linux-kernel - Re: [PATCH -tip] x86: trampoline_64.S - use predefined constants with simplification

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Date:	Wed, 28 Jan 2009 22:52:57 +0100
From:	"Alexander van Heukelum" <heukelum@...tmail.fm>
To:	"Cyrill Gorcunov" <gorcunov@...il.com>,
	"Ingo Molnar" <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	"Thomas Gleixner" <tglx@...utronix.de>
Cc:	"LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -tip] x86: trampoline_64.S - use predefined constants with  
 simplification

On Wed, 28 Jan 2009 23:21:25 +0300, "Cyrill Gorcunov"
<gorcunov@...il.com> said:
> Impact: cleanup
> 
> We may use macros from processor-flags.h instead
> of hardcoding bits. Actually it's not direct mapping
> of old instructions with new ones -- BTS does change
> CF flag while MOV does not. But i didn't find any
> dependency on CF in this code.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov@...nvz.org>
> ---
>
> Please review

Looks good.

Acked-by: Alexander van Heukelum <heukelum@...tmail.fm>

>  arch/x86/kernel/trampoline_64.S |   19 +++++++++----------
>  1 file changed, 9 insertions(+), 10 deletions(-)
> 
> Index: linux-2.6.git/arch/x86/kernel/trampoline_64.S
> ===================================================================
> --- linux-2.6.git.orig/arch/x86/kernel/trampoline_64.S
> +++ linux-2.6.git/arch/x86/kernel/trampoline_64.S
> @@ -29,6 +29,7 @@
>  #include <asm/page.h>
>  #include <asm/msr.h>
>  #include <asm/segment.h>
> +#include <asm/processor-flags.h>
>  
>  .section .rodata, "a", @progbits
>  
> @@ -37,7 +38,7 @@
>  ENTRY(trampoline_data)
>  r_base = .
>  	cli			# We should be safe anyway
> -	wbinvd	
> +	wbinvd
>  	mov	%cs, %ax	# Code and data in the same place
>  	mov	%ax, %ds
>  	mov	%ax, %es
> @@ -73,9 +74,8 @@ r_base = .
>  	lidtl	tidt - r_base	# load idt with 0, 0
>  	lgdtl	tgdt - r_base	# load gdt with whatever is appropriate
>  
> -	xor	%ax, %ax
> -	inc	%ax		# protected mode (PE) bit
> -	lmsw	%ax		# into protected mode
> +	mov	$X86_CR0_PE, %ax	# protected mode (PE) bit
> +	lmsw	%ax			# into protected mode
>  
>  	# flush prefetch and jump to startup_32
>  	ljmpl	*(startup_32_vector - r_base)
> @@ -86,9 +86,8 @@ startup_32:
>  	movl	$__KERNEL_DS, %eax	# Initialize the %ds segment register
>  	movl	%eax, %ds
>  
> -	xorl	%eax, %eax
> -	btsl	$5, %eax		# Enable PAE mode
> -	movl	%eax, %cr4
> +	movl	$X86_CR4_PAE, %eax
> +	movl	%eax, %cr4		# Enable PAE mode
>  
>  					# Setup trampoline 4 level pagetables
>  	leal	(trampoline_level4_pgt - r_base)(%esi), %eax
> @@ -99,9 +98,9 @@ startup_32:
>  	xorl	%edx, %edx
>  	wrmsr
>  
> -	xorl	%eax, %eax
> -	btsl	$31, %eax		# Enable paging and in turn activate Long Mode
> -	btsl	$0, %eax		# Enable protected mode
> +	# Enable paging and in turn activate Long Mode
> +	# Enable protected mode
> +	movl	$(X86_CR0_PG | X86_CR0_PE), %eax
>  	movl	%eax, %cr0
>  
>  	/*
-- 
  Alexander van Heukelum
  heukelum@...tmail.fm

-- 
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