dlinfo(3) — Linux manual page


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

NAME         top

       dlinfo - obtain information about a dynamically loaded object

SYNOPSIS         top

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

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

       Link with -ldl.

DESCRIPTION         top

       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 information 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 argument 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
              handle.  The info argument points to a pointer to a link_map
              structure, 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 corre‐
              sponding 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 perform 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

              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 allocat‐
              ing 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 correspond‐
              ing to this shared object's TLS segment.  If this object does
              not define a PT_TLS segment, or if the calling thread has not
              allocated a block for it, NULL is placed in *info.

RETURN VALUE         top

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

VERSIONS         top

       dlinfo() first appeared in glibc 2.3.3.

ATTRIBUTES         top

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

       │Interface Attribute     Value   │
       │dlinfo()  │ Thread safety │ MT-Safe │

CONFORMING TO         top

       This function is a nonstandard GNU extension.

NOTES         top

       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.

EXAMPLES         top

       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 object 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);


SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.08 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

Linux                            2020-06-09                        DLINFO(3)

Pages that refer to this page: dladdr1(3)dladdr(3)dlclose(3)dlerror(3)dlmopen(3)dlopen(3)dlsym(3)dlvsym(3)