Calling a virtual method from MAIN_MODULE in SIDE_MODULE leads to crash

[nightelf3]

There is a crash inside the virtual function when the base class is located inside the main module and the derived class is located inside the side module.

Side module is loaded via dlopen.
I found the similar issue here: #17150
IMPORTANT: there is no crash when the side module is pre-loaded on startup

Version of emscripten/emsdk: 3.1.20 (https://github.com/emscripten-core/emscripten/releases/tag/3.1.20)

CBaseFilter.h

#pragma once

#define EXPORTED __attribute__ ((visibility("default")))

class EXPORTED CBaseFilter
{
public:
	virtual int GetValue();
	virtual int MakeValue();
};

filter.cpp

#include "CBaseFilter.h"

class CFilter : public CBaseFilter
{
	int MakeValue() override
	{
		return 123;
	}
};

extern "C"
{
EXPORTED int GetFilterValue()
{
	CFilter flt;
	return flt.GetValue();
}
}

main.cpp

#include <iostream>
#include <dlfcn.h>

#include "CBaseFilter.h"
int CBaseFilter::GetValue()
{
	return MakeValue();
}
int CBaseFilter::MakeValue()
{
	return 0;
}

int main()
{
	std::cout << "Start" << std::endl;
	auto hModule = dlopen("flt.wasm", RTLD_NOW);
	if (!hModule)
		std::cout << dlerror() << std::endl;

	auto sym = reinterpret_cast<int (*)()>(dlsym(hModule, "GetFilterValue"));
	std::cout << sym() << std::endl;

	dlclose(hModule);
	std::cout << "Finished!" << std::endl;
	return 0;
}

Build:

• mkdir out
• emcc Filter.cpp -fPIC -fvisibility=hidden -c -o out\Filter.o
• emcc -sUSE_PTHREADS=1 -sSIDE_MODULE=1 -g -o out\flt.wasm out\Filter.o
• emcc main.cpp -fPIC -fvisibility=hidden -c -o out\main.o
• emcc -sMAIN_MODULE=1 -sPROXY_TO_PTHREAD -sUSE_PTHREADS=1 -g -o out\Filter.html out\main.o
  • P.S. no crash when:
    emcc -sMAIN_MODULE=1 -sPROXY_TO_PTHREAD -sUSE_PTHREADS=1 -g -o out\Filter.html out\main.o flt.wasm

Console:

Filter.worker.js:202 Uncaught RuntimeError: null function or function signature mismatch
    at CBaseFilter::GetValue() (Filter.wasm:0x75ff0)
    at GetFilterValue (4a5a1b72:0x38c)
    at __original_main (Filter.wasm:0x76198)
    at _main_thread (Filter.wasm:0x77840)
    at Object.invokeEntryPoint (Filter.js:4166:42)
    at self.onmessage (Filter.worker.js:155:35)

[nightelf3]

Hello @sbc100, are you able to reproduce the issue?
Do you need some additional info?

[sbc100]

I didn't get change reproduce this yet no, but I think it might the same issue that I'm working on fixing in #18311 .. the fact the passing the module on the command line fixes the issue makes it very likely.

[sbc100]

Should be fixed in #18311

[nightelf3]

@sbc100, thank you a lot!