105 lines
4.1 KiB
Plaintext
105 lines
4.1 KiB
Plaintext
Debugging i3: How To
|
||
====================
|
||
Michael Stapelberg <michael+i3@stapelberg.de>
|
||
April 2009
|
||
|
||
This document describes how to debug i3 suitably for sending us useful bug
|
||
reports, even if you have no clue of C programming.
|
||
|
||
First of all: Thank you for being interested in debugging i3. It really means
|
||
something to us to get your bug fixed. If you have any questions about the
|
||
debugging and/or need further help, do not hesitate to contact us!
|
||
|
||
== Enabling logging
|
||
|
||
i3 spits out much information onto stdout. To have a clearly defined place
|
||
where log files will be saved, you should redirect stdout and stderr in
|
||
xsession. While you’re at it, putting each run of i3 in a separate log file
|
||
with date/time in it is a good idea to not get confused about the different
|
||
log files later on.
|
||
|
||
--------------------------------------------------------------------
|
||
exec /usr/bin/i3 >/home/michael/i3/i3log-$(date +'%F-%k-%M-%S') 2>&1
|
||
--------------------------------------------------------------------
|
||
|
||
== Enabling core dumps
|
||
|
||
When i3 crashes, often you have the chance of getting a 'core dump' (an image
|
||
of the memory of the i3 process which can be loaded into a debugger). To get a
|
||
core dump, you have to make sure that the user limit for core dump files is set
|
||
high enough. Many systems ship with a default value which even forbids core
|
||
dumps completely. To disable the limit completely and thus enable core dumps,
|
||
use the following command (in your .xsession, before starting i3):
|
||
|
||
-------------------
|
||
ulimit -c unlimited
|
||
-------------------
|
||
|
||
Furthermore, to easily recognize core dumps and allow multiple of them, you
|
||
should set a custom core dump filename pattern, using a command like the
|
||
following:
|
||
|
||
---------------------------------------------
|
||
sudo sysctl -w kernel.core_pattern=core.%e.%p
|
||
---------------------------------------------
|
||
|
||
This will generate files which have the executable’s file name (%e) and the
|
||
process id (%p) in it. You can save this setting across reboots using
|
||
+/etc/sysctl.conf+.
|
||
|
||
== Compiling with debug symbols
|
||
|
||
To actually get useful core dumps, you should make sure that your version of i3
|
||
is compiled with debug symbols, that is, that they are not stripped during the
|
||
build process. You can check whether your executable contains symbols by
|
||
issuing the following command:
|
||
|
||
----------------
|
||
file $(which i3)
|
||
----------------
|
||
|
||
You should get an output like this:
|
||
------------------------------------------------------------------------------
|
||
/usr/bin/i3: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically
|
||
linked (uses shared libs), for GNU/Linux 2.6.18, not stripped
|
||
------------------------------------------------------------------------------
|
||
|
||
Notice the +not stripped+, which is the important part. If you have a version
|
||
which is stripped, please have a look if your distribution provides debug
|
||
symbols (package +i3-wm-dbg+ on Debian for example) or if you can turn off
|
||
stripping. If nothing helps, please build i3 from source.
|
||
|
||
== Generating a backtrace
|
||
|
||
Once you have made sure that your i3 is compiled with debug symbols and that
|
||
core dumps are enabled, you can start making sense out of the core dumps.
|
||
|
||
Because the core dump depends on the original executable (and its debug
|
||
symbols), please do this as soon as you encounter the problem. If you
|
||
re-compile i3, your core dump might be useless afterwards.
|
||
|
||
Please install +gdb+, a debugger for C. No worries, you don’t need to learn it
|
||
now. Start gdb using the following command (replacing the actual name of the
|
||
core dump of course):
|
||
|
||
----------------------------
|
||
gdb $(which i3) core.i3.3849
|
||
----------------------------
|
||
|
||
Then, generate a backtrace using:
|
||
|
||
--------------
|
||
backtrace full
|
||
--------------
|
||
|
||
== Sending bug reports/debugging on IRC
|
||
|
||
When sending bug reports, please paste the relevant part of the log (if in
|
||
doubt, please send us rather too much information than too less) and the whole
|
||
backtrace (if there was a core dump).
|
||
|
||
When debugging with us in IRC, be prepared to use a so called nopaste service
|
||
such as http://nopaste.info or http://pastebin.com because pasting large
|
||
amounts of text in IRC sometimes leads to incomplete lines (servers have line
|
||
length limitations) or flood kicks.
|