Re: [9fans] sysrfork fp bug?

[erik quanstrom <quanstro@quanstro.net>]

On Mon Nov 21 10:34:15 EST 2011, charles.forsyth@gmail.com wrote:
> registers are dead on entry to a function, so there's no point in saving
> particular values, because they won't be used. on an amd64, however,
> the kernel should
> reset the FP-used flag, to cause the preset values to be set in the high FP
> registers if the fork'd process does touch the FP.
>
> On 21 November 2011 07:08, erik quanstrom <quanstro@quanstro.net> wrote:
> > sysrfork() does *not* do a procsave before forking.  thus the
> > floating point registers in the new process are just going to
> > be a copy of whatever was last saved, and perhaps nothing.

so you're suggesting that the forked process always pretend that it
has never used floating point?

anyway, the real bug i'm chasing is on the intel atom i get exactly the same
symptom from stats.  about once a day, i get this sort of diagnostic:
(obviously this isn't from stats)

ladd; 8.fp
8.fp 233351: suicide: sys: fp: stack underflow fppc=0x104c status=0x80c1 pc=0x4922
1

perhaps it's some other bug, but i think i've exhausted all the straightforward
answers.

- erik