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

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Message-ID: <4E5415BA.5000301@zytor.com>
Date:	Tue, 23 Aug 2011 14:03:54 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Christoph Lameter <cl@...ux.com>, "H.J. Lu" <hjl.tools@...il.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	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 12:52 PM, Christoph Lameter wrote:
> 
> Should be relatively straightforward if you make the processor flag a
> builtin variable.
> 
> i.e. __processor_flag_zero, __processor_flag__gt etc.
> 
> Then the inline cmpxchg functions could simply do a
> 
> 	return __processor_flag_zero;
> 
> The code generator then needs to realize from the expression that we are
> referring to the zero flag and insert the correct jxx instruction.
>

The right thing is probably to have not the *flags* but the *conditions*
(exposed as variables):

bool __builtin_x86_s,  __builtin_x86_ns;
bool __builtin_x86_pe, __builtin_x86_po;
...


Or perhaps even

register bool x86_s asm("s");?

H.J. thoughts/ideas?

	-hpa
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