linux-kernel - Re: [PATCH] x86: relocate_kernel - use predefined PAGE

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Date:	Fri, 21 Mar 2008 13:50:33 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>
CC:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86: relocate_kernel - use predefined PAGE_SIZE	instead
 of own alias

Cyrill Gorcunov wrote:
> [H. Peter Anvin - Fri, Mar 21, 2008 at 01:18:13PM -0700]
>> Cyrill Gorcunov wrote:
>>> This patch does clean up relocate_kernel_(32|64).S a bit by getting rid
>>> of local PAGE_ALIGNED macro. We should use well-known PAGE_SIZE instead
>>> Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
>> Looks good!
>>
>> 	-hpa
>>
> 
> Thanks Peter for review, btw we have in relocate_kernel_32.S
> 
> 188:	movl	%cr4, %eax
> 189:	andl	$0, %eax
> 190:	movl	%eax, %cr4
> 
> but maybe would be better just replace it with
> 
> 	xorl	%eax, %eax
> 	movl	%eax, %cr4
> 
> or there is some nonobvious reason not to do so?
> 

The only case I can think of would be if the code expects to patch the 
zero, but even then it'd be cantankerous, because gas will optimize that 
zero down to a single byte.

So, no :)

	-hpa

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