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SubjectRe: test10-pre3
Date
Hmmm.. Wonder if this might be affecting my problem 
I compile on a Pentium for a 486. Worked but after I applied the FreeS/WAN
pathes, now it won't boot on the 486's (immediate reboot, on 'now booting the
kern..' message) Doubled checked the make outputs, and config's and it says
it is 486 but will only run on the Pentiums...

Still reasearching..

On Mon, 16 Oct 2000, Mikael Pettersson wrote:
> On Fri, 13 Oct 2000, Linus Torvalds wrote:
> > - pre3:
> > ...
> > - Dave Jones: x86 setup fixes (recognize Pentium IV etc).
>
> And then in test10-pre3 we find the following code added to
> arch/i386/kernel/setup.c:
>
> + /* Pentium IV. */
> + if (c->x86 == 15) {
> + c->x86 = 6;
> + get_model_name(c);
> + goto name_decoded;
> + }
>
> I believe the "c->x86 = 6" assignment to be broken.
> If it's there to make uname -m return i686 for Pentium IV,
> then surely that could be done differently. (See patch below.)
>
> The assignment throws away perfectly good information, but worse,
> it also destroys the implicit invariant that boot_cpu_data.x86
> equals the "family" code as returned by CPUID. Low-level cpu-specific
> code may then malfunction, or it will have to be updated to do its
> own CPUID identification. Think about MTRRs, model-specific registers,
> performance counters, and bug workarounds.
>
> One harmless example is the "sep_bug" identification code in setup.c:
>
> sep_bug = c->x86_vendor == X86_VENDOR_INTEL &&
> c->x86 == 0x06 &&
> c->cpuid_level >= 0 &&
> (c->x86_capability & X86_FEATURE_SEP) &&
> c->x86_model < 3 &&
> c->x86_mask < 3;
>
> Since initial Pentium IV processors have model 0 according to Intel's
> Pentium IV supplement to the CPUID manual (AP-485), this code may
> actually deduce that a Pentium IV has the bug (if the mask < 3).
> Imagine a similar mistake in an MTRR/MSR/whatever driver...
>
> I propose the following patch against test10-pre3:
>
> --- linux-2.4.0-test10-pre3/arch/i386/kernel/setup.c.~1~ Mon Oct 16
> 17:29:05 2000 +++ linux-2.4.0-test10-pre3/arch/i386/kernel/setup.c Mon Oct
> 16 23:13:21 2000 @@ -1548,7 +1548,6 @@
>
> /* Pentium IV. */
> if (c->x86 == 15) {
> - c->x86 = 6;
> get_model_name(c);
> goto name_decoded;
> }
> --- linux-2.4.0-test10-pre3/include/asm-i386/bugs.h.~1~ Sat Sep 9 12:49:40
> 2000 +++ linux-2.4.0-test10-pre3/include/asm-i386/bugs.h Mon Oct 16
> 23:14:42 2000 @@ -426,5 +426,5 @@
> check_pentium_f00f();
> #endif
> check_cyrix_coma();
> - system_utsname.machine[1] = '0' + boot_cpu_data.x86;
> + system_utsname.machine[1] = '0' + (boot_cpu_data.x86 > 6 ? 6 :
> boot_cpu_data.x86); }
>
>
> mtrr.c will need fixing too, but we can't really do that until Intel
> releases a new IA-32 System Programming manual with Pentium IV updates.
>
> /Mikael
> -
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