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

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Date:   Thu, 10 Mar 2022 06:36:09 -0600
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Miroslav Benes <mbenes@...e.cz>, Mark Brown <broonie@...nel.org>
Cc:     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 3/10/22 02:33, Miroslav Benes wrote:
> 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?
> 

Yes. I am working on that right now. Hope to send it out soon.

Madhavan