linux-kernel - Re: [PATCH 7/7] DWARF: add the config option

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Date:   Wed, 10 May 2017 09:46:38 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Ingo Molnar <mingo@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        live-patching@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH 7/7] DWARF: add the config option

On 05/06/2017, 09:19 AM, Ingo Molnar wrote:
> 
> * Linus Torvalds <torvalds@...ux-foundation.org> wrote:
> 
>> On Fri, May 5, 2017 at 5:22 AM, Jiri Slaby <jslaby@...e.cz> wrote:
>>> The DWARF unwinder is in place and ready. So introduce the config option
>>> to allow users to enable it. It is by default off due to missing
>>> assembly annotations.
>>
>> Who actually ends up using this?
> 
> Also, why wasn't Josh Poimboeuf Cc:-ed, who de-facto maintains the x86 unwinding 
> code?

I explicitly CCed Josh on 5/7 and 6/7 which touches the code. Besides
that, I assumed he is implicitly CCed via live-patching@...r.kernel.org
which is carbon-copied on each of the patches.

> AFAICS this series is just repeating the old mistakes of the old Dwarf unwinders 
> of trusting GCC's unwinder data. So NAK for the time being on the whole approach:
> 
> NAcked-by: Ingo Molnar <mingo@...nel.org>

OK, as the series stands now, we indeed do. Noteworthy, we, in SUSE, had
no problems with this reliance for all the time we have been using the
unwinder.

Anyway, objtool is about to vaidate the DWARF data, generate it for
assembly and potentially fix it if problems occur. Could you elaborate
on what else would help you to change your stance?

thanks,
-- 
js
suse labs