Re: Cyrix 6x86MX and Centaur C6 CPUs in 2.1.102

Martin Mares (
Fri, 22 May 1998 13:03:46 +0200


> As I understand it, all the bugs listed in /proc/cpuinfo HAVE A
> WORKAROUND INSTALLED, so that ANY program trying to activate that bug
> MUST fail to do so. As a result, the ONLY meaning that ANY program can
> take from a particular processor bug NOT being listed in /proc/cpuinfo
> is "Ah, this machine doesn't have a workaround for bug X, so I can use
> it to crash this machine" which is the sort of reasoning that VIRUS
> programs tend to use and isn't applicable for anything else...

No, several bugs are non-workaroundable -- for example the Pentium
FDIV bug. In case an application detects the FDIV bug, it can for example
switch to slower fixed-point algorithms which don't suffer from this bug.

> As I see it, there must be a FIXED relationship between CPU clock
> speed and TSC frequency, simply due to the fact that anything else
> would mean that some sort of random number generator was present.
> Remembering the sort of lengths Linux goes to to generate random
> numbers, I would find that VERY hard to believe...

I'm not sure about what do specs of different CPU's say on this topic,
but I think TSC could possibly be an instruction counter, thus depending
on the actual instructions executed.

Have a nice fortnight

Martin `MJ' Mares   <>
Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
"It said, "Insert disk #3," but only two will fit!"

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