On May 7, 2014, at 4:16 PM, Baptiste Daroussin <[email protected]> wrote: > >> On Thu, May 08, 2014 at 12:24:20AM +0200, Tijl Coosemans wrote: >> Hi, >> >> I've been asked to write something about USES=libtool to clarify a few >> things about what it does and why. >> >> >> First: what is libtool? >> >> Libtool is a build script that acts as a wrapper around a compiler. You >> can compile code or link a library (or executable) with libtool and it will >> invoke the right compiler, linker and other commands for you. It supports >> multiple languages, compilers and platforms and simplifies writing >> makefiles when used in combination with automake. Many ports use it. >> >> >> The problems with libtool on FreeBSD. >> >> Libraries created with libtool have three version numbers X.Y.Z. How they >> are calculated is not straightforward but that's not important right now. >> The important thing is that the major version number X is the only one >> that really matters. An executable that links to libA will ask for >> libA.so.X and doesn't care about Y and Z. Only when the major version >> number of a library changes does everything that link to it need to be >> recompiled. On FreeBSD however libtool uses X+Y as major version number >> which means that changes in Y also require rebuilding all ports that >> depend on the library. >> >> A second problem is that libtool flattens the dependency tree. When you >> link an executable or library with libA while libA in turn links to libB >> then libtool will make the executable or library also link with libB. >> This means that when the major version number of libB changes, the >> executable or library will also have to be rebuilt. Some libraries get >> propagated into hundreds and even thousands of ports this way while only >> a few actually use them directly. >> >> These two problems make major version number changes too frequent and too >> painful, not only for users who build their own ports, but also for >> package users, because too many packages need to be rebuilt, mirrored and >> downloaded every week than strictly necessary. >> >> A third problem is with ports that have USE_AUTOTOOLS=libtool in their >> Makefile. Normally the libtool script is generated by the configure >> script so it uses the compiler, linker and other tools that you configure >> a port with. Ports with USE_AUTOTOOLS=libtool however use >> /use/local/bin/libtool. This is the libtool script generated by the >> configure script of devel/libtool. This mechanism was meant for ports >> that ship with a version of libtool that doesn't work properly, but the >> problem is that such ports aren't necessarily built with the same tools as >> devel/libtool. An upcoming feature that allows cross-building ports and >> that will be used to provide ARM packages is currently blocked by this >> because these ports don't use the right cross compiler and linker. >> >> >> The solution. >> >> All ports that use libtool need to have USES=libtool added to their >> Makefile and USE_AUTOTOOLS=libtool removed. USES=libtool will patch the >> port to address the problems above along with a few smaller problems with >> older versions of libtool that some ports still ship with. USES=libtool >> also replaces USE_GNOME=ltverhack so that should be removed as well. In >> fact, all libtool related hacks and patches that a port contains can >> probably be removed (typically patches or post-patch commands for files >> like ltconfig, ltmain.sh and configure). >> >> The easiest way to know if a port uses libtool is to build it first. You >> can then search the work directory for a file named "libtool": >> >> # cd some/port >> # make >> # find work -name libtool >> >> Another giveaway is the installation of files with .la extension. >> >> >> USES=libtool modifiers :keepla and :oldver. >> >> One of the ways libtool propagates links is through .la libraries. These >> are ordinary text files that contain some meta-data about a library, >> including a record of all dependencies. These files are normally not >> needed and USES=libtool removes them from the staging area. For the rare >> cases where a port does need these files USES=libtool:keepla can be used. >> In this case .la files are kept but the dependency record is cleared so >> dependencies won't be propagated to other ports. >> >> Another important reason to keep .la files is that in this transition >> period other ports may still contain references to them in the dependency >> record of their .la files. These ports first need to have some form of >> USES=libtool added to their Makefile such that these references are >> removed. So, as long as there are dependent ports that install .la files >> but do not have some form of USES=libtool, a port must use >> USES=libtool:keepla. >> >> Finally, because the major version number goes from X+Y to X, if Y is >> non-zero, the library version will go backwards. This is not a problem >> in the sense of API compatibility (because of the way libtool versioning >> works everything between X and X+Y is backwards compatible and a new >> release that isn't backwards compatible will see its major version number >> jump to newX=oldX+oldY+1), but it may be a problem if due to link >> propagation many ports depend on the library and they all need to get a >> PORTREVISION bump. To avoid this, USES=libtool:oldver can be used. A >> port will then continue to use the old X+Y version scheme but it will >> no longer propagate its own dependencies to other ports. Once enough >> ports use some form of USES=libtool the number of dependent ports will >> drop to a point that removing :oldver becomes possible. Note that >> USES=libtool:oldver is a transitional measure and support for it will >> eventually be removed. > > Thank you very much for this write up! and for all your work helping us > solving a very long standing major problem in the ports tree! > > regards, > Bapt
+1 cheers hats off to ya that was both so helpful and informative. I'm so glad to see that's been simplified _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-ports To unsubscribe, send any mail to "[email protected]"
