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Date: Thu, 20 Mar 2003 11:04:48 +0000 (GMT)
From: Hugh Dickins <hugh@veritas.com>
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To: Keith Owens <kaos@ocs.com.au>
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Subject: Re: 2.5.63 accesses below %esp (was: Re: ntfs OOPS (2.5.63)) 
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On Thu, 20 Mar 2003, Keith Owens wrote:
> On Tue, 18 Mar 2003 07:13:18 +0000 (GMT), 
> Hugh Dickins <hugh@veritas.com> wrote:
> >If you go ahead with this (I'm indifferent)
> 
> ksymoops 2.4.9 can decode variable length instructions before eip
> without affecting the reliabiloity of the code from eip onwards.  It is
> up to the kernel whether it dumps before eip or not.
> 
> >please remember that to
> >get reliable code from eip onwards, you need to handle the way both
> >2.4 and 2.5 nowadays pack short __LINE__ number and long __FILE__
> >pointer after BUG()'s ud2a (on i386).
> 
> Nothing I can do about that.  ksymoops uses objdump to decode the
> instructions and objdump does not know that the kernel abuses ud2a to
> add embedded line and file numbers.  In any case it is irrelevant, the
> only thing that ud2a ever tells you is "here there be BUG()".  For
> BUG() the code before eip is much more useful, see above.

But better not to describe the code shown from eip onwards as
"always reliable": if after a BUG() it's alarming nonsense!

Hugh

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