Re: PREEMPT

[john cooper <john.cooper@timesys.com>]

Ralf Baechle wrote:
> On Thu, Oct 06, 2005 at 02:52:22PM -0400, Greg Weeks wrote:
>
>
> > I'd remembered some problems ages ago, but had thought they'd been 
> > fixed. John was just picking my brain about it so I thought I'd ask to 
> > be sure.
>
> The problems I recall were all related to being preempted just while
> fiddling with the hardware FPU - can't happen on the fpu-less 4Kc.
> Another issue fixesd recently even though more cosmetic were a bunch
> of global variables.
The code base I'm dealing with is a 2.6.13 derivative
with PREEMPT_RT support.  Looks like the problem was
due to PREEMPT_RT confusing fpu_emulator_cop1Handler()
resulting in a SIGBUS nailing the associated task.

I have it sort of working for soft FPU but expect it
requires some attention to safely access a HW FPU where
emulation assistance is needed.

-john

--
john.cooper@timesys.com