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 indlpi_phdr*/ /* The following fields were added in glibc 2.4, after the first version of this structure was available. Check thesizeargument passed to the dl_iterate_phdr callback to determine whether or not each later member is available. */ unsigned long long int dlpi_adds; /* Incremented when a new object may have been added */ unsigned long long int dlpi_subs; /* Incremented when an object may have been removed */ size_t dlpi_tls_modid; /* If there is a PT_TLS segment, its module ID as used in TLS relocations, else zero */ void *dlpi_tls_data; /* The address of the calling thread's instance of this module's PT_TLS segment, if it has one and it has been allocated in the calling thread, otherwise a null pointer */ };
(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><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;Elf32_Off p_offset;Elf32_Addr p_vaddr;Elf32_Addr p_paddr;Elf32_Word p_filesz;Elf32_Word p_memsz;Elf32_Word p_flags;Elf32_Word p_align;} 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.
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
dl_iterate_phdr() |
Thread safety | MT-Safe |
The dl_iterate_phdr()
function is not specified in any standard. Various other
systems provide a version of this function, although details
of the returned dl_phdr_info
structure differ. On the BSDs and Solaris, the structure
includes the fields dlpi_addr,
dlpi_name, dlpi_phdr, and dlpi_phnum in addition to other
implementation-specific fields.
Future versions of the C library may add further fields to
the dl_phdr_info structure; in
that event, the size
argument provides a mechanism for the callback function to
discover whether it is running on a system with added
fields.
The first object visited by callback is the main program.
For the main program, the dlpi_name field will be an empty string.
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), dladdr(3), dlopen(3), elf(5), ld.so(8)
Executable and Linking Format Specification, available at various locations online.
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
Copyright (c) 2003 by Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |