Re: [RFC PATCH v8 3/4] arm64: Introduce stack trace reliability checks in the unwinder

On 8/26/21 10:57 AM, Mark Brown wrote:

On Thu, Aug 12, 2021 at 02:06:02PM -0500, madvenka@linux.microsoft.com wrote:

quoted

+	if (frame->need_reliable && !unwind_is_reliable(frame)) {
+		/* Cannot unwind to the next frame reliably. */
+		frame->failed = true;
+		return false;
+	}

This means we only collect reliability information in the case
where we're specifically doing a reliable stacktrace.  For
example when printing stack traces on the console it might be
useful to print a ? or something if the frame is unreliable as a
hint to the reader that the information might be misleading.
Could we therefore change the flag here to a reliability one and
our need_reliable check so that we always run
unwind_is_reliable()?

I'm not sure if we need to abandon the trace on first error when
doing a reliable trace but I can see it's a bit safer so perhaps
better to do so.  If we don't abandon then we don't require the
need_reliable check at all.

I think that the caller should be able to specify that the stack trace
should be abandoned. Like Livepatch.

So, we could always do the reliability check. But keep need_reliable.

Thanks.

Madhavan
	

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