[mpich-discuss] MPI_Get on the same memory location

[Nick Radcliffe]

I didn't mean there was a bug in memcpy. I meant the bug was in MPI_Get, which should indeed be checking that pointers are not aliased.

-Nick

________________________________
From: Brian Van Straalen [bvstraalen at lbl.gov]
Sent: Thursday, August 21, 2014 6:21 PM
To: discuss at mpich.org
Subject: Re: [mpich-discuss] MPI_Get on the same memory location

It depends on what version of memcpy you are using.  If you are calling IEEE std 1003.1 2004 then memcpy is defined as

void *memcpy(void *restrict s1, const void *restrict s2, size_t n);

so this form of calling memcpy is illegal and the error from memcpy is correct.

The routine calling memcpy should verify you are not aliased, or incorrect behavior is very likely on newer architectures.  It would be better to check for aliased data before calling memcpy.

Brian Van Straalen


On Aug 21, 2014, at 3:47 PM, Nick Radcliffe <nradclif at cray.com<mailto:nradclif at cray.com>> wrote:

MPIR_Localcopy(357): memcpy arguments alias each other, dst=0x19a5f40
src=0x19a5f40 len=4

It looks like memcpy is doing a check to make sure the source and destination buffers don't overlap. This seems like a bug to me -- when doing an MPI_Get from a buffer to itself, the implementation should probably just do nothing and return.

-Nick

________________________________________
From: alessandro.fanfarillo at gmail.com<mailto:alessandro.fanfarillo at gmail.com> [alessandro.fanfarillo at gmail.com<mailto:alessandro.fanfarillo at gmail.com>] on behalf of Alessandro Fanfarillo [fanfarillo at ing.uniroma2.it<mailto:fanfarillo at ing.uniroma2.it>]
Sent: Thursday, August 21, 2014 5:25 PM
To: discuss at mpich.org<mailto:discuss at mpich.org>
Subject: [mpich-discuss] MPI_Get on the same memory location

Dear all,

I'm having the following error:

Fatal error in MPI_Get: Internal MPI error!, error stack:
MPI_Get(156).......: MPI_Get(origin_addr=0x19a5f40, origin_count=4,
MPI_BYTE, target_rank=0, target_disp=0, target_count=4, MPI_BYTE,
win=0xa0000000) failed
MPIDI_Get(247).....:
MPIR_Localcopy(357): memcpy arguments alias each other, dst=0x19a5f40
src=0x19a5f40 len=4

if I try to execute MPI_Get on the same memory location on a shared
memory machine (my laptop).

I cannot find anything in the standard that denies it for the one-sided.

Running with OpenMPI everything works fine.

Is it a bug or I missed something in the standard?

Thanks.

Alessandro

--

Alessandro Fanfarillo
Dip. di Ingegneria Civile ed Ingegneria Informatica
Università di Roma "Tor Vergata"
NCAR Office: +1 (303) 497-2442
Tel: +39-06-7259 7719
_______________________________________________
discuss mailing list     discuss at mpich.org<mailto:discuss at mpich.org>
To manage subscription options or unsubscribe:
https://lists.mpich.org/mailman/listinfo/discuss
_______________________________________________
discuss mailing list     discuss at mpich.org
To manage subscription options or unsubscribe:
https://lists.mpich.org/mailman/listinfo/discuss




-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mpich.org/pipermail/discuss/attachments/20140822/28eb3dae/attachment.html>