[Pkg-cmake-team] Bug#943312: Bug#943312: cmake: FindMPI.cmake does not work during cross compilation

[Felix Geyer]

Hi Helmut,

On 23.10.19 09:47, Helmut Grohne wrote:
> Package: cmake
> Version: 3.13.4-1
> Tags: patch upstream
> User: debian-cross at lists.debian.org
> Usertags: ftcbfs
> Control: affects -1 + src:flann src:hyphy src:liggghts src:sopt
> 
> FindMPI.cmake uses compiler wrappers such as mpicc to discover the
> relevant compiler and linker flags. During cross compilation, these
> compiler wrappers do not work and they will not be supported on Debian.
> Beyond breaking cross compilation, you cannot easily combine multiple
> compiler wrappers (e.g. ccache/distcc/mpicc). It is best to avoid
> compiler wrappers entirely and for MPI, this is well supported as all
> major implementations ship pkg-config files since ages. I am asking to
> stop using mpicc and switch over to pkg-config.
> 
> Unfortunately, FindMPI.cmake exposes MPI_*_COMPILER and a number of
> downstreams use these wrappers that cannot be used during cross
> compilation. Every downstream that wants to be cross buildable must stop
> using them and I've filed a relevant patch for liggghts. Avoiding
> MPI_*_COMPILER is easy enough in the majority of cases, because
> FindMPI.cmake also provides the relevant flags in via other variables.
> Still, we must maintain backwards compatibility and thus continue
> supplying MPI_*_COMPILER when it is available (i.e. during native
> compilation).
> 
> The attached patch thus tries the wrappers first before falling back to
> pkg-config. I've tested it with flann, hyphy, liggghts and sopt. Of
> these, flann and sopt are fixed by this patch. hyphy and liggghts need
> further patches, which are submitted separately. Please consider
> applying the attached patch.
> 
> Helmut

Thanks for providing a patch. Have you submitted this upstream?
I imagine there isn't anything Debian-specific there?

Cheers,
Felix