Re: [BUG] x86 kenel won't boot under Virtual PC

[H. Peter Anvin]

This is a multi-part message in MIME format.Linus Torvalds wrote:
> > >
> > Yes, it does:
> >
> >   /* We need to decide which NOP sequence to use for 32bit and
> >      64bit. When -mtune= is used:
> >
> >      1. For PROCESSOR_I386, PROCESSOR_I486, PROCESSOR_PENTIUM and
> >      PROCESSOR_GENERIC32, f32_patt will be used.
> >      2. For PROCESSOR_PENTIUMPRO, PROCESSOR_PENTIUM4, PROCESSOR_NOCONA,
> >      PROCESSOR_CORE, PROCESSOR_CORE2, and PROCESSOR_GENERIC64,
> >      alt_long_patt will be used.
> >      3. For PROCESSOR_ATHLON, PROCESSOR_K6, PROCESSOR_K8 and
> >      PROCESSOR_AMDFAM10, alt_short_patt will be used.
> >
> >      When -mtune= isn't used, alt_long_patt will be used if
> >      cpu_arch_isa_flags has Cpu686. Otherwise, f32_patt will
> >      be used.
> >
> > "alt_long_patt" uses NOPL and its variants.
>
> That is A TOTAL PIECE OF SH*T, and against gcc's own documentation.
>
> "-mtune=x" is very much defined to be a performance _tuning_ option, not 
> an "architectural" option. 
>
> Quite frankly, this is a gcc bug. Plain and simple. 

OK, digging some more into this garbage...

Apparently the situation isn't quite as dire as it first seems.
At least gcc 4.3.0 doesn't actually pass -mtune= to gas; it just drops 
the option on the floor.  This means this bug isn't manifest when 
calling from gcc (as opposed to invoking as directly.)

However, I would still like to push the following patch to be on the 
safe side, ok?

	-hpa