linux-kernel - Re: [PATCH] THE LINUX/I386 BOOT PROTOCOL

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Date:	Mon, 28 Aug 2006 13:43:11 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Matt Domsch <Matt_Domsch@...l.com>
CC:	Alon Bar-Lev <alon.barlev@...il.com>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	johninsd@....rr.com
Subject: Re: [PATCH] THE LINUX/I386 BOOT PROTOCOL - Breaking the 256 limit
 (ping)

Matt Domsch wrote:
> On Mon, Aug 28, 2006 at 12:00:37PM -0700, H. Peter Anvin wrote:
>> Matt Domsch wrote:
>>> No reason.  I was just trying to be careful, not leaving data in the
>>> upper bits of those registers going uninitialized.  If we know they're
>>> not being used ever, then it's not a problem.  But I don't think
>>> that's the source of the command line size concern, is it?
>>>
>> No, it's treating the command line as a fixed buffer, as opposed to a 
>> null-terminated string.  This was always a bug, by the way.
> 
> OK, I'll look at fixing that, and using %esi throughout.
> 

There is a lot of weirdness in this code; it's broken in an enormous 
amount of ways (sorry, Matt).  This comment, for example:

	pushl	%esi
     	cmpl	$0, %cs:cmd_line_ptr
	jz	done_cl
	movl	%cs:(cmd_line_ptr), %esi
# ds:esi has the pointer to the command line now

... doesn't handle the old boot protocol, and doesn't at all deal with 
the fact that cmd_line_ptr is an absolute address, and not at all 
relative to SETUPSEG, which is the normal value for %ds at this point. 
For the old protocol, this is a 16-bit pointer which is relative to 
INITSEG (not SETUPSEG), but this code just completely ignores it.

I'll hack up a patch for this.

	-hpa
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