1 /*
2  * Copyright (C) 2015 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 import java.lang.reflect.Field;
18 import java.lang.reflect.Method;
19 import java.util.List;
20 
21 class MyClassLoader extends ClassLoader {
MyClassLoader()22   MyClassLoader() throws Exception {
23     super(MyClassLoader.class.getClassLoader());
24 
25     // Some magic to get access to the pathList field of BaseDexClassLoader.
26     ClassLoader loader = getClass().getClassLoader();
27     Class<?> baseDexClassLoader = loader.getClass().getSuperclass();
28     Field f = baseDexClassLoader.getDeclaredField("pathList");
29     f.setAccessible(true);
30     Object pathList = f.get(loader);
31 
32     // Some magic to get access to the dexField field of pathList.
33     f = pathList.getClass().getDeclaredField("dexElements");
34     f.setAccessible(true);
35     dexElements = (Object[]) f.get(pathList);
36     dexFileField = dexElements[0].getClass().getDeclaredField("dexFile");
37     dexFileField.setAccessible(true);
38   }
39 
40   Object[] dexElements;
41   Field dexFileField;
42 
43   static ClassLoader level1ClassLoader;
44 
loadClass(String className, boolean resolve)45   protected Class<?> loadClass(String className, boolean resolve) throws ClassNotFoundException {
46     if (this != level1ClassLoader) {
47       if (className.equals("Level1")) {
48         return level1ClassLoader.loadClass(className);
49       } else if (className.equals("Level2")) {
50         throw new ClassNotFoundException("None of my methods require Level2!");
51       } else if (!className.equals("LoadedByMyClassLoader")) {
52         // We're only going to handle LoadedByMyClassLoader.
53         return getParent().loadClass(className);
54       }
55     } else {
56       if (className != "Level1" && className != "Level2") {
57         return getParent().loadClass(className);
58       }
59     }
60 
61     // Mimic what DexPathList.findClass is doing.
62     try {
63       for (Object element : dexElements) {
64         Object dex = dexFileField.get(element);
65         Method method = dex.getClass().getDeclaredMethod(
66             "loadClassBinaryName", String.class, ClassLoader.class, List.class);
67 
68         if (dex != null) {
69           Class<?> clazz = (Class<?>)method.invoke(dex, className, this, null);
70           if (clazz != null) {
71             return clazz;
72           }
73         }
74       }
75     } catch (Exception e) { /* Ignore */ }
76     return null;
77   }
78 }
79 
80 class LoadedByMyClassLoader {
bar()81   public static void bar() {
82     Level1.$inline$bar();
83   }
84 }
85 
86 class Main {
main(String[] args)87   public static void main(String[] args) throws Exception {
88     System.loadLibrary(args[0]);
89     // Clone resolved methods, to restore the original version just
90     // before we walk the stack in $noinline$bar.
91     savedResolvedMethods = cloneResolvedMethods(Main.class);
92 
93     MyClassLoader o = new MyClassLoader();
94     MyClassLoader.level1ClassLoader = new MyClassLoader();
95     Class<?> foo = o.loadClass("LoadedByMyClassLoader");
96     Method m = foo.getDeclaredMethod("bar");
97     try {
98       m.invoke(null);
99     } catch (Error e) { /* Ignore */ }
100   }
101 
$inline$bar()102   public static void $inline$bar() {
103   }
104 
$noinline$bar()105   public static void $noinline$bar() {
106     try {
107       // Be evil and clear all dex cache entries.
108       Field f = Class.class.getDeclaredField("dexCache");
109       f.setAccessible(true);
110       Object dexCache = f.get(Main.class);
111       f = dexCache.getClass().getDeclaredField("resolvedTypes");
112       f.setAccessible(true);
113       Object[] array = (Object[]) f.get(dexCache);
114       for (int i = 0; i < array.length; i++) {
115         array[i] = null;
116       }
117       restoreResolvedMethods(Main.class, savedResolvedMethods);
118     } catch (Throwable t) { /* Ignore */ }
119 
120     // This will walk the stack, trying to resolve methods in it.
121     // Because we cleared dex cache entries, we will have to find
122     // classes again, which require to use the correct class loader
123     // in the presence of inlining.
124     new Exception().printStackTrace(System.out);
125   }
126   static Object savedResolvedMethods;
127 
cloneResolvedMethods(Class<?> cls)128   static native Object cloneResolvedMethods(Class<?> cls);
restoreResolvedMethods(Class<?> cls, Object saved)129   static native void restoreResolvedMethods(Class<?> cls, Object saved);
130 }
131