Linux Tools Project/Autotools/User Guide
The Autotools plug-in for Eclipse extends the CDT (C/C++ Development Tools) to add support for maintaining and building C/C++ projects that use GNU Autotools.
The GNU Autotools are a set of tools used to make a project portable to multiple systems or build environments. The tools aid the developer to create a configure script which is meant to be invoked prior to performing the build. The configure script may perform tests such as testing the current platform, the OS, what is locally installed, or any number of things. Parameters can be passed as well to provide information that is not calculable (e.g. what will be the target platform the project will be run on). Results of tests and parameters are used to create the Makefiles for the build or in some cases, additional files such as header files or code sequences.
What gets tested is fully controllable by the developer by way of special input files which are fed to the Autotools. Typically, the most commonly used Autotools are 'autoconf', 'automake', and 'aclocal'. The 'autoconf' tool takes a 'configure.in' or 'configure.ac' input file and creates the 'configure' script previously discussed. It is possible to have multiple configure scripts in various subdirectories, but a project should be designed so there is one top-level configure script that calls any lower-level ones automatically.
The 'automake' tool takes a 'Makefile.am' input file and creates a 'Makefile.in' file which is used at configuration time by the configure script as a template for creating a Makefile. Each Makefile will have its own corresponding Makefile.in file. There may be if/else logic used to determine what ends up in the Makefile or there may be requests to directly substitute variables calculated in the configure step.
The 'aclocal' tool creates a repository of macros that are specified directly or indirectly in the 'autoconf' input files. Such macros are provided to perform commonly used tests or actions (e.g. test that a certain header file exists or find the C compiler). The macros are written in a language called m4 and the developer is free to create their own macros to add to the repository.
Creating an Autotools Project
There a number of ways to create an Autotools project. The first method is through the CDT C and C++ Project wizards which can be activated from the File -> New -> C Project and File -> New -> C++ Project menu items, respectively, which are available while in the C/C++ Perspective. These two wizards can also be located by clicking on the File -> New -> Project... menu item and then opening the C/C++ folder found there.
Looking at the C Wizard, we see that there is a GNU Autotools category.
Opening the category, there are two choices: Empty Project or Hello World Ansi C Project. The Empty Project means that no files will be supplied to the new project while the Hello World project will supply a sample hello world program that uses Autotools for configuring the build. The C++ Project Wizard also has the same GNU Autotools category and two project templates: an Empty Project and a Hello World C++ sample program. If you are creating the project from scratch, it is recommended that you use the Hello World sample project and make modifications. Otherwise, you will need to create a configure script for the Autotools plug-in to invoke at build time or provide a Makefile so the configuration step does not fail.
The C and C++ Wizards can also be used when importing an existing Autotools project. For example, when importing a project from CVS using File -> Import... -> CVS -> you are given the choice to "Check out as a project configured by the new project wizard".
From the New Project menu, open the C/C++ category and choose either a C Project or C++ Project, depending on the type of project being imported. If the code is both C and C++, choose C++ Project.
This will bring up the C Project Wizard as displayed earlier. In this case, choose the Empty Project from the GNU Autotools category.
Another method to create an Autotools project is to convert an existing project to an Autotools project. For example, if we import a project from SVN or CVS and do not configure using the new project wizard, the project will simply be downloaded into the workspace. At this point, it cannot be built or access various tools from the CDT.
To convert it, select the project in the Project Explorere then open the File -> New -> Convert to C/C++ Project menu item as found in the C/C++ Perspective. If in another perspective, this same wizard can be found by selecting File -> New -> Project... -> C/C++ -> Convert to a C/C++ Project. This brings up the C/C++ Conversion wizard.
Note how there is a set of projects that are candidates for conversion. These are any projects that are not already C or C++ projects. A C or C++ project includes regular CDT Managed Make and Makefile projects. Also note that the project you selected is already checked off when the wizard opens.
There is a choice of C or C++ project and a set of project types to choose from. Select the GNU Autotools category and this will convert the project to an Autotools project. Once converted, this project will not show up as a candidate project in the conversion wizard.
The final way to create an Autotools project is to use the Autotools Conversion wizard. This wizard allows one to convert from another form of C/C++ project to an Autotools project. Again, you need to first select the project you wish to convert. After selecting, go to File -> New -> Other -> C/C++, open the category, select "Convert to a C/C++ Autotools Project" and hit the Next button.
This brings up the following dialog:
Again there are candidates for conversion. This list contains all projects that are not currently C or C++ Autotools projects. You are given the choice of C or C++ as with the other conversion wizard. Hitting the Finish button is all that is needed, but if you hit the Next button and continue on you can select referenced projects, if desired.
Prior to running a build, the Autotools plug-in runs the configure script. Parameters to be passed to configure may be entered via the Project -> Properties -> Autotools -> Configure Settings UI shown below:
In some cases, a project may choose not to invoke the Autotools ahead of time and instead require this be done prior to configuration. The input files that are fed to the Autotools are provided, but the output of the Autotools are not. This may be done to lower the download size and additionally to avoid having to constantly regenerate the output files as the Autotools are updated. In such cases, an autogen.sh script may be provided which is simply a script that runs the various Autotools required. This script may or may not run the configure script at the end. Alternatively, there is also the autoreconf tool which can be invoked to recursively run through the source tree and run all Autotools where the input files are newer than the output files (this includes the case where no output file is present). Any options required when invoking the Autotools can be encoded within the input files themselves.
The following defines how the Autotools plug-in performs a configure
As mentioned, a project using Autotools requires a step prior to building known as configuration. There are multiple alternatives as to what files exist in the project before-hand and how Autotools will perform the configuration. The following documents various set-ups and what Autotools does.
- A config.status file exists
- This file indicates a configuration has already been performed. If the file already exists in the build directory, it is simply run with a --recheck option
- A configure script exists
- In this case, the configure script is run with any configuration options specified in the project properties.
- An autogen script exists
- In this case, the autogen.sh script is run and following that, a check is made to see if it has run configure. If not, configure is run automatically.
- A Makefile.cvs file exists
- In this case, make is performed for this file. If a configure script is created and not run by invoking make, it is run automatically.
- autoreconf -i is performed
- The autoreconf -i will invoke autotools for all input files that are older than their output targets or if their output targets do not exist. If the configure script is generated, it is run automatically
If after all of this, the top-level Makefile is not created, an error is generated and building stops. The entire configuration step is performed by a special builder that is added by the Autotools plug-in. A separate console is used for the output of all tools runs by this builder. To access this special console, click the little t.v. icons in the Console tab as follows:
Note that the configure console output is per project and shows configuration output for the last build of the project. It is not saved between Eclipse sessions.