Messages in this thread |  | | From | "Lyle Coder" <> | Subject | Re: Question: Using floating point in the kernel | Date | Wed, 20 Sep 2000 22:37:29 -0700 |
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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 > > > - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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