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What am I looking at

This repository contains UDB extensions for debugging Python programs.

The extensions are built on top of the cpython GDB library.

Install

Clone the repository or copy the following files into your current working directory

  • libpython.gdb
  • libpython.py
  • libpython_extensions.py
  • libpython_ui.py
  • tui_windows.py

and start UDB while sourcing the libpython.gdb file from the same directory

$ udb --ex "source ./libpython.gdb"

The supported version of Python is currently cpython 3.10. The interpreter must have been compiled with full debug information (-g3) and without cpython's "computed gotos" feature.

You can use the ./setup-python script to install a suitable version of Python with pyenv:

$ source ./setup-python
$ python --version
Python 3.10.15

Usage

Use the following commands to inspect Python state:

  • py-print (pp) to print Python objects
  • py-eval (pe) to evaluate Python expressions
  • py-list to list Python source code
  • py-bt to show Python backtrace
  • py-locals to show local Python variables
  • py-dis to list Python bytecode disassembly

Use the following commands to navigate:

  • py-step (pys) to step Python bytecode
  • py-reverse-step (pyrs) to step Python bytecode backwards
  • py-advance-function (pya) to continue until the next Python function call
  • py-reverse-advance-function (pyra) to continue backwards until the previous Python function call
  • py-last-attr (pyla) to search backwards or forwards until an object attribute is assigned

The py-step and py-reverse-step commands take an optional argument specifying the Python bytecode opcode to step until.

The py-advance-function and py-reverse-advance-function commands take an optional argument specifying which function to advance to.

The py-last-attr command takes an optional argument to specify which attribute name to search for.

Switch to the Python layout in TUI mode to get a better overview of your program.

> layout python

If your Python source code does not show up you might have to use the py-substitute-path command to inform the debugger about the location of your local checkout of the Python source code.