Debug - Getting Traces
This article will try to give you an idea how to create Arch package, which provides debug and traces information for reporting software bugs.
Discovering name of package(s)
A few facts of debug messages
When looking at debug message, such as (stripped):
... Backtrace was generated from '/usr/bin/epiphany' (no debugging symbols found) Using host libthread_db library "/lib/libthread_db.so.1". (no debugging symbols found) [Thread debugging using libthread_db enabled] [New Thread -1241265952 (LWP 12630)] (no debugging symbols found) 0xb7f25410 in __kernel_vsyscall () #0 0xb7f25410 in __kernel_vsyscall () #1 0xb741b45b in ?? () from /lib/libpthread.so.0 ...
you can see ?? at the place where debugging info is missing and also the name of library or executable which called the function. Similarly, when the line (no debugging symbols found) appears in a message, it means that you have to look for a file whose name is stated.
Use Pacman to retrieve name of package:
# pacman -Qo /lib/libthread_db.so.1 /lib/libthread_db.so.1 is owned by glibc 2.5-8
We have found that package is called glibc in version 2.5-8. By repeating this step, we are able to create a list of packages which we have to compile ourselves to get full stack trace.
In order to build a package from source, the PKGBUILD file is required. The location from which you can obtain PKGBUILDs is, in general:
Use AUR search page to find the package. If it is not present, the package is stored in one of the official repository trees of Arch Linux. If found, click on its name and download the Tarball. Store it in location of your choice. Use
tar to extract it and change directory:
$ tar xvzf name_of_tarball.tar.gz $ cd name_of_tarball
If the package is a part of official tree, install ABS, fetch the source for the package and then build it:
$ ABSROOT=. abs core/glibc $ cd core/glibc $ makepkg -s
At this stage, you can modify the global configuration file of
makepkg if you will be using it only for debug purposes. In other cases, you should modify package's PKGBUILD file only for each package you would like to rebuild.
makepkg's configuration file
/etc/makepkg.conf to contain following lines:
CFLAGS="-g -march=i686 -O1 -pipe" CXXFLAGS="-g -march=i686 -O1 -pipe"
OPTIONS=(!strip !docs libtool emptydirs)
These settings (in bold) will force compilation with debugging information and will disable stripping of executable.
One package settings only
foo's PKGBUILD file to contain the following lines:
build() function, add following lines at the very beginning:
export CFLAGS="$CFLAGS -g -O1" export CXXFLAGS="$CXXFLAGS -g -O1"
-O1cannot be generally recommended as gcc then uses implementations of functions in the GNU C library that can be considered too different from the optimized ones. Also, changes in headers' includes and disabled functions may prevent successful compilation.
Building and installing the package
Build the package from source using
makepkg while in the PKGBUILD's directory. This could take some time:
Then install the built package:
# pacman -U glibc-2.5-8-i686.pkg.tar.gz
Getting the trace
The actual backtrace resp. stack trace can now be obtained via e. g.
gdb, the GNU Debugger. Run it either via
# gdb /path/to/file
# gdb (gdb) exec /path/to/file
The path is optional if it is already in the
run followed by any arguments you wish the program to start with, e. g.
(gdb) run --no-daemon --verbose
to start execution of the file. Do whatever necessary to evoke the bug. For the actual log, type the lines
(gdb) set logging file trace.log (gdb) set logging on
to output the trace to
trace.log into the directory
gdb was started in. To exit, enter:
(gdb) set logging off (gdb) quit
# gdb /usr/bin/python (gdb) run <python application>
Use the complete stack trace to inform developers of a bug you have discovered before. This will be highly appreciated by them and will help to improve your favorite program.