1 /*

     2  * Copyright (c) 2017, Red Hat, 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.

     8  *

     9  * This code is distributed in the hope that it will be useful, but WITHOUT

    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    12  * version 2 for more details (a copy is included in the LICENSE file that

    13  * accompanied this code).

    14  *

    15  * You should have received a copy of the GNU General Public License version

    16  * 2 along with this work; if not, write to the Free Software Foundation,

    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    18  *

    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    20  * or visit www.oracle.com if you need additional information or have any

    21  * questions.

    22  */

    23 

    24 /**

    25  * @test

    26  * @bug 8176506

    27  * @summary cast before unsafe access moved in dominating null check null path causes crash

    28  * @modules java.base/jdk.internal.misc:+open

    29  *

    30  * @run main/othervm -Xbatch -XX:-UseOnStackReplacement TestMaybeNullUnsafeAccess

    31  *

    32  */

    33 

    34 import jdk.internal.misc.Unsafe;

    35 import java.lang.reflect.Field;

    36 

    37 public class TestMaybeNullUnsafeAccess {

    38 

    39     static final jdk.internal.misc.Unsafe UNSAFE = Unsafe.getUnsafe();

    40     static final long F_OFFSET;

    41 

    42     static class A {

    43         int f;

    44         A(int f) {

    45             this.f = f;

    46         }

    47     }

    48 

    49     static {

    50         try {

    51             Field fField = A.class.getDeclaredField("f");

    52             F_OFFSET = UNSAFE.objectFieldOffset(fField);

    53         } catch (Exception e) {

    54             throw new RuntimeException(e);

    55         }

    56     }

    57 

    58     static A test_helper(Object o) {

    59         // this includes a check for null with both branches taken

    60         return (A)o;

    61     }

    62 

    63 

    64     // Loop is unswitched because of the test for null from the

    65     // checkcast above, unsafe access is copied in each branch, the

    66     // compiler sees a memory access to a null object

    67     static int test1(Object o, long offset) {

    68         int f = 0;

    69         for (int i = 0; i < 100; i++) {

    70             A a = test_helper(o);

    71             f = UNSAFE.getInt(a, offset);

    72         }

    73         return f;

    74     }

    75 

    76     // Same as above except because we know the offset of the access

    77     // is small, we can deduce object a cannot be null

    78     static int test2(Object o) {

    79         int f = 0;

    80         for (int i = 0; i < 100; i++) {

    81             A a = test_helper(o);

    82             f = UNSAFE.getInt(a, F_OFFSET);

    83         }

    84         return f;

    85     }

    86 

    87     static public void main(String[] args) {

    88         A a = new A(0x42);

    89         for (int i = 0; i < 20000; i++) {

    90             test_helper(null);

    91             test_helper(a);

    92             test1(a, F_OFFSET);

    93             test2(a);

    94         }

    95     }

    96 

    97 }