Lua：C++模块无法互相引用，未定义的符号。

我创建了两个模块（共享对象）CPU和SaveState作为模拟器的一部分。它们都被独立编译成.so文件，并且在运行时由一个Lua脚本使用require()加载，例如：

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

在CPU中，有一个操作SaveState的方法：

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;
}

它编译得很好，但require("CPU")这一行失败了：

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

使用nm -D我可以在savestate.so中看到精确的符号，但运行时由某种原因看不到。