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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  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),     fea-
       ture_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 3.25 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)
 

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