dlinfo(3) - NetBSD Manual Pages

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DLINFO(3)               NetBSD 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 dynam-
     ically 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) func-
     tion call or special handle RTLD_SELF.  If handle is the value returned
     from dlopen(3), the information returned by the dlinfo() function per-
     tains 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 struc-
               tures 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 fol-
               lowing 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 mem-
                             ory.

               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 check-
     ing 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 10.1                    January 13, 2020                    NetBSD 10.1