linux-kernel - Re: cmpxchg and x86 flags output

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Message-ID: <d92e22b3-d0af-de6f-def6-9dfe73b91542@zytor.com>
Date:   Fri, 19 Aug 2016 10:22:59 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     David Howells <dhowells@...hat.com>
Cc:     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

On 06/22/16 09:14, David Howells wrote:
> 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.
> 

Hi David,

Any news on this?  Can we perhaps help making this go forward at some point?

	-hpa