Hi Brian,<br><br>you could help before with a Segfault in the BlueGene MPI layer (in scatterv). Do you consider the below described segfault a bug in the MPI layer or in Gromacs?<br><br>Roland<br><br><div class="gmail_quote">
---------- Forwarded message ----------<br>From: <b class="gmail_sendername">Mark Abraham</b> <span dir="ltr"><<a href="mailto:Mark.Abraham@anu.edu.au">Mark.Abraham@anu.edu.au</a>></span><br>Date: Sun, Nov 22, 2009 at 10:11 PM<br>
Subject: [gmx-developers] broadcast of zero-length arrays<br>To: Gromacs Developers <<a href="mailto:gmx-developers@gromacs.org">gmx-developers@gromacs.org</a>><br><br><br>Hi,<br>
<br>
During src/gmxlib/mvdata.c bc_grpopts(), my BlueGene/L segfaults during the broadcasts of the QMMM stuff. The lines that break are attempts to broadcast arrays of zero length. Adding a check for non-zero length into the definition of nblock_bc fixes the problem. Presumably a null pointer is being dereferenced inside the MPI library.<br>
<br>
I'm not sure whether this observation is indicative of (this version of) IBM's MPI library not having implemented the full standard, the standard not specifying behaviour in this case, or GROMACS not being sufficiently defensive. I haven't found anything useful in the MPI documentation I have to hand. You could argue cases either way - the implementors of the library want to avoid such checks to speed performance, and the users of the library expect it either to take care of such housekeeping for them, or not dereference pointers unnecessarily (think buffering)...<br>
<br>
Does anyone know what expected behaviour is here?<br>
<br>
Cheers,<br>
<br>
Mark<br><font color="#888888">
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