dlinfo3

Usage

Library

Standard C Library (libc, -lc)

Overview

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);
}