просмотреть список общих объектов (walk through list of shared objects)
Имя (Name)
dl_iterate_phdr - walk through list of shared objects
Синопсис (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);
Описание (Description)
The dl_iterate_phdr() function allows an application to inquire
at run time to find out which shared objects it has loaded, and
the order in which they were 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 following fields were added in glibc 2.4, after the first
version of this structure was available. Check the size
argument passed to the dl_iterate_phdr callback to determine
whether or not each later member is available. */
unsigned long long dlpi_adds;
/* Incremented when a new object may
have been added */
unsigned long long 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> 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;
Possible values for p_type include the following (see <elf.h> for
further details):
#define PT_LOAD 1 /* Loadable program segment */
#define PT_DYNAMIC 2 /* Dynamic linking information */
#define PT_INTERP 3 /* Program interpreter */
#define PT_NOTE 4 /* Auxiliary information */
#define PT_SHLIB 5 /* Reserved */
#define PT_PHDR 6 /* Entry for header table itself */
#define PT_TLS 7 /* Thread-local storage segment */
#define PT_GNU_EH_FRAME 0x6474e550 /* GCC .eh_frame_hdr segment */
#define PT_GNU_STACK 0x6474e551 /* Indicates stack executability */
#define PT_GNU_RELRO 0x6474e552 /* Read-only after relocation */
Возвращаемое значение (Return value)
The dl_iterate_phdr() function returns whatever value was
returned by the last call to callback.
Версии (Versions)
dl_iterate_phdr() has been supported in glibc since version
2.2.4.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│dl_iterate_phdr() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
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.
Примечание (Note)
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.
Примеры (Examples)
The following program displays a list of pathnames of the shared
objects it has loaded. For each shared object, the program lists
some information (virtual address, size, flags, and type) for
each of the objects ELF segments.
The following shell session demonstrates the output produced by
the program on an x86-64 system. The first shared object for
which output is displayed (where the name is an empty string) is
the main program.
$ ./a.out
Name: "" (9 segments)
0: [ 0x400040; memsz: 1f8] flags: 0x5; PT_PHDR
1: [ 0x400238; memsz: 1c] flags: 0x4; PT_INTERP
2: [ 0x400000; memsz: ac4] flags: 0x5; PT_LOAD
3: [ 0x600e10; memsz: 240] flags: 0x6; PT_LOAD
4: [ 0x600e28; memsz: 1d0] flags: 0x6; PT_DYNAMIC
5: [ 0x400254; memsz: 44] flags: 0x4; PT_NOTE
6: [ 0x400970; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME
7: [ (nil); memsz: 0] flags: 0x6; PT_GNU_STACK
8: [ 0x600e10; memsz: 1f0] flags: 0x4; PT_GNU_RELRO
Name: "linux-vdso.so.1" (4 segments)
0: [0x7ffc6edd1000; memsz: e89] flags: 0x5; PT_LOAD
1: [0x7ffc6edd1360; memsz: 110] flags: 0x4; PT_DYNAMIC
2: [0x7ffc6edd17b0; memsz: 3c] flags: 0x4; PT_NOTE
3: [0x7ffc6edd17ec; memsz: 3c] flags: 0x4; PT_GNU_EH_FRAME
Name: "/lib64/libc.so.6" (10 segments)
0: [0x7f55712ce040; memsz: 230] flags: 0x5; PT_PHDR
1: [0x7f557145b980; memsz: 1c] flags: 0x4; PT_INTERP
2: [0x7f55712ce000; memsz: 1b6a5c] flags: 0x5; PT_LOAD
3: [0x7f55716857a0; memsz: 9240] flags: 0x6; PT_LOAD
4: [0x7f5571688b80; memsz: 1f0] flags: 0x6; PT_DYNAMIC
5: [0x7f55712ce270; memsz: 44] flags: 0x4; PT_NOTE
6: [0x7f55716857a0; memsz: 78] flags: 0x4; PT_TLS
7: [0x7f557145b99c; memsz: 544c] flags: 0x4; PT_GNU_EH_FRAME
8: [0x7f55712ce000; memsz: 0] flags: 0x6; PT_GNU_STACK
9: [0x7f55716857a0; memsz: 3860] flags: 0x4; PT_GNU_RELRO
Name: "/lib64/ld-linux-x86-64.so.2" (7 segments)
0: [0x7f557168f000; memsz: 20828] flags: 0x5; PT_LOAD
1: [0x7f55718afba0; memsz: 15a8] flags: 0x6; PT_LOAD
2: [0x7f55718afe10; memsz: 190] flags: 0x6; PT_DYNAMIC
3: [0x7f557168f1c8; memsz: 24] flags: 0x4; PT_NOTE
4: [0x7f55716acec4; memsz: 604] flags: 0x4; PT_GNU_EH_FRAME
5: [0x7f557168f000; memsz: 0] flags: 0x6; PT_GNU_STACK
6: [0x7f55718afba0; memsz: 460] flags: 0x4; PT_GNU_RELRO
Program source
#define _GNU_SOURCE
#include <link.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
static int
callback(struct dl_phdr_info *info, size_t size, void *data)
{
char *type;
int p_type;
printf("Name: \"%s\" (%d segments)\n", info->dlpi_name,
info->dlpi_phnum);
for (int j = 0; j < info->dlpi_phnum; j++) {
p_type = info->dlpi_phdr[j].p_type;
type = (p_type == PT_LOAD) ? "PT_LOAD" :
(p_type == PT_DYNAMIC) ? "PT_DYNAMIC" :
(p_type == PT_INTERP) ? "PT_INTERP" :
(p_type == PT_NOTE) ? "PT_NOTE" :
(p_type == PT_INTERP) ? "PT_INTERP" :
(p_type == PT_PHDR) ? "PT_PHDR" :
(p_type == PT_TLS) ? "PT_TLS" :
(p_type == PT_GNU_EH_FRAME) ? "PT_GNU_EH_FRAME" :
(p_type == PT_GNU_STACK) ? "PT_GNU_STACK" :
(p_type == PT_GNU_RELRO) ? "PT_GNU_RELRO" : NULL;
printf(" %2d: [%14p; memsz:%7jx] flags: %#jx; ", j,
(void *) (info->dlpi_addr + info->dlpi_phdr[j].p_vaddr),
(uintmax_t) info->dlpi_phdr[j].p_memsz,
(uintmax_t) info->dlpi_phdr[j].p_flags);
if (type != NULL)
printf("%s\n", type);
else
printf("[other (%#x)]\n", p_type);
}
return 0;
}
int
main(int argc, char *argv[])
{
dl_iterate_phdr(callback, NULL);
exit(EXIT_SUCCESS);
}
Смотри также (See also)
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.
