GNU Libtool and the missing .so extension

GNU Libtool supports an extremely wide variety of different platforms, some of which do not use the .so extension for shared libraries you might be used to on the Linux platform.

The decision as to which extension is correct for your system is made during your package's configure script during the AC_PROG_LIBTOOL macro. The correct result for Debian systems is always “.so”.

If you've been directed to read this page then this isn't being correctly chosen, and most likely no shared extension has been chosen at all.

This is almost certainly not caused by incorrect detection of your system, but by a bad update of the Libtool code within your package. The AC_PROG_LIBTOOL macro is responsible for detecting your system and generating a working libtool script for it. It does this by attaching blocks of variables to the top and bottom of the ltmain.sh file in your source package.

The ltmain.sh file is placed there and updated using the libtoolize tool in the Libtool package. However, the AC_PROG_LIBTOOL macro code doesn't get updated with this tool. It's contained in the libtool.m4 file in your /usr/share/aclocal directory; aclocal, a tool that comes with GNU Automake, identifies all the macros your configure.in file uses and concatenates all the files together into the aclocal.m4 in your source package which is then used by the autoconf tool to generate your final configure script.

If ltmain.sh is updated, but the required chain of steps to update the configure script to use the AC_PROG_LIBTOOL macro code from the same version are not performed, problems can occur. If the variable name ltmain.sh expects is different from the one generated, the resulting libtool script will not function correctly.

The most common visible effect of this mismatch is that your shared libraries will be generated without the correct file extension.

In order to cure this problem for your package you will need to update the version of Libtool it uses. This document explains how to do that.

Copyright © 2004 Scott James Remnant <scott@netsplit.com>.
Permission is hereby granted, free of charge, to any person obtaining a copy of this document (the "Document"), to deal in the Document without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Document, and to permit persons to whom the Document is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Document.

THE DOCUMENT IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE DOCUMENT OR THE USE OR OTHER DEALINGS IN THE DOCUMENT.