[RFC PATCH 0/3] arm64: Implement reliable stack trace

[Madhavan T. Venkataraman]

On 10/12/20 12:26 PM, Mark Brown wrote:
> This patch series aims to implement reliable stacktrace for arm64. 
> Reliable stacktrace exists mainly to support live patching, it provides
> a version of stacktrace that checks for consistency problems in the
> traces it generates and provides an error code to callers indicating if
> any problems were detected.      
> 
> This is a first cut of support for arm64, I've not really even started
> testing it meaningfully at this point.  The main thing I'm looking for
> here is that I'm not sure if there are any more potential indicators of
> unrelabile stacks that I'm missing tests for or anything about the
> interfaces that I've misunderstood.
> 
> There's more work that can be done here, mainly that we could sync our
> unwinder more with what's done on S/390 and x86 which should if nothing
> else help with keeping up to date with generic changes, but this should 
> be what's needed to allow reliable stack trace.
> 
> Mark Brown (2):
>   arm64: stacktrace: Report when we reach the end of the stack
>   arm64: stacktrace: Implement reliable stacktrace
> 
> Mark Rutland (1):
>   arm64: remove EL0 exception frame record
> 
>  arch/arm64/Kconfig             |  1 +
>  arch/arm64/kernel/entry.S      | 10 +++----
>  arch/arm64/kernel/stacktrace.c | 55 ++++++++++++++++++++++++++++------
>  3 files changed, 52 insertions(+), 14 deletions(-)
> 

This is mostly a question to improve my understanding of the current ARM64
unwinder.

Currently, ARM64 defines different stack types - task stack, IRQ stack, etc.
When it unwinds, it appears to unwind only the currently active stack.
Specifically, if an interrupt has happened and the IRQ stack is the one that
is active, only the IRQ stack is unwound. The task stack is not. Is this
accurate?

My question is - for live patching, we would need to look at the task stack
as well, right? May be, we need to pass a flag to the unwinder to check the
task stack in addition to the active task?

Madhavan