DLINFO(3)		   Linux Programmer's Manual		     DLINFO(3)



NAME
       dlinfo - obtain information about a dynamically loaded object

SYNOPSIS
       #define _GNU_SOURCE
       #include <link.h>
       #include <dlfcn.h>

       int dlinfo(void *handle, int request, void *info);

       Link with -ldl.

DESCRIPTION
       The  dlinfo() function obtains information about the dynamically loaded
       object referred to by handle (typically obtained by an earlier call  to
       dlopen(3)  or dlmopen(3)).  The request argument specifies which infor-
       mation is to be returned.  The info argument is a pointer to  a	buffer
       used  to store information returned by the call; the type of this argu-
       ment depends on request.

       The following values are supported for request (with the	 corresponding
       type for info shown in parentheses):

       RTLD_DI_LMID (Lmid_t *)
	      Obtain  the  ID of the link-map list (namespace) in which handle
	      is loaded.

       RTLD_DI_LINKMAP (struct link_map **)
	      Obtain a pointer to the link_map structure corresponding to han-
	      dle.  The info argument points to a pointer to a link_map struc-
	      ture, defined in <link.h> as:

		  struct link_map {
		      ElfW(Addr) l_addr;  /* Difference between the
					     address in the ELF file and
					     the address in memory */
		      char	*l_name;  /* Absolute pathname where
					     object was found */
		      ElfW(Dyn) *l_ld;	  /* Dynamic section of the
					     shared object */
		      struct link_map *l_next, *l_prev;
					  /* Chain of loaded objects */

		      /* Plus additional fields private to the
			 implementation */
		  };

       RTLD_DI_ORIGIN (char *)
	      Copy the pathname of the origin of the shared object correspond-
	      ing to handle to the location pointed to by info.

       RTLD_DI_SERINFO (Dl_serinfo *)
	      Obtain  the  library search paths for the shared object referred
	      to by handle.  The info argument is a pointer  to	 a  Dl_serinfo
	      that  contains  the  search paths.  Because the number of search
	      paths may vary, the size of the structure pointed to by info can
	      vary.   The  RTLD_DI_SERINFOSIZE	request described below allows
	      applications to size the buffer suitably.	 The caller must  per-
	      form the following steps:

	      1. Use  a	 RTLD_DI_SERINFOSIZE  request to populate a Dl_serinfo
		 structure with the size (dls_size) of	the  structure	needed
		 for the subsequent RTLD_DI_SERINFO request.

	      2. Allocate a Dl_serinfo buffer of the correct size (dls_size).

	      3. Use  a	 further  RTLD_DI_SERINFOSIZE  request to populate the
		 dls_size and dls_cnt fields of the buffer  allocated  in  the
		 previous step.

	      4. Use a RTLD_DI_SERINFO to obtain the library search paths.

	      The Dl_serinfo structure is defined as follows:

		  typedef struct {
		      size_t dls_size;		 /* Size in bytes of
						    the whole buffer */
		      unsigned int dls_cnt;	 /* Number of elements
						    in 'dls_serpath' */
		      Dl_serpath dls_serpath[1]; /* Actually longer,
						    'dls_cnt' elements */
		  } Dl_serinfo;

	      Each  of	the  dls_serpath  elements in the above structure is a
	      structure of the following form:

		  typedef struct {
		      char *dls_name;		 /* Name of library search
						    path directory */
		      unsigned int dls_flags;	 /* Indicates where this
						    directory came from */
		  } Dl_serpath;

	      The dls_flags field is currently	unused,	 and  always  contains
	      zero.

       RTLD_DI_SERINFOSIZE (Dl_serinfo *)
	      Populate	the  dls_size  and  dls_cnt  fields  of the Dl_serinfo
	      structure pointed to by info with values suitable for allocating
	      a buffer for use in a subsequent RTLD_DI_SERINFO request.

       RTLD_DI_TLS_MODID (size_t *, since glibc 2.4)
	      Obtain  the  module ID of this shared object's TLS (thread-local
	      storage) segment, as used in TLS relocations.   If  this	object
	      does not define a TLS segment, zero is placed in *info.

       RTLD_DI_TLS_DATA (void **, since glibc 2.4)
	      Obtain a pointer to the calling thread's TLS block corresponding
	      to this shared object's TLS segment.  If this  object  does  not
	      define  a PT_TLS segment, or if the calling thread has not allo-
	      cated a block for it, NULL is placed in *info.

RETURN VALUE
       On success, dlinfo() returns 0.	On failure, it returns -1;  the	 cause
       of the error can be diagnosed using dlerror(3).

VERSIONS
       dlinfo() first appeared in glibc 2.3.3.

ATTRIBUTES
       For   an	  explanation	of   the  terms	 used  in  this	 section,  see
       attributes(7).

       +----------+---------------+---------+
       |Interface | Attribute	  | Value   |
       +----------+---------------+---------+
       |dlinfo()  | Thread safety | MT-Safe |
       +----------+---------------+---------+
CONFORMING TO
       This function is a nonstandard GNU extension.

NOTES
       This function derives from the Solaris function of the  same  name  and
       also  appears on some other systems.  The sets of requests supported by
       the various implementations overlaps only partially.

EXAMPLE
       The program below opens a shared objects using dlopen(3) and then  uses
       the  RTLD_DI_SERINFOSIZE	 and  RTLD_DI_SERINFO  requests	 to obtain the
       library search path list for the library.  Here is an example  of  what
       we might see when running the program:

	   $ ./a.out /lib64/libm.so.6
	   dls_serpath[0].dls_name = /lib64
	   dls_serpath[1].dls_name = /usr/lib64

   Program source

       #define _GNU_SOURCE
       #include <dlfcn.h>
       #include <link.h>
       #include <stdio.h>
       #include <stdlib.h>

       int
       main(int argc, char *argv[])
       {
	   void *handle;
	   Dl_serinfo serinfo;
	   Dl_serinfo *sip;
	   int j;

	   if (argc != 2) {
	       fprintf(stderr, "Usage: %s <libpath>\n", argv[0]);
	       exit(EXIT_FAILURE);
	   }

	   /* Obtain a handle for shared objects specified on command line */

	   handle = dlopen(argv[1], RTLD_NOW);
	   if (handle == NULL) {
	       fprintf(stderr, "dlopen() failed: %s\n", dlerror());
	       exit(EXIT_FAILURE);
	   }

	   /* Discover the size of the buffer that we must pass to
	      RTLD_DI_SERINFO */

	   if (dlinfo(handle, RTLD_DI_SERINFOSIZE, &serinfo) == -1) {
	       fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\n", dlerror());
	       exit(EXIT_FAILURE);
	   }

	   /* Allocate the buffer for use with RTLD_DI_SERINFO */

	   sip = malloc(serinfo.dls_size);
	   if (sip == NULL) {
	       perror("malloc");
	       exit(EXIT_FAILURE);
	   }

	   /* Initialize the 'dls_size' and 'dls_cnt' fields in the newly
	      allocated buffer */

	   if (dlinfo(handle, RTLD_DI_SERINFOSIZE, sip) == -1) {
	       fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\n", dlerror());
	       exit(EXIT_FAILURE);
	   }

	   /* Fetch and print library search list */

	   if (dlinfo(handle, RTLD_DI_SERINFO, sip) == -1) {
	       fprintf(stderr, "RTLD_DI_SERINFO failed: %s\n", dlerror());
	       exit(EXIT_FAILURE);
	   }

	   for (j = 0; j < serinfo.dls_cnt; j++)
	       printf("dls_serpath[%d].dls_name = %s\n",
		       j, sip->dls_serpath[j].dls_name);

	   exit(EXIT_SUCCESS);
       }

SEE ALSO
       dl_iterate_phdr(3),   dladdr(3),	  dlerror(3),	dlopen(3),   dlsym(3),
       ld.so(8)

COLOPHON
       This page is part of release 4.10 of the Linux  man-pages  project.   A
       description  of	the project, information about reporting bugs, and the
       latest	 version    of	  this	  page,	   can	   be	  found	    at
       https://www.kernel.org/doc/man-pages/.



Linux				  2015-08-08			     DLINFO(3)