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