rev 51958 : 8211122: Reduce the number of internal classes made accessible to jdk.unsupported
Reviewed-by: alanb, dfuchs, kvn

   1 /*
   2  * Copyright (c) 2001, 2018, Oracle and/or its affiliates. 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
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  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
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  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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  23  * questions.
  24  */
  25 
  26 package jdk.internal.reflect;
  27 
  28 import java.security.AccessController;
  29 import java.security.PrivilegedAction;
  30 import jdk.internal.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 = AccessController.doPrivileged(
  58             new PrivilegedAction<ClassLoader>() {
  59                 public ClassLoader 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 }
--- EOF ---