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



NAME
       dl_iterate_phdr - walk through list of shared objects

SYNOPSIS
       #define _GNU_SOURCE
       #include <link.h>

       int dl_iterate_phdr(
                 int (*callback) (struct dl_phdr_info *info,
                                  size_t size, void *data),
                 void *data);

DESCRIPTION
       The dl_iterate_phdr() function allows an application to inquire at run time to find out which shared objects it
       has loaded.

       The dl_iterate_phdr() function walks through the list of an application's shared objects and calls the function
       callback  once  for each object, until either all shared objects have been processed or callback returns a non-
       zero value.

       Each call to callback receives three arguments: info, which is a pointer to a structure containing  information
       about the shared object; size, which is the size of the structure pointed to by info; and data, which is a copy
       of whatever value was passed by the calling program as the second argument (also named data)  in  the  call  to
       dl_iterate_phdr().

       The info argument is a structure of the following type:

           struct dl_phdr_info {
               ElfW(Addr)        dlpi_addr;  /* Base address of object */
               const char       *dlpi_name;  /* (Null-terminated) name of
                                                object */
               const ElfW(Phdr) *dlpi_phdr;  /* Pointer to array of
                                                ELF program headers
                                                for this object */
               ElfW(Half)        dlpi_phnum; /* # of items in dlpi_phdr */
           };

       (The  ElfW()  macro  definition  turns its argument into the name of an ELF data type suitable for the hardware
       architecture.  For example, on a 32-bit platform, ElfW(Addr) yields the data  type  name  Elf32_Addr.   Further
       information on these types can be found in the <elf.h> and <link.h> header files.)

       The  dlpi_addr  field indicates the base address of the shared object (i.e., the difference between the virtual
       memory address of the shared object and the offset of that object in the file from which it was  loaded).   The
       dlpi_name field is a null-terminated string giving the pathname from which the shared object was loaded.

       To understand the meaning of the dlpi_phdr and dlpi_phnum fields, we need to be aware that an ELF shared object
       consists of a number of segments, each of which has a corresponding program header describing the segment.  The
       dlpi_phdr  field  is a pointer to an array of the program headers for this shared object.  The dlpi_phnum field
       indicates the size of this array.

       These program headers are structures of the following form:

           typedef struct {
               Elf32_Word  p_type;    /* Segment type */
               Elf32_Off   p_offset;  /* Segment file offset */
               Elf32_Addr  p_vaddr;   /* Segment virtual address */
               Elf32_Addr  p_paddr;   /* Segment physical address */
               Elf32_Word  p_filesz;  /* Segment size in file */
               Elf32_Word  p_memsz;   /* Segment size in memory */
               Elf32_Word  p_flags;   /* Segment flags */
               Elf32_Word  p_align;   /* Segment alignment */
           } Elf32_Phdr;

       Note that we can calculate the location of a particular program header, x, in virtual memory using the formula:

         addr == info->dlpi_addr + info->dlpi_phdr[x].p_vaddr;

RETURN VALUE
       The dl_iterate_phdr() function returns whatever value was returned by the last call to callback.

VERSIONS
       dl_iterate_phdr() has been supported in glibc since version 2.2.4.

CONFORMING TO
       The dl_iterate_phdr() function is Linux-specific and should be avoided in portable applications.

EXAMPLE
       The  following  program  displays  a  list  of  pathnames of the shared objects it has loaded.  For each shared
       object, the program lists the virtual addresses at which the object's ELF segments are loaded.

       #define _GNU_SOURCE
       #include <link.h>
       #include <stdlib.h>
       #include <stdio.h>

       static int
       callback(struct dl_phdr_info *info, size_t size, void *data)
       {
           int j;

           printf("name=%s (%d segments)\n", info->dlpi_name,
               info->dlpi_phnum);

           for (j = 0; j < info->dlpi_phnum; j++)
                printf("\t\t header %2d: address=%10p\n", j,
                    (void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr));
           return 0;
       }

       int
       main(int argc, char *argv[])
       {
           dl_iterate_phdr(callback, NULL);

           exit(EXIT_SUCCESS);
       }

SEE ALSO
       ldd(1), objdump(1), readelf(1), dlopen(3), elf(5), feature_test_macros(7), ld.so(8),  and  the  Executable  and
       Linking Format Specification available at various locations online.

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                               2007-05-18                DL_ITERATE_PHDR(3)