linux-kernel - Re: cmpxchg and x86 flags output

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Message-ID: <c4704d53-e6eb-4cc4-4d3f-023ff36157b6@zytor.com>
Date:	Wed, 22 Jun 2016 10:49:06 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	David Howells <dhowells@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: cmpxchg and x86 flags output

On 06/22/16 10:11, Linus Torvalds wrote:
> 
> I thought Richard Henderson already had a patch for the condition code
> asm outputs, but maybe I misremember.
> 

It is already in the released version of gcc 6.1; there is a patchset in
-tip already for using it for everything other than cmpxchg using the
CC_SET/CC_OUT macros I proposed a while ago.  cmpxchg is special because
it requires API changes to take advantage of, which as far as I
understand happens to be exactly the API changes that David has already
implemented.  Apparently some other architectures really can benefit
from intrinsics, so that is okay; we can use inline asm with flags
output on x86.

	-hpa