Re: Cyrix 6x86MX and Centaur C6 CPUs in 2.1.102

C. Scott Ananian (
Fri, 22 May 1998 16:50:35 -0400 (EDT)

On Fri, 22 May 1998 Riley Williams <> wrote:

> > /proc/cpuinfo is not intended for reading _only_ by human users
> > (who can see all detected CPU bugs during system boot anyway), but
> > also for parsing by programs which need to know whether they can
> > rely on the CPU not having the specific bug. It seems obvious to me
> > that missing bug info should mean `bug not known to this kernel'
> > rather than `bug not present', so that the apps can get all info
> > they need at once without having to remember which kernels know the
> > bug in question or having to parse yet another file.
> Am I misunderstanding what's going on then?
> 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, that's not right. Many bugs do not have workarounds. Intel fdiv,
several of the AMD bugs in include/asm-386/bugs.h, etc. There aren't many
examples of programs that use this information, but if I had a Very
Important Financial Application, for example, I might want to fall back on
an integer-only algorithm if I knew that the CPU had the fdiv bug.
Also, the cpuinfo section details processor *features*, as well, so by
parsing /proc/cpuinfo I could find out whether (for example) I can use MMX
instructions. Not listing MMX in /proc/cpuinfo means that the kernel
doesn't know about it, not that I don't have MMX. (this is a somewhat
bogus example, because MMX doesn't have a line of its own in /proc (it
would display as a number in the flags line before the kernel knew about
it), but the point is valid, I think.)
@ @
C. Scott Ananian: / Declare the Truth boldly and
Laboratory for Computer Science/Crypto / without hindrance.
Massachusetts Institute of Technology /META-PARRESIAS AKOLUTOS:Acts 28:31
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