Riru is a very simple but useful thing. Only requires to replace one system file, it will provide the ability to Riru modules to run their code in apps' or system server's process.

The name Riru is from https://www.pixiv.net/member_illust.php?mode=medium&illust_id=56169989

中文说明

• Rooted Android 6.0+ devices
• Magisk (use to replace system files, temporarily only provide Magisk zip)

In short, replace a shared library which will be loaded by the zygote process.

First, we need to find that library. The library needs to be as simple as possible, so we found libmemtrack, with only 10 exported functions. Then we can provide a library named libmemtrack with all its functions, so the functionality will not be affected and we will able to in the zygote process. (However, it seems that choose libmemtrack is not so appropriate now)

Now the next question, how to know if we are in an app process or a system server process. We found some JNI functions (com.android.internal.os.Zygote#nativeForkAndSpecialize & com.android.internal.os.Zygote#nativeForkSystemServer) will be called when a app or system server is forked. So we just need to replace these functions to ours. This part is simple, just hook jniRegisterNativeMethods since all Java native method in libandroid_runtime is registered with this function. Then we can call RegisterNatives again to replace them.

There is only one libmemtrack.so, if someone wants to do something by replacing it, others can't. So I made Riru occupy libmemtrack but provide the ability to make modules.

Android NDK (add the directory with ndk-build to PATH)

• Magisk Module

  Run :riru-core:assembleMagiskRelease task in the command line (use gradlew) or Android Studio, zip will be saved to release

1. Copy riru-module-template and rename to your name
2. Change module name in riru-your-module/jni/main/Android.mk
3. Change module information in build.gradle
4. Write your code
5. Run :riru-your-module:assembleMagiskRelease task in command line (use gradlew) or Android Studio, zip will be saved to release

From v8, core starts to providing some APIs, see riru.h.

• DO NOT overwrite android.os.SystemProperties#native_set in core, or your data may be wiped (Detail info) (If you really need to hook this, remember to clear exception)
• DO NO print log (__android_log_print) in nativeForkAndSpecialize(Pre/Post) nativeForkSystemServer(Pre/Post) when in zygote process, or it may cause zygote not work (magic not confirmed, Detail info)
• Add -ffixed-x18 to both compiler and linker parameter, or it will cause problems on Android Q (see template)

• Currently, one module version can only support one API version
• See template for details

• Add api=3 to riru_module.prop to declare API version
• Check and deny installation if Riru version is below v18 in config.sh
• Parameter of nativeForkAndSpecializePre changes (compare to v2, added jstring *packageName, jobjectArray *packagesForUID, jobjectArray *visibleVolIDs in the end)

• Export int getApiVersion() { return 2; } to declare API version
• Parameter of nativeForkAndSpecializePre changes (compare to v1, all parameter is pointer)

Current only support Magisk.

1. Install core zip in Magisk
2. Install module zip in Magisk

Riru-LocationReportEnabler (also a good example)