DLINFO(3) BSD Library Functions Manual DLINFO(3)NAMEdlinfo — 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.
A handle argument is either the value returned from a dlopen() function
call or special handle RTLD_SELF. If handle is the value returned from
dlopen() call, the information returned by the dlinfo() function is per‐
tains the specified object. If handle is the special handle RTLD_SELF,
the information returned pertains to the caller itself.
The following are possible values for request argument to be passed into
dlinfo():
RTLD_DI_LINKMAP
Retrieve the Link_map (or struct link_map) structure pointer for
handle specified. On successful return the p argument is filled
with pointer to Link_map structure (Link_map **p) describing
shared object specified by handle argument. Link_map structures
are maintained as double-linked list by rtld(1) in same order as
dlopen() and dlclose() are called. See EXAMPLES (Example 1.)
The Link_map structure is defined in <link.h> and has the follow‐
ing members:
caddr_t l_addr; /* Base Address of library */
const char *l_name; /* Absolute Path to Library */
const void *l_ld; /* Pointer to .dynamic in memory */
struct link_map *l_next, /* linked list of of mapped libs */
*l_prev;
l_addr The base address of the object loaded into memory.
l_name The full name of loaded shared object.
l_ld The address of dynamic linking information segment
(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 given handle
argument. The p argument should point to Dl_serinfo structure
buffer (Dl_serinfo *p). Dl_serinfo structure must be initialized
first with a 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 indi‐
cating the origin of the path (see the LA_SER_* flags defined in
the <link.h> header file.) See EXAMPLES (Example 2) for 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 usage example.
RTLD_DI_ORIGIN
Retrieve the origin of the dynamic object associated with the
handle. On successful return p argument is filled with char
pointer (char *p).
RETURN VALUESdlinfo() returns 0 on success, or -1 if error occurred. Whenever an
error has been detected, a message detailing it can be retrieved via a
call to dlerror().
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 check‐
ing has been omitted.
Link_map *map;
dlinfo(RTLD_SELF, RTLD_DI_LINKMAP, &map);
while (map != NULL) {
printf("%p: %s\n", 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(). 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: %s\n", cnt, path->dls_name);
}
SEE ALSOrtld(1), dladdr(3), dlopen(3), dlsym(3)HISTORY
The dlinfo() function first appeared in the Solaris operating system. In
FreeBSD it first appeared in FreeBSD 4.8.
AUTHORS
The FreeBSD implementation of dlinfo() function was originally written by
Alexey Zelkin ⟨phantom@FreeBSD.org⟩ and later extended 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
