我需要像这样连接C++的异常抛出机制：

namespace __cxxabiv1
{
    extern "C" void __cxa_throw(void* voidPointerToActualObject, std::type_info* stdTypeInfoOfActualObject, void (*destructor)(void *))
    {
        // If thrownException is a custom exception type or something deriving from it, poke a value into it.
    }
}

If you're wondering "Why would you do that?"
我有一个抛出异常的简单例子，它是一个非常简单的类层次结构的一部分：

#include <stdexcept>

class Upper : public std::exception
{
    public:
        int pokeMe = 111111;
};
class Lower : public Upper {};

int main()
{
    throw Lower();
}

#include <cxxabi.h>

namespace __cxxabiv1
{
    extern "C" void __cxa_throw(void* voidPointerToActualObject, std::type_info* stdTypeInfoOfActualObject, void (*destructor)(void *))
    {
        // The point is to do the equivalent of this:
        Lower* staticallyTypedPointerToActualObject = reinterpret_cast<Lower*>(voidPointerToActualObject);
        auto thisWorks = dynamic_cast<Upper*>(staticallyTypedPointerToActualObject);
        thisWorks->pokeMe = 222222;

        // But we don't know the actual static type, so we can't get a statically typed pointer. We only have a void* and a type_info:
        auto abiTypeInfoOfActualObject = dynamic_cast<const abi::__class_type_info*>(stdTypeInfoOfActualObject);
        auto abiTypeInfoOfUpper = dynamic_cast<const abi::__class_type_info*>(&typeid(Upper));
        Upper* thisDoesNotWork = reinterpret_cast<Upper*>(abi::__dynamic_cast(voidPointerToActualObject, abiTypeInfoOfActualObject, abiTypeInfoOfUpper, -1));
        thisDoesNotWork->pokeMe = 333333;

        // Elided for clarity: Call the original __cxa_throw function here
        // Instead, suppress these warnings:
        (void)destructor; // Unused parameter
        while (1) { } // Return from non-returning function
    }
}

我看不出为什么__dynamic_cast不能向上转换，但是它返回nullptr。
为什么？我怎么才能让它工作？
它似乎能够做的向下投刚刚好，顺便说一句：

auto abiTypeInfoOfActualObject = dynamic_cast<const abi::__class_type_info*>(&typeid(Upper)); // Plonking this here for testing
auto abiTypeInfoOfUpper = dynamic_cast<const abi::__class_type_info*>(&typeid(Lower)); // Casting to Lower instead of Upper
Lower* thisDoesNotWork = reinterpret_cast<Lower*>(abi::__dynamic_cast(voidPointerToActualObject, abiTypeInfoOfActualObject, abiTypeInfoOfUpper, -1));