linux-kernel - Re: [Kgdb-bugreport] [RFC] [Crash-utility] Patch to use gdb's bt in crash - works great with kgdb!

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Message-Id: <1157056874.24314.67.camel@piet2.bluelane.com>
Date:	Thu, 31 Aug 2006 13:41:13 -0700
From:	Piet Delaney <piet@...elane.com>
To:	Tom Rini <trini@...nel.crashing.org>
Cc:	Piet Delaney <piet@...elane.com>, Andi Kleen <ak@...e.de>,
	Andrew Morton <akpm@...l.org>,
	kgdb-bugreport@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	George Anzinger <george@...dturkeyranch.net>,
	vgoyal@...ibm.com, Subhachandra Chandra <schandra@...elane.com>,
	Discussion
	 "list for crash utility usage, maintenance and development" 
	<crash-utility@...hat.com>
Subject: Re: [Kgdb-bugreport] [RFC] [Crash-utility] Patch to use gdb's bt
	in crash - works	great with kgdb! - KGDB in Linus Kernel.

On Thu, 2006-08-31 at 07:20 -0700, Tom Rini wrote:
> On Thu, Aug 31, 2006 at 04:07:15PM +0200, Andi Kleen wrote:
> > Piet Delaney <piet@...elane.com> writes:
> > > > 
> > > > ENOPATCH
> > > 
> > > Opps. 
> > 
> > What an ugly patch!
> > 
> > But it should be totally obsolete with the unwinder work Jan and me have been
> > doing recently which does this all properly. .18 isn't quite there
> > yet in all cases, but .19 will be hopefully.
> 
> Indeed.  But quite functional.  Have you guys been doing i386 as well?
> This kind of thing was needed to convince gdb when it really was time to
> stop trying unwind in a few cases, but looks quite bad on x86_64/i386.
> Thankfully getting it to stop on ARM was pretty easy (but it wasn't
> full/true annotations).

I wonder if we are killing a fly with a sledgehammer. On SunOS 4.1.4 I
just patched the top of stack with a NULL pointer. With SPARC the kernel
uses different registers than the user and don't recall their being a
problem with a NULL pointer being at the top of the kernel stack. Is
there a problem with the i386 architecture with the top of the kernel
stack having a NULL pointer? My guess is that it's needed to return
to the right place in user space.

-piet

> 
-- 
Piet Delaney
BlueLane Teck
W: (408) 200-5256; piet@...elane.com
H: (408) 243-8872; piet@...t.net


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