linux-kernel - Re: [PATCH] x86: documentation fix regarding boot protocol

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Date:	Mon, 15 Dec 2008 12:27:24 +0100
From:	Philipp Kohlbecher <xt28@....de>
To:	Ian Campbell <ijc@...lion.org.uk>
CC:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: documentation fix regarding boot protocol

Ian Campbell wrote:
> On Sun, 2008-12-14 at 18:50 +0100, Philipp Kohlbecher wrote:
>> Documentation/x86/boot.txt describes payload_offset as the offset
>> from the end of the real-mode code. In fact, it is more accurately
>> described as the offset from the beginning of the protected-mode
>> code, as (a) this is how it is actually calculated and (b) the padding
>> after the real-mode code is not included in the offset.
>>
>> Signed-off-by: Philipp Kohlbecher <xt28@....de>
> 
> Acked-by: Ian Campbell <ijc@...lion.org.uk>
> 
> The padding after the real-mode code which you mention is just the
> implicit padding because the size of the real-mode code is specified in
> sectors (and hence is rounded up), isn't it?

Yes, it is. You can certainly view the padding as an implicit part of 
the real-mode code, which is why the current statement isn't wrong -- 
there is simply room for improvement.

> Is it worth saying that the payload_offset is relative to (setup_sectors
> +1) * 512?

The fact that the protected-mode code starts at that address is already 
mentioned under the heading "LOADING THE REST OF THE KERNEL" (where 
protected mode is for some reason referred to as "non-real-mode").
(Please note that the header field is called "setup_sects", not 
"setup_sectors".)

>> ---
>>
>>   Documentation/x86/boot.txt |    4 ++--
>>   1 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/Documentation/x86/boot.txt b/Documentation/x86/boot.txt
>> index 83c0033..414b6fb 100644
>> --- a/Documentation/x86/boot.txt
>> +++ b/Documentation/x86/boot.txt
>> @@ -537,8 +537,8 @@ Type:		read
>>   Offset/size:	0x248/4
>>   Protocol:	2.08+
>>
>> -  If non-zero then this field contains the offset from the end of the
>> -  real-mode code to the payload.
>> +  If non-zero then this field contains the offset from the beginning
>> +  of the protected-mode code to the payload.
>>
>>     The payload may be compressed. The format of both the compressed and
>>     uncompressed data should be determined using the standard magic
>>

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