342 lines
10 KiB
Groff
342 lines
10 KiB
Groff
.\" $NetBSD: dlfcn.3,v 1.31 2011/02/13 16:01:39 wiz 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.
|
|
.\"
|
|
.\" 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 February 13, 2011
|
|
.Dt DLFCN 3
|
|
.Os
|
|
.Sh NAME
|
|
.Nm dlopen ,
|
|
.Nm dlclose ,
|
|
.Nm dlsym ,
|
|
.Nm dladdr ,
|
|
.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
|
|
.In dlfcn.h
|
|
.Ft "void *"
|
|
.Fn dlopen "const char *path" "int mode"
|
|
.Ft "int"
|
|
.Fn dlclose "void *handle"
|
|
.Ft "void *"
|
|
.Fn dlsym "void * restrict handle" "const char * restrict symbol"
|
|
.Ft "int"
|
|
.Fn dladdr "void * restrict addr" "Dl_info * restrict 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.
|
|
.Pp
|
|
The
|
|
.Fn dlopen
|
|
function takes the name of a shared object as the first argument.
|
|
The
|
|
.Fa path
|
|
argument can be specified as either an absolute pathname to a shared object
|
|
or just the name of the shared object itself.
|
|
When an absolute pathname is specified,
|
|
only the path provided will be searched.
|
|
When just a shared object name is specified, the same search rules apply that
|
|
are used for
|
|
.Dq intrinsic
|
|
shared object searches.
|
|
.Po
|
|
see
|
|
.Xr ld.elf_so 1
|
|
.Pc
|
|
.Pp
|
|
Shared libraries take the following form:
|
|
.Do lib Ns Ao name Ac Ns .so Ns Oo .xx Ns Oo .yy Oc Oc Dc .
|
|
.Pp
|
|
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.
|
|
.Pp
|
|
If the first argument is
|
|
.Dv NULL ,
|
|
.Fn dlopen
|
|
returns a
|
|
.Fa 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
|
|
.Fa mode
|
|
parameter specifies symbol resolution time and symbol visibility.
|
|
One of the following values may be used to specify symbol resolution time:
|
|
.Bl -tag -width "RTLD_GLOBALXX" -offset indent
|
|
.It Dv RTLD_NOW
|
|
Symbols are resolved immediately.
|
|
.It Dv RTLD_LAZY
|
|
Symbols are resolved when they are first referred to.
|
|
This is the default value if resolution time is unspecified.
|
|
.El
|
|
.Pp
|
|
One of the following values may be used to specify symbol visibility:
|
|
.Pp
|
|
.Bl -tag -width "RTLD_GLOBALXX" -offset indent
|
|
.It Dv RTLD_GLOBAL
|
|
The object's symbols and the symbols of its dependencies will be visible to
|
|
other objects.
|
|
.It Dv RTLD_LOCAL
|
|
The object's symbols and the symbols of its dependencies will not be visible to
|
|
other objects.
|
|
This is the default value if visibility is unspecified.
|
|
.El
|
|
.Pp
|
|
To specify both resolution time and visibility, bitwise inclusive OR one of
|
|
each of the above values together.
|
|
If an object was opened with
|
|
.Dv RTLD_LOCAL
|
|
and later opened with
|
|
.Dv RTLD_GLOBAL ,
|
|
then it is promoted to
|
|
.Dv RTLD_GLOBAL .
|
|
.Pp
|
|
Additionally, one of the following flags may be ORed into the
|
|
.Fa mode
|
|
argument:
|
|
.Bl -tag -width "RTLD_NODELETEXX" -offset indent
|
|
.It Dv RTLD_NODELETE
|
|
Prevents unload of the loaded object on
|
|
.Fn dlclose .
|
|
The same behaviour may be requested by
|
|
.Fl "z nodelete"
|
|
option of the static linker
|
|
.Xr ld 1 .
|
|
.It Dv RTLD_NOLOAD
|
|
Only return valid handle for the object if it is already loaded in
|
|
the process address space, otherwise do not load the object and return
|
|
.Dv NULL .
|
|
.El
|
|
.Pp
|
|
.Fn dlopen
|
|
returns a
|
|
.Fa 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
|
|
.Fa handle
|
|
referring 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, or the object was one loaded at startup time,
|
|
or the object is a dependency of another object
|
|
then the object is removed when its reference count drops to zero.
|
|
.Fn dlclose
|
|
returns 0 on success and non-zero on failure.
|
|
.Pp
|
|
.Fn dlsym
|
|
looks for a definition of
|
|
.Fa symbol
|
|
in the shared object designated by
|
|
.Fa handle ,
|
|
and all shared objects that are listed as dependencies.
|
|
The symbol's address is returned.
|
|
If the symbol cannot be resolved,
|
|
.Dv NULL
|
|
is returned.
|
|
.Pp
|
|
.Fn dlsym
|
|
may also be called with special
|
|
.Fa handle
|
|
values.
|
|
.Fn dlsym
|
|
respects symbol visibility as specified by the
|
|
.Fn dlopen
|
|
.Fa mode
|
|
parameter.
|
|
However, the symbols of an object's dependencies are always visible to it.
|
|
All shared objects loaded at program startup are globally visible.
|
|
Only the symbols in the main executable that are referenced by a
|
|
shared object at link time will be visible unless it has been linked
|
|
with the --export-dynamic option where all of its symbols will be
|
|
visible.
|
|
The following special
|
|
.Fa handle
|
|
values may be used with
|
|
.Fn dlsym :
|
|
.Bl -tag -width "RTLD_DEFAULTXX" -offset indent
|
|
.It Dv NULL
|
|
Interpreted as a reference to the executable or shared object
|
|
from which the call is being made.
|
|
Thus an object can reference its own symbols and the symbols of its
|
|
dependencies without calling
|
|
.Fn dlopen .
|
|
.It Dv RTLD_DEFAULT
|
|
All the visible shared objects and the executable will be searched in the order
|
|
they were loaded.
|
|
.It Dv RTLD_NEXT
|
|
The search for
|
|
.Fa symbol
|
|
is limited to the visible shared objects which were loaded after the one
|
|
issuing the call to
|
|
.Fn dlsym .
|
|
Thus, if
|
|
.Fn dlsym
|
|
is called from the main program, all the visible shared libraries are searched.
|
|
If it is called from a shared library, all subsequently visible shared
|
|
libraries are searched.
|
|
.It Dv RTLD_SELF
|
|
The search for
|
|
.Fa symbol
|
|
is limited to the shared object issuing the call to
|
|
.Fn dlsym
|
|
and those shared objects which were loaded after it that are visible.
|
|
.El
|
|
.Pp
|
|
.Fn dladdr
|
|
examines all currently mapped shared objects for a symbol whose address --
|
|
as mapped in the process 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 */
|
|
const void *dli_saddr; /* Symbol address */
|
|
} Dl_info;
|
|
.Ed
|
|
.Pp
|
|
The structure members are further described as follows:
|
|
.Bl -tag -width "dli_fnameXX"
|
|
.It Li "dli_fname"
|
|
The pathname of the shared object containing the address
|
|
.Fa addr .
|
|
.It Li "dli_fbase"
|
|
The base address at which this shared object is loaded in the process
|
|
address space.
|
|
This 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.
|
|
.It Li "dli_sname"
|
|
points at the nul-terminated name of the selected symbol
|
|
.It Li "dli_saddr"
|
|
is the actual address
|
|
.Pq as it appears in the process address space
|
|
of the symbol.
|
|
.El
|
|
.Pp
|
|
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
|
|
In dynamically linked programs, the address of a global function will
|
|
point to its program linkage table entry, rather than to the entry
|
|
point of the function itself.
|
|
This causes most global functions to appear to be defined within the
|
|
main executable, rather than in the shared libraries where the actual
|
|
code resides.
|
|
.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
|
|
returns 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 ERRORS
|
|
The error
|
|
.Dq Cannot dlopen non-loadable /usr/lib/libpthread.so.1
|
|
is generated when a program
|
|
.Fn dlopen Ns No s
|
|
a module that needs libpthread but isn't linked against it itself.
|
|
.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.
|