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 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.  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 pro-
       gram 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 For-
       mat Specification available at various locations online.

COLOPHON
       This page is part of release 3.25 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)