1 /*
   2  * Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "classfile/classLoaderDataGraph.hpp"
  26 #include "classfile/javaClasses.inline.hpp"
  27 #include "classfile/symbolTable.hpp"
  28 #include "classfile/vmClasses.hpp"
  29 #include "classfile/vmSymbols.hpp"
  30 #include "gc/shared/collectedHeap.hpp"
  31 #include "jvmtifiles/jvmtiEnv.hpp"
  32 #include "logging/log.hpp"
  33 #include "memory/allocation.inline.hpp"
  34 #include "memory/resourceArea.hpp"
  35 #include "memory/universe.hpp"
  36 #include "oops/access.inline.hpp"
  37 #include "oops/arrayOop.hpp"
  38 #include "oops/constantPool.inline.hpp"
  39 #include "oops/fieldStreams.inline.hpp"
  40 #include "oops/instanceMirrorKlass.hpp"
  41 #include "oops/klass.inline.hpp"
  42 #include "oops/objArrayKlass.hpp"
  43 #include "oops/objArrayOop.inline.hpp"
  44 #include "oops/oop.inline.hpp"
  45 #include "oops/typeArrayOop.inline.hpp"
  46 #include "prims/jvmtiEventController.inline.hpp"
  47 #include "prims/jvmtiExport.hpp"
  48 #include "prims/jvmtiImpl.hpp"
  49 #include "prims/jvmtiTagMap.hpp"
  50 #include "prims/jvmtiTagMapTable.hpp"
  51 #include "prims/jvmtiThreadState.hpp"
  52 #include "runtime/continuationWrapper.inline.hpp"
  53 #include "runtime/deoptimization.hpp"
  54 #include "runtime/frame.inline.hpp"
  55 #include "runtime/handles.inline.hpp"
  56 #include "runtime/interfaceSupport.inline.hpp"
  57 #include "runtime/javaCalls.hpp"
  58 #include "runtime/javaThread.inline.hpp"
  59 #include "runtime/jniHandles.inline.hpp"
  60 #include "runtime/mutex.hpp"
  61 #include "runtime/mutexLocker.hpp"
  62 #include "runtime/safepoint.hpp"
  63 #include "runtime/threadSMR.hpp"
  64 #include "runtime/timerTrace.hpp"
  65 #include "runtime/vframe.hpp"
  66 #include "runtime/vmOperations.hpp"
  67 #include "runtime/vmThread.hpp"
  68 #include "utilities/macros.hpp"
  69 #include "utilities/objectBitSet.inline.hpp"
  70 
  71 typedef ObjectBitSet<mtServiceability> JVMTIBitSet;
  72 
  73 
  74 // Helper class to store objects to visit.
  75 class JvmtiHeapwalkVisitStack {
  76 private:
  77   enum {
  78     initial_visit_stack_size = 4000
  79   };
  80 
  81   GrowableArray<JvmtiHeapwalkObject>* _visit_stack;
  82   JVMTIBitSet _bitset;
  83 
  84   static GrowableArray<JvmtiHeapwalkObject>* create_visit_stack() {
  85     return new (mtServiceability) GrowableArray<JvmtiHeapwalkObject>(initial_visit_stack_size, mtServiceability);
  86   }
  87 
  88 public:
  89   JvmtiHeapwalkVisitStack(): _visit_stack(create_visit_stack()) {
  90   }
  91   ~JvmtiHeapwalkVisitStack() {
  92     if (_visit_stack != nullptr) {
  93       delete _visit_stack;
  94     }
  95   }
  96 
  97   bool is_empty() const {
  98     return _visit_stack->is_empty();
  99   }
 100 
 101   void push(const JvmtiHeapwalkObject& obj) {
 102     _visit_stack->push(obj);
 103   }
 104 
 105   // If the object hasn't been visited then push it onto the visit stack
 106   // so that it will be visited later.
 107   void check_for_visit(const JvmtiHeapwalkObject& obj) {
 108     if (!is_visited(obj)) {
 109       _visit_stack->push(obj);
 110     }
 111   }
 112 
 113   JvmtiHeapwalkObject pop() {
 114     return _visit_stack->pop();
 115   }
 116 
 117   bool is_visited(const JvmtiHeapwalkObject& obj) /*const*/ { // TODO: _bitset.is_marked() should be const
 118     // The method is called only for objects from visit_stack to ensure an object is not visited twice.
 119     // Flat objects can be added to visit_stack only when we visit their holder object, so we cannot get duplicate reference to it.
 120     if (obj.is_flat()) {
 121       return false;
 122     }
 123     return _bitset.is_marked(obj.obj());
 124   }
 125 
 126   void mark_visited(const JvmtiHeapwalkObject& obj) {
 127     if (!obj.is_flat()) {
 128       _bitset.mark_obj(obj.obj());
 129     }
 130   }
 131 };
 132 
 133 
 134 bool JvmtiTagMap::_has_object_free_events = false;
 135 
 136 // create a JvmtiTagMap
 137 JvmtiTagMap::JvmtiTagMap(JvmtiEnv* env) :
 138   _env(env),
 139   _lock(Mutex::nosafepoint, "JvmtiTagMap_lock"),
 140   _needs_cleaning(false),
 141   _posting_events(false),
 142   _converting_flat_object(false) {
 143 
 144   assert(JvmtiThreadState_lock->is_locked(), "sanity check");
 145   assert(((JvmtiEnvBase *)env)->tag_map() == nullptr, "tag map already exists for environment");
 146 
 147   _hashmap = new JvmtiTagMapTable();
 148   _flat_hashmap = new JvmtiFlatTagMapTable();
 149 
 150   // finally add us to the environment
 151   ((JvmtiEnvBase *)env)->release_set_tag_map(this);
 152 }
 153 
 154 // destroy a JvmtiTagMap
 155 JvmtiTagMap::~JvmtiTagMap() {
 156 
 157   // no lock acquired as we assume the enclosing environment is
 158   // also being destroyed.
 159   ((JvmtiEnvBase *)_env)->set_tag_map(nullptr);
 160 
 161   // finally destroy the hashmap
 162   delete _hashmap;
 163   _hashmap = nullptr;
 164   delete _flat_hashmap;
 165 }
 166 
 167 // Called by env_dispose() to reclaim memory before deallocation.
 168 // Remove all the entries but keep the empty table intact.
 169 // This needs the table lock.
 170 void JvmtiTagMap::clear() {
 171   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 172   _hashmap->clear();
 173   _flat_hashmap->clear();
 174 }
 175 
 176 // returns the tag map for the given environments. If the tag map
 177 // doesn't exist then it is created.
 178 JvmtiTagMap* JvmtiTagMap::tag_map_for(JvmtiEnv* env) {
 179   JvmtiTagMap* tag_map = ((JvmtiEnvBase*)env)->tag_map_acquire();
 180   if (tag_map == nullptr) {
 181     MutexLocker mu(JvmtiThreadState_lock);
 182     tag_map = ((JvmtiEnvBase*)env)->tag_map();
 183     if (tag_map == nullptr) {
 184       tag_map = new JvmtiTagMap(env);
 185     }
 186   } else {
 187     DEBUG_ONLY(JavaThread::current()->check_possible_safepoint());
 188   }
 189   return tag_map;
 190 }
 191 
 192 // returns true if the hashmaps are empty
 193 bool JvmtiTagMap::is_empty() const {
 194   assert(SafepointSynchronize::is_at_safepoint() || is_locked(), "checking");
 195   return _hashmap->is_empty() && _flat_hashmap->is_empty();
 196 }
 197 
 198 // This checks for posting before operations that use
 199 // this tagmap table.
 200 void JvmtiTagMap::check_hashmap(GrowableArray<jlong>* objects) {
 201   assert(is_locked(), "checking");
 202 
 203   if (is_empty()) { return; }
 204 
 205   if (_needs_cleaning &&
 206       objects != nullptr &&
 207       env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
 208     remove_dead_entries_locked(objects);
 209   }
 210 }
 211 
 212 // This checks for posting and is called from the heap walks.
 213 void JvmtiTagMap::check_hashmaps_for_heapwalk(GrowableArray<jlong>* objects) {
 214   assert(SafepointSynchronize::is_at_safepoint(), "called from safepoints");
 215 
 216   // Verify that the tag map tables are valid and unconditionally post events
 217   // that are expected to be posted before gc_notification.
 218   JvmtiEnvIterator it;
 219   for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
 220     JvmtiTagMap* tag_map = env->tag_map_acquire();
 221     if (tag_map != nullptr) {
 222       // The ZDriver may be walking the hashmaps concurrently so this lock is needed.
 223       MutexLocker ml(tag_map->lock(), Mutex::_no_safepoint_check_flag);
 224       tag_map->check_hashmap(objects);
 225     }
 226   }
 227 }
 228 
 229 // Converts entries from JvmtiFlatTagMapTable to JvmtiTagMapTable in batches.
 230 //   1. (JvmtiTagMap is locked)
 231 //      reads entries from JvmtiFlatTagMapTable (describe flat value objects);
 232 //   2. (JvmtiTagMap is unlocked)
 233 //      creates heap-allocated copies of the flat object;
 234 //   3. (JvmtiTagMap is locked)
 235 //      ensures source entry still exists, removes it from JvmtiFlatTagMapTable, adds new entry to JvmtiTagMapTable.
 236 // If some error occurs in step 2 (OOM?), the process stops.
 237 class JvmtiTagMapFlatEntryConverter: public StackObj {
 238 private:
 239   struct Entry {
 240     // source flat value object
 241     Handle holder;
 242     int offset;
 243     InlineKlass* inline_klass;
 244     LayoutKind layout_kind;
 245     // converted heap-allocated object
 246     Handle dst;
 247 
 248     Entry(): holder(), offset(0), inline_klass(nullptr), dst() {}
 249     Entry(Handle holder, int offset, InlineKlass* inline_klass, LayoutKind lk)
 250       : holder(holder), offset(offset), inline_klass(inline_klass), layout_kind(lk), dst() {}
 251   };
 252 
 253   int _batch_size;
 254   GrowableArray<Entry> _entries;
 255   bool _has_error;
 256 
 257 public:
 258   JvmtiTagMapFlatEntryConverter(int batch_size): _batch_size(batch_size), _entries(batch_size, mtServiceability), _has_error(false) { }
 259   ~JvmtiTagMapFlatEntryConverter() {}
 260 
 261   // returns false if there is nothing to convert
 262   bool import_entries(JvmtiFlatTagMapTable* table) {
 263     if (_has_error) {
 264       // stop the process to avoid infinite loop
 265       return false;
 266     }
 267 
 268     class Importer: public JvmtiFlatTagMapKeyClosure {
 269     private:
 270       GrowableArray<Entry>& _entries;
 271       int _batch_size;
 272     public:
 273       Importer(GrowableArray<Entry>& entries, int batch_size): _entries(entries), _batch_size(batch_size) {}
 274 
 275       bool do_entry(JvmtiFlatTagMapKey& key, jlong& tag) {
 276         Entry entry(Handle(Thread::current(), key.holder()), key.offset(), key.inline_klass(), key.layout_kind());
 277         _entries.append(entry);
 278 
 279         return _entries.length() < _batch_size;
 280       }
 281     } importer(_entries, _batch_size);
 282     table->entry_iterate(&importer);
 283 
 284     return !_entries.is_empty();
 285   }
 286 
 287   void convert() {
 288     for (int i = 0; i < _entries.length(); i++) {
 289       EXCEPTION_MARK;
 290       Entry& entry = _entries.at(i);
 291       oop obj = entry.inline_klass->read_payload_from_addr(entry.holder(), entry.offset, entry.layout_kind, JavaThread::current());
 292 
 293       if (HAS_PENDING_EXCEPTION) {
 294         tty->print_cr("Exception in JvmtiTagMapFlatEntryConverter: ");
 295         java_lang_Throwable::print(PENDING_EXCEPTION, tty);
 296         tty->cr();
 297         CLEAR_PENDING_EXCEPTION;
 298         // stop the conversion
 299         _has_error = true;
 300       } else {
 301         entry.dst = Handle(Thread::current(), obj);
 302       }
 303     }
 304   }
 305 
 306   // returns number of converted entries
 307   int move(JvmtiFlatTagMapTable* src_table, JvmtiTagMapTable* dst_table) {
 308     int count = 0;
 309     for (int i = 0; i < _entries.length(); i++) {
 310       Entry& entry = _entries.at(i);
 311       if (entry.dst() == nullptr) {
 312         // some error during conversion, skip the entry
 313         continue;
 314       }
 315       JvmtiHeapwalkObject obj(entry.holder(), entry.offset, entry.inline_klass, entry.layout_kind);
 316       jlong tag = src_table->remove(obj);
 317 
 318       if (tag != 0) { // ensure the entry is still in the src_table
 319         dst_table->add(entry.dst(), tag);
 320         count++;
 321       } else {
 322 
 323       }
 324     }
 325     // and clean the array
 326     _entries.clear();
 327     return count;
 328   }
 329 };
 330 
 331 
 332 void JvmtiTagMap::convert_flat_object_entries() {
 333   Thread* current = Thread::current();
 334   assert(current->is_Java_thread(), "must be executed on JavaThread");
 335 
 336   log_debug(jvmti, table)("convert_flat_object_entries, main table size = %d, flat table size = %d",
 337                           _hashmap->number_of_entries(), _flat_hashmap->number_of_entries());
 338 
 339   {
 340     MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 341     // If another thread is converting, let it finish.
 342     while (_converting_flat_object) {
 343       ml.wait();
 344     }
 345     if (_flat_hashmap->is_empty()) {
 346       // nothing to convert
 347       return;
 348     }
 349     _converting_flat_object = true;
 350   }
 351 
 352   const int BATCH_SIZE = 1024;
 353   JvmtiTagMapFlatEntryConverter converter(BATCH_SIZE);
 354 
 355   int count = 0;
 356   while (true) {
 357     HandleMark hm(current);
 358     {
 359       MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 360       if (!converter.import_entries(_flat_hashmap)) {
 361         break;
 362       }
 363     }
 364     // Convert flat objects to heap-allocated without table lock (so agent callbacks can get/set tags).
 365     converter.convert();
 366     {
 367       MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 368       count += converter.move(_flat_hashmap, _hashmap);
 369     }
 370   }
 371 
 372   log_info(jvmti, table)("%d flat value objects are converted, flat table size = %d",
 373                          count, _flat_hashmap->number_of_entries());
 374   {
 375     MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 376     _converting_flat_object = false;
 377     ml.notify_all();
 378   }
 379 }
 380 
 381 jlong JvmtiTagMap::find(const JvmtiHeapwalkObject& obj) const {
 382   jlong tag = _hashmap->find(obj);
 383   if (tag == 0 && obj.is_value()) {
 384     tag = _flat_hashmap->find(obj);
 385   }
 386   return tag;
 387 }
 388 
 389 void JvmtiTagMap::add(const JvmtiHeapwalkObject& obj, jlong tag) {
 390   if (obj.is_flat()) {
 391     // we may have tag for equal (non-flat) object in _hashmap, try to update it 1st
 392     if (!_hashmap->update(obj, tag)) {
 393       // no entry in _hashmap, add to _flat_hashmap
 394       _flat_hashmap->add(obj, tag);
 395     }
 396   } else {
 397     _hashmap->add(obj, tag);
 398   }
 399 }
 400 
 401 void JvmtiTagMap::remove(const JvmtiHeapwalkObject& obj) {
 402   if (!_hashmap->remove(obj)) {
 403     if (obj.is_value()) {
 404       _flat_hashmap->remove(obj);
 405     }
 406   }
 407 }
 408 
 409 
 410 // A CallbackWrapper is a support class for querying and tagging an object
 411 // around a callback to a profiler. The constructor does pre-callback
 412 // work to get the tag value, klass tag value, ... and the destructor
 413 // does the post-callback work of tagging or untagging the object.
 414 //
 415 // {
 416 //   CallbackWrapper wrapper(tag_map, o);
 417 //
 418 //   (*callback)(wrapper.klass_tag(), wrapper.obj_size(), wrapper.obj_tag_p(), ...)
 419 //
 420 // }
 421 // wrapper goes out of scope here which results in the destructor
 422 // checking to see if the object has been tagged, untagged, or the
 423 // tag value has changed.
 424 //
 425 class CallbackWrapper : public StackObj {
 426  private:
 427   JvmtiTagMap* _tag_map;
 428   const JvmtiHeapwalkObject& _o;
 429   jlong _obj_size;
 430   jlong _obj_tag;
 431   jlong _klass_tag;
 432 
 433  protected:
 434   JvmtiTagMap* tag_map() const { return _tag_map; }
 435 
 436   // invoked post-callback to tag, untag, or update the tag of an object
 437   void inline post_callback_tag_update(const JvmtiHeapwalkObject& o, JvmtiTagMap* tag_map, jlong obj_tag);
 438 
 439  public:
 440   CallbackWrapper(JvmtiTagMap* tag_map, const JvmtiHeapwalkObject& o)
 441     : _tag_map(tag_map), _o(o)
 442   {
 443     assert(Thread::current()->is_VM_thread() || tag_map->is_locked(),
 444            "MT unsafe or must be VM thread");
 445 
 446     // object size
 447     if (!o.is_flat()) {
 448       // common case: we have oop
 449       _obj_size = (jlong)o.obj()->size() * wordSize;
 450     } else {
 451       // flat value object, we know its InstanceKlass
 452       assert(_o.inline_klass() != nullptr, "must be");
 453       _obj_size = _o.inline_klass()->size() * wordSize;;
 454     }
 455 
 456     // get object tag
 457     _obj_tag = _tag_map->find(_o);
 458 
 459     // get the class and the class's tag value
 460     assert(vmClasses::Class_klass()->is_mirror_instance_klass(), "Is not?");
 461 
 462     _klass_tag = _tag_map->find(_o.klass()->java_mirror());
 463   }
 464 
 465   ~CallbackWrapper() {
 466     post_callback_tag_update(_o, _tag_map, _obj_tag);
 467   }
 468 
 469   inline jlong* obj_tag_p()                     { return &_obj_tag; }
 470   inline jlong obj_size() const                 { return _obj_size; }
 471   inline jlong obj_tag() const                  { return _obj_tag; }
 472   inline jlong klass_tag() const                { return _klass_tag; }
 473 };
 474 
 475 // callback post-callback to tag, untag, or update the tag of an object
 476 void inline CallbackWrapper::post_callback_tag_update(const JvmtiHeapwalkObject& o,
 477                                                       JvmtiTagMap* tag_map,
 478                                                       jlong obj_tag) {
 479   if (obj_tag == 0) {
 480     // callback has untagged the object, remove the entry if present
 481     tag_map->remove(o);
 482   } else {
 483     // object was previously tagged or not present - the callback may have
 484     // changed the tag value
 485     assert(Thread::current()->is_VM_thread(), "must be VMThread");
 486     tag_map->add(o, obj_tag);
 487   }
 488 }
 489 
 490 // An extended CallbackWrapper used when reporting an object reference
 491 // to the agent.
 492 //
 493 // {
 494 //   TwoOopCallbackWrapper wrapper(tag_map, referrer, o);
 495 //
 496 //   (*callback)(wrapper.klass_tag(),
 497 //               wrapper.obj_size(),
 498 //               wrapper.obj_tag_p()
 499 //               wrapper.referrer_tag_p(), ...)
 500 //
 501 // }
 502 // wrapper goes out of scope here which results in the destructor
 503 // checking to see if the referrer object has been tagged, untagged,
 504 // or the tag value has changed.
 505 //
 506 class TwoOopCallbackWrapper : public CallbackWrapper {
 507  private:
 508   const JvmtiHeapwalkObject& _referrer;
 509   bool _is_reference_to_self;
 510   jlong _referrer_obj_tag;
 511   jlong _referrer_klass_tag;
 512   jlong* _referrer_tag_p;
 513 
 514   bool is_reference_to_self() const             { return _is_reference_to_self; }
 515 
 516  public:
 517   TwoOopCallbackWrapper(JvmtiTagMap* tag_map, const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& o) :
 518     CallbackWrapper(tag_map, o), _referrer(referrer)
 519   {
 520     // self reference needs to be handled in a special way
 521     _is_reference_to_self = (referrer == o);
 522 
 523     if (_is_reference_to_self) {
 524       _referrer_klass_tag = klass_tag();
 525       _referrer_tag_p = obj_tag_p();
 526     } else {
 527       // get object tag
 528       _referrer_obj_tag = tag_map->find(_referrer);
 529 
 530       _referrer_tag_p = &_referrer_obj_tag;
 531 
 532       // get referrer class tag.
 533       _referrer_klass_tag = tag_map->find(_referrer.klass()->java_mirror());
 534     }
 535   }
 536 
 537   ~TwoOopCallbackWrapper() {
 538     if (!is_reference_to_self()) {
 539       post_callback_tag_update(_referrer,
 540                                tag_map(),
 541                                _referrer_obj_tag);
 542     }
 543   }
 544 
 545   // address of referrer tag
 546   // (for a self reference this will return the same thing as obj_tag_p())
 547   inline jlong* referrer_tag_p() { return _referrer_tag_p; }
 548 
 549   // referrer's class tag
 550   inline jlong referrer_klass_tag() { return _referrer_klass_tag; }
 551 };
 552 
 553 // tag an object
 554 //
 555 // This function is performance critical. If many threads attempt to tag objects
 556 // around the same time then it's possible that the Mutex associated with the
 557 // tag map will be a hot lock.
 558 void JvmtiTagMap::set_tag(jobject object, jlong tag) {
 559   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 560 
 561   // SetTag should not post events because the JavaThread has to
 562   // transition to native for the callback and this cannot stop for
 563   // safepoints with the hashmap lock held.
 564   check_hashmap(nullptr);  /* don't collect dead objects */
 565 
 566   // resolve the object
 567   oop o = JNIHandles::resolve_non_null(object);
 568   // see if the object is already tagged
 569   JvmtiHeapwalkObject obj(o);
 570   if (tag == 0) {
 571     // remove the entry if present
 572     _hashmap->remove(obj);
 573   } else {
 574     // if the object is already tagged or not present then we add/update
 575     // the tag
 576     add(obj, tag);
 577   }
 578 }
 579 
 580 // get the tag for an object
 581 jlong JvmtiTagMap::get_tag(jobject object) {
 582   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
 583 
 584   // GetTag should not post events because the JavaThread has to
 585   // transition to native for the callback and this cannot stop for
 586   // safepoints with the hashmap lock held.
 587   check_hashmap(nullptr); /* don't collect dead objects */
 588 
 589   // resolve the object
 590   oop o = JNIHandles::resolve_non_null(object);
 591 
 592   return find(o);
 593 }
 594 
 595 
 596 // Helper class used to describe the static or instance fields of a class.
 597 // For each field it holds the field index (as defined by the JVMTI specification),
 598 // the field type, and the offset.
 599 
 600 class ClassFieldDescriptor: public CHeapObj<mtInternal> {
 601  private:
 602   int _field_index;
 603   int _field_offset;
 604   char _field_type;
 605   InlineKlass* _inline_klass; // nullptr for heap object
 606   LayoutKind _layout_kind;
 607  public:
 608   ClassFieldDescriptor(int index, const FieldStreamBase& fld) :
 609       _field_index(index), _field_offset(fld.offset()), _field_type(fld.signature()->char_at(0)) {
 610     if (fld.is_flat()) {
 611       const fieldDescriptor& fd = fld.field_descriptor();
 612       InstanceKlass* holder_klass = fd.field_holder();
 613       InlineLayoutInfo* layout_info = holder_klass->inline_layout_info_adr(fd.index());
 614       _inline_klass = layout_info->klass();
 615       _layout_kind = layout_info->kind();
 616     } else {
 617       _inline_klass = nullptr;
 618       _layout_kind = LayoutKind::REFERENCE;
 619     }
 620   }
 621   int field_index()  const  { return _field_index; }
 622   char field_type()  const  { return _field_type; }
 623   int field_offset() const  { return _field_offset; }
 624   bool is_flat()     const  { return _inline_klass != nullptr; }
 625   InlineKlass* inline_klass() const { return _inline_klass; }
 626   LayoutKind layout_kind() const { return _layout_kind; }
 627 };
 628 
 629 class ClassFieldMap: public CHeapObj<mtInternal> {
 630  private:
 631   enum {
 632     initial_field_count = 5
 633   };
 634 
 635   // list of field descriptors
 636   GrowableArray<ClassFieldDescriptor*>* _fields;
 637 
 638   // constructor
 639   ClassFieldMap();
 640 
 641   // calculates number of fields in all interfaces
 642   static int interfaces_field_count(InstanceKlass* ik);
 643 
 644   // add a field
 645   void add(int index, const FieldStreamBase& fld);
 646 
 647  public:
 648   ~ClassFieldMap();
 649 
 650   // access
 651   int field_count()                     { return _fields->length(); }
 652   ClassFieldDescriptor* field_at(int i) { return _fields->at(i); }
 653 
 654   // functions to create maps of static or instance fields
 655   static ClassFieldMap* create_map_of_static_fields(Klass* k);
 656   static ClassFieldMap* create_map_of_instance_fields(Klass* k);
 657 };
 658 
 659 ClassFieldMap::ClassFieldMap() {
 660   _fields = new (mtServiceability)
 661     GrowableArray<ClassFieldDescriptor*>(initial_field_count, mtServiceability);
 662 }
 663 
 664 ClassFieldMap::~ClassFieldMap() {
 665   for (int i=0; i<_fields->length(); i++) {
 666     delete _fields->at(i);
 667   }
 668   delete _fields;
 669 }
 670 
 671 int ClassFieldMap::interfaces_field_count(InstanceKlass* ik) {
 672   const Array<InstanceKlass*>* interfaces = ik->transitive_interfaces();
 673   int count = 0;
 674   for (int i = 0; i < interfaces->length(); i++) {
 675     count += interfaces->at(i)->java_fields_count();
 676 
 677   }
 678   return count;
 679 }
 680 
 681 void ClassFieldMap::add(int index, const FieldStreamBase& fld) {
 682   ClassFieldDescriptor* field = new ClassFieldDescriptor(index, fld);
 683   _fields->append(field);
 684 }
 685 
 686 // Returns a heap allocated ClassFieldMap to describe the static fields
 687 // of the given class.
 688 ClassFieldMap* ClassFieldMap::create_map_of_static_fields(Klass* k) {
 689   InstanceKlass* ik = InstanceKlass::cast(k);
 690 
 691   // create the field map
 692   ClassFieldMap* field_map = new ClassFieldMap();
 693 
 694   // Static fields of interfaces and superclasses are reported as references from the interfaces/superclasses.
 695   // Need to calculate start index of this class fields: number of fields in all interfaces and superclasses.
 696   int index = interfaces_field_count(ik);
 697   for (InstanceKlass* super_klass = ik->super(); super_klass != nullptr; super_klass = super_klass->super()) {
 698     index += super_klass->java_fields_count();
 699   }
 700 
 701   for (JavaFieldStream fld(ik); !fld.done(); fld.next(), index++) {
 702     // ignore instance fields
 703     if (!fld.access_flags().is_static()) {
 704       continue;
 705     }
 706     field_map->add(index, fld);
 707   }
 708 
 709   return field_map;
 710 }
 711 
 712 // Returns a heap allocated ClassFieldMap to describe the instance fields
 713 // of the given class. All instance fields are included (this means public
 714 // and private fields declared in superclasses too).
 715 ClassFieldMap* ClassFieldMap::create_map_of_instance_fields(Klass* k) {
 716   InstanceKlass* ik = InstanceKlass::cast(k);
 717 
 718   // create the field map
 719   ClassFieldMap* field_map = new ClassFieldMap();
 720 
 721   // fields of the superclasses are reported first, so need to know total field number to calculate field indices
 722   int total_field_number = interfaces_field_count(ik);
 723   for (InstanceKlass* klass = ik; klass != nullptr; klass = klass->super()) {
 724     total_field_number += klass->java_fields_count();
 725   }
 726 
 727   for (InstanceKlass* klass = ik; klass != nullptr; klass = klass->super()) {
 728     JavaFieldStream fld(klass);
 729     int start_index = total_field_number - klass->java_fields_count();
 730     for (int index = 0; !fld.done(); fld.next(), index++) {
 731       // ignore static fields
 732       if (fld.access_flags().is_static()) {
 733         continue;
 734       }
 735       field_map->add(start_index + index, fld);
 736     }
 737     // update total_field_number for superclass (decrease by the field count in the current class)
 738     total_field_number = start_index;
 739   }
 740 
 741   return field_map;
 742 }
 743 
 744 // Helper class used to cache a ClassFileMap for the instance fields of
 745 // a cache. A JvmtiCachedClassFieldMap can be cached by an InstanceKlass during
 746 // heap iteration and avoid creating a field map for each object in the heap
 747 // (only need to create the map when the first instance of a class is encountered).
 748 //
 749 class JvmtiCachedClassFieldMap : public CHeapObj<mtInternal> {
 750  private:
 751   enum {
 752      initial_class_count = 200
 753   };
 754   ClassFieldMap* _field_map;
 755 
 756   ClassFieldMap* field_map() const { return _field_map; }
 757 
 758   JvmtiCachedClassFieldMap(ClassFieldMap* field_map);
 759   ~JvmtiCachedClassFieldMap();
 760 
 761   static GrowableArray<InstanceKlass*>* _class_list;
 762   static void add_to_class_list(InstanceKlass* ik);
 763 
 764  public:
 765   // returns the field map for a given klass (returning map cached
 766   // by InstanceKlass if possible
 767   static ClassFieldMap* get_map_of_instance_fields(Klass* k);
 768 
 769   // removes the field map from all instanceKlasses - should be
 770   // called before VM operation completes
 771   static void clear_cache();
 772 
 773   // returns the number of ClassFieldMap cached by instanceKlasses
 774   static int cached_field_map_count();
 775 };
 776 
 777 GrowableArray<InstanceKlass*>* JvmtiCachedClassFieldMap::_class_list;
 778 
 779 JvmtiCachedClassFieldMap::JvmtiCachedClassFieldMap(ClassFieldMap* field_map) {
 780   _field_map = field_map;
 781 }
 782 
 783 JvmtiCachedClassFieldMap::~JvmtiCachedClassFieldMap() {
 784   if (_field_map != nullptr) {
 785     delete _field_map;
 786   }
 787 }
 788 
 789 // Marker class to ensure that the class file map cache is only used in a defined
 790 // scope.
 791 class ClassFieldMapCacheMark : public StackObj {
 792  private:
 793    static bool _is_active;
 794  public:
 795    ClassFieldMapCacheMark() {
 796      assert(Thread::current()->is_VM_thread(), "must be VMThread");
 797      assert(JvmtiCachedClassFieldMap::cached_field_map_count() == 0, "cache not empty");
 798      assert(!_is_active, "ClassFieldMapCacheMark cannot be nested");
 799      _is_active = true;
 800    }
 801    ~ClassFieldMapCacheMark() {
 802      JvmtiCachedClassFieldMap::clear_cache();
 803      _is_active = false;
 804    }
 805    static bool is_active() { return _is_active; }
 806 };
 807 
 808 bool ClassFieldMapCacheMark::_is_active;
 809 
 810 // record that the given InstanceKlass is caching a field map
 811 void JvmtiCachedClassFieldMap::add_to_class_list(InstanceKlass* ik) {
 812   if (_class_list == nullptr) {
 813     _class_list = new (mtServiceability)
 814       GrowableArray<InstanceKlass*>(initial_class_count, mtServiceability);
 815   }
 816   _class_list->push(ik);
 817 }
 818 
 819 // returns the instance field map for the given klass
 820 // (returns field map cached by the InstanceKlass if possible)
 821 ClassFieldMap* JvmtiCachedClassFieldMap::get_map_of_instance_fields(Klass *k) {
 822   assert(Thread::current()->is_VM_thread(), "must be VMThread");
 823   assert(ClassFieldMapCacheMark::is_active(), "ClassFieldMapCacheMark not active");
 824 
 825   InstanceKlass* ik = InstanceKlass::cast(k);
 826 
 827   // return cached map if possible
 828   JvmtiCachedClassFieldMap* cached_map = ik->jvmti_cached_class_field_map();
 829   if (cached_map != nullptr) {
 830     assert(cached_map->field_map() != nullptr, "missing field list");
 831     return cached_map->field_map();
 832   } else {
 833     ClassFieldMap* field_map = ClassFieldMap::create_map_of_instance_fields(k);
 834     cached_map = new JvmtiCachedClassFieldMap(field_map);
 835     ik->set_jvmti_cached_class_field_map(cached_map);
 836     add_to_class_list(ik);
 837     return field_map;
 838   }
 839 }
 840 
 841 // remove the fields maps cached from all instanceKlasses
 842 void JvmtiCachedClassFieldMap::clear_cache() {
 843   assert(Thread::current()->is_VM_thread(), "must be VMThread");
 844   if (_class_list != nullptr) {
 845     for (int i = 0; i < _class_list->length(); i++) {
 846       InstanceKlass* ik = _class_list->at(i);
 847       JvmtiCachedClassFieldMap* cached_map = ik->jvmti_cached_class_field_map();
 848       assert(cached_map != nullptr, "should not be null");
 849       ik->set_jvmti_cached_class_field_map(nullptr);
 850       delete cached_map;  // deletes the encapsulated field map
 851     }
 852     delete _class_list;
 853     _class_list = nullptr;
 854   }
 855 }
 856 
 857 // returns the number of ClassFieldMap cached by instanceKlasses
 858 int JvmtiCachedClassFieldMap::cached_field_map_count() {
 859   return (_class_list == nullptr) ? 0 : _class_list->length();
 860 }
 861 
 862 // helper function to indicate if an object is filtered by its tag or class tag
 863 static inline bool is_filtered_by_heap_filter(jlong obj_tag,
 864                                               jlong klass_tag,
 865                                               int heap_filter) {
 866   // apply the heap filter
 867   if (obj_tag != 0) {
 868     // filter out tagged objects
 869     if (heap_filter & JVMTI_HEAP_FILTER_TAGGED) return true;
 870   } else {
 871     // filter out untagged objects
 872     if (heap_filter & JVMTI_HEAP_FILTER_UNTAGGED) return true;
 873   }
 874   if (klass_tag != 0) {
 875     // filter out objects with tagged classes
 876     if (heap_filter & JVMTI_HEAP_FILTER_CLASS_TAGGED) return true;
 877   } else {
 878     // filter out objects with untagged classes.
 879     if (heap_filter & JVMTI_HEAP_FILTER_CLASS_UNTAGGED) return true;
 880   }
 881   return false;
 882 }
 883 
 884 // helper function to indicate if an object is filtered by a klass filter
 885 static inline bool is_filtered_by_klass_filter(const JvmtiHeapwalkObject& obj, Klass* klass_filter) {
 886   if (klass_filter != nullptr) {
 887     if (obj.klass() != klass_filter) {
 888       return true;
 889     }
 890   }
 891   return false;
 892 }
 893 
 894 // helper function to tell if a field is a primitive field or not
 895 static inline bool is_primitive_field_type(char type) {
 896   return (type != JVM_SIGNATURE_CLASS && type != JVM_SIGNATURE_ARRAY);
 897 }
 898 
 899 // helper function to copy the value from location addr to jvalue.
 900 static inline void copy_to_jvalue(jvalue *v, address addr, jvmtiPrimitiveType value_type) {
 901   switch (value_type) {
 902     case JVMTI_PRIMITIVE_TYPE_BOOLEAN : { v->z = *(jboolean*)addr; break; }
 903     case JVMTI_PRIMITIVE_TYPE_BYTE    : { v->b = *(jbyte*)addr;    break; }
 904     case JVMTI_PRIMITIVE_TYPE_CHAR    : { v->c = *(jchar*)addr;    break; }
 905     case JVMTI_PRIMITIVE_TYPE_SHORT   : { v->s = *(jshort*)addr;   break; }
 906     case JVMTI_PRIMITIVE_TYPE_INT     : { v->i = *(jint*)addr;     break; }
 907     case JVMTI_PRIMITIVE_TYPE_LONG    : { v->j = *(jlong*)addr;    break; }
 908     case JVMTI_PRIMITIVE_TYPE_FLOAT   : { v->f = *(jfloat*)addr;   break; }
 909     case JVMTI_PRIMITIVE_TYPE_DOUBLE  : { v->d = *(jdouble*)addr;  break; }
 910     default: ShouldNotReachHere();
 911   }
 912 }
 913 
 914 // helper function to invoke string primitive value callback
 915 // returns visit control flags
 916 static jint invoke_string_value_callback(jvmtiStringPrimitiveValueCallback cb,
 917                                          CallbackWrapper* wrapper,
 918                                          const JvmtiHeapwalkObject& obj,
 919                                          void* user_data)
 920 {
 921   assert(!obj.is_flat(), "cannot be flat");
 922   oop str = obj.obj();
 923   assert(str->klass() == vmClasses::String_klass(), "not a string");
 924 
 925   typeArrayOop s_value = java_lang_String::value(str);
 926 
 927   // JDK-6584008: the value field may be null if a String instance is
 928   // partially constructed.
 929   if (s_value == nullptr) {
 930     return 0;
 931   }
 932   // get the string value and length
 933   // (string value may be offset from the base)
 934   int s_len = java_lang_String::length(str);
 935   bool is_latin1 = java_lang_String::is_latin1(str);
 936   jchar* value;
 937   if (s_len > 0) {
 938     if (!is_latin1) {
 939       value = s_value->char_at_addr(0);
 940     } else {
 941       // Inflate latin1 encoded string to UTF16
 942       jchar* buf = NEW_C_HEAP_ARRAY(jchar, s_len, mtInternal);
 943       for (int i = 0; i < s_len; i++) {
 944         buf[i] = ((jchar) s_value->byte_at(i)) & 0xff;
 945       }
 946       value = &buf[0];
 947     }
 948   } else {
 949     // Don't use char_at_addr(0) if length is 0
 950     value = (jchar*) s_value->base(T_CHAR);
 951   }
 952 
 953   // invoke the callback
 954   jint res = (*cb)(wrapper->klass_tag(),
 955                    wrapper->obj_size(),
 956                    wrapper->obj_tag_p(),
 957                    value,
 958                    (jint)s_len,
 959                    user_data);
 960 
 961   if (is_latin1 && s_len > 0) {
 962     FREE_C_HEAP_ARRAY(jchar, value);
 963   }
 964   return res;
 965 }
 966 
 967 // helper function to invoke string primitive value callback
 968 // returns visit control flags
 969 static jint invoke_array_primitive_value_callback(jvmtiArrayPrimitiveValueCallback cb,
 970                                                   CallbackWrapper* wrapper,
 971                                                   const JvmtiHeapwalkObject& obj,
 972                                                   void* user_data)
 973 {
 974   assert(!obj.is_flat(), "cannot be flat");
 975   assert(obj.obj()->is_typeArray(), "not a primitive array");
 976 
 977   // get base address of first element
 978   typeArrayOop array = typeArrayOop(obj.obj());
 979   BasicType type = TypeArrayKlass::cast(array->klass())->element_type();
 980   void* elements = array->base(type);
 981 
 982   // jvmtiPrimitiveType is defined so this mapping is always correct
 983   jvmtiPrimitiveType elem_type = (jvmtiPrimitiveType)type2char(type);
 984 
 985   return (*cb)(wrapper->klass_tag(),
 986                wrapper->obj_size(),
 987                wrapper->obj_tag_p(),
 988                (jint)array->length(),
 989                elem_type,
 990                elements,
 991                user_data);
 992 }
 993 
 994 // helper function to invoke the primitive field callback for all static fields
 995 // of a given class
 996 static jint invoke_primitive_field_callback_for_static_fields
 997   (CallbackWrapper* wrapper,
 998    oop obj,
 999    jvmtiPrimitiveFieldCallback cb,
1000    void* user_data)
1001 {
1002   // for static fields only the index will be set
1003   static jvmtiHeapReferenceInfo reference_info = { 0 };
1004 
1005   assert(obj->klass() == vmClasses::Class_klass(), "not a class");
1006   if (java_lang_Class::is_primitive(obj)) {
1007     return 0;
1008   }
1009   Klass* klass = java_lang_Class::as_Klass(obj);
1010 
1011   // ignore classes for object and type arrays
1012   if (!klass->is_instance_klass()) {
1013     return 0;
1014   }
1015 
1016   // ignore classes which aren't linked yet
1017   InstanceKlass* ik = InstanceKlass::cast(klass);
1018   if (!ik->is_linked()) {
1019     return 0;
1020   }
1021 
1022   // get the field map
1023   ClassFieldMap* field_map = ClassFieldMap::create_map_of_static_fields(klass);
1024 
1025   // invoke the callback for each static primitive field
1026   for (int i=0; i<field_map->field_count(); i++) {
1027     ClassFieldDescriptor* field = field_map->field_at(i);
1028 
1029     // ignore non-primitive fields
1030     char type = field->field_type();
1031     if (!is_primitive_field_type(type)) {
1032       continue;
1033     }
1034     // one-to-one mapping
1035     jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
1036 
1037     // get offset and field value
1038     int offset = field->field_offset();
1039     address addr = cast_from_oop<address>(klass->java_mirror()) + offset;
1040     jvalue value;
1041     copy_to_jvalue(&value, addr, value_type);
1042 
1043     // field index
1044     reference_info.field.index = field->field_index();
1045 
1046     // invoke the callback
1047     jint res = (*cb)(JVMTI_HEAP_REFERENCE_STATIC_FIELD,
1048                      &reference_info,
1049                      wrapper->klass_tag(),
1050                      wrapper->obj_tag_p(),
1051                      value,
1052                      value_type,
1053                      user_data);
1054     if (res & JVMTI_VISIT_ABORT) {
1055       delete field_map;
1056       return res;
1057     }
1058   }
1059 
1060   delete field_map;
1061   return 0;
1062 }
1063 
1064 // helper function to invoke the primitive field callback for all instance fields
1065 // of a given object
1066 static jint invoke_primitive_field_callback_for_instance_fields(
1067   CallbackWrapper* wrapper,
1068   const JvmtiHeapwalkObject& obj,
1069   jvmtiPrimitiveFieldCallback cb,
1070   void* user_data)
1071 {
1072   // for instance fields only the index will be set
1073   static jvmtiHeapReferenceInfo reference_info = { 0 };
1074 
1075   // get the map of the instance fields
1076   ClassFieldMap* fields = JvmtiCachedClassFieldMap::get_map_of_instance_fields(obj.klass());
1077 
1078   // invoke the callback for each instance primitive field
1079   for (int i=0; i<fields->field_count(); i++) {
1080     ClassFieldDescriptor* field = fields->field_at(i);
1081 
1082     // ignore non-primitive fields
1083     char type = field->field_type();
1084     if (!is_primitive_field_type(type)) {
1085       continue;
1086     }
1087     // one-to-one mapping
1088     jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
1089 
1090     // get field value
1091     address addr = cast_from_oop<address>(obj.obj()) + obj.offset() + field->field_offset();
1092     jvalue value;
1093     copy_to_jvalue(&value, addr, value_type);
1094 
1095     // field index
1096     reference_info.field.index = field->field_index();
1097 
1098     // invoke the callback
1099     jint res = (*cb)(JVMTI_HEAP_REFERENCE_FIELD,
1100                      &reference_info,
1101                      wrapper->klass_tag(),
1102                      wrapper->obj_tag_p(),
1103                      value,
1104                      value_type,
1105                      user_data);
1106     if (res & JVMTI_VISIT_ABORT) {
1107       return res;
1108     }
1109   }
1110   return 0;
1111 }
1112 
1113 
1114 // VM operation to iterate over all objects in the heap (both reachable
1115 // and unreachable)
1116 class VM_HeapIterateOperation: public VM_Operation {
1117  private:
1118   ObjectClosure* _blk;
1119   GrowableArray<jlong>* const _dead_objects;
1120  public:
1121   VM_HeapIterateOperation(ObjectClosure* blk, GrowableArray<jlong>* objects) :
1122     _blk(blk), _dead_objects(objects) { }
1123 
1124   VMOp_Type type() const { return VMOp_HeapIterateOperation; }
1125   void doit() {
1126     // allows class files maps to be cached during iteration
1127     ClassFieldMapCacheMark cm;
1128 
1129     JvmtiTagMap::check_hashmaps_for_heapwalk(_dead_objects);
1130 
1131     // make sure that heap is parsable (fills TLABs with filler objects)
1132     Universe::heap()->ensure_parsability(false);  // no need to retire TLABs
1133 
1134     // Verify heap before iteration - if the heap gets corrupted then
1135     // JVMTI's IterateOverHeap will crash.
1136     if (VerifyBeforeIteration) {
1137       Universe::verify();
1138     }
1139 
1140     // do the iteration
1141     Universe::heap()->object_iterate(_blk);
1142   }
1143 };
1144 
1145 
1146 // An ObjectClosure used to support the deprecated IterateOverHeap and
1147 // IterateOverInstancesOfClass functions
1148 class IterateOverHeapObjectClosure: public ObjectClosure {
1149  private:
1150   JvmtiTagMap* _tag_map;
1151   Klass* _klass;
1152   jvmtiHeapObjectFilter _object_filter;
1153   jvmtiHeapObjectCallback _heap_object_callback;
1154   const void* _user_data;
1155 
1156   // accessors
1157   JvmtiTagMap* tag_map() const                    { return _tag_map; }
1158   jvmtiHeapObjectFilter object_filter() const     { return _object_filter; }
1159   jvmtiHeapObjectCallback object_callback() const { return _heap_object_callback; }
1160   Klass* klass() const                            { return _klass; }
1161   const void* user_data() const                   { return _user_data; }
1162 
1163   // indicates if iteration has been aborted
1164   bool _iteration_aborted;
1165   bool is_iteration_aborted() const               { return _iteration_aborted; }
1166   void set_iteration_aborted(bool aborted)        { _iteration_aborted = aborted; }
1167 
1168  public:
1169   IterateOverHeapObjectClosure(JvmtiTagMap* tag_map,
1170                                Klass* klass,
1171                                jvmtiHeapObjectFilter object_filter,
1172                                jvmtiHeapObjectCallback heap_object_callback,
1173                                const void* user_data) :
1174     _tag_map(tag_map),
1175     _klass(klass),
1176     _object_filter(object_filter),
1177     _heap_object_callback(heap_object_callback),
1178     _user_data(user_data),
1179     _iteration_aborted(false)
1180   {
1181   }
1182 
1183   void do_object(oop o);
1184 };
1185 
1186 // invoked for each object in the heap
1187 void IterateOverHeapObjectClosure::do_object(oop o) {
1188   assert(o != nullptr, "Heap iteration should never produce null!");
1189   // check if iteration has been halted
1190   if (is_iteration_aborted()) return;
1191 
1192   // instanceof check when filtering by klass
1193   if (klass() != nullptr && !o->is_a(klass())) {
1194     return;
1195   }
1196 
1197   // skip if object is a dormant shared object whose mirror hasn't been loaded
1198   if (o->klass()->java_mirror() == nullptr) {
1199     log_debug(aot, heap)("skipped dormant archived object " INTPTR_FORMAT " (%s)", p2i(o),
1200                          o->klass()->external_name());
1201     return;
1202   }
1203 
1204   // prepare for the calllback
1205   JvmtiHeapwalkObject wrapper_obj(o);
1206   CallbackWrapper wrapper(tag_map(), wrapper_obj);
1207 
1208   // if the object is tagged and we're only interested in untagged objects
1209   // then don't invoke the callback. Similarly, if the object is untagged
1210   // and we're only interested in tagged objects we skip the callback.
1211   if (wrapper.obj_tag() != 0) {
1212     if (object_filter() == JVMTI_HEAP_OBJECT_UNTAGGED) return;
1213   } else {
1214     if (object_filter() == JVMTI_HEAP_OBJECT_TAGGED) return;
1215   }
1216 
1217   // invoke the agent's callback
1218   jvmtiIterationControl control = (*object_callback())(wrapper.klass_tag(),
1219                                                        wrapper.obj_size(),
1220                                                        wrapper.obj_tag_p(),
1221                                                        (void*)user_data());
1222   if (control == JVMTI_ITERATION_ABORT) {
1223     set_iteration_aborted(true);
1224   }
1225 }
1226 
1227 // An ObjectClosure used to support the IterateThroughHeap function
1228 class IterateThroughHeapObjectClosure: public ObjectClosure {
1229  private:
1230   JvmtiTagMap* _tag_map;
1231   Klass* _klass;
1232   int _heap_filter;
1233   const jvmtiHeapCallbacks* _callbacks;
1234   const void* _user_data;
1235 
1236   // accessor functions
1237   JvmtiTagMap* tag_map() const                     { return _tag_map; }
1238   int heap_filter() const                          { return _heap_filter; }
1239   const jvmtiHeapCallbacks* callbacks() const      { return _callbacks; }
1240   Klass* klass() const                             { return _klass; }
1241   const void* user_data() const                    { return _user_data; }
1242 
1243   // indicates if the iteration has been aborted
1244   bool _iteration_aborted;
1245   bool is_iteration_aborted() const                { return _iteration_aborted; }
1246 
1247   // used to check the visit control flags. If the abort flag is set
1248   // then we set the iteration aborted flag so that the iteration completes
1249   // without processing any further objects
1250   bool check_flags_for_abort(jint flags) {
1251     bool is_abort = (flags & JVMTI_VISIT_ABORT) != 0;
1252     if (is_abort) {
1253       _iteration_aborted = true;
1254     }
1255     return is_abort;
1256   }
1257 
1258   void visit_object(const JvmtiHeapwalkObject& obj);
1259   void visit_flat_fields(const JvmtiHeapwalkObject& obj);
1260   void visit_flat_array_elements(const JvmtiHeapwalkObject& obj);
1261 
1262  public:
1263   IterateThroughHeapObjectClosure(JvmtiTagMap* tag_map,
1264                                   Klass* klass,
1265                                   int heap_filter,
1266                                   const jvmtiHeapCallbacks* heap_callbacks,
1267                                   const void* user_data) :
1268     _tag_map(tag_map),
1269     _klass(klass),
1270     _heap_filter(heap_filter),
1271     _callbacks(heap_callbacks),
1272     _user_data(user_data),
1273     _iteration_aborted(false)
1274   {
1275   }
1276 
1277   void do_object(oop obj);
1278 };
1279 
1280 // invoked for each object in the heap
1281 void IterateThroughHeapObjectClosure::do_object(oop obj) {
1282   assert(obj != nullptr, "Heap iteration should never produce null!");
1283   // check if iteration has been halted
1284   if (is_iteration_aborted()) return;
1285 
1286   // skip if object is a dormant shared object whose mirror hasn't been loaded
1287   if (obj != nullptr && obj->klass()->java_mirror() == nullptr) {
1288     log_debug(aot, heap)("skipped dormant archived object " INTPTR_FORMAT " (%s)", p2i(obj),
1289                          obj->klass()->external_name());
1290     return;
1291   }
1292 
1293   visit_object(obj);
1294 }
1295 
1296 void IterateThroughHeapObjectClosure::visit_object(const JvmtiHeapwalkObject& obj) {
1297   // apply class filter
1298   if (is_filtered_by_klass_filter(obj, klass())) return;
1299 
1300   // prepare for callback
1301   CallbackWrapper wrapper(tag_map(), obj);
1302 
1303   // check if filtered by the heap filter
1304   if (is_filtered_by_heap_filter(wrapper.obj_tag(), wrapper.klass_tag(), heap_filter())) {
1305     return;
1306   }
1307 
1308   // for arrays we need the length, otherwise -1
1309   bool is_array = obj.klass()->is_array_klass();
1310   int len = is_array ? arrayOop(obj.obj())->length() : -1;
1311 
1312   // invoke the object callback (if callback is provided)
1313   if (callbacks()->heap_iteration_callback != nullptr) {
1314     jvmtiHeapIterationCallback cb = callbacks()->heap_iteration_callback;
1315     jint res = (*cb)(wrapper.klass_tag(),
1316                      wrapper.obj_size(),
1317                      wrapper.obj_tag_p(),
1318                      (jint)len,
1319                      (void*)user_data());
1320     if (check_flags_for_abort(res)) return;
1321   }
1322 
1323   // for objects and classes we report primitive fields if callback provided
1324   if (callbacks()->primitive_field_callback != nullptr && obj.klass()->is_instance_klass()) {
1325     jint res;
1326     jvmtiPrimitiveFieldCallback cb = callbacks()->primitive_field_callback;
1327     if (obj.klass() == vmClasses::Class_klass()) {
1328       assert(!obj.is_flat(), "Class object cannot be flattened");
1329       res = invoke_primitive_field_callback_for_static_fields(&wrapper,
1330                                                               obj.obj(),
1331                                                               cb,
1332                                                               (void*)user_data());
1333     } else {
1334       res = invoke_primitive_field_callback_for_instance_fields(&wrapper,
1335                                                                 obj,
1336                                                                 cb,
1337                                                                 (void*)user_data());
1338     }
1339     if (check_flags_for_abort(res)) return;
1340   }
1341 
1342   // string callback
1343   if (!is_array &&
1344       callbacks()->string_primitive_value_callback != nullptr &&
1345       obj.klass() == vmClasses::String_klass()) {
1346     jint res = invoke_string_value_callback(
1347                 callbacks()->string_primitive_value_callback,
1348                 &wrapper,
1349                 obj,
1350                 (void*)user_data());
1351     if (check_flags_for_abort(res)) return;
1352   }
1353 
1354   // array callback
1355   if (is_array &&
1356       callbacks()->array_primitive_value_callback != nullptr &&
1357       obj.klass()->is_typeArray_klass()) {
1358     jint res = invoke_array_primitive_value_callback(
1359                callbacks()->array_primitive_value_callback,
1360                &wrapper,
1361                obj,
1362                (void*)user_data());
1363     if (check_flags_for_abort(res)) return;
1364   }
1365 
1366   // All info for the object is reported.
1367 
1368   // If the object has flat fields, report them as heap objects.
1369   if (obj.klass()->is_instance_klass()) {
1370     if (InstanceKlass::cast(obj.klass())->has_inline_type_fields()) {
1371       visit_flat_fields(obj);
1372       // check if iteration has been halted
1373       if (is_iteration_aborted()) {
1374         return;
1375       }
1376     }
1377   }
1378   // If the object is flat array, report all elements as heap objects.
1379   if (is_array && obj.obj()->is_flatArray()) {
1380     assert(!obj.is_flat(), "Array object cannot be flattened");
1381     visit_flat_array_elements(obj);
1382   }
1383 }
1384 
1385 void IterateThroughHeapObjectClosure::visit_flat_fields(const JvmtiHeapwalkObject& obj) {
1386   // iterate over instance fields
1387   ClassFieldMap* fields = JvmtiCachedClassFieldMap::get_map_of_instance_fields(obj.klass());
1388   for (int i = 0; i < fields->field_count(); i++) {
1389     ClassFieldDescriptor* field = fields->field_at(i);
1390     // skip non-flat and (for safety) primitive fields
1391     if (!field->is_flat() || is_primitive_field_type(field->field_type())) {
1392       continue;
1393     }
1394 
1395     int field_offset = field->field_offset();
1396     if (obj.is_flat()) {
1397       // the object is inlined, its fields are stored without the header
1398       field_offset += obj.offset() - obj.inline_klass()->payload_offset();
1399     }
1400     // check for possible nulls
1401     bool can_be_null = field->layout_kind() == LayoutKind::NULLABLE_ATOMIC_FLAT;
1402     if (can_be_null) {
1403       address payload = cast_from_oop<address>(obj.obj()) + field_offset;
1404       if (field->inline_klass()->is_payload_marked_as_null(payload)) {
1405         continue;
1406       }
1407     }
1408     JvmtiHeapwalkObject field_obj(obj.obj(), field_offset, field->inline_klass(), field->layout_kind());
1409 
1410     visit_object(field_obj);
1411 
1412     // check if iteration has been halted
1413     if (is_iteration_aborted()) {
1414       return;
1415     }
1416   }
1417 }
1418 
1419 void IterateThroughHeapObjectClosure::visit_flat_array_elements(const JvmtiHeapwalkObject& obj) {
1420   assert(!obj.is_flat() && obj.obj()->is_flatArray() , "sanity check");
1421   flatArrayOop array = flatArrayOop(obj.obj());
1422   FlatArrayKlass* faklass = FlatArrayKlass::cast(array->klass());
1423   InlineKlass* vk = InlineKlass::cast(faklass->element_klass());
1424   bool need_null_check = faklass->layout_kind() == LayoutKind::NULLABLE_ATOMIC_FLAT;
1425 
1426   for (int index = 0; index < array->length(); index++) {
1427     address addr = (address)array->value_at_addr(index, faklass->layout_helper());
1428     // check for null
1429     if (need_null_check) {
1430       if (vk->is_payload_marked_as_null(addr)) {
1431         continue;
1432       }
1433     }
1434 
1435     // offset in the array oop
1436     int offset = (int)(addr - cast_from_oop<address>(array));
1437     JvmtiHeapwalkObject elem(obj.obj(), offset, vk, faklass->layout_kind());
1438 
1439     visit_object(elem);
1440 
1441     // check if iteration has been halted
1442     if (is_iteration_aborted()) {
1443       return;
1444     }
1445   }
1446 }
1447 
1448 // Deprecated function to iterate over all objects in the heap
1449 void JvmtiTagMap::iterate_over_heap(jvmtiHeapObjectFilter object_filter,
1450                                     Klass* klass,
1451                                     jvmtiHeapObjectCallback heap_object_callback,
1452                                     const void* user_data)
1453 {
1454   // EA based optimizations on tagged objects are already reverted.
1455   EscapeBarrier eb(object_filter == JVMTI_HEAP_OBJECT_UNTAGGED ||
1456                    object_filter == JVMTI_HEAP_OBJECT_EITHER,
1457                    JavaThread::current());
1458   eb.deoptimize_objects_all_threads();
1459   Arena dead_object_arena(mtServiceability);
1460   GrowableArray <jlong> dead_objects(&dead_object_arena, 10, 0, 0);
1461   {
1462     MutexLocker ml(Heap_lock);
1463     IterateOverHeapObjectClosure blk(this,
1464                                      klass,
1465                                      object_filter,
1466                                      heap_object_callback,
1467                                      user_data);
1468     VM_HeapIterateOperation op(&blk, &dead_objects);
1469     VMThread::execute(&op);
1470   }
1471   convert_flat_object_entries();
1472 
1473   // Post events outside of Heap_lock
1474   post_dead_objects(&dead_objects);
1475 }
1476 
1477 
1478 // Iterates over all objects in the heap
1479 void JvmtiTagMap::iterate_through_heap(jint heap_filter,
1480                                        Klass* klass,
1481                                        const jvmtiHeapCallbacks* callbacks,
1482                                        const void* user_data)
1483 {
1484   // EA based optimizations on tagged objects are already reverted.
1485   EscapeBarrier eb(!(heap_filter & JVMTI_HEAP_FILTER_UNTAGGED), JavaThread::current());
1486   eb.deoptimize_objects_all_threads();
1487 
1488   Arena dead_object_arena(mtServiceability);
1489   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
1490   {
1491     MutexLocker ml(Heap_lock);
1492     IterateThroughHeapObjectClosure blk(this,
1493                                         klass,
1494                                         heap_filter,
1495                                         callbacks,
1496                                         user_data);
1497     VM_HeapIterateOperation op(&blk, &dead_objects);
1498     VMThread::execute(&op);
1499   }
1500   convert_flat_object_entries();
1501 
1502   // Post events outside of Heap_lock
1503   post_dead_objects(&dead_objects);
1504 }
1505 
1506 void JvmtiTagMap::remove_dead_entries_locked(GrowableArray<jlong>* objects) {
1507   assert(is_locked(), "precondition");
1508   if (_needs_cleaning) {
1509     // Recheck whether to post object free events under the lock.
1510     if (!env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
1511       objects = nullptr;
1512     }
1513     log_info(jvmti, table)("TagMap table needs cleaning%s",
1514                            ((objects != nullptr) ? " and posting" : ""));
1515     _hashmap->remove_dead_entries(objects);
1516     _needs_cleaning = false;
1517   }
1518 }
1519 
1520 void JvmtiTagMap::remove_dead_entries(GrowableArray<jlong>* objects) {
1521   MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1522   remove_dead_entries_locked(objects);
1523 }
1524 
1525 void JvmtiTagMap::post_dead_objects(GrowableArray<jlong>* const objects) {
1526   assert(Thread::current()->is_Java_thread(), "Must post from JavaThread");
1527   if (objects != nullptr && objects->length() > 0) {
1528     JvmtiExport::post_object_free(env(), objects);
1529     log_info(jvmti, table)("%d free object posted", objects->length());
1530   }
1531 }
1532 
1533 void JvmtiTagMap::remove_and_post_dead_objects() {
1534   ResourceMark rm;
1535   GrowableArray<jlong> objects;
1536   remove_dead_entries(&objects);
1537   post_dead_objects(&objects);
1538 }
1539 
1540 void JvmtiTagMap::flush_object_free_events() {
1541   assert_not_at_safepoint();
1542   if (env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
1543     {
1544       MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1545       // If another thread is posting events, let it finish
1546       while (_posting_events) {
1547         ml.wait();
1548       }
1549 
1550       if (!_needs_cleaning || is_empty()) {
1551         _needs_cleaning = false;
1552         return;
1553       }
1554       _posting_events = true;
1555     } // Drop the lock so we can do the cleaning on the VM thread.
1556     // Needs both cleaning and event posting (up to some other thread
1557     // getting there first after we dropped the lock).
1558     remove_and_post_dead_objects();
1559     {
1560       MonitorLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1561       _posting_events = false;
1562       ml.notify_all();
1563     }
1564   } else {
1565     remove_dead_entries(nullptr);
1566   }
1567 }
1568 
1569 // support class for get_objects_with_tags
1570 
1571 class TagObjectCollector : public JvmtiTagMapKeyClosure {
1572  private:
1573   JvmtiEnv* _env;
1574   JavaThread* _thread;
1575   jlong* _tags;
1576   jint _tag_count;
1577   bool _some_dead_found;
1578 
1579   GrowableArray<jobject>* _object_results;  // collected objects (JNI weak refs)
1580   GrowableArray<uint64_t>* _tag_results;    // collected tags
1581 
1582  public:
1583   TagObjectCollector(JvmtiEnv* env, const jlong* tags, jint tag_count) :
1584     _env(env),
1585     _thread(JavaThread::current()),
1586     _tags((jlong*)tags),
1587     _tag_count(tag_count),
1588     _some_dead_found(false),
1589     _object_results(new (mtServiceability) GrowableArray<jobject>(1, mtServiceability)),
1590     _tag_results(new (mtServiceability) GrowableArray<uint64_t>(1, mtServiceability)) { }
1591 
1592   ~TagObjectCollector() {
1593     delete _object_results;
1594     delete _tag_results;
1595   }
1596 
1597   bool some_dead_found() const { return _some_dead_found; }
1598 
1599   // for each tagged object check if the tag value matches
1600   // - if it matches then we create a JNI local reference to the object
1601   // and record the reference and tag value.
1602   // Always return true so the iteration continues.
1603   bool do_entry(JvmtiTagMapKey& key, jlong& value) {
1604     for (int i = 0; i < _tag_count; i++) {
1605       if (_tags[i] == value) {
1606         // The reference in this tag map could be the only (implicitly weak)
1607         // reference to that object. If we hand it out, we need to keep it live wrt
1608         // SATB marking similar to other j.l.ref.Reference referents. This is
1609         // achieved by using a phantom load in the object() accessor.
1610         oop o = key.object();
1611         if (o == nullptr) {
1612           _some_dead_found = true;
1613           // skip this whole entry
1614           return true;
1615         }
1616         assert(o != nullptr && Universe::heap()->is_in(o), "sanity check");
1617         jobject ref = JNIHandles::make_local(_thread, o);
1618         _object_results->append(ref);
1619         _tag_results->append(value);
1620       }
1621     }
1622     return true;
1623   }
1624 
1625   // return the results from the collection
1626   //
1627   jvmtiError result(jint* count_ptr, jobject** object_result_ptr, jlong** tag_result_ptr) {
1628     jvmtiError error;
1629     int count = _object_results->length();
1630     assert(count >= 0, "sanity check");
1631 
1632     // if object_result_ptr is not null then allocate the result and copy
1633     // in the object references.
1634     if (object_result_ptr != nullptr) {
1635       error = _env->Allocate(count * sizeof(jobject), (unsigned char**)object_result_ptr);
1636       if (error != JVMTI_ERROR_NONE) {
1637         return error;
1638       }
1639       for (int i=0; i<count; i++) {
1640         (*object_result_ptr)[i] = _object_results->at(i);
1641       }
1642     }
1643 
1644     // if tag_result_ptr is not null then allocate the result and copy
1645     // in the tag values.
1646     if (tag_result_ptr != nullptr) {
1647       error = _env->Allocate(count * sizeof(jlong), (unsigned char**)tag_result_ptr);
1648       if (error != JVMTI_ERROR_NONE) {
1649         if (object_result_ptr != nullptr) {
1650           _env->Deallocate((unsigned char*)object_result_ptr);
1651         }
1652         return error;
1653       }
1654       for (int i=0; i<count; i++) {
1655         (*tag_result_ptr)[i] = (jlong)_tag_results->at(i);
1656       }
1657     }
1658 
1659     *count_ptr = count;
1660     return JVMTI_ERROR_NONE;
1661   }
1662 };
1663 
1664 // return the list of objects with the specified tags
1665 jvmtiError JvmtiTagMap::get_objects_with_tags(const jlong* tags,
1666   jint count, jint* count_ptr, jobject** object_result_ptr, jlong** tag_result_ptr) {
1667 
1668   // ensure flat object conversion is completed
1669   convert_flat_object_entries();
1670 
1671   TagObjectCollector collector(env(), tags, count);
1672   {
1673     // iterate over all tagged objects
1674     MutexLocker ml(lock(), Mutex::_no_safepoint_check_flag);
1675     // Can't post ObjectFree events here from a JavaThread, so this
1676     // will race with the gc_notification thread in the tiny
1677     // window where the object is not marked but hasn't been notified that
1678     // it is collected yet.
1679     _hashmap->entry_iterate(&collector);
1680   }
1681   return collector.result(count_ptr, object_result_ptr, tag_result_ptr);
1682 }
1683 
1684 // helper to map a jvmtiHeapReferenceKind to an old style jvmtiHeapRootKind
1685 // (not performance critical as only used for roots)
1686 static jvmtiHeapRootKind toJvmtiHeapRootKind(jvmtiHeapReferenceKind kind) {
1687   switch (kind) {
1688     case JVMTI_HEAP_REFERENCE_JNI_GLOBAL:   return JVMTI_HEAP_ROOT_JNI_GLOBAL;
1689     case JVMTI_HEAP_REFERENCE_SYSTEM_CLASS: return JVMTI_HEAP_ROOT_SYSTEM_CLASS;
1690     case JVMTI_HEAP_REFERENCE_STACK_LOCAL:  return JVMTI_HEAP_ROOT_STACK_LOCAL;
1691     case JVMTI_HEAP_REFERENCE_JNI_LOCAL:    return JVMTI_HEAP_ROOT_JNI_LOCAL;
1692     case JVMTI_HEAP_REFERENCE_THREAD:       return JVMTI_HEAP_ROOT_THREAD;
1693     case JVMTI_HEAP_REFERENCE_OTHER:        return JVMTI_HEAP_ROOT_OTHER;
1694     default: ShouldNotReachHere();          return JVMTI_HEAP_ROOT_OTHER;
1695   }
1696 }
1697 
1698 // Base class for all heap walk contexts. The base class maintains a flag
1699 // to indicate if the context is valid or not.
1700 class HeapWalkContext {
1701  private:
1702   bool _valid;
1703  public:
1704   HeapWalkContext(bool valid)                   { _valid = valid; }
1705   void invalidate()                             { _valid = false; }
1706   bool is_valid() const                         { return _valid; }
1707 };
1708 
1709 // A basic heap walk context for the deprecated heap walking functions.
1710 // The context for a basic heap walk are the callbacks and fields used by
1711 // the referrer caching scheme.
1712 class BasicHeapWalkContext: public HeapWalkContext {
1713  private:
1714   jvmtiHeapRootCallback _heap_root_callback;
1715   jvmtiStackReferenceCallback _stack_ref_callback;
1716   jvmtiObjectReferenceCallback _object_ref_callback;
1717 
1718   // used for caching
1719   JvmtiHeapwalkObject _last_referrer;
1720   jlong _last_referrer_tag;
1721 
1722  public:
1723   BasicHeapWalkContext() : HeapWalkContext(false) { }
1724 
1725   BasicHeapWalkContext(jvmtiHeapRootCallback heap_root_callback,
1726                        jvmtiStackReferenceCallback stack_ref_callback,
1727                        jvmtiObjectReferenceCallback object_ref_callback) :
1728     HeapWalkContext(true),
1729     _heap_root_callback(heap_root_callback),
1730     _stack_ref_callback(stack_ref_callback),
1731     _object_ref_callback(object_ref_callback),
1732     _last_referrer(),
1733     _last_referrer_tag(0) {
1734   }
1735 
1736   // accessors
1737   jvmtiHeapRootCallback heap_root_callback() const         { return _heap_root_callback; }
1738   jvmtiStackReferenceCallback stack_ref_callback() const   { return _stack_ref_callback; }
1739   jvmtiObjectReferenceCallback object_ref_callback() const { return _object_ref_callback;  }
1740 
1741   JvmtiHeapwalkObject last_referrer() const    { return _last_referrer; }
1742   void set_last_referrer(const JvmtiHeapwalkObject& referrer) { _last_referrer = referrer; }
1743   jlong last_referrer_tag() const         { return _last_referrer_tag; }
1744   void set_last_referrer_tag(jlong value) { _last_referrer_tag = value; }
1745 };
1746 
1747 // The advanced heap walk context for the FollowReferences functions.
1748 // The context is the callbacks, and the fields used for filtering.
1749 class AdvancedHeapWalkContext: public HeapWalkContext {
1750  private:
1751   jint _heap_filter;
1752   Klass* _klass_filter;
1753   const jvmtiHeapCallbacks* _heap_callbacks;
1754 
1755  public:
1756   AdvancedHeapWalkContext() : HeapWalkContext(false) { }
1757 
1758   AdvancedHeapWalkContext(jint heap_filter,
1759                            Klass* klass_filter,
1760                            const jvmtiHeapCallbacks* heap_callbacks) :
1761     HeapWalkContext(true),
1762     _heap_filter(heap_filter),
1763     _klass_filter(klass_filter),
1764     _heap_callbacks(heap_callbacks) {
1765   }
1766 
1767   // accessors
1768   jint heap_filter() const         { return _heap_filter; }
1769   Klass* klass_filter() const      { return _klass_filter; }
1770 
1771   jvmtiHeapReferenceCallback heap_reference_callback() const {
1772     return _heap_callbacks->heap_reference_callback;
1773   };
1774   jvmtiPrimitiveFieldCallback primitive_field_callback() const {
1775     return _heap_callbacks->primitive_field_callback;
1776   }
1777   jvmtiArrayPrimitiveValueCallback array_primitive_value_callback() const {
1778     return _heap_callbacks->array_primitive_value_callback;
1779   }
1780   jvmtiStringPrimitiveValueCallback string_primitive_value_callback() const {
1781     return _heap_callbacks->string_primitive_value_callback;
1782   }
1783 };
1784 
1785 // The CallbackInvoker is a class with static functions that the heap walk can call
1786 // into to invoke callbacks. It works in one of two modes. The "basic" mode is
1787 // used for the deprecated IterateOverReachableObjects functions. The "advanced"
1788 // mode is for the newer FollowReferences function which supports a lot of
1789 // additional callbacks.
1790 class CallbackInvoker : AllStatic {
1791  private:
1792   // heap walk styles
1793   enum { basic, advanced };
1794   static int _heap_walk_type;
1795   static bool is_basic_heap_walk()           { return _heap_walk_type == basic; }
1796   static bool is_advanced_heap_walk()        { return _heap_walk_type == advanced; }
1797 
1798   // context for basic style heap walk
1799   static BasicHeapWalkContext _basic_context;
1800   static BasicHeapWalkContext* basic_context() {
1801     assert(_basic_context.is_valid(), "invalid");
1802     return &_basic_context;
1803   }
1804 
1805   // context for advanced style heap walk
1806   static AdvancedHeapWalkContext _advanced_context;
1807   static AdvancedHeapWalkContext* advanced_context() {
1808     assert(_advanced_context.is_valid(), "invalid");
1809     return &_advanced_context;
1810   }
1811 
1812   // context needed for all heap walks
1813   static JvmtiTagMap* _tag_map;
1814   static const void* _user_data;
1815   static JvmtiHeapwalkVisitStack* _visit_stack;
1816 
1817   // accessors
1818   static JvmtiTagMap* tag_map()                        { return _tag_map; }
1819   static const void* user_data()                       { return _user_data; }
1820   static JvmtiHeapwalkVisitStack* visit_stack()        { return _visit_stack; }
1821 
1822   // if the object hasn't been visited then push it onto the visit stack
1823   // so that it will be visited later
1824   static inline bool check_for_visit(const JvmtiHeapwalkObject&obj) {
1825     visit_stack()->check_for_visit(obj);
1826     return true;
1827   }
1828 
1829   // return element count if the obj is array, -1 otherwise
1830   static jint get_array_length(const JvmtiHeapwalkObject& obj) {
1831     if (!obj.klass()->is_array_klass()) {
1832       return -1;
1833     }
1834     assert(!obj.is_flat(), "array cannot be flat");
1835     return (jint)arrayOop(obj.obj())->length();
1836   }
1837 
1838 
1839   // invoke basic style callbacks
1840   static inline bool invoke_basic_heap_root_callback
1841     (jvmtiHeapRootKind root_kind, const JvmtiHeapwalkObject& obj);
1842   static inline bool invoke_basic_stack_ref_callback
1843     (jvmtiHeapRootKind root_kind, jlong thread_tag, jint depth, jmethodID method,
1844      int slot, const JvmtiHeapwalkObject& obj);
1845   static inline bool invoke_basic_object_reference_callback
1846     (jvmtiObjectReferenceKind ref_kind, const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint index);
1847 
1848   // invoke advanced style callbacks
1849   static inline bool invoke_advanced_heap_root_callback
1850     (jvmtiHeapReferenceKind ref_kind, const JvmtiHeapwalkObject& obj);
1851   static inline bool invoke_advanced_stack_ref_callback
1852     (jvmtiHeapReferenceKind ref_kind, jlong thread_tag, jlong tid, int depth,
1853      jmethodID method, jlocation bci, jint slot, const JvmtiHeapwalkObject& obj);
1854   static inline bool invoke_advanced_object_reference_callback
1855     (jvmtiHeapReferenceKind ref_kind, const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint index);
1856 
1857   // used to report the value of primitive fields
1858   static inline bool report_primitive_field
1859     (jvmtiHeapReferenceKind ref_kind, const JvmtiHeapwalkObject& obj, jint index, address addr, char type);
1860 
1861  public:
1862   // initialize for basic mode
1863   static void initialize_for_basic_heap_walk(JvmtiTagMap* tag_map,
1864                                              const void* user_data,
1865                                              BasicHeapWalkContext context,
1866                                              JvmtiHeapwalkVisitStack* visit_stack);
1867 
1868   // initialize for advanced mode
1869   static void initialize_for_advanced_heap_walk(JvmtiTagMap* tag_map,
1870                                                 const void* user_data,
1871                                                 AdvancedHeapWalkContext context,
1872                                                 JvmtiHeapwalkVisitStack* visit_stack);
1873 
1874    // functions to report roots
1875   static inline bool report_simple_root(jvmtiHeapReferenceKind kind, const JvmtiHeapwalkObject& o);
1876   static inline bool report_jni_local_root(jlong thread_tag, jlong tid, jint depth,
1877     jmethodID m, const JvmtiHeapwalkObject& o);
1878   static inline bool report_stack_ref_root(jlong thread_tag, jlong tid, jint depth,
1879     jmethodID method, jlocation bci, jint slot, const JvmtiHeapwalkObject& o);
1880 
1881   // functions to report references
1882   static inline bool report_array_element_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint index);
1883   static inline bool report_class_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree);
1884   static inline bool report_class_loader_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree);
1885   static inline bool report_signers_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree);
1886   static inline bool report_protection_domain_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree);
1887   static inline bool report_superclass_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree);
1888   static inline bool report_interface_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree);
1889   static inline bool report_static_field_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint slot);
1890   static inline bool report_field_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint slot);
1891   static inline bool report_constant_pool_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint index);
1892   static inline bool report_primitive_array_values(const JvmtiHeapwalkObject& array);
1893   static inline bool report_string_value(const JvmtiHeapwalkObject& str);
1894   static inline bool report_primitive_instance_field(const JvmtiHeapwalkObject& o, jint index, address value, char type);
1895   static inline bool report_primitive_static_field(const JvmtiHeapwalkObject& o, jint index, address value, char type);
1896 };
1897 
1898 // statics
1899 int CallbackInvoker::_heap_walk_type;
1900 BasicHeapWalkContext CallbackInvoker::_basic_context;
1901 AdvancedHeapWalkContext CallbackInvoker::_advanced_context;
1902 JvmtiTagMap* CallbackInvoker::_tag_map;
1903 const void* CallbackInvoker::_user_data;
1904 JvmtiHeapwalkVisitStack* CallbackInvoker::_visit_stack;
1905 
1906 // initialize for basic heap walk (IterateOverReachableObjects et al)
1907 void CallbackInvoker::initialize_for_basic_heap_walk(JvmtiTagMap* tag_map,
1908                                                      const void* user_data,
1909                                                      BasicHeapWalkContext context,
1910                                                      JvmtiHeapwalkVisitStack* visit_stack) {
1911   _tag_map = tag_map;
1912   _user_data = user_data;
1913   _basic_context = context;
1914   _advanced_context.invalidate();       // will trigger assertion if used
1915   _heap_walk_type = basic;
1916   _visit_stack = visit_stack;
1917 }
1918 
1919 // initialize for advanced heap walk (FollowReferences)
1920 void CallbackInvoker::initialize_for_advanced_heap_walk(JvmtiTagMap* tag_map,
1921                                                         const void* user_data,
1922                                                         AdvancedHeapWalkContext context,
1923                                                         JvmtiHeapwalkVisitStack* visit_stack) {
1924   _tag_map = tag_map;
1925   _user_data = user_data;
1926   _advanced_context = context;
1927   _basic_context.invalidate();      // will trigger assertion if used
1928   _heap_walk_type = advanced;
1929   _visit_stack = visit_stack;
1930 }
1931 
1932 
1933 // invoke basic style heap root callback
1934 inline bool CallbackInvoker::invoke_basic_heap_root_callback(jvmtiHeapRootKind root_kind, const JvmtiHeapwalkObject& obj) {
1935   // if we heap roots should be reported
1936   jvmtiHeapRootCallback cb = basic_context()->heap_root_callback();
1937   if (cb == nullptr) {
1938     return check_for_visit(obj);
1939   }
1940 
1941   CallbackWrapper wrapper(tag_map(), obj);
1942   jvmtiIterationControl control = (*cb)(root_kind,
1943                                         wrapper.klass_tag(),
1944                                         wrapper.obj_size(),
1945                                         wrapper.obj_tag_p(),
1946                                         (void*)user_data());
1947   // push root to visit stack when following references
1948   if (control == JVMTI_ITERATION_CONTINUE &&
1949       basic_context()->object_ref_callback() != nullptr) {
1950     visit_stack()->push(obj);
1951   }
1952   return control != JVMTI_ITERATION_ABORT;
1953 }
1954 
1955 // invoke basic style stack ref callback
1956 inline bool CallbackInvoker::invoke_basic_stack_ref_callback(jvmtiHeapRootKind root_kind,
1957                                                              jlong thread_tag,
1958                                                              jint depth,
1959                                                              jmethodID method,
1960                                                              int slot,
1961                                                              const JvmtiHeapwalkObject& obj) {
1962   // if we stack refs should be reported
1963   jvmtiStackReferenceCallback cb = basic_context()->stack_ref_callback();
1964   if (cb == nullptr) {
1965     return check_for_visit(obj);
1966   }
1967 
1968   CallbackWrapper wrapper(tag_map(), obj);
1969   jvmtiIterationControl control = (*cb)(root_kind,
1970                                         wrapper.klass_tag(),
1971                                         wrapper.obj_size(),
1972                                         wrapper.obj_tag_p(),
1973                                         thread_tag,
1974                                         depth,
1975                                         method,
1976                                         slot,
1977                                         (void*)user_data());
1978   // push root to visit stack when following references
1979   if (control == JVMTI_ITERATION_CONTINUE &&
1980       basic_context()->object_ref_callback() != nullptr) {
1981     visit_stack()->push(obj);
1982   }
1983   return control != JVMTI_ITERATION_ABORT;
1984 }
1985 
1986 // invoke basic style object reference callback
1987 inline bool CallbackInvoker::invoke_basic_object_reference_callback(jvmtiObjectReferenceKind ref_kind,
1988                                                                     const JvmtiHeapwalkObject& referrer,
1989                                                                     const JvmtiHeapwalkObject& referree,
1990                                                                     jint index) {
1991 
1992   BasicHeapWalkContext* context = basic_context();
1993 
1994   // callback requires the referrer's tag. If it's the same referrer
1995   // as the last call then we use the cached value.
1996   jlong referrer_tag;
1997   if (referrer == context->last_referrer()) {
1998     referrer_tag = context->last_referrer_tag();
1999   } else {
2000     referrer_tag = tag_map()->find(referrer);
2001   }
2002 
2003   // do the callback
2004   CallbackWrapper wrapper(tag_map(), referree);
2005   jvmtiObjectReferenceCallback cb = context->object_ref_callback();
2006   jvmtiIterationControl control = (*cb)(ref_kind,
2007                                         wrapper.klass_tag(),
2008                                         wrapper.obj_size(),
2009                                         wrapper.obj_tag_p(),
2010                                         referrer_tag,
2011                                         index,
2012                                         (void*)user_data());
2013 
2014   // record referrer and referrer tag. For self-references record the
2015   // tag value from the callback as this might differ from referrer_tag.
2016   context->set_last_referrer(referrer);
2017   if (referrer == referree) {
2018     context->set_last_referrer_tag(*wrapper.obj_tag_p());
2019   } else {
2020     context->set_last_referrer_tag(referrer_tag);
2021   }
2022 
2023   if (control == JVMTI_ITERATION_CONTINUE) {
2024     return check_for_visit(referree);
2025   } else {
2026     return control != JVMTI_ITERATION_ABORT;
2027   }
2028 }
2029 
2030 // invoke advanced style heap root callback
2031 inline bool CallbackInvoker::invoke_advanced_heap_root_callback(jvmtiHeapReferenceKind ref_kind,
2032                                                                 const JvmtiHeapwalkObject& obj) {
2033   AdvancedHeapWalkContext* context = advanced_context();
2034 
2035   // check that callback is provided
2036   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
2037   if (cb == nullptr) {
2038     return check_for_visit(obj);
2039   }
2040 
2041   // apply class filter
2042   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
2043     return check_for_visit(obj);
2044   }
2045 
2046   // setup the callback wrapper
2047   CallbackWrapper wrapper(tag_map(), obj);
2048 
2049   // apply tag filter
2050   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
2051                                  wrapper.klass_tag(),
2052                                  context->heap_filter())) {
2053     return check_for_visit(obj);
2054   }
2055 
2056   // for arrays we need the length, otherwise -1
2057   jint len = get_array_length(obj);
2058 
2059   // invoke the callback
2060   jint res  = (*cb)(ref_kind,
2061                     nullptr, // referrer info
2062                     wrapper.klass_tag(),
2063                     0,    // referrer_class_tag is 0 for heap root
2064                     wrapper.obj_size(),
2065                     wrapper.obj_tag_p(),
2066                     nullptr, // referrer_tag_p
2067                     len,
2068                     (void*)user_data());
2069   if (res & JVMTI_VISIT_ABORT) {
2070     return false;// referrer class tag
2071   }
2072   if (res & JVMTI_VISIT_OBJECTS) {
2073     check_for_visit(obj);
2074   }
2075   return true;
2076 }
2077 
2078 // report a reference from a thread stack to an object
2079 inline bool CallbackInvoker::invoke_advanced_stack_ref_callback(jvmtiHeapReferenceKind ref_kind,
2080                                                                 jlong thread_tag,
2081                                                                 jlong tid,
2082                                                                 int depth,
2083                                                                 jmethodID method,
2084                                                                 jlocation bci,
2085                                                                 jint slot,
2086                                                                 const JvmtiHeapwalkObject& obj) {
2087   AdvancedHeapWalkContext* context = advanced_context();
2088 
2089   // check that callback is provider
2090   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
2091   if (cb == nullptr) {
2092     return check_for_visit(obj);
2093   }
2094 
2095   // apply class filter
2096   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
2097     return check_for_visit(obj);
2098   }
2099 
2100   // setup the callback wrapper
2101   CallbackWrapper wrapper(tag_map(), obj);
2102 
2103   // apply tag filter
2104   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
2105                                  wrapper.klass_tag(),
2106                                  context->heap_filter())) {
2107     return check_for_visit(obj);
2108   }
2109 
2110   // setup the referrer info
2111   jvmtiHeapReferenceInfo reference_info;
2112   reference_info.stack_local.thread_tag = thread_tag;
2113   reference_info.stack_local.thread_id = tid;
2114   reference_info.stack_local.depth = depth;
2115   reference_info.stack_local.method = method;
2116   reference_info.stack_local.location = bci;
2117   reference_info.stack_local.slot = slot;
2118 
2119   // for arrays we need the length, otherwise -1
2120   jint len = get_array_length(obj);
2121 
2122   // call into the agent
2123   int res = (*cb)(ref_kind,
2124                   &reference_info,
2125                   wrapper.klass_tag(),
2126                   0,    // referrer_class_tag is 0 for heap root (stack)
2127                   wrapper.obj_size(),
2128                   wrapper.obj_tag_p(),
2129                   nullptr, // referrer_tag is 0 for root
2130                   len,
2131                   (void*)user_data());
2132 
2133   if (res & JVMTI_VISIT_ABORT) {
2134     return false;
2135   }
2136   if (res & JVMTI_VISIT_OBJECTS) {
2137     check_for_visit(obj);
2138   }
2139   return true;
2140 }
2141 
2142 // This mask is used to pass reference_info to a jvmtiHeapReferenceCallback
2143 // only for ref_kinds defined by the JVM TI spec. Otherwise, null is passed.
2144 #define REF_INFO_MASK  ((1 << JVMTI_HEAP_REFERENCE_FIELD)         \
2145                       | (1 << JVMTI_HEAP_REFERENCE_STATIC_FIELD)  \
2146                       | (1 << JVMTI_HEAP_REFERENCE_ARRAY_ELEMENT) \
2147                       | (1 << JVMTI_HEAP_REFERENCE_CONSTANT_POOL) \
2148                       | (1 << JVMTI_HEAP_REFERENCE_STACK_LOCAL)   \
2149                       | (1 << JVMTI_HEAP_REFERENCE_JNI_LOCAL))
2150 
2151 // invoke the object reference callback to report a reference
2152 inline bool CallbackInvoker::invoke_advanced_object_reference_callback(jvmtiHeapReferenceKind ref_kind,
2153                                                                        const JvmtiHeapwalkObject& referrer,
2154                                                                        const JvmtiHeapwalkObject& obj,
2155                                                                        jint index)
2156 {
2157   // field index is only valid field in reference_info
2158   static jvmtiHeapReferenceInfo reference_info = { 0 };
2159 
2160   AdvancedHeapWalkContext* context = advanced_context();
2161 
2162   // check that callback is provider
2163   jvmtiHeapReferenceCallback cb = context->heap_reference_callback();
2164   if (cb == nullptr) {
2165     return check_for_visit(obj);
2166   }
2167 
2168   // apply class filter
2169   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
2170     return check_for_visit(obj);
2171   }
2172 
2173   // setup the callback wrapper
2174   TwoOopCallbackWrapper wrapper(tag_map(), referrer, obj);
2175 
2176   // apply tag filter
2177   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
2178                                  wrapper.klass_tag(),
2179                                  context->heap_filter())) {
2180     return check_for_visit(obj);
2181   }
2182 
2183   // field index is only valid field in reference_info
2184   reference_info.field.index = index;
2185 
2186   // for arrays we need the length, otherwise -1
2187   jint len = get_array_length(obj);
2188 
2189   // invoke the callback
2190   int res = (*cb)(ref_kind,
2191                   (REF_INFO_MASK & (1 << ref_kind)) ? &reference_info : nullptr,
2192                   wrapper.klass_tag(),
2193                   wrapper.referrer_klass_tag(),
2194                   wrapper.obj_size(),
2195                   wrapper.obj_tag_p(),
2196                   wrapper.referrer_tag_p(),
2197                   len,
2198                   (void*)user_data());
2199 
2200   if (res & JVMTI_VISIT_ABORT) {
2201     return false;
2202   }
2203   if (res & JVMTI_VISIT_OBJECTS) {
2204     check_for_visit(obj);
2205   }
2206   return true;
2207 }
2208 
2209 // report a "simple root"
2210 inline bool CallbackInvoker::report_simple_root(jvmtiHeapReferenceKind kind, const JvmtiHeapwalkObject& obj) {
2211   assert(kind != JVMTI_HEAP_REFERENCE_STACK_LOCAL &&
2212          kind != JVMTI_HEAP_REFERENCE_JNI_LOCAL, "not a simple root");
2213 
2214   if (is_basic_heap_walk()) {
2215     // map to old style root kind
2216     jvmtiHeapRootKind root_kind = toJvmtiHeapRootKind(kind);
2217     return invoke_basic_heap_root_callback(root_kind, obj);
2218   } else {
2219     assert(is_advanced_heap_walk(), "wrong heap walk type");
2220     return invoke_advanced_heap_root_callback(kind, obj);
2221   }
2222 }
2223 
2224 
2225 // invoke the primitive array values
2226 inline bool CallbackInvoker::report_primitive_array_values(const JvmtiHeapwalkObject& obj) {
2227   assert(obj.klass()->is_typeArray_klass(), "not a primitive array");
2228 
2229   AdvancedHeapWalkContext* context = advanced_context();
2230   assert(context->array_primitive_value_callback() != nullptr, "no callback");
2231 
2232   // apply class filter
2233   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
2234     return true;
2235   }
2236 
2237   CallbackWrapper wrapper(tag_map(), obj);
2238 
2239   // apply tag filter
2240   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
2241                                  wrapper.klass_tag(),
2242                                  context->heap_filter())) {
2243     return true;
2244   }
2245 
2246   // invoke the callback
2247   int res = invoke_array_primitive_value_callback(context->array_primitive_value_callback(),
2248                                                   &wrapper,
2249                                                   obj,
2250                                                   (void*)user_data());
2251   return (!(res & JVMTI_VISIT_ABORT));
2252 }
2253 
2254 // invoke the string value callback
2255 inline bool CallbackInvoker::report_string_value(const JvmtiHeapwalkObject& str) {
2256   assert(str.klass() == vmClasses::String_klass(), "not a string");
2257 
2258   AdvancedHeapWalkContext* context = advanced_context();
2259   assert(context->string_primitive_value_callback() != nullptr, "no callback");
2260 
2261   // apply class filter
2262   if (is_filtered_by_klass_filter(str, context->klass_filter())) {
2263     return true;
2264   }
2265 
2266   CallbackWrapper wrapper(tag_map(), str);
2267 
2268   // apply tag filter
2269   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
2270                                  wrapper.klass_tag(),
2271                                  context->heap_filter())) {
2272     return true;
2273   }
2274 
2275   // invoke the callback
2276   int res = invoke_string_value_callback(context->string_primitive_value_callback(),
2277                                          &wrapper,
2278                                          str,
2279                                          (void*)user_data());
2280   return (!(res & JVMTI_VISIT_ABORT));
2281 }
2282 
2283 // invoke the primitive field callback
2284 inline bool CallbackInvoker::report_primitive_field(jvmtiHeapReferenceKind ref_kind,
2285                                                     const JvmtiHeapwalkObject& obj,
2286                                                     jint index,
2287                                                     address addr,
2288                                                     char type)
2289 {
2290   // for primitive fields only the index will be set
2291   static jvmtiHeapReferenceInfo reference_info = { 0 };
2292 
2293   AdvancedHeapWalkContext* context = advanced_context();
2294   assert(context->primitive_field_callback() != nullptr, "no callback");
2295 
2296   // apply class filter
2297   if (is_filtered_by_klass_filter(obj, context->klass_filter())) {
2298     return true;
2299   }
2300 
2301   CallbackWrapper wrapper(tag_map(), obj);
2302 
2303   // apply tag filter
2304   if (is_filtered_by_heap_filter(wrapper.obj_tag(),
2305                                  wrapper.klass_tag(),
2306                                  context->heap_filter())) {
2307     return true;
2308   }
2309 
2310   // the field index in the referrer
2311   reference_info.field.index = index;
2312 
2313   // map the type
2314   jvmtiPrimitiveType value_type = (jvmtiPrimitiveType)type;
2315 
2316   // setup the jvalue
2317   jvalue value;
2318   copy_to_jvalue(&value, addr, value_type);
2319 
2320   jvmtiPrimitiveFieldCallback cb = context->primitive_field_callback();
2321   int res = (*cb)(ref_kind,
2322                   &reference_info,
2323                   wrapper.klass_tag(),
2324                   wrapper.obj_tag_p(),
2325                   value,
2326                   value_type,
2327                   (void*)user_data());
2328   return (!(res & JVMTI_VISIT_ABORT));
2329 }
2330 
2331 
2332 // instance field
2333 inline bool CallbackInvoker::report_primitive_instance_field(const JvmtiHeapwalkObject& obj,
2334                                                              jint index,
2335                                                              address value,
2336                                                              char type) {
2337   return report_primitive_field(JVMTI_HEAP_REFERENCE_FIELD,
2338                                 obj,
2339                                 index,
2340                                 value,
2341                                 type);
2342 }
2343 
2344 // static field
2345 inline bool CallbackInvoker::report_primitive_static_field(const JvmtiHeapwalkObject& obj,
2346                                                            jint index,
2347                                                            address value,
2348                                                            char type) {
2349   return report_primitive_field(JVMTI_HEAP_REFERENCE_STATIC_FIELD,
2350                                 obj,
2351                                 index,
2352                                 value,
2353                                 type);
2354 }
2355 
2356 // report a JNI local (root object) to the profiler
2357 inline bool CallbackInvoker::report_jni_local_root(jlong thread_tag, jlong tid, jint depth, jmethodID m, const JvmtiHeapwalkObject& obj) {
2358   if (is_basic_heap_walk()) {
2359     return invoke_basic_stack_ref_callback(JVMTI_HEAP_ROOT_JNI_LOCAL,
2360                                            thread_tag,
2361                                            depth,
2362                                            m,
2363                                            -1,
2364                                            obj);
2365   } else {
2366     return invoke_advanced_stack_ref_callback(JVMTI_HEAP_REFERENCE_JNI_LOCAL,
2367                                               thread_tag, tid,
2368                                               depth,
2369                                               m,
2370                                               (jlocation)-1,
2371                                               -1,
2372                                               obj);
2373   }
2374 }
2375 
2376 
2377 // report a local (stack reference, root object)
2378 inline bool CallbackInvoker::report_stack_ref_root(jlong thread_tag,
2379                                                    jlong tid,
2380                                                    jint depth,
2381                                                    jmethodID method,
2382                                                    jlocation bci,
2383                                                    jint slot,
2384                                                    const JvmtiHeapwalkObject& obj) {
2385   if (is_basic_heap_walk()) {
2386     return invoke_basic_stack_ref_callback(JVMTI_HEAP_ROOT_STACK_LOCAL,
2387                                            thread_tag,
2388                                            depth,
2389                                            method,
2390                                            slot,
2391                                            obj);
2392   } else {
2393     return invoke_advanced_stack_ref_callback(JVMTI_HEAP_REFERENCE_STACK_LOCAL,
2394                                               thread_tag,
2395                                               tid,
2396                                               depth,
2397                                               method,
2398                                               bci,
2399                                               slot,
2400                                               obj);
2401   }
2402 }
2403 
2404 // report an object referencing a class.
2405 inline bool CallbackInvoker::report_class_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree) {
2406   if (is_basic_heap_walk()) {
2407     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS, referrer, referree, -1);
2408   } else {
2409     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CLASS, referrer, referree, -1);
2410   }
2411 }
2412 
2413 // report a class referencing its class loader.
2414 inline bool CallbackInvoker::report_class_loader_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree) {
2415   if (is_basic_heap_walk()) {
2416     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS_LOADER, referrer, referree, -1);
2417   } else {
2418     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CLASS_LOADER, referrer, referree, -1);
2419   }
2420 }
2421 
2422 // report a class referencing its signers.
2423 inline bool CallbackInvoker::report_signers_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree) {
2424   if (is_basic_heap_walk()) {
2425     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_SIGNERS, referrer, referree, -1);
2426   } else {
2427     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_SIGNERS, referrer, referree, -1);
2428   }
2429 }
2430 
2431 // report a class referencing its protection domain..
2432 inline bool CallbackInvoker::report_protection_domain_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree) {
2433   if (is_basic_heap_walk()) {
2434     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_PROTECTION_DOMAIN, referrer, referree, -1);
2435   } else {
2436     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_PROTECTION_DOMAIN, referrer, referree, -1);
2437   }
2438 }
2439 
2440 // report a class referencing its superclass.
2441 inline bool CallbackInvoker::report_superclass_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree) {
2442   if (is_basic_heap_walk()) {
2443     // Send this to be consistent with past implementation
2444     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CLASS, referrer, referree, -1);
2445   } else {
2446     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_SUPERCLASS, referrer, referree, -1);
2447   }
2448 }
2449 
2450 // report a class referencing one of its interfaces.
2451 inline bool CallbackInvoker::report_interface_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree) {
2452   if (is_basic_heap_walk()) {
2453     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_INTERFACE, referrer, referree, -1);
2454   } else {
2455     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_INTERFACE, referrer, referree, -1);
2456   }
2457 }
2458 
2459 // report a class referencing one of its static fields.
2460 inline bool CallbackInvoker::report_static_field_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint slot) {
2461   if (is_basic_heap_walk()) {
2462     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_STATIC_FIELD, referrer, referree, slot);
2463   } else {
2464     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_STATIC_FIELD, referrer, referree, slot);
2465   }
2466 }
2467 
2468 // report an array referencing an element object
2469 inline bool CallbackInvoker::report_array_element_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint index) {
2470   if (is_basic_heap_walk()) {
2471     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_ARRAY_ELEMENT, referrer, referree, index);
2472   } else {
2473     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_ARRAY_ELEMENT, referrer, referree, index);
2474   }
2475 }
2476 
2477 // report an object referencing an instance field object
2478 inline bool CallbackInvoker::report_field_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint slot) {
2479   if (is_basic_heap_walk()) {
2480     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_FIELD, referrer, referree, slot);
2481   } else {
2482     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_FIELD, referrer, referree, slot);
2483   }
2484 }
2485 
2486 // report an array referencing an element object
2487 inline bool CallbackInvoker::report_constant_pool_reference(const JvmtiHeapwalkObject& referrer, const JvmtiHeapwalkObject& referree, jint index) {
2488   if (is_basic_heap_walk()) {
2489     return invoke_basic_object_reference_callback(JVMTI_REFERENCE_CONSTANT_POOL, referrer, referree, index);
2490   } else {
2491     return invoke_advanced_object_reference_callback(JVMTI_HEAP_REFERENCE_CONSTANT_POOL, referrer, referree, index);
2492   }
2493 }
2494 
2495 // A supporting closure used to process simple roots
2496 class SimpleRootsClosure : public OopClosure {
2497  private:
2498   jvmtiHeapReferenceKind _kind;
2499   bool _continue;
2500 
2501   jvmtiHeapReferenceKind root_kind()    { return _kind; }
2502 
2503  public:
2504   void set_kind(jvmtiHeapReferenceKind kind) {
2505     _kind = kind;
2506     _continue = true;
2507   }
2508 
2509   inline bool stopped() {
2510     return !_continue;
2511   }
2512 
2513   void do_oop(oop* obj_p) {
2514     // iteration has terminated
2515     if (stopped()) {
2516       return;
2517     }
2518 
2519     oop o = NativeAccess<AS_NO_KEEPALIVE>::oop_load(obj_p);
2520     // ignore null
2521     if (o == nullptr) {
2522       return;
2523     }
2524 
2525     assert(Universe::heap()->is_in(o), "should be impossible");
2526 
2527     jvmtiHeapReferenceKind kind = root_kind();
2528 
2529     // invoke the callback
2530     _continue = CallbackInvoker::report_simple_root(kind, o);
2531 
2532   }
2533   virtual void do_oop(narrowOop* obj_p) { ShouldNotReachHere(); }
2534 };
2535 
2536 // A supporting closure used to process JNI locals
2537 class JNILocalRootsClosure : public OopClosure {
2538  private:
2539   jlong _thread_tag;
2540   jlong _tid;
2541   jint _depth;
2542   jmethodID _method;
2543   bool _continue;
2544  public:
2545   void set_context(jlong thread_tag, jlong tid, jint depth, jmethodID method) {
2546     _thread_tag = thread_tag;
2547     _tid = tid;
2548     _depth = depth;
2549     _method = method;
2550     _continue = true;
2551   }
2552 
2553   inline bool stopped() {
2554     return !_continue;
2555   }
2556 
2557   void do_oop(oop* obj_p) {
2558     // iteration has terminated
2559     if (stopped()) {
2560       return;
2561     }
2562 
2563     oop o = *obj_p;
2564     // ignore null
2565     if (o == nullptr) {
2566       return;
2567     }
2568 
2569     // invoke the callback
2570     _continue = CallbackInvoker::report_jni_local_root(_thread_tag, _tid, _depth, _method, o);
2571   }
2572   virtual void do_oop(narrowOop* obj_p) { ShouldNotReachHere(); }
2573 };
2574 
2575 // Helper class to collect/report stack references.
2576 class StackRefCollector {
2577 private:
2578   JvmtiTagMap* _tag_map;
2579   JNILocalRootsClosure* _blk;
2580   // java_thread is needed only to report JNI local on top native frame;
2581   // I.e. it's required only for platform/carrier threads or mounted virtual threads.
2582   JavaThread* _java_thread;
2583 
2584   oop _threadObj;
2585   jlong _thread_tag;
2586   jlong _tid;
2587 
2588   bool _is_top_frame;
2589   int _depth;
2590   frame* _last_entry_frame;
2591 
2592   bool report_java_stack_refs(StackValueCollection* values, jmethodID method, jlocation bci, jint slot_offset);
2593   bool report_native_stack_refs(jmethodID method);
2594 
2595 public:
2596   StackRefCollector(JvmtiTagMap* tag_map, JNILocalRootsClosure* blk, JavaThread* java_thread)
2597     : _tag_map(tag_map), _blk(blk), _java_thread(java_thread),
2598       _threadObj(nullptr), _thread_tag(0), _tid(0),
2599       _is_top_frame(true), _depth(0), _last_entry_frame(nullptr)
2600   {
2601   }
2602 
2603   bool set_thread(oop o);
2604   // Sets the thread and reports the reference to it with the specified kind.
2605   bool set_thread(jvmtiHeapReferenceKind kind, oop o);
2606 
2607   bool do_frame(vframe* vf);
2608   // Handles frames until vf->sender() is null.
2609   bool process_frames(vframe* vf);
2610 };
2611 
2612 bool StackRefCollector::set_thread(oop o) {
2613   _threadObj = o;
2614   _thread_tag = _tag_map->find(_threadObj);
2615   _tid = java_lang_Thread::thread_id(_threadObj);
2616 
2617   _is_top_frame = true;
2618   _depth = 0;
2619   _last_entry_frame = nullptr;
2620 
2621   return true;
2622 }
2623 
2624 bool StackRefCollector::set_thread(jvmtiHeapReferenceKind kind, oop o) {
2625   return set_thread(o)
2626          && CallbackInvoker::report_simple_root(kind, _threadObj);
2627 }
2628 
2629 bool StackRefCollector::report_java_stack_refs(StackValueCollection* values, jmethodID method, jlocation bci, jint slot_offset) {
2630   for (int index = 0; index < values->size(); index++) {
2631     if (values->at(index)->type() == T_OBJECT) {
2632       oop obj = values->obj_at(index)();
2633       if (obj == nullptr) {
2634         continue;
2635       }
2636       // stack reference
2637       if (!CallbackInvoker::report_stack_ref_root(_thread_tag, _tid, _depth, method,
2638                                                   bci, slot_offset + index, obj)) {
2639         return false;
2640       }
2641     }
2642   }
2643   return true;
2644 }
2645 
2646 bool StackRefCollector::report_native_stack_refs(jmethodID method) {
2647   _blk->set_context(_thread_tag, _tid, _depth, method);
2648   if (_is_top_frame) {
2649     // JNI locals for the top frame.
2650     if (_java_thread != nullptr) {
2651       _java_thread->active_handles()->oops_do(_blk);
2652       if (_blk->stopped()) {
2653         return false;
2654       }
2655     }
2656   } else {
2657     if (_last_entry_frame != nullptr) {
2658       // JNI locals for the entry frame.
2659       assert(_last_entry_frame->is_entry_frame(), "checking");
2660       _last_entry_frame->entry_frame_call_wrapper()->handles()->oops_do(_blk);
2661       if (_blk->stopped()) {
2662         return false;
2663       }
2664     }
2665   }
2666   return true;
2667 }
2668 
2669 bool StackRefCollector::do_frame(vframe* vf) {
2670   if (vf->is_java_frame()) {
2671     // java frame (interpreted, compiled, ...)
2672     javaVFrame* jvf = javaVFrame::cast(vf);
2673 
2674     jmethodID method = jvf->method()->jmethod_id();
2675 
2676     if (!(jvf->method()->is_native())) {
2677       jlocation bci = (jlocation)jvf->bci();
2678       StackValueCollection* locals = jvf->locals();
2679       if (!report_java_stack_refs(locals, method, bci, 0)) {
2680         return false;
2681       }
2682       if (!report_java_stack_refs(jvf->expressions(), method, bci, locals->size())) {
2683         return false;
2684       }
2685 
2686       // Follow oops from compiled nmethod.
2687       if (jvf->cb() != nullptr && jvf->cb()->is_nmethod()) {
2688         _blk->set_context(_thread_tag, _tid, _depth, method);
2689         // Need to apply load barriers for unmounted vthreads.
2690         nmethod* nm = jvf->cb()->as_nmethod();
2691         nm->run_nmethod_entry_barrier();
2692         nm->oops_do(_blk);
2693         if (_blk->stopped()) {
2694           return false;
2695         }
2696       }
2697     } else {
2698       // native frame
2699       if (!report_native_stack_refs(method)) {
2700         return false;
2701       }
2702     }
2703     _last_entry_frame = nullptr;
2704     _depth++;
2705   } else {
2706     // externalVFrame - for an entry frame then we report the JNI locals
2707     // when we find the corresponding javaVFrame
2708     frame* fr = vf->frame_pointer();
2709     assert(fr != nullptr, "sanity check");
2710     if (fr->is_entry_frame()) {
2711       _last_entry_frame = fr;
2712     }
2713   }
2714 
2715   _is_top_frame = false;
2716 
2717   return true;
2718 }
2719 
2720 bool StackRefCollector::process_frames(vframe* vf) {
2721   while (vf != nullptr) {
2722     if (!do_frame(vf)) {
2723       return false;
2724     }
2725     vf = vf->sender();
2726   }
2727   return true;
2728 }
2729 
2730 
2731 // A VM operation to iterate over objects that are reachable from
2732 // a set of roots or an initial object.
2733 //
2734 // For VM_HeapWalkOperation the set of roots used is :-
2735 //
2736 // - All JNI global references
2737 // - All inflated monitors
2738 // - All classes loaded by the boot class loader (or all classes
2739 //     in the event that class unloading is disabled)
2740 // - All java threads
2741 // - For each java thread then all locals and JNI local references
2742 //      on the thread's execution stack
2743 // - All visible/explainable objects from Universes::oops_do
2744 //
2745 class VM_HeapWalkOperation: public VM_Operation {
2746  private:
2747   bool _is_advanced_heap_walk;                      // indicates FollowReferences
2748   JvmtiTagMap* _tag_map;
2749   Handle _initial_object;
2750   JvmtiHeapwalkVisitStack _visit_stack;
2751 
2752   // Dead object tags in JvmtiTagMap
2753   GrowableArray<jlong>* _dead_objects;
2754 
2755   bool _following_object_refs;                      // are we following object references
2756 
2757   bool _reporting_primitive_fields;                 // optional reporting
2758   bool _reporting_primitive_array_values;
2759   bool _reporting_string_values;
2760 
2761   // accessors
2762   bool is_advanced_heap_walk() const               { return _is_advanced_heap_walk; }
2763   JvmtiTagMap* tag_map() const                     { return _tag_map; }
2764   Handle initial_object() const                    { return _initial_object; }
2765 
2766   bool is_following_references() const             { return _following_object_refs; }
2767 
2768   bool is_reporting_primitive_fields()  const      { return _reporting_primitive_fields; }
2769   bool is_reporting_primitive_array_values() const { return _reporting_primitive_array_values; }
2770   bool is_reporting_string_values() const          { return _reporting_string_values; }
2771 
2772   JvmtiHeapwalkVisitStack* visit_stack()           { return &_visit_stack; }
2773 
2774   // iterate over the various object types
2775   inline bool iterate_over_array(const JvmtiHeapwalkObject& o);
2776   inline bool iterate_over_flat_array(const JvmtiHeapwalkObject& o);
2777   inline bool iterate_over_type_array(const JvmtiHeapwalkObject& o);
2778   inline bool iterate_over_class(const JvmtiHeapwalkObject& o);
2779   inline bool iterate_over_object(const JvmtiHeapwalkObject& o);
2780 
2781   // root collection
2782   inline bool collect_simple_roots();
2783   inline bool collect_stack_roots();
2784   inline bool collect_stack_refs(JavaThread* java_thread, JNILocalRootsClosure* blk);
2785   inline bool collect_vthread_stack_refs(oop vt);
2786 
2787   // visit an object
2788   inline bool visit(const JvmtiHeapwalkObject& o);
2789 
2790  public:
2791   VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2792                        Handle initial_object,
2793                        BasicHeapWalkContext callbacks,
2794                        const void* user_data,
2795                        GrowableArray<jlong>* objects);
2796 
2797   VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2798                        Handle initial_object,
2799                        AdvancedHeapWalkContext callbacks,
2800                        const void* user_data,
2801                        GrowableArray<jlong>* objects);
2802 
2803   ~VM_HeapWalkOperation();
2804 
2805   VMOp_Type type() const { return VMOp_HeapWalkOperation; }
2806   void doit();
2807 };
2808 
2809 
2810 VM_HeapWalkOperation::VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2811                                            Handle initial_object,
2812                                            BasicHeapWalkContext callbacks,
2813                                            const void* user_data,
2814                                            GrowableArray<jlong>* objects) {
2815   _is_advanced_heap_walk = false;
2816   _tag_map = tag_map;
2817   _initial_object = initial_object;
2818   _following_object_refs = (callbacks.object_ref_callback() != nullptr);
2819   _reporting_primitive_fields = false;
2820   _reporting_primitive_array_values = false;
2821   _reporting_string_values = false;
2822   _dead_objects = objects;
2823   CallbackInvoker::initialize_for_basic_heap_walk(tag_map, user_data, callbacks, &_visit_stack);
2824 }
2825 
2826 VM_HeapWalkOperation::VM_HeapWalkOperation(JvmtiTagMap* tag_map,
2827                                            Handle initial_object,
2828                                            AdvancedHeapWalkContext callbacks,
2829                                            const void* user_data,
2830                                            GrowableArray<jlong>* objects) {
2831   _is_advanced_heap_walk = true;
2832   _tag_map = tag_map;
2833   _initial_object = initial_object;
2834   _following_object_refs = true;
2835   _reporting_primitive_fields = (callbacks.primitive_field_callback() != nullptr);;
2836   _reporting_primitive_array_values = (callbacks.array_primitive_value_callback() != nullptr);;
2837   _reporting_string_values = (callbacks.string_primitive_value_callback() != nullptr);;
2838   _dead_objects = objects;
2839   CallbackInvoker::initialize_for_advanced_heap_walk(tag_map, user_data, callbacks, &_visit_stack);
2840 }
2841 
2842 VM_HeapWalkOperation::~VM_HeapWalkOperation() {
2843 }
2844 
2845 // an array references its class and has a reference to
2846 // each element in the array
2847 inline bool VM_HeapWalkOperation::iterate_over_array(const JvmtiHeapwalkObject& o) {
2848   assert(!o.is_flat(), "Array object cannot be flattened");
2849   objArrayOop array = objArrayOop(o.obj());
2850 
2851   // array reference to its class
2852   oop mirror = ObjArrayKlass::cast(array->klass())->java_mirror();
2853   if (!CallbackInvoker::report_class_reference(o, mirror)) {
2854     return false;
2855   }
2856 
2857   // iterate over the array and report each reference to a
2858   // non-null element
2859   for (int index=0; index<array->length(); index++) {
2860     oop elem = array->obj_at(index);
2861     if (elem == nullptr) {
2862       continue;
2863     }
2864 
2865     // report the array reference o[index] = elem
2866     if (!CallbackInvoker::report_array_element_reference(o, elem, index)) {
2867       return false;
2868     }
2869   }
2870   return true;
2871 }
2872 
2873 // similar to iterate_over_array(), but itrates over flat array
2874 inline bool VM_HeapWalkOperation::iterate_over_flat_array(const JvmtiHeapwalkObject& o) {
2875   assert(!o.is_flat(), "Array object cannot be flattened");
2876   flatArrayOop array = flatArrayOop(o.obj());
2877   FlatArrayKlass* faklass = FlatArrayKlass::cast(array->klass());
2878   InlineKlass* vk = InlineKlass::cast(faklass->element_klass());
2879   bool need_null_check = faklass->layout_kind() == LayoutKind::NULLABLE_ATOMIC_FLAT;
2880 
2881   // array reference to its class
2882   oop mirror = faklass->java_mirror();
2883   if (!CallbackInvoker::report_class_reference(o, mirror)) {
2884     return false;
2885   }
2886 
2887   // iterate over the array and report each reference to a
2888   // non-null element
2889   for (int index = 0; index < array->length(); index++) {
2890     address addr = (address)array->value_at_addr(index, faklass->layout_helper());
2891 
2892     // check for null
2893     if (need_null_check) {
2894       if (vk->is_payload_marked_as_null(addr)) {
2895         continue;
2896       }
2897     }
2898 
2899     // offset in the array oop
2900     int offset = (int)(addr - cast_from_oop<address>(array));
2901     JvmtiHeapwalkObject elem(o.obj(), offset, vk, faklass->layout_kind());
2902 
2903     // report the array reference
2904     if (!CallbackInvoker::report_array_element_reference(o, elem, index)) {
2905       return false;
2906     }
2907   }
2908   return true;
2909 }
2910 
2911 // a type array references its class
2912 inline bool VM_HeapWalkOperation::iterate_over_type_array(const JvmtiHeapwalkObject& o) {
2913   assert(!o.is_flat(), "Array object cannot be flattened");
2914   Klass* k = o.klass();
2915   oop mirror = k->java_mirror();
2916   if (!CallbackInvoker::report_class_reference(o, mirror)) {
2917     return false;
2918   }
2919 
2920   // report the array contents if required
2921   if (is_reporting_primitive_array_values()) {
2922     if (!CallbackInvoker::report_primitive_array_values(o)) {
2923       return false;
2924     }
2925   }
2926   return true;
2927 }
2928 
2929 #ifdef ASSERT
2930 // verify that a static oop field is in range
2931 static inline bool verify_static_oop(InstanceKlass* ik,
2932                                      oop mirror, int offset) {
2933   address obj_p = cast_from_oop<address>(mirror) + offset;
2934   address start = (address)InstanceMirrorKlass::start_of_static_fields(mirror);
2935   address end = start + (java_lang_Class::static_oop_field_count(mirror) * heapOopSize);
2936   assert(end >= start, "sanity check");
2937 
2938   if (obj_p >= start && obj_p < end) {
2939     return true;
2940   } else {
2941     return false;
2942   }
2943 }
2944 #endif // #ifdef ASSERT
2945 
2946 // a class references its super class, interfaces, class loader, ...
2947 // and finally its static fields
2948 inline bool VM_HeapWalkOperation::iterate_over_class(const JvmtiHeapwalkObject& o) {
2949   assert(!o.is_flat(), "Klass object cannot be flattened");
2950   Klass* klass = java_lang_Class::as_Klass(o.obj());
2951   int i;
2952 
2953   if (klass->is_instance_klass()) {
2954     InstanceKlass* ik = InstanceKlass::cast(klass);
2955 
2956     // Ignore the class if it hasn't been initialized yet
2957     if (!ik->is_linked()) {
2958       return true;
2959     }
2960 
2961     // get the java mirror
2962     oop mirror_oop = klass->java_mirror();
2963     JvmtiHeapwalkObject mirror(mirror_oop);
2964 
2965     // super (only if something more interesting than java.lang.Object)
2966     InstanceKlass* super_klass = ik->super();
2967     if (super_klass != nullptr && super_klass != vmClasses::Object_klass()) {
2968       oop super_oop = super_klass->java_mirror();
2969       if (!CallbackInvoker::report_superclass_reference(mirror, super_oop)) {
2970         return false;
2971       }
2972     }
2973 
2974     // class loader
2975     oop cl = ik->class_loader();
2976     if (cl != nullptr) {
2977       if (!CallbackInvoker::report_class_loader_reference(mirror, cl)) {
2978         return false;
2979       }
2980     }
2981 
2982     // protection domain
2983     oop pd = ik->protection_domain();
2984     if (pd != nullptr) {
2985       if (!CallbackInvoker::report_protection_domain_reference(mirror, pd)) {
2986         return false;
2987       }
2988     }
2989 
2990     // signers
2991     oop signers = ik->signers();
2992     if (signers != nullptr) {
2993       if (!CallbackInvoker::report_signers_reference(mirror, signers)) {
2994         return false;
2995       }
2996     }
2997 
2998     // references from the constant pool
2999     {
3000       ConstantPool* pool = ik->constants();
3001       for (int i = 1; i < pool->length(); i++) {
3002         constantTag tag = pool->tag_at(i).value();
3003         if (tag.is_string() || tag.is_klass() || tag.is_unresolved_klass()) {
3004           oop entry;
3005           if (tag.is_string()) {
3006             entry = pool->resolved_string_at(i);
3007             // If the entry is non-null it is resolved.
3008             if (entry == nullptr) {
3009               continue;
3010             }
3011           } else if (tag.is_klass()) {
3012             entry = pool->resolved_klass_at(i)->java_mirror();
3013           } else {
3014             // Code generated by JIT compilers might not resolve constant
3015             // pool entries.  Treat them as resolved if they are loaded.
3016             assert(tag.is_unresolved_klass(), "must be");
3017             constantPoolHandle cp(Thread::current(), pool);
3018             Klass* klass = ConstantPool::klass_at_if_loaded(cp, i);
3019             if (klass == nullptr) {
3020               continue;
3021             }
3022             entry = klass->java_mirror();
3023           }
3024           if (!CallbackInvoker::report_constant_pool_reference(mirror, entry, (jint)i)) {
3025             return false;
3026           }
3027         }
3028       }
3029     }
3030 
3031     // interfaces
3032     // (These will already have been reported as references from the constant pool
3033     //  but are specified by IterateOverReachableObjects and must be reported).
3034     Array<InstanceKlass*>* interfaces = ik->local_interfaces();
3035     for (i = 0; i < interfaces->length(); i++) {
3036       oop interf = interfaces->at(i)->java_mirror();
3037       if (interf == nullptr) {
3038         continue;
3039       }
3040       if (!CallbackInvoker::report_interface_reference(mirror, interf)) {
3041         return false;
3042       }
3043     }
3044 
3045     // iterate over the static fields
3046 
3047     ClassFieldMap* field_map = ClassFieldMap::create_map_of_static_fields(klass);
3048     for (i=0; i<field_map->field_count(); i++) {
3049       ClassFieldDescriptor* field = field_map->field_at(i);
3050       char type = field->field_type();
3051       if (!is_primitive_field_type(type)) {
3052         oop fld_o = mirror_oop->obj_field(field->field_offset());
3053         assert(verify_static_oop(ik, mirror_oop, field->field_offset()), "sanity check");
3054         if (fld_o != nullptr) {
3055           int slot = field->field_index();
3056           if (!CallbackInvoker::report_static_field_reference(mirror, fld_o, slot)) {
3057             delete field_map;
3058             return false;
3059           }
3060         }
3061       } else {
3062          if (is_reporting_primitive_fields()) {
3063            address addr = cast_from_oop<address>(mirror_oop) + field->field_offset();
3064            int slot = field->field_index();
3065            if (!CallbackInvoker::report_primitive_static_field(mirror, slot, addr, type)) {
3066              delete field_map;
3067              return false;
3068           }
3069         }
3070       }
3071     }
3072     delete field_map;
3073 
3074     return true;
3075   }
3076 
3077   return true;
3078 }
3079 
3080 // an object references a class and its instance fields
3081 // (static fields are ignored here as we report these as
3082 // references from the class).
3083 inline bool VM_HeapWalkOperation::iterate_over_object(const JvmtiHeapwalkObject& o) {
3084   // reference to the class
3085   if (!CallbackInvoker::report_class_reference(o, o.klass()->java_mirror())) {
3086     return false;
3087   }
3088 
3089   // iterate over instance fields
3090   ClassFieldMap* field_map = JvmtiCachedClassFieldMap::get_map_of_instance_fields(o.klass());
3091   for (int i=0; i<field_map->field_count(); i++) {
3092     ClassFieldDescriptor* field = field_map->field_at(i);
3093     char type = field->field_type();
3094     int slot = field->field_index();
3095     int field_offset = field->field_offset();
3096     if (o.is_flat()) {
3097       // the object is inlined, its fields are stored without the header
3098       field_offset += o.offset() - o.inline_klass()->payload_offset();
3099     }
3100     if (!is_primitive_field_type(type)) {
3101       if (field->is_flat()) {
3102         // check for possible nulls
3103         bool can_be_null = field->layout_kind() == LayoutKind::NULLABLE_ATOMIC_FLAT;
3104         if (can_be_null) {
3105           address payload = cast_from_oop<address>(o.obj()) + field_offset;
3106           if (field->inline_klass()->is_payload_marked_as_null(payload)) {
3107             continue;
3108           }
3109         }
3110         JvmtiHeapwalkObject field_obj(o.obj(), field_offset, field->inline_klass(), field->layout_kind());
3111         if (!CallbackInvoker::report_field_reference(o, field_obj, slot)) {
3112           return false;
3113         }
3114       } else {
3115         oop fld_o = o.obj()->obj_field_access<AS_NO_KEEPALIVE | ON_UNKNOWN_OOP_REF>(field_offset);
3116         // ignore any objects that aren't visible to profiler
3117         if (fld_o != nullptr) {
3118           assert(Universe::heap()->is_in(fld_o), "unsafe code should not have references to Klass* anymore");
3119           if (!CallbackInvoker::report_field_reference(o, fld_o, slot)) {
3120             return false;
3121           }
3122         }
3123       }
3124     } else {
3125       if (is_reporting_primitive_fields()) {
3126         // primitive instance field
3127         address addr = cast_from_oop<address>(o.obj()) + field_offset;
3128         if (!CallbackInvoker::report_primitive_instance_field(o, slot, addr, type)) {
3129           return false;
3130         }
3131       }
3132     }
3133   }
3134 
3135   // if the object is a java.lang.String
3136   if (is_reporting_string_values() &&
3137       o.klass() == vmClasses::String_klass()) {
3138     if (!CallbackInvoker::report_string_value(o)) {
3139       return false;
3140     }
3141   }
3142   return true;
3143 }
3144 
3145 
3146 // Collects all simple (non-stack) roots except for threads;
3147 // threads are handled in collect_stack_roots() as an optimization.
3148 // if there's a heap root callback provided then the callback is
3149 // invoked for each simple root.
3150 // if an object reference callback is provided then all simple
3151 // roots are pushed onto the marking stack so that they can be
3152 // processed later
3153 //
3154 inline bool VM_HeapWalkOperation::collect_simple_roots() {
3155   SimpleRootsClosure blk;
3156 
3157   // JNI globals
3158   blk.set_kind(JVMTI_HEAP_REFERENCE_JNI_GLOBAL);
3159   JNIHandles::oops_do(&blk);
3160   if (blk.stopped()) {
3161     return false;
3162   }
3163 
3164   // Preloaded classes and loader from the system dictionary
3165   blk.set_kind(JVMTI_HEAP_REFERENCE_SYSTEM_CLASS);
3166   CLDToOopClosure cld_closure(&blk, ClassLoaderData::_claim_none);
3167   ClassLoaderDataGraph::always_strong_cld_do(&cld_closure);
3168   if (blk.stopped()) {
3169     return false;
3170   }
3171 
3172   // threads are now handled in collect_stack_roots()
3173 
3174   // Other kinds of roots maintained by HotSpot
3175   // Many of these won't be visible but others (such as instances of important
3176   // exceptions) will be visible.
3177   blk.set_kind(JVMTI_HEAP_REFERENCE_OTHER);
3178   Universe::vm_global()->oops_do(&blk);
3179   if (blk.stopped()) {
3180     return false;
3181   }
3182 
3183   return true;
3184 }
3185 
3186 // Reports the thread as JVMTI_HEAP_REFERENCE_THREAD,
3187 // walks the stack of the thread, finds all references (locals
3188 // and JNI calls) and reports these as stack references.
3189 inline bool VM_HeapWalkOperation::collect_stack_refs(JavaThread* java_thread,
3190                                                      JNILocalRootsClosure* blk)
3191 {
3192   oop threadObj = java_thread->threadObj();
3193   oop mounted_vt = java_thread->is_vthread_mounted() ? java_thread->vthread() : nullptr;
3194   if (mounted_vt != nullptr && !JvmtiEnvBase::is_vthread_alive(mounted_vt)) {
3195     mounted_vt = nullptr;
3196   }
3197   assert(threadObj != nullptr, "sanity check");
3198 
3199   StackRefCollector stack_collector(tag_map(), blk, java_thread);
3200 
3201   if (!java_thread->has_last_Java_frame()) {
3202     if (!stack_collector.set_thread(JVMTI_HEAP_REFERENCE_THREAD, threadObj)) {
3203       return false;
3204     }
3205     // no last java frame but there may be JNI locals
3206     blk->set_context(_tag_map->find(threadObj), java_lang_Thread::thread_id(threadObj), 0, (jmethodID)nullptr);
3207     java_thread->active_handles()->oops_do(blk);
3208     return !blk->stopped();
3209   }
3210   // vframes are resource allocated
3211   Thread* current_thread = Thread::current();
3212   ResourceMark rm(current_thread);
3213   HandleMark hm(current_thread);
3214 
3215   RegisterMap reg_map(java_thread,
3216                       RegisterMap::UpdateMap::include,
3217                       RegisterMap::ProcessFrames::include,
3218                       RegisterMap::WalkContinuation::include);
3219 
3220   // first handle mounted vthread (if any)
3221   if (mounted_vt != nullptr) {
3222     frame f = java_thread->last_frame();
3223     vframe* vf = vframe::new_vframe(&f, &reg_map, java_thread);
3224     // report virtual thread as JVMTI_HEAP_REFERENCE_OTHER
3225     if (!stack_collector.set_thread(JVMTI_HEAP_REFERENCE_OTHER, mounted_vt)) {
3226       return false;
3227     }
3228     // split virtual thread and carrier thread stacks by vthread entry ("enterSpecial") frame,
3229     // consider vthread entry frame as the last vthread stack frame
3230     while (vf != nullptr) {
3231       if (!stack_collector.do_frame(vf)) {
3232         return false;
3233       }
3234       if (vf->is_vthread_entry()) {
3235         break;
3236       }
3237       vf = vf->sender();
3238     }
3239   }
3240   // Platform or carrier thread.
3241   vframe* vf = JvmtiEnvBase::get_cthread_last_java_vframe(java_thread, &reg_map);
3242   if (!stack_collector.set_thread(JVMTI_HEAP_REFERENCE_THREAD, threadObj)) {
3243     return false;
3244   }
3245   return stack_collector.process_frames(vf);
3246 }
3247 
3248 
3249 // Collects the simple roots for all threads and collects all
3250 // stack roots - for each thread it walks the execution
3251 // stack to find all references and local JNI refs.
3252 inline bool VM_HeapWalkOperation::collect_stack_roots() {
3253   JNILocalRootsClosure blk;
3254   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thread = jtiwh.next(); ) {
3255     oop threadObj = thread->threadObj();
3256     if (threadObj != nullptr && !thread->is_exiting() && !thread->is_hidden_from_external_view()) {
3257       if (!collect_stack_refs(thread, &blk)) {
3258         return false;
3259       }
3260     }
3261   }
3262   return true;
3263 }
3264 
3265 // Reports stack references for the unmounted virtual thread.
3266 inline bool VM_HeapWalkOperation::collect_vthread_stack_refs(oop vt) {
3267   if (!JvmtiEnvBase::is_vthread_alive(vt)) {
3268     return true;
3269   }
3270   ContinuationWrapper cont(java_lang_VirtualThread::continuation(vt));
3271   if (cont.is_empty()) {
3272     return true;
3273   }
3274   assert(!cont.is_mounted(), "sanity check");
3275 
3276   stackChunkOop chunk = cont.last_nonempty_chunk();
3277   if (chunk == nullptr || chunk->is_empty()) {
3278     return true;
3279   }
3280 
3281   // vframes are resource allocated
3282   Thread* current_thread = Thread::current();
3283   ResourceMark rm(current_thread);
3284   HandleMark hm(current_thread);
3285 
3286   RegisterMap reg_map(cont.continuation(), RegisterMap::UpdateMap::include);
3287 
3288   JNILocalRootsClosure blk;
3289   // JavaThread is not required for unmounted virtual threads
3290   StackRefCollector stack_collector(tag_map(), &blk, nullptr);
3291   // reference to the vthread is already reported
3292   if (!stack_collector.set_thread(vt)) {
3293     return false;
3294   }
3295 
3296   frame fr = chunk->top_frame(&reg_map);
3297   vframe* vf = vframe::new_vframe(&fr, &reg_map, nullptr);
3298   return stack_collector.process_frames(vf);
3299 }
3300 
3301 // visit an object
3302 // first mark the object as visited
3303 // second get all the outbound references from this object (in other words, all
3304 // the objects referenced by this object).
3305 //
3306 bool VM_HeapWalkOperation::visit(const JvmtiHeapwalkObject& o) {
3307   // mark object as visited
3308   assert(!visit_stack()->is_visited(o), "can't visit same object more than once");
3309   visit_stack()->mark_visited(o);
3310 
3311   Klass* klass = o.klass();
3312   // instance
3313   if (klass->is_instance_klass()) {
3314     if (klass == vmClasses::Class_klass()) {
3315       assert(!o.is_flat(), "Class object cannot be flattened");
3316       if (!java_lang_Class::is_primitive(o.obj())) {
3317         // a java.lang.Class
3318         return iterate_over_class(o);
3319       }
3320     } else {
3321       // we report stack references only when initial object is not specified
3322       // (in the case we start from heap roots which include platform thread stack references)
3323       if (initial_object().is_null() && java_lang_VirtualThread::is_subclass(klass)) {
3324         assert(!o.is_flat(), "VirtualThread object cannot be flattened");
3325         if (!collect_vthread_stack_refs(o.obj())) {
3326           return false;
3327         }
3328       }
3329       return iterate_over_object(o);
3330     }
3331   }
3332 
3333   // flat object array
3334   if (klass->is_flatArray_klass()) {
3335       return iterate_over_flat_array(o);
3336   }
3337 
3338   // object array
3339   if (klass->is_objArray_klass()) {
3340     return iterate_over_array(o);
3341   }
3342 
3343   // type array
3344   if (klass->is_typeArray_klass()) {
3345     return iterate_over_type_array(o);
3346   }
3347 
3348   return true;
3349 }
3350 
3351 void VM_HeapWalkOperation::doit() {
3352   ResourceMark rm;
3353   ClassFieldMapCacheMark cm;
3354 
3355   JvmtiTagMap::check_hashmaps_for_heapwalk(_dead_objects);
3356 
3357   assert(visit_stack()->is_empty(), "visit stack must be empty");
3358 
3359   // the heap walk starts with an initial object or the heap roots
3360   if (initial_object().is_null()) {
3361     // can result in a big performance boost for an agent that is
3362     // focused on analyzing references in the thread stacks.
3363     if (!collect_stack_roots()) return;
3364 
3365     if (!collect_simple_roots()) return;
3366   } else {
3367     visit_stack()->push(initial_object()());
3368   }
3369 
3370   // object references required
3371   if (is_following_references()) {
3372 
3373     // visit each object until all reachable objects have been
3374     // visited or the callback asked to terminate the iteration.
3375     while (!visit_stack()->is_empty()) {
3376       const JvmtiHeapwalkObject o = visit_stack()->pop();
3377       if (!visit_stack()->is_visited(o)) {
3378         if (!visit(o)) {
3379           break;
3380         }
3381       }
3382     }
3383   }
3384 }
3385 
3386 // iterate over all objects that are reachable from a set of roots
3387 void JvmtiTagMap::iterate_over_reachable_objects(jvmtiHeapRootCallback heap_root_callback,
3388                                                  jvmtiStackReferenceCallback stack_ref_callback,
3389                                                  jvmtiObjectReferenceCallback object_ref_callback,
3390                                                  const void* user_data) {
3391   // VTMS transitions must be disabled before the EscapeBarrier.
3392   JvmtiVTMSTransitionDisabler disabler;
3393 
3394   JavaThread* jt = JavaThread::current();
3395   EscapeBarrier eb(true, jt);
3396   eb.deoptimize_objects_all_threads();
3397   Arena dead_object_arena(mtServiceability);
3398   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
3399 
3400   {
3401     MutexLocker ml(Heap_lock);
3402     BasicHeapWalkContext context(heap_root_callback, stack_ref_callback, object_ref_callback);
3403     VM_HeapWalkOperation op(this, Handle(), context, user_data, &dead_objects);
3404     VMThread::execute(&op);
3405   }
3406   convert_flat_object_entries();
3407 
3408   // Post events outside of Heap_lock
3409   post_dead_objects(&dead_objects);
3410 }
3411 
3412 // iterate over all objects that are reachable from a given object
3413 void JvmtiTagMap::iterate_over_objects_reachable_from_object(jobject object,
3414                                                              jvmtiObjectReferenceCallback object_ref_callback,
3415                                                              const void* user_data) {
3416   oop obj = JNIHandles::resolve(object);
3417   Handle initial_object(Thread::current(), obj);
3418 
3419   Arena dead_object_arena(mtServiceability);
3420   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
3421 
3422   JvmtiVTMSTransitionDisabler disabler;
3423 
3424   {
3425     MutexLocker ml(Heap_lock);
3426     BasicHeapWalkContext context(nullptr, nullptr, object_ref_callback);
3427     VM_HeapWalkOperation op(this, initial_object, context, user_data, &dead_objects);
3428     VMThread::execute(&op);
3429   }
3430   convert_flat_object_entries();
3431 
3432   // Post events outside of Heap_lock
3433   post_dead_objects(&dead_objects);
3434 }
3435 
3436 // follow references from an initial object or the GC roots
3437 void JvmtiTagMap::follow_references(jint heap_filter,
3438                                     Klass* klass,
3439                                     jobject object,
3440                                     const jvmtiHeapCallbacks* callbacks,
3441                                     const void* user_data)
3442 {
3443   // VTMS transitions must be disabled before the EscapeBarrier.
3444   JvmtiVTMSTransitionDisabler disabler;
3445 
3446   oop obj = JNIHandles::resolve(object);
3447   JavaThread* jt = JavaThread::current();
3448   Handle initial_object(jt, obj);
3449   // EA based optimizations that are tagged or reachable from initial_object are already reverted.
3450   EscapeBarrier eb(initial_object.is_null() &&
3451                    !(heap_filter & JVMTI_HEAP_FILTER_UNTAGGED),
3452                    jt);
3453   eb.deoptimize_objects_all_threads();
3454 
3455   Arena dead_object_arena(mtServiceability);
3456   GrowableArray<jlong> dead_objects(&dead_object_arena, 10, 0, 0);
3457 
3458   {
3459     MutexLocker ml(Heap_lock);
3460     AdvancedHeapWalkContext context(heap_filter, klass, callbacks);
3461     VM_HeapWalkOperation op(this, initial_object, context, user_data, &dead_objects);
3462     VMThread::execute(&op);
3463   }
3464   convert_flat_object_entries();
3465 
3466   // Post events outside of Heap_lock
3467   post_dead_objects(&dead_objects);
3468 }
3469 
3470 // Verify gc_notification follows set_needs_cleaning.
3471 DEBUG_ONLY(static bool notified_needs_cleaning = false;)
3472 
3473 void JvmtiTagMap::set_needs_cleaning() {
3474   assert(SafepointSynchronize::is_at_safepoint(), "called in gc pause");
3475   assert(Thread::current()->is_VM_thread(), "should be the VM thread");
3476   // Can't assert !notified_needs_cleaning; a partial GC might be upgraded
3477   // to a full GC and do this twice without intervening gc_notification.
3478   DEBUG_ONLY(notified_needs_cleaning = true;)
3479 
3480   JvmtiEnvIterator it;
3481   for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
3482     JvmtiTagMap* tag_map = env->tag_map_acquire();
3483     if (tag_map != nullptr) {
3484       tag_map->_needs_cleaning = !tag_map->is_empty();
3485     }
3486   }
3487 }
3488 
3489 void JvmtiTagMap::gc_notification(size_t num_dead_entries) {
3490   assert(notified_needs_cleaning, "missing GC notification");
3491   DEBUG_ONLY(notified_needs_cleaning = false;)
3492 
3493   // Notify ServiceThread if there's work to do.
3494   {
3495     MonitorLocker ml(Service_lock, Mutex::_no_safepoint_check_flag);
3496     _has_object_free_events = (num_dead_entries != 0);
3497     if (_has_object_free_events) ml.notify_all();
3498   }
3499 
3500   // If no dead entries then cancel cleaning requests.
3501   if (num_dead_entries == 0) {
3502     JvmtiEnvIterator it;
3503     for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
3504       JvmtiTagMap* tag_map = env->tag_map_acquire();
3505       if (tag_map != nullptr) {
3506         MutexLocker ml (tag_map->lock(), Mutex::_no_safepoint_check_flag);
3507         tag_map->_needs_cleaning = false;
3508       }
3509     }
3510   }
3511 }
3512 
3513 // Used by ServiceThread to discover there is work to do.
3514 bool JvmtiTagMap::has_object_free_events_and_reset() {
3515   assert_lock_strong(Service_lock);
3516   bool result = _has_object_free_events;
3517   _has_object_free_events = false;
3518   return result;
3519 }
3520 
3521 // Used by ServiceThread to clean up tagmaps.
3522 void JvmtiTagMap::flush_all_object_free_events() {
3523   JavaThread* thread = JavaThread::current();
3524   JvmtiEnvIterator it;
3525   for (JvmtiEnv* env = it.first(); env != nullptr; env = it.next(env)) {
3526     JvmtiTagMap* tag_map = env->tag_map_acquire();
3527     if (tag_map != nullptr) {
3528       tag_map->flush_object_free_events();
3529       ThreadBlockInVM tbiv(thread); // Be safepoint-polite while looping.
3530     }
3531   }
3532 }