Getting Started with Writing Your Own Basic Kernel in Rust

Writing an operating system kernel is a challenging endeavor that can significantly deepen your understanding of computer science and systems programming. Rust, with its focus on safety and performance, is an increasingly popular language for systems programming. This article will outline the steps to get started with writing your own basic kernel in Rust.

Why Rust?

Rust offers several features that make it suitable for kernel development:

• Memory Safety: Rust’s ownership model ensures safety in memory access, which is crucial in kernel development where a misstep can crash the entire system.
• Type Safety: Rust’s type system prevents many bugs that would otherwise only be caught at runtime.
• Concurrency: Rust’s approach to concurrency removes the risk of data races, a common issue in parallel computing.
• Zero-Cost Abstractions: Rust provides abstractions that do not impose overhead at runtime, which is important for a kernel which needs to be as efficient as possible.

Prerequisites

Before diving into kernel development with Rust, you should:

• Be comfortable with Rust programming language concepts and syntax.
• Have a basic understanding of operating systems and computer architecture.
• Install Rust using rustup to manage Rust versions and targets.
• Install cargo-xbuild and rust-src for cross-compiling essential library support.
• Understand the basics of the target architecture (x86_64, ARM, etc.).

Setting Up Your Development Environment

1. Install Rust Nightly: Kernel development often uses features only available in Rust’s nightly builds.

   rustup default nightly
   

2. Add Rust’s Source Code:

   rustup component add rust-src
   

3. Add The cargo-xbuild for cross-compiling the Rust core library:

   cargo install cargo-xbuild
   

4. Install llvm-tools and binutils for additional build tools:

   rustup component add llvm-tools-preview
   sudo apt install binutils
   

Writing Your Kernel

Step 1: Create a New Rust Project

cargo new my_kernel
cd my_kernel

Step 2: Configure Cargo for Cross-Compilation

Create a .cargo/config.toml file and setup the target specifications:

[target.x86_64-my_kernel]
rustflags = [
  "-C", "link-arg=-nostartfiles",
]

[build]

target = “x86_64-my_kernel.json”

This tells Cargo to use special rustflags and targets for your kernel.

Step 3: Configure Your Target Specification

Create a x86_64-my_kernel.json file to specify target architecture parameters. This JSON file will indicate to Rust how it should build your kernel for your chosen architecture.

Step 4: Writing the Entry Point

Your kernel needs an entry point, _start, which is its first function to run:

#![no_std]
#![no_main]

use core::panic::PanicInfo;

#[no_mangle]
pub extern "C" fn _start() -> ! {
    loop {}
}

#[panic_handler]
fn panic(_info: &PanicInfo) -> ! {
    loop {}
}

Step 5: Building Your Kernel

Now you can build your kernel with cargo xbuild:

cargo xbuild --target x86_64-my_kernel.json

Step 6: Running Your Kernel

To run your kernel, you’ll generally use a virtual machine such as QEMU or an emulator relevant to your target architecture.

qemu-system-x86_64 -kernel target/x86_64-my_kernel/debug/my_kernel

This command will launch your kernel in a virtual machine window.

Testing Your Kernel

Developing a testing framework is essential. Rust supports unit tests out of the box, but since standard libraries are not available in no_std environments, using crates like libtest is not possible. You will have to implement test runners adapted to a kernel environment.

Next Steps

Your kernel is still far from being a full-fledged operating system. Consider the following as next steps:

• Setting up VGA buffer for printing to the screen.
• Handling interrupts and CPU exceptions.
• Implementing memory management features, such as a heap allocator.

Conclusion

Writing a kernel in Rust is complex and requires a lot of low-level systems knowledge. However, it’s a rewarding process that teaches you a lot about how computers work. The Rust language’s guarantees help make the process safer and can alleviate some common issues faced in systems programming. This article provided a roadmap to get started, but there’s a long journey ahead in the world of kernel development. Keep experimenting, reading documentation, and engaging with the community to advance your kernel project.