FP save/restore code in ppc32/ppc64 kernels

Anton Blanchard anton at samba.org
Thu Aug 8 23:18:33 EST 2002

> The final thing to look at is what ptrace returns for the MSR. I
> suggested that we should copy in the FE0/FE1 bits out of the thread
> struct (since the MSR_FP, FE0 and FE1 bits will always be zero as
> ptrace does a giveup_fpu just before reading any FP stuff). Paul
> pointed out for completeness we should always set the MSR_FP bit too.

To follow up, this is what we currently see via ptrace:

msr = d032

And here is what we see with the above fixes:

msr = f932

fpemode is a small program from Paulus that changes the FE0 and
FE1 bits via the prctl. This shows:

./fpemode 0 ./msr
msr = f032

./fpemode 1 ./msr
msr = f132

./fpemode 2 ./msr
msr = f832

./fpemode 3 ./msr
msr = f932


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