Writing an OS in Rust

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.

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.

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.

Hardware Interrupts

In this post we set up the programmable interrupt controller to correctly forward hardware interrupts to the CPU. To handle these interrupts we add new entries to our interrupt descriptor table, just like we did for our exception handlers. We will learn how to get periodic timer interrupts and how to get input from the keyboard.

Introduction to Paging

This post introduces paging, a very common memory management scheme that we will also use for our operating system. It explains why memory isolation is needed, how segmentation works, what virtual memory is, and how paging solves memory fragmentation issues. It also explores the layout of multilevel page tables on the x86_64 architecture.

Paging Implementation

This post shows how to implement paging support in our kernel. It first explores different techniques to make the physical page table frames accessible to the kernel and discusses their respective advantages and drawbacks. It then implements an address translation function and a function to create a new mapping.

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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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Writing an OS in Rust (Second Edition)

A Freestanding Rust Binary

A Minimal Rust Kernel

VGA Text Mode

Unit Testing

Integration Tests

CPU Exceptions

Double Faults

Hardware Interrupts

Introduction to Paging

Paging Implementation

First Edition

Support Me

Extra Content