[GR-49879] Backport to 23.0: Add an option to artificially increase the header size.

PullRequest: graal/16103

Author: medoussboug

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/SubstrateOptions.java

@@ -452,6 +452,16 @@ protected void onValueUpdate(EconomicMap<OptionKey<?>, Object> values, Boolean o
     @Option(help = "How many bytes to pad fields and classes marked @Contended with.") //
     public static final HostedOptionKey<Integer> ContendedPaddingWidth = new HostedOptionKey<>(128);
 
+    @Option(help = "Add additional header bytes to each object, for diagnostic purposes.", type = OptionType.Debug) //
+    public static final HostedOptionKey<Integer> AdditionalHeaderBytes = new HostedOptionKey<>(0, SubstrateOptions::validateAdditionalHeaderBytes);
+
+    private static void validateAdditionalHeaderBytes(HostedOptionKey<Integer> optionKey) {
+        int value = optionKey.getValue();
+        if (value < 0 || value % 4 != 0) {
+            throw UserError.abort("The option '%s' must be 0 or a multiple of 4.", optionKey.getName());
+        }
+    }
+
     /*
      * Isolate tear down options.
      */

substratevm/src/com.oracle.svm.core/src/com/oracle/svm/core/config/ObjectLayout.java

@@ -58,10 +58,11 @@ public final class ObjectLayout {
 
     public ObjectLayout(SubstrateTargetDescription target, int referenceSize, int objectAlignment, int hubOffset,
                     int firstFieldOffset, int arrayLengthOffset, int arrayBaseOffset, int fixedIdentityHashOffset) {
-        assert CodeUtil.isPowerOf2(referenceSize);
-        assert CodeUtil.isPowerOf2(objectAlignment);
-        assert hubOffset < firstFieldOffset && hubOffset < arrayLengthOffset;
-        assert fixedIdentityHashOffset == -1 || (fixedIdentityHashOffset > 0 && fixedIdentityHashOffset < arrayLengthOffset);
+        assert CodeUtil.isPowerOf2(referenceSize) : referenceSize;
+        assert CodeUtil.isPowerOf2(objectAlignment) : objectAlignment;
+        assert arrayLengthOffset % Integer.BYTES == 0;
+        assert hubOffset < firstFieldOffset && hubOffset < arrayLengthOffset : hubOffset;
+        assert fixedIdentityHashOffset == -1 || (fixedIdentityHashOffset > 0 && fixedIdentityHashOffset < arrayLengthOffset) : fixedIdentityHashOffset;
 
         this.target = target;
         this.referenceSize = referenceSize;

substratevm/src/com.oracle.svm.hosted/src/com/oracle/svm/hosted/HostedConfiguration.java

@@ -140,13 +140,13 @@ public static ObjectLayout createObjectLayout() {
     public static ObjectLayout createObjectLayout(JavaKind referenceKind, boolean disableOptionalIdentityHash) {
         SubstrateTargetDescription target = ConfigurationValues.getTarget();
         int referenceSize = target.arch.getPlatformKind(referenceKind).getSizeInBytes();
-        int headerSize = referenceSize;
         int intSize = target.arch.getPlatformKind(JavaKind.Int).getSizeInBytes();
         int objectAlignment = 8;
 
-        int headerOffset = 0;
+        int hubOffset = 0;
+        int headerSize = hubOffset + referenceSize;
+
         int identityHashCodeOffset;
-        int firstFieldOffset;
         if (!disableOptionalIdentityHash && SubstrateOptions.SpawnIsolates.getValue() && headerSize + referenceSize <= objectAlignment) {
             /*
              * References are relative to the heap base, so we should be able to use fewer bits in
@@ -158,15 +158,18 @@ public static ObjectLayout createObjectLayout(JavaKind referenceKind, boolean di
              * individual object was assigned an identity hash code after allocation.
              */
             identityHashCodeOffset = -1;
-            firstFieldOffset = headerOffset + headerSize;
         } else { // need all object header bits except for lowest-order bits freed up by alignment
-            identityHashCodeOffset = headerOffset + referenceSize;
-            firstFieldOffset = identityHashCodeOffset + intSize;
+            identityHashCodeOffset = headerSize;
+            headerSize += intSize;
         }
-        int arrayLengthOffset = firstFieldOffset;
+
+        headerSize += SubstrateOptions.AdditionalHeaderBytes.getValue();
+
+        int firstFieldOffset = headerSize;
+        int arrayLengthOffset = headerSize;
         int arrayBaseOffset = arrayLengthOffset + intSize;
 
-        return new ObjectLayout(target, referenceSize, objectAlignment, headerOffset, firstFieldOffset, arrayLengthOffset, arrayBaseOffset, identityHashCodeOffset);
+        return new ObjectLayout(target, referenceSize, objectAlignment, hubOffset, firstFieldOffset, arrayLengthOffset, arrayBaseOffset, identityHashCodeOffset);
     }
 
     public SVMHost createHostVM(OptionValues options, ClassLoader classLoader, ClassInitializationSupport classInitializationSupport,