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Subject: [OMPI devel] MPI_Recv pre memory checks
From: Prasadcse Perera (prasadcse0_at_[hidden])
Date: 2009-07-07 16:35:26


Hi,
I'm new to open mpi and I'm currently studying the code and writing my own
simple parallel test programs. I wrote a simple program to send and receive
a character buffer using
MPI::COMM_WORLD.Send, MPI::COMM_WORLD.Recv function calls. After playing
with some stupid parameters I could observe the following:
When I passed a buffer of length say 10, and set the receiving count to say
100, I could see that even the sending buffer (around 30 - 40) exceeds the
receiving buffer, the characters were successfully copied. And at some
points, after increasing these values, the receiving buffer started to show
some garbage characters due to usage of unassigned memory. I took a look at
the implementation and saw that opal_memchecker_base_isaddressable is used
to check if the buffer is addressible and OMPI_WANT_MEMCHECKER is used as a
flag too. But unfortunately I couldnt find the impl of
opal_memchecker_base_isaddressable.

So my questions is, Do we have to set OMPI_WANT_MEMCHECKER in order to
verify the recieving buffer internally? if it is, then shouldn't it be
always done ?
I know its a stupid thing to burden these functions to do this since its up
to the programmer to make the sanity checks or make sure not to feed up with
wrong parameters, yet since it leaves to dangerous memory allocation/usage,
doesn't it serve as a security threat ?

Pardon me if I misunderstood things since I'm still learning and testing
with these codes...

Thanks,
Prasad.

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