![Access Python with GDB - Basic Commands
● python [command]
● py-list
● py-bt
● py-up/py-down
● py-locals
● py-print](https://image.slidesharecdn.com/pybay2019-gdb-python-190818200349/85/Extending-GDB-with-Python-14-320.jpg)
Extending GDB with Python
- 1. Extending GDB With Python Lisa Roach
- 2. About Me ● CPython Core Developer ● Facebook Production Engineer on the Python Foundation team
- 3. What is Today’s Goal? Access a running Python process and perform live debugging beyond GDB’s typical capabilities
- 4. GDB Primer
- 5. Allows you to see what is going on ‘inside’ a program while it executes. GDB – The GNU Project Debugger
- 6. GDB- What can it do? ● Read and write data from the program
- 7. What languages are supported? ● Ada ● Assembly ● C ● C++ ● D ● Fortran ● Go ● Objective-C ● OpenCL ● Modula-2 ● Pascal ● Rust
- 8. GDB Commands ● break <line-number|function-name> ● next ● help ● call <expr>
- 9. A text file containing GDB commands that are executed sequentially (unless flow control changes the order). GDB Command Files
- 10. source <filename> gdb –x <filename> GDB Command Files
- 11. Extending GDB
- 12. ./configure --with-python + Python Debug Symbols
- 13. What does the GDB python extension get us? 1. Access high-level CPython interpreter information from GDB 2. Access GDB commands from Python code 3. Build custom GDB commands written in Python
- 14. Access Python with GDB - Basic Commands ● python [command] ● py-list ● py-bt ● py-up/py-down ● py-locals ● py-print
- 16. Access GDB From Python
- 17. GDB CPython System Python
- 19. gdb_commands.py Let’s not write code in the interpreter
- 20. Let’s not write code in the interpreter
- 21. Access GDB From Python
- 22. Execute Code in the Debugged Process
- 23. Execute Code in the Debugged Process call <expr>
- 24. I’m a Python Developer! I don’t know C! C API
- 25. C API
- 26. Execute Code in the Native Process gdb.execute(“call <C Code>”)
- 27. Execute Code in the Debugged Process
- 29. Execute Code in the Native Process
- 30. The GIL
- 31. C API ● PyGILState_Ensure() ● PyGILState_Release()
- 32. ● Video of the above happening
- 33. Build Custom GDB Commands gdb_commands.py
- 35. Use Case Example Debugging memory usage in a running Python process
- 36. Step 1: Write a Python Script to Analyze Memory memory_analysis.py
- 37. Step 2: Acquire the GIL gdb_commands.py
- 38. Step 3: Create a Custom GDB Command gdb_commands.py
- 39. Step 4: Execute the New Command gdb_commands.py
- 40. Step 5: Launch GDB with the Command File main.py
- 41. Step 6: Run
- 43. Conclusion ● See the full code: ○ https://github.com/facebookincubator/memory-analyzer ● GDB Documentation: ○ https://sourceware.org/gdb/onlinedocs/gdb/Python.html#Python ● Python GDB Documentation ○ https://devguide.python.org/gdb/
Editor's Notes
- #6: Start your program, specifying anything that might affect its behavior. Make your program stop on specified conditions. Examine what has happened, when your program has stopped. Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.
- #7: Start your program, specifying anything that might affect its behavior. Make your program stop on specified conditions. Examine what has happened, when your program has stopped. Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.
- #9: Part of the linux kernel. Allows a process the control the execution of another, and can poke at the innards. Has access to all the kernel level information about the process. GDB also works on non-linux systems, but I don’t have time to dive into all the specifics there.
- #17: Start your program, specifying anything that might affect its behavior. Make your program stop on specified conditions. Examine what has happened, when your program has stopped. Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.
- #20: Start your program, specifying anything that might affect its behavior. Make your program stop on specified conditions. Examine what has happened, when your program has stopped. Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.
- #23: Now you can access information about Python using GDB, but there is a second part to the extension. You can access GDB from Python. Which means we can control GDB (meaning ptrace under the hood for linux) and script it to do interesting and repeatable debugging on Python code (or beyond Python code!). You can only access the gdb module from within python if you are using gdb, you cannot access it from a standard interpreter session.
- #28: Executing Python code from GDB will just execute code in the GDB process To execute code in the inferior process we need to use: Gdb.execute executes the string command passed to it as a gdb CLI command
- #29: You can pass C Code into GDB execute and it will be sent directly to the infererior process
- #30: Executing Python code from GDB will just execute code in the GDB process To execute code in the inferior process we need to use: Gdb.execute executes the string command passed to it as a gdb CLI command
- #33: Can execute functions that have symbols loaded in GDB --with-python extensions and python debug symbols load symbols for the Cpython interpreter, we don’t have symbols have Python code Cannot run print(‘hello world”) no symbol in current context
- #37: You can pass C Code into GDB execute and it will be sent directly to the infererior process
- #38: You can pass C Code into GDB execute and it will be sent directly to the infererior process
- #40: You can pass C Code into GDB execute and it will be sent directly to the infererior process