.\"	$NetBSD: dlfcn.3,v 1.3 1996/01/09 19:43:34 pk Exp $
.\"
.\" Copyright (c) 1995 Paul Kranenburg
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.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 SYNOPSIS
.Fd #include <dlfcn.h>
.Ft "void *"
.Fn dlopen "char *path" "int mode"
.Ft "int"
.Fn dlclose "void *handle"
.Ft "void *"
.Fn dlsym "void *handle" "char *symbol"
.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 .
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.
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 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.
.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.