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Building
Packages with the GNU Autotools
Understanding
GNU Autotools
The
GNU Autotools consist of Automake, Autoconf, and Libtool. They are
three separate packages when put together, comprise a very powerful tool
for building source projects.
Libtool
Libtool
is the only portable mechanism for building shared libraries available.
Simply put, this is a must have for Open CASCADE. Libtool consists
of a set of shell scripts that hide the details of PIC code generation
options, specific options for building shared libraries, library naming
conventions, versioning, and more. Libtool is actively being developed
by various contributors submitting patches, and four maintainers.
Although AIX 5 and the IA64 chip have not been released yet, support for
these has already been incorporated into Libtool's CVS repository.
This is one example of how Libtool has a distinct advantage over hand-building
scripts or makefiles to build shared libraries.
Autoconf
The
purpose of Autoconf is to take a general template for a Makefile and using
a portable bourne shell script, create a set of Makefiles (and other files)
specifically taylored to the system being configured. This allows
someone compiling a source tree to conform the Makefile(s) specifically
to the machine being used. While this could be accomplished by directly
writing a shell script to check for header files, definitions of structures
and library locations, Autoconf greatly simplifies this process using the
m4 language to create scripts. Autoconf also provides most of the
tests that are needed for a typical source project. The best thing
about Autoconf is that systems can be tested for portability issues directly.
Because of this, properly Autoconfiscated projects need no porting whatsoever
to run on a new system, just running configure takes care of everything.
Typically the input to Autoconf is a single file, configure.ac. From
this file Autoconf generates the portable bourne shell script "configure".
The configure script takes templates, usually with the suffix ".in" and
generates the specific files required for the build. Users of an
"Autoconfiscated" package do not have to have Autoconf installed, the configure
script requires only /bin/sh and a few standard UNIX utilities such as
rm and sed.
Automake
Automake
is used to easily create the templates that are altered by "configure".
It is not necessary to use Automake, but it creates Makefiles that are
very useful, automatically adding rules for compiling, dependency tracking,
cleaning, and installing. Automake takes as input Autoconf's "configure.ac"
as well as a set of makefile templates usually named "Makefile.am".
Because Automake generates most of the rules automatically, the Makefile.am
consists of little more than include directories, target names, and source
file names. Automake also has closely integrated support for Libtool,
making it an easy choice.
Documentation
Autoconf Manual
Automake Manual
Libtool Manual
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