Emuko: Fast RISC-V emulator written in Rust, boots Linux

Published: 2 days ago (February 27, 2026 at 06:01 PM EST)

4 min read

Source: Hacker News

Source: Hacker News

Emuko

Fast RISC-V emulator written in Rust. Boots Linux.
emuko.dev

Features

RV64IMAFDC with M/S/U privilege levels and Sv39 virtual memory
JIT compilation for ARM64 and x86_64 hosts (adaptive selection)
Full Linux boot with BusyBox userland and interactive shell
Snapshot/restore for saving and resuming full machine state
Daemon mode with HTTP API and live UART command injection
Differential checker to validate JIT against interpreter
Peripherals: UART 16550, CLINT, PLIC, SBI 1.0, FDT generation
Single dependency (zstd), pure Rust

RISC‑V Emulator Comparison (emuko vs others)

Feature	emuko	QEMU (RISC‑V `virt`)	Spike (`riscv-isa-sim`)	Renode
JIT / dynamic translation backend	✅	✅	—	—
Snapshot save + restore	✅	✅	—	✅
Autosnapshot (periodic)	✅	—	—	✅
HTTP API for machine control	✅	—	—	—
WebSocket UART console endpoint	✅	—	—	—
Scriptable UART host bridge primitives	✅	—	—	✅
One‑command Debian kernel/initrd download with SHA256 verification	✅	—	—	—
Built‑in JIT‑vs‑interpreter differential checker	✅	—	—	—
GDB debugging workflow	—	✅	✅	✅
Large RISC‑V board/device ecosystem (PCIe/virtio on `virt`)	—	✅	—	—
Multi‑node simulation focus	—	—	—	✅
Broad ISA extension coverage (incl. RVV, crypto, etc.)	—	—	✅	—

Sources

QEMU RISC‑V virt machine docs:
QEMU RISC‑V system overview:
QEMU GDB usage:
QMP reference:
QEMU monitor (savevm, loadvm):
QEMU VM snapshots:
Spike README:
Renode README:
Renode state save/load + autosave:
Renode GDB integration:
Renode UART host integration:

Build

cargo build --release

The main binary is target/release/emuko.

Quick Start

1. Download a kernel

alias emuko=target/release/emuko
emuko dow

Downloads the Debian RISC‑V netboot kernel and initrd to ~/.emuko/ with SHA256 verification.

2. Boot Linux

emuko start

Starts the emulator daemon and attaches an interactive console. Keyboard shortcuts:

Key	Action
Ctrl+]	Detach from console (daemon keeps running)
Ctrl+C	Sent to guest (interrupt running command)
Ctrl+D	Sent to guest (EOF)

3. Reattach or control

emuko start            # reattach console to running daemon
emuko dump             # print CPU state
emuko stop             # pause execution
emuko con              # continue execution
emuko step 1000        # step N instructions
emuko snap             # take a snapshot
emuko kill             # shut down daemon

The daemon exposes an HTTP API at http://127.0.0.1:7788/v1/api/ and a WebSocket console at ws://127.0.0.1:7788/v1/ws/uart.

Snapshots

emuko snap                 # take a snapshot now
emuko snap 5000000         # auto‑snapshot every 5 M steps
emuko snap stop            # disable auto‑snapshots
emuko ls                   # list snapshots
emuko restore    # restore a snapshot

Configuration

Pass options after emuko start, or set via environment variables or emuko.yml:

Option	Env Var	Default	Description
`--ram-size`	`RAM_SIZE`	`1 GB`	RAM size in bytes
`--backend`	`EMUKO_BACKEND`	`adaptive`	`adaptive`, `arm64_jit`, `amd64_jit`, `arm64`, `x86_64`
`--bootargs`	`BOOTARGS`	`serial console`	Kernel command line

Getting a Kernel

Use emuko dow (see Quick Start) or grab pre‑built images from DQIB (Debian Quick Image Baker). To download a specific set:

emuko dow debian-netboot

License

Apache 2.0. See the LICENSE.