Mesa and Its Debugging, Вадим Шовкопляс
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This document discusses debugging tools for the Mesa library. It begins with introductions and then covers Mesa environment variables, basic debugging tools like printf and static analyzers, using GDB for debugging, tools like Apitrace and Frameretrace for capturing OpenGL calls, and Piglit for running automated tests on OpenGL implementations. It also provides tips for debugging Steam games with Mesa like determining the process ID and attaching GDB or customizing the launch environment.
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Use static analyzers to find possible causes
• Some bugs or issues can be caused by simple mistakes that can be found by
automated tools.
• Like smatch or cppcheck
For example, smatch warning:
[src/intel/vulkan/anv_nir_apply_pipeline_layout.c:457]: (error)
Possible null pointer dereference: null_data
And the library code itself:
struct anv_push_constants *null_data = NULL;
const struct brw_image_param *image_param = null_data->images;](https://image.slidesharecdn.com/mesaanditsdebugging-181220100500/85/Mesa-and-Its-Debugging-19-320.jpg)
Mesa and Its Debugging, Вадим Шовкопляс
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- 2. 2 Mesa and its debugging Vadym Shovkoplias Andrii Khulap December 11, 2018
- 3. 3 Agenda 1. About myself 2. Mesa library 3. Debugging tools 3.1. Mesa environment variables 3.2. Basic debugging tools 3.3. GDB 3.4. Apitrace and Frameretrace 3.5. Steam specifics
- 5. 5 About my self Vadym and Andrii have more than 10 years of development experience. The main specialty of Andrii is the built-in devices and software for them and main speciality of Vadim is the development of software applications for embedded systems based on Linux and Android.
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- 9. 9 Mesa • Open source project with OpenGL and Vulkan implementations • Multi platform support by several graphics vendors • Used in Linux, Windows and MacOS
- 10. 10 Hardware support • Intel • AMD • Nvidia • Broadcom • Qualcomm • VMWare • Vivante
- 11. 11 Software drivers • llvmpipe Uses LLVM for x86 JIT code generation and is multi-threaded • Softpipe A reference Gallium driver • Swrast The legacy/original Mesa software rasterizer
- 12. 12 https://mesamatrix.net/ # Driver Extentions OpenGL OpenGL ES 1 mesa (92.6%) 226 4.5 3.2 2 radeonsi (90.2%) 220 4.5 3.1 3 i965 (89.8%) 219 4.5 3.2 4 nvc0 (87.7%) 214 4.5 3.1 5 r600 (81.1%) 198 4.4 3.1 6 softpipe (70.9%) 173 3.3 N/A 7 llvmpipe (64.8%) 158 3.3 N/A 8 nv50 (62.3%) 152 3.3 N/A 9 freedreno (62.3%) 152 3.1 N/A 10 swr (57.8%) 141 3.3 N/A OpenGL support
- 13. 13 Development workflow https://bugs.freedesktop.org/descri becomponents.cgi?product=Mesa Bugzilla https://www.mesa3d.org/lists.html Mailing lists and IRC https://www.mesa3d.org/submitting patches.html Submitting patches
- 14. 14 Project statistics Patches: Pushed: 67 On review: 51 Rejected: 26 Bugs: Total: 156 - Debugged/analyzed: 86 - Fixed: 70
- 16. 16 Mesa environment variables Normally, no environment variables need to be set. Most of the environment variables used by Mesa are for debugging purposes, but they can sometimes be useful for debugging end-user issues. Example: export LIBGL_ALWAYS_SOFTWARE=1 (if set, always use software rendering)
- 17. 17 Mesa environment variables: Shader dump
- 18. 18 The basic debugging tool is console output • Use printf() or fprintf() to output any valuable information • It will output to the terminal where tested application is started
- 19. 19 Use static analyzers to find possible causes • Some bugs or issues can be caused by simple mistakes that can be found by automated tools. • Like smatch or cppcheck For example, smatch warning: [src/intel/vulkan/anv_nir_apply_pipeline_layout.c:457]: (error) Possible null pointer dereference: null_data And the library code itself: struct anv_push_constants *null_data = NULL; const struct brw_image_param *image_param = null_data->images;
- 20. 20 GDB Building mesa with GDB support # export CFLAGS='-O0 -ggdb3' # export CXXFLAGS='-O0 -ggdb3' # ./autogen.sh --with-gallium-drivers="" --with-dri-drivers=i965 # make -j4
- 21. 21 You able to debug Mesa even with comercial apps and games without debug symbols. Run the application in GDB: GDB
- 22. 22 Run the program with r and receive a backtrace with bt: GDB
- 23. 23 Apitrace is a tool to capture and replay OpenGL calls
- 24. 24 Frameretrace - view and analyze each render for any frame
- 25. 25 Renderdoc
- 26. 26 Piglit is a collection of automated tests for OpenGL implementations. • At this moment, there are around 60k tests total. There are performance (rendering time) test as well as compatibility tests. Test results can be used for regression testing. • Useful to check if patch has some side effects on other areas. • Piglit tests can be run either directly or as a profiles (test sets). Running quick profile will take around 20 minutes. Profiles like “all” will run for several hours. • The results will be in json format. But the html (good looking) summaries can also be created.
- 27. 27 Steam games specifics - using GDB • Usually steam games doesn’t contain any debug information. But we still can see useful backtraces and mesa calls. • You need to determine game’s PID. Not steam or some launcher/helper. Use ps -aux for example. • Then you may easily attach gdb to that process (gdb) attach 2057 (gdb) continue
- 28. 28 Steam games specifics - customizing environment You can configure steam GUI to launch the script with “preparations”: • Create the script and place it in the /home/${USER}/bin E.g steam_dbg.sh: #!/bin/bash export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/home/andriy/mesa/lib "$@" > /home/andriy/steam_game.log • Go to library, right click on a game and choose “Properties” • On General tab click “Set launch options” • Specify the run options: steam_dbg.sh %command%
- 29. 29 Useful Links • https://cgit.freedesktop.org/mesa/mesa/ • https://lists.freedesktop.org/mailman/listinfo/mesa-dev • https://lists.freedesktop.org/mailman/listinfo/piglit • https://bugs.freedesktop.org/describecomponents.cgi?product=Mesa • https://fosdem.org/2018/schedule/event/apitrace/ • https://github.com/janesma/apitrace/wiki/frameretrace-branch
- 30. 30 Thank you
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