linux-kernel - Re: [RFC PATCH v2 1/8] arm64: Implement stack trace termination record

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Message-ID: <6e3ac22b-99b8-7d99-59bd-6a2d1158b3c9@linux.microsoft.com>
Date:   Fri, 19 Mar 2021 13:19:19 -0500
From:   "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
To:     Mark Brown <broonie@...nel.org>
Cc:     mark.rutland@....com, jpoimboe@...hat.com, jthierry@...hat.com,
        catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v2 1/8] arm64: Implement stack trace termination
 record



On 3/19/21 9:29 AM, Madhavan T. Venkataraman wrote:
> 
> 
> On 3/19/21 7:30 AM, Mark Brown wrote:
>> On Thu, Mar 18, 2021 at 03:26:13PM -0500, Madhavan T. Venkataraman wrote:
>>> On 3/18/21 10:09 AM, Mark Brown wrote:
>>
>>>> If we are going to add the extra record there would probably be less
>>>> potential for confusion if we pointed it at some sensibly named dummy
>>>> function so anything or anyone that does see it on the stack doesn't get
>>>> confused by a NULL.
>>
>>> I agree. I will think about this some more. If no other solution presents
>>> itself, I will add the dummy function.
>>
>> After discussing this with Mark Rutland offlist he convinced me that so
>> long as we ensure the kernel doesn't print the NULL record we're
>> probably OK here, the effort setting the function pointer up correctly
>> in all circumstances (especially when we're not in the normal memory
>> map) is probably not worth it for the limited impact it's likely to have
>> to see the NULL pointer (probably mainly a person working with some
>> external debugger).  It should be noted in the changelog though, and/or
>> merged in with the relevant change to the unwinder.
>>
> 
> OK. I will add a comment as well as note it in the changelog.
> 
> Thanks to both of you.
> 
> Madhavan
> 

I thought about this some more. I think I have a simple solution. I will
prepare a patch and send it out. If you and Mark Rutland approve, I will
include it in the next version of this RFC.

Madhavan