8367375: Crash when using CDS archive created with -XX:+UseCompactObjectHeaders and preview mode

Reviewed-by: chagedorn, matsaave

Author: coleenp

src/hotspot/share/cds/archiveBuilder.cpp

@@ -850,7 +850,7 @@ void ArchiveBuilder::make_klasses_shareable() {
       address narrow_klass_base = _requested_static_archive_bottom; // runtime encoding base == runtime mapping start
       const int narrow_klass_shift = precomputed_narrow_klass_shift();
       narrowKlass nk = CompressedKlassPointers::encode_not_null_without_asserts(requested_k, narrow_klass_base, narrow_klass_shift);
-      k->set_prototype_header(markWord::prototype().set_narrow_klass(nk));
+      k->set_prototype_header_klass(nk);
     }
 #endif //_LP64
     if (k->is_flatArray_klass()) {

src/hotspot/share/cds/archiveHeapWriter.cpp

@@ -192,6 +192,7 @@ objArrayOop ArchiveHeapWriter::allocate_root_segment(size_t offset, int element_
   if (UseCompactObjectHeaders) {
     oopDesc::release_set_mark(mem, Universe::objectArrayKlass()->prototype_header());
   } else {
+    assert(!EnableValhalla || Universe::objectArrayKlass()->prototype_header() == markWord::prototype(), "should be the same");
     oopDesc::set_mark(mem, markWord::prototype());
     oopDesc::release_set_klass(mem, Universe::objectArrayKlass());
   }

src/hotspot/share/cds/heapShared.cpp

@@ -598,6 +598,7 @@ static void copy_java_mirror_hashcode(oop orig_mirror, oop scratch_m) {
       narrowKlass nk = CompressedKlassPointers::encode(orig_mirror->klass());
       scratch_m->set_mark(markWord::prototype().set_narrow_klass(nk).copy_set_hash(src_hash));
     } else {
+      // For valhalla, the prototype header is the same as markWord::prototype();
       scratch_m->set_mark(markWord::prototype().copy_set_hash(src_hash));
     }
     assert(scratch_m->mark().is_unlocked(), "sanity");

src/hotspot/share/oops/klass.hpp

@@ -755,6 +755,7 @@ class Klass : public Metadata {
   inline void set_prototype_header(markWord header);
   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
   static inline markWord default_prototype_header(Klass* k);
+  inline void set_prototype_header_klass(narrowKlass klass);
 
   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
 

src/hotspot/share/oops/klass.inline.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2005, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2005, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -95,6 +95,10 @@ inline markWord Klass::default_prototype_header(Klass* k) {
   return (k == nullptr) ? markWord::prototype() : k->prototype_header();
 }
 
+inline void Klass::set_prototype_header_klass(narrowKlass klass) {
+  // Merge narrowKlass in existing prototype header.
+  _prototype_header = _prototype_header.set_narrow_klass(klass);
+}
 
 // Loading the java_mirror does not keep its holder alive. See Klass::keep_alive().
 inline oop Klass::java_mirror() const {