The document discusses the GNU Build System, which helps simplify the development and building of portable software distributed as source code. It provides an overview of the key components of the GNU Build System - autoconf, automake, and libtool - and how they are used to generate configuration scripts and Makefile templates from initial files. The document also outlines the typical process of applying the GNU Build System tools to create software packages that can be easily built, installed, and distributed.

1. Presentation
on
GNU Build System
for
(FOSS) From the Open Source Shelf
CDAC Monthly Seminar Series
Presented by
Sagun Baijal
Organised by
CDAC, Kharghar, Navi Mumbai
E-mail: course_kh@cdacmumbai.in

2. WELCOME

3. Overview
Background
Why GNU Build System
Introduction to GNU Build System
Using GNU Build System
Conclusion
References

4. Background
• Typical Methods of installing a software in Unix-
like systems
• Installation by using a package manager
• Installtion from source code
• GNU standard method of installation
• Packages normally come as a tarball.
• Decompress the package.
• Run configure script e.g. ...:~$./configure
• Run make e.g. ...:~$make
• Run make install e.g. ...:~$sudo make install

5. Background contd...
• Issues while packaging the system for release
• Naming and Versioning of the package.
• Portability of system on a variety of platforms.
• Configuration script configure with standrad
configurations options.
• Makefile.inS required by configure script.
• Conformity of Makefile and directory layout as per
GNU standards.
• Necessary documentation files and tests.
• Bundling of the package into a tarball.
• Licensing of the system.

6. Why GNU Build System
• Creating a configuration script and Makefiles
from scratch is a tedious, time-consuming and
error-prone task.
• Some users may be left unsatisfied due to
unavailability of some desired features.
• It may be needed to upgrade the overall setup to
follow the changes to the GNU Coding Standards.

7. Contd...
• GNU Build System helps:
• simplify the development of portable programs.
• simplify the building of programs distributed as
source code.
• Any bux fixes and improvements can be made at
one place.
• Users don't require any utilities of build system
at their end.

8. Introduction to GNU Build System
• GNU Build System comprises:
• autoconf: For generating configuration script configure.
• automake: For generating makefile templates
Makfile.inS
• libtool: Helps creating the portable compiled libraries.
• Some other auxilary tools:
• Autoscan: For generating intial input file for autoconf.
• Autoheader: For generating template header for
configure.
• aclocal: For generating aclocal.m4.

9. Contd...
• Installation:
• To check, if installed in their most recent versions:
• ...:~$autoconf - -version
• ...:~$automake - -version
• ...:~$libtool - -version
• If not installed, then (on any debian-like system):
• ...:~$apt-cache search <tool-name> - searches for the
tool-name in available package list.
• ...:~$sudo apt-get install <tool-name> - installs the
<tool-name>.

10. Using GNU Build System
• Basic requirements:
Source and documentation files of the package.
•
• One configure.ac/.in as initial input file for
autoconf.
• One Makefile.am for each directory in the package.
• Source and Documentation files:
• Files containing source code and necessary
documentation to be distributed in the package.
• Ex.: .c, .cpp files, README etc..

11. Contd...
• What is configure.ac?
• Initial input file for autoconf to generate configure
script. Also used by automake, while creating
Makefile.amS.
• Contains macros needed to test the system features
required or used by the package.
• Using autoscan:
• autoscan scans source files and creates configure.scan.
• After making some adjustments, if required,
configure.scan can be renamed to configure.ac.
• Adjustments may be like adding some missing macros
or changing the order of some macros etc..

12. Contd...
• Common macros:
• AC_PREREQ: specifies the minimum version of autoconf that can
successfully compile a given configure.ac.
• AC_INIT: initializes autoconf.
• AM_INIT_AUTOMAKE: initializes automake.
• AC_PROG_CC: determines a C compiler to use and sets output
variable CC to its value.
• AC_PROG_CXX: determines a C++ compiler to use and sets output
variable CXX to its value.
• AC_CONFIG_HEADER: causes to create a config.h file gathering
‘#define’s defined by other macros in configure.ac.
• AC_CONFIG_FILES: declares the list of files to be created from their
*.in templates.
• AC_OUTPUT: generates and runs config.status, which in turn creates
the makefiles and any other files resulting from configuration.

13. Contd...
• Example configure.ac:
AC_PREREQ(2.61)
AC_INIT([hello], [0.1], [sagun@cdacmumbai.in])
AM_INIT_AUTOMAKE([-Wall -Werror])
AC_PROG_CC
AC_CONFIG_HEADER([config.h])
AC_CONFIG_FILES([
Makefile
src/Makefile
])
AC_OUTPUT

14. Contd...
• What is Makefile.am?
• Initial input file for automake to generate
Makefile.in.
• One Makefile.am for each directory in package
including root directory.
• Normally contains a list of variable (and rule)
definitions required when make is invoked.
• Common Makefile targets:
• make all: Build programs, libraries, documentation,
etc.
• make install: Install what needs to be installed,
copying the files from the package's tree to system-
wide directories.

15. Contd...
• make uninstall: The opposite of make install: erase the
installed files.
• make clean: Erase from the build tree the files built by
make all.
• make distclean: Additionally erase anything
./configure created.
• make check: Run the test suite, if any.
• make installcheck: Check the installed programs or
libraries, if supported.
• make dist: Recreate package-version.tar.gz from all
the source files.

16. Contd...
• Common variables for Makefile.am:
• bin_PROGRAMS: specifies the <program> to be built
and installed on .../bin directory.
• <program>_SOURCES: lists one or more source files
compiled to build the <program>.
• SUBDIRS: lists all sub-directories to be built.
• dist_doc_DATA: lists documentation files to be
distributed and installed in ../doc directory.
• <program>_DEPENDENCIES: specifies dependencies,
if any.
• <program>_<FLAGS>: various compilation flags can
be set.

17. Contd...
• <program>_LDADD: specifies extra objects and
libraries to be added with <program>.
• <program>_LDFLAGS: specifies extra linker flags for
<program>.
• An example Makefile.am:
bin_PROGRAMS = hello
hello_SOURCES = hello.c

18. Contd...
• Some characteristics of GNU Build System:
• VPATH Builds: When source tree and build tree
are different, such builds are called VPATH builds.
• Cross-compilation: When a program is built on one
platform and run on another platform is called
cross-compilation.
• Renaming: GNU build system allows to
automatically rename executables etc. before
installation.
• Dependency tracking: GNU build system allows to
track dependencies automatically.
• Nested packages: Autoconfiscated packages can be
nested to arbitrary depth.

19. Contd...
• Applying tools to create the package:
• Ensure all necessary source, documentation and
Makefiel.amS files have been created.
• Run autoscan to create prelimanary configure.scan.
• ..:~/<pkg-dir>$autoscan
• If required, edit configure.scan to update package-
name, version, invocation to
AM_INIT_AUTOMAKE macro etc. and rename it
to configure.ac.
• Run aclocal to create aclocal.m4. This file contains
macro definitions not part of standard autoconf
macros.
• ..:~/<pkg-dir>$aclocal

20. Contd...
• Run autoheader to create config.h.in. This file is a
template header for configure.
• ..:~/<pkg-dir>$autoheader
• Run autoconf to create configure from configure.ac
and aclocal.m4.
• ..:~/<pkg-dir>$autoconf
• Run automake to create Makefile.inS from
Makefile.amS.
• ..:~/<pkg-dir>$automake
• Run configure to create Makefiles from
Makefile.inS, config.h from config.h.in and perform
various checks about the environment.
• ..:~/<pkg-dir>$./configure

21. Contd...
• Now run make to build the system.
• ..:~/<pkg-dir>$make
• If make executes successfully, run make distcheck to
create the package for distribution as a tarball.
• ..:~/<pkg-dir>$make distcheck
• Run make install to install the package.
• ..:~/<pkg-dir>$sudo make install
• Run make uninstall to uninstall the package.
• ..:~/<pkg-dir>$sudo make uninstall

22. Conclusion
• From User's point of view:
• provides a standard procedure for installation.
• procedure consists of only a small set of commands.
• From Developer's point of view:
• Creating portable distributions become easy.
• Updations or improvements, if any, can be done at
one place.

23. References
 http://autotoolset.sourceforge.net/tutorial.html
 http://www.gnu.org/software/automake/manual/automake.html
 http://sources.redhat.com/autobook/
 http://www.gnu.org/software/hello/manual/autoconf/autoscan-
Invocation.html#autoscan-Invocation
 http://www.lrde.epita.fr/~adl/autotools.html
 http://en.wikipedia.org/wiki/GNU_build_system
 http://www.gnu.org/prep/standards/standards.html
 http://www.dwheeler.com/essays/releasing-floss-software.html
 http://www.gnu.org/software/hello/manual/autoconf/Autoconf-Macro-
Index.html
 http://www.devshed.com/c/a/Administration/Linux-Administration-Installing-
Software/9/
 http://www.control-escape.com/linux/lx-swinstall.html
 http://www.unixguide.net/linux/faq/05.02.shtml
 http://www.gnu.org/software/libtool/

24. Thank You
E-mail: course_kh@cdacmumbai.in