nesfuzz/README.md

# nesfuzz 

nesfuzz is a fuzzer for Nes Games by [@SarahJamieLewis](https://twitter.com/sarahjamielewis)

nessfuzz built on top of the [nestur](https://github.com/spieglt/nestur) emulator by [@spieglt](https://github.com/spieglt).

## Usage & Methodology 

To begin fuzzing you will need a rom file, and a sample input file. For sample inputs see [TasVids](http://tasvideos.org/).

`nessfuzz <rom> <tas file>` 
`nessfuzz smb.rom happylee-supermariobros,warped.fm2`

nesfuzz uses the same input to see novel RAM configurations and search the possible input space. It will also
tile 28 (by default), windows to allow you to see the fuzzing happen.

![](./fuzzimages/screenshot.png)


## Parameters

Found at the top of `main.rs` a few parameters control the types and effectiveness of fuzzing.

    // The number of cpu instances to spawn..
    const NUM_THREADS: usize = 28;
    
    // The number of frames to fuzz and process
    // A small number exploits the current point more at the expense of
    // large exploration - and vice versa.
    const FRAMES_TO_CONSIDER: usize = 400;
    
    // Same input should generate the same output...
    // (I make no guarantee of that at the moment)
    const RNG_SEED: u32 = 0x5463753;
    
    // If set to a low number, this disables start presses after the given frame
    // Useful for some games where pausing does nothing to advance the game...
    const DISABLE_START_PRESSES_AFTER: usize = 50;
    
    // The rate at which seed inputs become corrupted..
    const MUTATION_RATE: f64 = 0.1;
    
    // The rate at which seed inputs may become soft resets..
    const MUTATION_RATE_SOFT_RESET: f64 = 0.000;



## Future Extensions

Right now novelty is driven by the hamming distance of the ram of the cpu compared to observed values. You can get
better performance by changing the novelty to focus on specific values / be more game specific.

There are also a number of possible extensions in the replacement algorithm. Right now the fuzzer makes no
attempt to "lock-in" good paths and so the engine is likely to reconsider all past values. This leads to the
queue of inputs growing without bound (eventually causing the application itself to be refused memory from the kernel).


## Emulator Tests

### CPU Timing Test

Pass

### Sprite Hit

| Test Name | Current Status |
|-----------|----------------|
| 01.basics.nes| Pass | 
| 02.alignment.nes| Pass|
| 03.corners.nes | Pass|
| 04.flip.nes| Pass|
| 05.left_clip.nes| Pass|
| 06.right_edge.nes| Pass|
| 07.screen_bottom.nes| Fail #4 - `y=255 should not hit`|
| 08.double height.nes| Pass |
| 09.timing basics.nes| Pass|
| 10.timing order.nes| Pass|
| 11.edge_timing.nes| Pass|