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From: George Bosilca (bosilca_at_[hidden])
Date: 2007-08-16 11:27:12

Well, finally someone discovered it :) I know about this problem for
quite a while now, it pop up during our own valgrind test of the
collective module in Open MPI. However, it never create any problems
in the applications, at least not as far as I know. That's why I'm
reticent to replace the memcpy by a memmove (where the arguments are
allowed to overlap) as there is a performance penalty.


On Aug 16, 2007, at 9:31 AM, Allen Barnett wrote:

> Hi:
> I was running my OpenMPI 1.2.3 application under Valgrind and I
> observed
> this error message:
> ==14322== Source and destination overlap in memcpy(0x41F5BD0,
> 0x41F5BD8,
> 16)
> ==14322== at 0x49070AD: memcpy (mc_replace_strmem.c:116)
> ==14322== by 0x4A45CF4: ompi_ddt_copy_content_same_ddt
> (in /home/scratch/DMP/RHEL4-GCC4/lib/
> ==14322== by 0x7A6C386: ompi_coll_tuned_allgather_intra_bruck
> (in /home/scratch/DMP/RHEL4-GCC4/lib/openmpi/
> ==14322== by 0x4A29FFE: ompi_comm_split
> (in /home/scratch/DMP/RHEL4-GCC4/lib/
> ==14322== by 0x4A4E322: MPI_Comm_split
> (in /home/scratch/DMP/RHEL4-GCC4/lib/
> ==14322== by 0x400A26: main
> (in /home/scratch/DMP/severian_tests/ompi/a.out)
> Attached is a reduced code example. I run it like:
> mpirun -np 3 valgrind ./a.out
> I only see this error if there are an odd number of processes! I don't
> know if this is really a problem or not, though. My OMPI application
> seems to work OK. However, the linux man page for memcpy says
> overlapping range copying is undefined.
> Other details: x86_64 (one box, two dual-core opterons), RHEL 4.5,
> OpenMPI-1.2.3 compiled with the RHEL-supplied GCC 4 (gcc4 (GCC) 4.1.1
> 20070105 (Red Hat 4.1.1-53)), valgrind 3.2.3.
> Thanks,
> Allen
> --
> Allen Barnett
> Transpire, Inc.
> e-mail: allen_at_[hidden]
> Ph: 518-887-2930
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