dlinfo man page on FreeBSD

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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) func‐
     tion call or special handle RTLD_SELF.  If handle is the value returned
     from dlopen(3), the information returned by the dlinfo() function per‐
     tains 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 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 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 indi‐
	     cating 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 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(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 writ‐
     ten 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
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