FP save/restore code in ppc32/ppc64 kernels

Peter Bergner bergner at borg.umn.edu
Thu Aug 8 02:23:02 EST 2002


Can you describe (if you know/remember since a lot of this code has Cort's name
on it) how the FP save/restore code is supposed to work?  I'm wondering why we're
clearing the MSR_FE{0,1} bits along with the MSR_FP bit.  Is there a reason why
they must be cleared when we clear the MSR_FP bit?

The reason I ask is that someone was running some userland app that explicitly
set the fpscr (using asm) and he got an FP exception even though gdb showed
his MSR_FE{0,1} bits to be zero.  This got me looking at the code which seems
to be inherited old ppc32 code.  I noticed that you've updated the ppc32, so
before I update our ppc64 code, I'd like to understand more about how this is
all supposed to work.


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