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8371637: allocateNativeInternal sometimes return incorrectly aligned memory #28235

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8371637: allocateNativeInternal sometimes return incorrectly aligned memory #28235

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0d1bb66
8371637: allocateNativeInternal sometimes return incorrectly aligned …
snake66 Nov 11, 2025
2090700
Test that native segments don't overlap
snake66 Nov 13, 2025
2b8266f
Second try to fix alignment for native segments
snake66 Nov 13, 2025
15daa51
OS agnostic fix for alignment of native segments
snake66 Nov 14, 2025
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2 changes: 1 addition & 1 deletion src/java.base/share/classes/jdk/internal/foreign/SegmentFactories.java
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Original file line number Diff line number Diff line change
Expand Up @@ -203,7 +203,7 @@ private static long allocateNativeInternal(long byteSize, long byteAlignment, Me
long allocationSize;
long allocationBase;
long result;
if (byteAlignment > MAX_MALLOC_ALIGN) {
if (byteAlignment > MAX_MALLOC_ALIGN || alignedSize % byteAlignment != 0) {
allocationSize = alignedSize + byteAlignment - MAX_MALLOC_ALIGN;
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@JornVernee JornVernee Nov 15, 2025

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The calculation of allocationSize looks no longer correct now that byteAlignment might be smaller than MAX_MALLOC_ALIGN, and it can result in a negative size.

if (shouldReserve) {
AbstractMemorySegmentImpl.NIO_ACCESS.reserveMemory(allocationSize, byteSize);
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8 changes: 7 additions & 1 deletion test/jdk/java/foreign/TestMemoryAlignment.java
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Expand Up @@ -60,8 +60,14 @@ public void testAlignedAccess(long align) {
assertEquals(aligned.byteAlignment(), align); //unreasonable alignment here, to make sure access throws
VarHandle vh = aligned.varHandle();
try (Arena arena = Arena.ofConfined()) {
MemorySegment segment = arena.allocate(aligned);;
MemorySegment segment = arena.allocate(aligned);
vh.set(segment, 0L, -42);

// Allocate another segment and fill it with data to
// check that the first segment is not overwritten
MemorySegment nextSegment = arena.allocate(aligned);
vh.set(nextSegment, 0L, 0xffffff);

int val = (int)vh.get(segment, 0L);
assertEquals(val, -42);
}
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