user842225 user842225 - 11 days ago 10
Android Question

System.loadLibrary(...) couldn't find native library in my case

I want to use a existing native library from another Android project, so I just copied the NDK built library (libcalculate.so) to my new Android project. In my new Android project I created a folder

libs/armeabi/
and put libcalculate.so there. There is no jni/ folder. My testing device has ARM architecture.

In my java code I load the library by:

static{
System.loadLibrary("calculate");
}


When I run my new android project, I got error:

java.lang.UnsatisfiedLinkError: ...
nativeLibraryDirectories=[/vendor/lib, /system/lib]]] couldn't find "libcalculate.so"


So, as error says, the copied native library is not in /verdor/lib or /system/lib , how to resolve this problem in my case?

(I unziped the apk package, under lib/ there is libcalculate.so)

====UPDATE=====

I also tried to create a jni/ folder under project root, and add an Android.mk file under jni/. The content of Android.mk is:

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)
LOCAL_MODULE := libcalculate
LOCAL_SRC_FILES := libcalculate.so
include $(PREBUILT_SHARED_LIBRARY)


Then, under project root, I executed ndk-build . After that, the armeabi/ and armeabi-v7a/ directories are generated by ndk-build (with libcalculate.so inside the folder).

Then I run my maven build the project successfully. In the final apk package, there are:

lib/armeabi/libcalculate.so
lib/armeabi-v7a/libcalculate.so


But when I run my app, the same error throw:

java.lang.UnsatisfiedLinkError: ...
nativeLibraryDirectories=[/vendor/lib, /system/lib]]] couldn't find "libcalculate.so"

Answer

To root cause (and maybe solve your issue in the same time), here is what you can do:

  1. Remove the jni folder and all the .mk files. You don't need these nor the NDK if you aren't compiling anything.

  2. Copy your libcalculate.so file inside <project>/libs/(armeabi|armeabi-v7a|x86|...) . When using Android Studio, it's jniLibs instead of libs, but I see you're using eclipse.

  3. Build your APK and open it as a zip file, to check that your libcalculate.so file is inside lib/(armeabi|armeabi-v7a|x86|...).

  4. Remove and install your application

  5. Run dumpsys package packages | grep yourpackagename to get the nativeLibraryPath or legacyNativeLibraryDir of your application.

  6. Run ls on the nativeLibraryPath you had or on legacyNativeLibraryDir/armeabi, to check if your libcalculate.so is indeed there.

  7. If it's there, check if it hasn't been altered from your original libcalculate.so file: is it compiled against the right architecture, does it contain the expected symbols, are there any missing dependencies. You can analyze libcalculate.so using readelf.

In order to check step 5-7, you can use my application instead of command lines and readelf: Native Libs Monitor

PS: It's easy to get confused on where .so files should be put or generated by default, here is a summary:

  • libs/CPU_ABI inside an eclipse project

  • jniLibs/CPU_ABI inside an Android Studio project

  • jni/CPU_ABI inside an AAR

  • lib/CPU_ABI inside the final APK

  • inside the app's nativeLibraryPath on a <5.0 device, and inside the app's legacyNativeLibraryDir/CPU_ARCH on a >=5.0 device.

Where CPU_ABI is any of: armeabi, armeabi-v7a, arm64-v8a, x86, x86_64, mips, mips64. Depending on which architectures you're targeting and your libs have been compiled for.

Note also that libs aren't mixed between CPU_ABI directories: you need the full set of what you're using, a lib that is inside the armeabi folder will not be installed on a armeabi-v7a device if there are any libs inside the armeabi-v7a folder from the APK.

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