freebsd-skq/share/man/man5/libmap.conf.5

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.Dd January 31, 2004
.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
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 .