jdk-24/test/hotspot/jtreg/runtime/FieldLayout/OldLayoutCheck.java

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/*
 * @test
 * @bug 8239014
 * @summary -XX:-UseEmptySlotsInSupers sometime fails to reproduce the layout of the old code
 * @library /test/lib
 * @modules java.base/jdk.internal.misc
 *          java.management
 * @requires vm.bits == "64" & vm.opt.final.UseCompressedOops == true & vm.gc != "Z"
 * @run main/othervm -XX:+UseCompressedClassPointers -XX:-UseEmptySlotsInSupers OldLayoutCheck
 */

/*
 * @test
 * @requires vm.bits == "32"
 * @library /test/lib
 * @modules java.base/jdk.internal.misc
 *          java.management
 * @run main/othervm -XX:-UseEmptySlotsInSupers OldLayoutCheck
 */

import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.Comparator;
import jdk.internal.misc.Unsafe;

import jdk.test.lib.Asserts;
import jdk.test.lib.Platform;

public class OldLayoutCheck {

    static class LIClass {
        public long l;
        public int i;
    }

    // 32-bit VMs: @0:  8 byte header,  @8: long field, @16:  int field
    // 64-bit VMs: @0: 12 byte header, @12:  int field, @16: long field
    static final long INT_OFFSET  = Platform.is64bit() ? 12L : 16L;
    static final long LONG_OFFSET = Platform.is64bit() ? 16L :  8L;

    static public void main(String[] args) {
        Unsafe unsafe = Unsafe.getUnsafe();
        Class c = LIClass.class;
        Field[] fields = c.getFields();
        for (int i = 0; i < fields.length; i++) {
            long offset = unsafe.objectFieldOffset(fields[i]);
            if (fields[i].getType() == int.class) {
                Asserts.assertEquals(offset, INT_OFFSET, "Misplaced int field");
            } else if (fields[i].getType() == long.class) {
                Asserts.assertEquals(offset, LONG_OFFSET, "Misplaced long field");
            } else {
                Asserts.fail("Unexpected field type");
            }
        }
    }
}