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SubjectRe: [RFC PATCH v1 1/1] arm64: Unwinder enhancements for reliable stack trace
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On 2/24/21 6:33 AM, Mark Brown wrote:
> On Tue, Feb 23, 2021 at 01:20:49PM -0600, Madhavan T. Venkataraman wrote:
>> On 2/23/21 1:02 PM, Mark Brown wrote:
>>> On Tue, Feb 23, 2021 at 12:12:43PM -0600, madvenka@linux.microsoft.com wrote:
>
>>>> Reliable stack trace function
>>>> =============================
>>>>
>>>> Implement arch_stack_walk_reliable(). This function walks the stack like
>>>> the existing stack trace functions with a couple of additional checks:
>
>>> Again, this should be at least one separate patch. How does this ensure
>>> that we don't have any issues with any of the various probe mechanisms?
>>> If there's no need to explicitly check anything that should be called
>>> out in the changelog.
>
>> I am trying to do this in an incremental fashion. I have to study the probe
>> mechanisms a little bit more before I can come up with a solution. But
>> if you want to see that addressed in this patch set, I could do that.
>> It will take a little bit of time. That is all.
>
> Handling of the probes stuff seems like it's critical to reliable stack
> walk so we shouldn't claim to have support for reliable stack walk
> without it. If it was a working implementation we could improve that'd
> be one thing but this would be buggy which is a different thing.
>

OK. I will address the probe stuff in my resend.

>>>> + (void) on_accessible_stack(task, stackframe, &info);
>
>>> Shouldn't we return NULL if we are not on an accessible stack?
>
>> The prev_fp has already been checked by the unwinder in the previous
>> frame. That is why I don't check the return value. If that is acceptable,
>> I will add a comment.
>
> TBH if you're adding the comment it seems like you may as well add the
> check, it's not like it's expensive and it means there's no possibility
> that some future change could result in this assumption being broken.
>

OK. I will add the check.

Thanks.

Madhavan

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