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8341471: [macOS_aarch64] Reversed field layout caused by unstable sor…
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…ting

For class Test:
```
    public class Test {
        char a000;
        char a001;
        char a002;
        char a003;
        char a004;
        char a005;
        char a006;
        char a007;
        char a008;
        char a009;
        char a00a;
        char a00b;
    }
```

We found its field layout on macOS was:

Layout of class Test
  Instance fields:
   @0 12/- RESERVED
   @12 "a00b" C 2/2 REGULAR
   @14 "a001" C 2/2 REGULAR
   @16 "a002" C 2/2 REGULAR
   @18 "a003" C 2/2 REGULAR
   @20 "a004" C 2/2 REGULAR
   @22 "a005" C 2/2 REGULAR
   @24 "a006" C 2/2 REGULAR
   @26 "a007" C 2/2 REGULAR
   @28 "a008" C 2/2 REGULAR
   @30 "a009" C 2/2 REGULAR
   @32 "a00a" C 2/2 REGULAR
   @34 "a000" C 2/2 REGULAR

`a000` was put in the end while `a00b` was put in the beginning.

Fields get sorted according to size in [1]. `qsort()` on macOS
reverses the order of fields with the same size. We should extend
the comparison function to preserve the order on macOS, as we
did on Windows.

Tier 1-3 passed on macOS.

[1] https://github.com/openjdk/jdk/blob/3ee94e040a7395d11a294a6b660d707c97f188f8/src/hotspot/share/classfile/fieldLayoutBuilder.cpp#L102
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fg1417 committed Oct 7, 2024
1 parent ec020f3 commit c19e07d
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Showing 2 changed files with 80 additions and 4 deletions.
8 changes: 4 additions & 4 deletions src/hotspot/share/classfile/fieldLayoutBuilder.hpp
Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
/*
* Copyright (c) 2020, 2023, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
Expand Down Expand Up @@ -101,8 +101,8 @@ class LayoutRawBlock : public ResourceObj {
// sort fields in decreasing order.
// Note: with line types, the comparison should include alignment constraint if sizes are equals
static int compare_size_inverted(LayoutRawBlock** x, LayoutRawBlock** y) {
#ifdef _WINDOWS
// qsort() on Windows reverse the order of fields with the same size
#if defined (_WINDOWS) || defined (__APPLE__)
// qsort() on Windows/macOS reverse the order of fields with the same size
// the extension of the comparison function below preserves this order
int diff = (*y)->size() - (*x)->size();
if (diff == 0) {
Expand All @@ -111,7 +111,7 @@ class LayoutRawBlock : public ResourceObj {
return diff;
#else
return (*y)->size() - (*x)->size();
#endif // _WINDOWS
#endif // _WINDOWS || __APPLE__
}

};
Expand Down
76 changes: 76 additions & 0 deletions test/hotspot/jtreg/runtime/FieldLayout/TestFieldLayout.java
Original file line number Diff line number Diff line change
@@ -0,0 +1,76 @@
/*
* Copyright (c) 2024, Arm Limited. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
* questions.
*/

import java.lang.reflect.Field;
import jdk.internal.misc.Unsafe;

/*
* @test
* @bug 8341471
* @summary [macOS_aarch64] Reversed field layout caused by unstable sorting
* @modules java.base/jdk.internal.misc
* @run main/othervm TestFieldLayout
*/

public class TestFieldLayout {

private static final Unsafe U = Unsafe.getUnsafe();

public static void main(String[] args) throws Exception {

boolean endResult = true;
long previous = 0;

for (Field f : Test.class.getDeclaredFields()) {
long current = U.objectFieldOffset(f);
if (current < previous) {
System.out.printf("FAILED: field %s offset %d previous %d\n",
f.getName(), current, previous);
endResult = false;
}
previous = current;
}

System.out.println(endResult ? "Test PASSES" : "Test FAILS");
if (!endResult) {
throw new Error("Test failed");
}
}

public class Test {
char a000;
char a001;
char a002;
char a003;
char a004;
char a005;
char a006;
char a007;
char a008;
char a009;
char a00a;
char a00b;
}

}

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