From 93ab76963898281cadb175b49cbe36cf75c5bd97 Mon Sep 17 00:00:00 2001
From: Christian Haeubl <christian.haeubl@oracle.com>
Date: Thu, 13 Nov 2025 16:43:18 +0100
Subject: [PATCH] Verify that objects in the young gen don't have a remembered
 set bit.

---
 .../com/oracle/svm/core/genscavenge/FillerObjectUtil.java   | 6 +++---
 .../src/com/oracle/svm/core/genscavenge/HeapVerifier.java   | 5 +++++
 .../src/com/oracle/svm/core/genscavenge/TlabSupport.java    | 2 +-
 .../svm/core/genscavenge/compacting/SweepingVisitor.java    | 2 +-
 4 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/FillerObjectUtil.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/FillerObjectUtil.java
index ffbfe5c3c750..c790b5bf8d5d 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/FillerObjectUtil.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/FillerObjectUtil.java
@@ -65,13 +65,13 @@ static int arrayBaseOffset() {
     }
 
     @Uninterruptible(reason = CALLED_FROM_UNINTERRUPTIBLE_CODE, mayBeInlined = true)
-    public static void writeFillerObjectAt(Pointer p, UnsignedWord size) {
+    public static void writeFillerObjectAt(Pointer p, UnsignedWord size, boolean rememberedSet) {
         assert size.aboveThan(0);
         if (size.aboveOrEqual(arrayMinSize())) {
             int length = UnsignedUtils.safeToInt(size.subtract(arrayBaseOffset()).unsignedDivide(ARRAY_ELEMENT_SIZE));
-            FormatArrayNode.formatArray(p, ARRAY_CLASS, length, true, false, WITH_GARBAGE_IF_ASSERTIONS_ENABLED, false);
+            FormatArrayNode.formatArray(p, ARRAY_CLASS, length, rememberedSet, false, WITH_GARBAGE_IF_ASSERTIONS_ENABLED, false);
         } else {
-            FormatObjectNode.formatObject(p, FillerObject.class, true, WITH_GARBAGE_IF_ASSERTIONS_ENABLED, false);
+            FormatObjectNode.formatObject(p, FillerObject.class, rememberedSet, WITH_GARBAGE_IF_ASSERTIONS_ENABLED, false);
         }
         assert LayoutEncoding.getSizeFromObjectInGC(p.toObject()).equal(size);
     }
diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapVerifier.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapVerifier.java
index 47d89662c684..f90ec6b46dbd 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapVerifier.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapVerifier.java
@@ -323,6 +323,11 @@ private static boolean verifyObject(Object obj, AlignedHeader aChunk, UnalignedH
                 Log.log().string("Object ").zhex(ptr).string(" is in ").string(space.getName()).string(" chunk ").zhex(chunk).string(" but does not have a remembered set.").newline();
                 return false;
             }
+        } else if (space.isYoungSpace()) {
+            if (SerialGCOptions.useRememberedSet() && RememberedSet.get().hasRememberedSet(header)) {
+                Log.log().string("Object ").zhex(ptr).string(" is in ").string(space.getName()).string(" chunk ").zhex(chunk).string(" but has a remembered set.").newline();
+                return false;
+            }
         }
 
         return verifyReferences(obj);
diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/TlabSupport.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/TlabSupport.java
index 504d39982867..20a35e9f2405 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/TlabSupport.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/TlabSupport.java
@@ -363,7 +363,7 @@ private static void insertFiller(ThreadLocalAllocation.Descriptor tlab) {
         UnsignedWord size = hardEnd.subtract(top);
 
         if (top.belowThan(hardEnd)) {
-            FillerObjectUtil.writeFillerObjectAt(top, size);
+            FillerObjectUtil.writeFillerObjectAt(top, size, false);
         }
     }
 
diff --git a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/SweepingVisitor.java b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/SweepingVisitor.java
index 16b999e37cdc..c523740f3f69 100644
--- a/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/SweepingVisitor.java
+++ b/substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/compacting/SweepingVisitor.java
@@ -43,7 +43,7 @@ public boolean visit(Pointer objSeq, UnsignedWord size, Pointer newAddress, Poin
         if (nextObjSeq.isNonNull()) {
             Pointer gapStart = objSeq.add(size);
             assert gapStart.belowThan(nextObjSeq);
-            FillerObjectUtil.writeFillerObjectAt(gapStart, nextObjSeq.subtract(gapStart));
+            FillerObjectUtil.writeFillerObjectAt(gapStart, nextObjSeq.subtract(gapStart), true);
             // Note that we have already added first object table entries for fillers during fixup.
         } else {
             AlignedHeapChunk.AlignedHeader chunk = AlignedHeapChunk.getEnclosingChunkFromObjectPointer(objSeq);