More variants of getSizeFromObject and getObjectEnd based on usage for safety.

Author: peter-hofer

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

@@ -101,7 +101,7 @@ public boolean visitObjectReferenceInline(Pointer objRef, int innerOffset, boole
 
             // Promote the Object if necessary, making it at least grey, and ...
             Object obj = p.toObject();
-            assert innerOffset < LayoutEncoding.getSizeFromObject(obj).rawValue();
+            assert innerOffset < LayoutEncoding.getSizeFromObjectInGC(obj).rawValue();
             Object copy = GCImpl.getGCImpl().promoteObject(obj, header);
             if (copy != obj) {
                 // ... update the reference to point to the copy, making the reference black.

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

@@ -196,11 +196,11 @@ public UnalignedHeader getFirstWritableUnalignedChunk() {
     }
 
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    private static Word getObjectEnd(Object obj) {
+    private static Pointer getObjectEnd(Object obj) {
         if (obj == null) {
             return WordFactory.nullPointer();
         }
-        return Word.objectToUntrackedPointer(obj).add(LayoutEncoding.getSizeFromObject(obj));
+        return LayoutEncoding.getImageHeapObjectEnd(obj);
     }
 
     @SuppressWarnings("unchecked")

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

@@ -119,7 +119,7 @@ private static boolean walkPartitionInline(Object firstObject, Object lastObject
                 } else if (!visitor.visitObject(currentObject)) {
                     return false;
                 }
-                current = LayoutEncoding.getObjectEnd(current.toObject());
+                current = LayoutEncoding.getImageHeapObjectEnd(current.toObject());
             }
             if (HeapImpl.usesImageHeapChunks() && current.belowThan(lastPointer)) {
                 currentChunk = HeapChunk.getNext(currentChunk);
@@ -157,7 +157,7 @@ public UnsignedWord getSize(ImageHeapInfo info) {
         if (firstStart.isNull()) { // no objects
             return WordFactory.zero();
         }
-        Pointer lastEnd = LayoutEncoding.getObjectEnd(getLastObject(info));
+        Pointer lastEnd = LayoutEncoding.getImageHeapObjectEnd(getLastObject(info));
         return lastEnd.subtract(firstStart);
     }
 

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/remset/AlignedChunkRememberedSet.java

@@ -85,7 +85,7 @@ public static void enableRememberedSetForObject(AlignedHeader chunk, Object obj)
         Pointer fotStart = getFirstObjectTableStart(chunk);
         Pointer objectsStart = AlignedHeapChunk.getObjectsStart(chunk);
         Pointer startOffset = Word.objectToUntrackedPointer(obj).subtract(objectsStart);
-        Pointer endOffset = LayoutEncoding.getObjectEnd(obj).subtract(objectsStart);
+        Pointer endOffset = LayoutEncoding.getObjectEndInGC(obj).subtract(objectsStart);
         FirstObjectTable.setTableForObject(fotStart, startOffset, endOffset);
         ObjectHeaderImpl.setRememberedSetBit(obj);
     }
@@ -101,7 +101,7 @@ public static void enableRememberedSet(AlignedHeader chunk) {
         while (offset.belowThan(top)) {
             Object obj = offset.toObject();
             enableRememberedSetForObject(chunk, obj);
-            offset = offset.add(LayoutEncoding.getSizeFromObject(obj));
+            offset = offset.add(LayoutEncoding.getSizeFromObjectInGC(obj));
         }
     }
 

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/remset/CardTable.java

@@ -160,7 +160,7 @@ public static boolean verify(Pointer cardTableStart, Pointer objectsStart, Point
                     success &= verifyReferent(ref, cardTableStart, objectsStart);
                 }
             }
-            curPtr = LayoutEncoding.getObjectEnd(obj);
+            curPtr = LayoutEncoding.getObjectEndInGC(obj);
         }
         return success;
     }

substratevm/src/com.oracle.svm.core.genscavenge/src/com/oracle/svm/core/genscavenge/remset/FirstObjectTable.java

@@ -239,7 +239,7 @@ public static Pointer getFirstObjectImprecise(Pointer tableStart, Pointer object
         // If the object starts before the memory for this index, skip over it.
         if (firstObject.belowThan(indexedMemoryStart)) {
             Object crossingObject = firstObject.toObject();
-            result = LayoutEncoding.getObjectEnd(crossingObject);
+            result = LayoutEncoding.getObjectEndInGC(crossingObject);
         } else {
             assert firstObject.equal(indexedMemoryStart) : "preciseFirstPointer.equal(indexedMemoryStart)";
             result = indexedMemoryStart;
@@ -308,7 +308,7 @@ public static boolean verify(Pointer tableStart, Pointer objectsStart, Pointer o
             }
 
             Object obj = objStart.toObject();
-            Pointer objEnd = LayoutEncoding.getObjectEnd(obj);
+            Pointer objEnd = LayoutEncoding.getObjectEndInGC(obj);
             if (!entryStart.belowThan(objEnd)) {
                 Log.log().string("The first object table entry at index ").unsigned(index).string(" points to an object is not crossing nor starting at a card boundary:  obj: ").zhex(objStart)
                                 .string(" - ").zhex(objEnd).string(", chunk: ").zhex(objectsStart).string(" - ").zhex(objectsLimit).newline();

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

@@ -47,7 +47,7 @@ public boolean visitObject(Object o) {
             return false;
         }
         entry.instanceCount++;
-        entry.instanceSpace += LayoutEncoding.getSizeFromObject(o).rawValue();
+        entry.instanceSpace += LayoutEncoding.getMomentarySizeFromObject(o).rawValue();
         return true;
     }
 

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/heapdump/HeapDumpUtils.java

@@ -325,7 +325,7 @@ public long sizeOf(Object obj) {
             if (obj == null) {
                 result = 0;
             } else {
-                final UnsignedWord objectSize = LayoutEncoding.getSizeFromObject(obj);
+                final UnsignedWord objectSize = LayoutEncoding.getMomentarySizeFromObject(obj);
                 result = objectSize.rawValue();
             }
             return result;

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/hub/LayoutEncoding.java

@@ -310,21 +310,27 @@ public static int getOptionalIdentityHashOffset(Object obj) {
         }
     }
 
-    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
+    @Uninterruptible(reason = "Prevent a GC moving the object or interfering with its identity hash state.", callerMustBe = true)
     public static UnsignedWord getSizeFromObject(Object obj) {
-        return getSizeFromObject(obj, false);
+        boolean withOptionalIdHashField = !ConfigurationValues.getObjectLayout().hasFixedIdentityHashField() && checkOptionalIdentityHashField(obj);
+        return getSizeFromObjectInline(obj, withOptionalIdHashField);
     }
 
-    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
-    public static UnsignedWord getSizeFromObject(Object obj, boolean addOptionalIdHashField) {
-        boolean withOptionalIdHashField = addOptionalIdHashField ||
-                        (!ConfigurationValues.getObjectLayout().hasFixedIdentityHashField() && checkOptionalIdentityHashFieldUninterruptibly(obj));
-        return getSizeFromObjectInline(obj, withOptionalIdHashField);
+    public static UnsignedWord getSizeFromObjectAddOptionalIdHashField(Object obj) {
+        return getSizeFromObjectInline(obj, true);
     }
 
-    @Uninterruptible(reason = "Prevent a GC moving the object or interfering with its identity hash state.")
-    private static boolean checkOptionalIdentityHashFieldUninterruptibly(Object obj) {
-        return checkOptionalIdentityHashField(obj);
+    /**
+     * Returns the size of the object in the instant of the call, which can have already become
+     * stale after returning. This can be useful for diagnostic output.
+     */
+    @Uninterruptible(reason = "Caller is aware the value can be stale, but required by callee.")
+    public static UnsignedWord getMomentarySizeFromObject(Object obj) {
+        return getSizeFromObject(obj);
+    }
+
+    public static UnsignedWord getSizeFromObjectInGC(Object obj) {
+        return getSizeFromObjectInlineInGC(obj);
     }
 
     @AlwaysInline("GC performance")
@@ -339,7 +345,7 @@ public static UnsignedWord getSizeFromObjectInlineInGC(Object obj, boolean addOp
         return getSizeFromObjectInline(obj, withOptionalIdHashField);
     }
 
-    @AlwaysInline("GC performance")
+    @AlwaysInline("Actual inlining decided by callers.")
     @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
     private static UnsignedWord getSizeFromObjectInline(Object obj, boolean withOptionalIdHashField) {
         DynamicHub hub = KnownIntrinsics.readHub(obj);
@@ -359,15 +365,20 @@ private static boolean checkOptionalIdentityHashField(Object obj) {
         return oh.hasOptionalIdentityHashField(header);
     }
 
-    /** Returns the end of the Object when the call started, e.g., for logging. */
-    public static Pointer getObjectEnd(Object obj) {
-        UnsignedWord size = getSizeFromObject(obj);
-        return Word.objectToUntrackedPointer(obj).add(size);
+    public static Pointer getObjectEndInGC(Object obj) {
+        return getObjectEndInlineInGC(obj);
     }
 
     @AlwaysInline("GC performance")
     public static Pointer getObjectEndInlineInGC(Object obj) {
-        UnsignedWord size = getSizeFromObjectInlineInGC(obj);
+        UnsignedWord size = getSizeFromObjectInlineInGC(obj, false);
+        return Word.objectToUntrackedPointer(obj).add(size);
+    }
+
+    @Uninterruptible(reason = "Called from uninterruptible code.", mayBeInlined = true)
+    public static Pointer getImageHeapObjectEnd(Object obj) {
+        // Image heap objects never move and always have an identity hash code field.
+        UnsignedWord size = getSizeFromObjectInline(obj, true);
         return Word.objectToUntrackedPointer(obj).add(size);
     }
 

substratevm/src/com.oracle.svm.graal/src/com/oracle/svm/graal/meta/SubstrateMemoryAccessProviderImpl.java

@@ -150,7 +150,7 @@ private static JavaConstant readPrimitiveChecked(JavaKind kind, Constant baseCon
         } else if (displacement <= 0) {
             /* Trying to read before the object, or the hub. No need to look into the object. */
             return null;
-        } else if (WordFactory.unsigned(displacement + bits / 8).aboveThan(LayoutEncoding.getSizeFromObject(baseObject))) {
+        } else if (WordFactory.unsigned(displacement + bits / 8).aboveThan(LayoutEncoding.getMomentarySizeFromObject(baseObject))) {
             /* Trying to read after the end of the object. */
             return null;
         }