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

Using static kprobes – demo 3 and demo 4

Continuing to work via the traditional static kprobes approach (recall: the word static implies any change will require a code recompile), let's learn to do more with kprobes – useful and practical stuff that really helps when debugging. Retrieving the parameters of the probed function certainly qualifies as being a very useful skill!

The two demo programs that follow (demos 3 and 4), will show you how to do precisely this, with demo 4 using an interesting approach – we'll generate our kprobe C code (and Makefile file) via a bash script. Let's work on and understand these demos!

Demo 3 – static kprobe – probing the file open syscall and retrieving the filename parameter

You'll agree, I think, that the second demo is better than the first – it allows the passing of any function to be probed (as a module parameter). Now, continuing with our example of probing do_sys_open(...