linux-kernel - Re: [Fastboot] [CFT] ELF Relocatable x86 and x86

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Message-ID: <m17j1kctb8.fsf@ebiederm.dsl.xmission.com>
Date:	Mon, 07 Aug 2006 12:08:27 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Don Zickus <dzickus@...hat.com>
Cc:	fastboot@...l.org, Horms <horms@...ge.net.au>,
	Jan Kratochvil <lace@...kratochvil.net>,
	"H. Peter Anvin" <hpa@...or.com>,
	Magnus Damm <magnus.damm@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Fastboot] [CFT] ELF Relocatable x86 and x86_64 bzImages

Don Zickus <dzickus@...hat.com> writes:

> On Sat, Aug 05, 2006 at 10:07:01AM -0600, Eric W. Biederman wrote:
>> Don Zickus <dzickus@...hat.com> writes:
>> 
>> >> The length error comes from lib/inflate.c 
>> >> 
>> >> I think it would be interesting to look at orig_len and bytes_out.
>> >> 
>> >> My hunch is that I have tripped over a tool chain bug or a weird
>> >> alignment issue.
>> >
>> > I thought so too, but I took vmlinuz images from people (Vivek) who had it
>> > boot on their systems but those images still failed on my two machines.  
>> >
>> >> 
>> >> The error is the uncompressed length does not math the stored length
>> >> of the data before from before we compressed it.  Now what is
>> >> fascinating is that our crc's match (as that check is performed first).
>> >> 
>> >> Something is very slightly off and I don't see what it is.
>> >
>> > I printed out orig_len -> 5910532 (which matches vmlinux.bin)
>> >              bytes_out -> 5910531
>> >
>> >> 
>> >> After looking at the state variables I would probably start looking
>> >> at the uncompressed data to see if it really was decompressing
>> >> properly.  If nothing else that is the kind of process that would tend
>> >> to spark a clue.
>> >
>> > I am not familiar with the code, so very few sparks are flying.  I'll
>> > still dig through though.  Thanks for the tips.
>> 
>> I guess the interesting thing to do would be to 
>> - Recompute the crc to see if we still match.
>> - Possibly instrument of flush_window.
>> 
>> I have a strange feeling that the uncompressed data is getting corrupted
>> after we have flushed the window.
>
> It seems to be an AMD64 vs EM64T problem.  AMD chipsets work but Intel
> chipsets don't.  
>
> I also blindly incremented bytes_out (as a really cheap hack), it didn't
> work until I added some random putstr's below it (timing??).  Then the
> kernel booted. 
>
> Still looking into things.  

Odd.  I wonder if I'm missing a serializing instruction somewhere,
to ensure the effects of ``self modifying code'' aren't a problem.
As I read Intels Documentation if you have a jump before you get
to the code there shouldn't be a problem.

Still that doesn't really explain bytes_out.


Eric
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