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 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 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 locations 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/.