linux-kernel - Re: boot failure, "DWARF2 unwinder stuck at 0xc0100199"

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Date:	Tue, 22 Aug 2006 10:18:49 +0200
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Andrew Morton" <akpm@...l.org>, "Andi Kleen" <ak@...e.de>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	<linux-kernel@...r.kernel.org>,
	"Randy.Dunlap" <rdunlap@...otime.net>
Subject: Re: boot failure, "DWARF2 unwinder stuck at 0xc0100199"

>> Has anyone even tried to reproduce Bruce's crash?
>
>I looked at it a bit, but it puzzles me. The chaining for the interrupt stacks
>on i386 -- which is what seems to be corrupted here -- shouldn't have changed at all 
>by the unwinder changes.

Not necessarily:

	if (UNW_SP(&info))
		stack = (void *)UNW_SP(&info);

is rather fragile - the minimum extra protection here should be to only use
UNW_SP() for the continuation stack pointer if it actually points into kernel
space (as is being done in one of the 2.6.19 patches), ...

>I suspect it would crash without unwinder too. Bruce, do you get the 
>same crash when you boot with "call_trace=old" ? 

... but of course I continue to agree that doing things like

	addr = *stack++;

in the legacy stack trace code cannot be good, given that this code
generally is expected to run when things are already bad in some way.

Jan
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