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

[K]GDB – a few tips and tricks

GDB is a large and powerful program with many features. We'll describe a few top-of-mind tips and tricks here that can prove useful when using GDB (and KGDB).

Setting up and using GDB scripts with CONFIG_GDB_SCRIPTS

Dating back to the 4.0 kernel, Linux provides several Python-based helper scripts – seen as additional GDB commands – to help debug the kernel (and kernel modules). Their code's within the kernel source in scripts/gdb.

Enable them by setting CONFIG_GDB_SCRIPTS=y. Once enabled, it's advisable to put the following line in your GDB startup file ~/.gdbinit:

add-auto-load-safe-path <...>/scripts/gdb/vmlinux-gdb.py

Or, simpler but more permissive, add-auto-load-safe-path /. This has GDB parse this Python script within the kernel source tree (scripts/gdb/vmlinux-gdb.py) and thus recognize the Python-based GDB helper scripts – a very useful thing! All the helper scripts are prefixed...