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SubjectRe: Question: Using floating point in the kernel
Date
Hi
The real issue is that if you use MMX or FP state, the kernel _must_ save
and restore the original state other wise user programs will see corruption.
We all know this too well since redhat's 6.1 (I think) kernel had this
optimized MMX functions that _screwed_ up user programs. The fact is... it
is tricky to save and restore state (device not available and all).
The basic kernel itself does not provide support for kernel code to use
these registers. If some device drivers or some modifications to the kernel
are using it.. then I hope they have the save/restore path right

- Lyle

----- Original Message -----
From: "Ricky Beam" <jfbeam@bluetopia.net>
To: "Lyle Coder" <x_coder@hotmail.com>
Cc: <linux-kernel@vger.kernel.org>
Sent: Wednesday, September 20, 2000 9:13 PM
Subject: Re: Question: Using floating point in the kernel


> On Wed, 20 Sep 2000, Lyle Coder wrote:
> >You cannot use MMX registers in the kernel either, since the kernel
doesen't
> >save and restore FX state (fxsave, fxrstor) either (just like
> >(fsave/frstor).
>
> You might want to tell the software RAID maintainers that... RAID5 CRC
> calculations can be done with MMX. (I'm sure they save and restore the
> FPU state, however. Yes, the save/restore cycle is _damned_ expensive.)
>
> --Ricky
>
>
>
-
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