Not really, it could equally well be a pre-6.3 GCC bug which resulted in outputting bad code. What makes me think it may be CPU rather than GCC is that the seg

Not really, it could equally well be a pre-6.3 GCC bug which resulted in outputting bad code. What makes me think it may be CPU rather than GCC is that the segfault seems to happen nondeterministicly in a single-threaded bash binary running the same shell script with the same arguments each time. Somebody also reported this oddity: Strangely enough, the machine can run mprime for days on end without any trouble. However, an average run of the Glasgow Haskell Compiler's testsuite exhibits a handful of failures (typically segmentation faults). Even stranger, if I run a few mprime threads alongside a run of GHC's testsuite, mprime will itself sometimes crash with a segmentation fault. So you have the same mprime binary which either crashes or not depending on whether GHC tests are running at the same time.