arm64: stacktrace: Implement arch_stack_walk_reliable()

Add arch_stack_walk_reliable(), which will be used during kernel live
patching to detect when threads have completed executing old versions of
functions.

Note that arch_stack_walk_reliable() only needs to guarantee that it
returns an error code when it cannot provide a reliable stacktrace. It
is not required to provide a reliable stacktrace in all scenarios so
long as it returns said error code.

At present we can only reliably unwind up to an exception boundary. In
future we should be able to improve this with additional data from the
compiler (e.g. sframe).

Signed-off-by: Song Liu <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
[ Mark: Simplify logic, clarify commit message ]
Signed-off-by: Mark Rutland <[email protected]>
Cc: Andrea della Porta <[email protected]>
Cc: Breno Leitao <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Miroslav Benes <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Will Deacon <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Catalin Marinas <[email protected]>

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