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debug-lldb

@regenrek/agent-skills
2
0

Capture and analyze thread backtraces with LLDB/GDB to debug hangs, deadlocks, UI freezes, IPC stalls, or high-CPU loops across any language or project. Use when an app becomes unresponsive, switching contexts stalls, or you need thread stacks to locate lock inversion or blocking calls.

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SKILL.md

name debug-lldb
description Capture and analyze thread backtraces with LLDB/GDB to debug hangs, deadlocks, UI freezes, IPC stalls, or high-CPU loops across any language or project. Use when an app becomes unresponsive, switching contexts stalls, or you need thread stacks to locate lock inversion or blocking calls.

Debug Lldb

Overview

Capture stack traces from a live process to explain stalls and freezes, then triage for deadlocks, blocking IPC, or tight loops. Prefer repeat sampling so the hang signature is obvious.

Workflow

1) Identify the process

  • Use ps/pgrep to get the PID.
  • Prefer the foreground app PID (not the dev server).

2) Capture backtraces (fast path)

  • Use the bundled script:
    • scripts/collect_stacks.sh --pid <pid> --out /tmp/hang --repeat 3 --sleep 0.5
    • Or by name: scripts/collect_stacks.sh --name "<process-substring>" --out /tmp/hang
  • Run in a separate terminal if the current one is interactive with the hung app.

3) Capture backtraces (manual)

  • macOS (LLDB):
    • lldb -p <pid> -o 'thread backtrace all' -o 'detach' -o 'quit' > /tmp/hang.txt 2>&1
  • Linux (GDB):
    • gdb -q -p <pid> -ex "thread apply all bt" -ex "detach" -ex "quit" > /tmp/hang.txt 2>&1
  • Windows:
    • Use WinDbg or cdb to capture all-thread backtraces.

4) Triage the hang

  • Compare 3–5 samples taken 0.2–1s apart.
  • Use references/triage.md for quick pattern matching (deadlock vs busy loop vs blocking I/O).

5) Attach context

  • Include what action triggered the stall and the exact time window.
  • Add relevant app logs around the stall.

Resources

scripts/

  • scripts/collect_stacks.sh - attach to a PID or process name and capture N stack dumps.

references/

  • references/triage.md - quick patterns for deadlocks, blocking IPC, and busy loops.