docs/lldbinit.md

# Usage of tools/lldb/lldbinit.py

Usage of Chromium's [lldbinit.py](../tools/lldb/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.

If you want visualizer support for common pointer, string, and vector types in the Chromium codebase, you can also 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 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](https://wiki.ubuntu.com/SecurityTeam/Roadmap/KernelHardening#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](https://developer.apple.com/library/archive/documentation/IDEs/Conceptual/gdb_to_lldb_transition_guide/document/lldb-basics.html#//apple_ref/doc/uid/TP40012917-CH2-SW1).