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Configuration Names

The GNU configure system names all systems using a configuration name. All such names used to be triplets (they may now contain four parts in certain cases), and the term configuration triplet is still seen.

Configuration Name Definition

This is a string of the form cpu-manufacturer-operating_system. In some cases, this is extended to a four part form: cpu-manufacturer-kernel-operating_system.

When using a configuration name in a configure option, it is normally not necessary to specify an entire name. In particular, the manufacturer field is often omitted, leading to strings such as `i386-linux' or `sparc-sunos'. The shell script `config.sub' will translate these shortened strings into the canonical form. autoconf will arrange for `config.sub' to be run automatically when it is needed.

The fields of a configuration name are as follows:

The type of processor. This is typically something like `i386' or `sparc'. More specific variants are used as well, such as `mipsel' to indicate a little endian MIPS processor.
A somewhat freeform field which indicates the manufacturer of the system. This is often simply `unknown'. Other common strings are `pc' for an IBM PC compatible system, or the name of a workstation vendor, such as `sun'.
The name of the operating system which is run on the system. This will be something like `solaris2.5' or `irix6.3'. There is no particular restriction on the version number, and strings like `aix4.1.4.0' are seen. For an embedded system, which has no operating system, this field normally indicates the type of object file format, such as `elf' or `coff'.
This is used mainly for GNU/Linux. A typical GNU/Linux configuration name is `i586-pc-linux-gnulibc1'. In this case the kernel, `linux', is separated from the operating system, `gnulibc1'.

The shell script `config.guess' will normally print the correct configuration name for the system on which it is run. It does by running `uname' and by examining other characteristics of the system.

Because `config.guess' can normally determine the configuration name for a machine, it is normally only necessary to specify a configuration name when building a cross-compiler or when building using a cross-compiler.

Using Configuration Names

A configure script will sometimes have to make a decision based on a configuration name. You will need to do this if you have to compile code differently based on something which can not be tested using a standard autoconf feature test.

It is normally better to test for particular features, rather than to test for a particular system. This is because as Unix evolves, different systems copy features from one another. Even if you need to determine whether the feature is supported based on a configuration name, you should define a macro which describes the feature, rather than defining a macro which describes the particular system you are on.

Testing for a particular system is normally done using a case statement in `configure.in'. The case statement might look something like the following, assuming that `host' is a shell variable holding a canonical configuration name (which will be the case if `configure.in' uses the `AC_CANONICAL_HOST' or `AC_CANONICAL_SYSTEM' macro).

case "${host}" in
i[3456]86-*-linux-gnu*) do something ;;
sparc*-sun-solaris2.[56789]*) do something ;;
sparc*-sun-solaris*) do something ;;
mips*-*-elf*) do something ;;

It is particularly important to use `*' after the operating system field, in order to match the version number which will be generated by `config.guess'.

In most cases you must be careful to match a range of processor types. For most processor families, a trailing `*' suffices, as in `mips*' above. For the i386 family, something along the lines of `i[3456]86' suffices at present. For the m68k family, you will need something like `m68*'. Of course, if you do not need to match on the processor, it is simpler to just replace the entire field by a `*', as in `*-*-irix*'.

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