KFS — Kernel From Scratch

This is the complete documentation for building a bare-metal i386 kernel in Rust, written as it was actually built — including the wrong turns, the debugging sessions at 5am, and the moments where everything finally clicked.

The Kernel From Scratch (KFS) series is a 42 school project, but the documentation here goes far beyond what the subject requires. Every concept is explained from first principles. Every decision has a “why”. Every bug that caused a headache has its own section.

What This Is

A working reference for anyone building or studying a kernel from scratch in Rust. Not a tutorial that skips the hard parts — a complete record of what it actually takes.

What You’ll Build

By following through all three projects:

• A kernel that boots via GRUB on i386 bare metal
• VGA text mode output with color, scrolling, and cursor control
• Interrupt-driven keyboard input
• A proper interrupt subsystem (IDT + PIC + exception handlers)
• A Global Descriptor Table (GDT) with kernel and user segments
• An interactive shell
• A working memory paging system with frame allocation

How to Use This Book

Each chapter documents a concept at the theory level first, then walks through the implementation in Rust. Code examples are taken directly from the actual kernel source.

The debugging chapters are not optional reading — they contain the lessons that can’t be found in any spec.

Prerequisites

• Basic Rust knowledge (ownership, unsafe, no_std)
• Comfortable reading x86 assembly
• A Linux system with QEMU and NASM installed

Built with 🦀 Rust, fuelled by too much coffee, and the eternal optimism that this time it won’t triple fault.