linux-kernel - Re: [PATCH v13 06/11] arm64: Use stack_trace_consume

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Date:   Thu, 10 Mar 2022 09:33:36 +0100 (CET)
From:   Miroslav Benes <mbenes@...e.cz>
To:     Mark Brown <broonie@...nel.org>
cc:     "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>,
        Mark Rutland <mark.rutland@....com>, jpoimboe@...hat.com,
        ardb@...nel.org, nobuta.keiya@...itsu.com,
        sjitindarsingh@...il.com, catalin.marinas@....com, will@...nel.org,
        jmorris@...ei.org, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v13 06/11] arm64: Use stack_trace_consume_fn and rename
 args to unwind()

On Wed, 9 Mar 2022, Mark Brown wrote:

> On Tue, Mar 08, 2022 at 04:00:35PM -0600, Madhavan T. Venkataraman wrote:
> 
> > It is just that patch 11 that defines "select
> > HAVE_RELIABLE_STACKTRACE" did not receive any comments from you
> > (unless I missed a comment that came from you. That is entirely
> > possible. If I missed it, my bad). Since you suggested that change, I
> > just wanted to make sure that that patch looks OK to you.
> 
> I think that's more a question for the livepatch people to be honest -
> it's not entirely a technical one, there's a bunch of confidence level
> stuff going on.  For example there was some suggestion that people might
> insist on having objtool support, though there's also substantial
> pushback on making objtool a requirement for anything from other
> quarters.  I was hoping that posting that patch would provoke some
> discussion about what exactly is needed but that's not happened thus
> far.

I think everyone will be happy with HAVE_RELIABLE_STACKTRACE on arm64 as 
long as there is a guarantee that stack traces are really reliable. My 
understanding is that there is still some work to be done on arm64 arch 
side (but I may have misunderstood what Mark R. said elsewhere). And yes, 
then there is a question of objtool. It is one option but not the only 
one. There have been proposals of implementing guarantees on a compiler 
side and leaving objtool for x86_64 only (albeit objtool may bring more 
features to the table... ORC, arch features checking).

Madhavan also mentioned that he enhanced objtool and he planned to submit 
it eventually 
(https://lore.kernel.org/all/1a0e19db-a7f8-4c8e-0163-398fcd364d54@linux.microsoft.com/T/#u), 
so maybe arm64 maintainers could decide on a future direction based on 
that?

Regards
Miroslav