Hey there,

So, I can't 100% get this running (https://github.com/Rust-SDL2/rust-sdl2/issues/865), but I wanted to show you a diff that I think will get things working:

diff --git a/src/headless.rs b/src/headless.rs
index dbe25e0..73f831a 100644
--- a/src/headless.rs
+++ b/src/headless.rs
@@ -14,7 +14,6 @@ use std::io::Read;
 use std::io::Write;
 use std::fs::File;
 use std::fmt::Debug;
-use std::os::unix::io::FromRawFd;

 use crate::joystick::Joystick;
 use crate::mapper::AddressSpace;
@@ -27,8 +26,8 @@ use crate::common::Clocked;

 fn main() {
     // Standard stdout() object is line-buffered
-    let stdin = unsafe { File::from_raw_fd(0) };
-    let stdout = unsafe { File::from_raw_fd(1) };
+    let stdin = std::io::stdin();
+    let stdout = std::io::stdout();
     let mut headless = Headless::new(
         Box::new(stdin),
         Box::new(stdout),

In general, using the standard library here helps with portability. Of course, it's your project, and so feel free to ignore/close this issue!

per header https://wiki.nesdev.com/w/index.php/INES , calculation should shift header 7 nibble and then add header 6 nibble. An example is the Zelda rom, it uses mapper 1, but the code as written detects it as mapper 16 because it is adding 0 to 1 and shifting the result by 4, instead of shifting 0 by 4 and adding it to 1.

https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/headless.rs#L117

https://doc.rust-lang.org/reference/behavior-considered-undefined.html : Dereferencing a null or dangling raw pointer.

Headless::joystick1/2 are initialized with:

impl Headless {
    fn command_load_rom(&mut self) {
        let mut record_tas = self.read_byte();
        let filename = self.read_length_string();
        let mut joystick1 = Box::new(Joystick::new());
        let mut joystick2 = Box::new(Joystick::new());
        self.joystick1 = &mut *joystick1;
        self.joystick2 = &mut *joystick2;
        ...
        // drop joystick1 joystick2
        // Headless::joystick1/2 are dangling pointers since joystick1 joystick2 are freed
    }

Building with nightly instead of stable produces:

error[E0597]: `texture_creator` does not live long enough
   --> src\main.rs:96:32
    |
96  |     let mut texture = Box::new(texture_creator.create_texture(
    |                                ^^^^^^^^^^^^^^^ borrowed value does not live long enough
...
142 |         texture: &mut *texture,
    |                  ------------- cast requires that `texture_creator` is borrowed for `'static`
...
179 | }
    | - `texture_creator` dropped here while still borrowed

I am not sure why this is an error in nightly but not in stable...

Anyway, what it's complaining about is this: as main ends, texture_creator will be freed, and then GLOBAL_STATE will be holding invalid memory; any destructors that run after texture_creator is freed could access that invalid memory.

Ideally, GLOBAL_STATE would use lazy_static, I think. Not 100% sure how much contortion that would take.

https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/headless.rs#L30

What's wrong with line-buffered stdout?

https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/serialization.rs#L144

impl<T: Savable> Savable for Vec<T> {
...
    fn load(&mut self, fh: &mut Read) {
        let mut len = 0usize;
        len.load(fh);
        self.truncate(0);
        self.reserve(len);
        for i in 0..len {
            let mut x:T = unsafe { std::mem::uninitialized() };
            x.load(fh);
            self.push(x);
        }
}

In case of Vec<bool> we got:

let mut x:bool = unsafe { std::mem::uninitialized() };

Which is UB by definition: https://doc.rust-lang.org/reference/behavior-considered-undefined.html

See comment https://github.com/rust-lang/rust/issues/53491#issuecomment-456775716

https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/joystick.rs#L49

https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/ppu.rs#L493

https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/joystick.rs#L43 https://github.com/MichaelBurge/nes-emulator/blob/0b9e321832360b93ed6fcd9d54bb3c3f11eca00a/src/joystick.rs#L49