Programmable debugger
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Omar Sandoval faad25d7b2 libdrgn: debug_info: fix address of objects with size zero
The stack trace variable work introduced a regression that causes
objects with size zero to always be marked absent even if they have an
address. This matters because GCC sometimes seems to omit the complete
array type for arrays declared without a length, so an array variable
can end up with an incomplete array type. I saw this with the
"swapper_spaces" variable in mm/swap_state.c from the Linux kernel.

Make sure to use the address of an empty piece if the variable is also
empty.

Fixes: ffcb9ccb19 ("libdrgn: debug_info: implement creating objects from DWARF location descriptions")
Signed-off-by: Omar Sandoval <osandov@osandov.com>
2021-06-07 15:46:22 -07:00
.github/workflows CI: install correct version of libomp 2021-06-01 17:52:00 -07:00
docs libdrgn: support looking up parameters and variables in stack traces 2021-06-05 16:18:51 -07:00
drgn cli: show elfutils version in use 2021-06-07 11:10:50 -07:00
examples/linux examples: add missing shebangs 2021-04-20 11:20:06 -07:00
libdrgn libdrgn: debug_info: fix address of objects with size zero 2021-06-07 15:46:22 -07:00
scripts scripts: only build manylinux wheels for CPython. 2021-06-07 01:10:59 -07:00
tests libdrgn: debug_info: fix address of objects with size zero 2021-06-07 15:46:22 -07:00
tools Use GPL-3.0-or-later license identifier instead of GPL-3.0+ 2021-04-03 01:10:35 -07:00
vmtest vmtest: manage: get mainline releases from mainline linux repository 2021-05-10 10:55:06 -07:00
_drgn.pyi cli: show elfutils version in use 2021-06-07 11:10:50 -07:00
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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/main/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 gcc libelf make pkgconf python python-pip python-setuptools

Debian/Ubuntu:

.. code-block:: console

    $ sudo apt-get install gcc liblzma-dev libelf-dev libdw-dev make pkgconf python3 python3-dev python3-pip 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 elfutils-devel gcc make pkgconf python3 python3-devel python3-pip python3-setuptools

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