GC division by 0 fix for 0-stride flattened array

Update gc code to support 0-stride flattened array and get rid of division by 0 exceptions This is done by adding manually comparison against 0, might find better alternatives in the future. Related: eclipse-openj9#14027 Signed-off-by: Frank Kang <[email protected]>
kangyining · Aug 23, 2023 · 4f81482 · 4f81482
1 parent 56dcdd2
commit 4f81482
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Showing 5 changed files with 21 additions and 5 deletions.
diff --git a/runtime/gc_base/IndexableObjectAllocationModel.cpp b/runtime/gc_base/IndexableObjectAllocationModel.cpp
@@ -145,7 +145,13 @@ MM_IndexableObjectAllocationModel::initializeIndexableObject(MM_EnvironmentBase
 	/* Lay out arraylet and arrayoid pointers */
 	switch (_layout) {
 	case GC_ArrayletObjectModel::InlineContiguous:
-		Assert_MM_true(1 == _numberOfArraylets);
+		/**
+		* _numberOfArraylets is set to 0 for 0-stride flattened array, and we
+		* can recognize this case by checking if _dataSize is 0.
+		* Note there are two cases that _dataSize is 0: 0-stride flattened array or 0-length array
+		* But the latter is treated as discontiguous and not following this path
+		*/
+		Assert_MM_true((0 == _dataSize) || (1 == _numberOfArraylets));
 		break;
 
 	case GC_ArrayletObjectModel::Discontiguous:

diff --git a/runtime/gc_glue_java/ArrayletObjectModel.cpp b/runtime/gc_glue_java/ArrayletObjectModel.cpp
@@ -94,7 +94,7 @@ GC_ArrayletObjectModel::getArrayletLayout(J9Class* clazz, UDATA dataSizeInBytes,
 	/* CMVC 135307 : when checking for InlineContiguous layout, perform subtraction as adding to dataSizeInBytes could trigger overflow. */
 	if ((largestDesirableSpine == UDATA_MAX) || (dataSizeInBytes <= (largestDesirableSpine - minimumSpineSizeAfterGrowing - contiguousIndexableHeaderSize()))) {
 		layout = InlineContiguous;
-		if(0 == dataSizeInBytes) {
+		if ((0 == dataSizeInBytes) && (0 < J9ARRAYCLASS_GET_STRIDE(clazz))) {
 			/* Zero sized NUA uses the discontiguous shape */
 			layout = Discontiguous;
 		}

diff --git a/runtime/gc_glue_java/ArrayletObjectModel.hpp b/runtime/gc_glue_java/ArrayletObjectModel.hpp
@@ -366,7 +366,7 @@ class GC_ArrayletObjectModel : public GC_ArrayletObjectModelBase
 		uintptr_t stride = J9ARRAYCLASS_GET_STRIDE(clazzPtr);
 		uintptr_t size = numberOfElements * stride;
 		uintptr_t alignedSize = UDATA_MAX;
-		if ((size / stride) == numberOfElements) {
+		if ((0 == stride) || ((size / stride) == numberOfElements)) {
 			alignedSize = MM_Math::roundToSizeofUDATA(size);
 			if (alignedSize < size) {
 				alignedSize = UDATA_MAX;
@@ -478,6 +478,9 @@ class GC_ArrayletObjectModel : public GC_ArrayletObjectModelBase
 			void* srcData = getDataPointerForContiguous(srcObject);
 			switch(elementSize)
 			{
+			case 0:
+				break;
+
 			case 1:
 				// byte/boolean
 				{
@@ -637,6 +640,9 @@ class GC_ArrayletObjectModel : public GC_ArrayletObjectModelBase
 			void* destData = getDataPointerForContiguous(destObject);
 			switch(elementSize)
 			{
+			case 0:
+				break;
+
 			case 1:
 				// byte/boolean
 				{

diff --git a/runtime/gc_include/ObjectAllocationAPI.hpp b/runtime/gc_include/ObjectAllocationAPI.hpp
@@ -447,10 +447,11 @@ class MM_ObjectAllocationAPI
 	VMINLINE j9object_t
 	inlineAllocateIndexableValueTypeObject(J9VMThread *currentThread, J9Class *arrayClass, uint32_t size, bool initializeSlots = true, bool memoryBarrier = true, bool sizeCheck = true)
 	{
-		uintptr_t dataSize = ((uintptr_t)size) * J9ARRAYCLASS_GET_STRIDE(arrayClass);
+		uintptr_t stride = J9ARRAYCLASS_GET_STRIDE(arrayClass);
+		uintptr_t dataSize = ((uintptr_t)size) * stride;
 		bool validSize = true;
 #if !defined(J9VM_ENV_DATA64)
-		validSize = !sizeCheck || (size < ((uint32_t)J9_MAXIMUM_INDEXABLE_DATA_SIZE / J9ARRAYCLASS_GET_STRIDE(arrayClass)));
+		validSize = (!sizeCheck) || (0 == stride) || (size < ((uint32_t)J9_MAXIMUM_INDEXABLE_DATA_SIZE / stride));
 #endif /* J9VM_ENV_DATA64 */
 		return inlineAllocateIndexableObjectImpl(currentThread, arrayClass, size, dataSize, validSize, initializeSlots, memoryBarrier);
 	}

diff --git a/runtime/gc_structs/FlattenedContiguousArrayIterator.hpp b/runtime/gc_structs/FlattenedContiguousArrayIterator.hpp
@@ -91,6 +91,9 @@ class GC_FlattenedContiguousArrayIterator
 	 */
 	MMINLINE UDATA getIndex()
 	{
+		if (0 == _elementStride) {
+			return 0;
+		}
 		return ((uintptr_t)_scanPtr - (uintptr_t)_basePtr) / _elementStride;
 	}