gdbundle 0.0.4

Plugin Manager for GDB and LLDB

GDBundle - Plugin Manager for GDB and LLDB

gdbundle is short for GDB bundle and is a plugin manager for GDB and LLDB.

For detailed info about the origin story of gdbundle, read the announcement on Interrupt: gdbundle - GDB's Missing Plugin Manager

Benefits

There are a handful of indisputable benefits of using gdbundle over manually modifying .gdbinit and .lldbinit files.

1. Just pip install gdbundle-<plugin-name>. No more manually editing your ~/.gdbinit in specific ways depending on the extension.
2. It enables developers to use virtual environments (and encourages it!).
3. Personal projects and team projects can have project-specific requirements.txt and .gdbinit files. With these two in place, a new developer would just need to pip install -r requirements.txt.
4. Discoverability. Check out this PyPi filter to find new plugins.
5. Dependency management and version tracking is now done automatically by Python's packaging infrastructure.

Published Plugins

Published ones can be found on PyPi

For now, a list is kept here as well:

• example
• gdb-dashboard
• PyCortexMDebug
• voltron

Quickstart

NOTE: The Python compiled with GDB should be the same major version as the Python in the local virtual, Conda, or local environment that you are installing gdbundle and plugins into.

To check both versions of Python, you can run the following:

$ gdb
(gdb) pi
>>> import sys; sys.version
'3.6.9 (default, Nov  7 2019, 10:44:02) \n[GCC 8.3.0]'

$ python --version
Python 3.6.9

Install gdbundle

Install gdbundle from PyPi first. Using a virtual environment is recommended.

$ pip install gdbundle

If you'd rather not use a virtual environment, it's advised to use --user when installing the package.

$ pip install --user gdbundle

Just, whatever you do, don't use sudo .... And don't let your friends either.

Amend Init Scripts

Placing the following in the appropriate file will load all installed gdbundle plugins by default. If you would like to selectively load certain ones, please refer to the Configuration section.

GDB's .gdbinit

Append the following to your ~/.gdbinit or to a project-specific .gdbinit that is loaded with gdb --command .gdbinit

# -- gdbundle_BEGIN
python
import os,sys,subprocess
# Execute a Python using the user's shell and pull out the sys.path (for site-packages)
paths = subprocess.check_output('python -c "import os,sys;print(os.linesep.join(sys.path).strip())"',shell=True).decode("utf-8").split()
# Extend GDB's Python search path
sys.path.extend(paths)

# Initialize gdbundle
import gdbundle
gdbundle.init()
end
# -- gdbundle_END

LLDB's .lldbinit

Copy the sample_lldbinit.py somewhere. For now, let's assume it's at /path/to/gdbundle_lldbinit.py

# /path/to/gdbundle_lldbinit.py

# -- gdbundle_BEGIN
import os,subprocess,sys
# Execute a Python using the user's shell and pull out the sys.path (for site-packages)
paths = subprocess.check_output('python -c "import os,sys;print(os.linesep.join(sys.path).strip())"',shell=True).decode("utf-8").split()
# Extend LLDB's Python search path
sys.path.extend(paths)

# Initialize gdbundle
import gdbundle
gdbundle.init()
# -- gdbundle_END

Append the following to your ~/.lldbinit or to project-specific .lldbinit file that is loaded with lldb -s .lldbinit.

# .lldbinit

command script import '/path/to/gdbundle_lldbinit.py'

Background

GDB has built-in support for extensions written in in Python, Guile, or GDB's command language. However, there is no convenient way to package, distribute, and install these scripts.

GDB does provide a few mechanisms:

• Place scripts in /usr/local/share/gdb/auto-load or similar
• Use gdb --command ... to load the scripts on invocation

GDB's documentation gives us the following:

Python scripts used by GDB should be installed in data-directory/python, where data-directory is the data directory as determined at GDB startup

This leaves a lot to be desired, because a user would have to copy-paste script files to this directory. There are many drawbacks to this method, including:

• Requires manual intervention to install scripts to data-directory
• Scripts become out of date since they were copy-pasted
• data-directory is usually in a directory next to GDB's installation path, usually in /usr/local. Everyone should do their best not to manually edit files there.

There has to be a better way, and thankfully, there is! It's called gdbundle.

Installing Packages

Packages are prefixed with gdbundle- and are installing through pip from PyPi.

$ pip install gdbundle-example

Configuration

gdbundle today is simple and has only a few configuration knobs. Configuration is passed into the gdbundle.init(...) function call.

NOTE: The names passed into include and exclude should be the package name minus gdbundle_, and hyphens are underscores. (e.g. gdbundle-gdb-dashboard becomes gdb_dashboard)

# .gdbinit

import gdbundle

# Configure which packages to include
include = [
    # List of packages to load.
    # e.g. "example"
]

exclude = [
    # List of packages to exclude.
    # Useful if the same virtual environment is used for multiple
    #  projects and not all packages should be loaded
    # e.g. "example"
]
# Load the configured packages
gdbundle.init(include=include, exclude=exclude)

If you've created a Python package that has the necessary gdbundle hooks (e.g. gdbundle.gdb_loader.gdbundle_load()), you can manually load it using gdbundle.load_module().

# gdbundle will import this module and attempt to run `my_package.gdb_loader.gdbundle_load()`
gdbundle.load_module("my_package")

Creating and Distributing Packages

The goal was to keep gdbundle packages as simple as possible. A package only has a few responsibilities:

1. Define dependencies in the pyproject.toml so they are automatically installed.
2. Provide a version so users can easily pin and upgrade to specific versions.
3. Provide a hook gdb_loader.gdbundle_load() and/or lldb_loader.gdbundle_load() which is called by gdbundle, which should either:
   • Load the script into the debugger context by calling gdb.execute("source <file>") or lldb.debugger.HandleCommand("command script import <file>"
   • Import the Python module which does the sourcing itself: from mypackage import HelloWorld; HelloWorld()

To investigate a real package that works with both GDB and LLDB, check out the gdbundle-example plugin.

Let's go over each piece quickly.

pyproject.toml

A standard setup.py file. The main thing to note here is that our package name will be gdbundle-<something>, but our Python package will be called gdbundle_<something>.

[tool.poetry]
name = "gdbundle-example"
version = "0.0.1"
description = ""
authors = ["Tyler Hoffman <[e-mail]>"]
readme = "README.md"
include = ["gdbundle_example/scripts/*"]
license = "MIT"
classifiers = [
    [...]
]

[tool.poetry.dependencies]
python = "*"

[build-system]
requires = ["poetry>=0.12"]
build-backend = "poetry.masonry.api"

gdbundle_example/gdb_loader.py

import gdb
import os

PACKAGE_DIR = os.path.dirname(__file__)

SCRIPT_PATHS = [
    [PACKAGE_DIR, 'scripts', 'example_gdb.gdb'],
    [PACKAGE_DIR, 'scripts', 'example_gdb.py']
]

def _abs_path(path):
    return os.path.abspath(os.path.join(*path))

def gdbundle_load():
    for script_path in SCRIPT_PATHS:
        gdb.execute("source {}".format(_abs_path(script_path)))

gdbundle_example/scripts/

Place the script files here!

How It Works

If the GDB/LLDB executable you are using was downloaded rather than compiled from source, it's likely that it is linked against a system Python library and site-packages directory, rather than against a virtual environment, Conda environment, or another user installed version of Python.

For example, if we start arm-none-eabi-gdb-py downloaded from ARM, we'll see that it is searching within the system Python's site-packages folder for packages:

$ arm-none-eabi-gdb-py
(gdb) python-interactive
>>> import sysconfig
>>> sysconfig.get_paths()['purelib']
'/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages'

Similar with LLDB:

$ lldb
(lldb) script
Python Interactive Interpreter. To exit, type 'quit()', 'exit()' or Ctrl-D.
>>> import sysconfig; sysconfig.get_paths()['purelib']
'/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.7/lib/python3.7/site-packages'

When a user installs packages with an apt or brew Python, or one from a Conda or virtual environment, GDB will not automatically find those packages since Python's configured sys.path is only looking in the system's site-packages folder.

There are three recommended (but very bad) ways to handle this:

• Override PYTHONPATH on init or in the users shell.
• Create sym-links between the virtual environment and the system python installation.
• Deal with it, as said in LLDB's Python Caveat docs. Install the packages in the same installation anyways.

We want something that edits only GDB's Python context, and only appends to Python's sys.path, not overrides it.

The best solution I've found and have been using (along with 100 other engineers at my previous employer) is to shell out from within GDB, ask the local shell environment what the configured Python executable is, get its sys.path entries, and then append those to our current GDB session's Python environment. This allows GDB to find and use packages that are installed into a Conda or virtualenv environment, as well as any other user installed Python environment.

Who uses GDB Python Scripts

Many companies and projects use and include GDB scripts with their large open-source projects. They are usually buried in the repo, difficult to source, and built and used in various ways. They usually require the developer to discover that they exist, manually source them, and then look at the source code to figure out how they work.

Check out the gdbundle announcement for a list of ones that are public and open-source.

Neat GDB Script Repositories