Polymorphism doesn't work with SIDE_MODULE + USE_PTHREADS at all

[alexander-veselov]

It seems that polymorphism doesn't work with SIDE_MODULE + USE_PTHREADS at all (see code below):

• strange Implementation typeid name: emsc
• you can't call Implementation methods through pointers (neither through the base pointer nor through the derived)
• dynamic_cast / static_cast don't work

I think this is a serious problem. Am I missing something?

Important: If you remove -sUSE_PTHREADS=1 and -pthread, then everything works.

Implementation.h

#pragma once

struct Interface
{
    virtual ~Interface() {} // for std::unique_ptr
    virtual void Foo() const = 0;
};

struct Implementation : public Interface
{
    void Foo() const override;
};

Implementation.cpp

#include "Implementation.h"

#include <iostream>

void Implementation::Foo() const
{
    std::cout << "Foo" << std::endl;
};

main.cpp

#include "Implementation.h" // separate side module (dynamic linking)

#include <memory>
#include <iostream>

int main()
{
    std::cout << typeid(Interface).name() << std::endl; // 9Interface
    std::cout << typeid(Implementation).name() << std::endl; // emsc

    Implementation().Foo(); // works

    std::unique_ptr<Interface> interfacePointer(new Implementation());
    std::unique_ptr<Implementation> implementationPointer(new Implementation());

    // All calls below cause error 'null function or function signature mismatch'
    implementationPointer->Foo();
    interfacePointer->Foo(); 
    Interface* castedPointer = static_cast<Interface*>(implementationPointer.get());

    return 0;
}

Build commands:

emcc Implementation.cpp -fPIC -pthread -sSIDE_MODULE=1 -sUSE_PTHREADS=1 -o SideModule.wasm
emcc main.cpp -fPIC -pthread -sMAIN_MODULE=1 -sUSE_PTHREADS=1 -sPROXY_TO_PTHREAD=1 -o main.html SideModule.wasm

Runtime error:

Uncaught RuntimeError: null function or function signature mismatch

[Maksim-Bozhko]

This seems like a very serious bug, do emscripten devs have any comments or suggestions, are there any plans to fix this?

[sbc100]

Dynamic linking + threading is still experimental so its not unlikely this is real bug for something we don't yet have test coverage for. I'll take a look.

[goldwaving]

I'm not having any success with dynamic linking and pthreads in a real world multithreaded app. Statically linked, everything works as expected. Dynamically linked (on load or dlopen), strange and unexpected errors always occur. These errors occur on pure C libraries, so I think the issue goes beyond polymorphism.

[sbc100]

I'm working a fix this for this issue. It relates the weakly defined symbols that C++ uses for rtti info.

If you have other issues please file them.

[sbc100]

Fix is in flight upstream in llvm: https://reviews.llvm.org/D127333

[Maksim-Bozhko]

Thanks for a quick fix

[alexander-veselov]

Thank you so much!

[goldwaving]

Dynamically linked C and C++ modules are working great now. Thanks!