8343890: SEGV crash in RunTimeClassInfo::klass

Reviewed-by: ccheung
Backport-of: bf0debc

Author: Matias Saavedra Silva

src/hotspot/share/cds/runTimeClassInfo.cpp

@@ -76,10 +76,13 @@ void RunTimeClassInfo::init(DumpTimeClassInfo& info) {
 }
 
 InstanceKlass* RunTimeClassInfo::klass() const {
-  if (ArchiveBuilder::is_active() && ArchiveBuilder::current()->is_in_buffer_space((address)this)) {
-    return ArchiveBuilder::current()->offset_to_buffered<InstanceKlass*>(_klass_offset);
-  } else {
+  if (MetaspaceShared::is_in_shared_metaspace(this)) {
+    // <this> is inside a mmaped CDS archive.
     return ArchiveUtils::offset_to_archived_address<InstanceKlass*>(_klass_offset);
+  } else {
+    // <this> is a temporary copy of a RunTimeClassInfo that's being initialized
+    // by the ArchiveBuilder.
+    return ArchiveBuilder::current()->offset_to_buffered<InstanceKlass*>(_klass_offset);
   }
 }