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10.1 Creating libtool

When you install a distribution of Libtool on your development machine, a host specific libtool program is installed. The examples in the rest of this chapter use this installed instance of libtool.

When you start to use Libtool in the build process of your own projects, you shouldn’t require that libtool be installed on the user’s machine, particularly since they may have a different libtool version to the one used to develop your project. Instead, distribute some of the files installed by the Libtool distribution along with your project, and custom build a libtool script on the user’s machine before invoking ./libtool to build any objects. If you use Autoconf and Automake, these details are taken care of automatically (see section Using GNU Libtool with configure.in and Makefile.am). Otherwise you should copy the following files from your own Libtool installation into the source tree of your own project:

$ ls /usr/local/share/libtool
config.guess   config.sub   libltdl   ltconfig   ltmain.in
$ cp /usr/local/share/libtool/config.* /usr/local/share/libtool/lt* .
$ ls
config.guess   config.sub   ltconfig   ltmain.in

You must then arrange for your project build process to create an instance of libtool on the user’s machine, so that it is dependent on their target system and not your development machine. The creation process requires the four files you just added to your project. Let’s create a libtool instance by hand, so that you can see what is involved:

$ ./config.guess
$ ./ltconfig --disable-static --with-gcc ./ltmain.sh hppa1.1-hp-hpux10.20
checking host system type... hppa1.1-hp-hpux10.20
checking build system type... hppa1.1-hp-hpux10.20
checking whether ln -s works... yes
checking for ranlib... ranlib
checking for BSD-compatible nm... /usr/bin/nm -p
checking for strip... strip
checking for gcc... gcc
checking whether we are using GNU C... yes
checking for objdir... .libs
checking for object suffix... o
checking for executable suffix... no
checking for gcc option to produce PIC... -fPIC
checking if gcc PIC flag -fPIC works... yes
checking if gcc static flag -static works... yes
checking if gcc supports -c -o file.o... yes
checking if gcc supports -c -o file.lo... yes
checking if gcc supports -fno-rtti -fno-exceptions ... no
checking for ld used by GCC... /opt/gcc-lib/hp821/2.7.0/ld
checking if the linker (/opt/gcc-lib/hp821/2.7.0/ld) is GNU ld... no
checking whether the linker (/opt/gcc-lib/hp821/2.7.0/ld) supports \
shared libraries... yes
checking how to hardcode library paths into programs... relink
checking whether stripping libraries is possible... yes
checking for /opt/gcc-lib/hp821/2.7.0/ld option to reload object \
files... -r
checking dynamic linker characteristics... hpux10.20 dld.sl
checking command to parse /usr/bin/nm -p output... ok
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
creating libtool
$ ls
config.guess   config.sub   ltconfig
config.log     libtool      ltmain.sh
$ ./libtool --version
ltmain.sh (GNU libtool) 1.3c (1.629 1999/11/02 12:33:04)

The examples in this chapter are all performed on a HP-UX system, but the principles depicted are representative of any of the platforms to which Libtool has been ported (see section PLATFORMS).

Often you don’t need to specify any options, and if you omit the configuration triplet (see section Configuration Names), ltconfig will run config.guess itself. There are several options you can specify which affect the generated libtool, See Invoking ltconfig: (Libtool)Configuring Libtool section ‘Invoking ltconfig’ in The Libtool Manual. Unless your project has special requirements, you can usually use the simplified:

$ ./ltconfig ./ltmain.sh

With the current release of Libtool, you must be careful that ‘$CC’ is set to the same value when you call ltconfig as when you invoke the libtool it generates, otherwise libtool will use the compiler specified in ‘$CC’ currently, but with the semantics probed by ltconfig for the compiler specified in ‘$CC’ at the time it was executed.

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