224 lines
6.8 KiB
Groff
224 lines
6.8 KiB
Groff
.\" $NetBSD: dlfcn.3,v 1.19 2005/03/21 13:25:22 kleink Exp $
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.\"
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.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Paul Kranenburg.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd September 30, 1995
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.Dt DLFCN 3
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.Os
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.Sh NAME
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.Nm dlopen ,
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.Nm dlclose ,
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.Nm dlsym ,
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.Nm dladdr ,
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.Nm dlctl ,
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.Nm dlerror
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.Nd dynamic link interface
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.Sh LIBRARY
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(These functions are not in a library. They are included in every
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dynamically linked program automatically.)
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.Sh SYNOPSIS
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.In dlfcn.h
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.Ft "void *"
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.Fn dlopen "const char *path" "int mode"
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.Ft "int"
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.Fn dlclose "void *handle"
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.Ft "void *"
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.Fn dlsym "void * restrict handle" "const char * restrict symbol"
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.Ft "int"
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.Fn dladdr "void * restrict addr" "Dl_info * restrict dli"
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.Ft "int"
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.Fn dlctl "void *handle" "int cmd" "void *data"
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.Ft "char *"
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.Fn dlerror "void"
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.Sh DESCRIPTION
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These functions provide an interface to the run-time linker
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.Xr ld.so 1 .
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They allow new shared objects to be loaded into the process' address space
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under program control.
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The
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.Fn dlopen
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function takes a name of a shared object as the first argument.
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The shared object is mapped into the address space, relocated and
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its external references are resolved in the same way as is done
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with the implicitly loaded shared libraries at program startup.
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The argument can either be an absolute pathname or it can be of the form
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.Sm off
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.Do Xo lib Ao name Ac .so
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.Op .xx Op .yy Xc
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.Dc
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.Sm on
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in which case the same library search rules apply that are used for
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.Dq intrinsic
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shared library searches.
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If the first argument is
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.Dv NULL ,
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.Fn dlopen
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returns a handle on the global symbol object. This object
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provides access to all symbols from an ordered set of objects consisting
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of the original program image and any dependencies loaded during startup.
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.Pp
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The second argument has currently no effect, but should be set to
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.Dv DL_LAZY
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for future compatibility.
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.Fn dlopen
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returns a handle to be used in calls to
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.Fn dlclose ,
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.Fn dlsym
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and
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.Fn dlctl .
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If the named shared object has already
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been loaded by a previous call to
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.Fn dlopen
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.Pq and not yet unloaded by Fn dlclose ,
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a handle referring to the resident copy is returned.
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.Pp
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.Fn dlclose
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unlinks and removes the object referred to by
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.Fa handle
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from the process address space.
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If multiple calls to
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.Fn dlopen
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have been done on this object
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.Po or the object was one loaded at startup time
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.Pc
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the object is removed when its reference count drops to zero.
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.Pp
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.Fn dlsym
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looks for a definition of
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.Fa symbol
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in the shared object designated by
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.Fa handle .
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The symbols address is returned.
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If the symbol cannot be resolved,
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.Dv NULL
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is returned.
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.Pp
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.Fn dladdr
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examines all currently mapped shared objects for a symbol whose address --
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as mapped in the process address space -- is closest to but not exceeding
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the value passed in the first argument
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.Fa addr .
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The symbols of a shared object are only eligible if
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.Va addr
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is between the base address of the shared object and the value of the
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symbol
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.Dq _end
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in the same shared object. If no object for which this condition holds
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true can be found,
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.Fn dladdr
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will return 0. Otherwise, a non-zero value is returned and the
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.Fa dli
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argument will be used to provide information on the selected symbol
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and the shared object it is contained in.
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The
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.Fa dli
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argument points at a caller-provided
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.Va Dl_info
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structure defined as follows:
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.Bd -literal -offset indent
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typedef struct {
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const char *dli_fname; /* File defining the symbol */
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void *dli_fbase; /* Base address */
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const char *dli_sname; /* Symbol name */
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const void *dli_saddr; /* Symbol address */
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} Dl_info;
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.Ed
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.Pp
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The member
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.Va dli_sname
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points at the nul-terminated name of the selected symbol, and
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.Va dli_saddr
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is the actual address
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.Pq as it appears in the process address space
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of the symbol.
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The member
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.Va dli_fname
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points at the file name corresponding to the shared object in which the
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symbol was found, while
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.Va dli_fbase
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is the base address at which this shared object is loaded in the process
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address space.
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.Va dli_fname
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and
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.Va dli_fbase
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may be zero if the symbol was found in the internally generated
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.Dq copy
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section
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.Po
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see
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.Xr link 5
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.Pc
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which is not associated with a file.
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Note: both strings pointed at by
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.Va dli_fname
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and
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.Va dli_sname
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reside in memory private to the run-time linker module and should not
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be modified by the caller.
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.Pp
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.Fn dlctl
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provides an interface similar to
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.Xr ioctl 2
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to control several aspects of the run-time linker's operation.
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This interface
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is
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.Ud .
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.Pp
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.Fn dlerror
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returns a character string representing the most recent error that has
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occurred while processing one of the other functions described here.
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If no dynamic linking errors have occurred since the last invocation of
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.Fn dlerror ,
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.Fn dlerror
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returns
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.Dv NULL .
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Thus, invoking
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.Fn dlerror
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a second time, immediately following a prior invocation, will result in
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.Dv NULL
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being returned.
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.Sh SEE ALSO
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.Xr ld 1 ,
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.Xr rtld 1 ,
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.Xr link 5
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.Sh HISTORY
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Some of the
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.Nm dl*
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functions first appeared in SunOS 4.
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.Sh BUGS
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An error that occurs while processing a
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.Fn dlopen
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request results in the termination of the program.
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