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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	   /* See feature_test_macros(7) */
       #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  applica‐
       tion's  shared  objects	and  calls the function callback once for each
       object, until either all shared objects have been processed or callback
       returns a nonzero 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.  Fur‐
       ther 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 seg‐
       ments,  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), ld.so(8)

       Executable and Linking Format Specification, available at various loca‐
       tions online.

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of	the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2007-05-18		    DL_ITERATE_PHDR(3)
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