[mpich-discuss] Segfault with MPICH 3.2+Clang but not GCC

[Eric A. Borisch]

This might be the struct alignment bug I tracked down a few months ago?
(Alignment attribute in the wrong place.)

On Tuesday, July 26, 2016, Andreas Noack <andreasnoackjensen at gmail.com>
wrote:

> On my El Capitan macbook I get a segfault when running the program below
> with more than a single process but only when MPICH has been compiled with
> Clang.
>
> I don't get that good debug info but here is some of what I got
>
> (lldb) c
> Process 61129 resuming
> Process 61129 stopped
> * thread #1: tid = 0x32c438, 0x00000003119d0432
> libpmpi.12.dylib`MPID_Request_create + 244, queue =
> 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS (code=EXC_I386_GPFLT)
>     frame #0: 0x00000003119d0432 libpmpi.12.dylib`MPID_Request_create + 244
> libpmpi.12.dylib`MPID_Request_create:
> ->  0x3119d0432 <+244>: movaps %xmm0, 0x230(%rax)
>     0x3119d0439 <+251>: movq   $0x0, 0x240(%rax)
>     0x3119d0444 <+262>: movl   %ecx, 0x210(%rax)
>     0x3119d044a <+268>: popq   %rbp
>
> My version of Clang is
>
> Apple LLVM version 7.3.0 (clang-703.0.31)
> Target: x86_64-apple-darwin15.6.0
> Thread model: posix
> InstalledDir: /Library/Developer/CommandLineTools/usr/bin
>
> and the bug has been confirmed by my colleague who is running Linux and
> compiling with Clang 3.8. The program runs fine with OpenMPI+Clang.
>
> #include <mpi.h>
> #include <stdio.h>
> #include <stdlib.h>
>
> int main(int argc, char *argv[])
> {
>     MPI_Init(&argc, &argv);
>
>     MPI_Comm comm = MPI_COMM_WORLD;
>     uint64_t *A, *C;
>     int rnk;
>
>     MPI_Comm_rank(comm, &rnk);
>     A = calloc(1, sizeof(uint64_t));
>     C = calloc(2, sizeof(uint64_t));
>     A[0] = rnk + 1;
>
>     MPI_Allgather(A, 1, MPI_UINT64_T, C, 1, MPI_UINT64_T, comm);
>
>     MPI_Finalize();
>     return 0;
> }
>
>
> Best regards
>
> Andreas Noack
> Postdoctoral Associate
> Computer Science and Artificial Intelligence Laboratory
> Massachusetts Institute of Technology
>
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