GH-146475: Strip CFI directives from JIT stencils to allow using Apple LLVM 21#148364
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savannahostrowski wants to merge 10 commits intopython:mainfrom
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GH-146475: Strip CFI directives from JIT stencils to allow using Apple LLVM 21#148364savannahostrowski wants to merge 10 commits intopython:mainfrom
savannahostrowski wants to merge 10 commits intopython:mainfrom
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Gonna try out some other flags in a bit. Gotta assemble a new couch first. |
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After poking around at this a bit, it seems like Apple LLVM 21 is stricter about validating CFI frame nesting. In debug builds,
.cfi_endprocdirectives can end up in blocks that the optimizer removes as unreachable, leaving unbalanced.cfi_startprocdirectives that the assembler rejects (and so you'll get something like this #146478 (comment) while building).Since JIT stencils are already compiled with
-fno-asynchronous-unwind-tables, I believe the CFI directives are unused and so they can be stripped out. I also tried changing the flag to-fno-unwind-tablesinstead to just prevent us from emitting the directives in the first place but it seems like that's a bigger change as we'd have to handleSHT_X86_64_UNWINDsections on x86_64 Linux (https://github.com/python/cpython/actions/runs/24265500635/job/70859484777?pr=148364)? I'm not totally sure why that is. We could go that route but wanted to solicit opinions first before going down that road.This is an alternative to #146478 that tries to fix the root cause rather than blocking Apple LLVM 21.