Is it possible for implementations to prevent the user from attaching memory to a dynamic window that would cause this overflow? For example, MPI_Win_attach could fail if the base+size indicated that addresses could be used that were greater than the capacity of MPI_Aint? That seems like a way better option than breaking backwards compatibility or attaching all sorts of caveats to the use of MPI_Aint that a user is never going to remember. Jeff On Tue, Aug 28, 2012 at 10:00 AM, Jim Dinan <[email protected]> wrote:

Sorry, this wasn't too clear. A more detailed explanation of the problem is:

Passing a dynamic window displacement to an RMA operation currently requires the user to put an address (which is an unsigned quantity) into an MPI_Aint (which is signed). With the current spec, passing a negative displacement to an RMA operation is an error. When interpreted as signed integers, dynamic window displacements (i.e. addresses) can be negative because the unsigned to signed conversion effectively overflows.

~Jim.

On 8/28/12 9:49 AM, Jeff Hammond wrote:

...

I do not understand this:

"displacements associated with dynamic windows are addresses (unsigned) and can range into the space of negative integers"

How can they "range into the space of negative integers" if they are unsigned?

Jeff

On Tue, Aug 28, 2012 at 9:46 AM, Jim Dinan <[email protected]> wrote:

...

Hi All,

Currently, target displacements in put/get/acc/etc are defined to be non-negative integers of type, MPI_Aint. MPI_Aint is defined to be a signed integer. However, displacements associated with dynamic windows are addresses (unsigned) and can range into the space of negative integers.

It seems like the least impact change would be to add a special case that the displacement argument will be interpreted as unsigned for dynamic windows. Changing the interface to take an 'unsigned MPI_Aint' would be the most clear (and preserve the existing and intended new semantics), but would break backward compatibility.

Interested to hear your thoughts.

~Jim.

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-- Jeff Hammond Argonne Leadership Computing Facility University of Chicago Computation Institute [email protected] / (630) 252-5381 http://www.linkedin.com/in/jeffhammond https://wiki.alcf.anl.gov/parts/index.php/User:Jhammond