Example showing how to cast member function pointers and use proxy stubs during DLL injection / code reuse

member-func-ptr-cast.cpp

#undef USE_MAY20_VERSION
#define USE_OCT20_VERSION 1

#ifdef USE_OCT20_VERSION
#define OFFS_ValveBuffer_Constructor 0x83A9E0
#define OFFS_ValveBuffer_Destructor 0x83FC30
#define OFFS_ValveBuffer_PutByte 0x83C8D0
#define OFFS_ValveBuffer_PutByteBuffer 0x83BDA0
#define OFFS_ValveBuffer_PutString 0x44C940
#define OFFS_ValveBuffer_GetByteBuffer 0x44C070
#endif

// Code taken from StackExchange
template<typename classT, typename memberT>
union u_ptm_cast {
	memberT classT::*pmember;
	void *pvoid;
};

class ValveBuffer
{
protected:
	typedef ValveBuffer *(ValveBuffer::constructor)(uint32_t GrowSize, uint32_t AllocationCount, uint8_t flags);
	static u_ptm_cast<ValveBuffer,constructor> mFPConstructor;

	typedef void (ValveBuffer::destructor)();
	static u_ptm_cast<ValveBuffer, destructor> mFPDestructor;

	typedef void (ValveBuffer::putByte)(uint8_t);
	static u_ptm_cast<ValveBuffer, putByte> mFPPutByte;

	typedef void (ValveBuffer::putByteBuffer)(uint8_t *, size_t);
	static u_ptm_cast<ValveBuffer, putByteBuffer> mFPPutByteBuffer;

	typedef bool (__cdecl *putString)(ValveBuffer *, const char *);
	static putString mFPPutString;

	typedef bool (__cdecl *getByteBuffer)(ValveBuffer *, uint8_t *, size_t);
	static getByteBuffer mFPGetByteBuffer;

public:
	static void InitFuncPtrs(void *DLLBase) {
		//mFPConstructor.pvoid = NULL;
		mFPConstructor.pvoid = (reinterpret_cast<char *>(DLLBase) + OFFS_ValveBuffer_Constructor);
		mFPDestructor.pvoid = (reinterpret_cast<char *>(DLLBase) + OFFS_ValveBuffer_Destructor);
		mFPPutByte.pvoid = (reinterpret_cast<char *>(DLLBase) + OFFS_ValveBuffer_PutByte);
		mFPPutByteBuffer.pvoid = (reinterpret_cast<char *>(DLLBase) + OFFS_ValveBuffer_PutByteBuffer);
		mFPPutString= reinterpret_cast<putString>(reinterpret_cast<char *>(DLLBase) + OFFS_ValveBuffer_PutString);
		mFPGetByteBuffer = reinterpret_cast<getByteBuffer>(reinterpret_cast<char *>(DLLBase) + OFFS_ValveBuffer_GetByteBuffer);
	}

	ValveBuffer(uint32_t GrowSize = 64, uint32_t AllocationCount = 32, uint8_t flags = 0) {
		auto x = mFPConstructor.pmember;
		(this->*x)(GrowSize, AllocationCount, flags);
	}
	~ValveBuffer() {
		(this->*mFPDestructor.pmember)();
	}
	void PutByte(uint8_t b) {
		(this->*mFPPutByte.pmember)(b);
	}
	void PutWord(uint16_t w) {
		PutByteBuffer((uint8_t *)&w, sizeof(uint16_t));
	}
	void PutDword(uint32_t d) {
		PutByteBuffer((uint8_t *)&d, sizeof(uint32_t));
	}
	void PutQword(uint64_t q) {
		PutByteBuffer((uint8_t *)&q, sizeof(uint64_t));
	}
	void PutByteBuffer(uint8_t *b, size_t n) {
		(this->*mFPPutByteBuffer.pmember)(b, n);
	}
	void PutString(const char *str) {
		mFPPutString(this, str);
	}
	bool GetByteBuffer(uint8_t *b, size_t n) {
		return mFPGetByteBuffer(this, b, n);
	}
	bool GetByte(uint8_t *b) {
		return GetByteBuffer(b, sizeof(uint8_t));
	}
	bool GetWord(uint16_t *w) {
		return GetByteBuffer((uint8_t*)w, sizeof(uint16_t));
	}
	bool GetDword(uint32_t *d) {
		return GetByteBuffer((uint8_t*)d, sizeof(uint32_t));
	}
	bool GetQword(uint64_t *q) {
		return GetByteBuffer((uint8_t*)q, sizeof(uint64_t));
	}

};

decltype(ValveBuffer::mFPConstructor) ValveBuffer::mFPConstructor;
decltype(ValveBuffer::mFPDestructor) ValveBuffer::mFPDestructor;
decltype(ValveBuffer::mFPPutByte) ValveBuffer::mFPPutByte;
decltype(ValveBuffer::mFPPutByteBuffer) ValveBuffer::mFPPutByteBuffer;
decltype(ValveBuffer::mFPGetByteBuffer) ValveBuffer::mFPGetByteBuffer;
decltype(ValveBuffer::mFPPutString) ValveBuffer::mFPPutString;