Question

I’m writing a NES emulator in C/C++ for Mac OS (I’ve already written one, so I know the basics). Since many hardware registers are mapped to memory locations, I was wondering if there was some syscall I could use to map an address to the result of a function: when it would be accessed, the function would be called. (I’m pretty sure I can’t, but hey, it’s worth asking.)

Here is what I’d like to do:

int getStatusRegisterValue()
{
    return 0xCAFEBABE;
}

// obviously, more parameters than just this would be involved I suppose
int* statusRegister = syscall_to_map_function_to_address(getStatusRegisterValue);

// from here on, doing (*statusRegister) should call getStatusRegisterValue and
// return its value
*statusRegister == 0xCAFEBABE;

This project is going to be my try at LLVM, and my goal is to recompile the ROM to LLVM bytecode. That’s why it would be convenient if the simple memory access could trigger the function (just like on real NES hardware). The two other obvious possibilities to solve my problem are to either cache the register values and store them in actual memory, or call a function from the recompiled code to map the memory locations to whatever they really are.

Thanks!

Answer 1

Maybe you could try installing a SEGV handler and checking the faulting address there. As I don’t use Mac OS I can’t help you more.