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Linux Kernel Debugging

Linux Kernel Debugging

By : Kaiwan N. Billimoria
4.8 (6)
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Linux Kernel Debugging

Linux Kernel Debugging

4.8 (6)
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)
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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 the kernel's powerful dynamic debug feature

The instrumentation approach to debugging – interspersing your kernel (and module) code with many printk is indeed a good technique. It helps you narrow things down and debug them! But as you've no doubt realized, there can be a (pretty high) cost to this:

  • It eats into your disk (or flash) space as logs get filled in. This can be especially problematic on constrained embedded systems. Also, writing to disk is much slower than writing to RAM.
  • It's fast in RAM, but the ring buffer is not that large and would thus quickly get overwhelmed; older prints will soon be lost.
  • Even more important, on many production systems, a high volume of printks would have an adverse performance impact, creating bottlenecks and even possible livelocks! Rate limiting helps with this, to some extent...

A solution would be to use the pr_debug() and/or the dev_dbg() APIs! They're especially useful during development...

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