linux-kernel - Re: [GIT PULL] core kernel fixes

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Message-ID: <CA+55aFwvW9TKyQ7eUqahb8=FLr822JTxGOHF8ku=1P_toUmmMw@mail.gmail.com>
Date:   Sun, 5 Nov 2017 12:12:31 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] core kernel fixes

On Sun, Nov 5, 2017 at 11:53 AM, Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> The GCC manual says:
>
>   "asm statements that have no output operands, including asm goto
>    statements, are implicitly volatile."

Hmm. Fair enough.

And the manual does say that it can merge and duplicate those asms
(and suggests using "%=" to generate a unique number, but I guess
"%c0" with __COUNTER__ is equivalent).

I think the gcc manual has changed. I'm pretty certain it used to say
that "volatile" asms would not be "moved significantly". They've
silently changed semantics before too, oh well.

              Linus