尝试加载预编译的 .so Android NDK（异常 java.lang.UnsatisfiedLinkError: dlopen failed: library）

Question

I try to build an Android Project (ndk-build).

I´d like to use a precompiled library in my project. (libdemo.so)

Android.mk:

APP_STL := gnustl_static
APP_CPPFLAGS := -fexceptions
APP_ABI=armeabi armeabi-v7a

Application.mk:

LOCAL_PATH := $(call my-dir)
TARGET_ARCH_ABI := armeabi-v7a

include $(CLEAR_VARS)
LOCAL_MODULE := libdemo
LOCAL_SRC_FILES := $(TARGET_ARCH_ABI)/libdemo.so
LOCAL_EXPORT_C_INCLUDES := $(LOCAL_PATH)/include
include $(PREBUILT_SHARED_LIBRARY)

include $(CLEAR_VARS)
LOCAL_MODULE    := native-lib
LOCAL_SRC_FILES := native-lib.cpp
LOCAL_SHARED_LIBRARIES := libdemo
include $(BUILD_SHARED_LIBRARY)

MainActivity:

android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    // Used to load the 'native-lib' library on application startup.
     static {
        System.loadLibrary("demo");
        System.loadLibrary("native-lib");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TextView tv = (TextView) findViewById(R.id.sample_text);
        Log.d("TAG", stringFromJNI());
    }

    /**
     * A native method that is implemented by the 'native-lib' native library,
     * which is packaged with this application.
     */
    public native String stringFromJNI();
}

But I get the following exception on build:

java.lang.UnsatisfiedLinkError: dlopen failed: library "/Users/John/Documents/Apps/LibTest/app/build/intermediates/ndkBuild/debug/obj/local/armeabi-v7a/libdemo.so" not found

The file exists on the provided path. I think the path at all isn´t correct. Why is there the path from my desktop pc? There should be a path from my device or?

Anyone here to help? Thanks

Answer 1

I solved the question by myself.

I don´t knew that ndk-build isn´t processed automatically. I had go to my project folder (folder where jni is present) and does ndk-build manually.

After that the libs are compiled and copied automatically in the /libs folder.

Now just build and run the app as usual and everything is fine.

Answer 2

In my case this was caused by missing SONAME tag on the generated shared library. When this tag is missing, the Android build process will use the absolute path to the library instead of the device-specific path.

One has to explicitly specify the SONAME either via -soname or -install_name (macOS-specific) parameter to the linker.

For instance, this can happen when building shared libs from Go source, as mentioned in https://github.com/golang/go/issues/17807\\#issuecomment-259930881 .