dlinfo(3)

NAME

dlinfo - information about dynamically loaded object

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <link.h>
#include <dlfcn.h>
int
dlinfo(void * restrict handle, int request, void *  restrict
p);

DESCRIPTION

The dlinfo() function provides information about dynamically

loaded
object. The action taken by dlinfo() and exact meaning and

type of p
argument depend on value of the request argument provided by

caller.

The handle argument is either the value returned from the

dlopen(3) function call or special handle RTLD_SELF. If handle is the

value returned
from dlopen(3), the information returned by the dlinfo()

function pertains to the specified object. If handle is the special

handle
RTLD_SELF, the information returned pertains to the caller

itself.

Possible values for the request argument are:

RTLD_DI_LINKMAP

Retrieve the Link_map (struct link_map) structure

pointer for the
specified handle. On successful return, the p argu

ment is filled
with the pointer to the Link_map structure (Link_map

**p)
describing a shared object specified by the handle

argument. The
Link_map structures are maintained as a doubly

linked list by
ld.so(1), in the same order as dlopen(3) and dl

close(3) are
called. See EXAMPLES, example 1.

The Link_map structure is defined in #include

<link.h>
and has the following members:

caddr_t l_addr; /* Base Address of

library */
const char *l_name; /* Absolute Path to

Library */
const void *l_ld; /* Pointer to .dy

namic in memory */
struct link_map *l_next, /* linked list of

mapped libs */

*l_prev;

l_addr The base address of the object loaded

into memory.

l_name The full name of the loaded shared ob

ject.

l_ld The address of the dynamic linking in

formation seg

ment (PT_DYNAMIC) loaded into memory.

l_next The next Link_map structure on the link

map list.

l_prev The previous Link_map structure on the

link-map list.

RTLD_DI_SERINFO

Retrieve the library search paths associated with

the given
handle argument. The p argument should point to

Dl_serinfo
structure buffer (Dl_serinfo *p). The Dl_serinfo

structure must
be initialized first with the RTLD_DI_SERINFOSIZE

request.

The returned Dl_serinfo structure contains dls_cnt

Dl_serpath
entries. Each entry's dlp_name field points to the

search path.
The corresponding dlp_info field contains one of

more flags indicating the origin of the path (see the LA_SER_*

flags defined in
the #include <link.h>
header file). See EXAMPLES, example 2, for a usage

example.

RTLD_DI_SERINFOSIZE

Initialize a Dl_serinfo structure for use in a

RTLD_DI_SERINFO
request. Both the dls_cnt and dls_size fields are

returned to
indicate the number of search paths applicable to

the handle, and
the total size of a Dl_serinfo buffer required to

hold dls_cnt
Dl_serpath entries and the associated search path

strings. See
EXAMPLES, example 2, for a usage example.

RTLD_DI_ORIGIN

Retrieve the origin of the dynamic object associated

with the
handle. On successful return, p argument is filled

with the char
pointer (char *p).

RETURN VALUES

The dlinfo() function returns 0 on success, or -1 if an er

ror occurred.
Whenever an error has been detected, a message detailing it

can be
retrieved via a call to dlerror(3).

EXAMPLES

Example 1: Using dlinfo() to retrieve Link_map structure.

The following example shows how dynamic library can detect

the list of
shared libraries loaded after caller's one. For simplicity,

error checking has been omitted.

Link_map *map;

dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &map);

while (map != NULL) {

printf("%p: %s0, map->l_addr, map->l_name);
map = map->l_next;

}

Example 2: Using dlinfo() to retrieve the library search

paths.

The following example shows how a dynamic object can inspect

the library
search paths that would be used to locate a simple filename

with
dlopen(3). For simplicity, error checking has been omitted.

Dl_serinfo _info, *info = &_info;
Dl_serpath *path;
unsigned int cnt;

/* determine search path count and required buffer

size */
dlinfo(RTLD_SELF, RTLD_DI_SERINFOSIZE, (void *)info);

/* allocate new buffer and initialize */
info = malloc(_info.dls_size);
info->dls_size = _info.dls_size;
info->dls_cnt = _info.dls_cnt;

/* obtain sarch path information */
dlinfo(RTLD_SELF, RTLD_DI_SERINFO, (void *)info);

path = &info->dls_serpath[0];

for (cnt = 1; cnt <= info->dls_cnt; cnt++, path++) {

(void) printf("%2d: %s0, cnt, path->dls_name);

}

SEE ALSO

rtld(1), dladdr(3), dlopen(3), dlsym(3)

HISTORY

The dlinfo() function first appeared in the Solaris operat

ing system. In
FreeBSD, it first appeared in FreeBSD 4.8.

AUTHORS

The FreeBSD implementation of the dlinfo() function was

originally written by Alexey Zelkin <phantom@FreeBSD.org> and later extend

ed and
improved by Alexander Kabaev <kan@FreeBSD.org>.

The manual page for this function was written by Alexey

Zelkin
<phantom@FreeBSD.org>.

BSD February 14, 2003

BSD