The polymorphic C front-end (i.e. macros) can be bypassed by talking a pointer to the underlying function [1]. This is the desired behavior for backward compatibility. I agree that this could be surprising to users and it must be clearly documented. In the case where the user is not bypassing the C polymorphic front-end and the compiler does not support _Generic, we can either detect or prevent silent truncation using one of the approaches that I posted. ~Jim. [1] The C preprocessor only invokes a function-like macro if the macro name is followed by (. So, &MPI_Send takes the pointer of the function even though there is a function-like macro with the same name. On Thu, Aug 8, 2019 at 6:51 AM HOLMES Daniel <[email protected]> wrote:
Hi Jim,
Are we sure the function pointer “worked" in your example? It silently truncated the large value, because the function pointer bypasses the redirection macro.
Cheers, Dan. — Dr Daniel Holmes PhD Architect (HPC Research) [email protected] Phone: +44 (0) 131 651 3465 Mobile: +44 (0) 7940 524 088 Address: Room 2.09, Bayes Centre, 47 Potterrow, Central Area, Edinburgh, EH8 9BT — The University of Edinburgh is a charitable body, registered in Scotland, with registration number SC005336. —
On 7 Aug 2019, at 22:00, Jim Dinan via mpi-forum < [email protected]> wrote:
Even simpler than this, we could just forward all calls to the MPI_Count interface (see below). The int count argument should type convert to MPI_Count without issue. Note that it still needs to be a function-like macro so that function pointers work.
Don't give up yet! :D
~Jim.
#include <stdio.h>
typedef int MPI_Datatype; typedef int MPI_Comm;
int MPI_Send(const void* buf, int count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) { printf("MPI_Send(count = %d)\n", count); return 0; }
int MPI_Send_x(const void* buf, long long count, MPI_Datatype datatype, int dest, int tag, MPI_Comm comm) { printf("MPI_Send_x(count = %lld)\n", count); return 0; }
#define MPI_Send(buf, count, datatype, dest, tag, comm) MPI_Send_x(buf, count, datatype, dest, tag, comm)
int main(int argc, char *argv[]) { /* 8589934592LL == 2^33 */ long long i = 8589934592LL + 11; int ret; int (*snd_ptr)(const void*, int, MPI_Datatype, int, int, MPI_Comm) = &MPI_Send; ret = MPI_Send(NULL, i, 0, 0, 0, 0); ret = MPI_Send(NULL, 5, 0, 0, 0, 0); ret = (*snd_ptr)(NULL, i, 0, 0, 0, 0); ret = (*snd_ptr)(NULL, 5, 0, 0, 0, 0); return 0;
}
MPI_Send_x(count = 8589934603) MPI_Send_x(count = 5) MPI_Send(count = 11)
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