Execution — bi-12-debugging-tracing

Steps extracted from CONCEPTS.md. Read the concepts first; this file is the doing.

Record results in observation.md; tick checkpoints in verification.md.

3. Practice

Concrete procedures live in bi-00-roadmap/docs/chromium-build-debug-trace.md §4–§5: lldb setup and the in-tree pretty-printers, attaching to a paused renderer, conditional breakpoints, thread backtrace all, and the tracing categories worth recording.

Do thread backtrace all once, early. It converts bi-02's thread diagram from a claim into something you have seen.

6. Lab

  1. Thread census. Attach to a renderer, thread backtrace all, and write down every thread name. Map each to bi-02's diagram. Note any you did not expect.
  2. Pipeline breakpoints. Set breakpoints at DOM creation, style recalc, layout, and paint. Load a trivial page. Record the order and the call stacks connecting them. This is the rendering pipeline, observed rather than read.
  3. Conditional breakpoint. Break in setAttribute only when the attribute is class.
  4. Trace-to-source. Record a trace, pick three unfamiliar event names, and find each in the source. Write down what each one measures.
  5. Source-to-trace. Add your own TRACE_EVENT to a Blink function you studied in bi-03 or bi-07. Rebuild that target only. Confirm it appears.
  6. Break an invariant. Deliberately violate a DCHECK (for example by removing a guard), rebuild, and observe the assertion fire. Restore.

Deliverable: the thread census, the pipeline call-stack chain from (2), and the diff from (5).

7. Failure Lab

  1. Build with symbol_level = 0 and try to debug. Experience it once; it explains the flag.
  2. Set a Blink breakpoint on the browser process and observe it never hit. Diagnose from first principles.
  3. Break in a function that gets inlined. Find the workaround.
  4. Attach to a renderer without --disable-hang-monitor and wait 30 seconds. Explain the kill.