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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

Chapter 7: Oops! Interpreting the Kernel Bug Diagnostic

Kernel code is supposed to be perfect. It mustn't ever crash. But, of course, it does on occasion... Welcome to the real world.

When userspace code hits a (typical) bug – an invalid memory access, say – the processor's Memory Management Unit (MMU), upon failing to translate the invalid userspace virtual address to a physical one (via the process context's paging tables), raises a fault. The fault handler within the kernel then takes control. It ultimately (and typically) results in a fatal signal (often, SIGSEGV) being sent to the faulting process (or thread). This, of course, has the process possibly handle the signal and terminate.

Now take exactly the same case – except that this time, the invalid memory access occurs in kernel space (in kernel mode)! Hey, that's not supposed to happen, right? True, but bugs do happen, within kernel space too. This time, the kernel fault handler...

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