Not sure if this issue belong to this repo or https://github.com/pyodide/pyodide, but shouldn't be a big of deal.

Just came across the issue compiling pyodide Python extension and meeting error Error: Dynamic linking error: cannot resolve symbol invoke_iii when trying to import it in wasm-python.

Investigating in depth, I've found that one of the libraries I was using was referring to this invoke_iii symbol.
Narrowing it down, I've found that the issue was that this library had some exception handling in its code and its .o file was compiled with -fexceptions, but without -fwasm-exceptions - I don't really know how it works on low level, but then emscripten ends up using invoke_iii symbols when handling exceptions, which pyodide doesn't use.

The reason why there's no -fwasm-exceptions - it was .cpp file and therefore it was using CMAKE_CXX_FLAGS, which is initialized based on SIDE_MODULE_CXXFLAGS:

Which is initialized from Makefile.envs's CXXFLAGS_BASE which is empty.

https://github.com/pyodide/pyodide/blob/df94f6edcf3937d1d692c6e740e1be27c850af38/Makefile.envs#L153-L154

-fwasm-exceptions only provided for CFLAGS_BASE -> SIDE_MODULE_CFLAGS -> CMAKE_C_FLAGS

https://github.com/pyodide/pyodide/blob/df94f6edcf3937d1d692c6e740e1be27c850af38/Makefile.envs#L134-L140

Should CXXFLAGS_BASE reuse flags from CFLAGS_BASE to avoid issues when project is using c++ files with exceptions handling?

Note for others meeting similar issues:

A workarounds:

1. Initialize SIDE_MODULE_CXXFLAGS from cflags globally before running pyodide build-recipes-no-deps or other pyodide command you're using.

export SIDE_MODULE_CXXFLAGS=`pyodide config get cflags`

2. Or inside your meta.yaml recipe or wherever before your script runs emcmake cmake, initalize CXXFLAGS from CFLAGS env variable:

export SIDE_MODULE_CXXFLAGS=$SIDE_MODULE_CFLAGS

How to locate the exact failing library:
Symbol doesn't have to be invoke_iii exactly, it can be invoke_ii, invoke_vi, depending on the kind of exception.
If you want to find where this symbol is coming from, emnm won't help you with this - invoke_iii is not present in any of it's options.
What you can do, is to do grep -a invoke_iii library.so, which will give you output like below and maybe there will be clues (for me opencascade suggested that symbol is coming to opencascade library, so I was able investigate it this library in particular and find the exact file that introduces it).

invoke_iii ��env�_ZN15OSD_EnvironmentD2Ev ��env�pthread_detach ��envpthread_join ��envpthread_self ��env/_ZN11opencascade6handleI16Standard_FailureED2Ev ��env�__wasm_setjmp_test ��env�setTempRet0  �env

If someone wants to reproduce this qucikly:

// hello.cpp
#include <Python.h>

static PyObject* add(PyObject* self, PyObject* args) {
    int a, b;
    if (!PyArg_ParseTuple(args, "ii", &a, &b)) {
        return NULL;
    }
    try {
        return PyLong_FromLong(a + b);
    } catch (...) {
        return NULL;
    }
}

static PyMethodDef methods[] = {
    {"add", add, METH_VARARGS, "Add two numbers"},
    {NULL, NULL, 0, NULL}
};

static struct PyModuleDef module = {
    PyModuleDef_HEAD_INIT,
    "hello",
    NULL,
    -1,
    methods
};

PyMODINIT_FUNC PyInit_hello(void) {
    return PyModule_Create(&module);
}

# CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
project(hello)

set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fexceptions")
include_directories($ENV{Python_INCLUDE_DIRS})

add_library(hello MODULE hello.cpp)

set_target_properties(hello PROPERTIES PREFIX "")

export CMAKE_TOOLCHAIN_FILE="$(pyodide config get cmake_toolchain_file)"
export SIDE_MODULE_CFLAGS="$(pyodide config get cflags)"
export SIDE_MODULE_LDFLAGS="$(pyodide config get ldflags)"
export SIDE_MODULE_CXXFLAGS="$(pyodide config get cxxflags)"
export Python_INCLUDE_DIRS="$(pyodide config get python_include_dir)"
mkdir build
cd build
rm -rf ./* && emcmake cmake .. -G Ninja
ninja -v
wasm-python -c "import hello; print(hello.add(5,2))"

# Pyodide has suffered a fatal error. Please report this to the Pyodide maintainers.
# The cause of the fatal error was:
# Error: Dynamic linking error: cannot resolve symbol invoke_ii