Programmable debugger
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Omar Sandoval eec67768aa libdrgn: replace elfutils DWARF unwinder with our own
The elfutils DWARF unwinder has a couple of limitations:

1. libdwfl doesn't have an interface for getting register values, so we
   have to bundle a patched version of elfutils with drgn.
2. Error handling is very awkward: dwfl_getthread_frames() can return an
   error even on success, so we have to squirrel away our own errors in
   the callback.

Furthermore, there are a couple of things that will be easier with our
own unwinder:

1. Integrating unwinding using ORC will be easier when we're handling
   unwinding ourselves.
2. Support for local variables isn't too far away now that we have DWARF
   expression evaluation.

Now that we have the register state, CFI, and DWARF expression pieces in
place, stitch them together with the new unwinder, and tweak the public
API a bit to reflect it.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
2021-03-15 16:43:12 -07:00
.github/workflows CI: run apt-get update before apt-get install 2021-01-08 11:22:42 -08:00
docs libdrgn: remove half-baked support for complex types 2021-02-17 14:56:33 -08:00
drgn Remove unused 'type: ignore' comment for pkgutil.read_code() 2021-01-22 11:27:10 -08:00
examples/linux Format imports with isort 2020-08-20 16:55:07 -07:00
libdrgn libdrgn: replace elfutils DWARF unwinder with our own 2021-03-15 16:43:12 -07:00
scripts Fix some include-what-you-use warnings and update for Bear 3 2021-02-26 16:05:49 -08:00
tests libdrgn: debug_info: fix parsing specifications of declarations 2021-02-25 10:46:34 -08:00
tools Format imports with isort 2020-08-20 16:55:07 -07:00
vmtest vmtest: manage: use str() instead of repr() for Path in error message 2021-02-21 03:08:36 -08:00
_drgn.pyi libdrgn: replace elfutils DWARF unwinder with our own 2021-03-15 16:43:12 -07:00
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.git-blame-ignore-revs Add .git-blame-ignore-revs 2020-01-14 12:03:26 -08:00
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CONTRIBUTING.rst CONTRIBUTING: add guidelines for good commits 2021-01-12 16:56:54 -08:00
COPYING License under GPL-3.0 or later 2018-04-15 15:03:33 -07:00
MANIFEST.in Add examples and tools to source distribution 2020-04-27 16:53:14 -07:00
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setup.py setup.py: add 5.12 to vmtest kernels 2021-03-09 13:51:52 -08:00
util.py vmtest: use pathlib 2020-10-14 11:37:31 -07:00

drgn
====

.. image:: https://img.shields.io/pypi/v/drgn
    :target: https://pypi.org/project/drgn/
    :alt: PyPI

.. image:: https://github.com/osandov/drgn/workflows/CI/badge.svg
    :target: https://github.com/osandov/drgn/actions
    :alt: CI Status

.. image:: https://readthedocs.org/projects/drgn/badge/?version=latest
    :target: https://drgn.readthedocs.io/en/latest/?badge=latest
    :alt: Documentation Status

.. image:: https://img.shields.io/badge/code%20style-black-000000.svg
    :target: https://github.com/psf/black

.. start-introduction

drgn (pronounced "dragon") is a debugger with an emphasis on programmability.
drgn exposes the types and variables in a program for easy, expressive
scripting in Python. For example, you can debug the Linux kernel:

.. code-block:: pycon

    >>> 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"

Although other debuggers like `GDB <https://www.gnu.org/software/gdb/>`_ have
scripting support, drgn aims to make scripting as natural as possible so that
debugging feels like coding. This makes it well-suited for introspecting the
complex, inter-connected state in large programs. It is also designed as a
library that can be used to build debugging and introspection tools; see the
official `tools <https://github.com/osandov/drgn/tree/master/tools>`_.

drgn was developed for debugging the Linux kernel (as an alternative to the
`crash <http://people.redhat.com/anderson/>`_ utility), but it can also debug
userspace programs written in C. C++ support is in progress.

.. end-introduction

Documentation can be found at `drgn.readthedocs.io
<https://drgn.readthedocs.io>`_.

Installation
------------

.. start-install-dependencies

Install dependencies:

Arch Linux:

.. code-block:: console

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

Debian/Ubuntu:

.. code-block:: console

    $ 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:

.. code-block:: console

    $ 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 <https://github.com/ptesarik/libkdumpfile>`_ if you want
  support for kdump-compressed kernel core dumps

.. end-install-dependencies

Then, run:

.. code-block:: console

    $ sudo pip3 install drgn

See the `installation documentation
<https://drgn.readthedocs.io/en/latest/installation.html>`_ for more options.

Quick Start
-----------

.. start-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:

.. code-block:: pycon

    $ 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

.. end-quick-start

See the `user guide <https://drgn.readthedocs.io/en/latest/user_guide.html>`_
for more information.

License
-------

.. start-license

Copyright (c) Facebook, Inc. and its affiliates.

drgn is licensed under the `GPLv3
<https://www.gnu.org/licenses/gpl-3.0.en.html>`_ or later.

.. end-license