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
-nosplit 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>.