Autotools Mythbuster: who’s afraid of autotools?

I’ve been asked over on Twitter if I had any particular tutorial for an easy one-stop-shop tutorial for Autotools newbies… the answer was no, but I will try to make up for it by writing this post.

First of all, with the name autotools, we include quite a bit of different tools. If you have a very simple program (not hellow-simple, but still simple), you definitely want to use at the very least two: autoconf and automake. While you could use the former without the latter, you really don’t want to. This means that you need two files: configure.ac and Makefile.am.

The first of the two files (configure.ac) is processed to produce a configure script which the user will be executing at build time. It is also the bane of most people because, if you look at one for a complex project, you’ll see lots of content (and logic) and next to no comments on what things do. Lots of it is cargo-culting and I’m afraid I cannot help but just show you a possible basic configure.ac file:

AC_INIT([myproject], [123], [flameeyes@flameeyes.eu], [https://flameeyes.blog/tag/autotools-mythbuster/])
AM_INIT_AUTOMAKE([foreign no-dist-gz dist-xz])

AC_PROG_CC

AC_OUTPUT([Makefile])

Let me explain. The first two lines are used to initialize autoconf and automake respectively. The former is being told the name and version of the project, the place to report bugs, and an URL for the package to use in documentation. The latter is told that we’re not a GNU project (seriously, this is important — you wouldn’t believe how many tarballs I find with 0-sized files just because they are mandatory in the default GNU layout; even though I found at least one crazy package lately that wanted to have a 0-sized NEWS file), and that we want a .tar.xz tarball and not a .tar.gz one (which is the default).

After initializing the tools, you need to, at the very least, ask for a C compiler. You could have asked for a C++ compiler as well, but I’ll leave that as an exercise to the reader. Finally, you got to tell it to output Makefile (it’ll use Makefile.in but we’ll create Makefile.am instead soon).

To build a program, you need then to create a Makefile.am similar to this:

bin_PROGRAMS = hellow

dist_doc_DATA = README

Here we’re telling automake that we have a program called hellow (which sources are by default hellow.c) which has to be installed in the binary directory, and a README file that has to be distributed in the tarball and installed as a documentation piece. Yes this is really enough as a very basic Makefile.am.

If you were to have two programs, hellow and hellou, and a convenience library between the two you could do it this way:

bin_PROGRAMS = hellow hellou

hellow_SOURCES = src/hellow.c
hellow_LDADD = libhello.a

hellou_SOURCES = src/hellou.c
hellow_LDADD = libhello.a

noinst_LIBRARIES = libhello.a
libhello_a_SOURCES = lib/libhello.c lib/libhello.h

dist_doc_DATA = README

But then you’d have to add AC_PROG_RANLIB to the configure.ac calls. My suggestion is that if you want to link things statically and it’s just one or two files, just go for building it twice… it can actually makes it faster to build (one less serialization step) and with the new LTO options it should very well improve the optimization as well.

As you can see, this is really easy when done on the basis… I’ll keep writing a few more posts with easy solutions, and probably next week I’ll integrate all of this in Autotools Mythbuster and update the ebook with an “easy how to” as an appendix.

5 thoughts on “Autotools Mythbuster: who’s afraid of autotools?

  1. Awesome post. It might be interesting to think about creating the equivalent of an SDK around autotools, with a combination of many examples, docs, etc.

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  2. Great introduction. I’ve been using the autotools for some projects and didn’t know about the non GNU projects stuff. Thanks.

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  3. Thanks for your Intro!Your autotools mythbuster is already great (one of the few great autotools resources in the web – and up to date), but easy solutions for common problems are a killer feature – partly because the official documentation strongly focusses on fringe cases…I recently wrote a guide for using autotools to build non-programming projects and without the mythbuster it would have been much harder. If you find stuff in there which you want to use, feel free to use it under any license which at least allows non-commercial redistribution (aka sharing the guide): http://draketo.de/light/eng

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