Building the 6.x Linux Kernel from Source – Part 1

Building the Linux kernel from source code is an interesting way to begin your kernel development journey! Be assured, the journey’s a long and arduous one, but that’s the fun of it, right? The topic of kernel building itself is large enough to merit being divided into two chapters, this one and the next.

Recall what we have learned till now in the extended first chapter that has been published online (http://www.packtpub.com/sites/default/files/downloads/9781803232225_Online_Chapter.pdf): primarily, how to set the workspace for Linux kernel programming. You have also been introduced to user and kernel documentation sources and several useful projects that go hand-in-hand with kernel/driver development. By now, I assume you’ve completed the chapter that has been published online, and thus the setup of the workspace environment; if not, please do so before proceeding forward.

The primary purpose of this chapter and the next is to describe in detail how exactly you can build a modern Linux kernel from scratch using source code. In this chapter, you will first learn about the required basics: the kernel version nomenclature, development workflow, and the different types of source trees. Then, we’ll get hands-on: you’ll learn how to download a stable vanilla Linux kernel source tree onto a guest Linux Virtual Machine (VM). By “vanilla kernel,” we mean the plain and regular default kernel source code released by the Linux kernel community on its repository, https://www.kernel.org. After that, you will learn a little bit about the layout of the kernel source code – getting, in effect, a 10,000-foot view of the kernel code base. The actual kernel build recipe then follows.

Before proceeding, a key piece of information: any modern Linux system, be it a supercomputer or a tiny, embedded device, has three required components:

• A bootloader
• An Operating System (OS) kernel
• A root filesystem

It additionally has two optional components:

• If the processor family is ARM or PPC (32- or 64-bit), a Device Tree Blob (DTB) image file
• An initramfs (or initrd) image file

In these two chapters, we concern ourselves only with the building of the OS (Linux) kernel from source code. We do not delve into the root filesystem details. In the next chapter, we will learn how to minimally configure the x86-specific GNU GRUB bootloader.

The complete kernel build process – for x86[_64] at least – requires a total of six or seven steps. Besides the required preliminaries, we cover the first three here and the remaining in the next chapter.

In this chapter, we will cover the following topics:

• Preliminaries for the kernel build
• Steps to build the kernel from source
• Step 1 – Obtaining a Linux kernel source tree
• Step 2 – Extracting the kernel source tree
• Step 3 – Configuring the Linux kernel
• Customizing the kernel menu, Kconfig, and adding our own menu item

You may wonder: what about building the Linux kernel for another CPU architecture (like ARM 32 or 64 bit)? We do precisely this as well in the following chapter!