Book Image

Linux Kernel Debugging

By : Kaiwan N. Billimoria
Book Image

Linux Kernel Debugging

By: Kaiwan N. Billimoria

Overview of this book

The Linux kernel is at the very core of arguably the world’s best production-quality OS. Debugging it, though, can be a complex endeavor. Linux Kernel Debugging is a comprehensive guide to learning all about advanced kernel debugging. This book covers many areas in-depth, such as instrumentation-based debugging techniques (printk and the dynamic debug framework), and shows you how to use Kprobes. Memory-related bugs tend to be a nightmare – two chapters are packed with tools and techniques devoted to debugging them. When the kernel gifts you an Oops, how exactly do you interpret it to be able to debug the underlying issue? We’ve got you covered. Concurrency tends to be an inherently complex topic, so a chapter on lock debugging will help you to learn precisely what data races are, including using KCSAN to detect them. Some thorny issues, both debug- and performance-wise, require detailed kernel-level tracing; you’ll learn to wield the impressive power of Ftrace and its frontends. You’ll also discover how to handle kernel lockups, hangs, and the dreaded kernel panic, as well as leverage the venerable GDB tool within the kernel (KGDB), along with much more. By the end of this book, you will have at your disposal a wide range of powerful kernel debugging tools and techniques, along with a keen sense of when to use which.
Table of Contents (17 chapters)
1
Part 1: A General Introduction and Approaches to Kernel Debugging
4
Part 2: Kernel and Driver Debugging Tools and Techniques
11
Part 3: Additional Kernel Debugging Tools and Techniques

Summary

Awesome! Great job on completing this really important chapter!

Here, you first learned what a kernel Oops is. You can perhaps think of it as the equivalent to a user-mode segfault, but as it's the kernel that's buggy, all guarantees are off. We began by showing you how to generate a simple NULL pointer dereference bug, triggering an Oops (though it may sound silly and obvious, these bugs still do occur – the last portion of this chapter points you to some actual Oopses, some of which are NULL pointer dereference bugs). We then went a bit further, triggering bugs in the NULL trap page and then in a random sparse region of kernel VAS (recall the useful procmap utility, which allows you to see the entire memory map of any process). Still further, more realistically, we used the kernel's default events workqueue to have a kernel worker thread illegally access an invalid pointer, causing an Oops (case 3)! We used this as a useful test case throughout the...