DLINFO(3)

NAME
dlinfo - information about dynamically loaded object

LIBRARY
libc

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 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).

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);
    }

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).

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
-nosplit 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>.