1 /*
   2  * Copyright (c) 1997, 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 "cds/archiveHeapLoader.hpp"
  26 #include "cds/cdsConfig.hpp"
  27 #include "cds/heapShared.hpp"
  28 #include "classfile/classLoader.hpp"
  29 #include "classfile/classLoaderData.inline.hpp"
  30 #include "classfile/classLoaderDataGraph.inline.hpp"
  31 #include "classfile/javaClasses.inline.hpp"
  32 #include "classfile/moduleEntry.hpp"
  33 #include "classfile/systemDictionary.hpp"
  34 #include "classfile/systemDictionaryShared.hpp"
  35 #include "classfile/vmClasses.hpp"
  36 #include "classfile/vmSymbols.hpp"
  37 #include "gc/shared/collectedHeap.inline.hpp"
  38 #include "jvm_io.h"
  39 #include "logging/log.hpp"
  40 #include "memory/metadataFactory.hpp"
  41 #include "memory/metaspaceClosure.hpp"
  42 #include "memory/oopFactory.hpp"
  43 #include "memory/resourceArea.hpp"
  44 #include "memory/universe.hpp"
  45 #include "oops/compressedKlass.inline.hpp"
  46 #include "oops/compressedOops.inline.hpp"
  47 #include "oops/instanceKlass.hpp"
  48 #include "oops/klass.inline.hpp"
  49 #include "oops/objArrayKlass.hpp"
  50 #include "oops/oop.inline.hpp"
  51 #include "oops/oopHandle.inline.hpp"
  52 #include "prims/jvmtiExport.hpp"
  53 #include "runtime/atomic.hpp"
  54 #include "runtime/handles.inline.hpp"
  55 #include "runtime/perfData.hpp"
  56 #include "utilities/macros.hpp"
  57 #include "utilities/numberSeq.hpp"
  58 #include "utilities/powerOfTwo.hpp"
  59 #include "utilities/rotate_bits.hpp"
  60 #include "utilities/stack.inline.hpp"
  61 
  62 void Klass::set_java_mirror(Handle m) {
  63   assert(!m.is_null(), "New mirror should never be null.");
  64   assert(_java_mirror.is_empty(), "should only be used to initialize mirror");
  65   _java_mirror = class_loader_data()->add_handle(m);
  66 }
  67 
  68 bool Klass::is_cloneable() const {
  69   return _misc_flags.is_cloneable_fast() ||
  70          is_subtype_of(vmClasses::Cloneable_klass());
  71 }
  72 
  73 void Klass::set_is_cloneable() {
  74   if (name() == vmSymbols::java_lang_invoke_MemberName()) {
  75     assert(is_final(), "no subclasses allowed");
  76     // MemberName cloning should not be intrinsified and always happen in JVM_Clone.
  77   } else if (is_instance_klass() && InstanceKlass::cast(this)->reference_type() != REF_NONE) {
  78     // Reference cloning should not be intrinsified and always happen in JVM_Clone.
  79   } else {
  80     _misc_flags.set_is_cloneable_fast(true);
  81   }
  82 }
  83 
  84 uint8_t Klass::compute_hash_slot(Symbol* n) {
  85   uint hash_code;
  86   // Special cases for the two superclasses of all Array instances.
  87   // Code elsewhere assumes, for all instances of ArrayKlass, that
  88   // these two interfaces will be in this order.
  89 
  90   // We ensure there are some empty slots in the hash table between
  91   // these two very common interfaces because if they were adjacent
  92   // (e.g. Slots 0 and 1), then any other class which hashed to 0 or 1
  93   // would result in a probe length of 3.
  94   if (n == vmSymbols::java_lang_Cloneable()) {
  95     hash_code = 0;
  96   } else if (n == vmSymbols::java_io_Serializable()) {
  97     hash_code = SECONDARY_SUPERS_TABLE_SIZE / 2;
  98   } else {
  99     auto s = (const jbyte*) n->bytes();
 100     hash_code = java_lang_String::hash_code(s, n->utf8_length());
 101     // We use String::hash_code here (rather than e.g.
 102     // Symbol::identity_hash()) in order to have a hash code that
 103     // does not change from run to run. We want that because the
 104     // hash value for a secondary superclass appears in generated
 105     // code as a constant.
 106 
 107     // This constant is magic: see Knuth, "Fibonacci Hashing".
 108     constexpr uint multiplier
 109       = 2654435769; // (uint)(((u8)1 << 32) / ((1 + sqrt(5)) / 2 ))
 110     constexpr uint hash_shift = sizeof(hash_code) * 8 - 6;
 111     // The leading bits of the least significant half of the product.
 112     hash_code = (hash_code * multiplier) >> hash_shift;
 113 
 114     if (StressSecondarySupers) {
 115       // Generate many hash collisions in order to stress-test the
 116       // linear search fallback.
 117       hash_code = hash_code % 3;
 118       hash_code = hash_code * (SECONDARY_SUPERS_TABLE_SIZE / 3);
 119     }
 120   }
 121 
 122   return (hash_code & SECONDARY_SUPERS_TABLE_MASK);
 123 }
 124 
 125 void Klass::set_name(Symbol* n) {
 126   _name = n;
 127 
 128   if (_name != nullptr) {
 129     _name->increment_refcount();
 130   }
 131 
 132   {
 133     elapsedTimer selftime;
 134     selftime.start();
 135 
 136     _hash_slot = compute_hash_slot(n);
 137     assert(_hash_slot < SECONDARY_SUPERS_TABLE_SIZE, "required");
 138 
 139     selftime.stop();
 140     if (UsePerfData) {
 141       ClassLoader::perf_secondary_hash_time()->inc(selftime.ticks());
 142     }
 143   }
 144 
 145   if (CDSConfig::is_dumping_archive() && is_instance_klass()) {
 146     SystemDictionaryShared::init_dumptime_info(InstanceKlass::cast(this));
 147   }
 148 }
 149 
 150 bool Klass::is_subclass_of(const Klass* k) const {
 151   // Run up the super chain and check
 152   if (this == k) return true;
 153 
 154   Klass* t = const_cast<Klass*>(this)->super();
 155 
 156   while (t != nullptr) {
 157     if (t == k) return true;
 158     t = t->super();
 159   }
 160   return false;
 161 }
 162 
 163 void Klass::release_C_heap_structures(bool release_constant_pool) {
 164   if (_name != nullptr) _name->decrement_refcount();
 165 }
 166 
 167 bool Klass::linear_search_secondary_supers(const Klass* k) const {
 168   // Scan the array-of-objects for a match
 169   // FIXME: We could do something smarter here, maybe a vectorized
 170   // comparison or a binary search, but is that worth any added
 171   // complexity?
 172   int cnt = secondary_supers()->length();
 173   for (int i = 0; i < cnt; i++) {
 174     if (secondary_supers()->at(i) == k) {
 175       return true;
 176     }
 177   }
 178   return false;
 179 }
 180 
 181 // Given a secondary superklass k, an initial array index, and an
 182 // occupancy bitmap rotated such that Bit 1 is the next bit to test,
 183 // search for k.
 184 bool Klass::fallback_search_secondary_supers(const Klass* k, int index, uintx rotated_bitmap) const {
 185   // Once the occupancy bitmap is almost full, it's faster to use a
 186   // linear search.
 187   if (secondary_supers()->length() > SECONDARY_SUPERS_TABLE_SIZE - 2) {
 188     return linear_search_secondary_supers(k);
 189   }
 190 
 191   // This is conventional linear probing, but instead of terminating
 192   // when a null entry is found in the table, we maintain a bitmap
 193   // in which a 0 indicates missing entries.
 194 
 195   precond((int)population_count(rotated_bitmap) == secondary_supers()->length());
 196 
 197   // The check for secondary_supers()->length() <= SECONDARY_SUPERS_TABLE_SIZE - 2
 198   // at the start of this function guarantees there are 0s in the
 199   // bitmap, so this loop eventually terminates.
 200   while ((rotated_bitmap & 2) != 0) {
 201     if (++index == secondary_supers()->length()) {
 202       index = 0;
 203     }
 204     if (secondary_supers()->at(index) == k) {
 205       return true;
 206     }
 207     rotated_bitmap = rotate_right(rotated_bitmap, 1);
 208   }
 209   return false;
 210 }
 211 
 212 // Return self, except for abstract classes with exactly 1
 213 // implementor.  Then return the 1 concrete implementation.
 214 Klass *Klass::up_cast_abstract() {
 215   Klass *r = this;
 216   while( r->is_abstract() ) {   // Receiver is abstract?
 217     Klass *s = r->subklass();   // Check for exactly 1 subklass
 218     if (s == nullptr || s->next_sibling() != nullptr) // Oops; wrong count; give up
 219       return this;              // Return 'this' as a no-progress flag
 220     r = s;                    // Loop till find concrete class
 221   }
 222   return r;                   // Return the 1 concrete class
 223 }
 224 
 225 // Find LCA in class hierarchy
 226 Klass *Klass::LCA( Klass *k2 ) {
 227   Klass *k1 = this;
 228   while( 1 ) {
 229     if( k1->is_subtype_of(k2) ) return k2;
 230     if( k2->is_subtype_of(k1) ) return k1;
 231     k1 = k1->super();
 232     k2 = k2->super();
 233   }
 234 }
 235 
 236 
 237 void Klass::check_valid_for_instantiation(bool throwError, TRAPS) {
 238   ResourceMark rm(THREAD);
 239   THROW_MSG(throwError ? vmSymbols::java_lang_InstantiationError()
 240             : vmSymbols::java_lang_InstantiationException(), external_name());
 241 }
 242 
 243 
 244 void Klass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS) {
 245   ResourceMark rm(THREAD);
 246   assert(s != nullptr, "Throw NPE!");
 247   THROW_MSG(vmSymbols::java_lang_ArrayStoreException(),
 248             err_msg("arraycopy: source type %s is not an array", s->klass()->external_name()));
 249 }
 250 
 251 
 252 void Klass::initialize(TRAPS) {
 253   ShouldNotReachHere();
 254 }
 255 
 256 Klass* Klass::find_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const {
 257 #ifdef ASSERT
 258   tty->print_cr("Error: find_field called on a klass oop."
 259                 " Likely error: reflection method does not correctly"
 260                 " wrap return value in a mirror object.");
 261 #endif
 262   ShouldNotReachHere();
 263   return nullptr;
 264 }
 265 
 266 Method* Klass::uncached_lookup_method(const Symbol* name, const Symbol* signature,
 267                                       OverpassLookupMode overpass_mode,
 268                                       PrivateLookupMode private_mode) const {
 269 #ifdef ASSERT
 270   tty->print_cr("Error: uncached_lookup_method called on a klass oop."
 271                 " Likely error: reflection method does not correctly"
 272                 " wrap return value in a mirror object.");
 273 #endif
 274   ShouldNotReachHere();
 275   return nullptr;
 276 }
 277 
 278 static markWord make_prototype(const Klass* kls) {
 279   markWord prototype = markWord::prototype();
 280 #ifdef _LP64
 281   if (UseCompactObjectHeaders) {
 282     // With compact object headers, the narrow Klass ID is part of the mark word.
 283     // We therfore seed the mark word with the narrow Klass ID.
 284     // Note that only those Klass that can be instantiated have a narrow Klass ID.
 285     // For those who don't, we leave the klass bits empty and assert if someone
 286     // tries to use those.
 287     const narrowKlass nk = CompressedKlassPointers::is_encodable(kls) ?
 288         CompressedKlassPointers::encode(const_cast<Klass*>(kls)) : 0;
 289     prototype = prototype.set_narrow_klass(nk);
 290   }
 291 #endif
 292   return prototype;
 293 }
 294 
 295 Klass::Klass() : _kind(UnknownKlassKind) {
 296   assert(CDSConfig::is_dumping_static_archive() || CDSConfig::is_using_archive(), "only for cds");
 297 }
 298 
 299 // "Normal" instantiation is preceded by a MetaspaceObj allocation
 300 // which zeros out memory - calloc equivalent.
 301 // The constructor is also used from CppVtableCloner,
 302 // which doesn't zero out the memory before calling the constructor.
 303 Klass::Klass(KlassKind kind) : _kind(kind),
 304                                _prototype_header(make_prototype(this)),
 305                                _shared_class_path_index(-1) {
 306   CDS_ONLY(_shared_class_flags = 0;)
 307   CDS_JAVA_HEAP_ONLY(_archived_mirror_index = -1;)
 308   _primary_supers[0] = this;
 309   set_super_check_offset(in_bytes(primary_supers_offset()));
 310 }
 311 
 312 jint Klass::array_layout_helper(BasicType etype) {
 313   assert(etype >= T_BOOLEAN && etype <= T_OBJECT, "valid etype");
 314   // Note that T_ARRAY is not allowed here.
 315   int  hsize = arrayOopDesc::base_offset_in_bytes(etype);
 316   int  esize = type2aelembytes(etype);
 317   bool isobj = (etype == T_OBJECT);
 318   int  tag   =  isobj ? _lh_array_tag_obj_value : _lh_array_tag_type_value;
 319   int lh = array_layout_helper(tag, hsize, etype, exact_log2(esize));
 320 
 321   assert(lh < (int)_lh_neutral_value, "must look like an array layout");
 322   assert(layout_helper_is_array(lh), "correct kind");
 323   assert(layout_helper_is_objArray(lh) == isobj, "correct kind");
 324   assert(layout_helper_is_typeArray(lh) == !isobj, "correct kind");
 325   assert(layout_helper_header_size(lh) == hsize, "correct decode");
 326   assert(layout_helper_element_type(lh) == etype, "correct decode");
 327   assert(1 << layout_helper_log2_element_size(lh) == esize, "correct decode");
 328 
 329   return lh;
 330 }
 331 
 332 bool Klass::can_be_primary_super_slow() const {
 333   if (super() == nullptr)
 334     return true;
 335   else if (super()->super_depth() >= primary_super_limit()-1)
 336     return false;
 337   else
 338     return true;
 339 }
 340 
 341 void Klass::set_secondary_supers(Array<Klass*>* secondaries, uintx bitmap) {
 342 #ifdef ASSERT
 343   if (secondaries != nullptr) {
 344     uintx real_bitmap = compute_secondary_supers_bitmap(secondaries);
 345     assert(bitmap == real_bitmap, "must be");
 346     assert(secondaries->length() >= (int)population_count(bitmap), "must be");
 347   }
 348 #endif
 349   _secondary_supers_bitmap = bitmap;
 350   _secondary_supers = secondaries;
 351 
 352   if (secondaries != nullptr) {
 353     LogMessage(class, load) msg;
 354     NonInterleavingLogStream log {LogLevel::Debug, msg};
 355     if (log.is_enabled()) {
 356       ResourceMark rm;
 357       log.print_cr("set_secondary_supers: hash_slot: %d; klass: %s", hash_slot(), external_name());
 358       print_secondary_supers_on(&log);
 359     }
 360   }
 361 }
 362 
 363 // Hashed secondary superclasses
 364 //
 365 // We use a compressed 64-entry hash table with linear probing. We
 366 // start by creating a hash table in the usual way, followed by a pass
 367 // that removes all the null entries. To indicate which entries would
 368 // have been null we use a bitmap that contains a 1 in each position
 369 // where an entry is present, 0 otherwise. This bitmap also serves as
 370 // a kind of Bloom filter, which in many cases allows us quickly to
 371 // eliminate the possibility that something is a member of a set of
 372 // secondaries.
 373 uintx Klass::hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite) {
 374   const int length = secondaries->length();
 375 
 376   if (length == 0) {
 377     return SECONDARY_SUPERS_BITMAP_EMPTY;
 378   }
 379 
 380   if (length == 1) {
 381     int hash_slot = secondaries->at(0)->hash_slot();
 382     return uintx(1) << hash_slot;
 383   }
 384 
 385   // Invariant: _secondary_supers.length >= population_count(_secondary_supers_bitmap)
 386 
 387   // Don't attempt to hash a table that's completely full, because in
 388   // the case of an absent interface linear probing would not
 389   // terminate.
 390   if (length >= SECONDARY_SUPERS_TABLE_SIZE) {
 391     return SECONDARY_SUPERS_BITMAP_FULL;
 392   }
 393 
 394   {
 395     PerfTraceTime ptt(ClassLoader::perf_secondary_hash_time());
 396 
 397     ResourceMark rm;
 398     uintx bitmap = SECONDARY_SUPERS_BITMAP_EMPTY;
 399     auto hashed_secondaries = new GrowableArray<Klass*>(SECONDARY_SUPERS_TABLE_SIZE,
 400                                                         SECONDARY_SUPERS_TABLE_SIZE, nullptr);
 401 
 402     for (int j = 0; j < length; j++) {
 403       Klass* k = secondaries->at(j);
 404       hash_insert(k, hashed_secondaries, bitmap);
 405     }
 406 
 407     // Pack the hashed secondaries array by copying it into the
 408     // secondaries array, sans nulls, if modification is allowed.
 409     // Otherwise, validate the order.
 410     int i = 0;
 411     for (int slot = 0; slot < SECONDARY_SUPERS_TABLE_SIZE; slot++) {
 412       bool has_element = ((bitmap >> slot) & 1) != 0;
 413       assert(has_element == (hashed_secondaries->at(slot) != nullptr), "");
 414       if (has_element) {
 415         Klass* k = hashed_secondaries->at(slot);
 416         if (rewrite) {
 417           secondaries->at_put(i, k);
 418         } else if (secondaries->at(i) != k) {
 419           assert(false, "broken secondary supers hash table");
 420           return SECONDARY_SUPERS_BITMAP_FULL;
 421         }
 422         i++;
 423       }
 424     }
 425     assert(i == secondaries->length(), "mismatch");
 426     postcond((int)population_count(bitmap) == secondaries->length());
 427 
 428     return bitmap;
 429   }
 430 }
 431 
 432 void Klass::hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap) {
 433   assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 434 
 435   int dist = 0;
 436   for (int slot = klass->hash_slot(); true; slot = (slot + 1) & SECONDARY_SUPERS_TABLE_MASK) {
 437     Klass* existing = secondaries->at(slot);
 438     assert(((bitmap >> slot) & 1) == (existing != nullptr), "mismatch");
 439     if (existing == nullptr) { // no conflict
 440       secondaries->at_put(slot, klass);
 441       bitmap |= uintx(1) << slot;
 442       assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 443       return;
 444     } else {
 445       // Use Robin Hood hashing to minimize the worst case search.
 446       // Also, every permutation of the insertion sequence produces
 447       // the same final Robin Hood hash table, provided that a
 448       // consistent tie breaker is used.
 449       int existing_dist = (slot - existing->hash_slot()) & SECONDARY_SUPERS_TABLE_MASK;
 450       if (existing_dist < dist
 451           // This tie breaker ensures that the hash order is maintained.
 452           || ((existing_dist == dist)
 453               && (uintptr_t(existing) < uintptr_t(klass)))) {
 454         Klass* tmp = secondaries->at(slot);
 455         secondaries->at_put(slot, klass);
 456         klass = tmp;
 457         dist = existing_dist;
 458       }
 459       ++dist;
 460     }
 461   }
 462 }
 463 
 464 Array<Klass*>* Klass::pack_secondary_supers(ClassLoaderData* loader_data,
 465                                             GrowableArray<Klass*>* primaries,
 466                                             GrowableArray<Klass*>* secondaries,
 467                                             uintx& bitmap, TRAPS) {
 468   int new_length = primaries->length() + secondaries->length();
 469   Array<Klass*>* secondary_supers = MetadataFactory::new_array<Klass*>(loader_data, new_length, CHECK_NULL);
 470 
 471   // Combine the two arrays into a metadata object to pack the array.
 472   // The primaries are added in the reverse order, then the secondaries.
 473   int fill_p = primaries->length();
 474   for (int j = 0; j < fill_p; j++) {
 475     secondary_supers->at_put(j, primaries->pop());  // add primaries in reverse order.
 476   }
 477   for( int j = 0; j < secondaries->length(); j++ ) {
 478     secondary_supers->at_put(j+fill_p, secondaries->at(j));  // add secondaries on the end.
 479   }
 480 #ifdef ASSERT
 481   // We must not copy any null placeholders left over from bootstrap.
 482   for (int j = 0; j < secondary_supers->length(); j++) {
 483     assert(secondary_supers->at(j) != nullptr, "correct bootstrapping order");
 484   }
 485 #endif
 486 
 487   bitmap = hash_secondary_supers(secondary_supers, /*rewrite=*/true); // rewrites freshly allocated array
 488   return secondary_supers;
 489 }
 490 
 491 uintx Klass::compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers) {
 492   return hash_secondary_supers(secondary_supers, /*rewrite=*/false); // no rewrites allowed
 493 }
 494 
 495 uint8_t Klass::compute_home_slot(Klass* k, uintx bitmap) {
 496   uint8_t hash = k->hash_slot();
 497   if (hash > 0) {
 498     return population_count(bitmap << (SECONDARY_SUPERS_TABLE_SIZE - hash));
 499   }
 500   return 0;
 501 }
 502 
 503 
 504 void Klass::initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS) {
 505   if (k == nullptr) {
 506     set_super(nullptr);
 507     _primary_supers[0] = this;
 508     assert(super_depth() == 0, "Object must already be initialized properly");
 509   } else if (k != super() || k == vmClasses::Object_klass()) {
 510     assert(super() == nullptr || super() == vmClasses::Object_klass(),
 511            "initialize this only once to a non-trivial value");
 512     set_super(k);
 513     Klass* sup = k;
 514     int sup_depth = sup->super_depth();
 515     juint my_depth  = MIN2(sup_depth + 1, (int)primary_super_limit());
 516     if (!can_be_primary_super_slow())
 517       my_depth = primary_super_limit();
 518     for (juint i = 0; i < my_depth; i++) {
 519       _primary_supers[i] = sup->_primary_supers[i];
 520     }
 521     Klass* *super_check_cell;
 522     if (my_depth < primary_super_limit()) {
 523       _primary_supers[my_depth] = this;
 524       super_check_cell = &_primary_supers[my_depth];
 525     } else {
 526       // Overflow of the primary_supers array forces me to be secondary.
 527       super_check_cell = &_secondary_super_cache;
 528     }
 529     set_super_check_offset(u4((address)super_check_cell - (address) this));
 530 
 531 #ifdef ASSERT
 532     {
 533       juint j = super_depth();
 534       assert(j == my_depth, "computed accessor gets right answer");
 535       Klass* t = this;
 536       while (!t->can_be_primary_super()) {
 537         t = t->super();
 538         j = t->super_depth();
 539       }
 540       for (juint j1 = j+1; j1 < primary_super_limit(); j1++) {
 541         assert(primary_super_of_depth(j1) == nullptr, "super list padding");
 542       }
 543       while (t != nullptr) {
 544         assert(primary_super_of_depth(j) == t, "super list initialization");
 545         t = t->super();
 546         --j;
 547       }
 548       assert(j == (juint)-1, "correct depth count");
 549     }
 550 #endif
 551   }
 552 
 553   if (secondary_supers() == nullptr) {
 554 
 555     // Now compute the list of secondary supertypes.
 556     // Secondaries can occasionally be on the super chain,
 557     // if the inline "_primary_supers" array overflows.
 558     int extras = 0;
 559     Klass* p;
 560     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 561       ++extras;
 562     }
 563 
 564     ResourceMark rm(THREAD);  // need to reclaim GrowableArrays allocated below
 565 
 566     // Compute the "real" non-extra secondaries.
 567     GrowableArray<Klass*>* secondaries = compute_secondary_supers(extras, transitive_interfaces);
 568     if (secondaries == nullptr) {
 569       // secondary_supers set by compute_secondary_supers
 570       return;
 571     }
 572 
 573     GrowableArray<Klass*>* primaries = new GrowableArray<Klass*>(extras);
 574 
 575     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 576       int i;                    // Scan for overflow primaries being duplicates of 2nd'arys
 577 
 578       // This happens frequently for very deeply nested arrays: the
 579       // primary superclass chain overflows into the secondary.  The
 580       // secondary list contains the element_klass's secondaries with
 581       // an extra array dimension added.  If the element_klass's
 582       // secondary list already contains some primary overflows, they
 583       // (with the extra level of array-ness) will collide with the
 584       // normal primary superclass overflows.
 585       for( i = 0; i < secondaries->length(); i++ ) {
 586         if( secondaries->at(i) == p )
 587           break;
 588       }
 589       if( i < secondaries->length() )
 590         continue;               // It's a dup, don't put it in
 591       primaries->push(p);
 592     }
 593     // Combine the two arrays into a metadata object to pack the array.
 594     uintx bitmap = 0;
 595     Array<Klass*>* s2 = pack_secondary_supers(class_loader_data(), primaries, secondaries, bitmap, CHECK);
 596     set_secondary_supers(s2, bitmap);
 597   }
 598 }
 599 
 600 GrowableArray<Klass*>* Klass::compute_secondary_supers(int num_extra_slots,
 601                                                        Array<InstanceKlass*>* transitive_interfaces) {
 602   assert(num_extra_slots == 0, "override for complex klasses");
 603   assert(transitive_interfaces == nullptr, "sanity");
 604   set_secondary_supers(Universe::the_empty_klass_array(), Universe::the_empty_klass_bitmap());
 605   return nullptr;
 606 }
 607 
 608 
 609 // superklass links
 610 InstanceKlass* Klass::superklass() const {
 611   assert(super() == nullptr || super()->is_instance_klass(), "must be instance klass");
 612   return _super == nullptr ? nullptr : InstanceKlass::cast(_super);
 613 }
 614 
 615 // subklass links.  Used by the compiler (and vtable initialization)
 616 // May be cleaned concurrently, so must use the Compile_lock.
 617 // The log parameter is for clean_weak_klass_links to report unlinked classes.
 618 Klass* Klass::subklass(bool log) const {
 619   // Need load_acquire on the _subklass, because it races with inserts that
 620   // publishes freshly initialized data.
 621   for (Klass* chain = Atomic::load_acquire(&_subklass);
 622        chain != nullptr;
 623        // Do not need load_acquire on _next_sibling, because inserts never
 624        // create _next_sibling edges to dead data.
 625        chain = Atomic::load(&chain->_next_sibling))
 626   {
 627     if (chain->is_loader_alive()) {
 628       return chain;
 629     } else if (log) {
 630       if (log_is_enabled(Trace, class, unload)) {
 631         ResourceMark rm;
 632         log_trace(class, unload)("unlinking class (subclass): %s", chain->external_name());
 633       }
 634     }
 635   }
 636   return nullptr;
 637 }
 638 
 639 Klass* Klass::next_sibling(bool log) const {
 640   // Do not need load_acquire on _next_sibling, because inserts never
 641   // create _next_sibling edges to dead data.
 642   for (Klass* chain = Atomic::load(&_next_sibling);
 643        chain != nullptr;
 644        chain = Atomic::load(&chain->_next_sibling)) {
 645     // Only return alive klass, there may be stale klass
 646     // in this chain if cleaned concurrently.
 647     if (chain->is_loader_alive()) {
 648       return chain;
 649     } else if (log) {
 650       if (log_is_enabled(Trace, class, unload)) {
 651         ResourceMark rm;
 652         log_trace(class, unload)("unlinking class (sibling): %s", chain->external_name());
 653       }
 654     }
 655   }
 656   return nullptr;
 657 }
 658 
 659 void Klass::set_subklass(Klass* s) {
 660   assert(s != this, "sanity check");
 661   Atomic::release_store(&_subklass, s);
 662 }
 663 
 664 void Klass::set_next_sibling(Klass* s) {
 665   assert(s != this, "sanity check");
 666   // Does not need release semantics. If used by cleanup, it will link to
 667   // already safely published data, and if used by inserts, will be published
 668   // safely using cmpxchg.
 669   Atomic::store(&_next_sibling, s);
 670 }
 671 
 672 void Klass::append_to_sibling_list() {
 673   if (Universe::is_fully_initialized()) {
 674     assert_locked_or_safepoint(Compile_lock);
 675   }
 676   debug_only(verify();)
 677   // add ourselves to superklass' subklass list
 678   InstanceKlass* super = superklass();
 679   if (super == nullptr) return;     // special case: class Object
 680   assert((!super->is_interface()    // interfaces cannot be supers
 681           && (super->superklass() == nullptr || !is_interface())),
 682          "an interface can only be a subklass of Object");
 683 
 684   // Make sure there is no stale subklass head
 685   super->clean_subklass();
 686 
 687   for (;;) {
 688     Klass* prev_first_subklass = Atomic::load_acquire(&_super->_subklass);
 689     if (prev_first_subklass != nullptr) {
 690       // set our sibling to be the superklass' previous first subklass
 691       assert(prev_first_subklass->is_loader_alive(), "May not attach not alive klasses");
 692       set_next_sibling(prev_first_subklass);
 693     }
 694     // Note that the prev_first_subklass is always alive, meaning no sibling_next links
 695     // are ever created to not alive klasses. This is an important invariant of the lock-free
 696     // cleaning protocol, that allows us to safely unlink dead klasses from the sibling list.
 697     if (Atomic::cmpxchg(&super->_subklass, prev_first_subklass, this) == prev_first_subklass) {
 698       return;
 699     }
 700   }
 701   debug_only(verify();)
 702 }
 703 
 704 void Klass::clean_subklass() {
 705   for (;;) {
 706     // Need load_acquire, due to contending with concurrent inserts
 707     Klass* subklass = Atomic::load_acquire(&_subklass);
 708     if (subklass == nullptr || subklass->is_loader_alive()) {
 709       return;
 710     }
 711     // Try to fix _subklass until it points at something not dead.
 712     Atomic::cmpxchg(&_subklass, subklass, subklass->next_sibling());
 713   }
 714 }
 715 
 716 void Klass::clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses) {
 717   if (!ClassUnloading || !unloading_occurred) {
 718     return;
 719   }
 720 
 721   Klass* root = vmClasses::Object_klass();
 722   Stack<Klass*, mtGC> stack;
 723 
 724   stack.push(root);
 725   while (!stack.is_empty()) {
 726     Klass* current = stack.pop();
 727 
 728     assert(current->is_loader_alive(), "just checking, this should be live");
 729 
 730     // Find and set the first alive subklass
 731     Klass* sub = current->subklass(true);
 732     current->clean_subklass();
 733     if (sub != nullptr) {
 734       stack.push(sub);
 735     }
 736 
 737     // Find and set the first alive sibling
 738     Klass* sibling = current->next_sibling(true);
 739     current->set_next_sibling(sibling);
 740     if (sibling != nullptr) {
 741       stack.push(sibling);
 742     }
 743 
 744     // Clean the implementors list and method data.
 745     if (clean_alive_klasses && current->is_instance_klass()) {
 746       InstanceKlass* ik = InstanceKlass::cast(current);
 747       ik->clean_weak_instanceklass_links();
 748 
 749       // JVMTI RedefineClasses creates previous versions that are not in
 750       // the class hierarchy, so process them here.
 751       while ((ik = ik->previous_versions()) != nullptr) {
 752         ik->clean_weak_instanceklass_links();
 753       }
 754     }
 755   }
 756 }
 757 
 758 void Klass::metaspace_pointers_do(MetaspaceClosure* it) {
 759   if (log_is_enabled(Trace, cds)) {
 760     ResourceMark rm;
 761     log_trace(cds)("Iter(Klass): %p (%s)", this, external_name());
 762   }
 763 
 764   it->push(&_name);
 765   it->push(&_secondary_supers);
 766   for (int i = 0; i < _primary_super_limit; i++) {
 767     it->push(&_primary_supers[i]);
 768   }
 769   it->push(&_super);
 770   if (!CDSConfig::is_dumping_archive()) {
 771     // If dumping archive, these may point to excluded classes. There's no need
 772     // to follow these pointers anyway, as they will be set to null in
 773     // remove_unshareable_info().
 774     it->push((Klass**)&_subklass);
 775     it->push((Klass**)&_next_sibling);
 776     it->push(&_next_link);
 777   }
 778 
 779   vtableEntry* vt = start_of_vtable();
 780   for (int i=0; i<vtable_length(); i++) {
 781     it->push(vt[i].method_addr());
 782   }
 783 }
 784 
 785 #if INCLUDE_CDS
 786 void Klass::remove_unshareable_info() {
 787   assert(CDSConfig::is_dumping_archive(),
 788           "only called during CDS dump time");
 789   JFR_ONLY(REMOVE_ID(this);)
 790   if (log_is_enabled(Trace, cds, unshareable)) {
 791     ResourceMark rm;
 792     log_trace(cds, unshareable)("remove: %s", external_name());
 793   }
 794 
 795   // _secondary_super_cache may be updated by an is_subtype_of() call
 796   // while ArchiveBuilder is copying metaspace objects. Let's reset it to
 797   // null and let it be repopulated at runtime.
 798   set_secondary_super_cache(nullptr);
 799 
 800   set_subklass(nullptr);
 801   set_next_sibling(nullptr);
 802   set_next_link(nullptr);
 803 
 804   // Null out class_loader_data because we don't share that yet.
 805   set_class_loader_data(nullptr);
 806   set_is_shared();
 807 
 808   // FIXME: validation in Klass::hash_secondary_supers() may fail for shared klasses.
 809   // Even though the bitmaps always match, the canonical order of elements in the table
 810   // is not guaranteed to stay the same (see tie breaker during Robin Hood hashing in Klass::hash_insert).
 811   //assert(compute_secondary_supers_bitmap(secondary_supers()) == _secondary_supers_bitmap, "broken table");
 812 }
 813 
 814 void Klass::remove_java_mirror() {
 815   assert(CDSConfig::is_dumping_archive(), "sanity");
 816   if (log_is_enabled(Trace, cds, unshareable)) {
 817     ResourceMark rm;
 818     log_trace(cds, unshareable)("remove java_mirror: %s", external_name());
 819   }
 820 
 821 #if INCLUDE_CDS_JAVA_HEAP
 822   _archived_mirror_index = -1;
 823   if (CDSConfig::is_dumping_heap()) {
 824     Klass* src_k = ArchiveBuilder::current()->get_source_addr(this);
 825     oop orig_mirror = src_k->java_mirror();
 826     oop scratch_mirror = HeapShared::scratch_java_mirror(orig_mirror);
 827     if (scratch_mirror != nullptr) {
 828       _archived_mirror_index = HeapShared::append_root(scratch_mirror);
 829     }
 830   }
 831 #endif
 832 
 833   // Just null out the mirror.  The class_loader_data() no longer exists.
 834   clear_java_mirror_handle();
 835 }
 836 
 837 void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS) {
 838   assert(is_klass(), "ensure C++ vtable is restored");
 839   assert(is_shared(), "must be set");
 840   assert(secondary_supers()->length() >= (int)population_count(_secondary_supers_bitmap), "must be");
 841   JFR_ONLY(RESTORE_ID(this);)
 842   if (log_is_enabled(Trace, cds, unshareable)) {
 843     ResourceMark rm(THREAD);
 844     oop class_loader = loader_data->class_loader();
 845     log_trace(cds, unshareable)("restore: %s with class loader: %s", external_name(),
 846       class_loader != nullptr ? class_loader->klass()->external_name() : "boot");
 847   }
 848 
 849   // If an exception happened during CDS restore, some of these fields may already be
 850   // set.  We leave the class on the CLD list, even if incomplete so that we don't
 851   // modify the CLD list outside a safepoint.
 852   if (class_loader_data() == nullptr) {
 853     set_class_loader_data(loader_data);
 854 
 855     // Add to class loader list first before creating the mirror
 856     // (same order as class file parsing)
 857     loader_data->add_class(this);
 858   }
 859 
 860   Handle loader(THREAD, loader_data->class_loader());
 861   ModuleEntry* module_entry = nullptr;
 862   Klass* k = this;
 863   if (k->is_objArray_klass()) {
 864     k = ObjArrayKlass::cast(k)->bottom_klass();
 865   }
 866   // Obtain klass' module.
 867   if (k->is_instance_klass()) {
 868     InstanceKlass* ik = (InstanceKlass*) k;
 869     module_entry = ik->module();
 870   } else {
 871     module_entry = ModuleEntryTable::javabase_moduleEntry();
 872   }
 873   // Obtain java.lang.Module, if available
 874   Handle module_handle(THREAD, ((module_entry != nullptr) ? module_entry->module() : (oop)nullptr));
 875 
 876   if (this->has_archived_mirror_index()) {
 877     ResourceMark rm(THREAD);
 878     log_debug(cds, mirror)("%s has raw archived mirror", external_name());
 879     if (ArchiveHeapLoader::is_in_use()) {
 880       bool present = java_lang_Class::restore_archived_mirror(this, loader, module_handle,
 881                                                               protection_domain,
 882                                                               CHECK);
 883       if (present) {
 884         return;
 885       }
 886     }
 887 
 888     // No archived mirror data
 889     log_debug(cds, mirror)("No archived mirror data for %s", external_name());
 890     clear_java_mirror_handle();
 891     this->clear_archived_mirror_index();
 892   }
 893 
 894   // Only recreate it if not present.  A previous attempt to restore may have
 895   // gotten an OOM later but keep the mirror if it was created.
 896   if (java_mirror() == nullptr) {
 897     ResourceMark rm(THREAD);
 898     log_trace(cds, mirror)("Recreate mirror for %s", external_name());
 899     java_lang_Class::create_mirror(this, loader, module_handle, protection_domain, Handle(), CHECK);
 900   }
 901 }
 902 #endif // INCLUDE_CDS
 903 
 904 #if INCLUDE_CDS_JAVA_HEAP
 905 oop Klass::archived_java_mirror() {
 906   assert(has_archived_mirror_index(), "must have archived mirror");
 907   return HeapShared::get_root(_archived_mirror_index);
 908 }
 909 
 910 void Klass::clear_archived_mirror_index() {
 911   if (_archived_mirror_index >= 0) {
 912     HeapShared::clear_root(_archived_mirror_index);
 913   }
 914   _archived_mirror_index = -1;
 915 }
 916 #endif // INCLUDE_CDS_JAVA_HEAP
 917 
 918 void Klass::check_array_allocation_length(int length, int max_length, TRAPS) {
 919   if (length > max_length) {
 920     if (!THREAD->is_in_internal_oome_mark()) {
 921       report_java_out_of_memory("Requested array size exceeds VM limit");
 922       JvmtiExport::post_array_size_exhausted();
 923       THROW_OOP(Universe::out_of_memory_error_array_size());
 924     } else {
 925       THROW_OOP(Universe::out_of_memory_error_java_heap_without_backtrace());
 926     }
 927   } else if (length < 0) {
 928     THROW_MSG(vmSymbols::java_lang_NegativeArraySizeException(), err_msg("%d", length));
 929   }
 930 }
 931 
 932 // Replace the last '+' char with '/'.
 933 static char* convert_hidden_name_to_java(Symbol* name) {
 934   size_t name_len = name->utf8_length();
 935   char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 936   name->as_klass_external_name(result, (int)name_len + 1);
 937   for (int index = (int)name_len; index > 0; index--) {
 938     if (result[index] == '+') {
 939       result[index] = JVM_SIGNATURE_SLASH;
 940       break;
 941     }
 942   }
 943   return result;
 944 }
 945 
 946 // In product mode, this function doesn't have virtual function calls so
 947 // there might be some performance advantage to handling InstanceKlass here.
 948 const char* Klass::external_name() const {
 949   if (is_instance_klass()) {
 950     const InstanceKlass* ik = static_cast<const InstanceKlass*>(this);
 951     if (ik->is_hidden()) {
 952       char* result = convert_hidden_name_to_java(name());
 953       return result;
 954     }
 955   } else if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 956     char* result = convert_hidden_name_to_java(name());
 957     return result;
 958   }
 959   if (name() == nullptr)  return "<unknown>";
 960   return name()->as_klass_external_name();
 961 }
 962 
 963 const char* Klass::signature_name() const {
 964   if (name() == nullptr)  return "<unknown>";
 965   if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 966     size_t name_len = name()->utf8_length();
 967     char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 968     name()->as_C_string(result, (int)name_len + 1);
 969     for (int index = (int)name_len; index > 0; index--) {
 970       if (result[index] == '+') {
 971         result[index] = JVM_SIGNATURE_DOT;
 972         break;
 973       }
 974     }
 975     return result;
 976   }
 977   return name()->as_C_string();
 978 }
 979 
 980 const char* Klass::external_kind() const {
 981   if (is_interface()) return "interface";
 982   if (is_abstract()) return "abstract class";
 983   return "class";
 984 }
 985 
 986 // Unless overridden, jvmti_class_status has no flags set.
 987 jint Klass::jvmti_class_status() const {
 988   return 0;
 989 }
 990 
 991 
 992 // Printing
 993 
 994 void Klass::print_on(outputStream* st) const {
 995   ResourceMark rm;
 996   // print title
 997   st->print("%s", internal_name());
 998   print_address_on(st);
 999   st->cr();
1000 }
1001 
1002 #define BULLET  " - "
1003 
1004 // Caller needs ResourceMark
1005 void Klass::oop_print_on(oop obj, outputStream* st) {
1006   // print title
1007   st->print_cr("%s ", internal_name());
1008   obj->print_address_on(st);
1009 
1010   if (WizardMode) {
1011      // print header
1012      obj->mark().print_on(st);
1013      st->cr();
1014      if (UseCompactObjectHeaders) {
1015        st->print(BULLET"prototype_header: " INTPTR_FORMAT, _prototype_header.value());
1016        st->cr();
1017      }
1018   }
1019 
1020   // print class
1021   st->print(BULLET"klass: ");
1022   obj->klass()->print_value_on(st);
1023   st->print(BULLET"flags: "); _misc_flags.print_on(st); st->cr();
1024   st->cr();
1025 }
1026 
1027 void Klass::oop_print_value_on(oop obj, outputStream* st) {
1028   // print title
1029   ResourceMark rm;              // Cannot print in debug mode without this
1030   st->print("%s", internal_name());
1031   obj->print_address_on(st);
1032 }
1033 
1034 // Verification
1035 
1036 void Klass::verify_on(outputStream* st) {
1037 
1038   // This can be expensive, but it is worth checking that this klass is actually
1039   // in the CLD graph but not in production.
1040 #ifdef ASSERT
1041   if (UseCompressedClassPointers && needs_narrow_id()) {
1042     // Stricter checks for both correct alignment and placement
1043     CompressedKlassPointers::check_encodable(this);
1044   } else {
1045     assert(Metaspace::contains((address)this), "Should be");
1046   }
1047 #endif // ASSERT
1048 
1049   guarantee(this->is_klass(),"should be klass");
1050 
1051   if (super() != nullptr) {
1052     guarantee(super()->is_klass(), "should be klass");
1053   }
1054   if (secondary_super_cache() != nullptr) {
1055     Klass* ko = secondary_super_cache();
1056     guarantee(ko->is_klass(), "should be klass");
1057   }
1058   for ( uint i = 0; i < primary_super_limit(); i++ ) {
1059     Klass* ko = _primary_supers[i];
1060     if (ko != nullptr) {
1061       guarantee(ko->is_klass(), "should be klass");
1062     }
1063   }
1064 
1065   if (java_mirror_no_keepalive() != nullptr) {
1066     guarantee(java_lang_Class::is_instance(java_mirror_no_keepalive()), "should be instance");
1067   }
1068 }
1069 
1070 void Klass::oop_verify_on(oop obj, outputStream* st) {
1071   guarantee(oopDesc::is_oop(obj),  "should be oop");
1072   guarantee(obj->klass()->is_klass(), "klass field is not a klass");
1073 }
1074 
1075 // Note: this function is called with an address that may or may not be a Klass.
1076 // The point is not to assert it is but to check if it could be.
1077 bool Klass::is_valid(Klass* k) {
1078   if (!is_aligned(k, sizeof(MetaWord))) return false;
1079   if ((size_t)k < os::min_page_size()) return false;
1080 
1081   if (!os::is_readable_range(k, k + 1)) return false;
1082   if (!Metaspace::contains(k)) return false;
1083 
1084   if (!Symbol::is_valid(k->name())) return false;
1085   return ClassLoaderDataGraph::is_valid(k->class_loader_data());
1086 }
1087 
1088 Method* Klass::method_at_vtable(int index)  {
1089 #ifndef PRODUCT
1090   assert(index >= 0, "valid vtable index");
1091   if (DebugVtables) {
1092     verify_vtable_index(index);
1093   }
1094 #endif
1095   return start_of_vtable()[index].method();
1096 }
1097 
1098 
1099 #ifndef PRODUCT
1100 
1101 bool Klass::verify_vtable_index(int i) {
1102   int limit = vtable_length()/vtableEntry::size();
1103   assert(i >= 0 && i < limit, "index %d out of bounds %d", i, limit);
1104   return true;
1105 }
1106 
1107 #endif // PRODUCT
1108 
1109 // Caller needs ResourceMark
1110 // joint_in_module_of_loader provides an optimization if 2 classes are in
1111 // the same module to succinctly print out relevant information about their
1112 // module name and class loader's name_and_id for error messages.
1113 // Format:
1114 //   <fully-qualified-external-class-name1> and <fully-qualified-external-class-name2>
1115 //                      are in module <module-name>[@<version>]
1116 //                      of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1117 const char* Klass::joint_in_module_of_loader(const Klass* class2, bool include_parent_loader) const {
1118   assert(module() == class2->module(), "classes do not have the same module");
1119   const char* class1_name = external_name();
1120   size_t len = strlen(class1_name) + 1;
1121 
1122   const char* class2_description = class2->class_in_module_of_loader(true, include_parent_loader);
1123   len += strlen(class2_description);
1124 
1125   len += strlen(" and ");
1126 
1127   char* joint_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1128 
1129   // Just return the FQN if error when allocating string
1130   if (joint_description == nullptr) {
1131     return class1_name;
1132   }
1133 
1134   jio_snprintf(joint_description, len, "%s and %s",
1135                class1_name,
1136                class2_description);
1137 
1138   return joint_description;
1139 }
1140 
1141 // Caller needs ResourceMark
1142 // class_in_module_of_loader provides a standard way to include
1143 // relevant information about a class, such as its module name as
1144 // well as its class loader's name_and_id, in error messages and logging.
1145 // Format:
1146 //   <fully-qualified-external-class-name> is in module <module-name>[@<version>]
1147 //                                         of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1148 const char* Klass::class_in_module_of_loader(bool use_are, bool include_parent_loader) const {
1149   // 1. fully qualified external name of class
1150   const char* klass_name = external_name();
1151   size_t len = strlen(klass_name) + 1;
1152 
1153   // 2. module name + @version
1154   const char* module_name = "";
1155   const char* version = "";
1156   bool has_version = false;
1157   bool module_is_named = false;
1158   const char* module_name_phrase = "";
1159   const Klass* bottom_klass = is_objArray_klass() ?
1160                                 ObjArrayKlass::cast(this)->bottom_klass() : this;
1161   if (bottom_klass->is_instance_klass()) {
1162     ModuleEntry* module = InstanceKlass::cast(bottom_klass)->module();
1163     if (module->is_named()) {
1164       module_is_named = true;
1165       module_name_phrase = "module ";
1166       module_name = module->name()->as_C_string();
1167       len += strlen(module_name);
1168       // Use version if exists and is not a jdk module
1169       if (module->should_show_version()) {
1170         has_version = true;
1171         version = module->version()->as_C_string();
1172         // Include stlen(version) + 1 for the "@"
1173         len += strlen(version) + 1;
1174       }
1175     } else {
1176       module_name = UNNAMED_MODULE;
1177       len += UNNAMED_MODULE_LEN;
1178     }
1179   } else {
1180     // klass is an array of primitives, module is java.base
1181     module_is_named = true;
1182     module_name_phrase = "module ";
1183     module_name = JAVA_BASE_NAME;
1184     len += JAVA_BASE_NAME_LEN;
1185   }
1186 
1187   // 3. class loader's name_and_id
1188   ClassLoaderData* cld = class_loader_data();
1189   assert(cld != nullptr, "class_loader_data should not be null");
1190   const char* loader_name_and_id = cld->loader_name_and_id();
1191   len += strlen(loader_name_and_id);
1192 
1193   // 4. include parent loader information
1194   const char* parent_loader_phrase = "";
1195   const char* parent_loader_name_and_id = "";
1196   if (include_parent_loader &&
1197       !cld->is_builtin_class_loader_data()) {
1198     oop parent_loader = java_lang_ClassLoader::parent(class_loader());
1199     ClassLoaderData *parent_cld = ClassLoaderData::class_loader_data_or_null(parent_loader);
1200     // The parent loader's ClassLoaderData could be null if it is
1201     // a delegating class loader that has never defined a class.
1202     // In this case the loader's name must be obtained via the parent loader's oop.
1203     if (parent_cld == nullptr) {
1204       oop cl_name_and_id = java_lang_ClassLoader::nameAndId(parent_loader);
1205       if (cl_name_and_id != nullptr) {
1206         parent_loader_name_and_id = java_lang_String::as_utf8_string(cl_name_and_id);
1207       }
1208     } else {
1209       parent_loader_name_and_id = parent_cld->loader_name_and_id();
1210     }
1211     parent_loader_phrase = ", parent loader ";
1212     len += strlen(parent_loader_phrase) + strlen(parent_loader_name_and_id);
1213   }
1214 
1215   // Start to construct final full class description string
1216   len += ((use_are) ? strlen(" are in ") : strlen(" is in "));
1217   len += strlen(module_name_phrase) + strlen(" of loader ");
1218 
1219   char* class_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1220 
1221   // Just return the FQN if error when allocating string
1222   if (class_description == nullptr) {
1223     return klass_name;
1224   }
1225 
1226   jio_snprintf(class_description, len, "%s %s in %s%s%s%s of loader %s%s%s",
1227                klass_name,
1228                (use_are) ? "are" : "is",
1229                module_name_phrase,
1230                module_name,
1231                (has_version) ? "@" : "",
1232                (has_version) ? version : "",
1233                loader_name_and_id,
1234                parent_loader_phrase,
1235                parent_loader_name_and_id);
1236 
1237   return class_description;
1238 }
1239 
1240 class LookupStats : StackObj {
1241  private:
1242   uint _no_of_samples;
1243   uint _worst;
1244   uint _worst_count;
1245   uint _average;
1246   uint _best;
1247   uint _best_count;
1248  public:
1249   LookupStats() : _no_of_samples(0), _worst(0), _worst_count(0), _average(0), _best(INT_MAX), _best_count(0) {}
1250 
1251   ~LookupStats() {
1252     assert(_best <= _worst || _no_of_samples == 0, "sanity");
1253   }
1254 
1255   void sample(uint value) {
1256     ++_no_of_samples;
1257     _average += value;
1258 
1259     if (_worst < value) {
1260       _worst = value;
1261       _worst_count = 1;
1262     } else if (_worst == value) {
1263       ++_worst_count;
1264     }
1265 
1266     if (_best > value) {
1267       _best = value;
1268       _best_count = 1;
1269     } else if (_best == value) {
1270       ++_best_count;
1271     }
1272   }
1273 
1274   void print_on(outputStream* st) const {
1275     st->print("best: %2d (%4.1f%%)", _best, (100.0 * _best_count) / _no_of_samples);
1276     if (_best_count < _no_of_samples) {
1277       st->print("; average: %4.1f; worst: %2d (%4.1f%%)",
1278                 (1.0 * _average) / _no_of_samples,
1279                 _worst, (100.0 * _worst_count) / _no_of_samples);
1280     }
1281   }
1282 };
1283 
1284 static void print_positive_lookup_stats(Array<Klass*>* secondary_supers, uintx bitmap, outputStream* st) {
1285   int num_of_supers = secondary_supers->length();
1286 
1287   LookupStats s;
1288   for (int i = 0; i < num_of_supers; i++) {
1289     Klass* secondary_super = secondary_supers->at(i);
1290     int home_slot = Klass::compute_home_slot(secondary_super, bitmap);
1291     uint score = 1 + ((i - home_slot) & Klass::SECONDARY_SUPERS_TABLE_MASK);
1292     s.sample(score);
1293   }
1294   st->print("positive_lookup: "); s.print_on(st);
1295 }
1296 
1297 static uint compute_distance_to_nearest_zero(int slot, uintx bitmap) {
1298   assert(~bitmap != 0, "no zeroes");
1299   uintx start = rotate_right(bitmap, slot);
1300   return count_trailing_zeros(~start);
1301 }
1302 
1303 static void print_negative_lookup_stats(uintx bitmap, outputStream* st) {
1304   LookupStats s;
1305   for (int slot = 0; slot < Klass::SECONDARY_SUPERS_TABLE_SIZE; slot++) {
1306     uint score = compute_distance_to_nearest_zero(slot, bitmap);
1307     s.sample(score);
1308   }
1309   st->print("negative_lookup: "); s.print_on(st);
1310 }
1311 
1312 void Klass::print_secondary_supers_on(outputStream* st) const {
1313   if (secondary_supers() != nullptr) {
1314     st->print("  - "); st->print("%d elements;", _secondary_supers->length());
1315     st->print_cr(" bitmap: " UINTX_FORMAT_X_0, _secondary_supers_bitmap);
1316     if (_secondary_supers_bitmap != SECONDARY_SUPERS_BITMAP_EMPTY &&
1317         _secondary_supers_bitmap != SECONDARY_SUPERS_BITMAP_FULL) {
1318       st->print("  - "); print_positive_lookup_stats(secondary_supers(),
1319                                                      _secondary_supers_bitmap, st); st->cr();
1320       st->print("  - "); print_negative_lookup_stats(_secondary_supers_bitmap, st); st->cr();
1321     }
1322   } else {
1323     st->print("null");
1324   }
1325 }
1326 
1327 void Klass::on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg) {
1328   ResourceMark rm;
1329   super->print();
1330   sub->print();
1331   fatal("%s: %s implements %s: linear_search: %d; table_lookup: %d",
1332         msg, sub->external_name(), super->external_name(), linear_result, table_result);
1333 }
1334 
1335 static int expanded = 0;
1336 static int not_expanded = 0;
1337 static NumberSeq seq = NumberSeq();
1338 
1339 bool Klass::expand_for_hash(oop obj) const {
1340   assert(UseCompactObjectHeaders, "only with compact i-hash");
1341   assert((size_t)hash_offset_in_bytes(obj) <= (obj->base_size_given_klass(obj->mark(), this) * HeapWordSize), "hash offset must be eq or lt base size: hash offset: %d, base size: %zu", hash_offset_in_bytes(obj), obj->base_size_given_klass(obj->mark(), this) * HeapWordSize);
1342   return obj->base_size_given_klass(obj->mark(), this) * HeapWordSize - hash_offset_in_bytes(obj) < (int)sizeof(uint32_t);
1343 }