86 lines
3.0 KiB
Java
86 lines
3.0 KiB
Java
/*
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* Copyright (c) 2016, 2020, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* @test
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* @bug 8161720
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* @modules java.base/jdk.internal.misc
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* @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -Xbatch -XX:-TieredCompilation UnsafeSmallOffsetBooleanAccessTest
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* @run main/othervm -Xbatch UnsafeSmallOffsetBooleanAccessTest
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*/
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import java.util.Random;
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import jdk.internal.misc.Unsafe;
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public class UnsafeSmallOffsetBooleanAccessTest {
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static final Unsafe UNSAFE = Unsafe.getUnsafe();
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static final long F_OFFSET;
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static final Random random = new Random(42);
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static {
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try {
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F_OFFSET = UNSAFE.objectFieldOffset(T.class.getDeclaredField("f"));
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System.out.println("The offset is: " + F_OFFSET);
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} catch (Exception e) {
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throw new Error(e);
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}
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}
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static class T {
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boolean f;
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}
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// Always return false in a way that is not obvious to the compiler.
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public static boolean myRandom() {
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if (random.nextInt(101) > 134) {
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return true;
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} else {
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return false;
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}
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}
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public static boolean test(T t) {
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boolean result = false;
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for (int i = 0; i < 20000; i++) {
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boolean random = myRandom();
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// If myRandom() returns false, access t.f.
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//
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// If myRandom() returns true, access virtual address
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// F_OFFSET. That address is most likely not mapped,
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// therefore the access will most likely cause a
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// crash. We're not concerned about that, though, because
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// myRandom() always returns false. However, the C2
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// compiler avoids normalization of the value returned by
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// getBoolean in this case.
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result = UNSAFE.getBoolean(myRandom() ? null : t, F_OFFSET);
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}
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return result;
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}
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public static void main(String[] args) {
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T t = new T();
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UNSAFE.putBoolean(t, F_OFFSET, true);
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System.out.println("The result for t is: " + test(t));
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}
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}
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