Fat Binary - Haswell Detection Bug (and fix)

[Tim Valenzuela]

Hi guys, I've got the machine in question.

This patch you attached won't apply to the latest hg. It appears to have
been already applied, so I'm comparing the hg tip (16317:07a2dde2c971) vs
the last log entry before BMI2 is mentioned (16313:8b074a2e0134).

Mercurial tip:
===============
config.guess: coreisbr-unknown-linux-gnu
Check without fat: All Pass
Check with fat:  All Pass

Mercurial Pre-BMI2 changes:
===============
config.guess: coreihwl-unknown-linux-gnu
Check without fat: Illegal instruction
Check with fat: Illegal instruction

The changes seems to work as intended.

- Tim


On Thu, Feb 27, 2014 at 9:06 AM, Torbjorn Granlund <tg at gmplib.org> wrote:

> John Sully <john at csquare.ca> writes:
>
>   The proposed patch is:
>   --- a/mpn/x86_64/fat/fat.c      Sun Feb 16 07:08:24 2014 +0100
>   +++ b/mpn/x86_64/fat/fat.c      Wed Feb 19 23:47:40 2014 -0500
>   @@ -292,7 +292,9 @@
>                 CPUVEC_SETUP_core2;
>                 CPUVEC_SETUP_coreinhm;
>                 CPUVEC_SETUP_coreisbr;
>   -             CPUVEC_SETUP_coreihwl;
>   +             long featihwm = __gmpn_cpuid (dummy_string, 7);
>   +             if ( featihwm & (1 << 8) )        //check BMI2
>   +                     CPUVEC_SETUP_coreihwl;
>                 break;
>               }
>             break;
>
>
> I am at loss about the logics of your change.  I don't think `featihwm'
> will contain anything useful since (1) ecx is not set to zero by
> __gmpn_cpuid as it should for this inquiry and (2) rax has a useless
> value unrelated to BMI2 regardless of ecx input.  The bit to check is in
> ebx (stored at dummy_string[0...3]).
>
> Do you agree?
>
> I made what I think are the correct changes.  Please remove your patch
> and try the attached one instead:
>
>
>
> Please try both a plain build (without --enable-fat) and a fat build
> (with --enable-fat) and run "make && make check".
>
> What does config.guess output with this change (and before the change)
> for your system?
>
>
> Torbjörn
>
>