Writing an OS in Rust

This blog series creates a small operating system in the Rust programming language. Each post is a small tutorial and includes all needed code, so you can follow along if you like. The source code is also available in the corresponding Github repository.

A Freestanding Rust Binary

The first step in creating our own operating system kernel is to create a Rust executable that does not link the standard library. This makes it possible to run Rust code on the bare metal without an underlying operating system.

A Minimal Rust Kernel

In this post we create a minimal 64-bit Rust kernel for the x86 architecture. We build upon the freestanding Rust binary from the previous post to create a bootable disk image, that prints something to the screen.

VGA Text Mode

The VGA text mode is a simple way to print text to the screen. In this post, we create an interface that makes its usage safe and simple, by encapsulating all unsafety in a separate module. We also implement support for Rust's formatting macros.

Testing

Unit Testing

This post explores unit testing in no_std executables using Rust's built-in test framework. We will adjust our code so that cargo test works and add some basic unit tests to our VGA buffer module.

Integration Tests

To complete the testing picture we implement a basic integration test framework, which allows us to run tests on the target system. The idea is to run tests inside QEMU and report the results back to the host through the serial port.

Exceptions

CPU Exceptions

CPU exceptions occur in various erroneous situations, for example when accessing an invalid memory address or when dividing by zero. To react to them we have to set up an interrupt descriptor table that provides handler functions. At the end of this post, our kernel will be able to catch breakpoint exceptions and to resume normal execution afterwards.

Double Faults

This post explores the double fault exception in detail, which occurs when the CPU fails to invoke an exception handler. By handling this exception we avoid fatal triple faults that cause a system reset. To prevent triple faults in all cases we also set up an Interrupt Stack Table to catch double faults on a separate kernel stack.

First Edition

You are viewing the second edition of “Writing an OS in Rust”, which is still in progress. The first edition has more content, but is no longer updated. We try our best to incorporate the missing content soon.

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First Edition