linux-kernel - Re: [patch 1/2] x86: head_64.S cleanup - use straight move to CR4 register

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Message-ID: <20080513171422.GG6921@cvg>
Date:	Tue, 13 May 2008 21:14:22 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org,
	jirislaby@...il.com
Subject: Re: [patch 1/2] x86: head_64.S cleanup - use straight move to CR4
	register

[H. Peter Anvin - Tue, May 13, 2008 at 10:11:34AM -0700]
> Cyrill Gorcunov wrote:
>> [H. Peter Anvin - Tue, May 13, 2008 at 10:03:42AM -0700]
>>> Cyrill Gorcunov wrote:
>>>> There is no need for testing the values because we already know
>>>> what they should be. Just set them in straight way.
>>> He isn't testing them, he's setting individual bits.
>>>
>>> Either of these is pretty silly; the right way to do this is:
>>>
>>> 	movl	$(X86_CR4_PAE|X86_CR4_PGE), %eax
>>> 	movq	%rax, %cr4
>>>
>>> A movl in 64-bit mode zero extends.
>>>
>>> 	-hpa
>>>
>> Here is updated version
>> ---
>> [PATCH] x86: head_64.S cleanup - use straight move to CR4 register
>> Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
>> ---
>> Index: linux-2.6.git/arch/x86/kernel/head_64.S
>> ===================================================================
>> --- linux-2.6.git.orig/arch/x86/kernel/head_64.S	2008-05-13 
>> 20:04:23.000000000 +0400
>> +++ linux-2.6.git/arch/x86/kernel/head_64.S	2008-05-13 21:08:20.000000000 
>> +0400
>> @@ -155,9 +155,7 @@ ENTRY(secondary_startup_64)
>>  	 */
>>   	/* Enable PAE mode and PGE */
>> -	xorq	%rax, %rax
>> -	btsq	$5, %rax
>> -	btsq	$7, %rax
>> +	movl	$(X86_CR4_PAE | X86_CR4_PGE), %rax
>>  	movq	%rax, %cr4
>>  
>
> Syntax error.  %eax, not %rax.
>
> 	-hpa
>


Oh my, what I'm doing... sorry
Here we go

---
[PATCH] x86: head_64.S cleanup - use straight move to CR4 register

Signed-off-by: Cyrill Gorcunov <gorcunov@...il.com>
---

Index: linux-2.6.git/arch/x86/kernel/head_64.S
===================================================================
--- linux-2.6.git.orig/arch/x86/kernel/head_64.S	2008-05-13 20:04:23.000000000 +0400
+++ linux-2.6.git/arch/x86/kernel/head_64.S	2008-05-13 21:12:39.000000000 +0400
@@ -155,9 +155,7 @@ ENTRY(secondary_startup_64)
 	 */
 
 	/* Enable PAE mode and PGE */
-	xorq	%rax, %rax
-	btsq	$5, %rax
-	btsq	$7, %rax
+	movl	$(X86_CR4_PAE | X86_CR4_PGE), %eax
 	movq	%rax, %cr4
 
 	/* Setup early boot stage 4 level pagetables. */

		- Cyrill -
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