DLINFO(3) FreeBSD 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_base; /* 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;
caddr_t l_addr; /* Load Offset of library */
const char *l_refname; /* Object this one filters for */
l_base 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.
l_addr The load offset of the object, that is, the
difference between the actual load address and the
base virtual address the object was linked at.
l_refname A name of the object this object filters for, if any.
If there are more then one filtee, a name from the
first DT_FILTER dynamic entry is supplied.
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
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 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\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(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\n", 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>.
FreeBSD 13.1-RELEASE-p6 May 21, 2020 FreeBSD 13.1-RELEASE-p6
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