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考虑以下具有 3 级多重继承层次结构的代码。

auto addr = [](auto v) -> uint64_t { return *reinterpret_cast<uint64_t*>(v); };

struct BaseA
{
    void virtual a() {}
};

struct BaseB
{
    void virtual b() {}
};

struct BaseC : BaseA, BaseB
{
    void virtual a() override {}
    void virtual b() override {}
};

struct BaseD
{
    void virtual d() {}
};

struct BaseE : BaseD, BaseC
{
    void virtual d() override {}
    void virtual a() override {}
    void virtual b() override { auto a = this; std::cout << "called here: " << addr(&a) << "\n"; }
};

int main()
{

    BaseE obj;

    BaseE* ePtr = &obj;
    BaseD* dPtr = &obj;
    BaseC* cPtr = &obj;
    BaseB* bPtr = &obj;
    BaseA* aPtr = &obj;

    ePtr->b();
    cPtr->b();
    bPtr->b();

    std::cout << "e is at: " << addr(&ePtr) << "\n"
              << "d is at: " << addr(&dPtr) << "\n"
              << "a is at: " << addr(&aPtr) << "\n"
              << "c is at: " << addr(&cPtr) << "\n"
              << "b is at: " << addr(&bPtr) << "\n"
              << "total size is " << sizeof(BaseE) << "\n"
              << "vptr D and E " << vpt1 << "\n"
              << "vptr A and C " << vpt2 << "\n"
              << "vptr B " << vpt3 << "\n";
return 0;
}

此代码运行的输出如下：

called here: 140736308965696
called here: 140736308965696
called here: 140736308965696
e is at: 140736308965696
d is at: 140736308965696
a is at: 140736308965704
c is at: 140736308965704
b is at: 140736308965712
total size is 24
vptr D and E 4390608
vptr A and C 4390648
vptr B 4390680

这建议 BaseE obj 的以下内存布局（指针大小为 8 个字节）。

8 字节，BaseD 子对象，仅 vptr 到 D 表

8 字节，BaseA 子对象，vptr 只到 A 表

8 字节，BaseB 子对象，仅 vptr 到 B 表。

这里ePtr和dPtr都指向BaseD子对象，aPtr和都cPtr指向子BaseA对象和bPtr子BaseB对象。

我现在的问题是编译器将生成什么 thunk 代码来调整上述this两个调用中的指针以b()通过指针cPtr并bPtr确保this正确指向ePtr何时调用BaseE的实现b()？由于cPtr并且bPtr具有不同的地址，thunk 是否需要注意根据传递给它的基类指针的类型进行不同的调整？

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