freebsd-dev/lib/libc/gen/dlinfo.3

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.Dd February 14, 2003
.Os
.Dt DLINFO 3
.Sh NAME
.Nm dlinfo
.Nd information about dynamically loaded object
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In link.h
.In dlfcn.h
.Ft int
.Fn dlinfo "void * __restrict handle" "int request" "void * __restrict p"
.Sh DESCRIPTION
The
.Fn dlinfo
function provides information about dynamically loaded object.
The action taken by
.Fn dlinfo
and exact meaning and type of
.Fa p
argument depend on value of the
.Fa request
argument provided by caller.
.Pp
A
.Fa handle
argument is either the value returned from a
.Fn dlopen
function call or special handle
.Dv RTLD_SELF .
If handle is the value returned from
.Fn dlopen
call, the information returned by the
.Fn dlinfo
function is pertains the specified object.
If handle is the special handle
.Dv RTLD_SELF ,
the information returned pertains to the caller itself.
.Pp
The following are possible values for
.Fa request
argument to be passed into
.Fn dlinfo :
.Bl -tag -width Ds
.It RTLD_DI_LINKMAP
Retrieve the Link_map (or
.Ft struct link_map )
structure pointer for
.Fa handle
specified.
On successful return the
.Fa p
argument is filled with pointer to Link_map structure
.Ft ( Link_map **p )
describing shared object specified by
.Fa handle
argument.
.Ft Link_map
stuctures are maintained as double-linked list by
.Xr ld.so 1 
in same order as
.Fn dlopen
and
.Fn dlclose
are called.
See
.Sx EXAMPLES
(Example 1.)
.Pp
The
.Ft Link_map
structure is defined in <link.h> and have following members:
.Pp
.Bd -literal
  caddr_t         l_addr;    /* 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 of mapped libs */
                  *l_prev;     
.Ed
.Bl -tag -width Ds
.It l_addr
The base address of the object loaded into memory.
.It l_name
The full name of loaded shared object.
.It l_ld
The address of dynamic linking information segment
.Dv ( PT_DYNAMIC )
loaded into memory.
.It l_next
The next Link_map structure on the link-map list.
.It l_prev
The previous Link_map structure on the link-map list.
.El
.It RTLD_DI_SERINFO
Retrieve the library search paths associated with given
.Fa handle
argument.
The
.Fa p
argument should point to
.Ft Dl_serinfo
structure buffer
.Fa ( Dl_serinfo *p ) .
.Ft Dl_serinfo
structure must be initialized first with a
.Dv RTLD_DI_SERINFOSIZE
request.
.Pp
The returned
.Ft Dl_serinfo
structure contains
.Dv dls_cnt
.Ft Dl_serpath
entries.
Each entry's
.Dv dlp_name
field points to the search path.
The corresponding
.Dv dlp_info
field contains one of more flags indicating the origin of the path (see the
.Dv LA_SER_*
flags defined in <link.h> header file.)
See
.Sx EXAMPLES
(Example 2) for usage example.
.It RTLD_DI_SERINFOSIZE
Initialize a
.Ft Dl_serinfo
structure for use in a
.Dv RTLD_DI_SERINFO
request.
Both the
.Dv dls_cnt
and
.Dv dls_size
fields are returned to indicate the number of search paths applicable
to the handle, and the total size of a
.Ft Dl_serinfo
buffer required to hold
.Dv dls_cnt
.Ft Dl_serpath
entries and the associated search path strings.
See
.Sx EXAMPLES
(Example 2) for usage example.
.It RTLD_DI_ORIGIN
Retrieve the origin of the dynamic object associated with the handle.
On successful return
.Fa p
argument is filled with
.Ft char
pointer
.Ft ( char *p ) .
.El
.Sh EXAMPLES
Example 1: Using
.Fn dlinfo
to retrieve Link_map structure.
.Pp
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.
.Bd -literal
     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;
     }
.Ed
.Pp
Example 2: Using
.Fn dlinfo
to retrieve the library search paths.
.Pp
The following example shows how a dynamic object can inspect the library
search paths that would be used to locate a simple filename with
.Fn dlopen .
For simplicity, error checking has been omitted.
.Bd -literal
      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\n", cnt, path->dls_name);
      }
.Ed
.Sh RETURN VALUES
.Fn dlinfo
returns 0 on success, or -1 if error occured.
Whenever an error has been detected, a message detailing it can
be retrieved via a call to
.Fn dlerror .
.Sh SEE ALSO
.Xr rtld 1 ,
.Xr dladdr 3 ,
.Xr dlopen 3 ,
.Xr dlsym 3
.Sh HISTORY
The
.Fn dlinfo
function first appeared in the Solaris operating system.
In
.Fx
it first appeared in
.Fx 4.8 .
.Sh AUTHORS
The
.Fx
implementation of
.Fn dlinfo
function was originally written by
.An Alexey Zelkin
.Aq phantom@FreeBSD.org
and later extended and improved by
.An Alexander Kabaev
.Aq kan@FreeBSD.org .
.Pp
The manual page for this function was written by
.An Alexey Zelkin
.Aq phantom@FreeBSD.org .