Debugging

This article explains how to debug Arx Fatalis on the different targeted platforms.

Linux

Currently arx is not compiled as a native linux application, but as a winelib application that must be run with wine. This makes debugging a little more tricky.

Winedbg

To debug just run arx.exe.so with winedbg instead of with wine:

WINEDEBUG=-all winedbg ./arx.exe.so

Winedbg does not support C++ however. This means that backtraces won't show filename and line numbers for any non-C symbols (anything that is in a class or namespace). You also cannot set a breakpoint on C++ symbols.

Gdb

Using gdb allows to interact with C++ symbols. Since arx.exe.so is a winelib application, you can't run it directly with gdb , but winedbg supports automatically attaching gdb to the process when it starts:

WINEDEBUG=-all winedbg --gdb arx.exe.so

However, wine causes many segmentation faults internally (and handles them), which causes gdb to suspend the execution of the program. To tell gdb not to do this, enter the following into the gdb prompt:

handle SIGSEGV nostop noprint

This also prevents gdb from catching any segmentation faults caused by arx, which then exits and gdb just prints "Program exited normally." In those cases plain winedbg may still be needed.

Wine will also send a SIGTRAP once on startup, but SIGTRAP is also used by gdb, so ignoring it disables all breakpoints.

Many stl classes check for error conditions when compiling in debug mode and throw an exception on failure. To get a backtrace for where the exception was thrown, add a breakpoint on the exception constructor. Enter this in the gdb prompt.

b std::logic_error::logic_error

b std::runtime_error::runtime_error

If entering these commands into gdb on each run is to cumbersome, you can create a file called ".gdbinit" that is loaded by gdb on startup and contains default settings for gdb:

set breakpoint pending on
b std::logic_error::logic_error
b std::runtime_error::runtime_error
handle SIGSEGV nostop noprint

The extra "set breakpoint pending on" is needed because .gdbinit is loaded before any libraries and therefore gdb will not be able to find the breakpoints right away.

With this configuration, gdb will still stop twice during startup, once for a SIGSEGV and once for a SIGTRAP, both in wine. Use cont or just c each time to continue.

Valgrind

Like gdb, valgrind also needs a little help to run with wine. Specifically the --trace-children=yes and --vex-iropt-precise-memory-exns=yes options are needed. Here is the full command to debug arx with the memcheck tool:

valgrind --tool=memcheck --error-limit=no --leak-check=full --log-file=arx-valgrind.log -v --trace-children=yes --vex-iropt-precise-memory-exns=yes --track-origins=yes --suppressions=suppressions.txt -- wine arx.exe.so

Where suppressions.txt is the one found here: http://www.stud.uni-karlsruhe.de/~uocet/suppressions.txt

I get a warning preloader: Warning: failed to reserve range 00110000-68000000 from wine when running arx with valgrind, but the game seems to run anyway. Be patient, it will take a while before there is any console output from arx and even longer before the first frame renders.

The --track-origins=yes option slows down execution some more (arx is already unplayable without it), but provides useful additional information.

For mor information on wine and valgrind see http://wiki.winehq.org/Wine_and_Valgrind