Updated: 2020/Jul/29


DLINFO(3)                  Library Functions Manual                  DLINFO(3)

NAME
     dlinfo - information about a dynamically loaded object

LIBRARY
     (These functions are not in a library.  They are included in every
     dynamically linked program automatically.)

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

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

DESCRIPTION
     The dlinfo() function provides information about a 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)
     function call or special handle RTLD_SELF.  If handle is the value
     returned from dlopen(3), the information returned by the dlinfo()
     function pertains 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 pointer to the Link_map 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.

               The Link_map structure is defined in <link.h> and has the
               following members:

                     caddr_t         l_addr;    /* Base Address of library */
                     #ifdef __mips__
                     caddr_t         l_offs;    /* Load Offset of library */
                     #endif
                     const char      *l_name;   /* Absolute Path to Library */
                     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 absolute pathname 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.

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
     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
     checking 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;
           }

SEE ALSO
     rtld(1), dladdr(3), dlopen(3), dlsym(3)

HISTORY
     The dlinfo() function first appeared in the Solaris operating system.  In
     NetBSD, it first appeared in NetBSD 5.1.

AUTHORS
     The NetBSD implementation of the dlinfo() function was written by Antti
     Kantee <pooka@NetBSD.org>.

     The manual page for this function was written by Alexey Zelkin
     <phantom@FreeBSD.org> and adapted to NetBSD by Kamil Rytarowski
     <kamil@NetBSD.org>.

NetBSD 9.99                    January 13, 2020                    NetBSD 9.99