tree 77f4eecb0b679f31d47d36d0a43af7fcd5d1687c
parent 5a22a62b96a68c2dd31784c5e3427ad7b365388a
author Hood Chatham <roberthoodchatham@gmail.com> 1791584744 -0700
committer GitHub <noreply@github.com> 1791584744 +0000
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gh-129040: Use wasm-gc to handle pointer casts in wasi (GH-158617)

This makes it so that in wasi builds if `-DPY_CALL_TRAMPOLINE` is passed, a call trampoline adaptor is used to prevent traps when there is a call signature mismatch between a C slot handler and the signature that the interpreter uses to call it.

This requires Clang >= 22. PEP 11 specifies that builds of Python 3.15 use WASI SDK version 33 which includes clang 23.1.0, so this could be used with Python 3.15 WASI builds but not earlier ones.

It requires a WebAssembly runtime that supports wasm-gc. Wasmtime has supported wasm-gc since version 27.0 released November 25, 2024. Some other runtimes still don't support it, but for those runtimes people can use builds with the trampoline disabled.

This also removed the Emscripten trampoline support for JS runtimes with no wasm-gc support. This removes a lot of implementation complexity and allows WASI and Emscripten to share code. The main concern is that it drops support for some very old iPhones, but every iPhone model released since 2018 is compatible with versions of Safari that support wasm-gc.

Tests were added that define handlers with various wrong numbers of arguments. The tests also run on non-webassembly platforms since they should work there as well.