How Configuration Should Work

Each GNU distribution should come with a shell script named configure. This script is given arguments which describe the kind of machine and system you want to compile the program for.

The configure script must record the configuration options so that they affect compilation.

One way to do this is to make a link from a standard name such as `config.h' to the proper configuration file for the chosen system. If you use this technique, the distribution should not contain a file named `config.h'. This is so that people won't be able to build the program without configuring it first.

Another thing that configure can do is to edit the Makefile. If you do this, the distribution should not contain a file named `Makefile'. Instead, include a file `Makefile.in' which contains the input used for editing. Once again, this is so that people won't be able to build the program without configuring it first.

If configure does write the `Makefile', then `Makefile' should have a target named `Makefile' which causes configure to be rerun, setting up the same configuration that was set up last time. The files that configure reads should be listed as dependencies of `Makefile'.

All the files which are output from the configure script should have comments at the beginning explaining that they were generated automatically using configure. This is so that users won't think of trying to edit them by hand.

The configure script should write a file named `config.status' which describes which configuration options were specified when the program was last configured. This file should be a shell script which, if run, will recreate the same configuration.

The configure script should accept an option of the form `--srcdir=dirname' to specify the directory where sources are found (if it is not the current directory). This makes it possible to build the program in a separate directory, so that the actual source directory is not modified.

If the user does not specify `--srcdir', then configure should check both `.' and `..' to see if it can find the sources. If it finds the sources in one of these places, it should use them from there. Otherwise, it should report that it cannot find the sources, and should exit with nonzero status.

Usually the easy way to support `--srcdir' is by editing a definition of VPATH into the Makefile. Some rules may need to refer explicitly to the specified source directory. To make this possible, configure can add to the Makefile a variable named srcdir whose value is precisely the specified directory.

The configure script should also take an argument which specifies the type of system to build the program for. This argument should look like this:

cpu-company-system

For example, a Sun 3 might be `m68k-sun-sunos4.1'.

The configure script needs to be able to decode all plausible alternatives for how to describe a machine. Thus, `sun3-sunos4.1' would be a valid alias. So would `sun3-bsd4.2', since SunOS is basically BSD and no other BSD system is used on a Sun. For many programs, `vax-dec-ultrix' would be an alias for `vax-dec-bsd', simply because the differences between Ultrix and BSD are rarely noticeable, but a few programs might need to distinguish them.

There is a shell script called `config.sub' that you can use as a subroutine to validate system types and canonicalize aliases.

Other options are permitted to specify in more detail the software or hardware are present on the machine:

`--with-package'

The package package will be installed, so configure this package to work with package. Possible values of package include `x', `gnu-as' (or `gas'), `gnu-ld', `gnu-libc', and `gdb'.

`--nfp'

The target machine has no floating point processor.

`--gas'

The target machine assembler is GAS, the GNU assembler. This is obsolete; use `--with-gnu-as' instead.

`--x'

The target machine has the X Window system installed. This is obsolete; use `--with-x' instead.

All configure scripts should accept all of these "detail" options, whether or not they make any difference to the particular package at hand. In particular, they should accept any option that starts with `--with-'. This is so users will be able to configure an entire GNU source tree at once with a single set of options.

Packages that perform part of compilation may support cross-compilation. In such a case, the host and target machines for the program may be different. The configure script should normally treat the specified type of system as both the host and the target, thus producing a program which works for the same type of machine that it runs on.

The way to build a cross-compiler, cross-assembler, or what have you, is to specify the option `--host=hosttype' when running configure. This specifies the host system without changing the type of target system. The syntax for hosttype is the same as described above.

Programs for which cross-operation is not meaningful need not accept the `--host' option, because configuring an entire operating system for cross-operation is not a meaningful thing.

Some programs have ways of configuring themselves automatically. If your program is set up to do this, your configure script can simply ignore most of its arguments.