Tools/Debugging/GDB

Debugging with GDB

There are a couple ways to go about debugging crashes in Blender. Today I had to learn one of them. The steps are pretty easy to follow. These instructions should work for any platform with Bash and GDB, typically Unix system or with MinGW/Cygwin Windows.

Compile Debug Build

How to make a debug build depends on the build system used:

• For CMake, set CMAKE_BUILD_TYPE=Debug
• In Visual Studio, set the Release Configuration to Debug

Run GDB

Start GDB by changing the working directory to the location of your new debug build and typing one of the following, depending on the platform:

gdb blender.exe

gdb ./blender

Then to start Blender, type:

run

Now make Blender crash. Blender will freeze, so switch to the GDB prompt. Get a backtrace by typing:

bt

A more complete backtrace can be printed using:

thread apply all bt full

For more information, see this guide: How to Get a Backtrace.

Tip: Happy AMD graphic card owners

If you are using proprietary AMD drivers under Linux (fglrx), before doing any debugging, run (in a root terminal) :

# aticonfig --sb off

And reboot your PC (you can also, if you prefer, directly edit your xorg.conf file, and add, in the Device section, the line Option "BlockSignalsOnLock" "off")

Else, you may get some (really unfriendly) random freezes, deadlocks, as fglrx blocks signals in certain situations, and gdb waits for those signals…

Copy Crash Information

If you would like to make this information available to a developer you can copy and paste it from the command prompt.

On Windows, selecting and copying text from the command prompt works different than you might expect: by right clicking on the windows header, select Edit > Mark from the menu. Then highlight your selection. Then again right click on the header and select Edit > Copy.