Software Debugging for High-altitude Balloons
- 3. Maurice Wilkes (1950s) As soon as we started programming, we found to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs.
- 4. Writing code is hard But writing bugs is easy! Everyone does it all the time without even thinking about it. Estimates in GOOD code there are 2 to 4 defects per 1,000 lines You’re not that good You will spend many hours debugging
- 5. Programmer If a person who debugs code is a debugger than a person who writes the bugs must be a... bugger?
- 6. Always have a fighter pilot in your presentation
- 8. OODA Loop
- 9. THE GREATEST DEBUGGER YOU WILL EVER USE IS IN YOUR HEAD Ignore your tools!
- 10. ESSENTIAL SKILL: RUN CODE IN YOUR HEAD
- 11. RISE Reproduce Isolate Target Excise
- 12. Reproduce
- 13. Isolate Tighten the OODA loop ◦ The smallest ◦ Fastest ◦ Most easily repeated And automate it Then turn it into a test case
- 14. Target
- 15. ESSENTIAL SKILL: ALWAYS BE ASKING WHY
- 18. Excise Fix the bug Don’t introduce new bugs! You can check this with the test case that you made earlier
- 19. Talk to the teddy
- 20. Look Around Debugging Where there’s smoke... ... research shows that bugs tend to cluster When you fix a bug look for more in the same spot.
- 21. 5 bugs in a single line dir.permissions = 666; // Make the file writable Bug 1: updates permissions without asking Bug 2: doesn’t make the file writable Bug 3: creates security hole Bug 4: used decimal not octal Bug 5: comment is incorrect
- 22. Remember This One Thing! The most effective debugging tools are: your brain, a unit test, and the print statement.