Potential kernel problem with MMX chips?

Chris Evans (chris@ferret.lmh.ox.ac.uk)
Thu, 7 Aug 1997 12:21:59 +0100 (BST)


I've just dropped a P200MMX Intel chip in my home box. Nice and quick, but
I've hit a nasty problem;

The first time I try and run squake after boot, the game fires up fine,
and plays well. However, once you exit the process, ALL subsequent
attempts to play the game result in a seg fault. This is 100% repeatable
after every boot. I am sure it did not used to happen with my P100.

Hazarding a guess, perhaps this is a MMX mode vs. FP mode thing? I seem to
recall MMX chips toggle between the two modes. Perhaps the first
invocation of quake (which uses heavy FP) somehow manages to shove the
chip into the wrong mode upon exit, but assumes that upon process start,
the chip is in FP mode? If so perhaps it is the responsibility of the
kernel to ensure that the processor is in the same mode the process thinks
it is..?

After running quake, I've observed another program having FP trouble,
exiting with a floating point exception.

Any thoughts?