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Debugging Xposed/LSPosed Modules

Tools and techniques for troubleshooting custom module development.

Logcat filtering

# Watch only your module's logs
adb logcat | grep -i "your_module_name"

# Watch LSPosed manager logs
adb logcat | grep "LSPosed"

# Watch specific class hooks
adb logcat | grep "ClassLoader"

Common issues & fixes

Module doesn't apply to target app

Symptoms: Hooks never fire, no logcat output

Solutions:

# 1. Verify scope is correct (LSPosed Manager → Modules → check target app is enabled)
# 2. Check that package name is exact:
adb shell pm list packages | grep -i facebook

# 3. Force-stop and restart the app
adb shell am force-stop com.facebook.katana
adb shell am start com.facebook.katana/com.facebook.activity.LauncherActivity

# 4. Reload Zygisk (if using):
adb shell killall -9 zygote

Module causes boot loop

Symptoms: Device reboots infinitely after installation

Recovery:

# Boot to TWRP recovery
adb reboot recovery

# Disable all modules:
# In TWRP: Magisk → Modules → swipe left to disable all

# OR via ADB (if Magisk is running):
adb shell magisk module disable <module_name>

# Check which module crashed:
adb logcat -c
adb logcat | head -100  # look for crash in first lines

Crashes in hook method

Example problem: Illegal argument to invoke-virtual

// ❌ WRONG — trying to invoke non-virtual on interface
public static void hookInterfaceMethod() {
    var MyInterface = Java.use("com.example.MyInterface");
    MyInterface.someMethod.implementation = function() { ... };
}

// ✅ RIGHT — hook the concrete implementation class
public static void hookConcreteClass() {
    var MyImpl = Java.use("com.example.MyInterfaceImpl");
    MyImpl.someMethod.implementation = function() { ... };
}

Scoped hook doesn't persist across app restarts

Symptoms: Module works but stops after user force-closes app

Fix: Add persistent scope in LSPosed:

# LSPosed Manager → Modules → [your module]
# Check: "Persistent scope" or ensure DenyList is OFF for that app

Advanced debugging

Use Logcat with timestamps

adb logcat -v threadtime "YourModule:D *:S"
# Output: 05-18 17:25:33.123 12345 12345 D YourModule: message

Monitor Frida hooks alongside Xposed

Run Frida + Xposed hooks together to cross-validate:

// frida_debug.js
Java.perform(function() {
    console.log("[Frida] Attached to app");
    // Set a breakpoint that shows what Xposed is seeing
    var MyClass = Java.use("com.example.MyClass");
    MyClass.myMethod.implementation = function() {
        console.log("[Frida] myMethod called with: " + this);
        return this.myMethod.call(this);
    };
});
frida -U -f com.facebook.katana -l frida_debug.js --no-pause

Check if LSPosed is detecting your module

adb shell ls /data/adb/modules/
# Your module should be listed here

adb shell cat /data/adb/modules/your_module/module.prop
# Should show: id=your_module, name=, etc.

Force reload modules

# Method 1: Soft reboot via Magisk
adb shell magisk --install-module /path/to/module.zip

# Method 2: Hard reboot (slowest)
adb reboot

# Method 3: Kill system processes
adb shell killall -9 system_server

Performance monitoring

Check if module is causing slowdowns

# Baseline: measure without module
adb shell am start -W com.facebook.katana
# Look at "ThisTime" value

# Disable module, remeasure
# LSPosed → your module → toggle OFF
adb shell am start -W com.facebook.katana
# Compare ThisTime values

Profile hook performance

// In your module:
var startTime = java.lang.System.currentTimeMillis();
var MyClass = Java.use("com.example.MyClass");
MyClass.expensiveMethod.implementation = function() {
    var callStart = java.lang.System.currentTimeMillis();
    var result = this.expensiveMethod.call(this);
    var callTime = java.lang.System.currentTimeMillis() - callStart;
    console.log("[Profile] expensiveMethod took " + callTime + "ms");
    return result;
};

Debugging checklist

  • Scope set correctly in LSPosed Manager
  • Target app is enabled in module settings
  • No typos in package/class names
  • Logcat shows module is loaded ("LSPosed: Module X loaded")
  • Test with simpler hook first (e.g., Log.d() only)
  • Check for ClassNotFoundException in logs
  • Verify method signature matches reality (dumpMethodsAndFields())
  • Try Frida for comparison if stuck