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Manual Pages  — DLINFO


dlinfo – information about dynamically loaded object



Standard C Library (libc, -lc)


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

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


The dlinfo() function provides information about 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:
  Retrieve the Link_map (struct link_map) structure pointer 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. See EXAMPLES, example 1.

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

caddr_t         l_base;    /* Base Address of library */
const char      *l_name;   /* Absolute Path to Library */
const void      *l_ld;     /* Pointer to .dynamic in memory */
struct link_map *l_next,   /* linked list of mapped libs */
caddr_t         l_addr;     /* Load Offset of library */
const char      *l_refname; /* Object this one filters for */
  The base address of the object loaded into memory.
  The full name of the loaded shared object.
  The address of the dynamic linking information segment ( PT_DYNAMIC) loaded into memory.
  The next Link_map structure on the link-map list.
  The previous Link_map structure on the link-map list.
  The load offset of the object, that is, the difference between the actual load address and the base virtual address the object was linked at.
  A name of the object this object filters for, if any. If there are more then one filtee, a name from the first DT_FILTER dynamic entry is supplied.
  Retrieve the library search paths associated with the given handle argument. The p argument should point to Dl_serinfo structure buffer (Dl_serinfo *p). The Dl_serinfo structure must be initialized first with the RTLD_DI_SERINFOSIZE request.

The returned Dl_serinfo structure contains dls_cnt Dl_serpath entries. Each entry's dlp_name field points to the search path. The corresponding dlp_info field contains one of more flags indicating the origin of the path (see the LA_SER_* flags defined in the <link.h> header file). See EXAMPLES, example 2, for a usage example.

  Initialize a Dl_serinfo structure for use in a RTLD_DI_SERINFO request. Both the dls_cnt and dls_size fields are returned to indicate the number of search paths applicable to the handle, and the total size of a Dl_serinfo buffer required to hold dls_cnt Dl_serpath entries and the associated search path strings. See EXAMPLES, example 2, for a usage example.
  Retrieve the origin of the dynamic object associated with the handle. On successful return, p argument is filled with the char pointer (char *p).


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).


Example 1: 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;


while (map != NULL) {         printf("%p: %s , map->l_addr, map->l_name);         map = map->l_next; }

Example 2: Using dlinfo() to retrieve the library search paths.

The following example shows how a dynamic object can inspect the library search paths that would be used to locate a simple filename with dlopen(3). For simplicity, error checking has been omitted.

Dl_serinfo       _info, *info = &_info;
Dl_serpath      *path;
unsigned int     cnt;

/* determine search path count and required buffer size */ dlinfo(RTLD_SELF, RTLD_DI_SERINFOSIZE, (void *)info);

/* allocate new buffer and initialize */ info = malloc(_info.dls_size); info->dls_size = _info.dls_size; info->dls_cnt = _info.dls_cnt;

/* obtain sarch path information */ dlinfo(RTLD_SELF, RTLD_DI_SERINFO, (void *)info);

path = &info->dls_serpath[0];

for (cnt = 1; cnt <= info->dls_cnt; cnt++, path++) {         (void) printf("%2d: %s , cnt, path->dls_name); }


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


The dlinfo() function first appeared in the Solaris operating system. In FreeBSD , it first appeared in FreeBSD 4.8 .


The FreeBSD implementation of the dlinfo() function was originally written by Alexey Zelkin <Mt phantom@FreeBSD.org> and later extended and improved by Alexander Kabaev <Mt kan@FreeBSD.org>.

The manual page for this function was written by Alexey Zelkin <Mt phantom@FreeBSD.org>.

DLINFO (3) May 21, 2020

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