linux-kernel - Re: [PATCH 02/14] x86, boot: honor CONFIG_PHYSICAL

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Message-ID: <4A0464AC.9060308@zytor.com>
Date:	Fri, 08 May 2009 09:58:20 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Sam Ravnborg <sam@...nborg.org>
CC:	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, vgoyal@...hat.com, hbabu@...ibm.com,
	kexec@...ts.infradead.org, ying.huang@...el.com, mingo@...e.hu,
	tglx@...utronix.de, ebiederm@...ssion.com
Subject: Re: [PATCH 02/14] x86, boot: honor CONFIG_PHYSICAL_START when relocatable

Sam Ravnborg wrote:
> 
> On the coding style side of thing...
>> +     movl %ebp, %ebx
>> +     cmpl %ebx, %eax
>> +     jbe 1f
>> +     movl %eax, %ebx
> 
> This looks messy with different idention of the operand.
> 
> Compare it to this:
>> +	movl	%ebp, %ebx
>> +	cmpl	%ebx, %eax
>> +	jbe	1f
>> +	movl	%eax, %ebx
> 
> 
> I like the latter more with vertical alignment of the operand.
> I see that you add spaces around operators (,) - good.

head_32.S was already written in the style with space (rather than tab)
between opcode and operands.  There was a total of three instructions
that didn't follow the pattern.  Re-styling the whole file is possible,
of course, but should be a separate patch entirely.

>>  	pushl %esi
>> -	leal _ebss(%ebp), %esi
>> -	leal _ebss(%ebx), %edi
>> -	movl $(_ebss - startup_32), %ecx
>> +	leal (_bss-4)(%ebp), %esi
>> +	leal (_bss-4)(%ebx), %edi
>> +	movl $(_bss - startup_32), %ecx
>> +	shrl $2, %ecx
> 
> I do not see why you mess around with _bss here?
> Do you use .bss for decompression?

This chunk of code is about moving the initialized segments into place.
 Moving the contents of the bss is a bug (and it clobbers the stack, the
setup of which I moved earlier in the code.)

However, using _edata would give an unaligned symbol, so use _bss
instead as being an aligned symbol at the beginning of the _bss; we thus
move the range from startup_32 to _bss.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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