Passing modified options to nested configure

[Christian Rössel]

Consider following cross-compile scenario where I want to build programs
and libraries for the host (backend) as well as for the build
(frontend). There are programs/libraries that should be build for the
frontend only, for the backend only and for the frontend as well as for
the backend. I issue following configure command

./configure --build=powerpc64-unknown-linux-gnu
--host=powerpc-bgp-linux-gnu CC=bgxlc CC_FOR_BUILD=xlc

which calls two configures in specific subdirs defined via
AC_CONFIG_SUBDIRS:

if test "x${cross_compiling}" = xyes; then
   AC_CONFIG_SUBDIRS([build-cross-frontend build-cross-backend])
   SUBDIRS_TO_USE="build-cross-frontend build-cross-backend"
else
   AC_CONFIG_SUBDIRS([build-nocross])
   SUBDIRS_TO_USE="build-nocross"
fi

Let's concentrate on the frontend case. I put following commands into
build-cross-frontend/configure.ac in order to use the correct compiler
and to disable cross-compiling mode.

host_alias=${build_alias}
host=${build}
cross_compiling=no
CC=${CC_FOR_BUILD}

So far, this works (BTW if there are other/better ways to accomplish
this, please tell me). Now there is a new requirement. We need to
incorporate a third party autotools-enabled project that should be build
only for the frontend. If I add

AC_CONFIG_SUBDIRS([new-third-party-project])

to build-cross-frontend/configure.ac, then the third-party configure is
called with all the options build-cross-frontend/configure was called,
especially --build=powerpc64-unknown-linux-gnu
--host=powerpc-bgp-linux-gnu CC=bgxlc CC_FOR_BUILD=xlc.

The third-party configure switches to cross-compiling mode and uses the
wrong compiler, hm, that's not good.

The question is, is there a way to override/modify the options that
build-cross-frontend/configure passes to
new-third-party-project/configure? In particular I need to override CC
and --host. Can this be done without modifying the third-party configure.ac?

Thanks,
Christian


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