RuntimeError: unreachable when calling imported function in standalone mode

[vedantroy]

When importing a JS function from C & calling it in standalone mode, I get an unreachable error (WASM execution hit an "unreachable" statement).

Here's the reproduction:

void import_from_js();

int main() {
    import_from_js();
    return 0;
}

(async () => {
    const { instance } = await WebAssembly.instantiateStreaming(fetch("./sample.wasm"), {
        env: {
            import_from_js: () => {
                console.log("Hello World!")
            }
        },
        wasi_snapshot_preview1: {
            proc_exit: (code) => {
                console.log(code)
            }
        }
    })
    await instance.exports._start()
})()

The command: emcc sample.c -o sample.wasm -s ERROR_ON_UNDEFINED_SYMBOLS=0.

Emscripten version: emcc (Emscripten gcc/clang-like replacement) 2.0.4 (3047b77)

[sbc100]

I think we figured this out on discord. proc_exit is supposed to never return. You need to throw or exit the process or something like that.

I think llvm inserts and unreachable instruction after a call to any C/C++ function marked noreturn which __wasi_proc_exit is:

emscripten/system/include/wasi/api.h

Line 2604 in 0014175

_Noreturn void __wasi_proc_exit(