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DL_ITERATE_PHDR(3) Linux Programmer's Manual DL_ITERATE_PHDR(3)
dl_iterate_phdr - walk through list of shared objects
#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);
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;
The dl_iterate_phdr() function returns whatever value was returned by the last
call to callback.
dl_iterate_phdr() has been supported in glibc since version 2.2.4.
The dl_iterate_phdr() function is Linux-specific and should be avoided in
portable applications.
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);
}
ldd(1), objdump(1), readelf(1), dlopen(3), elf(5), ld.so(8), and the
Executable and Linking Format Specification available at various locations
online.
This page is part of release 3.32 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)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface