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January 2006

Basic Autotools

Setting up software for distribution can be a daunting task. Most of the the time, a well written makefile does the trick. Sometimes a little more is needed - or even expected. The GNU autotools for setting up a software distribution can help iron out some of the problems a programmer might run into.

Using autotools for a very simple piece of software still requires a few steps:

1. Move the Makefile to Makefile.in
2. Run autoscan
3. Edit the configure.in file
4. Run autoconf
5. Test ./configure
6. make any final adjustments

The Example - etu

The Enlightenment Thumbnailing Utility or etu makes use of a simple (but powerful) scaling API for jpeg images. Initially, etu was comprised of very few files:

• Makefile - to build and install it.
• README - a simple README file with news and credits.
• etu.c - the source file for the utility itself.

There are also some test images, however, they are not used for building in any way.

Move the Makefile

If the Makefile is relatively simple (as it is in the case of etu) then it can just be moved to Makefile.in.

Using autoscan

Running autoscan without results in the following:

[jrf@vela:~/proj/etu-notools$] ls
configure.scan  etu.c  Makefile  README  test-images/  test.jpg
...
[jrf@vela:~/proj/etu-notools$] autoscan
autom4te: configure.ac: no such file or directory
autoscan: /usr/bin/autom4te failed with exit status: 1

One nice thing, however, it generates a configure.scan file which can be used as a starting point. First, the configure.scan is copied to configure.in and edited.

The configure.in File Contents

The file sets up the checks to be performed, most of these are self explanatory:

# Process this file with autoconf to produce a configure script.
AC_PREREQ(2.59)
AC_INIT(FULL-PACKAGE-NAME, VERSION, BUG-REPORT-ADDRESS)
AC_CONFIG_SRCDIR([etu.c])

# Checks for programs.
AC_PROG_CC
AC_PROG_INSTALL

# Checks for libraries.

# Checks for header files.
AC_HEADER_DIRENT
AC_HEADER_STDC
AC_CHECK_HEADERS([stddef.h stdlib.h string.h unistd.h])

# Checks for typedefs, structures, and compiler characteristics.

# Checks for library functions.
AC_FUNC_CLOSEDIR_VOID
AC_FUNC_STAT
AC_CHECK_FUNCS([mkdir])

AC_CONFIG_FILES([Makefile])
AC_OUTPUT

Anyone who has viewed the source code for etu knows there is already one problem, there is no check for the Epeg.h file. This can be remedied by simply adding an entry to the # Checks for header files section, under the AC_CHECK_HEADERS:

AC_CHECK_HEADERS([stddef.h stdlib.h string.h unistd.h Epeg.h])

Using autoconf

Next it is time to run autoconf - those paying close attention may notice there is an error coming:

[jrf@vela:~/proj/etu-notools$] ./configure 
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
checking whether we are cross compiling... no
checking for suffix of executables... 
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether gcc accepts -g... yes
checking for gcc option to accept ANSI C... none needed
configure: error: cannot find install-sh or install.sh in . ./.. ./../..

An install.sh file isn't actually needed, the easiest way around this is to create a placeholder (besides, it may be needed at some point later).

echo "Do nothing - a placeholder for autofoo" >> install.sh

Now when autoconf runs, everything works. Note that the Epeg.h header is checked for:

...
checking Epeg.h usability... yes
checking Epeg.h presence... yes
checking for Epeg.h... yes
...

Testing

At the point where ./configure works, it is time to test it in a platform where it should fail. The distribution was copied into a NetBSD system that does not even have X windows installed:

checking Epeg.h usability... no
checking Epeg.h presence... no
checking for Epeg.h... no

So there it is, it will not work on this system and a notice was put out.

Final Touches

GNU tools do like a few other files although they are not required. In general it is nice (but not required) to add:

• A COPYING file with a copy of the license (unless this is noted in the source code itself).
• README file with general information.
• AUTHORS file with the names and contact information of the authors.
• INSTALL file with basic instructions.
• TODO file with a any work that might need to be done (a good way to attract other developers).
• ChangeLog file with a description of changes between versions.

Again, none of the above listed files are required unless a particular project needs them - but they are nice to have.

Summary

Using autotools even on a basic program (such as etu which is about as basic as it gets) can help to move a program from system to system without too much fuss. This article only touched on how to set up a simple autotools based distribution, hopefully in the future a more in depth look will be done here, however, in the meantime please take a read of the GNU Build manual for more details.