Re: Possible Pentium MMX CPU bug?

Thomas Wouters (thomas@xs4all.nl)
Fri, 28 Nov 1997 16:31:35 +0100 (CET)


On Fri, 28 Nov 1997, Ingo Molnar wrote:

> I think i have found the reason why certain applications (Quake, GCC)
> crash on certain Pentium MMX processors. I suspect it is a CPU bug. I have
> a testprogram that detects this bug/condition, and have made a Linux
> kernel patch that is a first attempt to work the bug around.

> Here is the testprogram i wrote to detect the (suspected!) CPU bug. It
> outputs this on a Stepping 6 'Classic' Pentium 100 MHz:
>
> $ ./mw_bug
> testing bug ... no Pentium MMX 'missed write' bug in this CPU.
>
> and this is displayed on a Stepping 3 Pentium/MMX 200 MHz processor:
>
> $ ./mw_bug
> testing bug ... possible Pentium MMX 'missed write' CPU bug detected!

However...

(centurion:~) # ./mw_bug
testing bug ... no Pentium MMX 'missed write' bug in this CPU.

And I have a Stepping 3 Pentium/MMX 200. Compiled the program with both gcc
2.7.2.1 (Standard RedHat version) and with egcs-2.90.17p (pgcc) with various
optimizations, ran it under kernel 2.0.30 (standard RedHat version) and
2.1.66.

processor : 0
cpu : 586
model : Pentium MMX
vendor_id : GenuineIntel
stepping : 3
fdiv_bug : no
hlt_bug : no
sep_bug : no
f00f_bug : yes
fpu : yes
fpu_exception : yes
cpuid : yes
wp : yes
flags : fpu vme de pse tsc msr mce cx8 mmx
bogomips : 249.04

Perhaps the problem lies with other hardware ? If you wish, i can give a
complete dump of my hardware & software setup.

Regards,
Thomas.

(Various people deleted from CC: for no apparent reason ;-)