[mpich-devel] supporting Fortran INTEGER when it's 64b

[William Gropp]

I know of no plans to fix the underlying problems.  buildiface can be told to generate code for the case where MPI_Fint is different from int, but this doesn’t address the use of the C interface from within the Fortran wrappers.

Bill

On May 20, 2015, at 3:43 AM, Jeff Hammond <jeff.science at gmail.com> wrote:

> I'm not aware of any place in the standard where it says that
> implementations do not have to support the full 64b range of a Fortran
> INTEGER when the compiler ordains that INTEGER is that size.  MPICH is
> at best dangerous when a Fortran INTEGER is larger than a C int.
> 
> The tail of mpif_h/sendf.c shows this problem:
> 
> /* Prototypes for the Fortran interfaces */
> #include "fproto.h"
> FORT_DLL_SPEC void FORT_CALL mpi_send_ ( void*v1, MPI_Fint *v2,
> MPI_Fint *v3, MPI_Fint *v4, MPI_Fint *v5, MPI_Fint *v6, MPI_Fint *ierr
> ){
>    *ierr = MPI_Send( v1, (int)*v2, (MPI_Datatype)(*v3), (int)*v4,
> (int)*v5, (MPI_Comm)(*v6) );
> }
> 
> The origin of the issue appears to be the unsafe cast generated by
> mpif_h/buildiface:
> 
> sub fint2int_inout_decl {
>    my $count = $_[0];
>    if ($within_fint) {
>        print $OUTFD "    int l$count = (int)*v$count;\n";
>    }
> 
> This is not just academic for me.  I know that unsafe down-casting
> inside of MPI breaks multiple quantum chemistry applications.  And
> while I wrote BigMPI in part to address this issue, users would be
> much happier if MPICH and its derivatives were sufficient.
> 
> Is there any plan to address this?  It appears to require lots of code
> changes.  For example, one could add e.g. MPIR_Send that takes
> mpid_size_t (or similar) counts and call that (instead of MPI_Send)
> from Fortran, as well as map C MPI_Send to it.  Of course MPID_Send
> would also have to convert to mpid_size_t and so forth across all the
> routines and down the stack.
> 
> Comments?
> 
> Thanks,
> 
> Jeff
> 
> -- 
> Jeff Hammond
> jeff.science at gmail.com
> http://jeffhammond.github.io/
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