hwpmc: simplify arm64 kernel stack unwinding

[mhorne]

Summary

Use the unwind_frame() function, which properly validates the frame
pointer and uses ADDR_MAKE_CANONICAL() for the pc, required when PAC is
enabled.

[mhorne]

FYI, locally I have a STACK_FOREACH() addition to the stack(9) KPI which would give us an MI way to loop through the list of PC addresses after a call to stack_save(). Possibly this can be used to simplify this or other cases further, at a small cost.

It is still half-baked, and not something I plan to tackle immediately.

[markj]

sys/dev/hwpmc/hwpmc_arm64_md.c

91

unwind_frame() doesn't check whether the returned PC is in the kernel, so this represents a behaviour change.

[mhorne]

Add back the check for PMC_IN_KERNEL(pc).

[mhorne]

sys/dev/hwpmc/hwpmc_arm64_md.c

91

Thank you, great catch.