Tracking Issue for asm_unwind

[Amanieu]

The feature gate for the issue is #![feature(asm_unwind)].

Summary

This feature adds a may_unwind option to asm! which allows an asm block to unwind stack and be part of the stack unwinding process. This option is only supported by the LLVM backend right now.

Status

Blocked on the stabilization of extern "C-unwind" (#74990).

Also it is uncertain whether this can be supported directly by non-LLVM backends. It is possible to support by outlining the assembly code to a separate function and calling it.

[bstrie]

Note that extern "C-unwind" has been stabilized as of #116088 . Are there any remaining blockers for this feature?

[Amanieu]

I'm having crashes in corosensei when using this feature which I've tracked down to LLVM's register allocator not handling unwinding from inline assembly correctly. However I have not been able to extract a minimal reproducer, and even extracting the LLVM IR and compiling it manually with llc fails to reproduce the problem.