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

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Date:	Mon, 7 Aug 2006 19:57:27 -0400
From:	Don Zickus <dzickus@...hat.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.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

> >> >
> >> >> 
> >> >> 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
> >> >
> >> >> 
> > 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.
> 

So I narrowed down the problem but it isn't obvious to me why this problem
exists.  Basically, even though bytes_out is supposed to be initialized to
0, it becomes -1 before entering decompress_kernel().  Of course, the
fallout is in flush_window() bytes_out wounds up being one less than
outcnt and hence my original problem.

Any thoughts on how to debug where this could be getting corrupted?  

Cheers,
Don

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