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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

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

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 path to Chromium source in there.
  • Inside of 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 Customize and Control Chromium (three dots) -> More Tools -> Task Manager
  • Depending on what tab or process you want to debug, note the process ID.
  • In the lldb shell:
    • Execute process attach -p PID. PID is the process ID of the tab (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 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, for example, breakpoint set -f inspector_overlay_agent.cc -l 627.
    • Execute cont to continue the execution of the process.
    • Perform the actions which would trigger the breakpoint. lldb will stop the execution for you to inspect.
    • You can pause the execution at any time by pressing Ctrl + C.
    • Type help to learn more about different lldb commands.
    • More open-source documentation could be found here.