Fix access to J9ModronThreadLocalHeap.realHeapAlloc in older core files

debugtools/DDR_VM/src/com/ibm/j9ddr/vm29/j9/J9ConstantHelper.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2019, 2019 IBM Corp. and others
+ * Copyright (c) 2019, 2020 IBM Corp. and others
  *
  * This program and the accompanying materials are made available under
  * the terms of the Eclipse Public License 2.0 which accompanies this
@@ -46,7 +46,7 @@ private static Field getStaticFinalField(Class<?> clazz, String name, Class<?> e
 			throw new InternalError("unexpected exception", e);
 		}
 	}
-	
+
 	/**
 	 * Using reflection, read the value of a public static final long field from the given
 	 * class or, if the field is not present, return the default value provided.
@@ -86,5 +86,25 @@ public static boolean getBoolean(Class<?> clazz, String name, boolean defaultVal
 			return defaultValue;
 		}
 	}
-
+
+	/**
+	 * Using reflection, read the value of a public static final int field from the given
+	 * class or, if the field is not present, return the default value provided.
+	 *
+	 * @param clazz the class which owns the field of interest
+	 * @param name the name of the field
+	 * @param defaultValue the value to be returned if the field is not present
+	 * @return the value of the field, or the default value
+	 */
+	public static int getInt(Class<?> clazz, String name, int defaultValue) {
+		try {
+			return getStaticFinalField(clazz, name, int.class).getInt(null);
+		} catch (IllegalAccessException e) {
+			// this should not happen - the field is public static
+			throw new InternalError("unexpected exception", e);
+		} catch (NoSuchFieldException e) {
+			return defaultValue;
+		}
+	}
+
 }

debugtools/DDR_VM/src/com/ibm/j9ddr/vm29/j9/gc/GCObjectHeapIteratorAddressOrderedList_V1.java

@@ -31,20 +31,22 @@
 import java.util.NoSuchElementException;
 
 import com.ibm.j9ddr.CorruptDataException;
+import com.ibm.j9ddr.vm29.j9.J9ConstantHelper;
 import com.ibm.j9ddr.vm29.j9.ObjectModel;
+import com.ibm.j9ddr.vm29.pointer.PointerPointer;
 import com.ibm.j9ddr.vm29.pointer.U8Pointer;
-import com.ibm.j9ddr.vm29.pointer.generated.J9ModronThreadLocalHeapPointer;
 import com.ibm.j9ddr.vm29.pointer.generated.J9BuildFlags;
+import com.ibm.j9ddr.vm29.pointer.generated.J9ModronThreadLocalHeapPointer;
 import com.ibm.j9ddr.vm29.pointer.generated.J9ObjectPointer;
 import com.ibm.j9ddr.vm29.pointer.generated.J9VMThreadPointer;
 import com.ibm.j9ddr.vm29.pointer.generated.MM_CopyScanCachePointer;
 import com.ibm.j9ddr.vm29.pointer.generated.MM_EnvironmentStandardPointer;
+import com.ibm.j9ddr.vm29.structure.J9ModronThreadLocalHeap;
 import com.ibm.j9ddr.vm29.types.UDATA;
 
-
 class GCObjectHeapIteratorAddressOrderedList_V1 extends GCObjectHeapIterator
 {
-	private static Method realHeapAllocMethod = null;
+	private static final int realHeapAllocOffset = J9ConstantHelper.getInt(J9ModronThreadLocalHeap.class, "_realHeapAllocOffset_", -1);
 
 	protected J9ObjectPointer currentObject;
 	protected U8Pointer  scanPtr;
@@ -154,29 +156,13 @@ protected U8Pointer getRealHeapTop(J9ModronThreadLocalHeapPointer threadLocalHea
 
 	protected U8Pointer getRealHeapAlloc(J9ModronThreadLocalHeapPointer threadLocalHeap, U8Pointer heapAlloc) throws CorruptDataException
 	{
-		Exception exception;
-		try {
-			if (null == realHeapAllocMethod) {
-				realHeapAllocMethod = threadLocalHeap.getClass().getMethod("realHeapAlloc");
-			}
-			return (U8Pointer) realHeapAllocMethod.invoke(threadLocalHeap);
-		} catch (NoSuchMethodException | IllegalAccessException | IllegalArgumentException e) {
-			exception = e;
-		} catch (InvocationTargetException e1) {
-			Throwable cause = e1.getCause();
-			if (cause instanceof CorruptDataException) {
-				throw (CorruptDataException)cause;
-			} else if (cause instanceof RuntimeException) {
-				throw (RuntimeException)cause;
-			} else if (cause instanceof Error) {
-				throw (Error)cause;
-			}
-			exception = e1;
+		if (realHeapAllocOffset < 0) {
+			throw new CorruptDataException("No such field: realHeapAlloc");
 		}
-		
-		/* unexpected exception using reflection */
-		CorruptDataException cd = new CorruptDataException(exception.toString(), exception);
-		throw cd;
+
+		PointerPointer realHeapAllocEA = PointerPointer.cast(threadLocalHeap).addOffset(realHeapAllocOffset);
+
+		return U8Pointer.cast(realHeapAllocEA.at(0));
 	}
 
 	private U8Pointer adjustedToRange(U8Pointer ptr, U8Pointer base, U8Pointer top)
@@ -311,4 +297,3 @@ public J9ObjectPointer peek()
 		}		
 	}
 }
-