The document discusses the GNU Debugger (GDB), a tool used for debugging programs. It provides an overview of what a debugger is and common debugging tasks like starting a program, setting breakpoints, examining state, and changing variables. The document outlines GDB's core commands like run, backtrace, break, watch, print, and continue. It provides examples of using GDB to debug different programs and stresses that debugging is an essential part of the development process.

1. GNU Debugger
goakley123@gmail.com
Glen Oakley

2. What is a debugger?

3. The Four Things
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Start your program
Make your program stop
Examine what has happened
Change things in your program

4. Your Things
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Start your program
Break / Watch
Checkpoint
Next / Step / Continue
Backtrace
Print

5. ZEROTH...

6. https://sourceware.org/gdb/current/onlinedocs/gdb/

8. Debugging Flow
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Testing Brute-forcing
Identify symptom - what happened?
Identify problem - why?
Locate problem
Blame someone (else)
Fix problem
Repeat with the new problems

9. GDB Execution
● Run program in ‘virtual’ environment
● Run until
○ Termination
○ Breakpoint
● Flow control
● State Information

10. Commands
● Run
○ Execute program with args
○ Redirection
● Backtrace
○ Stack trace of your location in the program
○ Identify where crash happened

11. Example
verbose_array.c

12. Commands
● Break
○ Location at which to halt the program
○ Breaks before execution of statement(s)
● Watch
○ Monitors a variable for changes
○ Requires variable to be in scope
● Clear
○ Remove breakpoints

13. Commands
● Checkpoint
○ Store the state of the program
○ Programs can be restarted at checkpoints
● Step
○ Step through the program line by line
● Next
○ Execute the next line in the current frame
○ Does not step through sub-functions

14. Example
osh.c

15. Commands
● Print
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Show the state of memory/variables
Works with array and struct/union notation
Will assume c-strings when applicable
@ can be used on arrays for grouping prints
● Set Var
○ Change memory/variables
● Continue
○ Run until another break/watch point is triggered

16. Example
sudoku.c

17. Recap
● Debugging process is unavoidable
● GDB provides assistance
○ If I see one more stray printf()...
● Basic flow control commands
○ Allow tracing a stopped program
○ Set breakpoints to stop the program
○ Enable querying/modifying the program state

18. Thanks!
http://glenoakley.com/
@goakley123
goakley123@gmail.com