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

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Message-ID: <alpine.DEB.2.00.1108231450130.28350@router.home>
Date:	Tue, 23 Aug 2011 14:52:25 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	"H. Peter Anvin" <hpa@...or.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 Tue, 23 Aug 2011, H. Peter Anvin wrote:

> I keep meaning to write up a proposal for the gcc people to output
> arithmetic flag status.

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.
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