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

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Message-ID: <20171105210108.znmhsbaxsiaqcxyb@treble>
Date:   Sun, 5 Nov 2017 15:01:08 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 05, 2017 at 12:12:31PM -0800, Linus Torvalds wrote:
> 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.

I had tried the '%=' thing before, because that was exactly what I
needed.  But alas, it's not supported by the older GCCs.

-- 
Josh