Re: 3.15.2 build error on AMD64

Nick Warne
2014-06-29T21:05:32Z

On 29/06/14 20:44, Borislav Petkov wrote:
>> This then is an old(er) version of GCC issue (but I dunno what).
>
> Right, so the error points at
>
> __spin_lock_mb_cache_entry(struct mb_cache_entry *ce)
> {
> spin_lock(bgl_lock_ptr(mb_cache_bg_lock, <---
> (hash_64((unsigned long)ce, __builtin_log2(8)))));
> }
>
> somewhere here and I'd guess that old gcc is issuing some lib function
> which uses SSE. And after we disabled all FPU stuff in the kernel with
> b399fe355b30 ("x86: Disable generation of traditional x87 instructions")
> that would issue such an error.
>
> And I was about to point at that __builtin_log2 thing which looked
> suspicious and found this by chance:
>
> http://lkml.kernel.org/r/1401471304-37479-1-git-send-email-tmac@hp.com
>
> You could test this patch with that old gcc 4.2.x as it looks like a
> good candidate for a fix for your issue.

Thanks Boris, but unfortunately I had to trash GCC 4.2.4 to build the
new 4.7.4 version - so I can't test the patch :(

At least this issue is now on record so others will not need to go to
penalties.

Many thanks,