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