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Compile a kernel with Rust support and run it in QEMU

My dev-env is Ubuntu 22.04 on x86_64.

Get source code of Linux kernel

This is the fork from Rust-for-Linux orgnization.

git clone https://github.com/Rust-for-Linux/linux -b rust-dev

Install required packages

Some packages are normally required for C projects:

Click me 
sudo apt install \
  binutils build-essential libtool texinfo \
  gzip zip unzip patchutils curl git \
  make cmake ninja-build automake bison flex gperf \
  grep sed gawk bc \
  zlib1g-dev libexpat1-dev libmpc-dev \
  libglib2.0-dev libfdt-dev libpixman-1-dev \
  libelf-dev libssl-dev

Since Rust is based on LLVM, we also need to install relative packages:

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sudo apt install \
  clang-format clang-tidy clang-tools clang clangd \
  libc++-dev libc++1 libc++abi-dev libc++abi1 \
  libclang-dev libclang1 liblldb-dev \
  libllvm-ocaml-dev libomp-dev libomp5 \
  lld lldb llvm llvm-dev llvm-runtime llvm \
  python3-clang

Set up Rust toolchain

# CWD=linux
## Rust for linux use a specific version of Rust
rustup override set $(scripts/min-tool-version.sh rustc)
rustup component add rust-src
## bindgen will be used to generate bindings from C source code
cargo install --locked --version $(scripts/min-tool-version.sh bindgen) bindgen-cli

Then verify with:

# CWD=linux
make rustavailable

It's expected to see "Rust is available!".

Generate kernel config

# CWD=linux
## LLVM is necessary for Rust
## O=build controls where to put the generated config file
make LLVM=1 O=build defconfig
# build/.config will be generated
make LLVM=1 O=build menuconfig

The config TUI will show up. We need to enable:

General setup
    -> Rust support

Build the kernel

cd build
# CWD=linux/build
make LLVM=1 -j$(nproc)

Using all 16 cores of my machine, it took only 3m21s to finish.

From the many build artifacts, the following ones are the most important for us:

> file vmlinux
vmlinux: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), statically linked, BuildID[sha1]=da85d3bdec6b89633a92af47e420a97bfef94fd5, not stripped

> file arch/x86/boot/bzImage
arch/x86/boot/bzImage: Linux kernel x86 boot executable bzImage, version 6.6.0-rc4-gf347fa1e02df (lwshang@devenv-lwshang) #1 SMP PREEMPT_DYNAMIC Tue Nov  7 21:58:41 UTC 2023, RO-rootFS, swap_dev 0XB, Normal VGA

And there should be a rust directory containing bindings and other files.

Create an initrd (initial RAM disk)

A Linux kernel itself is not a complete OS. There must be an inial RAM disk which contains necessary userspace files.

First, we need to download the prebuilt busybox which can serve as sh, poweroff and many other CLI tools.

# CWD=part1
curl https://busybox.net/downloads/binaries/1.35.0-x86_64-linux-musl/busybox > busybox

Then, we need to have a configutration file for the initrd and a init which will be executed as the init process.

Now we can create the initrd:

# CWD=part1
../linux/build/usr/gen_init_cpio qemu-initramfs.desc > qemu-initramfs.img

Run in QEMU

# CWD=part1
qemu-system-x86_64 \
  -kernel ../linux/build/arch/x86_64/boot/bzImage \
  -initrd qemu-initramfs.img
  -nographic \
  -append "console=ttyS0" \

The output will be like:

...
[    2.378959] Run /init as init process
[    2.419419] tsc: Refined TSC clocksource calibration: 2994.342 MHz
[    2.420056] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x2b296411175, max_idle_ns: 440795206904 ns
[    2.421392] clocksource: Switched to clocksource tsc
init from a minimal initrd!
[    2.442322] busybox (47) used greatest stack depth: 14008 bytes left
[    2.789509] input: ImExPS/2 Generic Explorer Mouse as /devices/platform/i8042/serio1/input/input3
[    2.961272] ACPI: PM: Preparing to enter system sleep state S5
[    2.962067] reboot: Power down