1. A computer implemented method of transforming a source computer program to form a transformed computer program for distributed execution upon a plurality of execution mechanisms of an asymmetric multiprocessing apparatus having an asymmetric memory hierarchy including a plurality of memories, said method comprising the steps of: receiving as an input variable an at least partial architectural description of said asymmetric multiprocessor apparatus including data identifying: (i) said plurality of execution mechanisms; (ii) said plurality of memories; and (iii) a communication path topology indicating which of said plurality of memories are accessible by which of said execution mechanisms; and in dependence upon said at least partial architectural description, adding mapping support to said source computer program to adapt said source computer program for execution upon said asymmetric multiprocessing apparatus as part of forming said transformed computer program, wherein said mapping support includes an exact execution mechanism specifier specifying one of said plurality of execution mechanisms to be used to execute a portion of said transformed computer program associated with said exact execution mechanism specifier.