Appendix A: Debugging

Practical debugging techniques for kernel driver development.

Debugging Strategy

flowchart TB
    BUG["Bug/Issue"]
    BUG --> Q1{"Can reproduce?"}
    Q1 -->|Yes| LOG["Add printk/dev_*"]
    Q1 -->|No| TRACE["Enable tracing"]
    LOG --> ANALYZE["Analyze output"]
    TRACE --> ANALYZE
    ANALYZE --> Q2{"Found cause?"}
    Q2 -->|Yes| FIX["Fix"]
    Q2 -->|No| DEBUG["debugfs/kgdb"]
    DEBUG --> FIX

    style LOG fill:#7a8f73,stroke:#2e7d32
    style TRACE fill:#738f99,stroke:#0277bd

Tools Overview

Tool	Use For	Overhead
`printk`/`dev_*`	Quick debugging, always available	Low
Dynamic debug	Enable/disable at runtime	Very low
ftrace	Function flow, latency	Medium
kprobes	Inspect without recompile	Medium
KGDB	Interactive debugging	High
kdump/crash	Post-mortem analysis	None (captures on crash)

Chapters

Chapter	What You’ll Learn
Logging	printk, dev_*, dynamic debug
Tracing	ftrace, kprobes
Crash Analysis	kdump and crash tool

Quick Reference

# View kernel log
dmesg -w

# Filter by driver
dmesg | grep my_driver

# Enable dynamic debug
echo 'module my_driver +p' > /sys/kernel/debug/dynamic_debug/control

# View function trace
echo function > /sys/kernel/debug/tracing/current_tracer
cat /sys/kernel/debug/tracing/trace

Appendix A: Debugging

Debugging Strategy

Tools Overview

Chapters

Quick Reference

Further Reading

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