Autotools is a GNU build system that provides a build-script generator.
By running the platform-independent
./configure script that comes
with the package, you can generate a platform-dependent Makefile.
AutotoolsPackage base class comes with the following phases:
autoreconf- generate the configure script
configure- generate the Makefiles
build- build the package
install- install the package
Most of the time, the
autoreconf phase will do nothing, but if the
package is missing a
autoreconf will generate
one for you.
The other phases run:
$ ./configure --prefix=/path/to/installation/prefix $ make $ make check # optional $ make install $ make installcheck # optional
Of course, you may need to add a few arguments to the
The most important file for an Autotools-based package is the
script. This script is automatically generated by Autotools and generates
the appropriate Makefile when run.
Watch out for fake Autotools packages!
Autotools is a very popular build system, and many people are used to the classic steps to install a package:
$ ./configure $ make $ make install
For this reason, some developers will write their own
scripts that have nothing to do with Autotools. These packages may
not accept the same flags as other Autotools packages, so it is
better to use the
Package base class and create a
custom build system. You can tell if a package
uses Autotools by running
./configure --help and comparing the output
to other known Autotools packages. You should also look for files like:
Packages that don’t use Autotools aren’t likely to have these files.
Build system dependencies¶
Whether or not your package requires Autotools to install depends on
how the source code is distributed. Most of the time, when developers
distribute tarballs, they will already contain the
necessary for installation. If this is the case, your package does not
require any Autotools dependencies.
However, a basic rule of version control systems is to never commit
code that can be generated. The source code repository itself likely
does not have a
configure script. Developers typically write
(or auto-generate) a
configure.ac script that contains configuration
preferences and a
Makefile.am script that contains build instructions.
autoconf is used to convert
automake is used to convert
Makefile.in is used by
configure to generate a platform-dependent
Makefile for you. The following diagram provides a high-level overview
of the process:
configure script is not present in your tarball, you will
need to generate one yourself. Luckily, Spack already has an
phase to do most of the work for you. By default, the
$ libtoolize $ aclocal $ autoreconf --install --verbose --force
All you need to do is add a few Autotools dependencies to the package.
Most stable releases will come with a
configure script, but if you
check out a commit from the
develop branch, you would want to add:
depends_on('autoconf', type='build', when='@develop') depends_on('automake', type='build', when='@develop') depends_on('libtool', type='build', when='@develop') depends_on('m4', type='build', when='@develop')
In some cases, developers might need to distribute a patch that modifies
one of the files used to generate
In this case, these scripts will need to be regenerated. It is
preferable to regenerate these manually using the patch, and then
create a new patch that directly modifies
configure. That way,
Spack can use the secondary patch and additional build system
dependencies aren’t necessary.
If for whatever reason you really want to add the original patch
and tell Spack to regenerate
configure, you can do so using the
force_autoreconf = True
This line tells Spack to wipe away the existing
and generate a new one. If you only need to do this for a single
version, this can be done like so:
@property def force_autoreconf(self): return self.version == Version('1.2.3'):
Finding configure flags¶
Once you have a
configure script present, the next step is to
determine what option flags are available. These flags can be found
$ ./configure --help
configure will display a list of valid flags separated into
some or all of the following sections:
Fine tuning of the installation directories
Some influential environment variables
For the most part, you can ignore all but the last 3 sections. The “Optional Features” sections lists flags that enable/disable features you may be interested in. The “Optional Packages” section often lists dependencies and the flags needed to locate them. The “environment variables” section lists environment variables that the build system uses to pass flags to the compiler and linker.
Addings flags to configure¶
For most of the flags you encounter, you will want a variant to
optionally enable/disable them. You can then optionally pass these
flags to the
configure call by overriding the
function like so:
def configure_args(self): args =  if '+mpi' in self.spec: args.append('--enable-mpi') else: args.append('--disable-mpi') return args
Note that we are explicitly disabling MPI support if it is not requested. This is important, as many Autotools packages will enable options by default if the dependencies are found, and disable them otherwise. We want Spack installations to be as deterministic as possible. If two users install a package with the same variants, the goal is that both installations work the same way. See here and here for a rationale as to why these so-called “automagic” dependencies are a problem.
By default, Autotools installs packages to
/usr. We don’t want this,
so Spack automatically adds
to your list of
configure_args. You don’t need to add this yourself.
You may have noticed that most of the Autotools flags are of the form
--without-baz. Since these flags are so common, Spack provides a
couple of helper functions to make your life easier.
Configure script in a sub-directory¶
Occasionally, developers will hide their source code and
script in a subdirectory like
src. If this happens, Spack won’t
be able to automatically detect the build system properly when running
spack create. You will have to manually change the package base
class and tell Spack where the
configure script resides. You can
do this like so:
configure_directory = 'src'
Building out of source¶
Some packages like
gcc recommend building their software in a
different directory than the source code to prevent build pollution.
This can be done using the
build_directory = 'spack-build'
By default, Spack will build the package in the same directory that
Build and install targets¶
For most Autotools packages, the usual:
$ configure $ make $ make install
is sufficient to install the package. However, if you need to run make with any other targets, for example, to build an optional library or build the documentation, you can add these like so:
build_targets = ['all', 'docs'] install_targets = ['install', 'docs']
Autotools-based packages typically provide unit testing via the
installcheck targets. If you build your software
spack install --test=root, Spack will check for the presence
test target in the Makefile and run
make check for you. After installation, it will check for an
installcheck target and run
make installcheck if it finds one.
For more information on the Autotools build system, see: https://www.gnu.org/software/automake/manual/html_node/Autotools-Introduction.html