Messages in this thread | | | Date | Mon, 10 Nov 1997 13:43:05 +0100 (MET) | From | Gabriel Paubert <> | Subject | Re: pentium bug continued |
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On Mon, 10 Nov 1997, Dale Amon as Operator wrote:
> This sort of thing isn't all that uncommon. The old 6800 > had what we used to call the HCF opcode, "Halt and Catch > Fire". When a program got lost in hyperspace it > would inevitably hit either a Halt or this undocumented > feature, at which point the address lines became a > binary counter and the machine required a power reset > to get it back. > > I wouldn't be surprised at all to find accidental or > QA opdcodes hidden away in other processors. >
Except that in this case the instruction does not behave according to Intel's own Pentium documentation (241430_4.pdf, page 25-71, there may be a more recent version):
"The destination operand must be a memory operand, not a register. If the CMPXCHG8B instruction is executed with a modr/m byte representing a register as the destination operand, #UD occurs."
A lock prefix should not change this behaviour, and much less enable to lockup the processor from user mode. It seems AMD has read Intel's doc better than Intel ;)
Gabriel.
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