Yes, I knew that mpicc isn't building its own compiler from the ground up. I reckoned though that maybe since the --target option in normal builds came closest to expressing the result I'm trying to achieve, maybe that's what you needed to do. I'd tried the --host option as well before but that errored when I tried to run mpicc.

What steps are needed to configure for Fortran? I tried setting several CROSS_F77_xxx flags but then ended up with the uninformative error during configure:

configure: error: '' is empty.

C cross-compilers would be adequate for early testing but the platform we are building is going to amongst other things going to be compiling and linking source files provided by external users, many of whom will undoubtely be using Fortran so in the long run it's going to be essential to have that cross-compiler available as well.



On Fri, Jun 2, 2017 at 4:15 PM, Kenneth Raffenetti <raffenet@mcs.anl.gov> wrote:
Hi Alex,

One thing to understand is that MPICH does not actually build compiler tools, so the --target option is not used. mpicc and friends are only wrapper scripts. Here is how I was able to configure/build MPICH on my laptop (Ubuntu 16.10) to cross-compile binaries arm-linux-gnueabi. Fortran is disabled since it requires additional steps.

./configure --build=x86_64-linux-gnu --host=arm-linux-gnueabi CC=/usr/bin/arm-linux-gnueabi-gcc-6 CXX=/usr/bin/arm-linux-gnueabi-g++-6 --disable-fortran

Ken

On 06/01/2017 10:22 AM, Alexander Rast wrote:
I assume you mean from the build intended for the ARM targets. In any case here they are.

On Thu, Jun 1, 2017 at 4:04 PM, Kenneth Raffenetti <raffenet@mcs.anl.gov <mailto:raffenet@mcs.anl.gov>> wrote:

    Hi Alex,

    I don't have experience with this type of build, but I can try to
    replicate it on a system here internally. Can you provide a couple
    of artifacts first?

    1. the config.log file from the top-level build directory
    2. the output of 'mpicc -show' from the installed build

    Thanks,
    Ken

    On 06/01/2017 10:00 AM, Alexander Rast wrote:

        All,

        I'm trying to build MPICH so that I can cross-compile MPI
        applications on my x86_64-linux system to run on an arm-linux
        machine. I want to emphasise that this is different from
        building a native ARM MPICH install that runs on ARM itself; the
        intent is that an x86-linux 'root' process compiles ARM MPI
        application binaries and distributes them to the ARM cores. I
        have a separate build for compiling the MPI binaries that lie on
        the root x86 system. I tried running configure with
        --build=x86_64-linux-gnu --host=x86_64-linux-gnu
        --target=arm-linux-gnueabi, but that didn't give me what I need.
        If, meanwhile, I try to run mpicc off the native x86 build (the
        MPICH installation used for running MPI applications on the root
        x86 system) it complains that the target type specified in the
        makefile (CFLAGS = -march=armv8-a -mtune=cortex-a53) isn't
        supported. It's not clear how one creates this sort of 'hybrid'
        build, running on one platform, compiling MPI applications for
        another.


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