GBS-HOWTO 2003 Mark Hoebeke Y Giridhar Appaji Nag Giridhar Appaji Nag Y

appaji{at}ibiblio{dot}org

Mark Hoebeke

mark{dot}hoebeke{at}orange{dot}fr

None Yet! 0.1 2003-11-05 mh first formatting of consensus TOC This HOWTO aims to help beginning developers to leverage the power the GNU Build System (GBS). The GBS is composed of well-known tools such as &make; and of less-used utilities such as &autoconf;, &automake; or &libtool;. The primary goal of the HOWTO is to ring developers up to speed with each of these tools, and, at another level to explain some of their inner workings. Document last updated $Date$. If you ever installed packages from source on a Unix environment, you will have encountered &makefile; that is used to compile the package. When there was no &automake; or &autoconf;, it was a non trivial task to get big source packages to compile, leave alone getting them to work for you. It often involved tweaking of the &makefile; and making changes to source. Finding the necessary things that you need (like libraries, the right version of the library needed) before you could compile a particular package, was a difficult task. Another major problem that many software developers face is that of maintaining portability, achieving platform independence and building libraries. This is important if the code written should run on a variety of platforms. Finding the specifics of a machine and the operating system, and configuring the source of a package for successful compilation and working, is also a problem of interest. The GNU Autotools address these issues. This HOWTO is a resource for first time users of the autotools. It is intended to be an introductory guide, to help with GNU &make;, &autoconf;, &automake; &libtool; etc. It also tries to provide an explanation as to how these tools work. To be able to follow the explanations given in here, the reader is expected to be familiar with Unix like operating systems and the basics of programming. New versions of this document that are released would be available from The LDP website and its mirrors. Since a few mirrors are broken or not up-to-date, it is highly recommended that the latest released version be accessed from http://tldp.org/HOWTO/GNU-Build-System-HOWTO/. The latest in-progress version of this document is available at the GNU-Build-System HOWTO home page. This document, the GNU-Build-System HOWTO, is distributed under the terms of the GNU General Public License. The word Program in the license is to be interpreted as document. The term source code refers to the DocBook/XML format of this document and the term object code refers to one, many or all the other formats that this document is available in, after conversion from the source code. This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. A copy of the license is available at http://www.gnu.org/licenses/gpl.txt and can be found in . You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. All copyrights are held by their by their respective owners, unless specifically noted otherwise. Use of a term in this document should not be regarded as affecting the validity of any trademark or service mark. Naming of particular products or brands should not be seen as endorsements. The GNU Build System encompasses a number of components that assist a developer in each stage of the configure, compile and distribute process. Projects using the suite of the GBS are recognizable by the ease with which they are installed. The ubiquitous ./configure && make && make install does it all. This section of the document introduces the build tools and explains how to use them. Though the treatment would not be in depth, it should help you understand the files that these tools operate on. The aim is to take the reader step by step, through the stages turning a set of source files of a project to conform to the ./configure && make && make install mantra. We will work through each of these components using a Hello World! styled example. If you are reading this document, it is possible that you already have prior experience with the &make; utility. However, any discussion of the build system would be incomplete without a mention of &make;. &make; is a utility for automatic compilation of a project's source code. It is used in projects to find out if the files (typically C sources) that a certain target (typically object files and executables) depends on have changed, and re-generates the target. It makes compiling only the necessary files of a big project as simple as typing &make;, when a few of them have been modified. The input to the &make; utility is a &makefile;. A very minimal &makefile; to &make; a program called foo from its C source file, foo.c would look like: &cmdline;cat Makefile foo: foo.c gcc -o foo foo.c &cmdline; The target in this &makefile; is foo and it depends on the foo.c dependency. The second line (command) tells make how to build the target in case the dependency changes. The command should be on its own line with a tab character (and not spaces) before it. The foo executable can then be created by issuing a make foo command in the directory where the above &makefile; is present. &cmdline;make gcc -o foo foo.c &cmdline; A slightly more useful example would be: &cmdline;cat Makefile all: hw hw: main.o hello.o world.o gcc main.o hello.o world.o -o hw world.o: world.c hello.h world.h gcc -Wall -c hello.c hello.o: hello.c hello.h gcc -Wall -c hello.c world.o: world.c world.h gcc -Wall -c world.c clean: rm -f hw hello.o world.o &cmdline; The default target in this &makefile; (which is the first target that appears in the &makefile;) is all. all depends on hw which in-turn depends on main.o, hello.o and world.o. These can be made using the rules that have been specified for them respectively. For example, hello.o is created using the command gcc -Wall -c hello.c whenever hello.c or hello.h are modified. &cmdline;make gcc -Wall -c main.c gcc -Wall -c hello.c gcc -Wall -c world.c gcc main.o hello.o world.o -o hw &cmdline; Another invocation of &make; (or make all) does nothing. This is because none of the files that &make; looks at have been modified. &cmdline;make all make: Nothing to be done for `all'. &cmdline; However, if one of the files is changed (say hello.h), &make; will figure out the right files to be re-compiled (based on the dependencies in the &makefile;) and generate a new hw. &cmdline;touch hello.h &cmdline;make all gcc -Wall -c main.c gcc -Wall -c hello.c gcc main.o hello.o world.o -o hw &cmdline; The other target clean in the &makefile; can be invoked explicitly to remove the target files that have been generated. &cmdline;make clean rm -f hw main.o hello.o world.o &cmdline; A &makefile; can also be written using variables and wild-cards making it easy to modify and maintain. For example, the above &makefile; can be re-written as: &cmdline;cat Makefile TARGET = hw OBJS = main.o hello.o world.o CC = gcc CCOPTS = -Wall -c RM = rm RMOPTS = -f all: $(TARGET) $(TARGET): $(OBJS) $(CC) $(OBJS) -o $(TARGET) main.o: main.c hello.h world.h $(CC) $(CCOPTS) $< %.o: %.c %.h $(CC) $(CCOPTS) $< clean: $(RM) $(RMOPTS) $(TARGET) $(OBJS) &cmdline; Every $(VARIABLE) in the &makefile; is replaced with its value. The generic rule %.o: %.c %.h In general, one source file would depend on more than one header file (like the main.o dependency) and the dependency rule is not as simple as this. It is infact difficult to keep track of dependencies on header files and their dependencies with nested includes. There are ways of handling this (see the manual page of makedepend on your Linux machine and the -M option to gcc), but using &automake; makes this a cake-walk. says that each .o file is dependent on the corresponding .c and the .h files. $@ refers to the current target and $< refers to the first one among the list of dependencies of the current target. Note that this version of the &makefile; does not need a lot of modifications if a single source file and the corresponding header files are added. GNU &make; provides several other useful features like the VPATH directive to locate the source files that are not co-located with the &makefile;, facility for sophisticated wildcards, etc. These are described in the official GNU &make; manual. A &makefile; that goes with software packages that follow the GNU &makefile; conventions has a few standard targets and provides useful and commonly used functionality like: all: to build the package clean: which removes all the generated files tags: generates the TAGS file for source browsing check: which executes any automated test cases that have been included with the package. dist: creates a .tar.gz distribution of the software package. install: installs the compiled binaries, manual pages, documents at their appropriate location. uninstall: removes the files that have been installed and many more ... Writing the dependencies and rules for these targets is a non-trivial task and involves some effort. &automake; solves this problem by generating all the standard targets. We need to rely on other tools to ensure that a project is built and runs correctly on most flavors of Unix (including Linux of course). These platform specific parameters are detected by the &configure_file; script generated by &autoconf;. &autoconf; also generates a &makefile;. The input to the &configure_file; script are the &makefile_in; and the &configure_in; files. The final (?) step to build a well-behaved and distributable software project is to supply &make; with a set of standard targets () and to use a set of thoroughly tested recipes to build them. This is where &automake; comes into play. Starting from a high-level description of the project's components (source files, binaries to be built, documentation, additional data files) found in a &makefile_am;, &automake; is capable of generating a suitable &makefile_in;. This can be used by the &configure_file; script to generate the &makefile;. So that's it? Now we've got our GBS compliant project architecture, isn't it? Indeed, but our toolkit would be incomplete if we omitted to mention &libtool;. The &libtool; component favors the use of program libraries (sets of related object files grouped into a single archive). These libraries can the be used by all executables of a project, and in some cases, without being copied in every single executable. Ways of building libraries vary much from platform to platform, fortunately, &libtool; simplifies this process, lifting the burden from the programmer. After the entry-level guided tour, a real world programming project will be subjected to the whole above slew of procedures here. A note on makedepend, autoheader, autoscan, ifnames, aclocal, autoproject, autoupdate, autoreconf etc. To the survivors of the former section, this is an inside look at the workings of all the GBS components. For starters, it describes the innards of the &make; before covering a rather ill-known macro programming language, m4 upon which several of the GBS tools are built. It then scrutinizes &autoconf;, &automake; and &libtool; to answer what and how. This section of the HOWTO covers the installation of the GBS components, either from pre-packaged files specific to Linux distributions, or from source .tar.gz (or .tar.bz2) archives (also called tarballs). Comments and suggestions regarding this document may be sent to mark{dot}hoebeke{at}orange{dot}fr and appaji@ibiblio.org. Please point out any mistakes, omissions, broken links and possible improvements so that they can be incorporated in future revisions of the document. In case you have additions and improvements that would change major portions of the document, it would be great if you could send them as a patch against the latest DocBook/XML version. The authors of this document have the pleasure of acknowledging the following people who have contributed to this document by sending in comments and suggestions for improvements. No example is good enough to expose the hurdles that inevitably show up when things get a bit more complex. The documents and references provided as references can be used to further experiment with the features that the tools described have to offer. Learning the GNU Development Tools by Eleftherios Gkioulekas is a good tutorial to understand the GNU build system and the documentation files associated with GNU style packages. The autotools referred to in the above tutorial can be downloaded from ftp://ftp.ugcs.caltech.edu/pub/elef/autotools. Though the author seems to be planning a rewrite, it is worth taking a look at. autoproject: In the authors words, autoproject - a script to start a programming project using &autoconf;, &automake;, and optionally a command line parser generator GNU Autoconf, Automake and Libtool is probably the best guide for mastering these tools. You can also read it online at http://sources.redhat.com/autobook/download.html The official GNU &make; manual http://www.gnu.org/software/make/manual/index.html. You are encouraged to explore and write more complex rules, commands in the rules, conditional parts, transformation of text in &makefile;s etc., all of which are detailed in the manual. The official &autoconf; manual http://www.gnu.org/software/autoconf/manual/autoconf-2.57/autoconf.html. Take a look at the documentation of existing tests and learn how to write new &autoconf; macros and tests. The indices of the manual are great for reference. Manuals of &automake; http://www.gnu.org/software/automake/manual/index.html. A few examples, alternative approaches to handling sub-directories, how various targets work, support for test suites etc. The official &libtool; manual http://www.gnu.org/software/libtool/manual.html Yet another language to pick up. The &m4; manual with lots of examples is at http://www.gnu.org/software/m4/manual/index.html Version 2, June 1991 1989, 1991 Free Software Foundation, Inc.

Free Software Foundation, Inc. 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. Version 2, June 1991 GNU-GPL The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software - to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too. When we speak of free software, we are referring to freedom, not price. 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It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found. <one line to give the program's name and a brief idea of what it does.> Copyright © <year> <name of author> This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: Gnomovision version 69, Copyright (C) year name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names: Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. <signature of Ty Coon>, 1 April 1989 Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.