linux-kernel - Re: [PATCH 04/10] i386: clean up bzImage generation

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Message-ID: <4672C383.7000304@zytor.com>
Date:	Fri, 15 Jun 2007 09:51:15 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>,
	v12n <virtualization@...ts.linux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Xen-Devel <xen-devel@...ts.xensource.com>
Subject: Re: [PATCH 04/10] i386: clean up bzImage generation

Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> Jeremy Fitzhardinge wrote:
>>   
>>> -setup_move_size: .word  0x8000		# size to move, when setup is not
>>> +setup_move_size: .word  _setup_size	# size to move, when setup is not
>>>  					# loaded at 0x90000. We will move setup
>>>  					# to 0x90000 then just before jumping
>>>  					# into the kernel. However, only the
>>>     
>> This is WRONG and will break 2.00 protocol bootloaders, if any still
>> exist, and quite possibly some 2.01 protocol bootloaders.  There are
>> definitiely bootloaders in the field that rely on this implicit value.   
> 
> Ah, I see.  I didn't see any documentation saying that this must be
> 0x8000.  Or does _setup_size just have to be <= 0x8000?
> 

The default for unaware bootloaders has been 0x8000 since the boot
protocol was created, and bootloaders are known to (improperly) rely on
it.  _setup_size does have to be <= 0x8000, but that's another issue.

>>> @@ -246,7 +246,6 @@ setup2:
>>>  	jnz	1f
>>>  	movw	$0xfffc, %sp	# Make sure we're not zero
>>>  1:	movzwl	%sp, %esp	# Clear upper half of %esp
>>> -	sti
>>>     
>> Motivation, please?
>>   
> 
> We talked about this, and you said it was a mistake.  It needn't be in
> this patch; it could be separate, or just dropped as far as I'm concerned.
> 

I said it probably wouldn't hurt to drop it.  I don't believe you ever
actually explained why you wanted it dropped.

	-hpa
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