ios-ettrace-performance

iOS ETTrace Performance

Use this skill to capture a focused, symbolicated ETTrace profile from an iOS simulator app. Pair it with ../ios-debugger-agent/SKILL.md when the task also needs simulator build, install, launch, UI driving, logs, or screenshots.

Core Workflow

1. Pick one focused flow and write down the expected start and stop points.
2. Build the exact simulator app that will be installed and profiled.
3. Temporarily link ETTrace into that app target for simulator/debug profiling.
4. Collect UUID-matched dSYMs for the app executable and embedded dynamic frameworks.
5. Capture one launch or runtime trace.
6. Preserve the processed flamegraph JSON immediately after the run.
7. Analyze only the processed JSON and report the flow, artifacts, hotspots, and caveats.

Avoid broad "use the app for a while" captures. One trace should correspond to one user-visible flow.

Setup

Use a writable run folder for each profiling session:

if [ -z "${RUN_DIR:-}" ]; then
  RUN_DIR="$(mktemp -d "${TMPDIR:-/tmp}/codex-ios-ettrace.XXXXXX")"
fi
mkdir -p "$RUN_DIR"

Install the ETTrace runner CLI if it is not already available:

brew install emergetools/homebrew-tap/ettrace

ettrace is the host-side macOS runner. The app must also link an ETTrace.xcframework for the iOS Simulator architecture. This workflow is validated for ETTrace v1.1.0 processed output_<thread>.json files with top-level nodes.

Link ETTrace Into The App

Wire ETTrace into the exact app target being profiled. Keep the integration in a clearly temporary patch and remove it when the profiling task is done unless the user explicitly asks to keep it.

Preferred options:

• Reuse an existing simulator-compatible ETTrace.xcframework if the repo already vendors one.
• If none exists, build a simulator-only copy into RUN_DIR from the upstream ETTrace package.
• Link the framework directly into the app target, not only into tests, resources, data files, or a nested launcher target.
• Confirm launch logs print Starting ETTrace.
• Profile only one ETTrace-instrumented simulator app at a time because simulator mode listens on a fixed localhost port.