func_inject.h

//generic codecave lib by 3dsboy08 - extremely lazy code, sorry.
//port to your meme of choice

#define GENERIC_CODECAVE(name, stype) DWORD name(stype* arg)
#define CodeCaveHeader DWORD Address;

HANDLE Proc; //edit to your process

DWORD GetFunctionSize(DWORD Func) 
{
	DWORD Size = 0;
	DWORD Amount = 0;
	do 
	{
		if (*(BYTE*)(Func + Size) == 0xF4) 
		{
			Amount++;
			if (Amount == 4) 
			{
				Size = Size - 3;
				break;
			}
		}
		Size++;
	} while (1);
	return Size;
}

DWORD semi_codecave_create(DWORD function_to_inject)
{
	DWORD size = GetFunctionSize((DWORD)function_to_inject);
	void* fAddr = VirtualAllocEx(ROBLOXProc, NULL, size, MEM_RESERVE | MEM_COMMIT, PAGE_EXECUTE_READWRITE);
	WriteProcessMemory(Proc, fAddr, (void*)function_to_inject, size, NULL);
	return (DWORD)fAddr;
}

template<typename T>
DWORD semi_codecave_run(DWORD codecave_addr, T argument)
{
	void* paramsAddr = VirtualAllocEx(Proc, NULL, sizeof(T), MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE);
	WriteProcessMemory(Proc, paramsAddr, &argument, sizeof(T), NULL);
	HANDLE t = CreateRemoteThread(ROBLOXProc, NULL, 0, (LPTHREAD_START_ROUTINE)codecave_addr, paramsAddr, 0, NULL);
	if (t) 
	{
		WaitForSingleObject(t, INFINITE);
		DWORD ret = 0;
		GetExitCodeThread(t, &ret);
		VirtualFree(paramsAddr, 0, MEM_RELEASE);
		CloseHandle(t);
		return ret;
	}
	return 0;
}

//example
struct s_test
{
	CodeCaveHeader;
};

GENERIC_CODECAVE(codecave_test, s_test)
{
	your_func_def dostuff = (your_func_def)arg->Address;
	return dostuff(0xDEADBEEF);
	FUNCTION_MARK();
}