1 /*

     2  * Copyright (c) 2017, 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.

     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 8178047

    27  * @run main/othervm -XX:CompileCommand=exclude,*.main -XX:-TieredCompilation -XX:-BackgroundCompilation compiler.unsafe.TestRawAliasing

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

    29  */

    30 

    31 package compiler.unsafe;

    32 

    33 import java.lang.reflect.Field;

    34 

    35 public class TestRawAliasing {

    36     static private final jdk.internal.misc.Unsafe UNSAFE;

    37     static {

    38         try {

    39             Field f = jdk.internal.misc.Unsafe.class.getDeclaredField("theUnsafe");

    40             f.setAccessible(true);

    41             UNSAFE = (jdk.internal.misc.Unsafe) f.get(null);

    42         } catch (Exception e) {

    43             throw new RuntimeException("Unable to get Unsafe instance.", e);

    44         }

    45     }

    46 

    47     static private final int OFFSET_X = 50;

    48     static private final int OFFSET_Y = 100;

    49 

    50     private static int test(long base_plus_offset_x, long base_plus_offset_y, int magic_value) {

    51         // write 0 to a location

    52         UNSAFE.putByte(base_plus_offset_x - OFFSET_X, (byte)0);

    53         // write unfoldable value to really the same location with another base

    54         UNSAFE.putByte(base_plus_offset_y - OFFSET_Y, (byte)magic_value);

    55         // read the value back, should be equal to "unfoldable_value"

    56         return UNSAFE.getByte(base_plus_offset_x - OFFSET_X);

    57     }

    58 

    59     private static final int OFF_HEAP_AREA_SIZE = 128;

    60     private static final byte MAGIC = 123;

    61 

    62     // main is excluded from compilation since we don't want the test method to inline and make base values fold

    63     public static void main(String... args) {

    64         long base = UNSAFE.allocateMemory(OFF_HEAP_AREA_SIZE);

    65         for (int i = 0; i < 100_000; i++) {

    66             if (test(base + OFFSET_X, base + OFFSET_Y, MAGIC) != MAGIC) {

    67                 throw new RuntimeException("Unexpected magic value");

    68             }

    69         }

    70     }

    71 }