The exact behavior can be configured using the script-extension' setting. *Note Extending GDB: Extending GDB. source [-s] [-v] FILENAME' Execute the command file FILENAME. The lines in a command file are generally executed sequentially, unless the order of execution is changed by one of the _flow-control commands_ described below. The commands are not printed as they are executed. An error in any command terminates execution of the command file and control is returned to the console. GDB first searches for FILENAME in the current directory. If the file is not found there, and FILENAME does not specify a directory, then GDB also looks for the file on the source search path (specified with the directory' command); except that $cdir' is not searched
because the compilation directory is not relevant to scripts.

If -s' is specified, then GDB searches for FILENAME on the search
path even if FILENAME specifies a directory.  The search is done by
appending FILENAME to each element of the search path.  So, for
example, if FILENAME is mylib/myscript' and the search path contains
/home/user' then GDB will look for the script
/home/user/mylib/myscript'.  The search is also done if FILENAME is an
absolute path.  For example, if FILENAME is /tmp/myscript' and the
search path contains /home/user' then GDB will look for the script
/home/user/tmp/myscript'.  For DOS-like systems, if FILENAME contains
a drive specification, it is stripped before concatenation.  For
example, if FILENAME is d:myscript' and the search path contains
c:/tmp' then GDB will look for the script c:/tmp/myscript'.

If -v', for verbose mode, is given then GDB displays each command
as it is executed.  The option must be given before FILENAME, and is
interpreted as part of the filename anywhere else.

Commands that would ask for confirmation if used interactively
proceed without asking when used in a command file.  Many GDB commands
that normally print messages to say what they are doing omit the
messages when called from command files.

GDB also accepts command input from standard input.  In this mode,
normal output goes to standard output and error output goes to standard
error.  Errors in a command file supplied on standard input do not
terminate execution of the command file--execution continues with the
next command.

gdb < cmds > log 2>&1

(The syntax above will vary depending on the shell used.) This
example will execute commands from the file cmds'. All output and
errors would be directed to log'.

Since commands stored on command files tend to be more general than
commands typed interactively, they frequently need to deal with
complicated situations, such as different or unexpected values of
variables and symbols, changes in how the program being debugged is
built, etc.  GDB provides a set of flow-control commands to deal with
these complexities.  Using these commands, you can write complex
scripts that loop over data structures, execute commands conditionally,
etc.

if'
else'
This command allows to include in your script conditionally
executed commands. The if' command takes a single argument, which
is an expression to evaluate.  It is followed by a series of
commands that are executed only if the expression is true (its
value is nonzero).  There can then optionally be an else' line,
followed by a series of commands that are only executed if the
expression was false.  The end of the list is marked by a line
containing end'.

while'
This command allows to write loops.  Its syntax is similar to
if': the command takes a single argument, which is an expression
to evaluate, and must be followed by the commands to execute, one
per line, terminated by an end'.  These commands are called the
"body" of the loop.  The commands in the body of while' are
executed repeatedly as long as the expression evaluates to true.

loop_break'
This command exits the while' loop in whose body it is included.
Execution of the script continues after that while's end' line.

loop_continue'
This command skips the execution of the rest of the body of
commands in the while' loop in whose body it is included.
Execution branches to the beginning of the while' loop, where it
evaluates the controlling expression.

end'
Terminate the block of commands that are the body of if', else',
or while' flow-control commands.

File: gdb.info,  Node: Output,  Prev: Command Files,  Up: Sequences

23.1.4 Commands for Controlled Output
-------------------------------------

During the execution of a command file or a user-defined command, normal
GDB output is suppressed; the only output that appears is what is
explicitly printed by the commands in the definition.  This section
describes three commands useful for generating exactly the output you
want.

echo TEXT'
Print TEXT.  Nonprinting characters can be included in TEXT using
C escape sequences, such as \n' to print a newline.  *No newline
is printed unless you specify one.* In addition to the standard C
escape sequences, a backslash followed by a space stands for a
space.  This is useful for displaying a string with spaces at the
beginning or the end, since leading and trailing spaces are
otherwise trimmed from all arguments.  To print  and foo = ', use
the command echo \ and foo = \ '.

A backslash at the end of TEXT can be used, as in C, to continue
the command onto subsequent lines.  For example,

echo This is some text\n\
which is continued\n\
onto several lines.\n

produces the same output as

echo This is some text\n
echo which is continued\n
echo onto several lines.\n

output EXPRESSION'
Print the value of EXPRESSION and nothing but that value: no
newlines, no $NN = '. The value is not entered in the value history either. *Note Expressions: Expressions, for more information on expressions. output/FMT EXPRESSION' Print the value of EXPRESSION in format FMT. You can use the same formats as for print'. *Note Output Formats: Output Formats, for more information. printf TEMPLATE, EXPRESSIONS...' Print the values of one or more EXPRESSIONS under the control of the string TEMPLATE. To print several values, make EXPRESSIONS be a comma-separated list of individual expressions, which may be either numbers or pointers. Their values are printed as specified by TEMPLATE, exactly as a C program would do by executing the code below: printf (TEMPLATE, EXPRESSIONS...); As in C' printf', ordinary characters in TEMPLATE are printed verbatim, while "conversion specification" introduced by the %' character cause subsequent EXPRESSIONS to be evaluated, their values converted and formatted according to type and style information encoded in the conversion specifications, and then printed. For example, you can print two values in hex like this: printf "foo, bar-foo = 0x%x, 0x%x\n", foo, bar-foo printf' supports all the standard C' conversion specifications, including the flags and modifiers between the %' character and the conversion letter, with the following exceptions: * The argument-ordering modifiers, such as 2$', are not
supported.

* The modifier *' is not supported for specifying precision or
width.

* The '' flag (for separation of digits into groups according
to LC_NUMERIC'') is not supported.

* The type modifiers hh', j', t', and z' are not supported.

* The conversion letter n' (as in %n') is not supported.

* The conversion letters a' and A' are not supported.

Note that the ll' type modifier is supported only if the
underlying C' implementation used to build GDB supports the long
long int' type, and the L' type modifier is supported only if
long double' type is available.

As in C', printf' supports simple backslash-escape sequences,
such as \n', \t', \\', \"', \a', and \f', that consist of
backslash followed by a single character.  Octal and hexadecimal
escape sequences are not supported.

Additionally, printf' supports conversion specifications for DFP
("Decimal Floating Point") types using the following length
modifiers together with a floating point specifier.  letters:

* H' for printing Decimal32' types.

* D' for printing Decimal64' types.

* DD' for printing Decimal128' types.

If the underlying C' implementation used to build GDB has support
for the three length modifiers for DFP types, other modifiers such
as width and precision will also be available for GDB to use.

In case there is no such C' support, no additional modifiers will
be available and the value will be printed in the standard way.

Here's an example of printing DFP types using the above conversion
letters:
printf "D32: %Hf - D64: %Df - D128: %DDf\n",1.2345df,1.2E10dd,1.2E1dl

eval TEMPLATE, EXPRESSIONS...'
Convert the values of one or more EXPRESSIONS under the control of
the string TEMPLATE to a command line, and call it.

File: gdb.info,  Node: Python,  Prev: Sequences,  Up: Extending GDB

23.2 Scripting GDB using Python
===============================

You can script GDB using the Python programming language
(http://www.python.org/).  This feature is available only if GDB was
configured using --with-python'.

Python scripts used by GDB should be installed in
DATA-DIRECTORY/python', where DATA-DIRECTORY is the data directory as
determined at GDB startup (*note Data Files::).  This directory, known
as the "python directory", is automatically added to the Python Search
Path in order to allow the Python interpreter to locate all scripts
installed at this location.

* Python Commands::             Accessing Python from GDB.
* Python API::                  Accessing GDB from Python.

File: gdb.info,  Node: Python Commands,  Next: Python API,  Up: Python

23.2.1 Python Commands
----------------------

GDB provides one command for accessing the Python interpreter, and one
related setting:

python [CODE]'
The python' command can be used to evaluate Python code.

If given an argument, the python' command will evaluate the
argument as a Python command.  For example:

(gdb) python print 23
23

If you do not provide an argument to python', it will act as a
multi-line command, like define'.  In this case, the Python
script is made up of subsequent command lines, given after the
python' command.  This command list is terminated using a line
containing end'.  For example:

(gdb) python
>print 23
>end
23

maint set python print-stack'
By default, GDB will print a stack trace when an error occurs in a
Python script.  This can be controlled using maint set python
print-stack': if on', the default, then Python stack printing is
enabled; if off', then Python stack printing is disabled.

maint set python auto-load'
By default, GDB will attempt to automatically load Python code
when an object file is opened.  This can be controlled using
maint set python auto-load': if on', the default, then Python
disabled.

It is also possible to execute a Python script from the GDB
interpreter:

source script-name''
The script name must end with .py' and GDB must be configured to
recognize the script language based on filename extension using
the script-extension' setting.  *Note Extending GDB: Extending
GDB.

python execfile ("script-name")'
This method is based on the execfile' Python built-in function,
and thus is always available.

File: gdb.info,  Node: Python API,  Next: Python Auto-loading,  Prev: Python Commands,  Up: Python

23.2.2 Python API
-----------------

You can get quick online help for GDB's Python API by issuing the
command python help (gdb)'.

Functions and methods which have two or more optional arguments allow
them to be specified using keyword syntax.  This allows passing some
optional arguments while skipping others.  Example:
gdb.some_function ('foo', bar = 1, baz = 2)'.

At startup, GDB overrides Python's sys.stdout' and sys.stderr' to
print using GDB's output-paging streams.  A Python program which
outputs to one of these streams may have its output interrupted by the
user (*note Screen Size::).  In this situation, a Python
KeyboardInterrupt' exception is thrown.

* Basic Python::                Basic Python Functions.
* Exception Handling::
* Values From Inferior::	Python representation of values.
* Types In Python::             Python representation of types.
* Pretty Printing API::         Pretty-printing values.
* Selecting Pretty-Printers::   How GDB chooses a pretty-printer.
* Disabling Pretty-Printers::   Disabling broken printers.
* Inferiors In Python::         Python representation of inferiors (processes)
* Threads In Python::           Accessing inferior threads from Python.
* Commands In Python::          Implementing new commands in Python.
* Parameters In Python::        Adding new GDB parameters.
* Functions In Python::         Writing new convenience functions.
* Progspaces In Python::        Program spaces.
* Objfiles In Python::          Object files.
* Frames In Python::            Accessing inferior stack frames from Python.
* Blocks In Python::            Accessing frame blocks from Python.
* Symbols In Python::           Python representation of symbols.
* Symbol Tables In Python::     Python representation of symbol tables.
* Lazy Strings In Python::      Python representation of lazy strings.
* Breakpoints In Python::       Manipulating breakpoints using Python.

File: gdb.info,  Node: Basic Python,  Next: Exception Handling,  Up: Python API

23.2.2.1 Basic Python
.....................

GDB introduces a new Python module, named gdb'.  All methods and
classes added by GDB are placed in this module.  GDB automatically
import's the gdb' module for use in all scripts evaluated by the
python' command.

-- Variable: PYTHONDIR
A string containing the python directory (*note Python::).

-- Function: execute command [from_tty] [to_string]
Evaluate COMMAND, a string, as a GDB CLI command.  If a GDB
exception happens while COMMAND runs, it is translated as
described in *note Exception Handling: Exception Handling.

FROM_TTY specifies whether GDB ought to consider this command as
having originated from the user invoking it interactively.  It
must be a boolean value.  If omitted, it defaults to False'.

By default, any output produced by COMMAND is sent to GDB's
standard output.  If the TO_STRING parameter is True', then
output will be collected by gdb.execute' and returned as a
string.  The default is False', in which case the return value is
None'.  If TO_STRING is True', the GDB virtual terminal will be
temporarily set to unlimited width and height, and its pagination
will be disabled; *note Screen Size::.

-- Function: breakpoints
Return a sequence holding all of GDB's breakpoints.  *Note

-- Function: breakpoints
Return a sequence holding all of GDB's breakpoints.  *Note

-- Function: parameter parameter
Return the value of a GDB parameter.  PARAMETER is a string naming
the parameter to look up; PARAMETER may contain spaces if the
parameter has a multi-part name.  For example, print object' is a
valid parameter name.

If the named parameter does not exist, this function throws a
RuntimeError'.  Otherwise, the parameter's value is converted to
a Python value of the appropriate type, and returned.

-- Function: history number
Return a value from GDB's value history (*note Value History::).
NUMBER indicates which history element to return.

If NUMBER is negative, then GDB will take its absolute value and
count backward from the last element (i.e., the most recent
element) to find the value to return.  If NUMBER is zero, then GDB
will return the most recent element.  If the element specified by
NUMBER doesn't exist in the value history, a RuntimeError'
exception will be raised.

If no exception is raised, the return value is always an instance
of gdb.Value' (*note Values From Inferior::).

-- Function: parse_and_eval expression
Parse EXPRESSION as an expression in the current language,
evaluate it, and return the result as a gdb.Value'.  EXPRESSION
must be a string.

This function can be useful when implementing a new command (*note
Commands In Python::), as it provides a way to parse the command's
argument as an expression.  It is also useful simply to compute
values, for example, it is the only way to get the value of a
convenience variable (*note Convenience Vars::) as a gdb.Value'.

-- Function: post_event event
Put EVENT, a callable object taking no arguments, into GDB's
internal event queue.  This callable will be invoked at some later
point, during GDB's event processing.  Events posted using
post_event' will be run in the order in which they were posted;
however, there is no way to know when they will be processed
relative to other events inside GDB.

GDB is not thread-safe.  If your Python program uses multiple
threads, you must be careful to only call GDB-specific functions
in the main GDB thread.  post_event' ensures this.

-- Function: write string
Print a string to GDB's paginated standard output stream.  Writing
to sys.stdout' or sys.stderr' will automatically call this
function.

-- Function: flush
Flush GDB's paginated standard output stream.  Flushing
sys.stdout' or sys.stderr' will automatically call this function.

-- Function: target_charset
Return the name of the current target character set (*note
Character Sets::).  This differs from
gdb.parameter('target-charset')' in that auto' is never returned.

-- Function: target_wide_charset
Return the name of the current target wide character set (*note
Character Sets::).  This differs from
gdb.parameter('target-wide-charset')' in that auto' is never
returned.

File: gdb.info,  Node: Exception Handling,  Next: Values From Inferior,  Prev: Basic Python,  Up: Python API

23.2.2.2 Exception Handling
...........................

When executing the python' command, Python exceptions uncaught within
the Python code are translated to calls to GDB error-reporting
mechanism.  If the command that called python' does not handle the
error, GDB will terminate it and print an error message containing the
Python exception name, the associated value, and the Python call stack
backtrace at the point where the exception was raised.  Example:

(gdb) python print foo
Traceback (most recent call last):
File "<string>", line 1, in <module>
NameError: name 'foo' is not defined

GDB errors that happen in GDB commands invoked by Python code are
converted to Python RuntimeError' exceptions.  User interrupt (via
C-c' or by typing q' at a pagination prompt) is translated to a
Python KeyboardInterrupt' exception.  If you catch these exceptions in
your Python code, your exception handler will see RuntimeError' or
KeyboardInterrupt' as the exception type, the GDB error message as its
value, and the Python call stack backtrace at the Python statement
closest to where the GDB error occured as the traceback.

When implementing GDB commands in Python via gdb.Command', it is
useful to be able to throw an exception that doesn't cause a traceback
to be printed.  For example, the user may have invoked the command
incorrectly.  Use the gdb.GdbError' exception to handle this case.
Example:

(gdb) python
>class HelloWorld (gdb.Command):
>  """Greet the whole world."""
>  def __init__ (self):
>    super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE)
>  def invoke (self, args, from_tty):
>    argv = gdb.string_to_argv (args)
>    if len (argv) != 0:
>      raise gdb.GdbError ("hello-world takes no arguments")
>    print "Hello, World!"
>HelloWorld ()
>end
(gdb) hello-world 42
hello-world takes no arguments

File: gdb.info,  Node: Values From Inferior,  Next: Types In Python,  Prev: Exception Handling,  Up: Python API

23.2.2.3 Values From Inferior
.............................

GDB provides values it obtains from the inferior program in an object
of type gdb.Value'.  GDB uses this object for its internal bookkeeping
of the inferior's values, and for fetching values when necessary.

Inferior values that are simple scalars can be used directly in
Python expressions that are valid for the value's data type.  Here's an
example for an integer or floating-point value some_val':

bar = some_val + 2

As result of this, bar' will also be a gdb.Value' object whose values
are of the same type as those of some_val'.

Inferior values that are structures or instances of some class can
be accessed using the Python "dictionary syntax".  For example, if
some_val' is a gdb.Value' instance holding a structure, you can
access its foo' element with:

bar = some_val['foo']

Again, bar' will also be a gdb.Value' object.

The following attributes are provided:

-- Instance Variable of Value: address
If this object is addressable, this read-only attribute holds
a gdb.Value' object representing the address.  Otherwise,
this attribute holds None'.

-- Instance Variable of Value: is_optimized_out
This read-only boolean attribute is true if the compiler
optimized out this value, thus it is not available for
fetching from the inferior.

-- Instance Variable of Value: type
The type of this gdb.Value'.  The value of this attribute is
a gdb.Type' object.

The following methods are provided:

-- Method on Value: cast type
Return a new instance of gdb.Value' that is the result of
casting this instance to the type described by TYPE, which
must be a gdb.Type' object.  If the cast cannot be performed
for some reason, this method throws an exception.

-- Method on Value: dereference
For pointer data types, this method returns a new gdb.Value'
object whose contents is the object pointed to by the
pointer.  For example, if foo' is a C pointer to an int',
declared in your C program as

int *foo;

then you can use the corresponding gdb.Value' to access what
foo' points to like this:

bar = foo.dereference ()

The result bar' will be a gdb.Value' object holding the
value pointed to by foo'.

-- Method on Value: string [encoding] [errors] [length]
If this gdb.Value' represents a string, then this method
converts the contents to a Python string.  Otherwise, this
method will throw an exception.

Strings are recognized in a language-specific way; whether a
given gdb.Value' represents a string is determined by the
current language.

For C-like languages, a value is a string if it is a pointer
to or an array of characters or ints.  The string is assumed
to be terminated by a zero of the appropriate width.  However
if the optional length argument is given, the string will be
converted to that given length, ignoring any embedded zeros
that the string may contain.

If the optional ENCODING argument is given, it must be a
string naming the encoding of the string in the gdb.Value',
such as "ascii"', "iso-8859-6"' or "utf-8"'.  It accepts
the same encodings as the corresponding argument to Python's
string.decode' method, and the Python codec machinery will
be used to convert the string.  If ENCODING is not given, or
if ENCODING is the empty string, then either the
target-charset' (*note Character Sets::) will be used, or a
language-specific encoding will be used, if the current
language is able to supply one.

The optional ERRORS argument is the same as the corresponding
argument to Python's string.decode' method.

If the optional LENGTH argument is given, the string will be
fetched and converted to the given length.

-- Method on Value: lazy_string [encoding] [length]
If this gdb.Value' represents a string, then this method
converts the contents to a gdb.LazyString' (*note Lazy
Strings In Python::).  Otherwise, this method will throw an
exception.

If the optional ENCODING argument is given, it must be a
string naming the encoding of the gdb.LazyString'.  Some
examples are: ascii', iso-8859-6' or utf-8'.  If the
ENCODING argument is an encoding that GDB does recognize, GDB
will raise an error.

When a lazy string is printed, the GDB encoding machinery is
used to convert the string during printing.  If the optional
ENCODING argument is not provided, or is an empty string, GDB
will automatically select the encoding most suitable for the
string type.  For further information on encoding in GDB
please see *note Character Sets::.

If the optional LENGTH argument is given, the string will be
fetched and encoded to the length of characters specified.  If
the LENGTH argument is not provided, the string will be
fetched and encoded until a null of appropriate width is
found.

File: gdb.info,  Node: Types In Python,  Next: Pretty Printing API,  Prev: Values From Inferior,  Up: Python API

23.2.2.4 Types In Python
........................

GDB represents types from the inferior using the class gdb.Type'.

The following type-related functions are available in the gdb'
module:

-- Function: lookup_type name [block]
This function looks up a type by name.  NAME is the name of the
type to look up.  It must be a string.

If BLOCK is given, then NAME is looked up in that scope.
Otherwise, it is searched for globally.

Ordinarily, this function will return an instance of gdb.Type'.
If the named type cannot be found, it will throw an exception.

An instance of Type' has the following attributes:

-- Instance Variable of Type: code
The type code for this type.  The type code will be one of the
TYPE_CODE_' constants defined below.

-- Instance Variable of Type: sizeof
The size of this type, in target char' units.  Usually, a
target's char' type will be an 8-bit byte.  However, on some
unusual platforms, this type may have a different size.

-- Instance Variable of Type: tag
The tag name for this type.  The tag name is the name after
struct', union', or enum' in C and C++; not all languages
have this concept.  If this type has no tag name, then None'
is returned.

The following methods are provided:

-- Method on Type: fields
For structure and union types, this method returns the
fields.  Range types have two fields, the minimum and maximum
values.  Enum types have one field per enum constant.
Function and method types have one field per parameter.  The
base types of C++ classes are also represented as fields.  If
the type has no fields, or does not fit into one of these
categories, an empty sequence will be returned.

Each field is an object, with some pre-defined attributes:
bitpos'
This attribute is not available for static' fields (as
in C++ or Java).  For non-static' fields, the value is
the bit position of the field.

name'
The name of the field, or None' for anonymous fields.

artificial'
This is True' if the field is artificial, usually
meaning that it was provided by the compiler and not the
user.  This attribute is always provided, and is False'
if the field is not artificial.

is_base_class'
This is True' if the field represents a base class of a
C++ structure.  This attribute is always provided, and
is False' if the field is not a base class of the type
that is the argument of fields', or if that type was
not a C++ class.

bitsize'
If the field is packed, or is a bitfield, then this will
have a non-zero value, which is the size of the field in
bits.  Otherwise, this will be zero; in this case the
field's size is given by its type.

type'
The type of the field.  This is usually an instance of
Type', but it can be None' in some situations.

-- Method on Type: const
Return a new gdb.Type' object which represents a
const'-qualified variant of this type.

-- Method on Type: volatile
Return a new gdb.Type' object which represents a
volatile'-qualified variant of this type.

-- Method on Type: unqualified
Return a new gdb.Type' object which represents an unqualified
variant of this type.  That is, the result is neither const'
nor volatile'.

-- Method on Type: range
Return a Python Tuple' object that contains two elements: the
low bound of the argument type and the high bound of that
type.  If the type does not have a range, GDB will raise a
RuntimeError' exception.

-- Method on Type: reference
Return a new gdb.Type' object which represents a reference
to this type.

-- Method on Type: pointer
Return a new gdb.Type' object which represents a pointer to
this type.

-- Method on Type: strip_typedefs
Return a new gdb.Type' that represents the real type, after
removing all layers of typedefs.

-- Method on Type: target
Return a new gdb.Type' object which represents the target
type of this type.

For a pointer type, the target type is the type of the
pointed-to object.  For an array type (meaning C-like
arrays), the target type is the type of the elements of the
array.  For a function or method type, the target type is the
type of the return value.  For a complex type, the target
type is the type of the elements.  For a typedef, the target
type is the aliased type.

If the type does not have a target, this method will throw an
exception.

-- Method on Type: template_argument n [block]
If this gdb.Type' is an instantiation of a template, this
will return a new gdb.Type' which represents the type of the
Nth template argument.

If this gdb.Type' is not a template type, this will throw an
exception.  Ordinarily, only C++ code will have template
types.

If BLOCK is given, then NAME is looked up in that scope.
Otherwise, it is searched for globally.

Each type has a code, which indicates what category this type falls
into.  The available type categories are represented by constants
defined in the gdb' module:

TYPE_CODE_PTR'
The type is a pointer.

TYPE_CODE_ARRAY'
The type is an array.

TYPE_CODE_STRUCT'
The type is a structure.

TYPE_CODE_UNION'
The type is a union.

TYPE_CODE_ENUM'
The type is an enum.

TYPE_CODE_FLAGS'
A bit flags type, used for things such as status registers.

TYPE_CODE_FUNC'
The type is a function.

TYPE_CODE_INT'
The type is an integer type.

TYPE_CODE_FLT'
A floating point type.

TYPE_CODE_VOID'
The special type void'.

TYPE_CODE_SET'
A Pascal set type.

TYPE_CODE_RANGE'
A range type, that is, an integer type with bounds.

TYPE_CODE_STRING'
A string type.  Note that this is only used for certain languages
with language-defined string types; C strings are not represented
this way.

TYPE_CODE_BITSTRING'
A string of bits.

TYPE_CODE_ERROR'
An unknown or erroneous type.

TYPE_CODE_METHOD'
A method type, as found in C++ or Java.

TYPE_CODE_METHODPTR'
A pointer-to-member-function.

TYPE_CODE_MEMBERPTR'
A pointer-to-member.

TYPE_CODE_REF'
A reference type.

TYPE_CODE_CHAR'
A character type.

TYPE_CODE_BOOL'
A boolean type.

TYPE_CODE_COMPLEX'
A complex float type.

TYPE_CODE_TYPEDEF'
A typedef to some other type.

TYPE_CODE_NAMESPACE'
A C++ namespace.

TYPE_CODE_DECFLOAT'
A decimal floating point type.

TYPE_CODE_INTERNAL_FUNCTION'
A function internal to GDB.  This is the type used to represent
convenience functions.

File: gdb.info,  Node: Pretty Printing API,  Next: Selecting Pretty-Printers,  Prev: Types In Python,  Up: Python API

23.2.2.5 Pretty Printing API
............................

An example output is provided (*note Pretty Printing::).

A pretty-printer is just an object that holds a value and implements
a specific interface, defined here.

-- Operation on pretty printer: children (self)
GDB will call this method on a pretty-printer to compute the
children of the pretty-printer's value.

This method must return an object conforming to the Python iterator
protocol.  Each item returned by the iterator must be a tuple
holding two elements.  The first element is the "name" of the
child; the second element is the child's value.  The value can be
any Python object which is convertible to a GDB value.

This method is optional.  If it does not exist, GDB will act as
though the value has no children.

-- Operation on pretty printer: display_hint (self)
The CLI may call this method and use its result to change the
formatting of a value.  The result will also be supplied to an MI
consumer as a displayhint' attribute of the variable being
printed.

This method is optional.  If it does exist, this method must
return a string.

Some display hints are predefined by GDB:

array'
Indicate that the object being printed is "array-like".  The
CLI uses this to respect parameters such as set print
elements' and set print array'.

map'
Indicate that the object being printed is "map-like", and
that the children of this value can be assumed to alternate
between keys and values.

string'
Indicate that the object being printed is "string-like".  If
the printer's to_string' method returns a Python string of
some kind, then GDB will call its internal language-specific
string-printing function to format the string.  For the CLI
this means adding quotation marks, possibly escaping some
characters, respecting set print elements', and the like.

-- Operation on pretty printer: to_string (self)
GDB will call this method to display the string representation of
the value passed to the object's constructor.

When printing from the CLI, if the to_string' method exists, then
GDB will prepend its result to the values returned by children'.
Exactly how this formatting is done is dependent on the display
hint, and may change as more hints are added.  Also, depending on
the print settings (*note Print Settings::), the CLI may print
just the result of to_string' in a stack trace, omitting the
result of children'.

If this method returns a string, it is printed verbatim.

Otherwise, if this method returns an instance of gdb.Value', then
GDB prints this value.  This may result in a call to another
pretty-printer.

If instead the method returns a Python value which is convertible
to a gdb.Value', then GDB performs the conversion and prints the
resulting value.  Again, this may result in a call to another
pretty-printer.  Python scalars (integers, floats, and booleans)
and strings are convertible to gdb.Value'; other types are not.

Finally, if this method returns None' then no further operations
are peformed in this method and nothing is printed.

If the result is not one of these types, an exception is raised.

GDB provides a function which can be used to look up the default
pretty-printer for a gdb.Value':

-- Function: default_visualizer value
This function takes a gdb.Value' object as an argument.  If a
pretty-printer for this value exists, then it is returned.  If no
such printer exists, then this returns None'.

File: gdb.info,  Node: Selecting Pretty-Printers,  Next: Disabling Pretty-Printers,  Prev: Pretty Printing API,  Up: Python API

23.2.2.6 Selecting Pretty-Printers
..................................

The Python list gdb.pretty_printers' contains an array of functions or
callable objects that have been registered via addition as a
pretty-printer.  Each gdb.Progspace' contains a pretty_printers'
attribute.  Each gdb.Objfile' also contains a pretty_printers'
attribute.

A function on one of these lists is passed a single gdb.Value'
argument and should return a pretty-printer object conforming to the
interface definition above (*note Pretty Printing API::).  If a function
cannot create a pretty-printer for the value, it should return None'.

GDB first checks the pretty_printers' attribute of each
gdb.Objfile' in the current program space and iteratively calls each
enabled function (*note Disabling Pretty-Printers::) in the list for
that gdb.Objfile' until it receives a pretty-printer object.  If no
pretty-printer is found in the objfile lists, GDB then searches the
pretty-printer list of the current program space, calling each enabled
function until an object is returned.  After these lists have been
exhausted, it tries the global gdb.pretty_printers' list, again
calling each enabled function until an object is returned.

The order in which the objfiles are searched is not specified.  For a
given list, functions are always invoked from the head of the list, and
iterated over sequentially until the end of the list, or a printer
object is returned.

Here is an example showing how a std::string' printer might be
written:

class StdStringPrinter:
"Print a std::string"

def __init__ (self, val):
self.val = val

def to_string (self):
return self.val['_M_dataplus']['_M_p']

def display_hint (self):
return 'string'

And here is an example showing how a lookup function for the printer
example above might be written.

def str_lookup_function (val):

lookup_tag = val.type.tag
regex = re.compile ("^std::basic_string<char,.*>$") if lookup_tag == None: return None if regex.match (lookup_tag): return StdStringPrinter (val) return None The example lookup function extracts the value's type, and attempts to match it to a type that it can pretty-print. If it is a type the printer can pretty-print, it will return a printer object. If not, it returns None'. We recommend that you put your core pretty-printers into a Python package. If your pretty-printers are for use with a library, we further recommend embedding a version number into the package name. This practice will enable GDB to load multiple versions of your pretty-printers at the same time, because they will have different names. You should write auto-loaded code (*note Python Auto-loading::) such that it can be evaluated multiple times without changing its meaning. An ideal auto-load file will consist solely of import's of your printer modules, followed by a call to a register pretty-printers with the current objfile. Taken as a whole, this approach will scale nicely to multiple inferiors, each potentially using a different library version. Embedding a version number in the Python package name will ensure that GDB is able to load both sets of printers simultaneously. Then, because the search for pretty-printers is done by objfile, and because your auto-loaded code took care to register your library's printers with a specific objfile, GDB will find the correct printers for the specific version of the library used by each inferior. To continue the std::string' example (*note Pretty Printing API::), this code might appear in gdb.libstdcxx.v6': def register_printers (objfile): objfile.pretty_printers.add (str_lookup_function) And then the corresponding contents of the auto-load file would be: import gdb.libstdcxx.v6 gdb.libstdcxx.v6.register_printers (gdb.current_objfile ()) File: gdb.info, Node: Disabling Pretty-Printers, Next: Inferiors In Python, Prev: Selecting Pretty-Printers, Up: Python API 23.2.2.7 Disabling Pretty-Printers .................................. For various reasons a pretty-printer may not work. For example, the underlying data structure may have changed and the pretty-printer is out of date. The consequences of a broken pretty-printer are severe enough that GDB provides support for enabling and disabling individual printers. For example, if print frame-arguments' is on, a backtrace can become highly illegible if any argument is printed with a broken printer. Pretty-printers are enabled and disabled by attaching an enabled' attribute to the registered function or callable object. If this attribute is present and its value is False', the printer is disabled, otherwise the printer is enabled. File: gdb.info, Node: Inferiors In Python, Next: Threads In Python, Prev: Disabling Pretty-Printers, Up: Python API 23.2.2.8 Inferiors In Python ............................ Programs which are being run under GDB are called inferiors (*note Inferiors and Programs::). Python scripts can access information about and manipulate inferiors controlled by GDB via objects of the gdb.Inferior' class. The following inferior-related functions are available in the gdb' module: -- Function: inferiors Return a tuple containing all inferior objects. A gdb.Inferior' object has the following attributes: -- Instance Variable of Inferior: num ID of inferior, as assigned by GDB. -- Instance Variable of Inferior: pid Process ID of the inferior, as assigned by the underlying operating system. -- Instance Variable of Inferior: was_attached Boolean signaling whether the inferior was created using attach', or started by GDB itself. A gdb.Inferior' object has the following methods: -- Method on Inferior: threads This method returns a tuple holding all the threads which are valid when it is called. If there are no valid threads, the method will return an empty tuple. -- Method on Inferior: read_memory address length Read LENGTH bytes of memory from the inferior, starting at ADDRESS. Returns a buffer object, which behaves much like an array or a string. It can be modified and given to the gdb.write_memory' function. -- Method on Inferior: write_memory address buffer [length] Write the contents of BUFFER to the inferior, starting at ADDRESS. The BUFFER parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from gdb.read_memory'. If given, LENGTH determines the number of bytes from BUFFER to be written. -- Method on Inferior: search_memory address length pattern Search a region of the inferior memory starting at ADDRESS with the given LENGTH using the search pattern supplied in PATTERN. The PATTERN parameter must be a Python object which supports the buffer protocol, i.e., a string, an array or the object returned from gdb.read_memory'. Returns a Python Long' containing the address where the pattern was found, or None' if the pattern could not be found. File: gdb.info, Node: Threads In Python, Next: Commands In Python, Prev: Inferiors In Python, Up: Python API 23.2.2.9 Threads In Python .......................... Python scripts can access information about, and manipulate inferior threads controlled by GDB, via objects of the gdb.InferiorThread' class. The following thread-related functions are available in the gdb' module: -- Function: selected_thread This function returns the thread object for the selected thread. If there is no selected thread, this will return None'. A gdb.InferiorThread' object has the following attributes: -- Instance Variable of InferiorThread: num ID of the thread, as assigned by GDB. -- Instance Variable of InferiorThread: ptid ID of the thread, as assigned by the operating system. This attribute is a tuple containing three integers. The first is the Process ID (PID); the second is the Lightweight Process ID (LWPID), and the third is the Thread ID (TID). Either the LWPID or TID may be 0, which indicates that the operating system does not use that identifier. A gdb.InferiorThread' object has the following methods: -- Method on InferiorThread: switch This changes GDB's currently selected thread to the one represented by this object. -- Method on InferiorThread: is_stopped Return a Boolean indicating whether the thread is stopped. -- Method on InferiorThread: is_running Return a Boolean indicating whether the thread is running. -- Method on InferiorThread: is_exited Return a Boolean indicating whether the thread is exited. File: gdb.info, Node: Commands In Python, Next: Parameters In Python, Prev: Threads In Python, Up: Python API 23.2.2.10 Commands In Python ............................ You can implement new GDB CLI commands in Python. A CLI command is implemented using an instance of the gdb.Command' class, most commonly using a subclass. -- Method on Command: __init__ name COMMAND_CLASS [COMPLETER_CLASS] [PREFIX] The object initializer for Command' registers the new command with GDB. This initializer is normally invoked from the subclass' own __init__' method. NAME is the name of the command. If NAME consists of multiple words, then the initial words are looked for as prefix commands. In this case, if one of the prefix commands does not exist, an exception is raised. There is no support for multi-line commands. COMMAND_CLASS should be one of the COMMAND_' constants defined below. This argument tells GDB how to categorize the new command in the help system. COMPLETER_CLASS is an optional argument. If given, it should be one of the COMPLETE_' constants defined below. This argument tells GDB how to perform completion for this command. If not given, GDB will attempt to complete using the object's complete' method (see below); if no such method is found, an error will occur when completion is attempted. PREFIX is an optional argument. If True', then the new command is a prefix command; sub-commands of this command may be registered. The help text for the new command is taken from the Python documentation string for the command's class, if there is one. If no documentation string is provided, the default value "This command is not documented." is used. -- Method on Command: dont_repeat By default, a GDB command is repeated when the user enters a blank line at the command prompt. A command can suppress this behavior by invoking the dont_repeat' method. This is similar to the user command dont-repeat', see *note dont-repeat: Define. -- Method on Command: invoke argument from_tty This method is called by GDB when this command is invoked. ARGUMENT is a string. It is the argument to the command, after leading and trailing whitespace has been stripped. FROM_TTY is a boolean argument. When true, this means that the command was entered by the user at the terminal; when false it means that the command came from elsewhere. If this method throws an exception, it is turned into a GDB error' call. Otherwise, the return value is ignored. To break ARGUMENT up into an argv-like string use gdb.string_to_argv'. This function behaves identically to GDB's internal argument lexer buildargv'. It is recommended to use this for consistency. Arguments are separated by spaces and may be quoted. Example: print gdb.string_to_argv ("1 2\ \\\"3 '4 \"5' \"6 '7\"") ['1', '2 "3', '4 "5', "6 '7"] -- Method on Command: complete text word This method is called by GDB when the user attempts completion on this command. All forms of completion are handled by this method, that is, the <TAB> and <M-?> key bindings (*note Completion::), and the complete' command (*note complete: Help.). The arguments TEXT and WORD are both strings. TEXT holds the complete command line up to the cursor's location. WORD holds the last word of the command line; this is computed using a word-breaking heuristic. The complete' method can return several values: * If the return value is a sequence, the contents of the sequence are used as the completions. It is up to complete' to ensure that the contents actually do complete the word. A zero-length sequence is allowed, it means that there were no completions available. Only string elements of the sequence are used; other elements in the sequence are ignored. * If the return value is one of the COMPLETE_' constants defined below, then the corresponding GDB-internal completion function is invoked, and its result is used. * All other results are treated as though there were no available completions. When a new command is registered, it must be declared as a member of some general class of commands. This is used to classify top-level commands in the on-line help system; note that prefix commands are not listed under their own category but rather that of their top-level command. The available classifications are represented by constants defined in the gdb' module: COMMAND_NONE' The command does not belong to any particular class. A command in this category will not be displayed in any of the help categories. COMMAND_RUNNING' The command is related to running the inferior. For example, start', step', and continue' are in this category. Type help running' at the GDB prompt to see a list of commands in this category. COMMAND_DATA' The command is related to data or variables. For example, call', find', and print' are in this category. Type help data' at the GDB prompt to see a list of commands in this category. COMMAND_STACK' The command has to do with manipulation of the stack. For example, backtrace', frame', and return' are in this category. Type help stack' at the GDB prompt to see a list of commands in this category. COMMAND_FILES' This class is used for file-related commands. For example, file', list' and section' are in this category. Type help files' at the GDB prompt to see a list of commands in this category. COMMAND_SUPPORT' This should be used for "support facilities", generally meaning things that are useful to the user when interacting with GDB, but not related to the state of the inferior. For example, help', make', and shell' are in this category. Type help support' at the GDB prompt to see a list of commands in this category. COMMAND_STATUS' The command is an info'-related command, that is, related to the state of GDB itself. For example, info', macro', and show' are in this category. Type help status' at the GDB prompt to see a list of commands in this category. COMMAND_BREAKPOINTS' The command has to do with breakpoints. For example, break', clear', and delete' are in this category. Type help breakpoints' at the GDB prompt to see a list of commands in this category. COMMAND_TRACEPOINTS' The command has to do with tracepoints. For example, trace', actions', and tfind' are in this category. Type help tracepoints' at the GDB prompt to see a list of commands in this category. COMMAND_OBSCURE' The command is only used in unusual circumstances, or is not of general interest to users. For example, checkpoint', fork', and stop' are in this category. Type help obscure' at the GDB prompt to see a list of commands in this category. COMMAND_MAINTENANCE' The command is only useful to GDB maintainers. The maintenance' and flushregs' commands are in this category. Type help internals' at the GDB prompt to see a list of commands in this category. A new command can use a predefined completion function, either by specifying it via an argument at initialization, or by returning it from the complete' method. These predefined completion constants are all defined in the gdb' module: COMPLETE_NONE' This constant means that no completion should be done. COMPLETE_FILENAME' This constant means that filename completion should be performed. COMPLETE_LOCATION' This constant means that location completion should be done. *Note Specify Location::. COMPLETE_COMMAND' This constant means that completion should examine GDB command names. COMPLETE_SYMBOL' This constant means that completion should be done using symbol names as the source. The following code snippet shows how a trivial CLI command can be implemented in Python: class HelloWorld (gdb.Command): """Greet the whole world.""" def __init__ (self): super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_OBSCURE) def invoke (self, arg, from_tty): print "Hello, World!" HelloWorld () The last line instantiates the class, and is necessary to trigger the registration of the command with GDB. Depending on how the Python code is read into GDB, you may need to import the gdb' module explicitly. File: gdb.info, Node: Parameters In Python, Next: Functions In Python, Prev: Commands In Python, Up: Python API 23.2.2.11 Parameters In Python .............................. You can implement new GDB parameters using Python. A new parameter is implemented as an instance of the gdb.Parameter' class. Parameters are exposed to the user via the set' and show' commands. *Note Help::. There are many parameters that already exist and can be set in GDB. Two examples are: set follow fork' and set charset'. Setting these parameters influences certain behavior in GDB. Similarly, you can define parameters that can be used to influence behavior in custom Python scripts and commands. -- Method on Parameter: __init__ name COMMAND-CLASS PARAMETER-CLASS [ENUM-SEQUENCE] The object initializer for Parameter' registers the new parameter with GDB. This initializer is normally invoked from the subclass' own __init__' method. NAME is the name of the new parameter. If NAME consists of multiple words, then the initial words are looked for as prefix parameters. An example of this can be illustrated with the set print' set of parameters. If NAME is print foo', then print' will be searched as the prefix parameter. In this case the parameter can subsequently be accessed in GDB as set print foo'. If NAME consists of multiple words, and no prefix parameter group can be found, an exception is raised. COMMAND-CLASS should be one of the COMMAND_' constants (*note Commands In Python::). This argument tells GDB how to categorize the new parameter in the help system. PARAMETER-CLASS should be one of the PARAM_' constants defined below. This argument tells GDB the type of the new parameter; this information is used for input validation and completion. If PARAMETER-CLASS is PARAM_ENUM', then ENUM-SEQUENCE must be a sequence of strings. These strings represent the possible values for the parameter. If PARAMETER-CLASS is not PARAM_ENUM', then the presence of a fourth argument will cause an exception to be thrown. The help text for the new parameter is taken from the Python documentation string for the parameter's class, if there is one. If there is no documentation string, a default value is used. -- Instance Variable of Parameter: set_doc If this attribute exists, and is a string, then its value is used as the help text for this parameter's set' command. The value is examined when Parameter.__init__' is invoked; subsequent changes have no effect. -- Instance Variable of Parameter: show_doc If this attribute exists, and is a string, then its value is used as the help text for this parameter's show' command. The value is examined when Parameter.__init__' is invoked; subsequent changes have no effect. -- Instance Variable of Parameter: value The value' attribute holds the underlying value of the parameter. It can be read and assigned to just as any other attribute. GDB does validation when assignments are made. When a new parameter is defined, its type must be specified. The available types are represented by constants defined in the gdb' module: PARAM_BOOLEAN' The value is a plain boolean. The Python boolean values, True' and False' are the only valid values. PARAM_AUTO_BOOLEAN' The value has three possible states: true, false, and auto'. In Python, true and false are represented using boolean constants, and auto' is represented using None'. PARAM_UINTEGER' The value is an unsigned integer. The value of 0 should be interpreted to mean "unlimited". PARAM_INTEGER' The value is a signed integer. The value of 0 should be interpreted to mean "unlimited". PARAM_STRING' The value is a string. When the user modifies the string, any escape sequences, such as \t', \f', and octal escapes, are translated into corresponding characters and encoded into the current host charset. PARAM_STRING_NOESCAPE' The value is a string. When the user modifies the string, escapes are passed through untranslated. PARAM_OPTIONAL_FILENAME' The value is a either a filename (a string), or None'. PARAM_FILENAME' The value is a filename. This is just like PARAM_STRING_NOESCAPE', but uses file names for completion. PARAM_ZINTEGER' The value is an integer. This is like PARAM_INTEGER', except 0 is interpreted as itself. PARAM_ENUM' The value is a string, which must be one of a collection string constants provided when the parameter is created. File: gdb.info, Node: Functions In Python, Next: Progspaces In Python, Prev: Parameters In Python, Up: Python API 23.2.2.12 Writing new convenience functions ........................................... You can implement new convenience functions (*note Convenience Vars::) in Python. A convenience function is an instance of a subclass of the class gdb.Function'. -- Method on Function: __init__ name The initializer for Function' registers the new function with GDB. The argument NAME is the name of the function, a string. The function will be visible to the user as a convenience variable of type internal function', whose name is the same as the given NAME. The documentation for the new function is taken from the documentation string for the new class. -- Method on Function: invoke *ARGS When a convenience function is evaluated, its arguments are converted to instances of gdb.Value', and then the function's invoke' method is called. Note that GDB does not predetermine the arity of convenience functions. Instead, all available arguments are passed to invoke', following the standard Python calling convention. In particular, a convenience function can have default values for parameters without ill effect. The return value of this method is used as its value in the enclosing expression. If an ordinary Python value is returned, it is converted to a gdb.Value' following the usual rules. The following code snippet shows how a trivial convenience function can be implemented in Python: class Greet (gdb.Function): """Return string to greet someone. Takes a name as argument.""" def __init__ (self): super (Greet, self).__init__ ("greet") def invoke (self, name): return "Hello, %s!" % name.string () Greet () The last line instantiates the class, and is necessary to trigger the registration of the function with GDB. Depending on how the Python code is read into GDB, you may need to import the gdb' module explicitly. File: gdb.info, Node: Progspaces In Python, Next: Objfiles In Python, Prev: Functions In Python, Up: Python API 23.2.2.13 Program Spaces In Python .................................. A program space, or "progspace", represents a symbolic view of an address space. It consists of all of the objfiles of the program. *Note Objfiles In Python::. *Note program spaces: Inferiors and Programs, for more details about program spaces. The following progspace-related functions are available in the gdb' module: -- Function: current_progspace This function returns the program space of the currently selected inferior. *Note Inferiors and Programs::. -- Function: progspaces Return a sequence of all the progspaces currently known to GDB. Each progspace is represented by an instance of the gdb.Progspace' class. -- Instance Variable of Progspace: filename The file name of the progspace as a string. -- Instance Variable of Progspace: pretty_printers The pretty_printers' attribute is a list of functions. It is used to look up pretty-printers. A Value' is passed to each function in order; if the function returns None', then the search continues. Otherwise, the return value should be an object which is used to format the value. *Note Pretty Printing API::, for more information. File: gdb.info, Node: Objfiles In Python, Next: Frames In Python, Prev: Progspaces In Python, Up: Python API 23.2.2.14 Objfiles In Python ............................ GDB loads symbols for an inferior from various symbol-containing files (*note Files::). These include the primary executable file, any shared libraries used by the inferior, and any separate debug info files (*note Separate Debug Files::). GDB calls these symbol-containing files "objfiles". The following objfile-related functions are available in the gdb' module: -- Function: current_objfile When auto-loading a Python script (*note Python Auto-loading::), GDB sets the "current objfile" to the corresponding objfile. This function returns the current objfile. If there is no current objfile, this function returns None'. -- Function: objfiles Return a sequence of all the objfiles current known to GDB. *Note Objfiles In Python::. Each objfile is represented by an instance of the gdb.Objfile' class. -- Instance Variable of Objfile: filename The file name of the objfile as a string. -- Instance Variable of Objfile: pretty_printers The pretty_printers' attribute is a list of functions. It is used to look up pretty-printers. A Value' is passed to each function in order; if the function returns None', then the search continues. Otherwise, the return value should be an object which is used to format the value. *Note Pretty Printing API::, for more information. File: gdb.info, Node: Frames In Python, Next: Blocks In Python, Prev: Objfiles In Python, Up: Python API 23.2.2.15 Accessing inferior stack frames from Python. ...................................................... When the debugged program stops, GDB is able to analyze its call stack (*note Stack frames: Frames.). The gdb.Frame' class represents a frame in the stack. A gdb.Frame' object is only valid while its corresponding frame exists in the inferior's stack. If you try to use an invalid frame object, GDB will throw a RuntimeError' exception. Two gdb.Frame' objects can be compared for equality with the ==' operator, like: (gdb) python print gdb.newest_frame() == gdb.selected_frame () True The following frame-related functions are available in the gdb' module: -- Function: selected_frame Return the selected frame object. (*note Selecting a Frame: Selection.). -- Function: frame_stop_reason_string reason Return a string explaining the reason why GDB stopped unwinding frames, as expressed by the given REASON code (an integer, see the unwind_stop_reason' method further down in this section). A gdb.Frame' object has the following methods: -- Method on Frame: is_valid Returns true if the gdb.Frame' object is valid, false if not. A frame object can become invalid if the frame it refers to doesn't exist anymore in the inferior. All gdb.Frame' methods will throw an exception if it is invalid at the time the method is called. -- Method on Frame: name Returns the function name of the frame, or None' if it can't be obtained. -- Method on Frame: type Returns the type of the frame. The value can be one of gdb.NORMAL_FRAME', gdb.DUMMY_FRAME', gdb.SIGTRAMP_FRAME' or gdb.SENTINEL_FRAME'. -- Method on Frame: unwind_stop_reason Return an integer representing the reason why it's not possible to find more frames toward the outermost frame. Use gdb.frame_stop_reason_string' to convert the value returned by this function to a string. -- Method on Frame: pc Returns the frame's resume address. -- Method on Frame: block Return the frame's code block. *Note Blocks In Python::. -- Method on Frame: function Return the symbol for the function corresponding to this frame. *Note Symbols In Python::. -- Method on Frame: older Return the frame that called this frame. -- Method on Frame: newer Return the frame called by this frame. -- Method on Frame: find_sal Return the frame's symtab and line object. *Note Symbol Tables In Python::. -- Method on Frame: read_var variable [block] Return the value of VARIABLE in this frame. If the optional argument BLOCK is provided, search for the variable from that block; otherwise start at the frame's current block (which is determined by the frame's current program counter). VARIABLE must be a string or a gdb.Symbol' object. BLOCK must be a gdb.Block' object. -- Method on Frame: select Set this frame to be the selected frame. *Note Examining the Stack: Stack. File: gdb.info, Node: Blocks In Python, Next: Symbols In Python, Prev: Frames In Python, Up: Python API 23.2.2.16 Accessing frame blocks from Python. ............................................. Within each frame, GDB maintains information on each block stored in that frame. These blocks are organized hierarchically, and are represented individually in Python as a gdb.Block'. Please see *note Frames In Python::, for a more in-depth discussion on frames. Furthermore, see *note Examining the Stack: Stack, for more detailed technical information on GDB's book-keeping of the stack. The following block-related functions are available in the gdb' module: -- Function: block_for_pc pc Return the gdb.Block' containing the given PC value. If the block cannot be found for the PC value specified, the function will return None'. A gdb.Block' object has the following attributes: -- Instance Variable of Block: start The start address of the block. This attribute is not writable. -- Instance Variable of Block: end The end address of the block. This attribute is not writable. -- Instance Variable of Block: function The name of the block represented as a gdb.Symbol'. If the block is not named, then this attribute holds None'. This attribute is not writable. -- Instance Variable of Block: superblock The block containing this block. If this parent block does not exist, this attribute holds None'. This attribute is not writable. File: gdb.info, Node: Symbols In Python, Next: Symbol Tables In Python, Prev: Blocks In Python, Up: Python API 23.2.2.17 Python representation of Symbols. ........................................... GDB represents every variable, function and type as an entry in a symbol table. *Note Examining the Symbol Table: Symbols. Similarly, Python represents these symbols in GDB with the gdb.Symbol' object. The following symbol-related functions are available in the gdb' module: -- Function: lookup_symbol name [block] [domain] This function searches for a symbol by name. The search scope can be restricted to the parameters defined in the optional domain and block arguments. NAME is the name of the symbol. It must be a string. The optional BLOCK argument restricts the search to symbols visible in that BLOCK. The BLOCK argument must be a gdb.Block' object. The optional DOMAIN argument restricts the search to the domain type. The DOMAIN argument must be a domain constant defined in the gdb' module and described later in this chapter. A gdb.Symbol' object has the following attributes: -- Instance Variable of Symbol: symtab The symbol table in which the symbol appears. This attribute is represented as a gdb.Symtab' object. *Note Symbol Tables In Python::. This attribute is not writable. -- Instance Variable of Symbol: name The name of the symbol as a string. This attribute is not writable. -- Instance Variable of Symbol: linkage_name The name of the symbol, as used by the linker (i.e., may be mangled). This attribute is not writable. -- Instance Variable of Symbol: print_name The name of the symbol in a form suitable for output. This is either name' or linkage_name', depending on whether the user asked GDB to display demangled or mangled names. -- Instance Variable of Symbol: addr_class The address class of the symbol. This classifies how to find the value of a symbol. Each address class is a constant defined in the gdb' module and described later in this chapter. -- Instance Variable of Symbol: is_argument True' if the symbol is an argument of a function. -- Instance Variable of Symbol: is_constant True' if the symbol is a constant. -- Instance Variable of Symbol: is_function True' if the symbol is a function or a method. -- Instance Variable of Symbol: is_variable True' if the symbol is a variable. The available domain categories in gdb.Symbol' are represented as constants in the gdb' module: SYMBOL_UNDEF_DOMAIN' This is used when a domain has not been discovered or none of the following domains apply. This usually indicates an error either in the symbol information or in GDB's handling of symbols. SYMBOL_VAR_DOMAIN' This domain contains variables, function names, typedef names and enum type values. SYMBOL_STRUCT_DOMAIN' This domain holds struct, union and enum type names. SYMBOL_LABEL_DOMAIN' This domain contains names of labels (for gotos). SYMBOL_VARIABLES_DOMAIN' This domain holds a subset of the SYMBOLS_VAR_DOMAIN'; it contains everything minus functions and types. SYMBOL_FUNCTION_DOMAIN' This domain contains all functions. SYMBOL_TYPES_DOMAIN' This domain contains all types. The available address class categories in gdb.Symbol' are represented as constants in the gdb' module: SYMBOL_LOC_UNDEF' If this is returned by address class, it indicates an error either in the symbol information or in GDB's handling of symbols. SYMBOL_LOC_CONST' Value is constant int. SYMBOL_LOC_STATIC' Value is at a fixed address. SYMBOL_LOC_REGISTER' Value is in a register. SYMBOL_LOC_ARG' Value is an argument. This value is at the offset stored within the symbol inside the frame's argument list. SYMBOL_LOC_REF_ARG' Value address is stored in the frame's argument list. Just like LOC_ARG' except that the value's address is stored at the offset, not the value itself. SYMBOL_LOC_REGPARM_ADDR' Value is a specified register. Just like LOC_REGISTER' except the register holds the address of the argument instead of the argument itself. SYMBOL_LOC_LOCAL' Value is a local variable. SYMBOL_LOC_TYPEDEF' Value not used. Symbols in the domain SYMBOL_STRUCT_DOMAIN' all have this class. SYMBOL_LOC_BLOCK' Value is a block. SYMBOL_LOC_CONST_BYTES' Value is a byte-sequence. SYMBOL_LOC_UNRESOLVED' Value is at a fixed address, but the address of the variable has to be determined from the minimal symbol table whenever the variable is referenced. SYMBOL_LOC_OPTIMIZED_OUT' The value does not actually exist in the program. SYMBOL_LOC_COMPUTED' The value's address is a computed location. File: gdb.info, Node: Symbol Tables In Python, Next: Lazy Strings In Python, Prev: Symbols In Python, Up: Python API 23.2.2.18 Symbol table representation in Python. ................................................ Access to symbol table data maintained by GDB on the inferior is exposed to Python via two objects: gdb.Symtab_and_line' and gdb.Symtab'. Symbol table and line data for a frame is returned from the find_sal' method in gdb.Frame' object. *Note Frames In Python::. For more information on GDB's symbol table management, see *note Examining the Symbol Table: Symbols, for more information. A gdb.Symtab_and_line' object has the following attributes: -- Instance Variable of Symtab_and_line: symtab The symbol table object (gdb.Symtab') for this frame. This attribute is not writable. -- Instance Variable of Symtab_and_line: pc Indicates the current program counter address. This attribute is not writable. -- Instance Variable of Symtab_and_line: line Indicates the current line number for this object. This attribute is not writable. A gdb.Symtab' object has the following attributes: -- Instance Variable of Symtab: filename The symbol table's source filename. This attribute is not writable. -- Instance Variable of Symtab: objfile The symbol table's backing object file. *Note Objfiles In Python::. This attribute is not writable. The following methods are provided: -- Method on Symtab: fullname Return the symbol table's source absolute file name. File: gdb.info, Node: Lazy Strings In Python, Next: Breakpoints In Python, Prev: Symbol Tables In Python, Up: Python API 23.2.2.20 Python representation of lazy strings. ................................................ A "lazy string" is a string whose contents is not retrieved or encoded until it is needed. A gdb.LazyString' is represented in GDB as an address' that points to a region of memory, an encoding' that will be used to encode that region of memory, and a length' to delimit the region of memory that represents the string. The difference between a gdb.LazyString' and a string wrapped within a gdb.Value' is that a gdb.LazyString' will be treated differently by GDB when printing. A gdb.LazyString' is retrieved and encoded during printing, while a gdb.Value' wrapping a string is immediately retrieved and encoded on creation. A gdb.LazyString' object has the following functions: -- Method on LazyString: value Convert the gdb.LazyString' to a gdb.Value'. This value will point to the string in memory, but will lose all the delayed retrieval, encoding and handling that GDB applies to a gdb.LazyString'. -- Instance Variable of LazyString: address This attribute holds the address of the string. This attribute is not writable. -- Instance Variable of LazyString: length This attribute holds the length of the string in characters. If the length is -1, then the string will be fetched and encoded up to the first null of appropriate width. This attribute is not writable. -- Instance Variable of LazyString: encoding This attribute holds the encoding that will be applied to the string when the string is printed by GDB. If the encoding is not set, or contains an empty string, then GDB will select the most appropriate encoding when the string is printed. This attribute is not writable. -- Instance Variable of LazyString: type This attribute holds the type that is represented by the lazy string's type. For a lazy string this will always be a pointer type. To resolve this to the lazy string's character type, use the type's target' method. *Note Types In Python::. This attribute is not writable. File: gdb.info, Node: Breakpoints In Python, Prev: Lazy Strings In Python, Up: Python API 23.2.2.19 Manipulating breakpoints using Python ............................................... Python code can manipulate breakpoints via the gdb.Breakpoint' class. -- Method on Breakpoint: __init__ spec [type] [wp_class] Create a new breakpoint. SPEC is a string naming the location of the breakpoint, or an expression that defines a watchpoint. The contents can be any location recognized by the break' command, or in the case of a watchpoint, by the watch' command. The optional TYPE denotes the breakpoint to create from the types defined later in this chapter. This argument can be either: BP_BREAKPOINT' or BP_WATCHPOINT'. TYPE defaults to BP_BREAKPOINT'. The optional WP_CLASS argument defines the class of watchpoint to create, if TYPE is defined as BP_WATCHPOINT'. If a watchpoint class is not provided, it is assumed to be a WP_WRITE class. The available watchpoint types represented by constants are defined in the gdb' module: WP_READ' Read only watchpoint. WP_WRITE' Write only watchpoint. WP_ACCESS' Read/Write watchpoint. -- Method on Breakpoint: is_valid Return True' if this Breakpoint' object is valid, False' otherwise. A Breakpoint' object can become invalid if the user deletes the breakpoint. In this case, the object still exists, but the underlying breakpoint does not. In the cases of watchpoint scope, the watchpoint remains valid even if execution of the inferior leaves the scope of that watchpoint. -- Instance Variable of Breakpoint: enabled This attribute is True' if the breakpoint is enabled, and False' otherwise. This attribute is writable. -- Instance Variable of Breakpoint: silent This attribute is True' if the breakpoint is silent, and False' otherwise. This attribute is writable. Note that a breakpoint can also be silent if it has commands and the first command is silent'. This is not reported by the silent' attribute. -- Instance Variable of Breakpoint: thread If the breakpoint is thread-specific, this attribute holds the thread id. If the breakpoint is not thread-specific, this attribute is None'. This attribute is writable. -- Instance Variable of Breakpoint: task If the breakpoint is Ada task-specific, this attribute holds the Ada task id. If the breakpoint is not task-specific (or the underlying language is not Ada), this attribute is None'. This attribute is writable. -- Instance Variable of Breakpoint: ignore_count This attribute holds the ignore count for the breakpoint, an integer. This attribute is writable. -- Instance Variable of Breakpoint: number This attribute holds the breakpoint's number -- the identifier used by the user to manipulate the breakpoint. This attribute is not writable. -- Instance Variable of Breakpoint: type This attribute holds the breakpoint's type -- the identifier used to determine the actual breakpoint type or use-case. This attribute is not writable. The available types are represented by constants defined in the gdb' module: BP_BREAKPOINT' Normal code breakpoint. BP_WATCHPOINT' Watchpoint breakpoint. BP_HARDWARE_WATCHPOINT' Hardware assisted watchpoint. BP_READ_WATCHPOINT' Hardware assisted read watchpoint. BP_ACCESS_WATCHPOINT' Hardware assisted access watchpoint. -- Instance Variable of Breakpoint: hit_count This attribute holds the hit count for the breakpoint, an integer. This attribute is writable, but currently it can only be set to zero. -- Instance Variable of Breakpoint: location This attribute holds the location of the breakpoint, as specified by the user. It is a string. If the breakpoint does not have a location (that is, it is a watchpoint) the attribute's value is None'. This attribute is not writable. -- Instance Variable of Breakpoint: expression This attribute holds a breakpoint expression, as specified by the user. It is a string. If the breakpoint does not have an expression (the breakpoint is not a watchpoint) the attribute's value is None'. This attribute is not writable. -- Instance Variable of Breakpoint: condition This attribute holds the condition of the breakpoint, as specified by the user. It is a string. If there is no condition, this attribute's value is None'. This attribute is writable. -- Instance Variable of Breakpoint: commands This attribute holds the commands attached to the breakpoint. If there are commands, this attribute's value is a string holding all the commands, separated by newlines. If there are no commands, this attribute is None'. This attribute is not writable. File: gdb.info, Node: Python Auto-loading, Prev: Python API, Up: Python 23.2.3 Python Auto-loading -------------------------- When a new object file is read (for example, due to the file' command, or because the inferior has loaded a shared library), GDB will look for Python support scripts in several ways: OBJFILE-gdb.py' and .debug_gdb_scripts' section. * Menu: * objfile-gdb.py file:: The OBJFILE-gdb.py' file * dotdebug_gdb_scripts section:: The .debug_gdb_scripts' section * Which flavor to choose?:: The auto-loading feature is useful for supplying application-specific debugging commands and scripts. Auto-loading can be enabled or disabled, and the list of auto-loaded scripts can be printed. set auto-load python-scripts [on|off]' Enable or disable the auto-loading of Python scripts. show auto-load python-scripts' Show whether auto-loading of Python scripts is enabled or disabled. info auto-load python-scripts [REGEXP]' Print the list of all Python scripts that GDB auto-loaded. Also printed is the list of Python scripts that were mentioned in the .debug_gdb_scripts' section and were not found (*note dotdebug_gdb_scripts section::). This is useful because their names are not printed when GDB tries to load them and fails. There may be many of them, and printing an error message for each one is problematic. If REGEXP is supplied only Python scripts with matching names are printed. Example: (gdb) info auto-load python-scripts Loaded Script Yes py-section-script.py full name: /tmp/py-section-script.py No my-foo-pretty-printers.py When reading an auto-loaded file, GDB sets the "current objfile". This is available via the gdb.current_objfile' function (*note Objfiles In Python::). This can be useful for registering objfile-specific pretty-printers. File: gdb.info, Node: objfile-gdb.py file, Next: dotdebug_gdb_scripts section, Up: Python Auto-loading 23.2.3.1 The OBJFILE-gdb.py' file .................................. When a new object file is read, GDB looks for a file named OBJFILE-gdb.py' (we call it SCRIPT-NAME below), where OBJFILE is the object file's real name, formed by ensuring that the file name is absolute, following all symlinks, and resolving .' and ..' components. If this file exists and is readable, GDB will evaluate it as a Python script. If this file does not exist, then GDB will look for SCRIPT-NAME file in all of the directories as specified below. Note that loading of this script file also requires accordingly configured auto-load safe-path' (*note Auto-loading safe path::). For object files using .exe' suffix GDB tries to load first the scripts normally according to its .exe' filename. But if no scripts are found GDB also tries script filenames matching the object file without its .exe' suffix. This .exe' stripping is case insensitive and it is attempted on any platform. This makes the script filenames compatible between Unix and MS-Windows hosts. set auto-load scripts-directory [DIRECTORIES]' Control GDB auto-loaded scripts location. Multiple directory entries may be delimited by the host platform path separator in use (:' on Unix, ;' on MS-Windows and MS-DOS). Each entry here needs to be covered also by the security setting set auto-load safe-path' (*note set auto-load safe-path::). This variable defaults to $debugdir:$datadir/auto-load'. The default set auto-load safe-path' value can be also overriden by GDB configuration option --with-auto-load-dir'. Any reference to $debugdir' will get replaced by
DEBUG-FILE-DIRECTORY value (*note Separate Debug Files::) and any
reference to $datadir' will get replaced by DATA-DIRECTORY which is determined at GDB startup (*note Data Files::). $debugdir' and
$datadir' must be placed as a directory component -- either alone or delimited by /' or \' directory separators, depending on the host platform. The list of directories uses path separator (:' on GNU and Unix systems, ;' on MS-Windows and MS-DOS) to separate directories, similarly to the PATH' environment variable. show auto-load scripts-directory' Show GDB auto-loaded scripts location. GDB does not track which files it has already auto-loaded this way. GDB will load the associated script every time the corresponding OBJFILE is opened. So your -gdb.py' file should be careful to avoid errors if it is evaluated more than once. File: gdb.info, Node: dotdebug_gdb_scripts section, Next: Which flavor to choose?, Prev: objfile-gdb.py file, Up: Python Auto-loading 23.2.3.2 The .debug_gdb_scripts' section ......................................... For systems using file formats like ELF and COFF, when GDB loads a new object file it will look for a special section named .debug_gdb_scripts'. If this section exists, its contents is a list of names of scripts to load. GDB will look for each specified script file first in the current directory and then along the source search path (*note Specifying Source Directories: Source Path.), except that $cdir' is not searched,
since the compilation directory is not relevant to scripts.

Entries can be placed in section .debug_gdb_scripts' with, for
example, this GCC macro:

/* Note: The "MS" section flags are to remove duplicates.  */
#define DEFINE_GDB_SCRIPT(script_name) \
asm("\
.pushsection \".debug_gdb_scripts\", \"MS\",@progbits,1\n\
.byte 1\n\
.asciz \"" script_name "\"\n\
.popsection \n\
");

Then one can reference the macro in a header or source file like this:

DEFINE_GDB_SCRIPT ("my-app-scripts.py")

The script name may include directories if desired.

Note that loading of this script file also requires accordingly

If the macro is put in a header, any application or library using
this header will get a reference to the specified script.

File: gdb.info,  Node: Which flavor to choose?,  Prev: dotdebug_gdb_scripts section,  Up: Python Auto-loading

23.2.3.3 Which flavor to choose?
................................

Given the multiple ways of auto-loading Python scripts, it might not
always be clear which one to choose.  This section provides some
guidance.

Benefits of the -gdb.py' way:

* Can be used with file formats that don't support multiple sections.

* Ease of finding scripts for public libraries.

Scripts specified in the .debug_gdb_scripts' section are searched
for in the source search path.  For publicly installed libraries,
e.g., libstdc++', there typically isn't a source directory in
which to find the script.

* Doesn't require source code additions.

Benefits of the .debug_gdb_scripts' way:

* Works with static linking.

Scripts for libraries done the -gdb.py' way require an objfile to
the only objfile available is the executable, and it is cumbersome
to attach all the scripts from all the input libraries to the
executable's -gdb.py' script.

* Works with classes that are entirely inlined.

Some classes can be entirely inlined, and thus there may not be an
associated shared library to attach a -gdb.py' script to.

* Scripts needn't be copied out of the source tree.

In some circumstances, apps can be built out of large collections
of internal libraries, and the build infrastructure necessary to
install the -gdb.py' scripts in a place where GDB can find them is
cumbersome.  It may be easier to specify the scripts in the
.debug_gdb_scripts' section as relative paths, and add a path to
the top of the source tree to the source search path.

File: gdb.info,  Node: Interpreters,  Next: TUI,  Prev: Extending GDB,  Up: Top

24 Command Interpreters
***********************

GDB supports multiple command interpreters, and some command
infrastructure to allow users or user interface writers to switch
between interpreters or run commands in other interpreters.

GDB currently supports two command interpreters, the console
interpreter (sometimes called the command-line interpreter or CLI) and
the machine interface interpreter (or GDB/MI).  This manual describes
both of these interfaces in great detail.

By default, GDB will start with the console interpreter.  However,
the user may choose to start GDB with another interpreter by specifying
the -i' or --interpreter' startup options.  Defined interpreters
include:

console'
The traditional console or command-line interpreter.  This is the
most often used interpreter with GDB. With no interpreter
specified at runtime, GDB will use this interpreter.

mi'
The newest GDB/MI interface (currently mi2').  Used primarily by
programs wishing to use GDB as a backend for a debugger GUI or an
IDE.  For more information, see *note The GDB/MI Interface: GDB/MI.

mi2'
The current GDB/MI interface.

mi1'
The GDB/MI interface included in GDB 5.1, 5.2, and 5.3.

The interpreter being used by GDB may not be dynamically switched at
runtime.  Although possible, this could lead to a very precarious
situation.  Consider an IDE using GDB/MI.  If a user enters the command
"interpreter-set console" in a console view, GDB would switch to using
the console interpreter, rendering the IDE inoperable!

Although you may only choose a single interpreter at startup, you
may execute commands in any interpreter from the current interpreter
using the appropriate command.  If you are running the console
interpreter, simply use the interpreter-exec' command:

interpreter-exec mi "-data-list-register-names"

GDB/MI has a similar command, although it is only available in
versions of GDB which support GDB/MI version 2 (or greater).

File: gdb.info,  Node: TUI,  Next: Emacs,  Prev: Interpreters,  Up: Top

25 GDB Text User Interface
**************************

* TUI Overview::                TUI overview
* TUI Keys::                    TUI key bindings
* TUI Single Key Mode::         TUI single key mode
* TUI Commands::                TUI-specific commands
* TUI Configuration::           TUI configuration variables

The GDB Text User Interface (TUI) is a terminal interface which uses
the curses' library to show the source file, the assembly output, the
program registers and GDB commands in separate text windows.  The TUI
mode is supported only on platforms where a suitable version of the
curses' library is available.

The TUI mode is enabled by default when you invoke GDB as either
gdbtui' or gdb -tui'.  You can also switch in and out of TUI mode
while GDB runs by using various TUI commands and key bindings, such as
C-x C-a'.  *Note TUI Key Bindings: TUI Keys.

File: gdb.info,  Node: TUI Overview,  Next: TUI Keys,  Up: TUI

25.1 TUI Overview
=================

In TUI mode, GDB can display several text windows:

_command_
This window is the GDB command window with the GDB prompt and the
GDB output.  The GDB input is still managed using readline.

_source_
The source window shows the source file of the program.  The
current line and active breakpoints are displayed in this window.

_assembly_
The assembly window shows the disassembly output of the program.

_register_
This window shows the processor registers.  Registers are
highlighted when their values change.

The source and assembly windows show the current program position by
highlighting the current line and marking it with a >' marker.
Breakpoints are indicated with two markers.  The first marker indicates
the breakpoint type:

B'
Breakpoint which was hit at least once.

b'
Breakpoint which was never hit.

H'
Hardware breakpoint which was hit at least once.

h'
Hardware breakpoint which was never hit.

The second marker indicates whether the breakpoint is enabled or not:

+'
Breakpoint is enabled.

-'
Breakpoint is disabled.

The source, assembly and register windows are updated when the
current thread changes, when the frame changes, or when the program
counter changes.

These windows are not all visible at the same time.  The command
window is always visible.  The others can be arranged in several
layouts:

* source only,

* assembly only,

* source and assembly,

* source and registers, or

* assembly and registers.

A status line above the command window shows the following
information:

_target_
Indicates the current GDB target.  (*note Specifying a Debugging
Target: Targets.).

_process_
Gives the current process or thread number.  When no process is
being debugged, this field is set to No process'.

_function_
Gives the current function name for the selected frame.  The name
is demangled if demangling is turned on (*note Print Settings::).
When there is no symbol corresponding to the current program
counter, the string ??' is displayed.

_line_
Indicates the current line number for the selected frame.  When
the current line number is not known, the string ??' is displayed.

_pc_
Indicates the current program counter address.

File: gdb.info,  Node: TUI Keys,  Next: TUI Single Key Mode,  Prev: TUI Overview,  Up: TUI

25.2 TUI Key Bindings
=====================

The TUI installs several key bindings in the readline keymaps (*note
Command Line Editing: (rluserman)Command Line Editing.).  The following
key bindings are installed for both TUI mode and the GDB standard mode.

C-x C-a'
C-x a'
C-x A'
Enter or leave the TUI mode.  When leaving the TUI mode, the
curses window management stops and GDB operates using its standard
mode, writing on the terminal directly.  When reentering the TUI
mode, control is given back to the curses windows.  The screen is
then refreshed.

C-x 1'
Use a TUI layout with only one window.  The layout will either be
source' or assembly'.  When the TUI mode is not active, it will
switch to the TUI mode.

Think of this key binding as the Emacs C-x 1' binding.

C-x 2'
Use a TUI layout with at least two windows.  When the current
layout already has two windows, the next layout with two windows
is used.  When a new layout is chosen, one window will always be
common to the previous layout and the new one.

Think of it as the Emacs C-x 2' binding.

C-x o'
Change the active window.  The TUI associates several key bindings
(like scrolling and arrow keys) with the active window.  This
command gives the focus to the next TUI window.

Think of it as the Emacs C-x o' binding.

C-x s'
Switch in and out of the TUI SingleKey mode that binds single keys
to GDB commands (*note TUI Single Key Mode::).

The following key bindings only work in the TUI mode:

<PgUp>
Scroll the active window one page up.

<PgDn>
Scroll the active window one page down.

<Up>
Scroll the active window one line up.

<Down>
Scroll the active window one line down.

<Left>
Scroll the active window one column left.

<Right>
Scroll the active window one column right.

C-L'
Refresh the screen.

Because the arrow keys scroll the active window in the TUI mode, they
are not available for their normal use by readline unless the command
window has the focus.  When another window is active, you must use
other readline key bindings such as C-p', C-n', C-b' and C-f' to
control the command window.

File: gdb.info,  Node: TUI Single Key Mode,  Next: TUI Commands,  Prev: TUI Keys,  Up: TUI

25.3 TUI Single Key Mode
========================

The TUI also provides a "SingleKey" mode, which binds several
frequently used GDB commands to single keys.  Type C-x s' to switch
into this mode, where the following key bindings are used:

c'
continue

d'
down

f'
finish

n'
next

q'
exit the SingleKey mode.

r'
run

s'
step

u'
up

v'
info locals

w'
where

Other keys temporarily switch to the GDB command prompt.  The key
that was pressed is inserted in the editing buffer so that it is
possible to type most GDB commands without interaction with the TUI
SingleKey mode.  Once the command is entered the TUI SingleKey mode is
restored.  The only way to permanently leave this mode is by typing q'
or C-x s'.

File: gdb.info,  Node: TUI Commands,  Next: TUI Configuration,  Prev: TUI Single Key Mode,  Up: TUI

25.4 TUI-specific Commands
==========================

The TUI has specific commands to control the text windows.  These
commands are always available, even when GDB is not in the TUI mode.
When GDB is in the standard mode, most of these commands will
automatically switch to the TUI mode.

Note that if GDB's stdout' is not connected to a terminal, or GDB
has been started with the machine interface interpreter (*note The
GDB/MI Interface: GDB/MI.), most of these commands will fail with an
error, because it would not be possible or desirable to enable curses
window management.

info win'
List and give the size of all displayed windows.

layout next'
Display the next layout.

layout prev'
Display the previous layout.

layout src'
Display the source window only.

layout asm'
Display the assembly window only.

layout split'
Display the source and assembly window.

layout regs'
Display the register window together with the source or assembly
window.

focus next'
Make the next window active for scrolling.

focus prev'
Make the previous window active for scrolling.

focus src'
Make the source window active for scrolling.

focus asm'
Make the assembly window active for scrolling.

focus regs'
Make the register window active for scrolling.

focus cmd'
Make the command window active for scrolling.

refresh'
Refresh the screen.  This is similar to typing C-L'.

tui reg float'
Show the floating point registers in the register window.

tui reg general'
Show the general registers in the register window.

tui reg next'
Show the next register group.  The list of register groups as well
as their order is target specific.  The predefined register groups
are the following: general', float', system', vector', all',
save', restore'.

tui reg system'
Show the system registers in the register window.

update'
Update the source window and the current execution point.

winheight NAME +COUNT'
winheight NAME -COUNT'
Change the height of the window NAME by COUNT lines.  Positive
counts increase the height, while negative counts decrease it.

tabset NCHARS'
Set the width of tab stops to be NCHARS characters.

File: gdb.info,  Node: TUI Configuration,  Prev: TUI Commands,  Up: TUI

25.5 TUI Configuration Variables
================================

Several configuration variables control the appearance of TUI windows.

set tui border-kind KIND'
Select the border appearance for the source, assembly and register
windows.  The possible values are the following:
space'
Use a space character to draw the border.

ascii'
Use ASCII characters +', -' and |' to draw the border.

acs'
Use the Alternate Character Set to draw the border.  The
border is drawn using character line graphics if the terminal
supports them.

set tui border-mode MODE'
set tui active-border-mode MODE'
Select the display attributes for the borders of the inactive
windows or the active window.  The MODE can be one of the
following:
normal'
Use normal attributes to display the border.

standout'
Use standout mode.

reverse'
Use reverse video mode.

half'
Use half bright mode.

half-standout'
Use half bright and standout mode.

bold'
Use extra bright or bold mode.

bold-standout'
Use extra bright or bold and standout mode.

File: gdb.info,  Node: Emacs,  Next: GDB/MI,  Prev: TUI,  Up: Top

26 Using GDB under GNU Emacs
****************************

A special interface allows you to use GNU Emacs to view (and edit) the
source files for the program you are debugging with GDB.

To use this interface, use the command M-x gdb' in Emacs.  Give the
executable file you want to debug as an argument.  This command starts
GDB as a subprocess of Emacs, with input and output through a newly
created Emacs buffer.

Running GDB under Emacs can be just like running GDB normally except
for two things:

* All "terminal" input and output goes through an Emacs buffer,
called the GUD buffer.

This applies both to GDB commands and their output, and to the
input and output done by the program you are debugging.

This is useful because it means that you can copy the text of
previous commands and input them again; you can even use parts of
the output in this way.

All the facilities of Emacs' Shell mode are available for
interacting with your program.  In particular, you can send
signals the usual way--for example, C-c C-c' for an interrupt,
C-c C-z' for a stop.

* GDB displays source code through Emacs.

Each time GDB displays a stack frame, Emacs automatically finds the
source file for that frame and puts an arrow (=>') at the left
margin of the current line.  Emacs uses a separate buffer for
source display, and splits the screen to show both your GDB session
and the source.

Explicit GDB list' or search commands still produce output as
usual, but you probably have no reason to use them from Emacs.

We call this "text command mode".  Emacs 22.1, and later, also uses
a graphical mode, enabled by default, which provides further buffers
that can control the execution and describe the state of your program.
*Note GDB Graphical Interface: (Emacs)GDB Graphical Interface.

If you specify an absolute file name when prompted for the M-x gdb'
argument, then Emacs sets your current working directory to where your
program resides.  If you only specify the file name, then Emacs sets
your current working directory to to the directory associated with the
previous buffer.  In this case, GDB may find your program by searching
your environment's PATH' variable, but on some operating systems it
might not find the source.  So, although the GDB input and output
session proceeds normally, the auxiliary buffer does not display the
current source and line of execution.

The initial working directory of GDB is printed on the top line of
the GUD buffer and this serves as a default for the commands that
specify files for GDB to operate on.  *Note Commands to Specify Files:
Files.

By default, M-x gdb' calls the program called gdb'.  If you need
to call GDB by a different name (for example, if you keep several
configurations around, with different names) you can customize the
Emacs variable gud-gdb-command-name' to run the one you want.

In the GUD buffer, you can use these special Emacs commands in
addition to the standard Shell mode commands:

C-h m'
Describe the features of Emacs' GUD Mode.

C-c C-s'
Execute to another source line, like the GDB step' command; also
update the display window to show the current file and location.

C-c C-n'
Execute to next source line in this function, skipping all function
calls, like the GDB next' command.  Then update the display window
to show the current file and location.

C-c C-i'
Execute one instruction, like the GDB stepi' command; update
display window accordingly.

C-c C-f'
Execute until exit from the selected stack frame, like the GDB
finish' command.

C-c C-r'
Continue execution of your program, like the GDB continue'
command.

C-c <'
Go up the number of frames indicated by the numeric argument
(*note Numeric Arguments: (Emacs)Arguments.), like the GDB up'
command.

C-c >'
Go down the number of frames indicated by the numeric argument,
like the GDB down' command.

In any source file, the Emacs command C-x <SPC>' (gud-break')
tells GDB to set a breakpoint on the source line point is on.

In text command mode, if you type M-x speedbar', Emacs displays a
separate frame which shows a backtrace when the GUD buffer is current.
Move point to any frame in the stack and type <RET> to make it become
the current frame and display the associated source in the source
buffer.  Alternatively, click Mouse-2' to make the selected frame
become the current one.  In graphical mode, the speedbar displays watch
expressions.

If you accidentally delete the source-display buffer, an easy way to
get it back is to type the command f' in the GDB buffer, to request a
frame display; when you run under Emacs, this recreates the source
buffer if necessary to show you the context of the current frame.

The source files displayed in Emacs are in ordinary Emacs buffers
which are visiting the source files in the usual way.  You can edit the
files with these buffers if you wish; but keep in mind that GDB
communicates with Emacs in terms of line numbers.  If you add or delete
lines from the text, the line numbers that GDB knows cease to
correspond properly with the code.

A more detailed description of Emacs' interaction with GDB is given
in the Emacs manual (*note Debuggers: (Emacs)Debuggers.).

File: gdb.info,  Node: GDB/MI,  Next: Annotations,  Prev: Emacs,  Up: Top

27 The GDB/MI Interface
***********************

Function and Purpose
====================

GDB/MI is a line based machine oriented text interface to GDB and is
activated by specifying using the --interpreter' command line option
(*note Mode Options::).  It is specifically intended to support the
development of systems which use the debugger as just one small
component of a larger system.

This chapter is a specification of the GDB/MI interface.  It is
written in the form of a reference manual.

Note that GDB/MI is still under construction, so some of the
features described below are incomplete and subject to change (*note
GDB/MI Development and Front Ends: GDB/MI Development and Front Ends.).

Notation and Terminology
========================

This chapter uses the following notation:

* |' separates two alternatives.

* [ SOMETHING ]' indicates that SOMETHING is optional: it may or
may not be given.

* ( GROUP )*' means that GROUP inside the parentheses may repeat
zero or more times.

* ( GROUP )+' means that GROUP inside the parentheses may repeat
one or more times.

* "STRING"' means a literal STRING.

* GDB/MI General Design::
* GDB/MI Command Syntax::
* GDB/MI Compatibility with CLI::
* GDB/MI Development and Front Ends::
* GDB/MI Output Records::
* GDB/MI Simple Examples::
* GDB/MI Command Description Format::
* GDB/MI Breakpoint Commands::
* GDB/MI Program Context::
* GDB/MI Thread Commands::
* GDB/MI Program Execution::
* GDB/MI Stack Manipulation::
* GDB/MI Variable Objects::
* GDB/MI Data Manipulation::
* GDB/MI Tracepoint Commands::
* GDB/MI Symbol Query::
* GDB/MI File Commands::
* GDB/MI Target Manipulation::
* GDB/MI File Transfer Commands::
* GDB/MI Miscellaneous Commands::

File: gdb.info,  Node: GDB/MI General Design,  Next: GDB/MI Command Syntax,  Up: GDB/MI

27.1 GDB/MI General Design
==========================

Interaction of a GDB/MI frontend with GDB involves three
parts--commands sent to GDB, responses to those commands and
notifications.  Each command results in exactly one response,
indicating either successful completion of the command, or an error.
For the commands that do not resume the target, the response contains
the requested information.  For the commands that resume the target, the
response only indicates whether the target was successfully resumed.
Notifications is the mechanism for reporting changes in the state of the
target, or in GDB state, that cannot conveniently be associated with a
command and reported as part of that command response.

The important examples of notifications are:
* Exec notifications.  These are used to report changes in target
state--when a target is resumed, or stopped.  It would not be
feasible to include this information in response of resuming
commands, because one resume commands can result in multiple
events in different threads.  Also, quite some time may pass
before any event happens in the target, while a frontend needs to
know whether the resuming command itself was successfully executed.

* Console output, and status notifications.  Console output
notifications are used to report output of CLI commands, as well as
diagnostics for other commands.  Status notifications are used to
report the progress of a long-running operation.  Naturally,
including this information in command response would mean no
output is produced until the command is finished, which is
undesirable.

* General notifications.  Commands may have various side effects on
the GDB or target state beyond their official purpose.  For
example, a command may change the selected thread.  Although such
changes can be included in command response, using notification
allows for more orthogonal frontend design.

There's no guarantee that whenever an MI command reports an error,
GDB or the target are in any specific state, and especially, the state
is not reverted to the state before the MI command was processed.
Therefore, whenever an MI command results in an error, we recommend
that the frontend refreshes all the information shown in the user
interface.

* Context management::
* Asynchronous and non-stop modes::

File: gdb.info,  Node: Context management,  Next: Asynchronous and non-stop modes,  Up: GDB/MI General Design

27.1.1 Context management
-------------------------

In most cases when GDB accesses the target, this access is done in
context of a specific thread and frame (*note Frames::).  Often, even
when accessing global data, the target requires that a thread be
specified.  The CLI interface maintains the selected thread and frame,
and supplies them to target on each command.  This is convenient,
because a command line user would not want to specify that information
explicitly on each command, and because user interacts with GDB via a
single terminal, so no confusion is possible as to what thread and
frame are the current ones.

In the case of MI, the concept of selected thread and frame is less
useful.  First, a frontend can easily remember this information itself.
Second, a graphical frontend can have more than one window, each one
used for debugging a different thread, and the frontend might want to
access additional threads for internal purposes.  This increases the
risk that by relying on implicitly selected thread, the frontend may be
operating on a wrong one.  Therefore, each MI command should explicitly
specify which thread and frame to operate on.  To make it possible,
each MI command accepts the --thread' and --frame' options, the value
to each is GDB identifier for thread and frame to operate on.

Usually, each top-level window in a frontend allows the user to
select a thread and a frame, and remembers the user selection for
further operations.  However, in some cases GDB may suggest that the
current thread be changed.  For example, when stopping on a breakpoint
it is reasonable to switch to the thread where breakpoint is hit.  For
another example, if the user issues the CLI thread' command via the
frontend, it is desirable to change the frontend's selected thread to
the one specified by user.  GDB communicates the suggestion to change
current thread using the =thread-selected' notification.  No such
notification is available for the selected frame at the moment.

Note that historically, MI shares the selected thread with CLI, so
frontends used the -thread-select' to execute commands in the right
context.  However, getting this to work right is cumbersome.  The
simplest way is for frontend to emit -thread-select' command before
every command.  This doubles the number of commands that need to be
sent.  The alternative approach is to suppress -thread-select' if the
selected thread in GDB is supposed to be identical to the thread the
frontend wants to operate on.  However, getting this optimization right
can be tricky.  In particular, if the frontend sends several commands
to GDB, and one of the commands changes the selected thread, then the
behaviour of subsequent commands will change.  So, a frontend should
either wait for response from such problematic commands, or explicitly
add -thread-select' for all subsequent commands.  No frontend is known
to do this exactly right, so it is suggested to just always pass the
--thread' and --frame' options.

File: gdb.info,  Node: Asynchronous and non-stop modes,  Next: Thread groups,  Prev: Context management,  Up: GDB/MI General Design

27.1.2 Asynchronous command execution and non-stop mode
-------------------------------------------------------

On some targets, GDB is capable of processing MI commands even while
the target is running.  This is called "asynchronous command execution"
(*note Background Execution::).  The frontend may specify a preferrence
for asynchronous execution using the -gdb-set target-async 1' command,
which should be emitted before either running the executable or
attaching to the target.  After the frontend has started the executable
or attached to the target, it can find if asynchronous execution is
enabled using the -list-target-features' command.

Even if GDB can accept a command while target is running, many
commands that access the target do not work when the target is running.
Therefore, asynchronous command execution is most useful when combined
with non-stop mode (*note Non-Stop Mode::).  Then, it is possible to
examine the state of one thread, while other threads are running.

When a given thread is running, MI commands that try to access the
target in the context of that thread may not work, or may work only on
some targets.  In particular, commands that try to operate on thread's
stack will not work, on any target.  Commands that read memory, or
modify breakpoints, may work or not work, depending on the target.  Note
that even commands that operate on global state, such as print',
set', and breakpoint commands, still access the target in the context
of a specific thread,  so frontend should try to find a stopped thread
and perform the operation on that thread (using the --thread' option).

Which commands will work in the context of a running thread is
highly target dependent.  However, the two commands -exec-interrupt',
to stop a thread, and -thread-info', to find the state of a thread,
will always work.

File: gdb.info,  Node: Thread groups,  Prev: Asynchronous and non-stop modes,  Up: GDB/MI General Design

--------------------

GDB may be used to debug several processes at the same time.  On some
platfroms, GDB may support debugging of several hardware systems, each
one having several cores with several different processes running on
each core.  This section describes the MI mechanism to support such
debugging scenarios.

The key observation is that regardless of the structure of the
target, MI can have a global list of threads, because most commands that
accept the --thread' option do not need to know what process that
thread belongs to.  Therefore, it is not necessary to introduce neither
additional --process' option, nor an notion of the current process in
the MI interface.  The only strictly new feature that is required is
the ability to find how the threads are grouped into processes.

To allow the user to discover such grouping, and to support arbitrary
hierarchy of machines/cores/processes, MI introduces the concept of a
"thread group".  Thread group is a collection of threads and other
thread groups.  A thread group always has a string identifier, a type,
and may have additional attributes specific to the type.  A new
command, -list-thread-groups', returns the list of top-level thread
groups, which correspond to processes that GDB is debugging at the
moment.  By passing an identifier of a thread group to the
-list-thread-groups' command, it is possible to obtain the members of

To allow the user to easily discover processes, and other objects, he
wishes to debug, a concept of "available thread group" is introduced.
Available thread group is an thread group that GDB is not debugging,
but that can be attached to, using the -target-attach' command.  The
list of available top-level thread groups can be obtained using
-list-thread-groups --available'.  In general, the content of a thread
group may be only retrieved only after attaching to that thread group.

Thread groups are related to inferiors (*note Inferiors and
Programs::).  Each inferior corresponds to a thread group of a special
type process', and some additional operations are permitted on such

File: gdb.info,  Node: GDB/MI Command Syntax,  Next: GDB/MI Compatibility with CLI,  Prev: GDB/MI General Design,  Up: GDB/MI

27.2 GDB/MI Command Syntax
==========================

* GDB/MI Input Syntax::
* GDB/MI Output Syntax::

File: gdb.info,  Node: GDB/MI Input Syntax,  Next: GDB/MI Output Syntax,  Up: GDB/MI Command Syntax

27.2.1 GDB/MI Input Syntax
--------------------------

COMMAND ==>'
CLI-COMMAND | MI-COMMAND'

CLI-COMMAND ==>'
[ TOKEN ] CLI-COMMAND NL', where CLI-COMMAND is any existing GDB
CLI command.

MI-COMMAND ==>'
[ TOKEN ] "-" OPERATION ( " " OPTION )* [' " --" ]' ( " "
PARAMETER )* NL'

TOKEN ==>'
"any sequence of digits"

OPTION ==>'
"-" PARAMETER [ " " PARAMETER ]'

PARAMETER ==>'
NON-BLANK-SEQUENCE | C-STRING'

OPERATION ==>'
_any of the operations described in this chapter_

NON-BLANK-SEQUENCE ==>'
_anything, provided it doesn't contain special characters such as
"-", NL, """ and of course " "_

C-STRING ==>'
""" SEVEN-BIT-ISO-C-STRING-CONTENT """'

NL ==>'
CR | CR-LF'

Notes:

* The CLI commands are still handled by the MI interpreter; their
output is described below.

* The TOKEN', when present, is passed back when the command
finishes.

* Some MI commands accept optional arguments as part of the parameter
list.  Each option is identified by a leading -' (dash) and may be
followed by an optional argument parameter.  Options occur first
in the parameter list and can be delimited from normal parameters
using --' (this is useful when some parameters begin with a dash).

Pragmatics:

* We want easy access to the existing CLI syntax (for debugging).

* We want it to be easy to spot a MI operation.

File: gdb.info,  Node: GDB/MI Output Syntax,  Prev: GDB/MI Input Syntax,  Up: GDB/MI Command Syntax

27.2.2 GDB/MI Output Syntax
---------------------------

The output from GDB/MI consists of zero or more out-of-band records
followed, optionally, by a single result record.  This result record is
for the most recent command.  The sequence of output records is
terminated by (gdb)'.

If an input command was prefixed with a TOKEN' then the
corresponding output for that command will also be prefixed by that same
TOKEN.

OUTPUT ==>'
( OUT-OF-BAND-RECORD )* [ RESULT-RECORD ] "(gdb)" NL'

RESULT-RECORD ==>'
 [ TOKEN ] "^" RESULT-CLASS ( "," RESULT )* NL'

OUT-OF-BAND-RECORD ==>'
ASYNC-RECORD | STREAM-RECORD'

ASYNC-RECORD ==>'
EXEC-ASYNC-OUTPUT | STATUS-ASYNC-OUTPUT | NOTIFY-ASYNC-OUTPUT'

EXEC-ASYNC-OUTPUT ==>'
[ TOKEN ] "*" ASYNC-OUTPUT'

STATUS-ASYNC-OUTPUT ==>'
[ TOKEN ] "+" ASYNC-OUTPUT'

NOTIFY-ASYNC-OUTPUT ==>'
[ TOKEN ] "=" ASYNC-OUTPUT'

ASYNC-OUTPUT ==>'
ASYNC-CLASS ( "," RESULT )* NL'

RESULT-CLASS ==>'
"done" | "running" | "connected" | "error" | "exit"'

ASYNC-CLASS ==>'
"stopped" | OTHERS' (where OTHERS will be added depending on the
needs--this is still in development).

RESULT ==>'
 VARIABLE "=" VALUE'

VARIABLE ==>'
 STRING '

VALUE ==>'
 CONST | TUPLE | LIST '

CONST ==>'
C-STRING'

TUPLE ==>'
 "{}" | "{" RESULT ( "," RESULT )* "}" '

LIST ==>'
 "[]" | "[" VALUE ( "," VALUE )* "]" | "[" RESULT ( "," RESULT )*
"]" '

STREAM-RECORD ==>'
CONSOLE-STREAM-OUTPUT | TARGET-STREAM-OUTPUT | LOG-STREAM-OUTPUT'

CONSOLE-STREAM-OUTPUT ==>'
"~" C-STRING'

TARGET-STREAM-OUTPUT ==>'
"@" C-STRING'

LOG-STREAM-OUTPUT ==>'
"&" C-STRING'

NL ==>'
CR | CR-LF'

TOKEN ==>'
_any sequence of digits_.

Notes:

* All output sequences end in a single line containing a period.

* The TOKEN' is from the corresponding request.  Note that for all
async output, while the token is allowed by the grammar and may be
output by future versions of GDB for select async output messages,
it is generally omitted.  Frontends should treat all async output
as reporting general changes in the state of the target and there
should be no need to associate async output to any prior command.

* STATUS-ASYNC-OUTPUT contains on-going status information about the
progress of a slow operation.  It can be discarded.  All status
output is prefixed by +'.

* EXEC-ASYNC-OUTPUT contains asynchronous state change on the target
(stopped, started, disappeared).  All async output is prefixed by
*'.

* NOTIFY-ASYNC-OUTPUT contains supplementary information that the
client should handle (e.g., a new breakpoint information).  All
notify output is prefixed by ='.

* CONSOLE-STREAM-OUTPUT is output that should be displayed as is in
the console.  It is the textual response to a CLI command.  All
the console output is prefixed by ~'.

* TARGET-STREAM-OUTPUT is the output produced by the target program.
All the target output is prefixed by @'.

* LOG-STREAM-OUTPUT is output text coming from GDB's internals, for
instance messages that should be displayed as part of an error
log.  All the log output is prefixed by &'.

* New GDB/MI commands should only output LISTS containing VALUES.

*Note GDB/MI Stream Records: GDB/MI Stream Records, for more details
about the various output records.

File: gdb.info,  Node: GDB/MI Compatibility with CLI,  Next: GDB/MI Development and Front Ends,  Prev: GDB/MI Command Syntax,  Up: GDB/MI

27.3 GDB/MI Compatibility with CLI
==================================

For the developers convenience CLI commands can be entered directly,
but there may be some unexpected behaviour.  For example, commands that
query the user will behave as if the user replied yes, breakpoint
command lists are not executed and some CLI commands, such as if',
when' and define', prompt for further input with >', which is not
valid MI output.

This feature may be removed at some stage in the future and it is
recommended that front ends use the -interpreter-exec' command (*note
-interpreter-exec::).

File: gdb.info,  Node: GDB/MI Development and Front Ends,  Next: GDB/MI Output Records,  Prev: GDB/MI Compatibility with CLI,  Up: GDB/MI

27.4 GDB/MI Development and Front Ends
======================================

The application which takes the MI output and presents the state of the
program being debugged to the user is called a "front end".

Although GDB/MI is still incomplete, it is currently being used by a
variety of front ends to GDB.  This makes it difficult to introduce new
functionality without breaking existing usage.  This section tries to
minimize the problems by describing how the protocol might change.

Some changes in MI need not break a carefully designed front end, and
for these the MI version will remain unchanged.  The following is a
list of changes that may occur within one level, so front ends should
parse MI output in a way that can handle them:

* New MI commands may be added.

* New fields may be added to the output of any MI command.

* The range of values for fields with specified values, e.g.,
in_scope' (*note -var-update::) may be extended.

If the changes are likely to break front ends, the MI version level
will be increased by one.  This will allow the front end to parse the
output according to the MI version.  Apart from mi0, new versions of
GDB will not support old versions of MI and it will be the
responsibility of the front end to work with the new one.

The best way to avoid unexpected changes in MI that might break your
front end is to make your project known to GDB developers and follow
development on <gdbATsourceware.org> and <gdb-patchesATsourceware.org>.

File: gdb.info,  Node: GDB/MI Output Records,  Next: GDB/MI Simple Examples,  Prev: GDB/MI Development and Front Ends,  Up: GDB/MI

27.5 GDB/MI Output Records
==========================

* GDB/MI Result Records::
* GDB/MI Stream Records::
* GDB/MI Async Records::
* GDB/MI Frame Information::
* GDB/MI Thread Information::

File: gdb.info,  Node: GDB/MI Result Records,  Next: GDB/MI Stream Records,  Up: GDB/MI Output Records

27.5.1 GDB/MI Result Records
----------------------------

In addition to a number of out-of-band notifications, the response to a
GDB/MI command includes one of the following result indications:

"^done" [ "," RESULTS ]'
The synchronous operation was successful, RESULTS' are the return
values.

"^running"'
This result record is equivalent to ^done'.  Historically, it was
output instead of ^done' if the command has resumed the target.
This behaviour is maintained for backward compatibility, but all
frontends should treat ^done' and ^running' identically and rely
on the *running' output record to determine which threads are
resumed.

"^connected"'
GDB has connected to a remote target.

"^error" "," C-STRING'
The operation failed.  The C-STRING' contains the corresponding
error message.

"^exit"'
GDB has terminated.

File: gdb.info,  Node: GDB/MI Stream Records,  Next: GDB/MI Async Records,  Prev: GDB/MI Result Records,  Up: GDB/MI Output Records

27.5.2 GDB/MI Stream Records
----------------------------

GDB internally maintains a number of output streams: the console, the
target, and the log.  The output intended for each of these streams is
funneled through the GDB/MI interface using "stream records".

Each stream record begins with a unique "prefix character" which
identifies its stream (*note GDB/MI Output Syntax: GDB/MI Output
Syntax.).  In addition to the prefix, each stream record contains a
STRING-OUTPUT'.  This is either raw text (with an implicit new line)
or a quoted C string (which does not contain an implicit newline).

"~" STRING-OUTPUT'
The console output stream contains text that should be displayed
in the CLI console window.  It contains the textual responses to
CLI commands.

"@" STRING-OUTPUT'
The target output stream contains any textual output from the
running target.  This is only present when GDB's event loop is
truly asynchronous, which is currently only the case for remote
targets.

"&" STRING-OUTPUT'
The log stream contains debugging messages being produced by GDB's
internals.

File: gdb.info,  Node: GDB/MI Async Records,  Next: GDB/MI Frame Information,  Prev: GDB/MI Stream Records,  Up: GDB/MI Output Records

27.5.3 GDB/MI Async Records
---------------------------

"Async" records are used to notify the GDB/MI client of additional
changes that have occurred.  Those changes can either be a consequence
of GDB/MI commands (e.g., a breakpoint modified) or a result of target
activity (e.g., target stopped).

The following is the list of possible async records:

The target is now running.  The THREAD field tells which specific
thread is now running, and can be all' if all threads are
running.  The frontend should assume that no interaction with a
running thread is possible after this notification is produced.
The frontend should not assume that this notification is output
only once for any command.  GDB may emit this notification several
times, either for different threads, because it cannot resume all
threads together, or even for a single thread, if the thread must
be stepped though some code before letting it run freely.

The target has stopped.  The REASON field can have one of the
following values:

breakpoint-hit'
A breakpoint was reached.

watchpoint-trigger'
A watchpoint was triggered.

read-watchpoint-trigger'
A read watchpoint was triggered.

access-watchpoint-trigger'
An access watchpoint was triggered.

function-finished'
An -exec-finish or similar CLI command was accomplished.

location-reached'
An -exec-until or similar CLI command was accomplished.

watchpoint-scope'
A watchpoint has gone out of scope.

end-stepping-range'
An -exec-next, -exec-next-instruction, -exec-step,
-exec-step-instruction or similar CLI command was
accomplished.

exited-signalled'
The inferior exited because of a signal.

exited'
The inferior exited.

exited-normally'
The inferior exited normally.

A signal was received by the inferior.

The ID field identifies the thread that directly caused the stop -
for example by hitting a breakpoint.  Depending on whether all-stop
mode is in effect (*note All-Stop Mode::), GDB may either stop all
threads, or only the thread that directly triggered the stop.  If
all threads are stopped, the STOPPED field will have the value of
"all"'.  Otherwise, the value of the STOPPED field will be a list
of thread identifiers.  Presently, this list will always include a
single thread, but frontend should be prepared to see several
threads in the list.  The CORE field reports the processor core on
which the stop event has happened.  This field may be absent if
such information is not available.

=thread-group-removed,id="ID"'
A thread group was either added or removed.  The ID field contains
the GDB identifier of the thread group.  When a thread group is
added, it generally might not be associated with a running
process.  When a thread group is removed, its id becomes invalid
and cannot be used in any way.

A thread group became associated with a running program, either
because the program was just started or the thread group was
attached to a program.  The ID field contains the GDB identifier
of the thread group.  The PID field contains process identifier,
specific to the operating system.

=thread-group-exited,id="ID"'
A thread group is no longer associated with a running program,
either because the program has exited, or because it was detached
from.  The ID field contains the GDB identifier of the thread
group.

=thread-exited,id="ID",group-id="GID"'
A thread either was created, or has exited.  The ID field contains
the GDB identifier of the thread.  The GID field identifies the

Informs that the selected thread was changed as result of the last
command.  This notification is not emitted as result of
-thread-select' command but is emitted whenever an MI command
that is not documented to change the selected thread actually
changes it.  In particular, invoking, directly or indirectly (via
user-defined command), the CLI thread' command, will generate

We suggest that in response to this notification, front ends
highlight the selected thread and cause subsequent commands to
apply to that thread.

=library-loaded,...'
Reports that a new library file was loaded by the program.  This
notification has 4 fields--ID, TARGET-NAME, HOST-NAME, and
SYMBOLS-LOADED.  The ID field is an opaque identifier of the
library.  For remote debugging case, TARGET-NAME and HOST-NAME
fields give the name of the library file on the target, and on the
host respectively.  For native debugging, both those fields have
the same value.  The SYMBOLS-LOADED field reports if the debug
symbols for this library are loaded.  The THREAD-GROUP field, if
present, specifies the id of the thread group in whose context the
library was loaded.  If the field is absent, it means the library
was loaded in the context of all present thread groups.

Reports that a library was unloaded by the program.  This
notification has 3 fields--ID, TARGET-NAME and HOST-NAME with the
same meaning as for the =library-loaded' notification.  The
THREAD-GROUP field, if present, specifies the id of the thread
group in whose context the library was unloaded.  If the field is
absent, it means the library was unloaded in the context of all

File: gdb.info,  Node: GDB/MI Frame Information,  Next: GDB/MI Thread Information,  Prev: GDB/MI Async Records,  Up: GDB/MI Output Records

27.5.4 GDB/MI Frame Information
-------------------------------

Response from many MI commands includes an information about stack
frame.  This information is a tuple that may have the following fields:

level'
The level of the stack frame.  The innermost frame has the level of
zero.  This field is always present.

func'
The name of the function corresponding to the frame.  This field
may be absent if GDB is unable to determine the function name.

The code address for the frame.  This field is always present.

file'
The name of the source files that correspond to the frame's code
address.  This field may be absent.

line'
The source line corresponding to the frames' code address.  This
field may be absent.

from'
The name of the binary file (either executable or shared library)
the corresponds to the frame's code address.  This field may be
absent.

File: gdb.info,  Node: GDB/MI Thread Information,  Prev: GDB/MI Frame Information,  Up: GDB/MI Output Records

27.5.5 GDB/MI Thread Information
--------------------------------

Whenever GDB has to report an information about a thread, it uses a
tuple with the following fields:

id'
The numeric id assigned to the thread by GDB.  This field is
always present.

target-id'
Target-specific string identifying the thread.  This field is
always present.

details'
It is supposed to be human-readable and not interpreted by the
frontend.  This field is optional.

state'
Either stopped' or running', depending on whether the thread is
presently running.  This field is always present.

core'
The value of this field is an integer number of the processor core
the thread was last seen on.  This field is optional.

File: gdb.info,  Node: GDB/MI Simple Examples,  Next: GDB/MI Command Description Format,  Prev: GDB/MI Output Records,  Up: GDB/MI

27.6 Simple Examples of GDB/MI Interaction
==========================================

This subsection presents several simple examples of interaction using
the GDB/MI interface.  In these examples, ->' means that the following
line is passed to GDB/MI as input, while <-' means the output received
from GDB/MI.

Note the line breaks shown in the examples are here only for
readability, they don't appear in the real output.

Setting a Breakpoint
--------------------

Setting a breakpoint generates synchronous output which contains
detailed information of the breakpoint.

-> -break-insert main
<- ^done,bkpt={number="1",type="breakpoint",disp="keep",
fullname="/home/nickrob/myprog.c",line="68",times="0"}
<- (gdb)

Program Execution
-----------------

Program execution generates asynchronous records and MI gives the
reason that execution stopped.

-> -exec-run
<- ^running
<- (gdb)
args=[{name="argc",value="1"},{name="argv",value="0xbfc4d4d4"}],
file="myprog.c",fullname="/home/nickrob/myprog.c",line="68"}
<- (gdb)
-> -exec-continue
<- ^running
<- (gdb)
<- *stopped,reason="exited-normally"
<- (gdb)

Quitting GDB
------------

Quitting GDB just prints the result class ^exit'.

-> (gdb)
<- -gdb-exit
<- ^exit

Please note that ^exit' is printed immediately, but it might take
some time for GDB to actually exit.  During that time, GDB performs
necessary cleanups, including killing programs being debugged or
disconnecting from debug hardware, so the frontend should wait till GDB
exits and should only forcibly kill GDB if it fails to exit in
reasonable time.

-------------

Here's what happens if you pass a non-existent command:

-> -rubbish
<- ^error,msg="Undefined MI command: rubbish"
<- (gdb)

File: gdb.info,  Node: GDB/MI Command Description Format,  Next: GDB/MI Breakpoint Commands,  Prev: GDB/MI Simple Examples,  Up: GDB/MI

27.7 GDB/MI Command Description Format
======================================

The remaining sections describe blocks of commands.  Each block of
commands is laid out in a fashion similar to this section.

Motivation
----------

The motivation for this collection of commands.

Introduction
------------

A brief introduction to this collection of commands as a whole.

Commands
--------

For each command in the block, the following is described:

Synopsis
........

-command ARGS...

Result
......

GDB Command
...........

The corresponding GDB CLI command(s), if any.

Example
.......

Example(s) formatted for readability.  Some of the described commands
have not been implemented yet and these are labeled N.A. (not
available).

File: gdb.info,  Node: GDB/MI Breakpoint Commands,  Next: GDB/MI Program Context,  Prev: GDB/MI Command Description Format,  Up: GDB/MI

27.8 GDB/MI Breakpoint Commands
===============================

This section documents GDB/MI commands for manipulating breakpoints.

The -break-after' Command
--------------------------

Synopsis
........

-break-after NUMBER COUNT

The breakpoint number NUMBER is not in effect until it has been hit
COUNT times.  To see how this is reflected in the output of the
-break-list' command, see the description of the -break-list' command
below.

GDB Command
...........

The corresponding GDB command is ignore'.

Example
.......

(gdb)
-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",
fullname="/home/foo/hello.c",line="5",times="0"}
(gdb)
-break-after 1 3
~
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
line="5",times="0",ignore="3"}]}
(gdb)

The -break-commands' Command
-----------------------------

Synopsis
........

-break-commands NUMBER [ COMMAND1 ... COMMANDN ]

Specifies the CLI commands that should be executed when breakpoint
NUMBER is hit.  The parameters COMMAND1 to COMMANDN are the commands.
If no command is specified, any previously-set commands are cleared.
*Note Break Commands::.  Typical use of this functionality is tracing a
program, that is, printing of values of some variables whenever
breakpoint is hit and then continuing.

GDB Command
...........

The corresponding GDB command is commands'.

Example
.......

(gdb)
-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",
fullname="/home/foo/hello.c",line="5",times="0"}
(gdb)
-break-commands 1 "print v" "continue"
^done
(gdb)

The -break-condition' Command
------------------------------

Synopsis
........

-break-condition NUMBER EXPR

Breakpoint NUMBER will stop the program only if the condition in
EXPR is true.  The condition becomes part of the -break-list' output
(see the description of the -break-list' command below).

GDB Command
...........

The corresponding GDB command is condition'.

Example
.......

(gdb)
-break-condition 1 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
line="5",cond="1",times="0",ignore="3"}]}
(gdb)

The -break-delete' Command
---------------------------

Synopsis
........

-break-delete ( BREAKPOINT )+

Delete the breakpoint(s) whose number(s) are specified in the
argument list.  This is obviously reflected in the breakpoint list.

GDB Command
...........

The corresponding GDB command is delete'.

Example
.......

(gdb)
-break-delete 1
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)

The -break-disable' Command
----------------------------

Synopsis
........

-break-disable ( BREAKPOINT )+

Disable the named BREAKPOINT(s).  The field enabled' in the break
list is now set to n' for the named BREAKPOINT(s).

GDB Command
...........

The corresponding GDB command is disable'.

Example
.......

(gdb)
-break-disable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="n",
line="5",times="0"}]}
(gdb)

The -break-enable' Command
---------------------------

Synopsis
........

-break-enable ( BREAKPOINT )+

Enable (previously disabled) BREAKPOINT(s).

GDB Command
...........

The corresponding GDB command is enable'.

Example
.......

(gdb)
-break-enable 2
^done
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
line="5",times="0"}]}
(gdb)

The -break-info' Command
-------------------------

Synopsis
........

-break-info BREAKPOINT

Get information about a single breakpoint.

GDB Command
...........

The corresponding GDB command is info break BREAKPOINT'.

Example
.......

N.A.

The -break-insert' Command
---------------------------

Synopsis
........

-break-insert [ -t ] [ -h ] [ -f ] [ -d ] [ -a ]
[ -c CONDITION ] [ -i IGNORE-COUNT ]
[ -p THREAD ] [ LOCATION ]

If specified, LOCATION, can be one of:

* function

* filename:linenum

* filename:function

The possible optional parameters of this command are:

-t'
Insert a temporary breakpoint.

-h'
Insert a hardware breakpoint.

-c CONDITION'
Make the breakpoint conditional on CONDITION.

-i IGNORE-COUNT'
Initialize the IGNORE-COUNT.

-f'
If LOCATION cannot be parsed (for example if it refers to unknown
files or functions), create a pending breakpoint. Without this
flag, GDB will report an error, and won't create a breakpoint, if
LOCATION cannot be parsed.

-d'
Create a disabled breakpoint.

-a'
Create a tracepoint.  *Note Tracepoints::.  When this parameter is
used together with -h', a fast tracepoint is created.

Result
......

The result is in the form:

^done,bkpt={number="NUMBER",type="TYPE",disp="del"|"keep",
times="TIMES"}

where NUMBER is the GDB number for this breakpoint, FUNCNAME is the
name of the function where the breakpoint was inserted, FILENAME is the
name of the source file which contains this function, LINENO is the
source line number within that file and TIMES the number of times that
the breakpoint has been hit (always 0 for -break-insert but may be
greater for -break-info or -break-list which use the same output).

Note: this format is open to change.

GDB Command
...........

The corresponding GDB commands are break', tbreak', hbreak',
thbreak', and rbreak'.

Example
.......

(gdb)
-break-insert main
fullname="/home/foo/recursive2.c,line="4",times="0"}
(gdb)
-break-insert -t foo
fullname="/home/foo/recursive2.c,line="11",times="0"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
fullname="/home/foo/recursive2.c,"line="4",times="0"},
bkpt={number="2",type="breakpoint",disp="del",enabled="y",
fullname="/home/foo/recursive2.c",line="11",times="0"}]}
(gdb)
-break-insert -r foo.*
~int foo(int, int);
"fullname="/home/foo/recursive2.c",line="11",times="0"}
(gdb)

The -break-list' Command
-------------------------

Synopsis
........

-break-list

Displays the list of inserted breakpoints, showing the following
fields:

Number'
number of the breakpoint

Type'
type of the breakpoint: breakpoint' or watchpoint'

Disposition'
should the breakpoint be deleted or disabled when it is hit: keep'
or nokeep'

Enabled'
is the breakpoint enabled or no: y' or n'

memory location at which the breakpoint is set

What'
logical location of the breakpoint, expressed by function name,
file name, line number

Times'
number of times the breakpoint has been hit

If there are no breakpoints or watchpoints, the BreakpointTable'
body' field is an empty list.

GDB Command
...........

The corresponding GDB command is info break'.

Example
.......

(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
bkpt={number="2",type="breakpoint",disp="keep",enabled="y",
line="13",times="0"}]}
(gdb)

Here's an example of the result when there are no breakpoints:

(gdb)
-break-list
^done,BreakpointTable={nr_rows="0",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[]}
(gdb)

The -break-passcount' Command
------------------------------

Synopsis
........

-break-passcount TRACEPOINT-NUMBER PASSCOUNT

Set the passcount for tracepoint TRACEPOINT-NUMBER to PASSCOUNT.  If
the breakpoint referred to by TRACEPOINT-NUMBER is not a tracepoint,
error is emitted.  This corresponds to CLI command passcount'.

The -break-watch' Command
--------------------------

Synopsis
........

-break-watch [ -a | -r ]

Create a watchpoint.  With the -a' option it will create an
"access" watchpoint, i.e., a watchpoint that triggers either on a read
from or on a write to the memory location.  With the -r' option, the
watchpoint created is a "read" watchpoint, i.e., it will trigger only
when the memory location is accessed for reading.  Without either of
the options, the watchpoint created is a regular watchpoint, i.e., it
will trigger when the memory location is accessed for writing.  *Note
Setting Watchpoints: Set Watchpoints.

Note that -break-list' will report a single list of watchpoints and
breakpoints inserted.

GDB Command
...........

The corresponding GDB commands are watch', awatch', and rwatch'.

Example
.......

Setting a watchpoint on a variable in the main' function:

(gdb)
-break-watch x
^done,wpt={number="2",exp="x"}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt={number="2",exp="x"},
value={old="-268439212",new="55"},
frame={func="main",args=[],file="recursive2.c",
fullname="/home/foo/bar/recursive2.c",line="5"}
(gdb)

Setting a watchpoint on a variable local to a function.  GDB will
stop the program execution twice: first for the variable changing
value, then for the watchpoint going out of scope.

(gdb)
-break-watch C
^done,wpt={number="5",exp="C"}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",
wpt={number="5",exp="C"},value={old="-276895068",new="3"},
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"}
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-scope",wpnum="5",
frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"}
(gdb)

Listing breakpoints and watchpoints, at different points in the
program execution.  Note that once the watchpoint goes out of scope, it
is deleted.

(gdb)
-break-watch C
^done,wpt={number="2",exp="C"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c"line="8",times="1"},
bkpt={number="2",type="watchpoint",disp="keep",
(gdb)
-exec-continue
^running
(gdb)
*stopped,reason="watchpoint-trigger",wpt={number="2",exp="C"},
value={old="-276895068",new="3"},
frame={func="callee4",args=[],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="13"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="2",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",times="1"},
bkpt={number="2",type="watchpoint",disp="keep",
(gdb)
-exec-continue
^running
^done,reason="watchpoint-scope",wpnum="2",
frame={func="callee3",args=[{name="strarg",
value="0x11940 \"A string argument.\""}],
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"}
(gdb)
-break-list
^done,BreakpointTable={nr_rows="1",nr_cols="6",
hdr=[{width="3",alignment="-1",col_name="number",colhdr="Num"},
{width="14",alignment="-1",col_name="type",colhdr="Type"},
{width="4",alignment="-1",col_name="disp",colhdr="Disp"},
{width="3",alignment="-1",col_name="enabled",colhdr="Enb"},
{width="40",alignment="2",col_name="what",colhdr="What"}],
body=[bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
file="../../../devo/gdb/testsuite/gdb.mi/basics.c",
fullname="/home/foo/devo/gdb/testsuite/gdb.mi/basics.c",line="8",
times="1"}]}
(gdb)

File: gdb.info,  Node: GDB/MI Program Context,  Next: GDB/MI Thread Commands,  Prev: GDB/MI Breakpoint Commands,  Up: GDB/MI

27.9 GDB/MI  Program Context
============================

The -exec-arguments' Command
-----------------------------

Synopsis
........

-exec-arguments ARGS

Set the inferior program arguments, to be used in the next
-exec-run'.

GDB Command
...........

The corresponding GDB command is set args'.

Example
.......

(gdb)
-exec-arguments -v word
^done
(gdb)

The -environment-cd' Command
-----------------------------

Synopsis
........

-environment-cd PATHDIR

Set GDB's working directory.

GDB Command
...........

The corresponding GDB command is cd'.

Example
.......

(gdb)
^done
(gdb)

The -environment-directory' Command
------------------------------------

Synopsis
........

-environment-directory [ -r ] [ PATHDIR ]+

Add directories PATHDIR to beginning of search path for source files.
If the -r' option is used, the search path is reset to the default
search path.  If directories PATHDIR are supplied in addition to the
-r' option, the search path is first reset and then addition occurs as
normal.  Multiple directories may be specified, separated by blanks.
Specifying multiple directories in a single command results in the
directories added to the beginning of the search path in the same order
they were presented in the command.  If blanks are needed as part of a
directory name, double-quotes should be used around the name.  In the
command output, the path will show up separated by the system
directory-separator character.  The directory-separator character must
not be used in any directory name.  If no directories are specified,
the current search path is displayed.

GDB Command
...........

The corresponding GDB command is dir'.

Example
.......

(gdb)
^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
(gdb)
-environment-directory ""
^done,source-path="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb:$cdir:$cwd"
(gdb)
-environment-directory -r /home/jjohnstn/src/gdb /usr/src
^done,source-path="/home/jjohnstn/src/gdb:/usr/src:$cdir:$cwd"
(gdb)
-environment-directory -r
^done,source-path="$cdir:$cwd"
(gdb)

The -environment-path' Command
-------------------------------

Synopsis
........

-environment-path [ -r ] [ PATHDIR ]+

Add directories PATHDIR to beginning of search path for object files.
If the -r' option is used, the search path is reset to the original
search path that existed at gdb start-up.  If directories PATHDIR are
supplied in addition to the -r' option, the search path is first reset
and then addition occurs as normal.  Multiple directories may be
specified, separated by blanks.  Specifying multiple directories in a
single command results in the directories added to the beginning of the
search path in the same order they were presented in the command.  If
blanks are needed as part of a directory name, double-quotes should be
used around the name.  In the command output, the path will show up
separated by the system directory-separator character.  The
directory-separator character must not be used in any directory name.
If no directories are specified, the current path is displayed.

GDB Command
...........

The corresponding GDB command is path'.

Example
.......

(gdb)
-environment-path
^done,path="/usr/bin"
(gdb)
(gdb)
-environment-path -r /usr/local/bin
^done,path="/usr/local/bin:/usr/bin"
(gdb)

The -environment-pwd' Command
------------------------------

Synopsis
........

-environment-pwd

Show the current working directory.

GDB Command
...........

The corresponding GDB command is pwd'.

Example
.......

(gdb)
-environment-pwd
(gdb)

File: gdb.info,  Node: GDB/MI Thread Commands,  Next: GDB/MI Program Execution,  Prev: GDB/MI Program Context,  Up: GDB/MI

27.10 GDB/MI Thread Commands
============================

The -thread-info' Command
--------------------------

Synopsis
........

Reports information about either a specific thread, if the THREAD-ID
parameter is present, or about all threads.  When printing information

GDB Command
...........

The info thread' command prints the same information about all threads.

Example
.......

{id="2",target-id="Thread 0xb7e14b90 (LWP 21257)",
{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
file="/tmp/a.c",fullname="/tmp/a.c",line="158"},state="running"}],
(gdb)

The state' field may have the following values:

stopped'
The thread is stopped.  Frame information is available for stopped

running'
The thread is running.  There's no frame information for running

------------------------------

Synopsis
........

Produces a list of the currently known GDB thread ids.  At the end
of the list it also prints the total number of such threads.

This command is retained for historical reasons, the -thread-info'
command should be used instead.

GDB Command
...........

Part of info threads' supplies the same information.

Example
.......

(gdb)
(gdb)

The -thread-select' Command
----------------------------

Synopsis
........

Make THREADNUM the current thread.  It prints the number of the new
current thread, and the topmost frame for that thread.

This command is deprecated in favor of explicitly using the
--thread' option to each command.

GDB Command
...........

The corresponding GDB command is thread'.

Example
.......

(gdb)
-exec-next
^running
(gdb)
(gdb)
^done,
(gdb)
frame={level="0",func="vprintf",
args=[{name="format",value="0x8048e9c \"%*s%c %d %c\\n\""},
{name="arg",value="0x2"}],file="vprintf.c",line="31"}
(gdb)

File: gdb.info,  Node: GDB/MI Program Execution,  Next: GDB/MI Stack Manipulation,  Prev: GDB/MI Thread Commands,  Up: GDB/MI

27.11 GDB/MI Program Execution
==============================

These are the asynchronous commands which generate the out-of-band
record *stopped'.  Currently GDB only really executes asynchronously
with remote targets and this interaction is mimicked in other cases.

The -exec-continue' Command
----------------------------

Synopsis
........

-exec-continue [--reverse] [--all|--thread-group N]

Resumes the execution of the inferior program, which will continue
to execute until it reaches a debugger stop event.  If the --reverse'
option is specified, execution resumes in reverse until it reaches a
stop event.  Stop events may include
* breakpoints or watchpoints

* signals or exceptions

* the end of the process (or its beginning under --reverse')

* the end or beginning of a replay log if one is being used.
In all-stop mode (*note All-Stop Mode::), may resume only one
thread, or all threads, depending on the value of the
scheduler-locking' variable.  If --all' is specified, all threads (in
all inferiors) will be resumed.  The --all' option is ignored in
all-stop mode.  If the --thread-group' options is specified, then all
threads in that thread group are resumed.

GDB Command
...........

The corresponding GDB corresponding is continue'.

Example
.......

-exec-continue
^running
(gdb)
@Hello world
*stopped,reason="breakpoint-hit",disp="keep",bkptno="2",frame={
func="foo",args=[],file="hello.c",fullname="/home/foo/bar/hello.c",
line="13"}
(gdb)

The -exec-finish' Command
--------------------------

Synopsis
........

-exec-finish [--reverse]

Resumes the execution of the inferior program until the current
function is exited.  Displays the results returned by the function.  If
the --reverse' option is specified, resumes the reverse execution of
the inferior program until the point where current function was called.

GDB Command
...........

The corresponding GDB command is finish'.

Example
.......

Function returning void'.

-exec-finish
^running
(gdb)
@hello from foo
*stopped,reason="function-finished",frame={func="main",args=[],
file="hello.c",fullname="/home/foo/bar/hello.c",line="7"}
(gdb)

Function returning other than void'.  The name of the internal GDB
variable storing the result is printed, together with the value itself.

-exec-finish
^running
(gdb)
args=[{name="a",value="1"],{name="b",value="9"}},
file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"},
gdb-result-var="$1",return-value="0" (gdb) The -exec-interrupt' Command ----------------------------- Synopsis ........ -exec-interrupt [--all|--thread-group N] Interrupts the background execution of the target. Note how the token associated with the stop message is the one for the execution command that has been interrupted. The token for the interrupt itself only appears in the ^done' output. If the user is trying to interrupt a non-running program, an error message will be printed. Note that when asynchronous execution is enabled, this command is asynchronous just like other execution commands. That is, first the ^done' response will be printed, and the target stop will be reported after that using the *stopped' notification. In non-stop mode, only the context thread is interrupted by default. All threads (in all inferiors) will be interrupted if the --all' option is specified. If the --thread-group' option is specified, all threads in that group will be interrupted. GDB Command ........... The corresponding GDB command is interrupt'. Example ....... (gdb) 111-exec-continue 111^running (gdb) 222-exec-interrupt 222^done (gdb) 111*stopped,signal-name="SIGINT",signal-meaning="Interrupt", frame={addr="0x00010140",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="13"} (gdb) (gdb) -exec-interrupt ^error,msg="mi_cmd_exec_interrupt: Inferior not executing." (gdb) The -exec-jump' Command ------------------------ Synopsis ........ -exec-jump LOCATION Resumes execution of the inferior program at the location specified by parameter. *Note Specify Location::, for a description of the different forms of LOCATION. GDB Command ........... The corresponding GDB command is jump'. Example ....... -exec-jump foo.c:10 *running,thread-id="all" ^running The -exec-next' Command ------------------------ Synopsis ........ -exec-next [--reverse] Resumes execution of the inferior program, stopping when the beginning of the next source line is reached. If the --reverse' option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previous source line. If you issue this command on the first line of a function, it will take you back to the caller of that function, to the source line where the function was called. GDB Command ........... The corresponding GDB command is next'. Example ....... -exec-next ^running (gdb) *stopped,reason="end-stepping-range",line="8",file="hello.c" (gdb) The -exec-next-instruction' Command ------------------------------------ Synopsis ........ -exec-next-instruction [--reverse] Executes one machine instruction. If the instruction is a function call, continues until the function returns. If the program stops at an instruction in the middle of a source line, the address will be printed as well. If the --reverse' option is specified, resumes reverse execution of the inferior program, stopping at the previous instruction. If the previously executed instruction was a return from another function, it will continue to execute in reverse until the call to that function (from the current stack frame) is reached. GDB Command ........... The corresponding GDB command is nexti'. Example ....... (gdb) -exec-next-instruction ^running (gdb) *stopped,reason="end-stepping-range", addr="0x000100d4",line="5",file="hello.c" (gdb) The -exec-return' Command -------------------------- Synopsis ........ -exec-return Makes current function return immediately. Doesn't execute the inferior. Displays the new current frame. GDB Command ........... The corresponding GDB command is return'. Example ....... (gdb) 200-break-insert callee4 200^done,bkpt={number="1",addr="0x00010734", file="../../../devo/gdb/testsuite/gdb.mi/basics.c",line="8"} (gdb) 000-exec-run 000^running (gdb) 000*stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame={func="callee4",args=[], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"} (gdb) 205-break-delete 205^done (gdb) 111-exec-return 111^done,frame={level="0",func="callee3", args=[{name="strarg", value="0x11940 \"A string argument.\""}], file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="18"} (gdb) The -exec-run' Command ----------------------- Synopsis ........ -exec-run [--all | --thread-group N] Starts execution of the inferior from the beginning. The inferior executes until either a breakpoint is encountered or the program exits. In the latter case the output will include an exit code, if the program has exited exceptionally. When no option is specified, the current inferior is started. If the --thread-group' option is specified, it should refer to a thread group of type process', and that thread group will be started. If the --all' option is specified, then all inferiors will be started. GDB Command ........... The corresponding GDB command is run'. Examples ........ (gdb) -break-insert main ^done,bkpt={number="1",addr="0x0001072c",file="recursive2.c",line="4"} (gdb) -exec-run ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1", frame={func="main",args=[],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="4"} (gdb) Program exited normally: (gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited-normally" (gdb) Program exited exceptionally: (gdb) -exec-run ^running (gdb) x = 55 *stopped,reason="exited",exit-code="01" (gdb) Another way the program can terminate is if it receives a signal such as SIGINT'. In this case, GDB/MI displays this: (gdb) *stopped,reason="exited-signalled",signal-name="SIGINT", signal-meaning="Interrupt" The -exec-step' Command ------------------------ Synopsis ........ -exec-step [--reverse] Resumes execution of the inferior program, stopping when the beginning of the next source line is reached, if the next source line is not a function call. If it is, stop at the first instruction of the called function. If the --reverse' option is specified, resumes reverse execution of the inferior program, stopping at the beginning of the previously executed source line. GDB Command ........... The corresponding GDB command is step'. Example ....... Stepping into a function: -exec-step ^running (gdb) *stopped,reason="end-stepping-range", frame={func="foo",args=[{name="a",value="10"}, {name="b",value="0"}],file="recursive2.c", fullname="/home/foo/bar/recursive2.c",line="11"} (gdb) Regular stepping: -exec-step ^running (gdb) *stopped,reason="end-stepping-range",line="14",file="recursive2.c" (gdb) The -exec-step-instruction' Command ------------------------------------ Synopsis ........ -exec-step-instruction [--reverse] Resumes the inferior which executes one machine instruction. If the --reverse' option is specified, resumes reverse execution of the inferior program, stopping at the previously executed instruction. The output, once GDB has stopped, will vary depending on whether we have stopped in the middle of a source line or not. In the former case, the address at which the program stopped will be printed as well. GDB Command ........... The corresponding GDB command is stepi'. Example ....... (gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame={func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10"} (gdb) -exec-step-instruction ^running (gdb) *stopped,reason="end-stepping-range", frame={addr="0x000100f4",func="foo",args=[],file="try.c", fullname="/home/foo/bar/try.c",line="10"} (gdb) The -exec-until' Command ------------------------- Synopsis ........ -exec-until [ LOCATION ] Executes the inferior until the LOCATION specified in the argument is reached. If there is no argument, the inferior executes until a source line greater than the current one is reached. The reason for stopping in this case will be location-reached'. GDB Command ........... The corresponding GDB command is until'. Example ....... (gdb) -exec-until recursive2.c:6 ^running (gdb) x = 55 *stopped,reason="location-reached",frame={func="main",args=[], file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="6"} (gdb) File: gdb.info, Node: GDB/MI Stack Manipulation, Next: GDB/MI Variable Objects, Prev: GDB/MI Program Execution, Up: GDB/MI 27.12 GDB/MI Stack Manipulation Commands ======================================== The -stack-info-frame' Command ------------------------------- Synopsis ........ -stack-info-frame Get info on the selected frame. GDB Command ........... The corresponding GDB command is info frame' or frame' (without arguments). Example ....... (gdb) -stack-info-frame ^done,frame={level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"} (gdb) The -stack-info-depth' Command ------------------------------- Synopsis ........ -stack-info-depth [ MAX-DEPTH ] Return the depth of the stack. If the integer argument MAX-DEPTH is specified, do not count beyond MAX-DEPTH frames. GDB Command ........... There's no equivalent GDB command. Example ....... For a stack with frame levels 0 through 11: (gdb) -stack-info-depth ^done,depth="12" (gdb) -stack-info-depth 4 ^done,depth="4" (gdb) -stack-info-depth 12 ^done,depth="12" (gdb) -stack-info-depth 11 ^done,depth="11" (gdb) -stack-info-depth 13 ^done,depth="12" (gdb) The -stack-list-arguments' Command ----------------------------------- Synopsis ........ -stack-list-arguments PRINT-VALUES [ LOW-FRAME HIGH-FRAME ] Display a list of the arguments for the frames between LOW-FRAME and HIGH-FRAME (inclusive). If LOW-FRAME and HIGH-FRAME are not provided, list the arguments for the whole call stack. If the two arguments are equal, show the single frame at the corresponding level. It is an error if LOW-FRAME is larger than the actual number of frames. On the other hand, HIGH-FRAME may be larger than the actual number of frames, in which case only existing frames will be returned. If PRINT-VALUES is 0 or --no-values', print only the names of the variables; if it is 1 or --all-values', print also their values; and if it is 2 or --simple-values', print the name, type and value for simple data types, and the name and type for arrays, structures and unions. Use of this command to obtain arguments in a single frame is deprecated in favor of the -stack-list-variables' command. GDB Command ........... GDB does not have an equivalent command. gdbtk' has a gdb_get_args' command which partially overlaps with the functionality of -stack-list-arguments'. Example ....... (gdb) -stack-list-frames ^done, stack=[ frame={level="0",addr="0x00010734",func="callee4", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="8"}, frame={level="1",addr="0x0001076c",func="callee3", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="17"}, frame={level="2",addr="0x0001078c",func="callee2", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="22"}, frame={level="3",addr="0x000107b4",func="callee1", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="27"}, frame={level="4",addr="0x000107e0",func="main", file="../../../devo/gdb/testsuite/gdb.mi/basics.c", fullname="/home/foo/bar/devo/gdb/testsuite/gdb.mi/basics.c",line="32"}] (gdb) -stack-list-arguments 0 ^done, stack-args=[ frame={level="0",args=[]}, frame={level="1",args=[name="strarg"]}, frame={level="2",args=[name="intarg",name="strarg"]}, frame={level="3",args=[name="intarg",name="strarg",name="fltarg"]}, frame={level="4",args=[]}] (gdb) -stack-list-arguments 1 ^done, stack-args=[ frame={level="0",args=[]}, frame={level="1", args=[{name="strarg",value="0x11940 \"A string argument.\""}]}, frame={level="2",args=[ {name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}]}, {frame={level="3",args=[ {name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}, {name="fltarg",value="3.5"}]}, frame={level="4",args=[]}] (gdb) -stack-list-arguments 0 2 2 ^done,stack-args=[frame={level="2",args=[name="intarg",name="strarg"]}] (gdb) -stack-list-arguments 1 2 2 ^done,stack-args=[frame={level="2", args=[{name="intarg",value="2"}, {name="strarg",value="0x11940 \"A string argument.\""}]}] (gdb) The -stack-list-frames' Command -------------------------------- Synopsis ........ -stack-list-frames [ LOW-FRAME HIGH-FRAME ] List the frames currently on the stack. For each frame it displays the following info: LEVEL' The frame number, 0 being the topmost frame, i.e., the innermost function. ADDR' The $pc' value for that frame.

FUNC'
Function name.

FILE'
File name of the source file where the function lives.

LINE'
Line number corresponding to the $pc'. If invoked without arguments, this command prints a backtrace for the whole stack. If given two integer arguments, it shows the frames whose levels are between the two arguments (inclusive). If the two arguments are equal, it shows the single frame at the corresponding level. It is an error if LOW-FRAME is larger than the actual number of frames. On the other hand, HIGH-FRAME may be larger than the actual number of frames, in which case only existing frames will be returned. GDB Command ........... The corresponding GDB commands are backtrace' and where'. Example ....... Full stack backtrace: (gdb) -stack-list-frames ^done,stack= [frame={level="0",addr="0x0001076c",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="11"}, frame={level="1",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="2",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="6",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="7",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="8",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="9",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="10",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="11",addr="0x00010738",func="main", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="4"}] (gdb) Show frames between LOW_FRAME and HIGH_FRAME: (gdb) -stack-list-frames 3 5 ^done,stack= [frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="4",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}, frame={level="5",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}] (gdb) Show a single frame: (gdb) -stack-list-frames 3 3 ^done,stack= [frame={level="3",addr="0x000107a4",func="foo", file="recursive2.c",fullname="/home/foo/bar/recursive2.c",line="14"}] (gdb) The -stack-list-locals' Command -------------------------------- Synopsis ........ -stack-list-locals PRINT-VALUES Display the local variable names for the selected frame. If PRINT-VALUES is 0 or --no-values', print only the names of the variables; if it is 1 or --all-values', print also their values; and if it is 2 or --simple-values', print the name, type and value for simple data types, and the name and type for arrays, structures and unions. In this last case, a frontend can immediately display the value of simple data types and create variable objects for other data types when the user wishes to explore their values in more detail. This command is deprecated in favor of the -stack-list-variables' command. GDB Command ........... info locals' in GDB, gdb_get_locals' in gdbtk'. Example ....... (gdb) -stack-list-locals 0 ^done,locals=[name="A",name="B",name="C"] (gdb) -stack-list-locals --all-values ^done,locals=[{name="A",value="1"},{name="B",value="2"}, {name="C",value="{1, 2, 3}"}] -stack-list-locals --simple-values ^done,locals=[{name="A",type="int",value="1"}, {name="B",type="int",value="2"},{name="C",type="int [3]"}] (gdb) The -stack-list-variables' Command ----------------------------------- Synopsis ........ -stack-list-variables PRINT-VALUES Display the names of local variables and function arguments for the selected frame. If PRINT-VALUES is 0 or --no-values', print only the names of the variables; if it is 1 or --all-values', print also their values; and if it is 2 or --simple-values', print the name, type and value for simple data types, and the name and type for arrays, structures and unions. Example ....... (gdb) -stack-list-variables --thread 1 --frame 0 --all-values ^done,variables=[{name="x",value="11"},{name="s",value="{a = 1, b = 2}"}] (gdb) The -stack-select-frame' Command --------------------------------- Synopsis ........ -stack-select-frame FRAMENUM Change the selected frame. Select a different frame FRAMENUM on the stack. This command in deprecated in favor of passing the --frame' option to every command. GDB Command ........... The corresponding GDB commands are frame', up', down', select-frame', up-silent', and down-silent'. Example ....... (gdb) -stack-select-frame 2 ^done (gdb) File: gdb.info, Node: GDB/MI Variable Objects, Next: GDB/MI Data Manipulation, Prev: GDB/MI Stack Manipulation, Up: GDB/MI 27.13 GDB/MI Variable Objects ============================= Introduction to Variable Objects -------------------------------- Variable objects are "object-oriented" MI interface for examining and changing values of expressions. Unlike some other MI interfaces that work with expressions, variable objects are specifically designed for simple and efficient presentation in the frontend. A variable object is identified by string name. When a variable object is created, the frontend specifies the expression for that variable object. The expression can be a simple variable, or it can be an arbitrary complex expression, and can even involve CPU registers. After creating a variable object, the frontend can invoke other variable object operations--for example to obtain or change the value of a variable object, or to change display format. Variable objects have hierarchical tree structure. Any variable object that corresponds to a composite type, such as structure in C, has a number of child variable objects, for example corresponding to each element of a structure. A child variable object can itself have children, recursively. Recursion ends when we reach leaf variable objects, which always have built-in types. Child variable objects are created only by explicit request, so if a frontend is not interested in the children of a particular variable object, no child will be created. For a leaf variable object it is possible to obtain its value as a string, or set the value from a string. String value can be also obtained for a non-leaf variable object, but it's generally a string that only indicates the type of the object, and does not list its contents. Assignment to a non-leaf variable object is not allowed. A frontend does not need to read the values of all variable objects each time the program stops. Instead, MI provides an update command that lists all variable objects whose values has changed since the last update operation. This considerably reduces the amount of data that must be transferred to the frontend. As noted above, children variable objects are created on demand, and only leaf variable objects have a real value. As result, gdb will read target memory only for leaf variables that frontend has created. The automatic update is not always desirable. For example, a frontend might want to keep a value of some expression for future reference, and never update it. For another example, fetching memory is relatively slow for embedded targets, so a frontend might want to disable automatic update for the variables that are either not visible on the screen, or "closed". This is possible using so called "frozen variable objects". Such variable objects are never implicitly updated. Variable objects can be either "fixed" or "floating". For the fixed variable object, the expression is parsed when the variable object is created, including associating identifiers to specific variables. The meaning of expression never changes. For a floating variable object the values of variables whose names appear in the expressions are re-evaluated every time in the context of the current frame. Consider this example: void do_work(...) { struct work_state state; if (...) do_work(...); } If a fixed variable object for the state' variable is created in this function, and we enter the recursive call, the the variable object will report the value of state' in the top-level do_work' invocation. On the other hand, a floating variable object will report the value of state' in the current frame. If an expression specified when creating a fixed variable object refers to a local variable, the variable object becomes bound to the thread and frame in which the variable object is created. When such variable object is updated, GDB makes sure that the thread/frame combination the variable object is bound to still exists, and re-evaluates the variable object in context of that thread/frame. The following is the complete set of GDB/MI operations defined to access this functionality: *Operation* *Description* -enable-pretty-printing' enable Python-based pretty-printing -var-create' create a variable object -var-delete' delete the variable object and/or its children -var-set-format' set the display format of this variable -var-show-format' show the display format of this variable -var-info-num-children' tells how many children this object has -var-list-children' return a list of the object's children -var-info-type' show the type of this variable object -var-info-expression' print parent-relative expression that this variable object represents -var-info-path-expression' print full expression that this variable object represents -var-show-attributes' is this variable editable? does it exist here? -var-evaluate-expression' get the value of this variable -var-assign' set the value of this variable -var-update' update the variable and its children -var-set-frozen' set frozeness attribute -var-set-update-range' set range of children to display on update In the next subsection we describe each operation in detail and suggest how it can be used. Description And Use of Operations on Variable Objects ----------------------------------------------------- The -enable-pretty-printing' Command ------------------------------------- -enable-pretty-printing GDB allows Python-based visualizers to affect the output of the MI variable object commands. However, because there was no way to implement this in a fully backward-compatible way, a front end must request that this functionality be enabled. Once enabled, this feature cannot be disabled. Note that if Python support has not been compiled into GDB, this command will still succeed (and do nothing). This feature is currently (as of GDB 7.0) experimental, and may work differently in future versions of GDB. The -var-create' Command ------------------------- Synopsis ........ -var-create {NAME | "-"} {FRAME-ADDR | "*" | "@"} EXPRESSION This operation creates a variable object, which allows the monitoring of a variable, the result of an expression, a memory cell or a CPU register. The NAME parameter is the string by which the object can be referenced. It must be unique. If -' is specified, the varobj system will generate a string "varNNNNNN" automatically. It will be unique provided that one does not specify NAME of that format. The command fails if a duplicate name is found. The frame under which the expression should be evaluated can be specified by FRAME-ADDR. A *' indicates that the current frame should be used. A @' indicates that a floating variable object must be created. EXPRESSION is any expression valid on the current language set (must not begin with a *'), or one of the following: * *ADDR', where ADDR is the address of a memory cell * *ADDR-ADDR' -- a memory address range (TBD) * $REGNAME' -- a CPU register name

A varobj's contents may be provided by a Python-based
pretty-printer.  In this case the varobj is known as a "dynamic
varobj".  Dynamic varobjs have slightly different semantics in some
cases.  If the -enable-pretty-printing' command is not sent, then GDB
will never create a dynamic varobj.  This ensures backward
compatibility for existing clients.

Result
......

This operation returns attributes of the newly-created varobj.  These
are:

name'
The name of the varobj.

numchild'
The number of children of the varobj.  This number is not
necessarily reliable for a dynamic varobj.  Instead, you must
examine the has_more' attribute.

value'
The varobj's scalar value.  For a varobj whose type is some sort of
aggregate (e.g., a struct'), or for a dynamic varobj, this value
will not be interesting.

type'
The varobj's type.  This is a string representation of the type, as
would be printed by the GDB CLI.

If a variable object is bound to a specific thread, then this is

has_more'
For a dynamic varobj, this indicates whether there appear to be any
children available.  For a non-dynamic varobj, this will be 0.

dynamic'
This attribute will be present and have the value 1' if the
varobj is a dynamic varobj.  If the varobj is not a dynamic varobj,
then this attribute will not be present.

displayhint'
A dynamic varobj can supply a display hint to the front end.  The
value comes directly from the Python pretty-printer object's
display_hint' method.  *Note Pretty Printing API::.

Typical output will look like this:

has_more="HAS_MORE"

The -var-delete' Command
-------------------------

Synopsis
........

-var-delete [ -c ] NAME

Deletes a previously created variable object and all of its children.
With the -c' option, just deletes the children.

Returns an error if the object NAME is not found.

The -var-set-format' Command
-----------------------------

Synopsis
........

-var-set-format NAME FORMAT-SPEC

Sets the output format for the value of the object NAME to be
FORMAT-SPEC.

The syntax for the FORMAT-SPEC is as follows:

FORMAT-SPEC ==>
{binary | decimal | hexadecimal | octal | natural}

The natural format is the default format choosen automatically based
on the variable type (like decimal for an int', hex for pointers,
etc.).

For a variable with children, the format is set only on the variable
itself, and the children are not affected.

The -var-show-format' Command
------------------------------

Synopsis
........

-var-show-format NAME

Returns the format used to display the value of the object NAME.

FORMAT ==>
FORMAT-SPEC

The -var-info-num-children' Command
------------------------------------

Synopsis
........

-var-info-num-children NAME

Returns the number of children of a variable object NAME:

numchild=N

Note that this number is not completely reliable for a dynamic
varobj.  It will return the current number of children, but more
children may be available.

The -var-list-children' Command
--------------------------------

Synopsis
........

-var-list-children [PRINT-VALUES] NAME [FROM TO]
Return a list of the children of the specified variable object and
create variable objects for them, if they do not already exist.  With a
single argument or if PRINT-VALUES has a value of 0 or --no-values',
print only the names of the variables; if PRINT-VALUES is 1 or
--all-values', also print their values; and if it is 2 or
--simple-values' print the name and value for simple data types and
just the name for arrays, structures and unions.

FROM and TO, if specified, indicate the range of children to report.
If FROM or TO is less than zero, the range is reset and all children
will be reported.  Otherwise, children starting at FROM (zero-based)
and up to and excluding TO will be reported.

If a child range is requested, it will only affect the current call
to -var-list-children', but not future calls to -var-update'.  For
this, you must instead use -var-set-update-range'.  The intent of this
approach is to enable a front end to implement any update approach it
likes; for example, scrolling a view may cause the front end to request
more children with -var-list-children', and then the front end could
call -var-set-update-range' with a different range to ensure that
future updates are restricted to just the visible items.

For each child the following results are returned:

NAME
Name of the variable object created for this child.

EXP
The expression to be shown to the user by the front end to
designate this child.  For example this may be the name of a
structure member.

For a dynamic varobj, this value cannot be used to form an
expression.  There is no way to do this at all with a dynamic
varobj.

For C/C++ structures there are several pseudo children returned to
designate access qualifiers.  For these pseudo children EXP is
public', private', or protected'.  In this case the type and
value are not present.

A dynamic varobj will not report the access qualifying
pseudo-children, regardless of the language.  This information is
not available at all with a dynamic varobj.

NUMCHILD
Number of children this child has.  For a dynamic varobj, this
will be 0.

TYPE
The type of the child.

VALUE
If values were requested, this is the value.

If this variable object is associated with a thread, this is the
thread id.  Otherwise this result is not present.

FROZEN
If the variable object is frozen, this variable will be present
with a value of 1.

The result may have its own attributes:

displayhint'
A dynamic varobj can supply a display hint to the front end.  The
value comes directly from the Python pretty-printer object's
display_hint' method.  *Note Pretty Printing API::.

has_more'
This is an integer attribute which is nonzero if there are children
remaining after the end of the selected range.

Example
.......

(gdb)
-var-list-children n
^done,numchild=N,children=[child={name=NAME,exp=EXP,
numchild=N,type=TYPE},(repeats N times)]
(gdb)
-var-list-children --all-values n
^done,numchild=N,children=[child={name=NAME,exp=EXP,
numchild=N,value=VALUE,type=TYPE},(repeats N times)]

The -var-info-type' Command
----------------------------

Synopsis
........

-var-info-type NAME

Returns the type of the specified variable NAME.  The type is
returned as a string in the same format as it is output by the GDB CLI:

type=TYPENAME

The -var-info-expression' Command
----------------------------------

Synopsis
........

-var-info-expression NAME

Returns a string that is suitable for presenting this variable
object in user interface.  The string is generally not valid expression
in the current language, and cannot be evaluated.

For example, if a' is an array, and variable object A' was created
for a', then we'll get this output:

(gdb) -var-info-expression A.1
^done,lang="C",exp="1"

Here, the values of lang' can be {"C" | "C++" | "Java"}'.

Note that the output of the -var-list-children' command also
includes those expressions, so the -var-info-expression' command is of
limited use.

The -var-info-path-expression' Command
---------------------------------------

Synopsis
........

-var-info-path-expression NAME

Returns an expression that can be evaluated in the current context
and will yield the same value that a variable object has.  Compare this
with the -var-info-expression' command, which result can be used only
for UI presentation.  Typical use of the -var-info-path-expression'
command is creating a watchpoint from a variable object.

This command is currently not valid for children of a dynamic varobj,
and will give an error when invoked on one.

For example, suppose C' is a C++ class, derived from class Base',
and that the Base' class has a member called m_size'.  Assume a
variable c' is has the type of C' and a variable object C' was
created for variable c'.  Then, we'll get this output:
(gdb) -var-info-path-expression C.Base.public.m_size
^done,path_expr=((Base)c).m_size)

The -var-show-attributes' Command
----------------------------------

Synopsis
........

-var-show-attributes NAME

List attributes of the specified variable object NAME:

status=ATTR [ ( ,ATTR )* ]

where ATTR is { { editable | noneditable } | TBD }'.

The -var-evaluate-expression' Command
--------------------------------------

Synopsis
........

-var-evaluate-expression [-f FORMAT-SPEC] NAME

Evaluates the expression that is represented by the specified
variable object and returns its value as a string.  The format of the
string can be specified with the -f' option.  The possible values of
this option are the same as for -var-set-format' (*note
-var-set-format::).  If the -f' option is not specified, the current
display format will be used.  The current display format can be changed
using the -var-set-format' command.

value=VALUE

Note that one must invoke -var-list-children' for a variable before
the value of a child variable can be evaluated.

The -var-assign' Command
-------------------------

Synopsis
........

-var-assign NAME EXPRESSION

Assigns the value of EXPRESSION to the variable object specified by
NAME.  The object must be editable'.  If the variable's value is
altered by the assign, the variable will show up in any subsequent
-var-update' list.

Example
.......

(gdb)
-var-assign var1 3
^done,value="3"
(gdb)
-var-update *
^done,changelist=[{name="var1",in_scope="true",type_changed="false"}]
(gdb)

The -var-update' Command
-------------------------

Synopsis
........

-var-update [PRINT-VALUES] {NAME | "*"}

Reevaluate the expressions corresponding to the variable object NAME
and all its direct and indirect children, and return the list of
variable objects whose values have changed; NAME must be a root
variable object.  Here, "changed" means that the result of
-var-evaluate-expression' before and after the -var-update' is
different.  If *' is used as the variable object names, all existing
variable objects are updated, except for frozen ones (*note
-var-set-frozen::).  The option PRINT-VALUES determines whether both
names and values, or just names are printed.  The possible values of
this option are the same as for -var-list-children' (*note
-var-list-children::).  It is recommended to use the --all-values'
option, to reduce the number of MI commands needed on each program stop.

With the *' parameter, if a variable object is bound to a currently
running thread, it will not be updated, without any diagnostic.

If -var-set-update-range' was previously used on a varobj, then
only the selected range of children will be reported.

-var-update' reports all the changed varobjs in a tuple named
changelist'.

Each item in the change list is itself a tuple holding:

name'
The name of the varobj.

value'
If values were requested for this update, then this field will be
present and will hold the value of the varobj.

in_scope'
This field is a string which may take one of three values:

"true"'
The variable object's current value is valid.

"false"'
The variable object does not currently hold a valid value but
it may hold one in the future if its associated expression
comes back into scope.

"invalid"'
The variable object no longer holds a valid value.  This can
occur when the executable file being debugged has changed,
either through recompilation or by using the GDB file'
command.  The front end should normally choose to delete
these variable objects.

In the future new values may be added to this list so the front
should be prepared for this possibility.  *Note GDB/MI Development
and Front Ends: GDB/MI Development and Front Ends.

type_changed'
This is only present if the varobj is still valid.  If the type
changed, then this will be the string true'; otherwise it will be
false'.

new_type'
If the varobj's type changed, then this field will be present and
will hold the new type.

new_num_children'
For a dynamic varobj, if the number of children changed, or if the
type changed, this will be the new number of children.

The numchild' field in other varobj responses is generally not
valid for a dynamic varobj - it will show the number of children
that GDB knows about, but because dynamic varobjs lazily
instantiate their children, this will not reflect the number of
children which may be available.

The new_num_children' attribute only reports changes to the
number of children known by GDB.  This is the only way to detect
whether an update has removed children (which necessarily can only
happen at the end of the update range).

displayhint'
The display hint, if any.

has_more'
This is an integer value, which will be 1 if there are more
children available outside the varobj's update range.

dynamic'
This attribute will be present and have the value 1' if the
varobj is a dynamic varobj.  If the varobj is not a dynamic varobj,
then this attribute will not be present.

new_children'
If new children were added to a dynamic varobj within the selected
update range (as set by -var-set-update-range'), then they will
be listed in this attribute.

Example
.......

(gdb)
-var-assign var1 3
^done,value="3"
(gdb)
-var-update --all-values var1
^done,changelist=[{name="var1",value="3",in_scope="true",
type_changed="false"}]
(gdb)

The -var-set-frozen' Command
-----------------------------

Synopsis
........

-var-set-frozen NAME FLAG

Set the frozenness flag on the variable object NAME.  The FLAG
parameter should be either 1' to make the variable frozen or 0' to
make it unfrozen.  If a variable object is frozen, then neither itself,
nor any of its children, are implicitly updated by -var-update' of a
parent variable or by -var-update *'.  Only -var-update' of the
variable itself will update its value and values of its children.
After a variable object is unfrozen, it is implicitly updated by all
subsequent -var-update' operations.  Unfreezing a variable does not
update it, only subsequent -var-update' does.

Example
.......

(gdb)
-var-set-frozen V 1
^done
(gdb)

The -var-set-update-range' command
-----------------------------------

Synopsis
........

-var-set-update-range NAME FROM TO

Set the range of children to be returned by future invocations of
-var-update'.

FROM and TO indicate the range of children to report.  If FROM or TO
is less than zero, the range is reset and all children will be
reported.  Otherwise, children starting at FROM (zero-based) and up to
and excluding TO will be reported.

Example
.......

(gdb)
-var-set-update-range V 1 2
^done

The -var-set-visualizer' command
---------------------------------

Synopsis
........

-var-set-visualizer NAME VISUALIZER

Set a visualizer for the variable object NAME.

VISUALIZER is the visualizer to use.  The special value None' means
to disable any visualizer in use.

If not None', VISUALIZER must be a Python expression.  This
expression must evaluate to a callable object which accepts a single
argument.  GDB will call this object with the value of the varobj NAME
as an argument (this is done so that the same Python pretty-printing
code can be used for both the CLI and MI).  When called, this object
must return an object which conforms to the pretty-printing interface
(*note Pretty Printing API::).

The pre-defined function gdb.default_visualizer' may be used to
select a visualizer by following the built-in process (*note Selecting
Pretty-Printers::).  This is done automatically when a varobj is
created, and so ordinarily is not needed.

This feature is only available if Python support is enabled.  The MI
command -list-features' (*note GDB/MI Miscellaneous Commands::) can be
used to check this.

Example
.......

Resetting the visualizer:

(gdb)
-var-set-visualizer V None
^done

Reselecting the default (type-based) visualizer:

(gdb)
-var-set-visualizer V gdb.default_visualizer
^done

Suppose SomeClass' is a visualizer class.  A lambda expression can
be used to instantiate this class for a varobj:

(gdb)
-var-set-visualizer V "lambda val: SomeClass()"
^done

File: gdb.info,  Node: GDB/MI Data Manipulation,  Next: GDB/MI Tracepoint Commands,  Prev: GDB/MI Variable Objects,  Up: GDB/MI

27.14 GDB/MI Data Manipulation
==============================

This section describes the GDB/MI commands that manipulate data:
examine memory and registers, evaluate expressions, etc.

The -data-disassemble' Command
-------------------------------

Synopsis
........

-data-disassemble
| [ -f FILENAME -l LINENUM [ -n LINES ] ]
-- MODE

Where:

START-ADDR'
is the beginning address (or $pc') END-ADDR' is the end address FILENAME' is the name of the file to disassemble LINENUM' is the line number to disassemble around LINES' is the number of disassembly lines to be produced. If it is -1, the whole function will be disassembled, in case no END-ADDR is specified. If END-ADDR is specified as a non-zero value, and LINES is lower than the number of disassembly lines between START-ADDR and END-ADDR, only LINES lines are displayed; if LINES is higher than the number of lines between START-ADDR and END-ADDR, only the lines up to END-ADDR are displayed. MODE' is either 0 (meaning only disassembly) or 1 (meaning mixed source and disassembly). Result ...... The output for each instruction is composed of four fields: * Address * Func-name * Offset * Instruction Note that whatever included in the instruction field, is not manipulated directly by GDB/MI, i.e., it is not possible to adjust its format. GDB Command ........... There's no direct mapping from this command to the CLI. Example ....... Disassemble from the current value of $pc' to $pc + 20': (gdb) -data-disassemble -s$pc -e "$pc + 20" -- 0 ^done, asm_insns=[ {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}, {address="0x000107c8",func-name="main",offset="12", inst="or %o2, 0x140, %o1\t! 0x11940 <_lib_version+8>"}, {address="0x000107cc",func-name="main",offset="16", inst="sethi %hi(0x11800), %o2"}, {address="0x000107d0",func-name="main",offset="20", inst="or %o2, 0x168, %o4\t! 0x11968 <_lib_version+48>"}] (gdb) Disassemble the whole main' function. Line 32 is part of main'. -data-disassemble -f basics.c -l 32 -- 0 ^done,asm_insns=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}, {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}, [...] {address="0x0001081c",func-name="main",offset="96",inst="ret "}, {address="0x00010820",func-name="main",offset="100",inst="restore "}] (gdb) Disassemble 3 instructions from the start of main': (gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 0 ^done,asm_insns=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}, {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}] (gdb) Disassemble 3 instructions from the start of main' in mixed mode: (gdb) -data-disassemble -f basics.c -l 32 -n 3 -- 1 ^done,asm_insns=[ src_and_asm_line={line="31", file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \ testsuite/gdb.mi/basics.c",line_asm_insn=[ {address="0x000107bc",func-name="main",offset="0", inst="save %sp, -112, %sp"}]}, src_and_asm_line={line="32", file="/kwikemart/marge/ezannoni/flathead-dev/devo/gdb/ \ testsuite/gdb.mi/basics.c",line_asm_insn=[ {address="0x000107c0",func-name="main",offset="4", inst="mov 2, %o0"}, {address="0x000107c4",func-name="main",offset="8", inst="sethi %hi(0x11800), %o2"}]}] (gdb) The -data-evaluate-expression' Command --------------------------------------- Synopsis ........ -data-evaluate-expression EXPR Evaluate EXPR as an expression. The expression could contain an inferior function call. The function call will execute synchronously. If the expression contains spaces, it must be enclosed in double quotes. GDB Command ........... The corresponding GDB commands are print', output', and call'. In gdbtk' only, there's a corresponding gdb_eval' command. Example ....... In the following example, the numbers that precede the commands are the "tokens" described in *note GDB/MI Command Syntax: GDB/MI Command Syntax. Notice how GDB/MI returns the same tokens in its output. 211-data-evaluate-expression A 211^done,value="1" (gdb) 311-data-evaluate-expression &A 311^done,value="0xefffeb7c" (gdb) 411-data-evaluate-expression A+3 411^done,value="4" (gdb) 511-data-evaluate-expression "A + 3" 511^done,value="4" (gdb) The -data-list-changed-registers' Command ------------------------------------------ Synopsis ........ -data-list-changed-registers Display a list of the registers that have changed. GDB Command ........... GDB doesn't have a direct analog for this command; gdbtk' has the corresponding command gdb_changed_register_list'. Example ....... On a PPC MBX board: (gdb) -exec-continue ^running (gdb) *stopped,reason="breakpoint-hit",disp="keep",bkptno="1",frame={ func="main",args=[],file="try.c",fullname="/home/foo/bar/try.c", line="5"} (gdb) -data-list-changed-registers ^done,changed-registers=["0","1","2","4","5","6","7","8","9", "10","11","13","14","15","16","17","18","19","20","21","22","23", "24","25","26","27","28","30","31","64","65","66","67","69"] (gdb) The -data-list-register-names' Command --------------------------------------- Synopsis ........ -data-list-register-names [ ( REGNO )+ ] Show a list of register names for the current target. If no arguments are given, it shows a list of the names of all the registers. If integer numbers are given as arguments, it will print a list of the names of the registers corresponding to the arguments. To ensure consistency between a register name and its number, the output list may include empty register names. GDB Command ........... GDB does not have a command which corresponds to -data-list-register-names'. In gdbtk' there is a corresponding command gdb_regnames'. Example ....... For the PPC MBX board: (gdb) -data-list-register-names ^done,register-names=["r0","r1","r2","r3","r4","r5","r6","r7", "r8","r9","r10","r11","r12","r13","r14","r15","r16","r17","r18", "r19","r20","r21","r22","r23","r24","r25","r26","r27","r28","r29", "r30","r31","f0","f1","f2","f3","f4","f5","f6","f7","f8","f9", "f10","f11","f12","f13","f14","f15","f16","f17","f18","f19","f20", "f21","f22","f23","f24","f25","f26","f27","f28","f29","f30","f31", "", "pc","ps","cr","lr","ctr","xer"] (gdb) -data-list-register-names 1 2 3 ^done,register-names=["r1","r2","r3"] (gdb) The -data-list-register-values' Command ---------------------------------------- Synopsis ........ -data-list-register-values FMT [ ( REGNO )*] Display the registers' contents. FMT is the format according to which the registers' contents are to be returned, followed by an optional list of numbers specifying the registers to display. A missing list of numbers indicates that the contents of all the registers must be returned. Allowed formats for FMT are: x' Hexadecimal o' Octal t' Binary d' Decimal r' Raw N' Natural GDB Command ........... The corresponding GDB commands are info reg', info all-reg', and (in gdbtk') gdb_fetch_registers'. Example ....... For a PPC MBX board (note: line breaks are for readability only, they don't appear in the actual output): (gdb) -data-list-register-values r 64 65 ^done,register-values=[{number="64",value="0xfe00a300"}, {number="65",value="0x00029002"}] (gdb) -data-list-register-values x ^done,register-values=[{number="0",value="0xfe0043c8"}, {number="1",value="0x3fff88"},{number="2",value="0xfffffffe"}, {number="3",value="0x0"},{number="4",value="0xa"}, {number="5",value="0x3fff68"},{number="6",value="0x3fff58"}, {number="7",value="0xfe011e98"},{number="8",value="0x2"}, {number="9",value="0xfa202820"},{number="10",value="0xfa202808"}, {number="11",value="0x1"},{number="12",value="0x0"}, {number="13",value="0x4544"},{number="14",value="0xffdfffff"}, {number="15",value="0xffffffff"},{number="16",value="0xfffffeff"}, {number="17",value="0xefffffed"},{number="18",value="0xfffffffe"}, {number="19",value="0xffffffff"},{number="20",value="0xffffffff"}, {number="21",value="0xffffffff"},{number="22",value="0xfffffff7"}, {number="23",value="0xffffffff"},{number="24",value="0xffffffff"}, {number="25",value="0xffffffff"},{number="26",value="0xfffffffb"}, {number="27",value="0xffffffff"},{number="28",value="0xf7bfffff"}, {number="29",value="0x0"},{number="30",value="0xfe010000"}, {number="31",value="0x0"},{number="32",value="0x0"}, {number="33",value="0x0"},{number="34",value="0x0"}, {number="35",value="0x0"},{number="36",value="0x0"}, {number="37",value="0x0"},{number="38",value="0x0"}, {number="39",value="0x0"},{number="40",value="0x0"}, {number="41",value="0x0"},{number="42",value="0x0"}, {number="43",value="0x0"},{number="44",value="0x0"}, {number="45",value="0x0"},{number="46",value="0x0"}, {number="47",value="0x0"},{number="48",value="0x0"}, {number="49",value="0x0"},{number="50",value="0x0"}, {number="51",value="0x0"},{number="52",value="0x0"}, {number="53",value="0x0"},{number="54",value="0x0"}, {number="55",value="0x0"},{number="56",value="0x0"}, {number="57",value="0x0"},{number="58",value="0x0"}, {number="59",value="0x0"},{number="60",value="0x0"}, {number="61",value="0x0"},{number="62",value="0x0"}, {number="63",value="0x0"},{number="64",value="0xfe00a300"}, {number="65",value="0x29002"},{number="66",value="0x202f04b5"}, {number="67",value="0xfe0043b0"},{number="68",value="0xfe00b3e4"}, {number="69",value="0x20002b03"}] (gdb) The -data-read-memory' Command ------------------------------- Synopsis ........ -data-read-memory [ -o BYTE-OFFSET ] ADDRESS WORD-FORMAT WORD-SIZE NR-ROWS NR-COLS [ ASCHAR ] where: ADDRESS' An expression specifying the address of the first memory word to be read. Complex expressions containing embedded white space should be quoted using the C convention. WORD-FORMAT' The format to be used to print the memory words. The notation is the same as for GDB's print' command (*note Output Formats: Output Formats.). WORD-SIZE' The size of each memory word in bytes. NR-ROWS' The number of rows in the output table. NR-COLS' The number of columns in the output table. ASCHAR' If present, indicates that each row should include an ASCII dump. The value of ASCHAR is used as a padding character when a byte is not a member of the printable ASCII character set (printable ASCII characters are those whose code is between 32 and 126, inclusively). BYTE-OFFSET' An offset to add to the ADDRESS before fetching memory. This command displays memory contents as a table of NR-ROWS by NR-COLS words, each word being WORD-SIZE bytes. In total, NR-ROWS * NR-COLS * WORD-SIZE' bytes are read (returned as total-bytes'). Should less than the requested number of bytes be returned by the target, the missing words are identified using N/A'. The number of bytes read from the target is returned in nr-bytes' and the starting address used to read memory in addr'. The address of the next/previous row or page is available in next-row' and prev-row', next-page' and prev-page'. GDB Command ........... The corresponding GDB command is x'. gdbtk' has gdb_get_mem' memory read command. Example ....... Read six bytes of memory starting at bytes+6' but then offset by -6' bytes. Format as three rows of two columns. One byte per word. Display each word in hex. (gdb) 9-data-read-memory -o -6 -- bytes+6 x 1 3 2 9^done,addr="0x00001390",nr-bytes="6",total-bytes="6", next-row="0x00001396",prev-row="0x0000138e",next-page="0x00001396", prev-page="0x0000138a",memory=[ {addr="0x00001390",data=["0x00","0x01"]}, {addr="0x00001392",data=["0x02","0x03"]}, {addr="0x00001394",data=["0x04","0x05"]}] (gdb) Read two bytes of memory starting at address shorts + 64' and display as a single word formatted in decimal. (gdb) 5-data-read-memory shorts+64 d 2 1 1 5^done,addr="0x00001510",nr-bytes="2",total-bytes="2", next-row="0x00001512",prev-row="0x0000150e", next-page="0x00001512",prev-page="0x0000150e",memory=[ {addr="0x00001510",data=["128"]}] (gdb) Read thirty two bytes of memory starting at bytes+16' and format as eight rows of four columns. Include a string encoding with x' used as the non-printable character. (gdb) 4-data-read-memory bytes+16 x 1 8 4 x 4^done,addr="0x000013a0",nr-bytes="32",total-bytes="32", next-row="0x000013c0",prev-row="0x0000139c", next-page="0x000013c0",prev-page="0x00001380",memory=[ {addr="0x000013a0",data=["0x10","0x11","0x12","0x13"],ascii="xxxx"}, {addr="0x000013a4",data=["0x14","0x15","0x16","0x17"],ascii="xxxx"}, {addr="0x000013a8",data=["0x18","0x19","0x1a","0x1b"],ascii="xxxx"}, {addr="0x000013ac",data=["0x1c","0x1d","0x1e","0x1f"],ascii="xxxx"}, {addr="0x000013b0",data=["0x20","0x21","0x22","0x23"],ascii=" !\"#"}, {addr="0x000013b4",data=["0x24","0x25","0x26","0x27"],ascii="$%&'"},
(gdb)

File: gdb.info,  Node: GDB/MI Tracepoint Commands,  Next: GDB/MI Symbol Query,  Prev: GDB/MI Data Manipulation,  Up: GDB/MI

27.15 GDB/MI Tracepoint Commands
================================

The commands defined in this section implement MI support for
tracepoints.  For detailed introduction, see *note Tracepoints::.

The -trace-find' Command
-------------------------

Synopsis
........

-trace-find MODE [PARAMETERS...]

Find a trace frame using criteria defined by MODE and PARAMETERS.
The following table lists permissible modes and their parameters.  For
details of operation, see *note tfind::.

none'
No parameters are required.  Stops examining trace frames.

frame-number'
An integer is required as parameter.  Selects tracepoint frame with
that index.

tracepoint-number'
An integer is required as parameter.  Finds next trace frame that
corresponds to tracepoint with the specified number.

pc'
An address is required as parameter.  Finds next trace frame that
corresponds to any tracepoint at the specified address.

pc-inside-range'
Two addresses are required as parameters.  Finds next trace frame
that corresponds to a tracepoint at an address inside the
specified range.  Both bounds are considered to be inside the
range.

pc-outside-range'
Two addresses are required as parameters.  Finds next trace frame
that corresponds to a tracepoint at an address outside the
specified range.  Both bounds are considered to be inside the
range.

line'
Line specification is required as parameter.  *Note Specify
Location::.  Finds next trace frame that corresponds to a
tracepoint at the specified location.

If none' was passed as MODE, the response does not have fields.
Otherwise, the response may have the following fields:

found'
This field has either 0' or 1' as the value, depending on
whether a matching tracepoint was found.

traceframe'
The index of the found traceframe.  This field is present iff the
found' field has value of 1'.

tracepoint'
The index of the found tracepoint.  This field is present iff the
found' field has value of 1'.

frame'
The information about the frame corresponding to the found trace
frame.  This field is present only if a trace frame was found.
*Note GDB/MI Frame Information::, for description of this field.

GDB Command
...........

The corresponding GDB command is tfind'.

-trace-define-variable
----------------------

Synopsis
........

-trace-define-variable NAME [ VALUE ]

Create trace variable NAME if it does not exist.  If VALUE is
specified, sets the initial value of the specified trace variable to
that value.  Note that the NAME should start with the ' character. GDB Command ........... The corresponding GDB command is tvariable'. -trace-list-variables --------------------- Synopsis ........ -trace-list-variables Return a table of all defined trace variables. Each element of the table has the following fields: name' The name of the trace variable. This field is always present. initial' The initial value. This is a 64-bit signed integer. This field is always present. current' The value the trace variable has at the moment. This is a 64-bit signed integer. This field is absent iff current value is not defined, for example if the trace was never run, or is presently running. GDB Command ........... The corresponding GDB command is tvariables'. Example ....... (gdb) -trace-list-variables ^done,trace-variables={nr_rows="1",nr_cols="3", hdr=[{width="15",alignment="-1",col_name="name",colhdr="Name"}, {width="11",alignment="-1",col_name="initial",colhdr="Initial"}, {width="11",alignment="-1",col_name="current",colhdr="Current"}], body=[variable={name="trace_timestamp",initial="0"}
variable={name="$foo",initial="10",current="15"}]} (gdb) -trace-save ----------- Synopsis ........ -trace-save [-r ] FILENAME Saves the collected trace data to FILENAME. Without the -r' option, the data is downloaded from the target and saved in a local file. With the -r' option the target is asked to perform the save. GDB Command ........... The corresponding GDB command is tsave'. -trace-start ------------ Synopsis ........ -trace-start Starts a tracing experiments. The result of this command does not have any fields. GDB Command ........... The corresponding GDB command is tstart'. -trace-status ------------- Synopsis ........ -trace-status Obtains the status of a tracing experiment. The result may include the following fields: supported' May have a value of either 0', when no tracing operations are supported, 1', when all tracing operations are supported, or file' when examining trace file. In the latter case, examining of trace frame is possible but new tracing experiement cannot be started. This field is always present. running' May have a value of either 0' or 1' depending on whether tracing experiement is in progress on target. This field is present if supported' field is not 0'. stop-reason' Report the reason why the tracing was stopped last time. This field may be absent iff tracing was never stopped on target yet. The value of request' means the tracing was stopped as result of the -trace-stop' command. The value of overflow' means the tracing buffer is full. The value of disconnection' means tracing was automatically stopped when GDB has disconnected. The value of passcount' means tracing was stopped when a tracepoint was passed a maximal number of times for that tracepoint. This field is present if supported' field is not 0'. stopping-tracepoint' The number of tracepoint whose passcount as exceeded. This field is present iff the stop-reason' field has the value of passcount'. frames' frames-created' The frames' field is a count of the total number of trace frames in the trace buffer, while frames-created' is the total created during the run, including ones that were discarded, such as when a circular trace buffer filled up. Both fields are optional. buffer-size' buffer-free' These fields tell the current size of the tracing buffer and the remaining space. These fields are optional. circular' The value of the circular trace buffer flag. 1' means that the trace buffer is circular and old trace frames will be discarded if necessary to make room, 0' means that the trace buffer is linear and may fill up. disconnected' The value of the disconnected tracing flag. 1' means that tracing will continue after GDB disconnects, 0' means that the trace run will stop. GDB Command ........... The corresponding GDB command is tstatus'. -trace-stop ----------- Synopsis ........ -trace-stop Stops a tracing experiment. The result of this command has the same fields as -trace-status', except that the supported' and running' fields are not output. GDB Command ........... The corresponding GDB command is tstop'. File: gdb.info, Node: GDB/MI Symbol Query, Next: GDB/MI File Commands, Prev: GDB/MI Tracepoint Commands, Up: GDB/MI 27.16 GDB/MI Symbol Query Commands ================================== The -symbol-list-lines' Command -------------------------------- Synopsis ........ -symbol-list-lines FILENAME Print the list of lines that contain code and their associated program addresses for the given source filename. The entries are sorted in ascending PC order. GDB Command ........... There is no corresponding GDB command. Example ....... (gdb) -symbol-list-lines basics.c ^done,lines=[{pc="0x08048554",line="7"},{pc="0x0804855a",line="8"}] (gdb) File: gdb.info, Node: GDB/MI File Commands, Next: GDB/MI Target Manipulation, Prev: GDB/MI Symbol Query, Up: GDB/MI 27.17 GDB/MI File Commands ========================== This section describes the GDB/MI commands to specify executable file names and to read in and obtain symbol table information. The -file-exec-and-symbols' Command ------------------------------------ Synopsis ........ -file-exec-and-symbols FILE Specify the executable file to be debugged. This file is the one from which the symbol table is also read. If no file is specified, the command clears the executable and symbol information. If breakpoints are set when using this command with no arguments, GDB will produce error messages. Otherwise, no output is produced, except a completion notification. GDB Command ........... The corresponding GDB command is file'. Example ....... (gdb) -file-exec-and-symbols /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb) The -file-exec-file' Command ----------------------------- Synopsis ........ -file-exec-file FILE Specify the executable file to be debugged. Unlike -file-exec-and-symbols', the symbol table is _not_ read from this file. If used without argument, GDB clears the information about the executable file. No output is produced, except a completion notification. GDB Command ........... The corresponding GDB command is exec-file'. Example ....... (gdb) -file-exec-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb) The -file-list-exec-source-file' Command ----------------------------------------- Synopsis ........ -file-list-exec-source-file List the line number, the current source file, and the absolute path to the current source file for the current executable. The macro information field has a value of 1' or 0' depending on whether or not the file includes preprocessor macro information. GDB Command ........... The GDB equivalent is info source' Example ....... (gdb) 123-file-list-exec-source-file 123^done,line="1",file="foo.c",fullname="/home/bar/foo.c,macro-info="1" (gdb) The -file-list-exec-source-files' Command ------------------------------------------ Synopsis ........ -file-list-exec-source-files List the source files for the current executable. It will always output the filename, but only when GDB can find the absolute file name of a source file, will it output the fullname. GDB Command ........... The GDB equivalent is info sources'. gdbtk' has an analogous command gdb_listfiles'. Example ....... (gdb) -file-list-exec-source-files ^done,files=[ {file=foo.c,fullname=/home/foo.c}, {file=/home/bar.c,fullname=/home/bar.c}, {file=gdb_could_not_find_fullpath.c}] (gdb) The -file-symbol-file' Command ------------------------------- Synopsis ........ -file-symbol-file FILE Read symbol table info from the specified FILE argument. When used without arguments, clears GDB's symbol table info. No output is produced, except for a completion notification. GDB Command ........... The corresponding GDB command is symbol-file'. Example ....... (gdb) -file-symbol-file /kwikemart/marge/ezannoni/TRUNK/mbx/hello.mbx ^done (gdb) File: gdb.info, Node: GDB/MI Target Manipulation, Next: GDB/MI File Transfer Commands, Prev: GDB/MI File Commands, Up: GDB/MI 27.18 GDB/MI Target Manipulation Commands ========================================= The -target-attach' Command ---------------------------- Synopsis ........ -target-attach PID | GID | FILE Attach to a process PID or a file FILE outside of GDB, or a thread group GID. If attaching to a thread group, the id previously returned by -list-thread-groups --available' must be used. GDB Command ........... The corresponding GDB command is attach'. Example ....... (gdb) -target-attach 34 =thread-created,id="1" *stopped,thread-id="1",frame={addr="0xb7f7e410",func="bar",args=[]} ^done (gdb) The -target-detach' Command ---------------------------- Synopsis ........ -target-detach [ PID | GID ] Detach from the remote target which normally resumes its execution. If either PID or GID is specified, detaches from either the specified process, or specified thread group. There's no output. GDB Command ........... The corresponding GDB command is detach'. Example ....... (gdb) -target-detach ^done (gdb) The -target-disconnect' Command -------------------------------- Synopsis ........ -target-disconnect Disconnect from the remote target. There's no output and the target is generally not resumed. GDB Command ........... The corresponding GDB command is disconnect'. Example ....... (gdb) -target-disconnect ^done (gdb) The -target-download' Command ------------------------------ Synopsis ........ -target-download Loads the executable onto the remote target. It prints out an update message every half second, which includes the fields: section' The name of the section. section-sent' The size of what has been sent so far for that section. section-size' The size of the section. total-sent' The total size of what was sent so far (the current and the previous sections). total-size' The size of the overall executable to download. Each message is sent as status record (*note GDB/MI Output Syntax: GDB/MI Output Syntax.). In addition, it prints the name and size of the sections, as they are downloaded. These messages include the following fields: section' The name of the section. section-size' The size of the section. total-size' The size of the overall executable to download. At the end, a summary is printed. GDB Command ........... The corresponding GDB command is load'. Example ....... Note: each status message appears on a single line. Here the messages have been broken down so that they can fit onto a page. (gdb) -target-download +download,{section=".text",section-size="6668",total-size="9880"} +download,{section=".text",section-sent="512",section-size="6668", total-sent="512",total-size="9880"} +download,{section=".text",section-sent="1024",section-size="6668", total-sent="1024",total-size="9880"} +download,{section=".text",section-sent="1536",section-size="6668", total-sent="1536",total-size="9880"} +download,{section=".text",section-sent="2048",section-size="6668", total-sent="2048",total-size="9880"} +download,{section=".text",section-sent="2560",section-size="6668", total-sent="2560",total-size="9880"} +download,{section=".text",section-sent="3072",section-size="6668", total-sent="3072",total-size="9880"} +download,{section=".text",section-sent="3584",section-size="6668", total-sent="3584",total-size="9880"} +download,{section=".text",section-sent="4096",section-size="6668", total-sent="4096",total-size="9880"} +download,{section=".text",section-sent="4608",section-size="6668", total-sent="4608",total-size="9880"} +download,{section=".text",section-sent="5120",section-size="6668", total-sent="5120",total-size="9880"} +download,{section=".text",section-sent="5632",section-size="6668", total-sent="5632",total-size="9880"} +download,{section=".text",section-sent="6144",section-size="6668", total-sent="6144",total-size="9880"} +download,{section=".text",section-sent="6656",section-size="6668", total-sent="6656",total-size="9880"} +download,{section=".init",section-size="28",total-size="9880"} +download,{section=".fini",section-size="28",total-size="9880"} +download,{section=".data",section-size="3156",total-size="9880"} +download,{section=".data",section-sent="512",section-size="3156", total-sent="7236",total-size="9880"} +download,{section=".data",section-sent="1024",section-size="3156", total-sent="7748",total-size="9880"} +download,{section=".data",section-sent="1536",section-size="3156", total-sent="8260",total-size="9880"} +download,{section=".data",section-sent="2048",section-size="3156", total-sent="8772",total-size="9880"} +download,{section=".data",section-sent="2560",section-size="3156", total-sent="9284",total-size="9880"} +download,{section=".data",section-sent="3072",section-size="3156", total-sent="9796",total-size="9880"} ^done,address="0x10004",load-size="9880",transfer-rate="6586", write-rate="429" (gdb) GDB Command ........... No equivalent. Example ....... N.A. The -target-select' Command ---------------------------- Synopsis ........ -target-select TYPE PARAMETERS ... Connect GDB to the remote target. This command takes two args: TYPE' The type of target, for instance remote', etc. PARAMETERS' Device names, host names and the like. *Note Commands for Managing Targets: Target Commands, for more details. The output is a connection notification, followed by the address at which the target program is, in the following form: ^connected,addr="ADDRESS",func="FUNCTION NAME", args=[ARG LIST] GDB Command ........... The corresponding GDB command is target'. Example ....... (gdb) -target-select remote /dev/ttya ^connected,addr="0xfe00a300",func="??",args=[] (gdb) File: gdb.info, Node: GDB/MI File Transfer Commands, Next: GDB/MI Miscellaneous Commands, Prev: GDB/MI Target Manipulation, Up: GDB/MI 27.19 GDB/MI File Transfer Commands =================================== The -target-file-put' Command ------------------------------ Synopsis ........ -target-file-put HOSTFILE TARGETFILE Copy file HOSTFILE from the host system (the machine running GDB) to TARGETFILE on the target system. GDB Command ........... The corresponding GDB command is remote put'. Example ....... (gdb) -target-file-put localfile remotefile ^done (gdb) The -target-file-get' Command ------------------------------ Synopsis ........ -target-file-get TARGETFILE HOSTFILE Copy file TARGETFILE from the target system to HOSTFILE on the host system. GDB Command ........... The corresponding GDB command is remote get'. Example ....... (gdb) -target-file-get remotefile localfile ^done (gdb) The -target-file-delete' Command --------------------------------- Synopsis ........ -target-file-delete TARGETFILE Delete TARGETFILE from the target system. GDB Command ........... The corresponding GDB command is remote delete'. Example ....... (gdb) -target-file-delete remotefile ^done (gdb) File: gdb.info, Node: GDB/MI Miscellaneous Commands, Prev: GDB/MI File Transfer Commands, Up: GDB/MI 27.20 Miscellaneous GDB/MI Commands =================================== The -gdb-exit' Command ----------------------- Synopsis ........ -gdb-exit Exit GDB immediately. GDB Command ........... Approximately corresponds to quit'. Example ....... (gdb) -gdb-exit ^exit The -gdb-set' Command ---------------------- Synopsis ........ -gdb-set Set an internal GDB variable. GDB Command ........... The corresponding GDB command is set'. Example ....... (gdb) -gdb-set$foo=3
^done
(gdb)

The -gdb-show' Command
-----------------------

Synopsis
........

-gdb-show

Show the current value of a GDB variable.

GDB Command
...........

The corresponding GDB command is show'.

Example
.......

(gdb)
-gdb-show annotate
^done,value="0"
(gdb)

The -gdb-version' Command
--------------------------

Synopsis
........

-gdb-version

Show version information for GDB.  Used mostly in testing.

GDB Command
...........

The GDB equivalent is show version'.  GDB by default shows this
information when you start an interactive session.

Example
.......

(gdb)
-gdb-version
~GNU gdb 5.2.1
~Copyright 2000 Free Software Foundation, Inc.
~GDB is free software, covered by the GNU General Public License, and
~you are welcome to change it and/or distribute copies of it under
~ certain conditions.
~Type "show copying" to see the conditions.
~There is absolutely no warranty for GDB.  Type "show warranty" for
~ details.
~This GDB was configured as
"--host=sparc-sun-solaris2.5.1 --target=ppc-eabi".
^done
(gdb)

The -list-features' Command
----------------------------

Returns a list of particular features of the MI protocol that this
version of gdb implements.  A feature can be a command, or a new field
in an output of some command, or even an important bugfix.  While a
frontend can sometimes detect presence of a feature at runtime, it is
easier to perform detection at debugger startup.

The command returns a list of strings, with each string naming an
available feature.  Each returned string is just a name, it does not
have any internal structure.  The list of possible feature names is
given below.

Example output:

(gdb) -list-features
^done,result=["feature1","feature2"]

The current list of features is:

frozen-varobjs'
Indicates presence of the -var-set-frozen' command, as well as
possible presense of the frozen' field in the output of
-varobj-create'.

pending-breakpoints'
Indicates presence of the -f' option to the -break-insert'
command.

python'
Indicates presence of Python scripting support, Python-based
pretty-printing commands, and possible presence of the
display_hint' field in the output of -var-list-children'

Indicates presence of the -thread-info' command.

The -list-target-features' Command
-----------------------------------

Returns a list of particular features that are supported by the target.
Those features affect the permitted MI commands, but unlike the
features reported by the -list-features' command, the features depend
on which target GDB is using at the moment.  Whenever a target can
change, due to commands such as -target-select', -target-attach' or
-exec-run', the list of target features may change, and the frontend
should obtain it again.  Example output:

(gdb) -list-features
^done,result=["async"]

The current list of features is:

async'
Indicates that the target is capable of asynchronous command
execution, which means that GDB will accept further commands while
the target is running.

reverse'
Indicates that the target is capable of reverse execution.  *Note

The -list-thread-groups' Command
---------------------------------

Synopsis
--------

-list-thread-groups [ --available ] [ --recurse 1 ] [ GROUP ... ]

Lists thread groups (*note Thread groups::).  When a single thread
group is passed as the argument, lists the children of that group.
When several thread group are passed, lists information about those
thread groups.  Without any parameters, lists information about all

Normally, thread groups that are being debugged are reported.  With
the --available' option, GDB reports thread groups available on the
target.

The output of this command may have either a threads' result or a
groups' result.  The thread' result has a list of tuples as value,
with each tuple describing a thread (*note GDB/MI Thread
Information::).  The groups' result has a list of tuples as value,
each tuple describing a thread group.  If top-level groups are
requested (that is, no parameter is passed), or when several groups are
passed, the output always has a groups' result.  The format of the
group' result is described below.

To reduce the number of roundtrips it's possible to list thread
groups together with their children, by passing the --recurse' option
and the recursion depth.  Presently, only recursion depth of 1 is
permitted.  If this option is present, then every reported thread group
will also include its children, either as group' or threads' field.

In general, any combination of option and parameters is permitted,
with the following caveats:

* When a single thread group is passed, the output will typically be
the threads' result.  Because threads may not contain anything,
the recurse' option will be ignored.

* When the --available' option is passed, limited information may
be available.  In particular, the list of threads of a process
might be inaccessible.  Further, specifying specific thread groups
might not give any performance advantage over listing all thread
groups.  The frontend should assume that -list-thread-groups
--available' is always an expensive operation and cache the
results.

The groups' result is a list of tuples, where each tuple may have
the following fields:

id'
Identifier of the thread group.  This field is always present.
The identifier is an opaque string; frontends should not try to
convert it to an integer, even though it might look like one.

type'
The type of the thread group.  At present, only process' is a
valid type.

pid'
The target-specific process identifier.  This field is only present
for thread groups of type process' and only if the process exists.

num_children'
The number of children this thread group has.  This field may be
absent for an available thread group.

threads'
This field has a list of tuples as value, each tuple describing a
thread.  It may be present if the --recurse' option is specified,
and it's actually possible to obtain the threads.

cores'
This field is a list of integers, each identifying a core that one
thread of the group is running on.  This field may be absent if
such information is not available.

executable'
The name of the executable file that corresponds to this thread
group.  The field is only present for thread groups of type
process', and only if there is a corresponding executable file.

Example
-------

gdb
^done,groups=[{id="17",type="process",pid="yyy",num_children="2"}]
{id="1",target-id="Thread 0xb7e156b0 (LWP 21254)",
file="/tmp/a.c",fullname="/tmp/a.c",line="158"},state="running"}]]
^done,groups=[{id="17",type="process",pid="yyy",num_children="2",cores=[1,2]}]
-list-thread-groups --available --recurse 1
^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],
-list-thread-groups --available --recurse 1 17 18
^done,groups=[{id="17", types="process",pid="yyy",num_children="2",cores=[1,2],

---------------------------

Synopsis
--------

Creates a new inferior (*note Inferiors and Programs::).  The created
inferior is not associated with any executable.  Such association may
be established with the -file-exec-and-symbols' command (*note GDB/MI
File Commands::).  The command response has a single field,
thread-group', whose value is the identifier of the thread group
corresponding to the new inferior.

Example
-------

gdb

The -interpreter-exec' Command
-------------------------------

Synopsis
--------

-interpreter-exec INTERPRETER COMMAND
Execute the specified COMMAND in the given INTERPRETER.

GDB Command
-----------

The corresponding GDB command is interpreter-exec'.

Example
-------

(gdb)
-interpreter-exec console "break main"
&"During symbol reading, couldn't parse type; debugger out of date?.\n"
~"Breakpoint 1 at 0x8074fc6: file ../../src/gdb/main.c, line 743.\n"
^done
(gdb)

The -inferior-tty-set' Command
-------------------------------

Synopsis
--------

-inferior-tty-set /dev/pts/1

Set terminal for future runs of the program being debugged.

GDB Command
-----------

The corresponding GDB command is set inferior-tty' /dev/pts/1.

Example
-------

(gdb)
-inferior-tty-set /dev/pts/1
^done
(gdb)

The -inferior-tty-show' Command
--------------------------------

Synopsis
--------

-inferior-tty-show

Show terminal for future runs of program being debugged.

GDB Command
-----------

The corresponding GDB command is show inferior-tty'.

Example
-------

(gdb)
-inferior-tty-set /dev/pts/1
^done
(gdb)
-inferior-tty-show
^done,inferior_tty_terminal="/dev/pts/1"
(gdb)

The -enable-timings' Command
-----------------------------

Synopsis
--------

-enable-timings [yes | no]

Toggle the printing of the wallclock, user and system times for an MI
command as a field in its output.  This command is to help frontend
developers optimize the performance of their code.  No argument is
equivalent to yes'.

GDB Command
-----------

No equivalent.

Example
-------

(gdb)
-enable-timings
^done
(gdb)
-break-insert main
^done,bkpt={number="1",type="breakpoint",disp="keep",enabled="y",
fullname="/home/nickrob/myprog.c",line="73",times="0"},
time={wallclock="0.05185",user="0.00800",system="0.00000"}
(gdb)
-enable-timings no
^done
(gdb)
-exec-run
^running
(gdb)
{name="argv",value="0xbfb60364"}],file="myprog.c",
fullname="/home/nickrob/myprog.c",line="73"}
(gdb)

File: gdb.info,  Node: Annotations,  Next: JIT Interface,  Prev: GDB/MI,  Up: Top

28 GDB Annotations
******************

This chapter describes annotations in GDB.  Annotations were designed
to interface GDB to graphical user interfaces or other similar programs
which want to interact with GDB at a relatively high level.

The annotation mechanism has largely been superseded by GDB/MI
(*note GDB/MI::).

* Annotations Overview::  What annotations are; the general syntax.
* Server Prefix::       Issuing a command without affecting user state.
* Prompting::           Annotations marking GDB's need for input.
* Errors::              Annotations for error messages.
* Invalidation::        Some annotations describe things now invalid.
* Annotations for Running::
Whether the program is running, how it stopped, etc.
* Source Annotations::  Annotations describing source code.

File: gdb.info,  Node: Annotations Overview,  Next: Server Prefix,  Up: Annotations

28.1 What is an Annotation?
===========================

Annotations start with a newline character, two control-z' characters,
and the name of the annotation.  If there is no additional information
associated with this annotation, the name of the annotation is followed
immediately by a newline.  If there is additional information, the name
of the annotation is followed by a space, the additional information,
and a newline.  The additional information cannot contain newline
characters.

Any output not beginning with a newline and two control-z'
characters denotes literal output from GDB.  Currently there is no need
for GDB to output a newline followed by two control-z' characters, but
if there was such a need, the annotations could be extended with an
escape' annotation which means those three characters as output.

The annotation LEVEL, which is specified using the --annotate'
command line option (*note Mode Options::), controls how much
information GDB prints together with its prompt, values of expressions,
source lines, and other types of output.  Level 0 is for no
annotations, level 1 is for use when GDB is run as a subprocess of GNU
Emacs, level 3 is the maximum annotation suitable for programs that
control GDB, and level 2 annotations have been made obsolete (*note
Limitations of the Annotation Interface: (annotate)Limitations.).

set annotate LEVEL'
The GDB command set annotate' sets the level of annotations to
the specified LEVEL.

show annotate'
Show the current annotation level.

This chapter describes level 3 annotations.

A simple example of starting up GDB with annotations is:

$gdb --annotate=3 GNU gdb 6.0 Copyright 2003 Free Software Foundation, Inc. GDB is free software, covered by the GNU General Public License, and you are welcome to change it and/or distribute copies of it under certain conditions. Type "show copying" to see the conditions. There is absolutely no warranty for GDB. Type "show warranty" for details. This GDB was configured as "i386-pc-linux-gnu" ^Z^Zpre-prompt (gdb) ^Z^Zprompt quit ^Z^Zpost-prompt$

Here quit' is input to GDB; the rest is output from GDB.  The three
lines beginning ^Z^Z' (where ^Z' denotes a control-z' character) are
annotations; the rest is output from GDB.

File: gdb.info,  Node: Server Prefix,  Next: Prompting,  Prev: Annotations Overview,  Up: Annotations

28.2 The Server Prefix
======================

If you prefix a command with server ' then it will not affect the
command history, nor will it affect GDB's notion of which command to
repeat if <RET> is pressed on a line by itself.  This means that
commands can be run behind a user's back by a front-end in a
transparent manner.

The server ' prefix does not affect the recording of values into
the value history; to print a value without recording it into the value
history, use the output' command instead of the print' command.

Using this prefix also disables confirmation requests (*note
confirmation requests::).

File: gdb.info,  Node: Prompting,  Next: Errors,  Prev: Server Prefix,  Up: Annotations

28.3 Annotation for GDB Input
=============================

When GDB prompts for input, it annotates this fact so it is possible to
know when to send output, when the output from a given command is over,
etc.

Different kinds of input each have a different "input type".  Each
input type has three annotations: a pre-' annotation, which denotes
the beginning of any prompt which is being output, a plain annotation,
which denotes the end of the prompt, and then a post-' annotation
which denotes the end of any echo which may (or may not) be associated
with the input.  For example, the prompt' input type features the
following annotations:

^Z^Zpre-prompt
^Z^Zprompt
^Z^Zpost-prompt

The input types are

prompt'
When GDB is prompting for a command (the main GDB prompt).

commands'
When GDB prompts for a set of commands, like in the commands'
command.  The annotations are repeated for each command which is
input.

overload-choice'
When GDB wants the user to select between various overloaded
functions.

query'
When GDB wants the user to confirm a potentially dangerous
operation.

prompt-for-continue'
When GDB is asking the user to press return to continue.  Note:
Don't expect this to work well; instead use set height 0' to
disable prompting.  This is because the counting of lines is buggy
in the presence of annotations.

File: gdb.info,  Node: Errors,  Next: Invalidation,  Prev: Prompting,  Up: Annotations

28.4 Errors
===========

^Z^Zquit

This annotation occurs right before GDB responds to an interrupt.

^Z^Zerror

This annotation occurs right before GDB responds to an error.

Quit and error annotations indicate that any annotations which GDB
was in the middle of may end abruptly.  For example, if a
value-history-begin' annotation is followed by a error', one cannot
expect to receive the matching value-history-end'.  One cannot expect
not to receive it either, however; an error annotation does not
necessarily mean that GDB is immediately returning all the way to the
top level.

A quit or error annotation may be preceded by

^Z^Zerror-begin

Any output between that and the quit or error annotation is the error
message.

Warning messages are not yet annotated.

File: gdb.info,  Node: Invalidation,  Next: Annotations for Running,  Prev: Errors,  Up: Annotations

28.5 Invalidation Notices
=========================

The following annotations say that certain pieces of state may have
changed.

^Z^Zframes-invalid'
The frames (for example, output from the backtrace' command) may
have changed.

^Z^Zbreakpoints-invalid'
The breakpoints may have changed.  For example, the user just
added or deleted a breakpoint.

File: gdb.info,  Node: Annotations for Running,  Next: Source Annotations,  Prev: Invalidation,  Up: Annotations

28.6 Running the Program
========================

When the program starts executing due to a GDB command such as step'
or continue',

^Z^Zstarting

is output.  When the program stops,

^Z^Zstopped

is output.  Before the stopped' annotation, a variety of
annotations describe how the program stopped.

^Z^Zexited EXIT-STATUS'
The program exited, and EXIT-STATUS is the exit status (zero for
successful exit, otherwise nonzero).

^Z^Zsignalled'
The program exited with a signal.  After the ^Z^Zsignalled', the
annotation continues:

INTRO-TEXT
^Z^Zsignal-name
NAME
^Z^Zsignal-name-end
MIDDLE-TEXT
^Z^Zsignal-string
STRING
^Z^Zsignal-string-end
END-TEXT

where NAME is the name of the signal, such as SIGILL' or
SIGSEGV', and STRING is the explanation of the signal, such as
Illegal Instruction' or Segmentation fault'.  INTRO-TEXT,
MIDDLE-TEXT, and END-TEXT are for the user's benefit and have no
particular format.

^Z^Zsignal'
The syntax of this annotation is just like signalled', but GDB is
just saying that the program received the signal, not that it was
terminated with it.

^Z^Zbreakpoint NUMBER'
The program hit breakpoint number NUMBER.

^Z^Zwatchpoint NUMBER'
The program hit watchpoint number NUMBER.

File: gdb.info,  Node: Source Annotations,  Prev: Annotations for Running,  Up: Annotations

28.7 Displaying Source
======================

The following annotation is used instead of displaying source code:

where FILENAME is an absolute file name indicating which source
file, LINE is the line number within that file (where 1 is the first
line in the file), CHARACTER is the character position within the file
(where 0 is the first character in the file) (for most debug formats
this will necessarily point to the beginning of a line), MIDDLE is
middle' if ADDR is in the middle of the line, or beg' if ADDR is at
the beginning of the line, and ADDR is the address in the target
program associated with the source which is being displayed.  ADDR is
in the form 0x' followed by one or more lowercase hex digits (note
that this does not depend on the language).

File: gdb.info,  Node: JIT Interface,  Next: GDB Bugs,  Prev: Annotations,  Up: Top

29 JIT Compilation Interface
****************************

This chapter documents GDB's "just-in-time" (JIT) compilation
interface.  A JIT compiler is a program or library that generates native
executable code at runtime and executes it, usually in order to achieve
good performance while maintaining platform independence.

Programs that use JIT compilation are normally difficult to debug
because portions of their code are generated at runtime, instead of
being loaded from object files, which is where GDB normally finds the
program's symbols and debug information.  In order to debug programs
that use JIT compilation, GDB has an interface that allows the program
to register in-memory symbol files with GDB at runtime.

If you are using GDB to debug a program that uses this interface,
then it should work transparently so long as you have not stripped the
binary.  If you are developing a JIT compiler, then the interface is
documented in the rest of this chapter.  At this time, the only known
client of this interface is the LLVM JIT.

Broadly speaking, the JIT interface mirrors the dynamic loader
interface.  The JIT compiler communicates with GDB by writing data into
a global variable and calling a fuction at a well-known symbol.  When
GDB attaches, it reads a linked list of symbol files from the global
variable to find existing code, and puts a breakpoint in the function
so that it can find out about additional code.

* Declarations::                Relevant C struct declarations
* Registering Code::            Steps to register code
* Unregistering Code::          Steps to unregister code

File: gdb.info,  Node: Declarations,  Next: Registering Code,  Up: JIT Interface

29.1 JIT Declarations
=====================

These are the relevant struct declarations that a C program should
include to implement the interface:

typedef enum
{
JIT_NOACTION = 0,
JIT_REGISTER_FN,
JIT_UNREGISTER_FN
} jit_actions_t;

struct jit_code_entry
{
struct jit_code_entry *next_entry;
struct jit_code_entry *prev_entry;
uint64_t symfile_size;
};

struct jit_descriptor
{
uint32_t version;
/* This type should be jit_actions_t, but we use uint32_t
to be explicit about the bitwidth.  */
uint32_t action_flag;
struct jit_code_entry *relevant_entry;
struct jit_code_entry *first_entry;
};

/* GDB puts a breakpoint in this function.  */
void __attribute__((noinline)) __jit_debug_register_code() { };

/* Make sure to specify the version statically, because the
debugger may check the version before we can set it.  */
struct jit_descriptor __jit_debug_descriptor = { 1, 0, 0, 0 };

If the JIT is multi-threaded, then it is important that the JIT
synchronize any modifications to this global data properly, which can
easily be done by putting a global mutex around modifications to these
structures.

File: gdb.info,  Node: Registering Code,  Next: Unregistering Code,  Prev: Declarations,  Up: JIT Interface

29.2 Registering Code
=====================

To register code with GDB, the JIT should follow this protocol:

* Generate an object file in memory with symbols and other desired
debug information.  The file must include the virtual addresses of
the sections.

* Create a code entry for the file, which gives the start and size
of the symbol file.

* Add it to the linked list in the JIT descriptor.

* Point the relevant_entry field of the descriptor at the entry.

* Set action_flag' to JIT_REGISTER' and call
__jit_debug_register_code'.

When GDB is attached and the breakpoint fires, GDB uses the
relevant_entry' pointer so it doesn't have to walk the list looking for
new code.  However, the linked list must still be maintained in order
to allow GDB to attach to a running process and still find the symbol
files.

File: gdb.info,  Node: Unregistering Code,  Prev: Registering Code,  Up: JIT Interface

29.3 Unregistering Code
=======================

If code is freed, then the JIT should use the following protocol:

* Remove the code entry corresponding to the code from the linked
list.

* Point the relevant_entry' field of the descriptor at the code
entry.

* Set action_flag' to JIT_UNREGISTER' and call
__jit_debug_register_code'.

If the JIT frees or recompiles code without unregistering it, then
GDB and the JIT will leak the memory used for the associated symbol
files.

File: gdb.info,  Node: GDB Bugs,  Next: (rluserman),  Prev: JIT Interface,  Up: Top

30 Reporting Bugs in GDB
************************

Your bug reports play an essential role in making GDB reliable.

Reporting a bug may help you by bringing a solution to your problem,
or it may not.  But in any case the principal function of a bug report
is to help the entire community by making the next version of GDB work
better.  Bug reports are your contribution to the maintenance of GDB.

In order for a bug report to serve its purpose, you must include the
information that enables us to fix the bug.

* Bug Criteria::                Have you found a bug?
* Bug Reporting::               How to report bugs

File: gdb.info,  Node: Bug Criteria,  Next: Bug Reporting,  Up: GDB Bugs

30.1 Have You Found a Bug?
==========================

If you are not sure whether you have found a bug, here are some
guidelines:

* If the debugger gets a fatal signal, for any input whatever, that
is a GDB bug.  Reliable debuggers never crash.

* If GDB produces an error message for valid input, that is a bug.
(Note that if you're cross debugging, the problem may also be
somewhere in the connection to the target.)

* If GDB does not produce an error message for invalid input, that
is a bug.  However, you should note that your idea of "invalid
input" might be our idea of "an extension" or "support for

* If you are an experienced user of debugging tools, your suggestions
for improvement of GDB are welcome in any case.

File: gdb.info,  Node: Bug Reporting,  Prev: Bug Criteria,  Up: GDB Bugs

30.2 How to Report Bugs
=======================

A number of companies and individuals offer support for GNU products.
If you obtained GDB from a support organization, we recommend you
contact that organization first.

You can find contact information for many support companies and
individuals in the file etc/SERVICE' in the GNU Emacs distribution.

In any event, we also recommend that you submit bug reports for GDB.
The preferred method is to submit them directly using GDB's Bugs web
page (http://www.gnu.org/software/gdb/bugs/).  Alternatively, the
e-mail gateway <bug-gdbATgnu.org> can be used.

*Do not send bug reports to info-gdb', or to help-gdb', or to any
newsgroups.*  Most users of GDB do not want to receive bug reports.
Those that do have arranged to receive bug-gdb'.

The mailing list bug-gdb' has a newsgroup gnu.gdb.bug' which
serves as a repeater.  The mailing list and the newsgroup carry exactly
the same messages.  Often people think of posting bug reports to the
newsgroup instead of mailing them.  This appears to work, but it has one
problem which can be crucial: a newsgroup posting often lacks a mail
path back to the sender.  Thus, if we need to ask for more information,
we may be unable to reach you.  For this reason, it is better to send
bug reports to the mailing list.

The fundamental principle of reporting bugs usefully is this:
*report all the facts*.  If you are not sure whether to state a fact or
leave it out, state it!

Often people omit facts because they think they know what causes the
problem and assume that some details do not matter.  Thus, you might
assume that the name of the variable you use in an example does not
matter.  Well, probably it does not, but one cannot be sure.  Perhaps
the bug is a stray memory reference which happens to fetch from the
location where that name is stored in memory; perhaps, if the name were
different, the contents of that location would fool the debugger into
doing the right thing despite the bug.  Play it safe and give a
specific, complete example.  That is the easiest thing for you to do,
and the most helpful.

Keep in mind that the purpose of a bug report is to enable us to fix
the bug.  It may be that the bug has been reported previously, but
neither you nor we can know that unless your bug report is complete and
self-contained.

Sometimes people give a few sketchy facts and ask, "Does this ring a
bell?"  Those bug reports are useless, and we urge everyone to _refuse
to respond to them_ except to chide the sender to report bugs properly.

To enable us to fix the bug, you should include all these things:

* The version of GDB.  GDB announces it if you start with no
arguments; you can also print it at any time using show version'.

Without this, we will not know whether there is any point in
looking for the bug in the current version of GDB.

* The type of machine you are using, and the operating system name
and version number.

* What compiler (and its version) was used to compile GDB--e.g.
"gcc-2.8.1".

* What compiler (and its version) was used to compile the program
you are debugging--e.g.  "gcc-2.8.1", or "HP92453-01 A.10.32.03 HP
C Compiler".  For GCC, you can say gcc --version' to get this
information; for other compilers, see the documentation for those
compilers.

* The command arguments you gave the compiler to compile your
example and observe the bug.  For example, did you use -O'?  To
guarantee you will not omit something important, list them all.  A
copy of the Makefile (or the output from make) is sufficient.

If we were to try to guess the arguments, we would probably guess
wrong and then we might not encounter the bug.

* A complete input script, and all necessary source files, that will
reproduce the bug.

* A description of what behavior you observe that you believe is
incorrect.  For example, "It gets a fatal signal."

Of course, if the bug is that GDB gets a fatal signal, then we
will certainly notice it.  But if the bug is incorrect output, we
might not notice unless it is glaringly wrong.  You might as well
not give us a chance to make a mistake.

Even if the problem you experience is a fatal signal, you should
still say so explicitly.  Suppose something strange is going on,
such as, your copy of GDB is out of synch, or you have encountered
a bug in the C library on your system.  (This has happened!)  Your
copy might crash and ours would not.  If you told us to expect a
crash, then when ours fails to crash, we would know that the bug
was not happening for us.  If you had not told us to expect a
crash, then we would not be able to draw any conclusion from our
observations.

To collect all this information, you can use a session recording
program such as script', which is available on many Unix systems.
Just run your GDB session inside script' and then include the
typescript' file with your bug report.

Another way to record a GDB session is to run GDB inside Emacs and
then save the entire buffer to a file.

* If you wish to suggest changes to the GDB source, send us context
diffs.  If you even discuss something in the GDB source, refer to
it by context, not by line number.

The line numbers in our development sources will not match those
in your sources.  Your line numbers would convey no useful
information to us.

Here are some things that are not necessary:

* A description of the envelope of the bug.

Often people who encounter a bug spend a lot of time investigating
which changes to the input file will make the bug go away and which
changes will not affect it.

This is often time consuming and not very useful, because the way
we will find the bug is by running a single example under the
debugger with breakpoints, not by pure deduction from a series of
examples.  We recommend that you save your time for something else.

Of course, if you can find a simpler example to report _instead_
of the original one, that is a convenience for us.  Errors in the
output will be easier to spot, running under the debugger will take
less time, and so on.

However, simplification is not vital; if you do not want to do
this, report the bug anyway and send us the entire test case you
used.

* A patch for the bug.

A patch for the bug does help us if it is a good one.  But do not
omit the necessary information, such as the test case, on the
assumption that a patch is all we need.  We might see problems
with your patch and decide to fix the problem another way, or we
might not understand it at all.

Sometimes with a program as complicated as GDB it is very hard to
construct an example that will make the program follow a certain
path through the code.  If you do not send us the example, we will
not be able to construct one, so we will not be able to verify
that the bug is fixed.

And if we cannot understand what bug you are trying to fix, or why
your patch should be an improvement, we will not install it.  A
test case will help us to understand.

* A guess about what the bug is or what it depends on.

Such guesses are usually wrong.  Even we cannot guess right about
such things without first using the debugger to find the facts.

File: gdb.info,  Node: Formatting Documentation,  Next: Installing GDB,  Prev: (history),  Up: Top

Appendix A Formatting Documentation
***********************************

The GDB 4 release includes an already-formatted reference card, ready
for printing with PostScript or Ghostscript, in the gdb' subdirectory
of the main source directory(1).  If you can use PostScript or
Ghostscript with your printer, you can print the reference card
immediately with refcard.ps'.

The release also includes the source for the reference card.  You
can format it, using TeX, by typing:

make refcard.dvi

The GDB reference card is designed to print in "landscape" mode on
US "letter" size paper; that is, on a sheet 11 inches wide by 8.5 inches
high.  You will need to specify this form of printing as an option to
your DVI output program.

All the documentation for GDB comes as part of the machine-readable
distribution.  The documentation is written in Texinfo format, which is
a documentation system that uses a single source file to produce both
on-line information and a printed manual.  You can use one of the Info
formatting commands to create the on-line version of the documentation
and TeX (or texi2roff') to typeset the printed version.

GDB includes an already formatted copy of the on-line Info version
of this manual in the gdb' subdirectory.  The main Info file is
gdb-7.2/gdb/gdb.info', and it refers to subordinate files matching
gdb.info*' in the same directory.  If necessary, you can print out
these files, or read them with any editor; but they are easier to read
using the info' subsystem in GNU Emacs or the standalone info'
program, available as part of the GNU Texinfo distribution.

If you want to format these Info files yourself, you need one of the
Info formatting programs, such as texinfo-format-buffer' or makeinfo'.

If you have makeinfo' installed, and are in the top level GDB
source directory (gdb-7.2', in the case of version 7.2), you can make
the Info file by typing:

cd gdb
make gdb.info

If you want to typeset and print copies of this manual, you need TeX,
a program to print its DVI output files, and texinfo.tex', the Texinfo
definitions file.

TeX is a typesetting program; it does not print files directly, but
produces output files called DVI files.  To print a typeset document,
you need a program to print DVI files.  If your system has TeX
installed, chances are it has such a program.  The precise command to
use depends on your system; lpr -d' is common; another (for PostScript
devices) is dvips'.  The DVI print command may require a file name
without any extension or a .dvi' extension.

TeX also requires a macro definitions file called texinfo.tex'.
This file tells TeX how to typeset a document written in Texinfo
format.  On its own, TeX cannot either read or typeset a Texinfo file.
texinfo.tex' is distributed with GDB and is located in the
gdb-VERSION-NUMBER/texinfo' directory.

If you have TeX and a DVI printer program installed, you can typeset
and print this manual.  First switch to the gdb' subdirectory of the
main source directory (for example, to gdb-7.2/gdb') and type:

make gdb.dvi

Then give gdb.dvi' to your DVI printing program.

---------- Footnotes ----------

(1) In gdb-7.2/gdb/refcard.ps' of the version 7.2 release.

File: gdb.info,  Node: Installing GDB,  Next: Maintenance Commands,  Prev: Formatting Documentation,  Up: Top

Appendix B Installing GDB
*************************

* Requirements::                Requirements for building GDB
* Running Configure::           Invoking the GDB configure' script
* Separate Objdir::             Compiling GDB in another directory
* Config Names::                Specifying names for hosts and targets
* Configure Options::           Summary of options for configure
* System-wide configuration::   Having a system-wide init file

File: gdb.info,  Node: Requirements,  Next: Running Configure,  Up: Installing GDB

B.1 Requirements for Building GDB
=================================

Building GDB requires various tools and packages to be available.
Other packages will be used only if they are found.

Tools/Packages Necessary for Building GDB
=========================================

ISO C90 compiler
GDB is written in ISO C90.  It should be buildable with any
working C90 compiler, e.g. GCC.

Tools/Packages Optional for Building GDB
========================================

Expat
GDB can use the Expat XML parsing library.  This library may be
included with your operating system distribution; if it is not, you
can get the latest version from http://expat.sourceforge.net'.
The configure' script will search for this library in several
standard locations; if it is installed in an unusual path, you can
use the --with-libexpat-prefix' option to specify its location.

Expat is used for:

* Remote protocol memory maps (*note Memory Map Format::)

* Target descriptions (*note Target Descriptions::)

* Remote shared library lists (*note Library List Format::)

* MS-Windows shared libraries (*note Shared Libraries::)

zlib
GDB will use the zlib' library, if available, to read compressed
debug sections.  Some linkers, such as GNU gold, are capable of
producing binaries with compressed debug sections.  If GDB is
compiled with zlib', it will be able to read the debug
information in such binaries.

The zlib' library is likely included with your operating system
distribution; if it is not, you can get the latest version from
http://zlib.net'.

iconv
GDB's features related to character sets (*note Character Sets::)
require a functioning iconv' implementation.  If you are on a GNU
system, then this is provided by the GNU C Library.  Some other
systems also provide a working iconv'.

On systems with iconv', you can install GNU Libiconv.  If you
have previously installed Libiconv, you can use the
--with-libiconv-prefix' option to configure.

GDB's top-level configure' and Makefile' will arrange to build
Libiconv if a directory named libiconv' appears in the top-most
source directory.  If Libiconv is built this way, and if the
operating system does not provide a suitable iconv'
implementation, then the just-built library will automatically be
used by GDB.  One easy way to set this up is to download GNU
Libiconv, unpack it, and then rename the directory holding the
Libiconv source code to libiconv'.

File: gdb.info,  Node: Running Configure,  Next: Separate Objdir,  Prev: Requirements,  Up: Installing GDB

B.2 Invoking the GDB configure' Script
=======================================

GDB comes with a configure' script that automates the process of
preparing GDB for installation; you can then use make' to build the
gdb' program.

The GDB distribution includes all the source code you need for GDB
in a single directory, whose name is usually composed by appending the
version number to gdb'.

For example, the GDB version 7.2 distribution is in the gdb-7.2'
directory.  That directory contains:

gdb-7.2/configure (and supporting files)'
script for configuring GDB and all its supporting libraries

gdb-7.2/gdb'
the source specific to GDB itself

gdb-7.2/bfd'
source for the Binary File Descriptor library

gdb-7.2/include'
GNU include files

gdb-7.2/libiberty'
source for the -liberty' free software library

gdb-7.2/opcodes'
source for the library of opcode tables and disassemblers

gdb-7.2/glob'
source for the GNU filename pattern-matching subroutine

gdb-7.2/mmalloc'
source for the GNU memory-mapped malloc package

The simplest way to configure and build GDB is to run configure'
from the gdb-VERSION-NUMBER' source directory, which in this example
is the gdb-7.2' directory.

First switch to the gdb-VERSION-NUMBER' source directory if you are
not already in it; then run configure'.  Pass the identifier for the
platform on which GDB will run as an argument.

For example:

cd gdb-7.2
./configure HOST
make

where HOST is an identifier such as sun4' or decstation', that
identifies the platform where GDB will run.  (You can often leave off
HOST; configure' tries to guess the correct value by examining your
system.)

Running configure HOST' and then running make' builds the bfd',
mmalloc', and libiberty' libraries, then gdb' itself.  The
configured source files, and the binaries, are left in the
corresponding source directories.

configure' is a Bourne-shell (/bin/sh') script; if your system
does not recognize this automatically when you run a different shell,
you may need to run sh' on it explicitly:

sh configure HOST

If you run configure' from a directory that contains source
directories for multiple libraries or programs, such as the gdb-7.2'
source directory for version 7.2, configure' creates configuration
files for every directory level underneath (unless you tell it not to,
with the --norecursion' option).

You should run the configure' script from the top directory in the
source tree, the gdb-VERSION-NUMBER' directory.  If you run
configure' from one of the subdirectories, you will configure only
that subdirectory.  That is usually not what you want.  In particular,
if you run the first configure' from the gdb' subdirectory of the
gdb-VERSION-NUMBER' directory, you will omit the configuration of
bfd', and other sibling directories of the gdb' subdirectory.  This
leads to build errors about missing include files such as bfd/bfd.h'.

You can install gdb' anywhere; it has no hardwired paths.  However,
you should make sure that the shell on your path (named by the SHELL'
environment variable) is publicly readable.  Remember that GDB uses the
shell to start your program--some systems refuse to let GDB debug child
processes whose programs are not readable.

File: gdb.info,  Node: Separate Objdir,  Next: Config Names,  Prev: Running Configure,  Up: Installing GDB

B.3 Compiling GDB in Another Directory
======================================

If you want to run GDB versions for several host or target machines,
you need a different gdb' compiled for each combination of host and
target.  configure' is designed to make this easy by allowing you to
generate each configuration in a separate subdirectory, rather than in
the source directory.  If your make' program handles the VPATH'
feature (GNU make' does), running make' in each of these directories
builds the gdb' program specified there.

To build gdb' in a separate directory, run configure' with the
--srcdir' option to specify where to find the source.  (You also need
to specify a path to find configure' itself from your working
directory.  If the path to configure' would be the same as the
argument to --srcdir', you can leave out the --srcdir' option; it is
assumed.)

For example, with version 7.2, you can build GDB in a separate
directory for a Sun 4 like this:

cd gdb-7.2
mkdir ../gdb-sun4
cd ../gdb-sun4
../gdb-7.2/configure sun4
make

When configure' builds a configuration using a remote source
directory, it creates a tree for the binaries with the same structure
(and using the same names) as the tree under the source directory.  In
the example, you'd find the Sun 4 library libiberty.a' in the
directory gdb-sun4/libiberty', and GDB itself in gdb-sun4/gdb'.

Make sure that your path to the configure' script has just one
instance of gdb' in it.  If your path to configure' looks like
../gdb-7.2/gdb/configure', you are configuring only one subdirectory
of GDB, not the whole package.  This leads to build errors about
missing include files such as bfd/bfd.h'.

One popular reason to build several GDB configurations in separate
directories is to configure GDB for cross-compiling (where GDB runs on
one machine--the "host"--while debugging programs that run on another
machine--the "target").  You specify a cross-debugging target by giving
the --target=TARGET' option to configure'.

When you run make' to build a program or library, you must run it
in a configured directory--whatever directory you were in when you
called configure' (or one of its subdirectories).

The Makefile' that configure' generates in each source directory
also runs recursively.  If you type make' in a source directory such
as gdb-7.2' (or in a separate configured directory configured with
--srcdir=DIRNAME/gdb-7.2'), you will build all the required libraries,
and then build GDB.

When you have multiple hosts or targets configured in separate
directories, you can run make' on them in parallel (for example, if
they are NFS-mounted on each of the hosts); they will not interfere
with each other.

File: gdb.info,  Node: Config Names,  Next: Configure Options,  Prev: Separate Objdir,  Up: Installing GDB

B.4 Specifying Names for Hosts and Targets
==========================================

The specifications used for hosts and targets in the configure' script
are based on a three-part naming scheme, but some short predefined
aliases are also supported.  The full naming scheme encodes three pieces
of information in the following pattern:

ARCHITECTURE-VENDOR-OS

For example, you can use the alias sun4' as a HOST argument, or as
the value for TARGET in a --target=TARGET' option.  The equivalent
full name is sparc-sun-sunos4'.

The configure' script accompanying GDB does not provide any query
facility to list all supported host and target names or aliases.
configure' calls the Bourne shell script config.sub' to map
abbreviations to full names; you can read the script, if you wish, or
you can use it to test your guesses on abbreviations--for example:

% sh config.sub i386-linux
i386-pc-linux-gnu
% sh config.sub alpha-linux
alpha-unknown-linux-gnu
% sh config.sub hp9k700
hppa1.1-hp-hpux
% sh config.sub sun4
sparc-sun-sunos4.1.1
% sh config.sub sun3
m68k-sun-sunos4.1.1
% sh config.sub i986v
Invalid configuration i986v': machine i986v' not recognized

config.sub' is also distributed in the GDB source directory
(gdb-7.2', for version 7.2).

File: gdb.info,  Node: Configure Options,  Next: System-wide configuration,  Prev: Config Names,  Up: Installing GDB

B.5 configure' Options
=======================

Here is a summary of the configure' options and arguments that are
most often useful for building GDB.  configure' also has several other
options not listed here.  *note (configure.info)What Configure Does::,
for a full explanation of configure'.

configure [--help]
[--prefix=DIR]
[--exec-prefix=DIR]
[--srcdir=DIRNAME]
[--norecursion] [--rm]
[--target=TARGET]
HOST

You may introduce options with a single -' rather than --' if you
prefer; but you may abbreviate option names if you use --'.

--help'
Display a quick summary of how to invoke configure'.

--prefix=DIR'
Configure the source to install programs and files under directory
DIR'.

--exec-prefix=DIR'
Configure the source to install programs under directory DIR'.

--srcdir=DIRNAME'
*Warning: using this option requires GNU make', or another make'
that implements the VPATH' feature.*
Use this option to make configurations in directories separate
from the GDB source directories.  Among other things, you can use
this to build (or maintain) several configurations simultaneously,
in separate directories.  configure' writes
configuration-specific files in the current directory, but
arranges for them to use the source in the directory DIRNAME.
configure' creates directories under the working directory in
parallel to the source directories below DIRNAME.

--norecursion'
Configure only the directory level where configure' is executed;
do not propagate configuration to subdirectories.

--target=TARGET'
Configure GDB for cross-debugging programs running on the specified
TARGET.  Without this option, GDB is configured to debug programs
that run on the same machine (HOST) as GDB itself.

There is no convenient way to generate a list of all available
targets.

HOST ...'
Configure GDB to run on the specified HOST.

There is no convenient way to generate a list of all available
hosts.

There are many other options available as well, but they are
generally needed for special purposes only.

File: gdb.info,  Node: System-wide configuration,  Prev: Configure Options,  Up: Installing GDB

B.6 System-wide configuration and settings
==========================================

GDB can be configured to have a system-wide init file; this file will
be read and executed at startup (*note What GDB does during startup:
Startup.).

Here is the corresponding configure option:

--with-system-gdbinit=FILE'
Specify that the default location of the system-wide init file is
FILE.

If GDB has been configured with the option --prefix=$prefix', it may be subject to relocation. Two possible cases: * If the default location of this init file contains $prefix', it
will be subject to relocation.  Suppose that the configure options
are --prefix=$prefix --with-system-gdbinit=$prefix/etc/gdbinit';
if GDB is moved from $prefix' to $install', the system init file
is looked for as $install/etc/gdbinit' instead of $prefix/etc/gdbinit'.

* By contrast, if the default location does not contain the prefix,
it will not be relocated.  E.g. if GDB has been configured with
--prefix=/usr/local --with-system-gdbinit=/usr/share/gdb/gdbinit',
then GDB will always look for /usr/share/gdb/gdbinit', wherever
GDB is installed.

File: gdb.info,  Node: Maintenance Commands,  Next: Remote Protocol,  Prev: Installing GDB,  Up: Top

Appendix C Maintenance Commands
*******************************

In addition to commands intended for GDB users, GDB includes a number
of commands intended for GDB developers, that are not documented
elsewhere in this manual.  These commands are provided here for
reference.  (For commands that turn on debugging messages, see *note
Debugging Output::.)

maint agent EXPRESSION'
maint agent-eval EXPRESSION'
Translate the given EXPRESSION into remote agent bytecodes.  This
command is useful for debugging the Agent Expression mechanism
(*note Agent Expressions::).  The agent' version produces an
expression useful for data collection, such as by tracepoints,
while maint agent-eval' produces an expression that evaluates
directly to a result.  For instance, a collection expression for
globa + globb' will include bytecodes to record four bytes of
memory at each of the addresses of globa' and globb', while
discarding the result of the addition, while an evaluation
expression will do the addition and return the sum.

maint info breakpoints'
Using the same format as info breakpoints', display both the
breakpoints you've set explicitly, and those GDB is using for
internal purposes.  Internal breakpoints are shown with negative
breakpoint numbers.  The type column identifies what kind of
breakpoint is shown:

breakpoint'
Normal, explicitly set breakpoint.

watchpoint'
Normal, explicitly set watchpoint.

longjmp'
Internal breakpoint, used to handle correctly stepping through
longjmp' calls.

longjmp resume'
Internal breakpoint at the target of a longjmp'.

until'
Temporary internal breakpoint used by the GDB until' command.

finish'
Temporary internal breakpoint used by the GDB finish'
command.

shlib events'
Shared library events.

set displaced-stepping'
show displaced-stepping'
Control whether or not GDB will do "displaced stepping" if the
target supports it.  Displaced stepping is a way to single-step
over breakpoints without removing them from the inferior, by
executing an out-of-line copy of the instruction that was
originally at the breakpoint location.  It is also known as
out-of-line single-stepping.

set displaced-stepping on'
If the target architecture supports it, GDB will use
displaced stepping to step over breakpoints.

set displaced-stepping off'
GDB will not use displaced stepping to step over breakpoints,
even if such is supported by the target architecture.

set displaced-stepping auto'
This is the default mode.  GDB will use displaced stepping
only if non-stop mode is active (*note Non-Stop Mode::) and
the target architecture supports displaced stepping.

maint check-symtabs'
Check the consistency of psymtabs and symtabs.

maint cplus first_component NAME'
Print the first C++ class/namespace component of NAME.

maint cplus namespace'
Print the list of possible C++ namespaces.

maint demangle NAME'
Demangle a C++ or Objective-C mangled NAME.

maint deprecate COMMAND [REPLACEMENT]'
maint undeprecate COMMAND'
Deprecate or undeprecate the named COMMAND.  Deprecated commands
cause GDB to issue a warning when you use them.  The optional
argument REPLACEMENT says which newer command should be used in
favor of the deprecated one; if it is given, GDB will mention the
replacement as part of the warning.

maint dump-me'
Cause a fatal signal in the debugger and force it to dump its core.
This is supported only on systems which support aborting a program
with the SIGQUIT' signal.

maint internal-error [MESSAGE-TEXT]'
maint internal-warning [MESSAGE-TEXT]'
Cause GDB to call the internal function internal_error' or
internal_warning' and hence behave as though an internal error or
internal warning has been detected.  In addition to reporting the
internal problem, these functions give the user the opportunity to
either quit GDB or create a core file of the current GDB session.

These commands take an optional parameter MESSAGE-TEXT that is
used as the text of the error or warning message.

Here's an example of using internal-error':

(gdb) maint internal-error testing, 1, 2
.../maint.c:121: internal-error: testing, 1, 2
A problem internal to GDB has been detected.  Further
debugging may prove unreliable.
Quit this debugging session? (y or n) n
Create a core file? (y or n) n
(gdb)

maint set internal-error ACTION [ask|yes|no]'
maint show internal-error ACTION'
maint set internal-warning ACTION [ask|yes|no]'
maint show internal-warning ACTION'
When GDB reports an internal problem (error or warning) it gives
the user the opportunity to both quit GDB and create a core file
of the current GDB session.  These commands let you override the
default behaviour for each particular ACTION, described in the
table below.

quit'
You can specify that GDB should always (yes) or never (no)
quit.  The default is to ask the user what to do.

corefile'
You can specify that GDB should always (yes) or never (no)
create a core file.  The default is to ask the user what to
do.

maint packet TEXT'
If GDB is talking to an inferior via the serial protocol, then
this command sends the string TEXT to the inferior, and displays
the response packet.  GDB supplies the initial $' character, the terminating #' character, and the checksum. maint print architecture [FILE]' Print the entire architecture configuration. The optional argument FILE names the file where the output goes. maint print c-tdesc' Print the current target description (*note Target Descriptions::) as a C source file. The created source file can be used in GDB when an XML parser is not available to parse the description. maint print dummy-frames' Prints the contents of GDB's internal dummy-frame stack. (gdb) b add ... (gdb) print add(2,3) Breakpoint 2, add (a=2, b=3) at ... 58 return (a + b); The program being debugged stopped while in a function called from GDB. ... (gdb) maint print dummy-frames 0x1a57c80: pc=0x01014068 fp=0x0200bddc sp=0x0200bdd6 top=0x0200bdd4 id={stack=0x200bddc,code=0x101405c} call_lo=0x01014000 call_hi=0x01014001 (gdb) Takes an optional file parameter. maint print registers [FILE]' maint print raw-registers [FILE]' maint print cooked-registers [FILE]' maint print register-groups [FILE]' Print GDB's internal register data structures. The command maint print raw-registers' includes the contents of the raw register cache; the command maint print cooked-registers' includes the (cooked) value of all registers, including registers which aren't available on the target nor visible to user; and the command maint print register-groups' includes the groups that each register is a member of. *Note Registers: (gdbint)Registers. These commands take an optional parameter, a file name to which to write the information. maint print reggroups [FILE]' Print GDB's internal register group data structures. The optional argument FILE tells to what file to write the information. The register groups info looks like this: (gdb) maint print reggroups Group Type general user float user all user vector user system user save internal restore internal flushregs' This command forces GDB to flush its internal register cache. maint print objfiles' Print a dump of all known object files. For each object file, this command prints its name, address in memory, and all of its psymtabs and symtabs. maint print section-scripts [REGEXP]' Print a dump of scripts specified in the .debug_gdb_section' section. If REGEXP is specified, only print scripts loaded by object files matching REGEXP. For each script, this command prints its name as specified in the objfile, and the full path if known. *Note dotdebug_gdb_scripts section::. maint print statistics' This command prints, for each object file in the program, various data about that object file followed by the byte cache ("bcache") statistics for the object file. The objfile data includes the number of minimal, partial, full, and stabs symbols, the number of types defined by the objfile, the number of as yet unexpanded psym tables, the number of line tables and string tables, and the amount of memory used by the various tables. The bcache statistics include the counts, sizes, and counts of duplicates of all and unique objects, max, average, and median entry size, total memory used and its overhead and savings, and various measures of the hash table size and chain lengths. maint print target-stack' A "target" is an interface between the debugger and a particular kind of file or process. Targets can be stacked in "strata", so that more than one target can potentially respond to a request. In particular, memory accesses will walk down the stack of targets until they find a target that is interested in handling that particular address. This command prints a short description of each layer that was pushed on the "target stack", starting from the top layer down to the bottom one. maint print type EXPR' Print the type chain for a type specified by EXPR. The argument can be either a type name or a symbol. If it is a symbol, the type of that symbol is described. The type chain produced by this command is a recursive definition of the data type as stored in GDB's data structures, including its flags and contained types. maint set dwarf2 always-disassemble' maint show dwarf2 always-disassemble' Control the behavior of info address' when using DWARF debugging information. The default is off', which means that GDB should try to describe a variable's location in an easily readable format. When on', GDB will instead display the DWARF location expression in an assembly-like format. Note that some locations are too complex for GDB to describe simply; in this case you will always see the disassembly form. Here is an example of the resulting disassembly: (gdb) info addr argc Symbol "argc" is a complex DWARF expression: 1: DW_OP_fbreg 0 For more information on these expressions, see the DWARF standard (http://www.dwarfstd.org/). maint set dwarf2 max-cache-age' maint show dwarf2 max-cache-age' Control the DWARF 2 compilation unit cache. In object files with inter-compilation-unit references, such as those produced by the GCC option -feliminate-dwarf2-dups', the DWARF 2 reader needs to frequently refer to previously read compilation units. This setting controls how long a compilation unit will remain in the cache if it is not referenced. A higher limit means that cached compilation units will be stored in memory longer, and more total memory will be used. Setting it to zero disables caching, which will slow down GDB startup, but reduce memory consumption. maint set profile' maint show profile' Control profiling of GDB. Profiling will be disabled until you use the maint set profile' command to enable it. When you enable profiling, the system will begin collecting timing and execution count data; when you disable profiling or exit GDB, the results will be written to a log file. Remember that if you use profiling, GDB will overwrite the profiling log file (often called gmon.out'). If you have a record of important profiling data in a gmon.out' file, be sure to move it to a safe location. Configuring with --enable-profiling' arranges for GDB to be compiled with the -pg' compiler option. maint set show-debug-regs' maint show show-debug-regs' Control whether to show variables that mirror the hardware debug registers. Use ON' to enable, OFF' to disable. If enabled, the debug registers values are shown when GDB inserts or removes a hardware breakpoint or watchpoint, and when the inferior triggers a hardware-assisted breakpoint or watchpoint. maint set show-all-tib' maint show show-all-tib' Control whether to show all non zero areas within a 1k block starting at thread local base, when using the info w32 thread-information-block' command. maint space' Control whether to display memory usage for each command. If set to a nonzero value, GDB will display how much memory each command took, following the command's own output. This can also be requested by invoking GDB with the --statistics' command-line switch (*note Mode Options::). maint time' Control whether to display the execution time for each command. If set to a nonzero value, GDB will display how much time it took to execute each command, following the command's own output. The time is not printed for the commands that run the target, since there's no mechanism currently to compute how much time was spend by GDB and how much time was spend by the program been debugged. it's not possibly currently This can also be requested by invoking GDB with the --statistics' command-line switch (*note Mode Options::). maint translate-address [SECTION] ADDR' Find the symbol stored at the location specified by the address ADDR and an optional section name SECTION. If found, GDB prints the name of the closest symbol and an offset from the symbol's location to the specified address. This is similar to the info address' command (*note Symbols::), except that this command also allows to find symbols in other sections. If section was not specified, the section in which the symbol was found is also printed. For dynamically linked executables, the name of executable or shared library containing the symbol is printed as well. The following command is useful for non-interactive invocations of GDB, such as in the test suite. set watchdog NSEC' Set the maximum number of seconds GDB will wait for the target operation to finish. If this time expires, GDB reports and error and the command is aborted. show watchdog' Show the current setting of the target wait timeout. File: gdb.info, Node: Remote Protocol, Next: Agent Expressions, Prev: Maintenance Commands, Up: Top Appendix D GDB Remote Serial Protocol ************************************* * Menu: * Overview:: * Packets:: * Stop Reply Packets:: * General Query Packets:: * Architecture-Specific Protocol Details:: * Tracepoint Packets:: * Host I/O Packets:: * Interrupts:: * Notification Packets:: * Remote Non-Stop:: * Packet Acknowledgment:: * Examples:: * File-I/O Remote Protocol Extension:: * Library List Format:: * Memory Map Format:: * Thread List Format:: File: gdb.info, Node: Overview, Next: Packets, Up: Remote Protocol D.1 Overview ============ There may be occasions when you need to know something about the protocol--for example, if there is only one serial port to your target machine, you might want your program to do something special if it recognizes a packet meant for GDB. In the examples below, ->' and <-' are used to indicate transmitted and received data, respectively. All GDB commands and responses (other than acknowledgments and notifications, see *note Notification Packets::) are sent as a PACKET. A PACKET is introduced with the character $', the actual PACKET-DATA,
and the terminating character #' followed by a two-digit CHECKSUM:

$'PACKET-DATA#'CHECKSUM The two-digit CHECKSUM is computed as the modulo 256 sum of all characters between the leading $' and the trailing #' (an eight bit
unsigned checksum).

Implementors should note that prior to GDB 5.0 the protocol
specification also included an optional two-digit SEQUENCE-ID:

$'SEQUENCE-ID:'PACKET-DATA#'CHECKSUM That SEQUENCE-ID was appended to the acknowledgment. GDB has never output SEQUENCE-IDs. Stubs that handle packets added since GDB 5.0 must not accept SEQUENCE-ID. When either the host or the target machine receives a packet, the first response expected is an acknowledgment: either +' (to indicate the package was received correctly) or -' (to request retransmission): -> $'PACKET-DATA#'CHECKSUM
<- +'
The +'/-' acknowledgments can be disabled once a connection is
established.  *Note Packet Acknowledgment::, for details.

The host (GDB) sends COMMANDs, and the target (the debugging stub
incorporated in your program) sends a RESPONSE.  In the case of step
and continue COMMANDs, the response is only sent when the operation has
completed, and the target has again stopped all threads in all attached
processes.  This is the default all-stop mode behavior, but the remote
protocol also supports GDB's non-stop execution mode; see *note Remote
Non-Stop::, for details.

PACKET-DATA consists of a sequence of characters with the exception
of #' and $' (see X' packet for additional exceptions). Fields within the packet should be separated using ,' ;' or :'. Except where otherwise noted all numbers are represented in HEX with leading zeros suppressed. Implementors should note that prior to GDB 5.0, the character :' could not appear as the third character in a packet (as it would potentially conflict with the SEQUENCE-ID). Binary data in most packets is encoded either as two hexadecimal digits per byte of binary data. This allowed the traditional remote protocol to work over connections which were only seven-bit clean. Some packets designed more recently assume an eight-bit clean connection, and use a more efficient encoding to send and receive binary data. The binary data representation uses 7d' (ASCII }') as an escape character. Any escaped byte is transmitted as the escape character followed by the original character XORed with 0x20'. For example, the byte 0x7d' would be transmitted as the two bytes 0x7d 0x5d'. The bytes 0x23' (ASCII #'), 0x24' (ASCII $'), and 0x7d' (ASCII }')
must always be escaped.  Responses sent by the stub must also escape
0x2a' (ASCII *'), so that it is not interpreted as the start of a
run-length encoded sequence (described next).

Response DATA can be run-length encoded to save space.  Run-length
encoding replaces runs of identical characters with one instance of the
repeated character, followed by a *' and a repeat count.  The repeat
count is itself sent encoded, to avoid binary characters in DATA: a
value of N is sent as N+29'.  For a repeat count greater or equal to
3, this produces a printable ASCII character, e.g. a space (ASCII code
32) for a repeat count of 3.  (This is because run-length encoding
starts to win for counts 3 or more.)  Thus, for example, 0* ' is a
run-length encoding of "0000": the space character after *' means
repeat the leading 0' 32 - 29 = 3' more times.

The printable characters #' and $' or with a numeric value greater than 126 must not be used. Runs of six repeats (#') or seven repeats ($') can be expanded using a repeat count of only five ("').  For
example, 00000000' can be encoded as 0*"00'.

The error response returned for some packets includes a two character
error number.  That number is not well defined.

For any COMMAND not supported by the stub, an empty response
(\$#00') should be returned.  That way it is possible to extend the
protocol.  A newer GDB can tell if a packet is supported based on that
response.

A stub is required to support the g', G', m', M', c', and s'
COMMANDs.  All other COMMANDs are optional.

File: gdb.info,  Node: Packets,  Next: Stop Reply Packets,  Prev: Overview,  Up: Remote Protocol

D.2 Packets
===========

The following table provides a complete list of all currently defined
COMMANDs and their corresponding response DATA.  *Note File-I/O Remote
Protocol Extension::, for details about the File I/O extension of the
remote protocol.

Each packet's description has a template showing the packet's overall
syntax, followed by an explanation of the packet's meaning.  We include
spaces in some of the templates for clarity; these are not part of the
packet's syntax.  No GDB packet uses spaces to separate its components.
For example, a template like foo BAR BAZ' describes a packet beginning
with the three ASCII bytes foo', followed by a BAR, followed directly
by a BAZ.  GDB does not transmit a space character between the foo'
and the BAR, or between the BAR and the BAZ.

Several packets and replies include a THREAD-ID field to identify a
thread.  Normally these are positive numbers with a target-specific
interpretation, formatted as big-endian hex strings.  A THREAD-ID can
also be a literal -1' to indicate all threads, or 0' to pick any

In addition, the remote protocol supports a multiprocess feature in
which the THREAD-ID syntax is extended to optionally include both
process and thread ID fields, as pPID.TID'.  The PID (process) and TID
(thread) components each have the format described above: a positive
number with target-specific interpretation formatted as a big-endian
hex string, literal -1' to indicate all processes or threads
(respectively), or 0' to indicate an arbitrary process or thread.
Specifying just a process, as pPID', is equivalent to pPID.-1'.  It
is an error to specify all processes but a specific thread, such as
p-1.TID'.  Note that the p' prefix is _not_ used for those packets
and replies explicitly documented to include a process ID, rather than
GDB and the stub report support for the multiprocess' feature using
letter, oth`