linux-kernel - Re: [PATCH 4.19 079/271] x86/atomic: Fix smp_mb__{before,after}

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Message-ID: <CACMCwJJm++=x0EOXYMvFvybE63rmHEq6f96ahfYUA83wGGHHLw@mail.gmail.com>
Date:   Fri, 26 Jul 2019 17:07:39 +0300
From:   Jari Ruusu <jari.ruusu@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 079/271] x86/atomic: Fix smp_mb__{before,after}_atomic()

On 7/26/19, Peter Zijlstra <peterz@...radead.org> wrote:
> On Fri, Jul 26, 2019 at 01:18:06PM +0300, Jari Ruusu wrote:
>> Shouldn't those clobber contraints actually be:  "memory","cc"
>> That is because addl subl (and other) machine instructions
>> actually modify the flags register too.
>>
>> gcc docs say: The "cc" clobber indicates that the assembler
>> code modifies the flags register.
>
> GCC x86 assumes any asm() will clobber "cc".

No worries then. Thanks for your clarification.

-- 
Jari Ruusu  4096R/8132F189 12D6 4C3A DCDA 0AA4 27BD  ACDF F073 3C80 8132 F189