[RFC PATCH v2 1/4] arm64: Implement infrastructure for stack trace reliability checks

[Mark Brown]

On Mon, Apr 05, 2021 at 03:43:10PM -0500, madvenka at linux.microsoft.com wrote:

> These checks will involve checking the return PC to see if it falls inside
> any special functions where the stack trace is considered unreliable.
> Implement the infrastructure needed for this.

Following up again based on an off-list discussion with Mark Rutland:
while I think this is a reasonable implementation for specifically
listing functions that cause problems we could make life easier for
ourselves by instead using annotations at the call sites to put things
into sections which indicate that they're unsafe for unwinding, we can
then check for any address in one of those sections (or possibly do the
reverse and check for any address in a section we specifically know is
safe) rather than having to enumerate problematic functions in the
unwinder.  This also has the advantage of not having a list that's
separate to the functions themselves so it's less likely that the
unwinder will get out of sync with the rest of the code as things evolve.

We already have SYM_CODE_START() annotations in the code for assembly
functions that aren't using the standard calling convention which should
help a lot here, we could add a variant of that for things that we know
are safe on stacks (like those we expect to find at the bottom of
stacks).
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