Android : UnsatisfiedLinkError

在android 上使用 .so作为apk的第三方库的时候，会发生java.lang.UnsatisfiedLinkError:

09-27 12:17:01.280 D/ListenSoundModel( 3635): Load libxxxjni 
09-27 12:17:01.292 D/AndroidRuntime( 3635): Shutting down VM 
——— beginning of crash 
09-27 12:17:01.293 E/AndroidRuntime( 3635): FATAL EXCEPTION: main 
09-27 12:17:01.293 E/AndroidRuntime( 3635): Process: com.xxx.xxx, PID: 3635 
09-27 12:17:01.293 E/AndroidRuntime( 3635): java.lang.UnsatisfiedLinkError: dalvik.system.PathClassLoader[DexPathList[[zip file “/data/app/xxxApp.apk”],nativeLibraryDirectories=[/data/app-lib/xxxApp, /system/lib64, /vendor/lib64]]] couldn’t find “libxxxjni.so” 
09-27 12:17:01.293 E/AndroidRuntime( 3635): at java.lang.Runtime.loadLibrary0(Runtime.java:972) 
09-27 12:17:01.293 E/AndroidRuntime( 3635): at java.lang.System.loadLibrary(System.java:1530) 
… 
09-27 12:17:01.293 E/AndroidRuntime( 3635): at android.os.Handler.dispatchMessage(Handler.java:102) 
09-27 12:17:01.293 E/AndroidRuntime( 3635): at android.os.Looper.loop(Looper.java:154)

google的变更说明有介绍https://developer.android.com/preview/behavior-changes.html#ndk
变更出现的这个 UnsatisfiedLinkError 原因是访问设置为公用库的so库
......
可以看看原生的这笔提交修改的。
android-review.googlesource.com/#/c/209029/

Android N上对so库加载的搜索路径方式为ld_library_path, runtime path, permit path，不在这个搜索路径下则加载失败。

从代码层面看，主要是类加载器ClassLoader的相关处理，

code1: (loadedApk.java getClassLoader()) check sdk version

// DO NOT SHIP: this is a workaround for apps loading native libraries 
// provided by 3rd party apps using absolute path instead of corresponding 
// classloader; see http://b/26954419 for example. 
if (mApplicationInfo.targetSdkVersion <= 23) { 
libraryPermittedPath += File.pathSeparator + “/data/app”; 
}

Code2: (loadedApk.java getClassLoader()) N add a new PermittedPath

String libraryPermittedPath = mDataDir;

Code3: (native_loader.cpp) use the new namespace rule with search path:

ld_library_path, runtime path, permit path.

解决方法

解决方法

public.libraries.txt Flow

1、system/core/libnativeloader/native_loader.cpp

在LibraryNamespaces类的Initialize()会读取这个文件，将so库设置为公共so库。

static constexpr const char* kPublicNativeLibrariesSystemConfigPathFromRoot = "/etc/public.libraries.txt";
static constexpr const char* kPublicNativeLibrariesVendorConfig = "/vendor/etc/public.libraries.txt";
  void Initialize() {
    ..................
    std::vector<std::string> sonames;
    ReadConfig(public_native_libraries_system_config, &sonames, &error_msg),
    ReadConfig(kPublicNativeLibrariesVendorConfig, &sonames);
    public_libraries_ = base::Join(sonames, ':');
    .............
  }

2、在创建一个虚拟机的时候，初始化NativeLoader

art/runtime/java_vm_ext.cc

extern "C" jint JNI_CreateJavaVM(JavaVM** p_vm, JNIEnv** p_env, void* vm_args) {
  ................
  // Initialize native loader. This step makes sure we have
  // everything set up before we start using JNI.
  android::InitializeNativeLoader();
  ..............
}

3、然后进入native_loader，进行初始化

system/core/libnativeloader/native_loader.cpp

 static LibraryNamespaces* g_namespaces = new LibraryNamespaces;
void InitializeNativeLoader() {
   g_namespaces->Initialize();
 }

4、Initialize调用LibraryNamespaces类的Initialize完成公共so库

void Initialize() {
    ..................
    std::vector<std::string> sonames;
    ReadConfig(public_native_libraries_system_config, &sonames, &error_msg),
    ReadConfig(kPublicNativeLibrariesVendorConfig, &sonames);
    public_libraries_ = base::Join(sonames, ':');
    .............
  }

总结：

1.Android N 不能直接调用系统的一些私有库了，公用的库都定义在public.libraries.txt里面。
2.系统应用刚刷机是能够调用system/lib or lib64下的库，但通过install升级该应用时，应用打开会挂。因为升级后permitted_paths就不再包含system/lib or lib64了，所以我们可以将apk要用到的库名称写到public.libraries.txt中去解决快速调试问题。

参考 https://www.cnblogs.com/zl1991/p/9409462.html