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

       dlinfo - obtain information about a dynamically loaded object

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

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

       Link with -ldl.

       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

       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.

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

       dlinfo() first appeared in glibc 2.3.3.

       For   an   explanation   of   the  terms  used  in  this  section,  see

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

       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.

       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>

       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]);

           /* 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());

           /* 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());

           /* Allocate the buffer for use with RTLD_DI_SERINFO */

           sip = malloc(serinfo.dls_size);
           if (sip == NULL) {

           /* 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());

           /* Fetch and print library search list */

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

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


       dl_iterate_phdr(3),   dladdr(3),   dlerror(3),   dlopen(3),   dlsym(3),

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Linux                             2017-09-15                         DLINFO(3)
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