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

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Date:	Sun, 27 Aug 2006 20:28:44 -0700
From:	John Coffman <johninsd@....rr.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <ak@...e.de>, Alon Bar-Lev <alon.barlev@...il.com>,
	Andrew Morton <akpm@...l.org>, linux-kernel@...r.kernel.org,
	johninsd@....rr.com, Matt_Domsch@...l.com
Subject: Re: [PATCH] THE LINUX/I386 BOOT PROTOCOL - Breaking the 256
  limit (ping)

LILO memory usage:

000600 - 001000 BIOS data check area.  Okay to overwrite.  LILO usage 
suppressed with command line "nobd" option.  There's also a config 
file option to suppress usage.

LILO typically loads at 9000:0000 up to the top of the EBDA.  Top of 
EBDA is determined by "int 12h."  Some BIOS's on add-in cards do not 
properly allocate the EBDA.  Use LILO Makefile option "BUG_SI_EBDA" 
to allocate extra EBDA for the BIOS.  If the BIOS data check area is 
created at boot time by LILO, then:

    >  lilo -T ebda

will tell you where LILO is loaded on your system.

--John


At 02:39 PM  Sunday 8/27/2006, H. Peter Anvin wrote:
>Andi Kleen wrote:
>>On Sunday 27 August 2006 21:32, H. Peter Anvin wrote:
>>>Andi Kleen wrote:
>>>>Just increasing that constant caused various lilo setups to not boot
>>>>anymore. I don't know who is actually to blame, just wanting to
>>>>point out that this "obvious" patch isn't actually that obvious.
>>>How would that even be possible (unless you recompiled LILO with 
>>>the new headers)?  There would be no difference in the memory 
>>>image at the point LILO hands off to the kernel.
>>AFAIK the problem was that some EDD data got overwritten.
>>
>>>In order to reproduce this we need some details about your 
>>>"various LILO setups", or this will remain as a source of cargo 
>>>cult programming.
>>You can search the mailing list archives, it's all in there if you don't
>>belive me.
>
>Found the references.  This seems to imply that EDD overwrites the 
>area used by LILO 22.6.1.  LILO 22.6.1 uses the new boot protocol, 
>with the full pointer, and seems to obey the spec as far as I can 
>read the code.  I'm going to try to run it in simulation and observe 
>the failure that way.
>
>However, something is still seriously out of joint.  The EDD data 
>actually overlays the setup code, not the bootsect code, and thus 
>there "shouldn't" be any way that this could interfere.  My best 
>guess at this time is that either the EDD code or LILO uses memory 
>it's not supposed to use, and the simulation should hopefully reveal that.
>
>Sorry if I seem snarky on this, but if we can't get to the bottom of 
>this we can't ever fix it.
>
>         -hpa


         PGP KeyID: 6781C9C8  (good until 31-Dec-2008)
         Keyserver at  ldap://keyserver.pgp.com  OR  http://pgp.mit.edu
         LILO links at http://freshmeat.net/projects/lilo
         and Help link at http://lilo.go.dyndns.org


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