Write Your Own 64-bit Operating System Kernel #1 - Boot code and multiboot header

Summary

In this first episode of a series on building a custom 64-bit operating system from scratch, the focus is on setting up the necessary tooling and creating a simple ‘Hello World’ program. The OS is initially designed for x86 compatibility and follows the MultiBoot 2 standard. The episode walks through setting up a Docker-based development environment, writing basic assembly code for the OS entry point, and configuring GRUB and linker settings. The goal is to generate a bootable ISO and emulate it using QEMU, with future episodes promising 64-bit mode, C language integration, and more.

Takeaways

• 😀 The goal of the series is to create a 64-bit operating system from scratch, starting with an x86-compatible OS that’s MultiBoot 2 compliant.
• 🖥️ The operating system will primarily be written in C, but assembly will also be used for hardware-specific code.
• 🚀 Docker is recommended for simplifying the build process and ensuring a reproducible build environment.
• 💻 You will need to install essential tools such as Docker, Keymuse, NASM, GRUB, and a GCC cross-compiler for building the OS.
• 🔧 A custom Docker image is created to include all the necessary development tools and dependencies for building the OS.
• 📂 The initial project setup involves creating a folder structure with separate directories for source code, boot files, and implementation files.
• 🔑 The first step in building the OS is creating a bootloader with assembly code, starting with a multi-boot header for compatibility.
• ⚙️ The OS bootloader will follow the MultiBoot 2 specification, which is used by most modern bootloaders to identify and load the OS.
• 📝 The first assembly code will print a simple 'OK' message to the screen via direct access to video memory.
• 📦 The build process will be organized using a Makefile to automate compiling and linking the assembly files into a bootable kernel.
• 💾 GRUB will be used to generate an ISO file for the OS, which can then be run in an emulator like QEMU for testing the OS.

Q & A

What is the purpose of creating a 64-bit operating system from scratch?

The goal is to build an x86-compatible operating system that is multi-boot 2 compliant, which can potentially be expanded to other architectures and boot loaders in the future. The series focuses on developing this OS using C and assembly for hardware-specific code.

Why is Docker recommended for setting up the development environment?

Docker simplifies the building process by allowing developers to create a reproducible build environment. This ensures that the exact same software is installed across all systems, making it easier for everyone to follow along and build the operating system in a consistent environment.

What are the essential tools needed to start building the operating system?

The essential tools include Docker, Keymuse for emulating the OS, NASM for compiling assembly code, GRUB for building the final ISO file, and a specific GCC cross-compiler for building the OS.

What is the function of a bootloader in the context of an operating system?

The bootloader is responsible for locating the operating system on a storage device (e.g., hard drive, USB, CD) and loading it into memory. It is the first thing that runs on the computer before the OS itself starts.

What is the significance of the multi-boot 2 specification in this project?

The multi-boot 2 specification is a standard used by most bootloaders to load and start operating systems. It ensures compatibility with the bootloader, allowing the operating system to be loaded correctly on any machine that supports the multi-boot 2 protocol.

What is the purpose of the header in the assembly code?

The header contains essential data that allows the bootloader to identify the OS as a valid one that can be run. This includes a magic number, architecture information, header length, checksum, and other details required for multi-boot 2 compatibility.

How does the operating system display text to the screen in the initial stages?

In the first episode, the OS writes directly to video memory at the address 0xB8000 to display text. This is done using assembly instructions, where the text 'ok' is placed in the video memory to be displayed on the screen.

What is the purpose of the linker script in the build process?

The linker script defines how to link the object files together to form the final operating system binary. It specifies the entry point of the OS and organizes the binary's sections, such as the boot section and text section, to ensure correct memory placement.

Why is GRUB used in the build process, and what does it do?

GRUB is a bootloader that is used to generate an ISO file for the operating system. It allows the OS to be booted from different devices and creates a bootable disk image that can be used on USB drives or other storage media.

What role does the Makefile play in building the operating system?

The Makefile automates the build process by defining commands to compile assembly code into object files, link those files together, and generate the final ISO. It also manages dependencies, ensuring that only modified files are recompiled, speeding up the build process.