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/.