The following macros make the system type available to configure scripts.
The variables ‘build_alias’, ‘host_alias’, and
‘target_alias’ are always exactly the arguments of --build,
--host, and --target; in particular, they are left empty
if the user did not use them, even if the corresponding
AC_CANONICAL macro was run. Any configure script may use these
variables anywhere. These are the variables that should be used when in
interaction with the user.
If you need to recognize some special environments based on their system type, run the following macros to get canonical system names. These variables are not set before the macro call.
If you use these macros, you must distribute config.guess and
config.sub along with your source code. See Output, for
information about the
AC_CONFIG_AUX_DIR macro which you can use
to control in which directory configure looks for those scripts.
If --build was specified, then
buildis the canonicalization of
build_aliasby config.sub, otherwise it is determined by the shell script config.guess.
If --host was specified, then
hostis the canonicalization of
host_aliasby config.sub, otherwise it defaults to
If --target was specified, then
targetis the canonicalization of
target_aliasby config.sub, otherwise it defaults to
Note that there can be artifacts due to the backward compatibility code. See Hosts and Cross-Compilation, for more.