Android下加载libUnreal.so文件

Android 下动态加载so库

具体有两种方式：

（1）调用 load(String filename) 方法

System.load("/data/data/com.example.mygame/files/libUnreal.so"); // 传递进去的是全路径

（2）调用 loadLibrary(String libname) 方法

System.loadLibrary("Unreal"); // 传递进去的是so文件的名称

具体的Android系统代码如下：

// https://android.googlesource.com/platform/libcore/+/15d8280/luni/src/main/java/java/lang/System.java
public final class System {// 。。。 。。。/*** Loads and links the dynamic library that is identified through the* specified path. This method is similar to {@link #loadLibrary(String)},* but it accepts a full path specification whereas {@code loadLibrary} just* accepts the name of the library to load.** @param pathName*            the path of the file to be loaded.*/public static void load(String pathName) {Runtime.getRuntime().load(pathName, VMStack.getCallingClassLoader());}/*** Loads and links the library with the specified name. The mapping of the* specified library name to the full path for loading the library is* implementation-dependent.** @param libName*            the name of the library to load.* @throws UnsatisfiedLinkError*             if the library could not be loaded.*/public static void loadLibrary(String libName) {Runtime.getRuntime().loadLibrary(libName, VMStack.getCallingClassLoader());}// 。。。 。。。
}// https://android.googlesource.com/platform/libcore/+/15d8280/luni/src/main/java/java/lang/Runtime.java
public class Runtime {// 。。。 。。。/*** Loads and links the dynamic library that is identified through the* specified path. This method is similar to {@link #loadLibrary(String)},* but it accepts a full path specification whereas {@code loadLibrary} just* accepts the name of the library to load.** @param pathName*            the absolute (platform dependent) path to the library to load.* @throws UnsatisfiedLinkError*             if the library can not be loaded.*/public void load(String pathName) {load(pathName, VMStack.getCallingClassLoader());}/** Loads and links the given library without security checks.*/void load(String pathName, ClassLoader loader) {if (pathName == null) {throw new NullPointerException("pathName == null");}String error = doLoad(pathName, loader);if (error != null) {throw new UnsatisfiedLinkError(error);}}/*** Loads and links the library with the specified name. The mapping of the* specified library name to the full path for loading the library is* implementation-dependent.** @param libName*            the name of the library to load.* @throws UnsatisfiedLinkError*             if the library can not be loaded.*/public void loadLibrary(String libName) {loadLibrary(libName, VMStack.getCallingClassLoader());}/** Searches for a library, then loads and links it without security checks.*/void loadLibrary(String libraryName, ClassLoader loader) {if (loader != null) {String filename = loader.findLibrary(libraryName);if (filename == null) {throw new UnsatisfiedLinkError("Couldn't load " + libraryName +" from loader " + loader +": findLibrary returned null");}String error = doLoad(filename, loader);if (error != null) {throw new UnsatisfiedLinkError(error);}return;}String filename = System.mapLibraryName(libraryName); // 实现是在System.c里面，返回so的文件名。例如System.mapLibraryName('Unreal') 返回的是libUnreal.soList<String> candidates = new ArrayList<String>();String lastError = null;for (String directory : mLibPaths) {String candidate = directory + filename;candidates.add(candidate);if (IoUtils.canOpenReadOnly(candidate)) {String error = doLoad(candidate, loader);if (error == null) {return; // We successfully loaded the library. Job done.
                }lastError = error;}}if (lastError != null) {throw new UnsatisfiedLinkError(lastError);}throw new UnsatisfiedLinkError("Library " + libraryName + " not found; tried " + candidates);}// 。。。 。。。private String doLoad(String name, ClassLoader loader) {// Android apps are forked from the zygote, so they can't have a custom LD_LIBRARY_PATH,// which means that by default an app's shared library directory isn't on LD_LIBRARY_PATH.// The PathClassLoader set up by frameworks/base knows the appropriate path, so we can load// libraries with no dependencies just fine, but an app that has multiple libraries that// depend on each other needed to load them in most-dependent-first order.// We added API to Android's dynamic linker so we can update the library path used for// the currently-running process. We pull the desired path out of the ClassLoader here// and pass it to nativeLoad so that it can call the private dynamic linker API.// We didn't just change frameworks/base to update the LD_LIBRARY_PATH once at the// beginning because multiple apks can run in the same process and third party code can// use its own BaseDexClassLoader.// We didn't just add a dlopen_with_custom_LD_LIBRARY_PATH call because we wanted any// dlopen(3) calls made from a .so's JNI_OnLoad to work too.// So, find out what the native library search path is for the ClassLoader in question...String ldLibraryPath = null;if (loader != null && loader instanceof BaseDexClassLoader) {ldLibraryPath = ((BaseDexClassLoader) loader).getLdLibraryPath();}// nativeLoad should be synchronized so there's only one LD_LIBRARY_PATH in use regardless// of how many ClassLoaders are in the system, but dalvik doesn't support synchronized// internal natives.synchronized (this) {return nativeLoad(name, loader, ldLibraryPath);}}// TODO: should be synchronized, but dalvik doesn't support synchronized internal natives.private static native String nativeLoad(String filename, ClassLoader loader, String ldLibraryPath);  // 注：该方法为c++实现// 。。。 。。。
}// https://android.googlesource.com/platform/libcore/+/master/dalvik/src/main/java/dalvik/system/BaseDexClassLoader.java
// https://www.androidos.net.cn/android/9.0.0_r8/xref/libcore/dalvik/src/main/java/dalvik/system/BaseDexClassLoader.java
/*** Base class for common functionality between various dex-based* {@link ClassLoader} implementations.*/
public class BaseDexClassLoader extends ClassLoader {/*** Hook for customizing how dex files loads are reported.** This enables the framework to monitor the use of dex files. The* goal is to simplify the mechanism for optimizing foreign dex files and* enable further optimizations of secondary dex files.** The reporting happens only when new instances of BaseDexClassLoader* are constructed and will be active only after this field is set with* {@link BaseDexClassLoader#setReporter}.*//* @NonNull */ private static volatile Reporter reporter = null;@UnsupportedAppUsageprivate final DexPathList pathList;// 。。。 。。。public BaseDexClassLoader(String dexPath,String librarySearchPath, ClassLoader parent, ClassLoader[] sharedLibraryLoaders,ClassLoader[] sharedLibraryLoadersAfter,boolean isTrusted) {super(parent);// Setup shared libraries before creating the path list. ART relies on the class loader// hierarchy being finalized before loading dex files.this.sharedLibraryLoaders = sharedLibraryLoaders == null? null: Arrays.copyOf(sharedLibraryLoaders, sharedLibraryLoaders.length);this.pathList = new DexPathList(this, dexPath, librarySearchPath, null, isTrusted);// 。。。 。。。
    }public BaseDexClassLoader(ByteBuffer[] dexFiles, String librarySearchPath, ClassLoader parent) {super(parent);this.sharedLibraryLoaders = null;this.sharedLibraryLoadersAfter = null;this.pathList = new DexPathList(this, librarySearchPath);this.pathList.initByteBufferDexPath(dexFiles);// Run background verification after having set 'pathList'.this.pathList.maybeRunBackgroundVerification(this);}@SystemApi(client = MODULE_LIBRARIES)public void addNativePath(@NonNull Collection<String> libPaths) {pathList.addNativePath(libPaths);}@Overridepublic String findLibrary(String name) {return pathList.findLibrary(name);}/*** Returns colon-separated set of directories where libraries should be* searched for first, before the standard set of directories.** @return colon-separated set of search directories** @hide*/@UnsupportedAppUsage@SystemApi(client = MODULE_LIBRARIES)public @NonNull String getLdLibraryPath() {StringBuilder result = new StringBuilder();for (File directory : pathList.getNativeLibraryDirectories()) {if (result.length() > 0) {result.append(':');}result.append(directory);}return result.toString();}// 。。。 。。。
}// https://android.googlesource.com/platform/libcore/+/master/dalvik/src/main/java/dalvik/system/DexPathList.java
// https://www.androidos.net.cn/android/9.0.0_r8/xref/libcore/dalvik/src/main/java/dalvik/system/DexPathList.java
public final class DexPathList {// 。。。 。。。/** List of native library path elements. */// Some applications rely on this field being an array or we'd use a final list here
    @UnsupportedAppUsage/* package visible for testing */ NativeLibraryElement[] nativeLibraryPathElements;/** List of application native library directories. */@UnsupportedAppUsageprivate final List<File> nativeLibraryDirectories;/** List of system native library directories. */@UnsupportedAppUsageprivate final List<File> systemNativeLibraryDirectories;// 。。。 。。。private List<File> getAllNativeLibraryDirectories() {List<File> allNativeLibraryDirectories = new ArrayList<>(nativeLibraryDirectories);allNativeLibraryDirectories.addAll(systemNativeLibraryDirectories);return allNativeLibraryDirectories;}public DexPathList(ClassLoader definingContext, String librarySearchPath) {if (definingContext == null) {throw new NullPointerException("definingContext == null");}this.definingContext = definingContext;this.nativeLibraryDirectories = splitPaths(librarySearchPath, false);this.systemNativeLibraryDirectories =splitPaths(System.getProperty("java.library.path"), true); // 系统的 "java.library.path" 路径   /system/lib/; /vendor/lib/; /product/lib/this.nativeLibraryPathElements = makePathElements(getAllNativeLibraryDirectories());}DexPathList(ClassLoader definingContext, String dexPath,String librarySearchPath, File optimizedDirectory, boolean isTrusted) {if (definingContext == null) {throw new NullPointerException("definingContext == null");}if (dexPath == null) {throw new NullPointerException("dexPath == null");}if (optimizedDirectory != null) {if (!optimizedDirectory.exists())  {throw new IllegalArgumentException("optimizedDirectory doesn't exist: "+ optimizedDirectory);}if (!(optimizedDirectory.canRead()&& optimizedDirectory.canWrite())) {throw new IllegalArgumentException("optimizedDirectory not readable/writable: "+ optimizedDirectory);}}this.definingContext = definingContext;ArrayList<IOException> suppressedExceptions = new ArrayList<IOException>();// save dexPath for BaseDexClassLoaderthis.dexElements = makeDexElements(splitDexPath(dexPath), optimizedDirectory,suppressedExceptions, definingContext, isTrusted);// Native libraries may exist in both the system and// application library paths, and we use this search order:////   1. This class loader's library path for application libraries (librarySearchPath)://   1.1. Native library directories//   1.2. Path to libraries in apk-files//   2. The VM's library path from the system property for system libraries//      also known as java.library.path//// This order was reversed prior to Gingerbread; see http://b/2933456.this.nativeLibraryDirectories = splitPaths(librarySearchPath, false);this.systemNativeLibraryDirectories =splitPaths(System.getProperty("java.library.path"), true);  // 系统的 "java.library.path" 路径   /system/lib/; /vendor/lib/; /product/lib/this.nativeLibraryPathElements = makePathElements(getAllNativeLibraryDirectories());if (suppressedExceptions.size() > 0) {this.dexElementsSuppressedExceptions =suppressedExceptions.toArray(new IOException[suppressedExceptions.size()]);} else {dexElementsSuppressedExceptions = null;}}/*** For BaseDexClassLoader.getLdLibraryPath.*/public List<File> getNativeLibraryDirectories() {return nativeLibraryDirectories;}public String findLibrary(String libraryName) {String fileName = System.mapLibraryName(libraryName);for (NativeLibraryElement element : nativeLibraryPathElements) {String path = element.findNativeLibrary(fileName);if (path != null) {return path;}}return null;}/*** Adds a collection of library paths from which to load native libraries. Paths can be absolute* native library directories (i.e. /data/app/foo/lib/arm64) or apk references (i.e.* /data/app/foo/base.apk!/lib/arm64).** Note: This method will attempt to dedupe elements.* Note: This method replaces the value of {@link #nativeLibraryPathElements}*/@UnsupportedAppUsagepublic void addNativePath(Collection<String> libPaths) {   // 添加新的查找路径  例如：/data/app/com.example.mygame-S72Tv4IGEow5LtbwxPQHpQ==/lib/arm64if (libPaths.isEmpty()) {return;}List<File> libFiles = new ArrayList<>(libPaths.size());for (String path : libPaths) {libFiles.add(new File(path));}ArrayList<NativeLibraryElement> newPaths =new ArrayList<>(nativeLibraryPathElements.length + libPaths.size());newPaths.addAll(Arrays.asList(nativeLibraryPathElements));for (NativeLibraryElement element : makePathElements(libFiles)) {if (!newPaths.contains(element)) {newPaths.add(element);}}nativeLibraryPathElements = newPaths.toArray(new NativeLibraryElement[newPaths.size()]);}// 。。。 。。。
}

在 Java 中，JVM 加载的是 .class 文件，而在 Android 中，Dalvik或ART虚拟机加载的是 dex 文件。

这里的 dex 文件不仅仅指 .dex 后缀的文件，而是指携带 classed.dex 项的任何文件（例如：jar / zip / apk）。

在 Android 中，Java 代码的编译产物是 dex 格式字节码，所以 Android 系统提供了 BaseDexClassLoader 类加载器，用于从 dex 文件中加载类。

PathClassLoader & DexClassLoader 是 BaseDexClassLoader 的子类，但它们都没有重写方法，所以主要的逻辑还是在 BaseDexClassLoader。

UE5动态加载libUnreal.so

GameApplication.java

import android.app.Application;
import android.content.Context;
import android.content.res.Configuration;
import androidx.lifecycle.Lifecycle;
import androidx.lifecycle.LifecycleObserver;
import androidx.lifecycle.OnLifecycleEvent;
import androidx.lifecycle.ProcessLifecycleOwner;public class GameApplication extends Application implements LifecycleObserver {// 。。。 。。。private static Context context;// 。。。 。。。
    @Overridepublic void onCreate() {super.onCreate();GameApplication.context = getApplicationContext();// 。。。 。。。。
    }public static Context getAppContext() {return GameApplication.context;}// 。。。 。。。
}

GameActivity.java

import dalvik.system.BaseDexClassLoader;
import java.util.Collection;
import java.util.Set;public class GameActivity extends NativeActivity implements SurfaceHolder.Callback2,SensorEventListener,Logger.ILoggerCallback,ComponentCallbacks2
{// 。。。 。。。
    @Overridepublic ClassLoader getClassLoader() {ClassLoader baseClassLoader = super.getClassLoader();try {BaseDexClassLoader dexClassLoader = (BaseDexClassLoader) baseClassLoader;if (dexClassLoader.findLibrary("Unreal") == null) {Field pathListField = BaseDexClassLoader.class.getDeclaredField("pathList");pathListField.setAccessible(true);Object pathListObj = pathListField.get(dexClassLoader);Method addNativePathMethod = pathListObj.getClass().getMethod("addNativePath", Collection.class);String filesDir = getApplicationContext().getFilesDir().getAbsolutePath();Log.verbose("Adding '" + filesDir + "' to GameActivity BaseDexClassLoader");Collection<String> paths = Arrays.asList(filesDir);addNativePathMethod.invoke(pathListObj, paths);}} catch (Exception e) {Log.warn("Failed to add native library path due to " + e);}return baseClassLoader;}// 。。。 。。。static{// We need to decide on enabling memory tracing before loading native code.// It's not trivial to get a full command line before GameActivity is constructed, so fallback to a sentinel file.try{Context context = GameApplication.getAppContext();Bundle bundle = context.getPackageManager().getApplicationInfo(context.getPackageName(), PackageManager.GET_META_DATA).metaData;boolean bShipping =bundle.containsKey("com.epicgames.unreal.GameActivity.BuildConfiguration") &&bundle.getString("com.epicgames.unreal.GameActivity.BuildConfiguration").equals("Shipping");if (!bShipping){ boolean bEnableFullMemoryTracing = new File(GameApplication.getAppContext().getFilesDir() + "/UEEnableMemoryTracing.txt").exists();boolean bEnableLightlMemoryTracing = new File(GameApplication.getAppContext().getFilesDir() + "/UEEnableMemoryTracingLight.txt").exists();if (bEnableFullMemoryTracing){Os.setenv("UEEnableMemoryTracing", "full", true);}else if (bEnableLightlMemoryTracing){Os.setenv("UEEnableMemoryTracing", "light", true);}}}catch (ErrnoException | NameNotFoundException e){Log.debug(e.toString());Log.debug("Cannot set \"UEEnableMemoryTracing\" environment variable");}if (!isUnderTest()){System.load(GameApplication.getAppContext().getFilesDir().getAbsolutePath() + "/libUnreal.so");}}
}

注1：上面从/data/data/com.example.mygame/files/libUnreal.so外部路径加载so文件，需要保证包中不要打入libUnreal.so，否则在JNI层还是会优先加载包中的libUnreal.so导致崩溃

注2：libUnreal.so要放在App的沙盒目录且设置为可执行，否则可能由于权限问题加载失败。可使用代码为libUnreal.so设置可执行权限

// 方式一：
File file = new File("/data/data/com.example.mygame/files/libUnreal.so");
boolean success = file.setExecutable(true); // 为所有用户添加可执行权限
// 如果只为“所有者”添加权限，使用 file.setExecutable(true, true); // 第1个参数：是否可执行; 第2个参数（可选）：是否只对所有者设置（true 为只对 owner，false 为所有用户）

// 方式二：
import java.nio.file.*;
import java.nio.file.attribute.*;
import java.util.*;Path path = Paths.get("/data/data/com.example.mygame/files/libUnreal.so");
Set<PosixFilePermission> perms = Files.getPosixFilePermissions(path);
// 添加可执行权限
perms.add(PosixFilePermission.OWNER_EXECUTE);
perms.add(PosixFilePermission.GROUP_EXECUTE);
perms.add(PosixFilePermission.OTHERS_EXECUTE);
// 可按需添加其他权限
Files.setPosixFilePermissions(path, perms);// 方式三：
Path path = Paths.get("/data/data/com.example.mygame/files/libUnreal.so");
Set<PosixFilePermission> perms = PosixFilePermissions.fromString("rwxr-xr-x");
Files.setPosixFilePermissions(path, perms);

注3：打包脚本要去掉-archive参数

"cmd.exe" /c ""D:/UnrealEngine/Engine/Build/BatchFiles/RunUAT.bat" -ScriptsForProject="D:/MyGame/MyGame.uproject" Turnkey -command=VerifySdk -platform=Android -UpdateIfNeeded -EditorIO -EditorIOPort=52576 -project="D:/MyGame/MyGame.uproject" BuildCookRun -nop4 -utf8output -nocompileeditor -skipbuildeditor -cook -project="D:/MyGame/MyGame.uproject" -unrealexe="D:\UnrealEngine\Engine\Binaries\Win64\UnrealEditor-Win64-DebugGame-Cmd.exe" -platform=Android -cookflavor=ASTC -stage -archive -package -build -pak -iostore -compressed -prereqs -archivedirectory="D:/MyGame/Achived" -clientconfig=Development" -nocompile -nocompileuat