path: root/lib/libc/gen/dlinfo.3

.\"
.\" Copyright (c) 2003 Alexey Zelkin <phantom@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.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
The
.Fa handle
argument is either the value returned from the
.Xr dlopen 3
function call or special handle
.Dv RTLD_SELF .
If
.Fa handle
is the value returned from
.Xr dlopen 3 ,
the information returned by the
.Fn dlinfo
function pertains to the specified object.
If handle is the special handle
.Dv RTLD_SELF ,
the information returned pertains to the caller itself.
.Pp
Possible values for the
.Fa request
argument are:
.Bl -tag -width indent
.It Dv RTLD_DI_LINKMAP
Retrieve the
.Vt Link_map
.Pq Vt "struct link_map"
structure pointer for the specified
.Fa handle .
On successful return, the
.Fa p
argument is filled with the pointer to the
.Vt Link_map
structure
.Pq Fa "Link_map **p"
describing a shared object specified by the
.Fa handle
argument.
The
.Vt Link_map
structures are maintained as a doubly linked list by
.Xr ld.so 1 ,
in the same order as
.Xr dlopen 3
and
.Xr dlclose 3
are called.
See
.Sx EXAMPLES ,
example 1.
.Pp
The
.Vt Link_map
structure is defined in
.In link.h
and has the following members:
.Bd -literal -offset indent
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 mapped libs */
                *l_prev;
.Ed
.Bl -tag -width ".Va l_addr"
.It Va l_addr
The base address of the object loaded into memory.
.It Va l_name
The full name of the loaded shared object.
.It Va l_ld
The address of the dynamic linking information segment
.Pq Dv PT_DYNAMIC
loaded into memory.
.It Va l_next
The next
.Vt Link_map
structure on the link-map list.
.It Va l_prev
The previous
.Vt Link_map
structure on the link-map list.
.El
.It Dv RTLD_DI_SERINFO
Retrieve the library search paths associated with the given
.Fa handle
argument.
The
.Fa p
argument should point to
.Vt Dl_serinfo
structure buffer
.Pq Fa "Dl_serinfo *p" .
The
.Vt Dl_serinfo
structure must be initialized first with the
.Dv RTLD_DI_SERINFOSIZE
request.
.Pp
The returned
.Vt Dl_serinfo
structure contains
.Va dls_cnt
.Vt Dl_serpath
entries.
Each entry's
.Va dlp_name
field points to the search path.
The corresponding
.Va dlp_info
field contains one of more flags indicating the origin of the path (see the
.Dv LA_SER_*
flags defined in the
.In link.h
header file).
See
.Sx EXAMPLES ,
example 2, for a usage example.
.It Dv RTLD_DI_SERINFOSIZE
Initialize a
.Vt Dl_serinfo
structure for use in a
.Dv RTLD_DI_SERINFO
request.
Both the
.Va dls_cnt
and
.Va dls_size
fields are returned to indicate the number of search paths applicable
to the handle, and the total size of a
.Vt Dl_serinfo
buffer required to hold
.Va dls_cnt
.Vt Dl_serpath
entries and the associated search path strings.
See
.Sx EXAMPLES ,
example 2, for a usage example.
.It Va RTLD_DI_ORIGIN
Retrieve the origin of the dynamic object associated with the handle.
On successful return,
.Fa p
argument is filled with the
.Vt char
pointer
.Pq Fa "char *p" .
.El
.Sh RETURN VALUES
The
.Fn 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
.Xr dlerror 3 .
.Sh EXAMPLES
Example 1: Using
.Fn dlinfo
to retrieve
.Vt 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 -offset indent
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
.Xr dlopen 3 .
For simplicity, error checking has been omitted.
.Bd -literal -offset indent
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 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
.An -nosplit
The
.Fx
implementation of the
.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 .