I need help to link rust PyO3 package to pyodide.

[km19809]

Hello, I am trying to build my simple pyo3 package for pyodide.
I've seen #2081, but my code is just a map between an alphabet and a Cyril letter and does not use the print! macro.
So I thought that my code will work.
However, I could not link my code to the pyodide properly.
When I use cargo build --target wasm32-unknown-emscripten, it throws errors such as:

note: emcc: warning: please replace -g4 with -gsource-map [-Wdeprecated]
          wasm-ld: error: /home/minsoo/hobby/py_cyril/target/wasm32-unknown-emscripten/debug/deps/libpyo3-3d1f6a9e6e0af0dc.rlib(pyo3-3d1f6a9e6e0af0dc.pyo3.2b037835-cgu.0.rcgu.o): undefined symbol: PyExc_AttributeError
          wasm-ld: error: /home/minsoo/hobby/py_cyril/target/wasm32-unknown-emscripten/debug/deps/libpyo3-3d1f6a9e6e0af0dc.rlib(pyo3-3d1f6a9e6e0af0dc.pyo3.2b037835-cgu.0.rcgu.o): undefined symbol: PyExc_BaseException
          wasm-ld: error: /home/minsoo/hobby/py_cyril/target/wasm32-unknown-emscripten/debug/deps/libpyo3-3d1f6a9e6e0af0dc.rlib(pyo3-3d1f6a9e6e0af0dc.pyo3.2b037835-cgu.0.rcgu.o): undefined symbol: PyExc_ValueError
          wasm-ld: error: /home/minsoo/hobby/py_cyril/target/wasm32-unknown-emscripten/debug/deps/libpyo3-3d1f6a9e6e0af0dc.rlib(pyo3-3d1f6a9e6e0af0dc.pyo3.2b037835-cgu.0.rcgu.o): undefined symbol: PyExc_TypeError
          emcc: error: '/home/minsoo/emsdk/upstream/bin/wasm-ld @/tmp/emscripten_kw6egf8y.rsp.utf-8' failed (returned 1)

So, here is the question:
If I want to link my package to pyodide, do I have to write meta.yaml and build the entire pyodide with it?
Is there any way to link pyodide without building the entire pyodide again?

Thank you.

[hoodmane]

You don't need to rebuild Pyodide. You will need to apply this patch to your copy of emscripten:
https://github.com/pyodide/pyodide/pull/2081/files#diff-4d3dbac9b16778c2f3c4e57a847de655a6d51b8b92d89d3ba926148a79dfeddb

Also, you need to build the rust standard library unless your package has #[no-std]. You also need:

    export RUSTFLAGS="\
      -C relocation-model=pic\
      -C target-feature=+mutable-globals\
      -C link-arg=-s\
      -C link-arg=SIDE_MODULE=1\
    "

You should imitate the build script here:
https://github.com/hoodmane/pyodide/blob/pyo3/packages/pyo3_samples/meta.yaml

[derivator]

Hey @km19809 , I'm having the same problem with __cxa_thread_atexit_impl, have you found a solution?

[hoodmane]

I think if you set the following environment variables:

export CARGO_BUILD_TARGET=wasm32-unknown-emscripten
export CARGO_UNSTABLE_BUILD_STD=true
export RUSTFLAGS= \
	-C relocation-model=pic \
	-C link-arg=-sSIDE_MODULE=2 \
	-C link-arg=-sWASM_BIGINT \
	-Z link-native-libraries=no

and then build with the most recent nightly Rust it should work.

[hoodmane]

• You don't need target-feature=+mutable-globals anymore I don't think
• emscripten/gxx_personality_v0_stub.o was fixed in Don't use __gxx_personality_v0 in panic_unwind on emscripten target rust-lang/rust#97888
• -fPIC isn't needed as an argument either, I think
• -s ASYNCIFY: are you building Pyodide's main module with this? I would guess that it won't work in the side module if it isn't in the main module
• To prevent wasm-ld: error: unable to find library -lc-debug use -sSIDE_MODULE=2 instead of -sSIDE_MODULE=1.

[hoodmane]

I wrote a blog post about this which may help:
https://blog.pyodide.org/posts/rust-pyo3-support-in-pyodide/

[km19809]

@derivator Sorry for the late reply. I suffered from this issue, but I followed hoodname's PR and then solved the issue. I suggest you follow his work too.

@hoodmane Thank you. I compiled my simple library successfully. It works well.
However, my ultimate goal is to compile an SDL-based library, pyxel for pyodide.
I used -s ASYNCFY for this. But if -s ASYNCFY would not work with side modules, I should check pygame-wasm.