linux-kernel - Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

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Date:	Wed, 20 May 2015 21:10:16 +0200 (CEST)
From:	Jiri Kosina <jkosina@...e.cz>
To:	Peter Zijlstra <peterz@...radead.org>
cc:	Andy Lutomirski <luto@...capital.net>,
	Ingo Molnar <mingo@...nel.org>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Michal Marek <mmarek@...e.cz>,
	X86 ML <x86@...nel.org>, live-patching@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	Brian Gerst <brgerst@...il.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation

On Wed, 20 May 2015, Peter Zijlstra wrote:

> > I think it would be nice to have full DWARF unwind support for
> > everything at some point.  Unfortunately, I don't see any easy path to
> > getting there.  It doesn't help that AFAIK no one has ever proposed a
> > usable in-kernel DWARF unwinder.
> 
> There's a bit of history here; SuSE (iirc) actually has one, however:
> 
>   https://lkml.org/lkml/2012/2/10/356

Oh absolutely, there are stories behind this :)

Just for the sake of completness -- the current implementation can be 
found in our public GIT repository, for not-really-complete picture see 
[1] [2] [3] [4].

It turned out to be rather useful on many ocasions when debugging customer 
reports, but I of course also understand what Linus is saying above. The 
bugs in unwinder can be *really* painful. Our experience so far has been 
that it did pay off at the end of the day (and of course analyzing 
stacktraces is our daily bread).

[1] http://kernel.suse.com/cgit/kernel-source/tree/patches.suse/stack-unwind?h=SLE12
[2] http://kernel.suse.com/cgit/kernel-source/tree/patches.suse/no-frame-pointer-select?h=SLE12
[3] http://kernel.suse.com/cgit/kernel-source/tree/patches.arch/stack-unwind-cfi_ignore-takes-more-arguments?h=SLE12
[4] http://kernel.suse.com/cgit/kernel-source/tree/patches.arch/x86_64-unwind-annotations?h=SLE12

-- 
Jiri Kosina
SUSE Labs
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