223 lines
6.8 KiB
Groff
223 lines
6.8 KiB
Groff
.\" $NetBSD: dlfcn.3,v 1.12 2001/04/25 02:19:49 simonb Exp $
|
|
.\"
|
|
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Paul Kranenburg.
|
|
.\"
|
|
.\" 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.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the NetBSD
|
|
.\" Foundation, Inc. and its contributors.
|
|
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
|
|
.\" contributors may be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
|
|
.\"
|
|
.Dd September 30, 1995
|
|
.Dt DLFCN 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm dlopen ,
|
|
.Nm dlclose ,
|
|
.Nm dlsym ,
|
|
.Nm dlctl ,
|
|
.Nm dlerror
|
|
.Nd dynamic link interface
|
|
.Sh LIBRARY
|
|
(These functions are not in a library. They are included in every
|
|
dynamically linked program automatically.)
|
|
.Sh SYNOPSIS
|
|
.Fd #include <dlfcn.h>
|
|
.Ft "void *"
|
|
.Fn dlopen "const char *path" "int mode"
|
|
.Ft "int"
|
|
.Fn dlclose "void *handle"
|
|
.Ft "void *"
|
|
.Fn dlsym "void *handle" "const char *symbol"
|
|
.Ft "int"
|
|
.Fn dladdr "void *addr" "Dl_info *dli"
|
|
.Ft "int"
|
|
.Fn dlctl "void *handle" "int cmd" "void *data"
|
|
.Ft "char *"
|
|
.Fn dlerror "void"
|
|
.Sh DESCRIPTION
|
|
These functions provide an interface to the run-time linker
|
|
.Xr ld.so 1 .
|
|
They allow new shared objects to be loaded into the process' address space
|
|
under program control.
|
|
The
|
|
.Fn dlopen
|
|
function takes a name of a shared object as the first argument.
|
|
The shared object is mapped into the address space, relocated and
|
|
its external references are resolved in the same way as is done
|
|
with the implicitly loaded shared libraries at program startup.
|
|
The argument can either be an absolute pathname or it can be of the form
|
|
.Sm off
|
|
.Do Xo lib Ao name Ac .so
|
|
.Op .xx Op .yy Xc
|
|
.Dc
|
|
.Sm on
|
|
in which case the same library search rules apply that are used for
|
|
.Dq intrinsic
|
|
shared library searches.
|
|
If the first argument is
|
|
.Dv NULL ,
|
|
.Fn dlopen
|
|
returns a handle on the global symbol object. This object
|
|
provides access to all symbols from an ordered set of objects consisting
|
|
of the original program image and any dependencies loaded during startup.
|
|
.Pp
|
|
The second argument has currently no effect, but should be set to
|
|
.Dv DL_LAZY
|
|
for future compatibility.
|
|
.Fn dlopen
|
|
returns a handle to be used in calls to
|
|
.Fn dlclose ,
|
|
.Fn dlsym
|
|
and
|
|
.Fn dlctl .
|
|
If the named shared object has already
|
|
been loaded by a previous call to
|
|
.Fn dlopen
|
|
.Pq and not yet unloaded by Fn dlclose ,
|
|
a handle refering to the resident copy is returned.
|
|
.Pp
|
|
.Fn dlclose
|
|
unlinks and removes the object referred to by
|
|
.Fa handle
|
|
from the process address space.
|
|
If multiple calls to
|
|
.fn dlopen
|
|
have been done on this object
|
|
.Po or the object was one loaded at startup time
|
|
.Pc
|
|
the object is removed when its reference count drops to zero.
|
|
.Pp
|
|
.Fn dlsym
|
|
looks for a definition of
|
|
.Fa symbol
|
|
in the shared object designated by
|
|
.Fa handle .
|
|
The symbols address is returned.
|
|
If the symbol cannot be resolved,
|
|
.Dv NULL
|
|
is returned.
|
|
.Pp
|
|
.Fn dladdr
|
|
examines all currently mapped shared objects for a symbol whose address --
|
|
as mapped in the proces address space -- is closest to but not exceeding
|
|
the value passed in the first argument
|
|
.Fa addr .
|
|
The symbols of a shared object are only eligible if
|
|
.Va addr
|
|
is between the base address of the shared object and the value of the
|
|
symbol
|
|
.Dq _end
|
|
in the same shared object. If no object for which this condition holds
|
|
true can be found,
|
|
.Fn dladdr
|
|
will return 0. Otherwise, a non-zero value is returned and the
|
|
.Fa dli
|
|
argument will be used to provide information on the selected symbol
|
|
and the shared object it is contained in.
|
|
The
|
|
.Fa dli
|
|
argument points at a caller-provided
|
|
.Va Dl_info
|
|
structure defined as follows:
|
|
.Bd -literal -offset indent
|
|
typedef struct {
|
|
const char *dli_fname; /* File defining the symbol */
|
|
void *dli_fbase; /* Base address */
|
|
const char *dli_sname; /* Symbol name */
|
|
void *dli_saddr; /* Symbol address */
|
|
} Dl_info;
|
|
.Ed
|
|
.Pp
|
|
The member
|
|
.Va dli_sname
|
|
points at the nul-terminated name of the selected symbol, and
|
|
.Va dli_saddr
|
|
is the actual address
|
|
.Pq as it appears in the process address space
|
|
of the symbol.
|
|
The member
|
|
.Va dli_fname
|
|
points at the file name corresponding to the shared object in which the
|
|
symbol was found, while
|
|
.Va dli_fbase
|
|
is the base address at which this shared object is loaded in the process
|
|
address space.
|
|
.Va dli_fname
|
|
and
|
|
.Va dli_fbase
|
|
may be zero if the symbol was found in the internally generated
|
|
.Dq copy
|
|
section
|
|
.Po
|
|
see
|
|
.Xr link 5
|
|
.Pc
|
|
which is not associated with a file.
|
|
Note: both strings pointed at by
|
|
.Va dli_fname
|
|
and
|
|
.Va dli_sname
|
|
reside in memory private to the run-time linker module and should not
|
|
be modified by the caller.
|
|
.Pp
|
|
.Fn dlctl
|
|
provides an interface similar to
|
|
.Xr ioctl 2
|
|
to control several aspects of the run-time linker's operation.
|
|
This interface
|
|
is
|
|
.Ud .
|
|
.Pp
|
|
.Fn dlerror
|
|
return a character string representing the most recent error that has
|
|
occurred while processing one of the other functions described here.
|
|
If no dynamic linking errors have occurred since the last invocation of
|
|
.Fn dlerror ,
|
|
.Fn dlerror
|
|
returns
|
|
.Dv NULL .
|
|
Thus, invoking
|
|
.Fn dlerror
|
|
a second time, immediately following a prior invocation, will result in
|
|
.Dv NULL
|
|
being returned.
|
|
.Sh SEE ALSO
|
|
.Xr ld 1 ,
|
|
.Xr rtld 1 ,
|
|
.Xr link 5
|
|
.Sh HISTORY
|
|
Some of the
|
|
.Nm dl*
|
|
functions first appeared in SunOS 4.
|
|
.Sh BUGS
|
|
An error that occurs while processing a
|
|
.Fn dlopen
|
|
request results in the termination of the program.
|