Usage of tools/lldb/lldbinit.py

Usage of Chromium's lldbinit.py is recommended when debugging with lldb. This is necessary for source-level debugging when strip_absolute_paths_from_debug_symbols is enabled [this is the default].

If you have not installed LLDB yet, run sudo apt-get install lldb to get it.

To use, add the following to your ~/.lldbinit:

# So that lldbinit.py takes precedence.
script sys.path[:0] = ['/<your-path>/chromium/src/tools/lldb']
script import lldbinit

Replace <your-path> above with the absolute path containing your Chromium repo.

Make sure the build configuration includes is_debug=true; this will set symbol_level=2 by default, which is required to view the content of frame-level local variables.

For visualizer support for common pointer, string, and vector types in Chromium, add the following:

script import chromium_visualizers

How to attach to a process with lldb and start debugging

• Follow the instructions above to create your ~/.lldbinit file; don't forget to put the correct absolute path to Chromium source in there.
• In your Chromium checkout, run lldb out/Default/chrome (or out/Debug/chrome)
  • On Mac, most likely, lldb out/Default/Chromium.app/Contents/MacOS/Chromium
• Keep lldb running and start Chromium separately with --no-sandbox flag:
  • On Linux, out/Default/chrome --no-sandbox
  • On Mac, out/Default/Chromium.app/Contents/MacOS/Chromium --no-sandbox
  • Note: if you start the process from lldb using process launch -- --no-sandbox, you will attach to the main browser process and will not be able to debug tab processes.
• In Chromium, go to the three-dot menu -> More Tools -> Task Manager
• Note the process ID for the tab or process you want to debug.
• In the lldb shell:
  • Execute process attach -p PID. PID is the process ID of the process you want to debug.
    • Note: it might take a while. Once lldb attaches to the process, you will see a message Process PID stopped and some stack traces.
    • If you see an error message such as attach failed: Operation not permitted, it is probably due to ptrace Protection. You can disable this feature using echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope.
  • Now you can set breakpoints, e.g., breakpoint set -f inspector_overlay_agent.cc -l 627.
  • Execute cont to continue the execution of the process.
  • Perform the actions that will trigger the breakpoint. lldb will stop the execution for you to inspect.
  • You can pause execution at any time by pressing Ctrl-C.
  • Type help to learn more about different lldb commands.
  • More open-source documentation can be found here.