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Subject: Re: Newest Pentium bug (fatal)
In-Reply-To: <3463605C.41C67EA6@whistle.com> from Julian Elischer at "Nov 7, 97 10:39:24 am"
To: julian@whistle.com (Julian Elischer)
Date: Fri, 7 Nov 1997 13:39:45 -0700 (MST)
Cc: hackers@FreeBSD.ORG
From: Kenneth Merry <ken@plutotech.com>
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Julian Elischer wrote...
> On a "genuine Intel" pentium (not pentium pro)
> execution of the following sequence, 0xf0 0x0f 0xc7 0xc8
> 
> will stop the processor. This is doable from user mode and in 
> 16bitmode, or in fact any mode.
> 
> try the following c program.

> unsigned char x[] = { 0xfo, 0x0f, 0xc7, 0xc8 };
                        ^^^^

	Shouldn't that be 0xf0?

> no idea about the pentium II or other pentium copies.
> K6?
> 
> other pentium variants?
> versions?
> 
> this one DEFINITLY dies:
> CPU: Pentium (99.38-MHz 586-class CPU)
>   Origin = "GenuineIntel"  Id = 0x525  Stepping=5
>   Features=0x1bf<FPU,VME,DE,PSE,TSC,MSR,MCE,CX8>

	This one blows up:

CPU: Pentium (132.17-MHz 586-class CPU)
  Origin = "GenuineIntel"  Id = 0x52b  Stepping=11
  Features=0x1bf<FPU,VME,DE,PSE,TSC,MSR,MCE,CX8>

	I tried it on a 486 and a P6, both worked okay.

	This could definitely be a problem for people running shell
servers, etc., on Pentium boxes.  Is there any way to work around it in
software?


Ken
-- 
Kenneth Merry
ken@plutotech.com