Lua: C++ modules can't reference eachother, un

问题:

I've created two modules (shared objects) CPU and SaveState as part of an emulator. Both are independently compiled into .so separate files, and loaded at runtime by a Lua script using require(); i.e.:

SaveState = require("SaveState")
CPU = require("CPU")

Within CPU, there's a method that operates on a SaveState:

int CPU::save_state(SaveState *state) {
    state->begin_section(savestate_namespace, savestate_data_size);

    state->write16(this->reg.af);
    state->write16(this->reg.bc);
    state->write16(this->reg.de);
    state->write16(this->reg.hl);
    state->write16(this->reg.sp);
    state->write16(this->reg.pc);
    state->write8 (this->interrupts_enabled);
    state->write8 (this->irq_flags);
    state->write8 (this->ie_flags);
    state->write8 (this->halted);
    state->write8 (this->halt_bug);
    state->write8 (this->extra_cycles);
    state->write64(this->total_cycles);
    state->write64(this->idle_cycles);

    return SaveState::OK;
}

It compiles fine, but the require("CPU") line fails:

lua5.1: error loading module 'cpu' from file './src/cpu/build/cpu.so':
    ./src/cpu/build/cpu.so: undefined symbol: _ZN9SaveState7write64Ey

Using nm -D I can see that exact symbol in savestate.so, but at runtime it's not seen for some reason.

回答1:

I managed to solve this by writing a third module, which gets loaded before the other two and just calls dlopen() in its luaopen_module method:

void *res = dlopen("src/savestate/build/savestate.so",
    RTLD_NOW | RTLD_GLOBAL);

I'm not sure this is the best solution, but it seems to do the trick. (I'll have to generalize it a bit to not use hardcoded paths and so on...)