J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package sun.reflect; |
| 27 | |
| 28 | import java.security.AccessController; |
| 29 | import java.security.PrivilegedAction; |
| 30 | import sun.misc.Unsafe; |
| 31 | |
| 32 | /** Utility class which assists in calling Unsafe.defineClass() by |
| 33 | creating a new class loader which delegates to the one needed in |
| 34 | order for proper resolution of the given bytecodes to occur. */ |
| 35 | |
| 36 | class ClassDefiner { |
| 37 | static final Unsafe unsafe = Unsafe.getUnsafe(); |
| 38 | |
| 39 | /** <P> We define generated code into a new class loader which |
| 40 | delegates to the defining loader of the target class. It is |
| 41 | necessary for the VM to be able to resolve references to the |
| 42 | target class from the generated bytecodes, which could not occur |
| 43 | if the generated code was loaded into the bootstrap class |
| 44 | loader. </P> |
| 45 | |
| 46 | <P> There are two primary reasons for creating a new loader |
| 47 | instead of defining these bytecodes directly into the defining |
| 48 | loader of the target class: first, it avoids any possible |
| 49 | security risk of having these bytecodes in the same loader. |
| 50 | Second, it allows the generated bytecodes to be unloaded earlier |
| 51 | than would otherwise be possible, decreasing run-time |
| 52 | footprint. </P> |
| 53 | */ |
| 54 | static Class defineClass(String name, byte[] bytes, int off, int len, |
| 55 | final ClassLoader parentClassLoader) |
| 56 | { |
| 57 | ClassLoader newLoader = (ClassLoader) |
| 58 | AccessController.doPrivileged(new PrivilegedAction() { |
| 59 | public Object run() { |
| 60 | return new DelegatingClassLoader(parentClassLoader); |
| 61 | } |
| 62 | }); |
| 63 | return unsafe.defineClass(name, bytes, off, len, newLoader, null); |
| 64 | } |
| 65 | } |
| 66 | |
| 67 | |
| 68 | // NOTE: this class's name and presence are known to the virtual |
| 69 | // machine as of the fix for 4474172. |
| 70 | class DelegatingClassLoader extends ClassLoader { |
| 71 | DelegatingClassLoader(ClassLoader parent) { |
| 72 | super(parent); |
| 73 | } |
| 74 | } |