albertygu / drgn

Scriptable debugger library

drgn

drgn (pronounced "dragon") is a debugger-as-a-library. In contrast to existing debuggers like GDB which focus on breakpoint-based debugging, drgn excels in live introspection. drgn exposes the types and variables in a program for easy, expressive scripting in Python. For example, you can debug the Linux kernel:

>>> from drgn.helpers.linux import list_for_each_entry
>>> for mod in list_for_each_entry('struct module',
...                                prog['modules'].address_of_(),
...                                'list'):
...    if mod.refcnt.counter > 10:
...        print(mod.name)
...
(char [56])"snd"
(char [56])"evdev"
(char [56])"i915"

drgn was developed for debugging the Linux kernel (as an alternative to the crash utility), but it can also debug userspace programs written in C. C++ support is planned.

Documentation can be found at drgn.readthedocs.io.

Installation

Install dependencies:

Arch Linux:

$ sudo pacman -S --needed autoconf automake bison bzip2 flex gawk gcc libtool make pkgconf python python-setuptools xz zlib

Debian/Ubuntu:

$ sudo apt-get install autoconf automake bison flex gawk gcc libbz2-dev liblzma-dev libtool make pkgconf python3 python3-dev python3-setuptools zlib1g-dev

Note that Debian Stretch, Ubuntu Trusty, and Ubuntu Xenial (and older) ship Python versions which are too old. Python 3.6 or newer must be installed manually.

Fedora:

$ sudo dnf install autoconf automake bison bzip2-devel flex gawk gcc libtool make pkgconf python3 python3-devel python3-setuptools xz-devel zlib-devel

Optionally, install:

• libkdumpfile if you want support for kdump-compressed kernel core dumps

Then, run:

$ git clone https://github.com/osandov/drgn.git
$ cd drgn
$ python3 setup.py build
$ sudo python3 setup.py install

See the installation documentation for more details.

Quick Start

drgn debugs the running kernel by default; run sudo drgn. To debug a running program, run sudo drgn -p $PID. To debug a core dump (either a kernel vmcore or a userspace core dump), run drgn -c $PATH. The program must have debugging symbols available.

Then, you can access variables in the program with prog['name'], access structure members with ., use various predefined helpers, and more:

$ sudo drgn
>>> prog['init_task'].comm
(char [16])"swapper/0"
>>> d_path(fget(find_task(prog, 1), 0).f_path.address_of_())
b'/dev/null'
>>> max(task.stime for task in for_each_task(prog))
(u64)4192109975952
>>> sum(disk.gendisk.part0.nr_sects for disk in for_each_disk(prog))
(sector_t)999705952

See the user guide for more information.

License

Copyright 2018-2019 Omar Sandoval

drgn is licensed under the GPLv3 or later.