Android-RRO

Sample app and runtime resource overlay for android 31

Use case

Install standard app (without elevated system permissions) and change it's resources using separate RRO APK (with elevated root permission). Install and activate RRO in Android OS runtime, without messing with build time static RROs. There is no need to change anything in Android OS, you can do it with standard system image (without Google play) on emulator

How to

Prepare emulator

Create an AVD virtual device with Android 31 target image. Choose a version without Google Play, otherwise you will not be able to grant root permissions
Run emulator from command line: emulator -avd {EMU_NAME} -writable-system, for example emulator -avd Pixel_5_API_31 -writable-system

Install Target App

Build an app from MyTarget directory
Install it on your device, the same way you always do

Build overlay

Open MyOverlay directory
Let's build an overlay APK

aapt2 compile -v --dir res/ -o Overlay.flata

aapt2 link -v --no-resource-removal \
-I ~/AppData/Local/Android/Sdk/platforms/android-31/android.jar \
--manifest AndroidManifest.xml \
-o myoverlays.apk.u Overlay.flata

We have unaligned apk file myoverlays.apk.u, let's align it using

zipalign 4 myoverlays.apk.u myoverlays.apk

Finally, we need to sign our APK, I use standard debug certificate

printf 'android' | jarsigner -keystore ~/.android/debug.keystore  myoverlays.apk androiddebugkey

Install overlay

Overlays are placed in system directories, and we need root permission to di it
We will be placing our overlay to /product/overlay folder
Prepare target file system, run

adb root
adb remount
adb shell remount

Copy overlay using

adb push myoverlays.apk product/overlay

Note: use buildOverlay.sh script to automate steps from Build and install overlay section

Enable overlay

After overlay install/reinstall you need to reboot your device

adb reboot

Verify your overlay is installed, you should see mappings defined by overlay and it's status. Run

adb root
adb shell cmd overlay dump com.example.myoverlay

Overlay is not enabled by default, enable it using

adb shell cmd overlay enable --user current com.example.myoverlay

You should see changes in your application

Note: use setupOverlay.sh script to automate steps from enable overlay section

MartinStyk/Android-RRO

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