Axiom Xctrace Ref

xctrace CLI Reference

Command-line interface for Instruments profiling. Enables headless performance analysis without GUI.

Overview

xctrace is the CLI tool behind Instruments.app. Use it for:

• Automated profiling in CI/CD pipelines
• Headless trace collection without GUI
• Programmatic trace analysis via XML export
• Performance regression detection

Requires: Xcode 12+ (xctrace 12.0+). This reference tested with Xcode 26.2.

Quick Reference

# Record a 10-second CPU profile
xcrun xctrace record --instrument 'CPU Profiler' --attach 'MyApp' --time-limit 10s --output profile.trace

# Export to XML for analysis
xcrun xctrace export --input profile.trace --toc  # See available tables
xcrun xctrace export --input profile.trace --xpath '/trace-toc/run[@number="1"]/data/table[@schema="cpu-profile"]'

# List available instruments
xcrun xctrace list instruments

# List available templates
xcrun xctrace list templates

Recording Traces

Basic Recording

# Using an instrument (recommended for CLI automation)
xcrun xctrace record --instrument 'CPU Profiler' --attach 'AppName' --time-limit 10s --output trace.trace

# Using a template (may fail on export in Xcode 26+)
xcrun xctrace record --template 'Time Profiler' --attach 'AppName' --time-limit 10s --output trace.trace

Note: In Xcode 26+, use --instrument instead of --template for reliable export. Templates may produce traces with "Document Missing Template Error" on export.

Target Selection

# Attach to running process by name
xcrun xctrace record --instrument 'CPU Profiler' --attach 'MyApp' --time-limit 10s

# Attach to running process by PID
xcrun xctrace record --instrument 'CPU Profiler' --attach 12345 --time-limit 10s

# Profile all processes
xcrun xctrace record --instrument 'CPU Profiler' --all-processes --time-limit 10s

# Launch and profile
xcrun xctrace record --instrument 'CPU Profiler' --launch -- /path/to/app arg1 arg2

# Target specific device (simulator or physical)
xcrun xctrace record --instrument 'CPU Profiler' --device 'iPhone 17 Pro' --attach 'MyApp' --time-limit 10s
xcrun xctrace record --instrument 'CPU Profiler' --device 947DF45C-4ACB-4B3E-A043-DF2CD59A59B3 --all-processes --time-limit 10s

Recording Options

Core Instruments

CPU Profiler

CPU sampling for finding hot functions.

xcrun xctrace record --instrument 'CPU Profiler' --attach 'MyApp' --time-limit 10s --output cpu.trace

Schema: cpu-profile Columns: time, thread, process, core, thread-state, weight (cycles), stack

Allocations

Memory allocation tracking.

xcrun xctrace record --instrument 'Allocations' --attach 'MyApp' --time-limit 30s --output alloc.trace

Schema: allocations Use for: Finding memory growth, object counts, allocation patterns

Leaks

Memory leak detection.

xcrun xctrace record --instrument 'Leaks' --attach 'MyApp' --time-limit 30s --output leaks.trace

Schema: leaks Use for: Detecting unreleased memory, retain cycles

SwiftUI

SwiftUI view body analysis.

xcrun xctrace record --instrument 'SwiftUI' --attach 'MyApp' --time-limit 10s --output swiftui.trace

Schema: swiftui Use for: Finding excessive view updates, body re-evaluations

Swift Concurrency

Actor and Task analysis.

xcrun xctrace record --instrument 'Swift Tasks' --instrument 'Swift Actors' --attach 'MyApp' --time-limit 10s --output concurrency.trace

Schemas: swift-task, swift-actor Use for: Task scheduling, actor isolation, async performance

All Available Instruments

Activity Monitor          Audio Client              Audio Server
Audio Statistics          CPU Counters              CPU Profiler
Core Animation Activity   Core Animation Commits    Core Animation FPS
Core Animation Server     Core ML                   Data Faults
Data Fetches              Data Saves                Disk I/O Latency
Disk Usage                Display                   Filesystem Activity
Filesystem Suggestions    Foundation Models         Frame Lifetimes
GCD Performance           GPU                       HTTP Traffic
Hangs                     Hitches                   Leaks
Location Energy Model     Metal Application         Metal GPU Counters
Metal Performance Overview Metal Resource Events    Network Connections
Neural Engine             Points of Interest        Power Profiler
Processor Trace           RealityKit Frames         RealityKit Metrics
Runloops                  Sampler                   SceneKit Application
Swift Actors              Swift Tasks               SwiftUI
System Call Trace         System Load               Thread States
Time Profiler             VM Tracker                Virtual Memory Trace

Exporting Traces

Table of Contents

# See all available data tables in a trace
xcrun xctrace export --input trace.trace --toc

Output structure:

<trace-toc>
    <run number="1">
        <info>
            <target>...</target>
            <summary>...</summary>
        </info>
        <processes>...</processes>
        <data>
            <table schema="cpu-profile" .../>
            <table schema="thread-info"/>
            <table schema="process-info"/>
        </data>
    </run>
</trace-toc>

XPath Export

# Export specific table by schema
xcrun xctrace export --input trace.trace --xpath '/trace-toc/run[@number="1"]/data/table[@schema="cpu-profile"]'

# Export process info
xcrun xctrace export --input trace.trace --xpath '/trace-toc/run[@number="1"]/data/table[@schema="process-info"]'

# Export thread info
xcrun xctrace export --input trace.trace --xpath '/trace-toc/run[@number="1"]/data/table[@schema="thread-info"]'

CPU Profile Schema

<schema name="cpu-profile">
    <col><mnemonic>time</mnemonic><name>Sample Time</name></col>
    <col><mnemonic>thread</mnemonic><name>Thread</name></col>
    <col><mnemonic>process</mnemonic><name>Process</name></col>
    <col><mnemonic>core</mnemonic><name>Core</name></col>
    <col><mnemonic>thread-state</mnemonic><name>State</name></col>
    <col><mnemonic>weight</mnemonic><name>Cycles</name></col>
    <col><mnemonic>stack</mnemonic><name>Backtrace</name></col>
</schema>

Each row contains:

• sample-time: Timestamp in nanoseconds
• thread: Thread ID and name
• process: Process name and PID
• core: CPU core number
• thread-state: Running, Blocked, etc.
• cycle-weight: CPU cycles
• backtrace: Call stack with function names

Process Discovery

Find Running Simulator Apps

# List apps in booted simulator
xcrun simctl spawn booted launchctl list | grep UIKitApplication

# Output format: PID  Status  com.apple.UIKitApplication:com.bundle.id[xxxx][rb-legacy]

Find Device UUID

# List booted simulators (JSON)
xcrun simctl list devices booted -j

# List all devices
xcrun simctl list devices

Find Process by Name

# Get PID of running app
pgrep -f "MyApp"

# List all processes with app name
ps aux | grep MyApp

Automation Patterns

CI/CD Integration

#!/bin/bash
# performance-test.sh

APP_NAME="MyApp"
TRACE_DIR="./traces"
TIME_LIMIT="30s"

# Boot simulator if needed
xcrun simctl boot "iPhone 17 Pro" 2>/dev/null || true

# Wait for app to launch
sleep 5

# Record CPU profile
xcrun xctrace record \
    --instrument 'CPU Profiler' \
    --device "iPhone 17 Pro" \
    --attach "$APP_NAME" \
    --time-limit "$TIME_LIMIT" \
    --no-prompt \
    --output "$TRACE_DIR/cpu.trace"

# Export for analysis
xcrun xctrace export \
    --input "$TRACE_DIR/cpu.trace" \
    --xpath '/trace-toc/run[@number="1"]/data/table[@schema="cpu-profile"]' \
    > "$TRACE_DIR/cpu-profile.xml"

# Parse and check thresholds
# (Use xmllint, python, or custom tool to parse XML)

Before/After Comparison

# Record baseline
xcrun xctrace record --instrument 'CPU Profiler' --attach 'MyApp' --time-limit 10s --output baseline.trace

# Make changes, rebuild app

# Record after changes
xcrun xctrace record --instrument 'CPU Profiler' --attach 'MyApp' --time-limit 10s --output after.trace

# Export both for comparison
xcrun xctrace export --input baseline.trace --xpath '...' > baseline.xml
xcrun xctrace export --input after.trace --xpath '...' > after.xml

Troubleshooting

"Document Missing Template Error" on Export

Cause: Recording used --template flag in Xcode 26+ Fix: Use --instrument instead:

# Instead of
xcrun xctrace record --template 'Time Profiler' ...

# Use
xcrun xctrace record --instrument 'CPU Profiler' ...

"Unable to attach to process"

Causes:

1. Process not running
2. Insufficient permissions
3. System Integrity Protection blocking

Fix:

# Verify process exists
pgrep -f "AppName"

# For simulator apps, verify simulator is booted
xcrun simctl list devices booted

# Try with --all-processes instead of --attach
xcrun xctrace record --instrument 'CPU Profiler' --all-processes --time-limit 5s

Empty Trace Export

Cause: Recording too short or no activity during recording Fix: Increase --time-limit or ensure app is actively used during recording

Symbolication Issues

Raw addresses in backtraces (e.g., 0x18f17ed94) instead of function names.

Fix: Ensure dSYMs are available:

# Symbolicate trace (if needed)
xcrun xctrace symbolicate --input trace.trace --dsym /path/to/App.dSYM

Post-Processing with filtercalltree

filtercalltree transforms call tree output for targeted analysis. It takes text files in the format produced by sample.

# 1. Capture a call tree with sample (writes to /tmp/*.sample.txt)
xcrun sample MyApp 5

# 2. Invert the call tree (show hottest leaf frames first)
xcrun filtercalltree -i /tmp/MyApp_*.sample.txt

# 3. Charge library costs to callers (attribute UIKitCore time to your code)
xcrun filtercalltree -chargeLibrary=UIKitCore /tmp/MyApp_*.sample.txt

# 4. Combine: invert + charge system libraries + prune noise
xcrun filtercalltree -i -chargeSystemLibraries -pruneCount 5 /tmp/MyApp_*.sample.txt

Companion CLI Tools

These tools complement xctrace for specific profiling needs:

# Quick CPU sample without full trace (5-second sample)
xcrun sample MyApp 5

# Sample by PID, save to file
xcrun sample 12345 5 -file output.txt

sample is lighter than xctrace — use for quick CPU checks when you don't need the full Instruments pipeline.

Limitations

1. Privacy restrictions: Some instruments require privacy permissions granted in System Preferences
2. Device support: Physical device profiling requires Developer Mode enabled
3. Background apps: Limited profiling of backgrounded apps
4. Export format: XML only (no JSON export)
5. Template vs Instrument: In Xcode 26+, templates may not export properly

Resources

Skills: axiom-performance-profiling, axiom-memory-debugging, axiom-swiftui-performance

Docs: /xcode/instruments, /os/logging/recording-performance-data

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