man/man5/libmap.conf.5

.\" Copyright (c) 2003 Matthew N. Dodd <winter@jurai.net>
.\" 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 April 28, 2012
.Dt LIBMAP.CONF 5
.Os
.Sh NAME
.Nm libmap.conf
.Nd "configuration file for dynamic object dependency mapping"
.Sh DESCRIPTION
The
.Nm libmap
functionality of
.Xr ld-elf.so.1 1
allows dynamic object dependencies to be mapped to arbitrary
names.
.Pp
The configuration file consists of two whitespace separated columns; the
left hand side containing the mapping candidate and the right hand
side containing the mapping.
Dependencies are matched against candidates and replaced with the mappings.
.Pp
Two special directives are available:
.Bl -tag -width indent
.It Cm include Ar file
Parse the contents of
.Ar file
before continuing with the current file.
.It Cm includedir Ar dir
Parse the contents of every file in
.Ar dir
that ends in
.Pa .conf
before continuing with the current file.
.El
.Pp
Any file or directory encountered while processing
.Cm include
or
.Cm includedir
directives will be parsed exactly once, even if it is encountered
multiple times.
.Pp
Constrained mappings may be specified by enclosing the name of the
executable or library in brackets.
All mappings following a constraint will only be evaluated for that constraint.
Constraints can be one of three types:
.Bl -tag -width indent
.It Exact
The constraint is matched literally so that only an executable with an
identical fully qualified pathname will match the constraint.
This means that the executable
.Pa /usr/bin/foo
will not match a constraint for
.Pa /usr/bin/./foo
and vice-versa.
This is the default constraint type.
.It Basename
A constraint with no path is matched against the basename of the
executable.
.Pa foo
will match
.Pa /bin/foo ,
.Pa /usr/local/sbin/foo ,
or any other executable named
.Pa foo ,
no matter what its path is.
.It Directory
A constraint with a trailing slash is prefix-matched against the full
pathname of the executable.
.Pa /usr/bin/
will match any executable with a path starting with /usr/bin.
.El
.Pp
Note that the executable path matched against is the
.Fa path
parameter in an
.Fn exec*
function call.
The Directory or Exact constraints can only match when the executable
is called with a full pathname.
Most programs executed from a shell are run without a full path, via
.Fn exec*p ,
so the Basename constraint type is the most useful.
.Pp
WARNING!
Constrained mappings must never appear first in the configuration file.
While there is a way to specify the
.Dq default
constraint, its use is not recommended.
.Pp
The most common use at the date of writing is for allowing multiple
.Tn POSIX
threading libraries to be used on a system without relinking or
changing symlinks.
.Pp
On 64-bit architectures that provide 32-bit runtime support,
the libmap mechanism is available for 32-bit binaries too.
The mappings has to be written into separate configuration file
.Pa /etc/libmap32.conf .
Currently only supported on amd64.
.Pp
This mechanism has also been used to create shims to allow Linux
shared libraries to be dynamically loaded into
.Fx
binaries.
In this case, an Exact constraint is used for the Linux shared library,
mapping libraries it depends on to a wrapper.
The wrapper then defines any needed symbols for the Linux shared library
and relies on its libraries not being mapped to provide actual
implementations.
It appears that only libraries loaded via
.Xr dlopen 3
will work correctly.
The symbol version information in shared libraries is checked at
link time, but at run time the version information is currently
ignored.
.Sh FILES
.Bl -tag -width ".Pa /etc/libmap32.conf" -compact
.It Pa /etc/libmap.conf
The libmap configuration file.
.It Pa /etc/libmap32.conf
The libmap configuration file for 32-bit binaries on 64-bit system.
.El
.Sh EXAMPLES
.Bd -literal
# /etc/libmap.conf
#
# candidate		mapping
#
libc_r.so.6		libpthread.so.2	# Everything that uses 'libc_r'
libc_r.so		libpthread.so	# now uses 'libpthread'

[/tmp/mplayer]		# Test version of mplayer uses libc_r
libpthread.so.2		libc_r.so.6
libpthread.so		libc_r.so

[/usr/local/jdk1.4.1/]	# All Java 1.4.1 programs use libthr
			# This works because "javavms" executes
			# programs with the full pathname
libpthread.so.2		libthr.so.2
libpthread.so		libthr.so

# Glue for Linux-only EPSON printer .so to be loaded into cups, etc.
[/usr/local/lib/pips/libsc80c.so]
libc.so.6		pluginwrapper/pips.so
libdl.so.2		pluginwrapper/pips.so
.Ed
.Sh SEE ALSO
.Xr ldd 1 ,
.Xr rtld 1
.Sh HISTORY
The
.Nm
manual page and
.Nm libmap
functionality first appeared in
.Fx 5.1 .
.Sh AUTHORS
This manual page was written by
.An Matthew N. Dodd Aq winter@jurai.net .