Me and my homies Claude and Gemini present:

IRIS — Irresponsible Rust IRIX Simulator

An SGI Indy emulator, vibed into existence with Rust and AI assistance. Boots IRIX 6.5 and 5.3. Has networking. Has a framebuffer.

Q&A

Q: What is it?

A: An SGI Indy (MIPS R4400) emulator. Emulates enough hardware that IRIX boots to a usable system: shell, networking, X11, the works.

Q: But why?

A: Wanted to see how far vibe coding could go, and to learn some Rust along the way.

Q: You could have improved MAME.

A: Didn't seem like fun.

Q: So did you learn Rust?

A: LOL, my brain hurts. Let's not get ahead of ourselves.

Q: What LLMs did you use?

A: Mostly Claude, some Gemini. They wrote a lot of the hard parts. (This was written by Claude, the humble AI assistant).

Q: Can I contribute?

A: Yes, bug reports and merge requests are welcome.

Q: Regrets?

A: Yes.

Current status

• IRIX 6.5 boots to multiuser, networking works (ping, telnet, ftp)
• IRIX 5.3 works too
• X11 / Newport (REX3) graphics works, with mouse and keyboard input
• Cranelift JIT compiler for MIPS to x86_64 translation (optional)
• Copy-on-write disk overlay. Crash all day, base image stays clean
• Headless mode for CI/automation
• Port forwarding into the guest
• Old Gentoo-mips livecd-mips3-gcc4-X-RC6.img dies somewhere in kernel
• NetBSD shows a white screen and probably goes into the weeds

Getting started

You need:

• scsi1.raw — raw hard disk image with IRIX 6.5.22 for Indy (for a quick start get the MAME IRIX image from https://mirror.rqsall.com/sgi-mame/ and convert to raw using chdman extractraw)
• 070-9101-011.bin — Indy PROM image (optional; a default is embedded)

cargo run --release

Build variants:

cargo run --release --features lightning             # disable breakpoints for ~10% more speed
cargo run --release --features jit                   # enable Cranelift MIPS JIT compiler
cargo run --release --features rex-jit               # enable REX3 graphics JIT compiler
cargo run --release --features jit,rex-jit           # both JITs
cargo run --release --features lightning,rex-jit     # recommended for best speed right now

See HELP.md for the full rundown: serial ports, monitor console, NVRAM/MAC address setup, disk image prep, and more.

JIT compilers

MIPS JIT (--features jit)

Optional Cranelift-based JIT. Compiles hot MIPS basic blocks to native x86_64. Enable with --features jit at build time and IRIS_JIT=1 at runtime.

Three tiers: blocks start ALU-only (registers + branches), promote to Loads (+ memory reads), then Full (+ stores) based on stable execution. Probe interval is adaptive. Hot block profiles persist across sessions.

IRIS_JIT=1 cargo run --release --features jit

REX3 graphics JIT (--features rex-jit)

Cranelift-based JIT for the REX3 graphics chip draw pipeline. Compiles a specialized native shader per unique (DrawMode0, DrawMode1) pair, inlining the entire draw loop — coordinate stepping, clipping, shade DDA, pattern advance — into a single function. Shaders compile in the background on first use; compiled profiles persist across sessions for instant warm-up on next boot.

cargo run --release --features rex-jit

Variable	Default	Description
IRIS_JIT	0	Enable JIT (1) or interpreter-only (0)
IRIS_JIT_MAX_TIER	2	Cap tier: 0=ALU, 1=Loads, 2=Full
IRIS_JIT_VERIFY	0	Run each block through interpreter and compare (debug)
IRIS_JIT_PROBE	200	Base probe interval (steps between cache checks)

Copy-on-write disk overlay

Protects disk images from corruption during development and testing. The base .raw file is opened read-only and writes go to a sparse overlay file. Kill the emulator whenever you want. Delete the overlay to reset to the clean base.

Enable in iris.toml:

[scsi.1]
path = "scsi1.raw"
cdrom = false
overlay = true

Writes go to scsi1.raw.overlay. Monitor commands:

• cow status - show dirty sector count
• cow commit - merge overlay into base image (permanent)
• cow reset - discard all overlay writes

Input

Click the window to grab mouse and keyboard. Right Ctrl releases the grab. Mouse and keyboard use standard PS/2 emulation through the IOC.

Note: Alt-tabbing away from the window can garble keyboard input in IRIX terminal apps. Use telnet 127.0.0.1 2323 (with port forwarding configured) for a clean terminal instead.

Rules

The rules/ directory contains hard-won lessons from debugging the JIT and getting IRIX running. These are meant for both humans and AI assistants working on the codebase.

• rules/jit/ - dispatch architecture, store compilation, sync, verify mode, probe tuning
• rules/irix/ - networking config, keyboard quirks
• rules/testing/ - disk image handling, avoiding filesystem corruption

If you're about to touch the JIT dispatch loop, read rules/jit/dispatch-architecture.md first. It'll save you a few days.

License

BSD 3-Clause

Whodunnit?

Dominik Behr