Simplifications and better naming.

Author: christianhaeubl

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/ChunkedImageHeapLayouter.java

@@ -40,14 +40,15 @@
 public class ChunkedImageHeapLayouter extends AbstractImageHeapLayouter<ChunkedImageHeapPartition> {
     private final ImageHeapInfo heapInfo;
     private final long startOffset;
-    private final boolean isAuxImageHeap;
+    private final int nullRegionSize;
     private final long hugeObjectThreshold;
     private ChunkedImageHeapAllocator allocator;
 
-    public ChunkedImageHeapLayouter(ImageHeapInfo heapInfo, boolean isAuxImageHeap, long startOffset) {
+    public ChunkedImageHeapLayouter(ImageHeapInfo heapInfo, long startOffset, int nullRegionSize) {
+        assert startOffset == 0 || startOffset >= Heap.getHeap().getImageHeapOffsetInAddressSpace() : "must be relative to the heap base";
         this.heapInfo = heapInfo;
         this.startOffset = startOffset;
-        this.isAuxImageHeap = isAuxImageHeap;
+        this.nullRegionSize = nullRegionSize;
         this.hugeObjectThreshold = HeapPolicy.getLargeArrayThreshold().rawValue();
     }
 
@@ -68,10 +69,7 @@ protected long getHugeObjectThreshold() {
 
     @Override
     protected ImageHeapLayoutInfo doLayout(ImageHeap imageHeap) {
-        long position = startOffset;
-        if (!isAuxImageHeap) {
-            position += Heap.getHeap().getImageHeapNullPageSize();
-        }
+        long position = startOffset + nullRegionSize;
         allocator = new ChunkedImageHeapAllocator(imageHeap, position);
         for (ChunkedImageHeapPartition partition : getPartitions()) {
             partition.layout(allocator);
@@ -106,7 +104,7 @@ private void initializeHeapInfo(int dynamicHubCount, long offsetOfFirstWritableA
         long writableAligned = offsetOfFirstWritableAlignedChunk;
         long writableUnaligned = offsetOfFirstWritableUnalignedChunk;
 
-        if (!isAuxImageHeap) {
+        if (startOffset == 0) {
             // Adjust all offsets by the offset of the image heap in the address space.
             int imageHeapOffsetInAddressSpace = Heap.getHeap().getImageHeapOffsetInAddressSpace();
             writableAligned += imageHeapOffsetInAddressSpace;

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/HeapImpl.java

@@ -444,7 +444,7 @@ public int getImageHeapOffsetInAddressSpace() {
 
     @Fold
     @Override
-    public int getImageHeapNullPageSize() {
+    public int getImageHeapNullRegionSize() {
         if (SubstrateOptions.SpawnIsolates.getValue() && !CommittedMemoryProvider.get().guaranteesHeapPreferredAddressSpaceAlignment()) {
             /*
              * Prepend a single null page to the image heap so that there is a memory protected gap
@@ -657,8 +657,8 @@ static Pointer getImageHeapStart() {
         if (imageHeapOffsetInAddressSpace > 0) {
             return KnownIntrinsics.heapBase().add(imageHeapOffsetInAddressSpace);
         } else {
-            int nullPageSize = Heap.getHeap().getImageHeapNullPageSize();
-            return KnownIntrinsics.heapBase().add(nullPageSize);
+            int nullRegionSize = Heap.getHeap().getImageHeapNullRegionSize();
+            return KnownIntrinsics.heapBase().add(nullRegionSize);
         }
     }
 

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/LinearImageHeapLayouter.java

@@ -31,12 +31,13 @@
 public class LinearImageHeapLayouter extends AbstractImageHeapLayouter<LinearImageHeapPartition> {
     private final ImageHeapInfo heapInfo;
     private final long startOffset;
-    private final boolean isAuxImageHeap;
+    private final int nullRegionSize;
 
-    public LinearImageHeapLayouter(ImageHeapInfo heapInfo, boolean isAuxImageHeap, long startOffset) {
+    public LinearImageHeapLayouter(ImageHeapInfo heapInfo, long startOffset, int nullRegionSize) {
+        assert startOffset == 0 || startOffset >= Heap.getHeap().getImageHeapOffsetInAddressSpace() : "must be relative to the heap base";
         this.heapInfo = heapInfo;
         this.startOffset = startOffset;
-        this.isAuxImageHeap = isAuxImageHeap;
+        this.nullRegionSize = nullRegionSize;
     }
 
     @Override
@@ -52,9 +53,7 @@ protected LinearImageHeapPartition createPartition(String name, boolean contains
     @Override
     protected ImageHeapLayoutInfo doLayout(ImageHeap imageHeap) {
         long beginOffset = startOffset;
-        if (!isAuxImageHeap) {
-            beginOffset += Heap.getHeap().getImageHeapNullPageSize();
-        }
+        beginOffset += nullRegionSize;
         LinearImageHeapAllocator allocator = new LinearImageHeapAllocator(beginOffset);
         for (LinearImageHeapPartition partition : getPartitions()) {
             partition.allocateObjects(allocator);

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/graal/HeapFeature.java

@@ -106,10 +106,11 @@ public void beforeAnalysis(BeforeAnalysisAccess access) {
     @Override
     public void afterAnalysis(AfterAnalysisAccess access) {
         ImageHeapLayouter heapLayouter;
+        int imageHeapNullRegionSize = Heap.getHeap().getImageHeapNullRegionSize();
         if (HeapImpl.usesImageHeapChunks()) { // needs CommittedMemoryProvider: registered late
-            heapLayouter = new ChunkedImageHeapLayouter(HeapImpl.getImageHeapInfo(), false, 0);
+            heapLayouter = new ChunkedImageHeapLayouter(HeapImpl.getImageHeapInfo(), 0, imageHeapNullRegionSize);
         } else {
-            heapLayouter = new LinearImageHeapLayouter(HeapImpl.getImageHeapInfo(), false, 0);
+            heapLayouter = new LinearImageHeapLayouter(HeapImpl.getImageHeapInfo(), 0, imageHeapNullRegionSize);
         }
         ImageSingletons.add(ImageHeapLayouter.class, heapLayouter);
     }

substratevm/src/com.oracle.svm.core.posix/src/com/oracle/svm/core/posix/linux/LinuxImageHeapProvider.java

@@ -176,10 +176,10 @@ public int initialize(Pointer reservedAddressSpace, UnsignedWord reservedSize, W
                 return CEntryPointErrors.PROTECT_HEAP_FAILED;
             }
 
-            // Protect the null pages.
-            int nullPageSize = Heap.getHeap().getImageHeapNullPageSize();
-            if (nullPageSize > 0) {
-                if (VirtualMemoryProvider.get().protect(imageHeapBegin, WordFactory.unsigned(nullPageSize), Access.NONE) != 0) {
+            // Protect the null region.
+            int nullRegionSize = Heap.getHeap().getImageHeapNullRegionSize();
+            if (nullRegionSize > 0) {
+                if (VirtualMemoryProvider.get().protect(imageHeapBegin, WordFactory.unsigned(nullRegionSize), Access.NONE) != 0) {
                     return CEntryPointErrors.PROTECT_HEAP_FAILED;
                 }
             }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heap/Heap.java

@@ -164,13 +164,13 @@ public List<Class<?>> getLoadedClasses() {
     public abstract int getImageHeapOffsetInAddressSpace();
 
     /**
-     * Returns the number of null bytes that should prepended to the image heap during the image
+     * Returns the number of null bytes that should be prepended to the image heap during the image
      * build. This value must be a multiple of the page size. When the image heap is mapped at
      * runtime, this extra memory gets mapped as well but is marked as inaccessible (see
      * {@link ImageHeapProvider} for more details).
      */
     @Fold
-    public abstract int getImageHeapNullPageSize();
+    public abstract int getImageHeapNullRegionSize();
 
     /**
      * Returns true if the given object is located in the image heap.

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/os/AbstractCommittedMemoryProvider.java

@@ -51,7 +51,7 @@ public boolean guaranteesHeapPreferredAddressSpaceAlignment() {
     @Uninterruptible(reason = "Still being initialized.")
     protected static int protectSingleIsolateImageHeap() {
         assert !SubstrateOptions.SpawnIsolates.getValue() : "Must be handled by ImageHeapProvider when SpawnIsolates is enabled";
-        assert Heap.getHeap().getImageHeapNullPageSize() == 0 : "Null pages don't make any sense without a heap base.";
+        assert Heap.getHeap().getImageHeapNullRegionSize() == 0 : "A null region only makes sense with a heap base.";
         Pointer heapBegin = IMAGE_HEAP_BEGIN.get();
         if (Heap.getHeap().getImageHeapOffsetInAddressSpace() != 0) {
             return CEntryPointErrors.MAP_HEAP_FAILED;

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/os/AbstractCopyingImageHeapProvider.java

@@ -87,9 +87,9 @@ public int initialize(Pointer reservedAddressSpace, UnsignedWord reservedSize, W
 
         // Protect the read-only parts at the start of the image heap.
         UnsignedWord pageSize = VirtualMemoryProvider.get().getGranularity();
-        int nullPageSize = Heap.getHeap().getImageHeapNullPageSize();
-        Pointer firstPartOfReadOnlyImageHeap = imageHeap.add(nullPageSize);
-        UnsignedWord writableBeginPageOffset = UnsignedUtils.roundDown(IMAGE_HEAP_WRITABLE_BEGIN.get().subtract(imageHeapBegin.add(nullPageSize)), pageSize);
+        int nullRegionSize = Heap.getHeap().getImageHeapNullRegionSize();
+        Pointer firstPartOfReadOnlyImageHeap = imageHeap.add(nullRegionSize);
+        UnsignedWord writableBeginPageOffset = UnsignedUtils.roundDown(IMAGE_HEAP_WRITABLE_BEGIN.get().subtract(imageHeapBegin.add(nullRegionSize)), pageSize);
         if (writableBeginPageOffset.aboveThan(0)) {
             if (VirtualMemoryProvider.get().protect(firstPartOfReadOnlyImageHeap, writableBeginPageOffset, VirtualMemoryProvider.Access.READ) != 0) {
                 freeImageHeap(allocatedMemory);
@@ -108,9 +108,9 @@ public int initialize(Pointer reservedAddressSpace, UnsignedWord reservedSize, W
             }
         }
 
-        // Protect the null pages.
-        if (nullPageSize > 0) {
-            if (VirtualMemoryProvider.get().protect(imageHeapBegin, WordFactory.unsigned(nullPageSize), Access.NONE) != 0) {
+        // Protect the null region.
+        if (nullRegionSize > 0) {
+            if (VirtualMemoryProvider.get().protect(imageHeapBegin, WordFactory.unsigned(nullRegionSize), Access.NONE) != 0) {
                 return CEntryPointErrors.PROTECT_HEAP_FAILED;
             }
         }

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/os/ImageHeapProvider.java

@@ -41,7 +41,7 @@
  * When a heap base is used, then the image heap is always mapped in a way that the memory at the
  * heap base is protected and marked as inaccessible. Depending on the specific scenario, that
  * memory may or may not be part of the Native Image file (see
- * {@link Heap#getImageHeapNullPageSize()} and {@link Heap#getImageHeapOffsetInAddressSpace()} for
+ * {@link Heap#getImageHeapNullRegionSize()} and {@link Heap#getImageHeapOffsetInAddressSpace()} for
  * more details). This is done regardless of the used GC, platform, or CPU architecture:
  *
  * <pre>