linux-kernel - Re: [PATCH] kcmp: Fix standard comparison bug

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Message-ID: <87sik7tn3k.fsf@rasmusvillemoes.dk>
Date:	Thu, 04 Sep 2014 17:35:43 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Cyrill Gorcunov <gorcunov@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org.openvz.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [PATCH] kcmp: Fix standard comparison bug

On Thu, Sep 04 2014, Cyrill Gorcunov <gorcunov@...il.com> wrote:

> On Thu, Sep 04, 2014 at 12:40:06PM +0200, Rasmus Villemoes wrote:
>> 
>> Note that it makes absolutely no difference that a transmogrying
                                                       ^^^^
                                                    transmogrifying

> It's more than that, I looked into disassembly code and
> found that compiler overoptimize obfuscation, instead of doing
> ^ and * sequently it substracts xor production of both operands
> first and only then multiplies the result.

...which it seems to be perfectly entitled to; xz - yz == (x-y)z holds
in any ring. 

Anyway, I'll stop beating the dead horse.

Rasmus
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