linux-kernel - Re: [PATCH v2 03/13] x86: Add macro for 64bit entry startup

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Message-ID: <50AAB5E8.5070807@zytor.com>
Date:	Mon, 19 Nov 2012 14:42:48 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, Matt Fleming <matt.fleming@...el.com>
Subject: Re: [PATCH v2 03/13] x86: Add macro for 64bit entry startup_64

On 11/17/2012 11:09 PM, Yinghai Lu wrote:
> We will add one 64bit entry for bzImage in boot header struct.
> 
> the contents in that field will be offset of startup_64.
> 
> Add macro for offset of startup_64 to keep two places consistent.
> 
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> Cc: Matt Fleming <matt.fleming@...el.com>
> ---
>  arch/x86/boot/compressed/head_64.S |    2 +-
>  arch/x86/include/asm/boot.h        |    2 ++
>  2 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index 375af23..e4964dd 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -195,7 +195,7 @@ no_longmode:
>  	 * it may change in the future.
>  	 */
>  	.code64
> -	.org 0x200
> +	.org BOOT_CODE64_START_OFFSET
>  ENTRY(startup_64)
>  	/*
>  	 * We come here either from startup_32 or directly from a
> diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
> index b13fe63..ef36497 100644
> --- a/arch/x86/include/asm/boot.h
> +++ b/arch/x86/include/asm/boot.h
> @@ -38,8 +38,10 @@
>  
>  #ifdef CONFIG_X86_64
>  #define BOOT_STACK_SIZE	0x4000
> +#define BOOT_CODE64_START_OFFSET 0x200
>  #else
>  #define BOOT_STACK_SIZE	0x1000
> +#define BOOT_CODE64_START_OFFSET 0
>  #endif
>  

We can't change the 0x200 value, ever, because there are already things
that use the 64-bit entry point.  As such, these macros and the bzImage
fields are pointless; let's not bother and instead document the 0x200 as
the permanently fixed address of the 64-bit entry point.

	-hpa


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