linux-kernel - Re: cmpxchg and x86 flags output

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Date:	Wed, 22 Jun 2016 17:14:23 +0100
From:	David Howells <dhowells@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	dhowells@...hat.com, Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: cmpxchg and x86 flags output

H. Peter Anvin <hpa@...or.com> wrote:

> So how do we make this move forward?

Getting my API additions in is relatively straightforward, I think.  The
whether-or-notness of the cmpxchg operation succeeding can be calculated by
comparing the original value read from memory with the value-to-be-replaced
inside the API function.

This can later be replaced with the boolean output from the CMPXCHG
instruction, the branch target from the LL/SC skipping or the result of the
intrinsics.

David