wasm-decompile: unexpected opcode 0x12

[DieracDelta]

When I run the decompiler on a simple haskell wasm program I get:

0003931: error: unexpected opcode: 0x12

Steps to reproduce:

• obtain ghc with a wasm backend
• echo 'main = putStrLn "hello world"' > hello.hs
• wasm32-wasi-ghc hello.hs -o hello.wasm
• decompile: wasm-decompile hello.wasm

Note: I get this error on 1.0.37 and the ghc version obtained with nix.

[kripken]

Attaching the wasm file would help investigate this. But 0x12 could be array.init_data, and wabt doesn't support GC yet.

[DieracDelta]

I've uploaded the wasm file here

[sbc100]

Seems like that question is already answered. The GC proposal is not yet implemented in wasm (array.init_data is part of that).

There are some open PRs to add support. See #2607 but also #2348

[DieracDelta]

Gotcha, that makes sense. Thank you for the quick and detailed reply!

[rossberg]

I think 0x12 is return_call, i.e., a tail call. AFAIK, GHC's Wasm backend does not use the GC proposal yet.

[sbc100]

In that case maybe --enable-tail-call would help?

[kripken]

Yes, looking at the wasm, it has return_call and no GC, so @rossberg 's guess was correct.

[sbc100]

Yup, adding --enable-tail-call resolves the issue. I would have though the decoder would mention that rather than just error.. .but it doesn't seem to.

[sbc100]

You can also use --enable-all with all the wabt tools to avoid this kind of issue going forward.

[DieracDelta]

--enable-tail-call has the decompiler run successfully. Thank you!