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 usingchdman extractraw)070-9101-011.bin— Indy PROM image (optional; a default is embedded)
cargo run --release
Build variants:
cargo run --release --features lightning # disable emulator breakpoints for a little bit 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 tlbvmap # enable 8k slot to tlb entry map (increases cache use but may help depending on host cpu arch)
cargo run --release --features lightning,rex-jit,tlbvmap # 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
| 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) |
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
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 countcow 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 tuningrules/irix/- networking config, keyboard quirksrules/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