cheatsheet

Starting GDB

• gdb - Start GDB with the specified program.
• gdb - Start GDB with no program specified; you can load a program later.
• gdb -p - Attach GDB to a running process with the specified PID.

Basic Commands

• run [args] - Start the program with optional arguments.
• quit - Exit GDB.
• help - Show help for GDB commands.
• info - Display information about various types (e.g., info registers).
• list - Display source code around the current line or function.
• next - Step over to the next line of code.
• step - Step into the next function call.
• continue - Resume program execution until the next breakpoint.
• finish - Continue execution until the current function returns.

Breakpoints

• break - Set a breakpoint at the specified location (e.g., break main or break file.c:10).
• delete - Delete the breakpoint with the specified number.
• clear - Clear a breakpoint at the specified location.
• info breakpoints - List all breakpoints and their statuses.
• disable - Disable the breakpoint with the specified number.
• enable - Enable the breakpoint with the specified number.

Inspecting Variables

• print - Evaluate and display the value of an expression.
• display - Display the value of an expression each time the program stops.
• undisplay - Stop displaying the expression with the specified number.
• info locals - Display the values of local variables in the current function.
• info args - Display the values of function arguments.

Stack Frames

• backtrace - Display the call stack.
• frame - Select a stack frame by its number.
• up - Move up the call stack to the previous frame.
• down - Move down the call stack to the next frame.

Code Execution

• return - Return from the current function with the specified value.
• jump - Jump to a specified line or function.

Watchpoints

• watch - Set a watchpoint for the specified expression.
• rwatch - Set a read watchpoint for the specified expression.
• awatch - Set an access watchpoint for the specified expression.
• delete - Delete the watchpoint with the specified number.

Threads

• info threads - List all threads.
• thread - Switch to the thread with the specified number.
• thread apply all - Apply a command to all threads (e.g., thread apply all bt).

Signals

• handle - Set how GDB handles a signal (e.g., handle SIGINT nostop).
• info signals - Display the current signal handling settings.

Files

• file - Load a different executable file into GDB.
• symbol-file - Load debugging symbols from a specified file.

Scripts

• source - Execute GDB commands from a script file.

Other

• set - Set a GDB variable to a specified value.
• show - Display the value of a GDB variable.
• record - Start recording the program's execution for replay.
• restore - Restore the program's state from a previously recorded state.

Common Usage Patterns

• Debugging Segmentation Faults:
  1. Run the program: run
  2. If it crashes, check the backtrace: backtrace or bt
  3. Inspect local variables: info locals and function arguments: info args
  4. Examine memory at a pointer: x/
     (e.g., x/16xb ptr)
• Setting Conditional Breakpoints:
  1. Break at a line or function only when a condition is true: break if
  2. Example: break main.cpp:42 if x > 10
• Inspecting Memory:
  1. Examine memory at an address: x/
  2. Format examples: x/16xb (16 bytes in hex), x/8xw (8 words in hex)
  3. Print pointer contents recursively: print *ptr
• Debugging Loops:
  1. Set a breakpoint inside the loop: break
  2. Use commands to run commands automatically when hitting a breakpoint (e.g., print a variable, continue)
• Catch Exceptions or Signals:
  1. Stop when a signal occurs: handle SIGSEGV stop
  2. Stop when a C++ exception is thrown: catch throw
• Debugging Multi-threaded Programs:
  1. List threads: info threads
  2. Switch thread: thread
  3. Apply commands to all threads: thread apply all bt
• Logging and Automation:
  1. Log GDB session to a file: set logging on
  2. Run a script of commands: source script.gdb