112 lines
4.5 KiB
Plaintext
112 lines
4.5 KiB
Plaintext
Debugging i3: How To
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====================
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Michael Stapelberg <michael+i3@stapelberg.de>
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July 2011
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This document describes how to debug i3 suitably for sending us useful bug
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reports, even if you have no clue of C programming.
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First of all: Thank you for being interested in debugging i3. It really means
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something to us to get your bug fixed. If you have any questions about the
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debugging and/or need further help, do not hesitate to contact us!
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== Enabling logging
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i3 logs useful information to stdout. To have a clearly defined place where log
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files will be saved, you should redirect stdout and stderr in your
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+~/.xsession+. While you’re at it, putting each run of i3 in a separate log
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file with date/time in its filename is a good idea to not get confused about
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the different log files later on.
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--------------------------------------------------------------------
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exec /usr/bin/i3 >~/i3log-$(date +'%F-%k-%M-%S') 2>&1
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--------------------------------------------------------------------
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To enable verbose output and all levels of debug output (required when
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attaching logfiles to bugreports), add the parameters +-V -d all+, like this:
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--------------------------------------------------------------------
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exec /usr/bin/i3 -V -d all >~/i3log-$(date +'%F-%k-%M-%S') 2>&1
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--------------------------------------------------------------------
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== Enabling core dumps
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When i3 crashes, often you have the chance of getting a 'core dump' (an image
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of the memory of the i3 process which can be loaded into a debugger). To get a
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core dump, you have to make sure that the user limit for core dump files is set
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high enough. Many systems ship with a default value which even forbids core
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dumps completely. To disable the limit completely and thus enable core dumps,
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use the following command (in your +~/.xsession+, before starting i3):
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-------------------
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ulimit -c unlimited
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-------------------
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Furthermore, to easily recognize core dumps and allow multiple of them, you
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should set a custom core dump filename pattern, using a command like the
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following:
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---------------------------------------------
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sudo sysctl -w kernel.core_pattern=core.%e.%p
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---------------------------------------------
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This will generate files which have the executable’s file name (%e) and the
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process id (%p) in it. You can save this setting across reboots using
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+/etc/sysctl.conf+.
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== Compiling with debug symbols
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To actually get useful core dumps, you should make sure that your version of i3
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is compiled with debug symbols, that is, that the symbols are not stripped
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during the build process. You can check whether your executable contains
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symbols by issuing the following command:
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----------------
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file $(which i3)
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----------------
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You should get an output like this:
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------------------------------------------------------------------------------
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/usr/bin/i3: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically
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linked (uses shared libs), for GNU/Linux 2.6.18, not stripped
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------------------------------------------------------------------------------
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Notice the +not stripped+, which is the important part. If you have a version
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which is stripped, please have a look if your distribution provides debug
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symbols (package +i3-wm-dbg+ on Debian for example) or if you can turn off
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stripping. If nothing helps, please build i3 from source.
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== Generating a backtrace
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Once you have made sure that your i3 is compiled with debug symbols and that
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core dumps are enabled, you can start making sense out of the core dumps.
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Because the core dump depends on the original executable (and its debug
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symbols), please do this as soon as you encounter the problem. If you
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re-compile i3, your core dump might be useless afterwards.
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Please install +gdb+, a debugger for C. No worries, you don’t need to learn it
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now. Start gdb using the following command (replacing the actual name of the
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core dump of course):
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----------------------------
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gdb $(which i3) core.i3.3849
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----------------------------
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Then, generate a backtrace using:
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--------------
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backtrace full
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--------------
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== Sending bug reports/debugging on IRC
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When sending bug reports, please paste the relevant part of the log (if in
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doubt, please send us rather too much information than too less) and the whole
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backtrace (if there was a core dump).
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When debugging with us in IRC, be prepared to use a so called nopaste service
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such as http://nopaste.info or http://pastebin.com because pasting large
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amounts of text in IRC sometimes leads to incomplete lines (servers have line
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length limitations) or flood kicks.
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