Date: Thu, 7 Apr 2016 11:43:33 +0200
From: Borislav Petkov <bp@suse.de>
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Andi Kleen <andi@firstfloor.org>, zengzhaoxiu@163.com,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Denys Vlasenko <dvlasenk@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>, LKML <linux-kernel@vger.kernel.org>,
        Zhaoxiu Zeng <zhaoxiu.zeng@gmail.com>
Subject: Re: [PATCH v2 10/30] Add x86-specific parity functions
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On Thu, Apr 07, 2016 at 08:31:09AM +0200, Dmitry Vyukov wrote:
> Hweight custom calling convention caused crashes with KCOV coverage.
> We had to disable instrumentation of the file.

I guess we can do something like this:

       if (likely(static_cpu_has(X86_FEATURE_POPCNT)))
               asm volatile(POPCNT32
                            : "="REG_OUT (res)
                            : REG_IN (w));
       else
               res = __sw_hweight32(w);

and get rid of the custom calling convention.

Along with some numbers showing that the change doesn't cause any
noticeable slowdown...

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--