8375569: Store Java mirrors in AOT configuration file

Reviewed-by: iveresov, kvn, asmehra

src/hotspot/share/cds/aotMappedHeapLoader.cpp

@@ -360,10 +360,8 @@ bool AOTMappedHeapLoader::load_heap_region(FileMapInfo* mapinfo) {
 }
 
 objArrayOop AOTMappedHeapLoader::root_segment(int segment_idx) {
-  if (CDSConfig::is_dumping_heap()) {
-    assert(Thread::current() == (Thread*)VMThread::vm_thread(), "should be in vm thread");
-  } else {
-    assert(CDSConfig::is_using_archive(), "must be");
+  if (!CDSConfig::is_using_archive()) {
+    assert(CDSConfig::is_dumping_heap() && Thread::current() == (Thread*)VMThread::vm_thread(), "sanity");
   }
 
   objArrayOop segment = (objArrayOop)_root_segments->at(segment_idx).resolve();
@@ -465,6 +463,10 @@ void AOTMappedHeapLoader::finish_initialization(FileMapInfo* info) {
       assert(segment_oop->is_objArray(), "Must be");
       add_root_segment((objArrayOop)segment_oop);
     }
+
+    if (CDSConfig::is_dumping_final_static_archive()) {
+      StringTable::move_shared_strings_into_runtime_table();
+    }
   }
 }
 

src/hotspot/share/cds/aotMetaspace.cpp

@@ -1104,7 +1104,12 @@ void AOTMetaspace::dump_static_archive_impl(StaticArchiveBuilder& builder, TRAPS
 
 #if INCLUDE_CDS_JAVA_HEAP
   if (CDSConfig::is_dumping_heap()) {
-    assert(CDSConfig::allow_only_single_java_thread(), "Required");
+    if (!CDSConfig::is_dumping_preimage_static_archive()) {
+      // A single thread is required for Reference handling and deterministic CDS archive.
+      // Its's not required for dumping preimage, where References won't be archived and
+      // determinism is not needed.
+      assert(CDSConfig::allow_only_single_java_thread(), "Required");
+    }
     if (!HeapShared::is_archived_boot_layer_available(THREAD)) {
       report_loading_error("archivedBootLayer not available, disabling full module graph");
       CDSConfig::stop_dumping_full_module_graph();

src/hotspot/share/cds/aotReferenceObjSupport.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, 2026, 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
@@ -177,12 +177,17 @@ void AOTReferenceObjSupport::init_keep_alive_objs_table() {
 
 // Returns true IFF obj is an instance of java.lang.ref.Reference. If so, perform extra eligibility checks.
 bool AOTReferenceObjSupport::check_if_ref_obj(oop obj) {
-  // We have a single Java thread. This means java.lang.ref.Reference$ReferenceHandler thread
-  // is not running. Otherwise the checks for next/discovered may not work.
-  precond(CDSConfig::allow_only_single_java_thread());
   assert_at_safepoint(); // _keep_alive_objs_table uses raw oops
 
   if (obj->klass()->is_subclass_of(vmClasses::Reference_klass())) {
+    // The following check works only if the java.lang.ref.Reference$ReferenceHandler thread
+    // is not running.
+    //
+    // This code is called on every object found by AOTArtifactFinder. When dumping the
+    // preimage archive, AOTArtifactFinder should not find any Reference objects.
+    precond(!CDSConfig::is_dumping_preimage_static_archive());
+    precond(CDSConfig::allow_only_single_java_thread());
+
     precond(AOTReferenceObjSupport::is_enabled());
     precond(JavaClasses::is_supported_for_archiving(obj));
     precond(_keep_alive_objs_table != nullptr);

src/hotspot/share/cds/cdsConfig.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2026, 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
@@ -556,7 +556,9 @@ void CDSConfig::check_aotmode_record() {
 
   // At VM exit, the module graph may be contaminated with program states.
   // We will rebuild the module graph when dumping the CDS final image.
-  disable_heap_dumping();
+  _is_using_optimized_module_handling = false;
+  _is_using_full_module_graph = false;
+  _is_dumping_full_module_graph = false;
 }
 
 void CDSConfig::check_aotmode_create() {
@@ -582,6 +584,7 @@ void CDSConfig::check_aotmode_create() {
   substitute_aot_filename(FLAG_MEMBER_ENUM(AOTCache));
 
   _is_dumping_final_static_archive = true;
+  _is_using_full_module_graph = false;
   UseSharedSpaces = true;
   RequireSharedSpaces = true;
 
@@ -954,7 +957,9 @@ bool CDSConfig::are_vm_options_incompatible_with_dumping_heap() {
 }
 
 bool CDSConfig::is_dumping_heap() {
-  if (!(is_dumping_classic_static_archive() || is_dumping_final_static_archive())
+  // Note: when dumping preimage static archive, only a very limited set of oops
+  // are dumped.
+  if (!is_dumping_static_archive()
       || are_vm_options_incompatible_with_dumping_heap()
       || _disable_heap_dumping) {
     return false;
@@ -966,6 +971,26 @@ bool CDSConfig::is_loading_heap() {
   return HeapShared::is_archived_heap_in_use();
 }
 
+bool CDSConfig::is_dumping_klass_subgraphs() {
+  if (is_dumping_classic_static_archive() || is_dumping_final_static_archive()) {
+    // KlassSubGraphs (see heapShared.cpp) is a legacy mechanism for archiving oops. It
+    // has been superceded by AOT class linking. This feature is used only when
+    // AOT class linking is disabled.
+    //
+    // KlassSubGraphs are disabled in the preimage static archive, which contains a very
+    // limited set of oops.
+    return is_dumping_heap() && !is_dumping_aot_linked_classes();
+  } else {
+    return false;
+  }
+}
+
+bool CDSConfig::is_using_klass_subgraphs() {
+  return (is_loading_heap() &&
+          !CDSConfig::is_using_aot_linked_classes() &&
+          !CDSConfig::is_dumping_final_static_archive());
+}
+
 bool CDSConfig::is_using_full_module_graph() {
   if (ClassLoaderDataShared::is_full_module_graph_loaded()) {
     return true;

src/hotspot/share/cds/cdsConfig.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2023, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2023, 2026, 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
@@ -188,6 +188,9 @@ public:
   static bool is_dumping_heap()                              NOT_CDS_JAVA_HEAP_RETURN_(false);
   static bool is_loading_heap()                              NOT_CDS_JAVA_HEAP_RETURN_(false);
 
+  static bool is_dumping_klass_subgraphs()                   NOT_CDS_JAVA_HEAP_RETURN_(false);
+  static bool is_using_klass_subgraphs()                     NOT_CDS_JAVA_HEAP_RETURN_(false);
+
   static bool is_dumping_invokedynamic()                     NOT_CDS_JAVA_HEAP_RETURN_(false);
   static bool is_dumping_method_handles()                    NOT_CDS_JAVA_HEAP_RETURN_(false);
 

src/hotspot/share/cds/heapShared.cpp

@@ -210,7 +210,7 @@ static bool is_subgraph_root_class_of(ArchivableStaticFieldInfo fields[], Instan
 
 bool HeapShared::is_subgraph_root_class(InstanceKlass* ik) {
   assert(CDSConfig::is_dumping_heap(), "dump-time only");
-  if (!CDSConfig::is_dumping_aot_linked_classes()) {
+  if (CDSConfig::is_dumping_klass_subgraphs()) {
     // Legacy CDS archive support (to be deprecated)
     return is_subgraph_root_class_of(archive_subgraph_entry_fields, ik) ||
            is_subgraph_root_class_of(fmg_archive_subgraph_entry_fields, ik);
@@ -455,7 +455,6 @@ int HeapShared::append_root(oop obj) {
 
 oop HeapShared::get_root(int index, bool clear) {
   assert(index >= 0, "sanity");
-  assert(!CDSConfig::is_dumping_heap() && CDSConfig::is_using_archive(), "runtime only");
   assert(is_archived_heap_in_use(), "getting roots into heap that is not used");
 
   oop result;
@@ -600,8 +599,7 @@ public:
   void set_oop(MetaspaceObj* ptr, oop o) {
     MutexLocker ml(ScratchObjects_lock, Mutex::_no_safepoint_check_flag);
     OopHandle handle(Universe::vm_global(), o);
-    bool is_new = put(ptr, handle);
-    assert(is_new, "cannot set twice");
+    put_when_absent(ptr, handle);
   }
   void remove_oop(MetaspaceObj* ptr) {
     MutexLocker ml(ScratchObjects_lock, Mutex::_no_safepoint_check_flag);
@@ -614,6 +612,11 @@ public:
 };
 
 void HeapShared::add_scratch_resolved_references(ConstantPool* src, objArrayOop dest) {
+  if (CDSConfig::is_dumping_preimage_static_archive() && scratch_resolved_references(src) != nullptr) {
+    // We are in AOT training run. The class has been redefined and we are giving it a new resolved_reference.
+    // Ignore it, as this class will be excluded from the AOT config.
+    return;
+  }
   if (SystemDictionaryShared::is_builtin_loader(src->pool_holder()->class_loader_data())) {
     _scratch_objects_table->set_oop(src, dest);
   }
@@ -934,7 +937,7 @@ void HeapShared::scan_java_class(Klass* orig_k) {
 void HeapShared::archive_subgraphs() {
   assert(CDSConfig::is_dumping_heap(), "must be");
 
-  if (!CDSConfig::is_dumping_aot_linked_classes()) {
+  if (CDSConfig::is_dumping_klass_subgraphs()) {
     archive_object_subgraphs(archive_subgraph_entry_fields,
                              false /* is_full_module_graph */);
     if (CDSConfig::is_dumping_full_module_graph()) {
@@ -1292,10 +1295,7 @@ static void verify_the_heap(Klass* k, const char* which) {
 // this case, we will not load the ArchivedKlassSubGraphInfoRecord and will clear its roots.
 void HeapShared::resolve_classes(JavaThread* current) {
   assert(CDSConfig::is_using_archive(), "runtime only!");
-  if (!is_archived_heap_in_use()) {
-    return; // nothing to do
-  }
-  if (!CDSConfig::is_using_aot_linked_classes()) {
+  if (CDSConfig::is_using_klass_subgraphs()) {
     resolve_classes_for_subgraphs(current, archive_subgraph_entry_fields);
     resolve_classes_for_subgraphs(current, fmg_archive_subgraph_entry_fields);
   }
@@ -1385,7 +1385,7 @@ void HeapShared::init_classes_for_special_subgraph(Handle class_loader, TRAPS) {
 
 void HeapShared::initialize_from_archived_subgraph(JavaThread* current, Klass* k) {
   JavaThread* THREAD = current;
-  if (!is_archived_heap_in_use()) {
+  if (!CDSConfig::is_using_klass_subgraphs()) {
     return; // nothing to do
   }
 
@@ -1861,7 +1861,7 @@ void HeapShared::archive_reachable_objects_from_static_field(InstanceKlass *k,
                                                              const char* klass_name,
                                                              int field_offset,
                                                              const char* field_name) {
-  assert(CDSConfig::is_dumping_heap(), "dump time only");
+  precond(CDSConfig::is_dumping_klass_subgraphs());
   assert(k->defined_by_boot_loader(), "must be boot class");
 
   oop m = k->java_mirror();
@@ -1912,7 +1912,7 @@ class VerifySharedOopClosure: public BasicOopIterateClosure {
 };
 
 void HeapShared::verify_subgraph_from_static_field(InstanceKlass* k, int field_offset) {
-  assert(CDSConfig::is_dumping_heap(), "dump time only");
+  precond(CDSConfig::is_dumping_klass_subgraphs());
   assert(k->defined_by_boot_loader(), "must be boot class");
 
   oop m = k->java_mirror();
@@ -2138,7 +2138,7 @@ void HeapShared::init_subgraph_entry_fields(ArchivableStaticFieldInfo fields[],
 void HeapShared::init_subgraph_entry_fields(TRAPS) {
   assert(CDSConfig::is_dumping_heap(), "must be");
   _dump_time_subgraph_info_table = new (mtClass)DumpTimeKlassSubGraphInfoTable();
-  if (!CDSConfig::is_dumping_aot_linked_classes()) {
+  if (CDSConfig::is_dumping_klass_subgraphs()) {
     init_subgraph_entry_fields(archive_subgraph_entry_fields, CHECK);
     if (CDSConfig::is_dumping_full_module_graph()) {
       init_subgraph_entry_fields(fmg_archive_subgraph_entry_fields, CHECK);

src/hotspot/share/classfile/javaClasses.cpp

@@ -1263,6 +1263,10 @@ bool java_lang_Class::restore_archived_mirror(Klass *k,
         "Restored %s archived mirror " PTR_FORMAT, k->external_name(), p2i(mirror()));
   }
 
+  if (CDSConfig::is_dumping_heap()) {
+    create_scratch_mirror(k, CHECK_(false));
+  }
+
   return true;
 }
 #endif // INCLUDE_CDS_JAVA_HEAP

src/hotspot/share/classfile/stringTable.cpp

@@ -987,4 +987,26 @@ void StringTable::serialize_shared_table_header(SerializeClosure* soc) {
     _shared_table.reset();
   }
 }
+
+void StringTable::move_shared_strings_into_runtime_table() {
+  precond(CDSConfig::is_dumping_final_static_archive());
+  JavaThread* THREAD = JavaThread::current();
+  HandleMark hm(THREAD);
+
+  int n = 0;
+  _shared_table.iterate_all([&](oop string) {
+    int length = java_lang_String::length(string);
+    Handle h_string (THREAD, string);
+    StringWrapper name(h_string, length);
+    unsigned int hash = hash_wrapped_string(name);
+
+    assert(!_alt_hash, "too early");
+    oop interned = do_intern(name, hash, THREAD);
+    assert(string == interned, "must be");
+    n++;
+  });
+
+  _shared_table.reset();
+  log_info(aot)("Moved %d interned strings to runtime table", n);
+}
 #endif //INCLUDE_CDS_JAVA_HEAP

src/hotspot/share/classfile/stringTable.hpp

@@ -119,6 +119,7 @@ public:
   static void init_shared_table() NOT_CDS_JAVA_HEAP_RETURN;
   static void write_shared_table() NOT_CDS_JAVA_HEAP_RETURN;
   static void serialize_shared_table_header(SerializeClosure* soc) NOT_CDS_JAVA_HEAP_RETURN;
+  static void move_shared_strings_into_runtime_table();
 
   // Jcmd
   static void dump(outputStream* st, bool verbose=false);

test/hotspot/jtreg/runtime/cds/appcds/aotCache/AOTMapTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2025, 2026, 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
@@ -136,6 +136,7 @@ public class AOTMapTest {
 }
 
 class AOTMapTestApp {
+    static URLClassLoader loader; // keep Hello class alive
     public static void main(String[] args) throws Exception {
         System.out.println("Hello AOTMapTestApp");
         testCustomLoader();
@@ -144,7 +145,7 @@ class AOTMapTestApp {
     static void testCustomLoader() throws Exception {
         File custJar = new File("cust.jar");
         URL[] urls = new URL[] {custJar.toURI().toURL()};
-        URLClassLoader loader = new URLClassLoader(urls, AOTMapTestApp.class.getClassLoader());
+        loader = new URLClassLoader(urls, AOTMapTestApp.class.getClassLoader());
         Class<?> c = loader.loadClass("Hello");
         System.out.println(c);
     }