Provided by: manpages-dev_4.16-1_all bug

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 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 corresponding 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 (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 allocated 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).

       ┌──────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├──────────┼───────────────┼─────────┤
       │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 4.16 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/.