src/hotspot/share/classfile/fieldLayoutBuilder.cpp

@@ -207,10 +207,27 @@
  
      insert_field_block(candidate, b);
    }
  }
  
+ // Finds a slot for the identity hash-code.
+ // Same basic algorithm as above add() method, but simplified
+ // and does not actually insert the field.
+ int FieldLayout::find_hash_offset() {
+   LayoutRawBlock* start = this->_start;
+   LayoutRawBlock* last = last_block();
+   LayoutRawBlock* cursor = start;
+   while (cursor != last) {
+     assert(cursor != nullptr, "Sanity check");
+     if (cursor->kind() == LayoutRawBlock::EMPTY && cursor->fit(4, 1)) {
+       break;
+     }
+     cursor = cursor->next_block();
+   }
+   return cursor->offset();
+ }
+ 
  // Used for classes with hard coded field offsets, insert a field at the specified offset */
  void FieldLayout::add_field_at_offset(LayoutRawBlock* block, int offset, LayoutRawBlock* start) {
    assert(block != nullptr, "Sanity check");
    block->set_offset(offset);
    if (start == nullptr) {

@@ -672,10 +689,13 @@
  
    // Pass back information needed for InstanceKlass creation
  
    _info->oop_map_blocks = nonstatic_oop_maps;
    _info->_instance_size = align_object_size(instance_end / wordSize);
+   if (UseCompactObjectHeaders) {
+     _info->_hash_offset   = _layout->find_hash_offset();
+   }
    _info->_static_field_size = static_fields_size;
    _info->_nonstatic_field_size = (nonstatic_field_end - instanceOopDesc::base_offset_in_bytes()) / heapOopSize;
    _info->_has_nonstatic_fields = _has_nonstatic_fields;
  
    if (PrintFieldLayout) {