linux-kernel - Re: [PATCH 13/15] x86: add cmpxchg

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Message-ID: <4E541154.6090805@zytor.com>
Date:	Tue, 23 Aug 2011 13:45:08 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Christoph Lameter <cl@...ux.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Subject: Re: [PATCH 13/15] x86: add cmpxchg_flag() variant

On 08/23/2011 12:53 PM, Jeremy Fitzhardinge wrote:
> 
> Yes, that would ideal.  The closest you can get is asm goto(), but the
> syntax for that would be awful; something like:
> 
> #define cmpxchg_jump(ptr, old, new, fail)\
> 	asm goto (...)
> 
> 
> :
> :
> 
> again:
> 	old = *thingp;
> 	new = frobulate(old);
> 	cmpxchg_jump(thingp, old, new, again);
> 	/* worked */
> 
> Would this be useful enough?
> 

Actually there is a trick:

static inline bool ....
{
	asm goto(... yes);
no:
	return false;
yes:
	return true;
}

... which makes syntax a heckuva lot less awkward.

	-hpa
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