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

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Message-ID: <20070721204458.GG1193@rhun.ibm.com>
Date:	Sat, 21 Jul 2007 23:44:58 +0300
From:	Muli Ben-Yehuda <muli@...ibm.com>
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 Sat, Jul 21, 2007 at 01:18:54PM -0700, H. Peter Anvin wrote:
> Muli Ben-Yehuda wrote:
> > 
> > So it looks like we have a purely syntactic patch that does something
> > different than the original code in one of the above places. What am I
> > missing?
> > 
> 
> +static inline void clflush(volatile void *__p)
> +{
> +	asm volatile("clflush %0" : "+m" (*(char __force *)__p));
>                                           ^
> +}

Ok, let's try again:

You're changing this (pageattr.c)

                asm volatile("clflush (%0)" :: "r" (adr + i));

into this:

		asm volatile("clflush %0" : "+m" (*(char __force*)(adr + i)));

The original one calls clflush with (adr + i), the new one with (*(adr
+ i)). Are these calls equivalent? if not, and I don't think they are,
you are changing the semantics of the code (presumably, because it
fixes a bug), and *that should be a separate patch*.

Cheers,
Muli

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