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SubjectRe: Direct access to hardware
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James Sutherland <jas88@cam.ac.uk> writes:

[FDIV errors on pentiums]

> > So what does the kernel (can) do to prevent this problem on defective
> > pentiums?
>
> Trap the defective instructions, and implement a replacement instruction
> in software. On later Intel CPUs, you can sometimes use a microcode update
> to fix it - this also requires OS intervention.
>
> Either way, essentially you tell the OS to block the duff instructions,
> and it does so.

Have you bothered to check this, or it's just a guess?

The truth is that the kernel does exactly nothing except printing
warning message about defective FPU. It's up to the application
to deal with the problem. Yes, it would be possible for the kernel
to check all executed instructions - guess why it doesn't do that?

The bug is only present on some non-MMX Pentium CPUs, they have no
updatable (nor downloadable) microcode.
--
Krzysztof Halasa
Network Administrator

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