[PATCH] D111863: [libunwind] Add an interface for dynamic .eh_frame registration

[Lang Hames via Phabricator via cfe-commits]

lhames added a comment.

@joerg, @emaste -- I finally got a chance to experiment with a Linux docker container and confirmed that libgcc_s's `__register_frame` can handle individual frames. Unfortunately that does not help us on FreeBSD.

If we ignore FreeBSD for a moment we could imagine switch to registering single frames everywhere, but this would be an unrecoverable performance regression on Linux -- we would necessarily have to walk all CFI entries in the section to use the API.

One possible alternative solution would be to update libunwind's __register_ehframe function to also accept whole sections the same way libgcc_s does, but I don't think this is a good solution: We'd be overloading the behavior in a surprising way to match a libgcc_s behavior that doesn't seem well-documented, and we'd still be left needing some other way to detect whether the current unwinder supported the desired semantics.

I think the ideal solution would be to always pass in whole sections, as @housel's proposed solution does.

I think we can debate the right API signature (e.g. should it pass the section range so that we really can skip walking the CFI records, or is this cheap enough not to bother?), function name, and implementation, but does anyone have any objection to the direction? If so, why?


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  https://reviews.llvm.org/D111863/new/

https://reviews.llvm.org/D111863