linux-kernel - Re: [PATCH] x86: Create clflush() inline, remove hardcoded wbinvd

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Message-ID: <20070722195532.GA1432@one.firstfloor.org>
Date:	Sun, 22 Jul 2007 21:55:32 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Glauber de Oliveira Costa <gcosta@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: Create clflush() inline, remove hardcoded wbinvd

On Sun, Jul 22, 2007 at 11:05:24AM -0700, H. Peter Anvin wrote:
> Andi Kleen wrote:
> >> The main reason is that everyone seems to invoke it either incorrectly
> > Where is it incorrect? 
> 
> Using "r" or "m" (as opposed as "+m") gives gcc the wrong dependency
> information, and it could, at least in theory, cause memory references
> to be moved around it -- especially when using "r".

That doesn't sound correct. Taking the address should be like an escaping
pointer and equivalent to read/write and effectively disable optimizations
on this memory.

-Andi
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