I sent this to the boost-build list, but I think it should have been CC'ed to this list as well. I'd like to commit this change to the SVN trunk if there are no objections. I think its a big win for anyone who uses --layout=system. This is the way BBv1 (correctly IMHO) handled --layout=system. ---------- Forwarded message ---------- From: Caleb Epstein <caleb.epstein@gmail.com> Date: Aug 2, 2007 2:23 PM Subject: Improving --layout=system To: "Boost.Build developer's and user's list" <boost-build@lists.boost.org> On systems that support shared library version numbers, I believe that these should be used even when building with --layout=system. At present, when you build Boost with --layout=system, you end up with libraries called libboost_xyz-mt.so that have this same value set at their ELF SONAME (this is the shared library version number embedded into the library itself). The problem with these libraries is that you can never have multiple versions of them installed side-by-side in the same place. Go too far down this road and you end up with Windows-style 'DLL hell'. If instead the BOOST_VERSION is appended to the target name as it is with --layout=versioned, you end up with SONAME'd libraries that can live side-by-side with earlier/later versions of Boost. For example, by adding the version number to the libraries, you end up with a lib directory that looks like: lrwxrwxrwx 1 cepstein 33 Aug 2 13:44 libboost_date_time-mt-d.so -> libboost_date_time-mt-d.so.1.35.0 -rwxrwxr-x 1 cepstein 388K Aug 2 13:44 libboost_date_time-mt-d.so.1.35.0 lrwxrwxrwx 1 cepstein 31 Aug 2 13:44 libboost_date_time-mt.so -> libboost_date_time-mt.so.1.35.0 -rwxrwxr-x 1 cepstein 52K Aug 2 13:44 libboost_date_time-mt.so.1.35.0 ... Now when you link applications using -lboost_date_time-mt, the linker records the dependency on the library's SONAME, which is libboost_date_time_mt.so.1.35.0. No other name will satisfy this runtime dependency. As a result, you can install the (hypothetical) Boost 1.36.0libs into the same directory and old applications will continue to pick up the *.so.1.35.0 libs correctly, while new applications built when the symlink points to the new library versions will pick up *.so.1.36.0. This is how Boost.Build v1 handled --layout=system and I believe this is the most correct and desirable behavior for platforms that support versioned shared libraries. Attached is my simple patch against the latest SVN trunk to make this work. -- Caleb Epstein