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

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Date:	Thu, 31 Aug 2006 09:48:50 +0200
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Andi Kleen" <ak@...e.de>
Cc:	"J. Bruce Fields" <bfields@...ldses.org>,
	"Badari Pulavarty" <pbadari@...il.com>,
	<petkov@...h.uni-muenster.de>, <akpm@...l.org>,
	"lkml" <linux-kernel@...r.kernel.org>
Subject: Re: Was: boot failure, "DWARF2 unwinder stuck at 0xc0100199"

>>> Andi Kleen <ak@...e.de> 31.08.06 09:41 >>>
>On Thursday 31 August 2006 09:35, Jan Beulich wrote:
>> Andi submitted a fix for this to Linus, but that's post-rc5. Jan
>
>I assume you mean the fallback validation fix. Linus unfortunately
>didn't merge any of my new patches yet :/

Actually, the same patch, but other pieces of it ...

>But did you ever work out why the stack backtrace completely restarted? 
>I never got this. In theory the RSP gotten out of the unwind
>context and used for the fallback should have been already near the end
>and the old unwinder shouldn't have found much.

In the old (up to -rc5) code, we had

		if (unw_ret > 0 && !arch_unw_user_mode(&info)) {
			< all the fallback handling>
		}

with no else, thus just falling through (without even changing the
stack pointer, which was wrong when unw_ret > 0 but we reached
a user mode address (i.e. as in the example here, after unwinding
out of a syscall frame).

Jan
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