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END(3)                     Linux Programmer's Manual                    END(3)



NAME
       etext, edata, end - end of program segments

SYNOPSIS
       extern etext;
       extern edata;
       extern end;

DESCRIPTION
       The addresses of these symbols indicate the end of various program segments:

       etext  This is the first address past the end of the text segment (the program code).

       edata  This is the first address past the end of the initialized data segment.

       end    This  is  the  first  address past the end of the uninitialized data segment (also known as the BSS seg-
              ment).

CONFORMING TO
       Although these symbols have long been provided on most Unix systems, they are not standardized; use  with  cau-
       tion.

NOTES
       The program must explicitly declare these symbols; they are not defined in any header file.

       On  some systems the names of these symbols are preceded by underscores, thus: _etext, _edata, and _end.  These
       symbols are also defined for programs compiled on Linux.

       At the start of program execution, the program break will be somewhere near &end (perhaps at the start  of  the
       following  page).   However, the break will change as memory is allocated via brk(2) or malloc(3).  Use sbrk(2)
       with an argument of zero to find the current value of the program break.

EXAMPLE
       When run, the program below produces output such as the following:

           $ ./a.out
           First address past:
               program text (etext)       0x8048568
               initialized data (edata)   0x804a01c
               uninitialized data (end)   0x804a024

   Program source

       #include <stdio.h>
       #include <stdlib.h>

       extern char etext, edata, end; /* The symbols must have some type,
                                          or "gcc -Wall" complains */

       int
       main(int argc, char *argv[])
       {
           printf("First address past:\n");
           printf("    program text (etext)      %10p\n", &etext);
           printf("    initialized data (edata)  %10p\n", &edata);
           printf("    uninitialized data (end)  %10p\n", &end);

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       objdump(1), readelf(1), sbrk(2), elf(5)

COLOPHON
       This page is part of release 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                               2008-07-17                            END(3)