DLINFO(3) BSD Library Functions Manual 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 argument 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 dlclose(3) are called. See
EXAMPLES, example 1.
The Link_map structure is defined in <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 .dynamic 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 object.
l_ld The address of the 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 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
<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 indi-
cate 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 error 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: %s
", 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: %s
", cnt, path->dls_name);
}
SEE ALSO
rtld(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 the 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