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

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Date:	Mon, 19 Nov 2012 14:53:36 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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 Mon, Nov 19, 2012 at 2:42 PM, H. Peter Anvin <hpa@...or.com> wrote:
> 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.

ok,

any other field, in header struct field that we can use to tell
bzImage could be used that
0x200 directly?

hardware_subarch?
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