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 int Klass::modifier_flags() const {
 333   int mods = java_lang_Class::modifiers(java_mirror());
 334   assert(mods == compute_modifier_flags(), "should be same");
 335   return mods;
 336 }
 337 
 338 bool Klass::can_be_primary_super_slow() const {
 339   if (super() == nullptr)
 340     return true;
 341   else if (super()->super_depth() >= primary_super_limit()-1)
 342     return false;
 343   else
 344     return true;
 345 }
 346 
 347 void Klass::set_secondary_supers(Array<Klass*>* secondaries, uintx bitmap) {
 348 #ifdef ASSERT
 349   if (secondaries != nullptr) {
 350     uintx real_bitmap = compute_secondary_supers_bitmap(secondaries);
 351     assert(bitmap == real_bitmap, "must be");
 352     assert(secondaries->length() >= (int)population_count(bitmap), "must be");
 353   }
 354 #endif
 355   _secondary_supers_bitmap = bitmap;
 356   _secondary_supers = secondaries;
 357 
 358   if (secondaries != nullptr) {
 359     LogMessage(class, load) msg;
 360     NonInterleavingLogStream log {LogLevel::Debug, msg};
 361     if (log.is_enabled()) {
 362       ResourceMark rm;
 363       log.print_cr("set_secondary_supers: hash_slot: %d; klass: %s", hash_slot(), external_name());
 364       print_secondary_supers_on(&log);
 365     }
 366   }
 367 }
 368 
 369 // Hashed secondary superclasses
 370 //
 371 // We use a compressed 64-entry hash table with linear probing. We
 372 // start by creating a hash table in the usual way, followed by a pass
 373 // that removes all the null entries. To indicate which entries would
 374 // have been null we use a bitmap that contains a 1 in each position
 375 // where an entry is present, 0 otherwise. This bitmap also serves as
 376 // a kind of Bloom filter, which in many cases allows us quickly to
 377 // eliminate the possibility that something is a member of a set of
 378 // secondaries.
 379 uintx Klass::hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite) {
 380   const int length = secondaries->length();
 381 
 382   if (length == 0) {
 383     return SECONDARY_SUPERS_BITMAP_EMPTY;
 384   }
 385 
 386   if (length == 1) {
 387     int hash_slot = secondaries->at(0)->hash_slot();
 388     return uintx(1) << hash_slot;
 389   }
 390 
 391   // Invariant: _secondary_supers.length >= population_count(_secondary_supers_bitmap)
 392 
 393   // Don't attempt to hash a table that's completely full, because in
 394   // the case of an absent interface linear probing would not
 395   // terminate.
 396   if (length >= SECONDARY_SUPERS_TABLE_SIZE) {
 397     return SECONDARY_SUPERS_BITMAP_FULL;
 398   }
 399 
 400   {
 401     PerfTraceTime ptt(ClassLoader::perf_secondary_hash_time());
 402 
 403     ResourceMark rm;
 404     uintx bitmap = SECONDARY_SUPERS_BITMAP_EMPTY;
 405     auto hashed_secondaries = new GrowableArray<Klass*>(SECONDARY_SUPERS_TABLE_SIZE,
 406                                                         SECONDARY_SUPERS_TABLE_SIZE, nullptr);
 407 
 408     for (int j = 0; j < length; j++) {
 409       Klass* k = secondaries->at(j);
 410       hash_insert(k, hashed_secondaries, bitmap);
 411     }
 412 
 413     // Pack the hashed secondaries array by copying it into the
 414     // secondaries array, sans nulls, if modification is allowed.
 415     // Otherwise, validate the order.
 416     int i = 0;
 417     for (int slot = 0; slot < SECONDARY_SUPERS_TABLE_SIZE; slot++) {
 418       bool has_element = ((bitmap >> slot) & 1) != 0;
 419       assert(has_element == (hashed_secondaries->at(slot) != nullptr), "");
 420       if (has_element) {
 421         Klass* k = hashed_secondaries->at(slot);
 422         if (rewrite) {
 423           secondaries->at_put(i, k);
 424         } else if (secondaries->at(i) != k) {
 425           assert(false, "broken secondary supers hash table");
 426           return SECONDARY_SUPERS_BITMAP_FULL;
 427         }
 428         i++;
 429       }
 430     }
 431     assert(i == secondaries->length(), "mismatch");
 432     postcond((int)population_count(bitmap) == secondaries->length());
 433 
 434     return bitmap;
 435   }
 436 }
 437 
 438 void Klass::hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap) {
 439   assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 440 
 441   int dist = 0;
 442   for (int slot = klass->hash_slot(); true; slot = (slot + 1) & SECONDARY_SUPERS_TABLE_MASK) {
 443     Klass* existing = secondaries->at(slot);
 444     assert(((bitmap >> slot) & 1) == (existing != nullptr), "mismatch");
 445     if (existing == nullptr) { // no conflict
 446       secondaries->at_put(slot, klass);
 447       bitmap |= uintx(1) << slot;
 448       assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 449       return;
 450     } else {
 451       // Use Robin Hood hashing to minimize the worst case search.
 452       // Also, every permutation of the insertion sequence produces
 453       // the same final Robin Hood hash table, provided that a
 454       // consistent tie breaker is used.
 455       int existing_dist = (slot - existing->hash_slot()) & SECONDARY_SUPERS_TABLE_MASK;
 456       if (existing_dist < dist
 457           // This tie breaker ensures that the hash order is maintained.
 458           || ((existing_dist == dist)
 459               && (uintptr_t(existing) < uintptr_t(klass)))) {
 460         Klass* tmp = secondaries->at(slot);
 461         secondaries->at_put(slot, klass);
 462         klass = tmp;
 463         dist = existing_dist;
 464       }
 465       ++dist;
 466     }
 467   }
 468 }
 469 
 470 Array<Klass*>* Klass::pack_secondary_supers(ClassLoaderData* loader_data,
 471                                             GrowableArray<Klass*>* primaries,
 472                                             GrowableArray<Klass*>* secondaries,
 473                                             uintx& bitmap, TRAPS) {
 474   int new_length = primaries->length() + secondaries->length();
 475   Array<Klass*>* secondary_supers = MetadataFactory::new_array<Klass*>(loader_data, new_length, CHECK_NULL);
 476 
 477   // Combine the two arrays into a metadata object to pack the array.
 478   // The primaries are added in the reverse order, then the secondaries.
 479   int fill_p = primaries->length();
 480   for (int j = 0; j < fill_p; j++) {
 481     secondary_supers->at_put(j, primaries->pop());  // add primaries in reverse order.
 482   }
 483   for( int j = 0; j < secondaries->length(); j++ ) {
 484     secondary_supers->at_put(j+fill_p, secondaries->at(j));  // add secondaries on the end.
 485   }
 486 #ifdef ASSERT
 487   // We must not copy any null placeholders left over from bootstrap.
 488   for (int j = 0; j < secondary_supers->length(); j++) {
 489     assert(secondary_supers->at(j) != nullptr, "correct bootstrapping order");
 490   }
 491 #endif
 492 
 493   bitmap = hash_secondary_supers(secondary_supers, /*rewrite=*/true); // rewrites freshly allocated array
 494   return secondary_supers;
 495 }
 496 
 497 uintx Klass::compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers) {
 498   return hash_secondary_supers(secondary_supers, /*rewrite=*/false); // no rewrites allowed
 499 }
 500 
 501 uint8_t Klass::compute_home_slot(Klass* k, uintx bitmap) {
 502   uint8_t hash = k->hash_slot();
 503   if (hash > 0) {
 504     return population_count(bitmap << (SECONDARY_SUPERS_TABLE_SIZE - hash));
 505   }
 506   return 0;
 507 }
 508 
 509 
 510 void Klass::initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS) {
 511   if (k == nullptr) {
 512     set_super(nullptr);
 513     _primary_supers[0] = this;
 514     assert(super_depth() == 0, "Object must already be initialized properly");
 515   } else if (k != super() || k == vmClasses::Object_klass()) {
 516     assert(super() == nullptr || super() == vmClasses::Object_klass(),
 517            "initialize this only once to a non-trivial value");
 518     set_super(k);
 519     Klass* sup = k;
 520     int sup_depth = sup->super_depth();
 521     juint my_depth  = MIN2(sup_depth + 1, (int)primary_super_limit());
 522     if (!can_be_primary_super_slow())
 523       my_depth = primary_super_limit();
 524     for (juint i = 0; i < my_depth; i++) {
 525       _primary_supers[i] = sup->_primary_supers[i];
 526     }
 527     Klass* *super_check_cell;
 528     if (my_depth < primary_super_limit()) {
 529       _primary_supers[my_depth] = this;
 530       super_check_cell = &_primary_supers[my_depth];
 531     } else {
 532       // Overflow of the primary_supers array forces me to be secondary.
 533       super_check_cell = &_secondary_super_cache;
 534     }
 535     set_super_check_offset(u4((address)super_check_cell - (address) this));
 536 
 537 #ifdef ASSERT
 538     {
 539       juint j = super_depth();
 540       assert(j == my_depth, "computed accessor gets right answer");
 541       Klass* t = this;
 542       while (!t->can_be_primary_super()) {
 543         t = t->super();
 544         j = t->super_depth();
 545       }
 546       for (juint j1 = j+1; j1 < primary_super_limit(); j1++) {
 547         assert(primary_super_of_depth(j1) == nullptr, "super list padding");
 548       }
 549       while (t != nullptr) {
 550         assert(primary_super_of_depth(j) == t, "super list initialization");
 551         t = t->super();
 552         --j;
 553       }
 554       assert(j == (juint)-1, "correct depth count");
 555     }
 556 #endif
 557   }
 558 
 559   if (secondary_supers() == nullptr) {
 560 
 561     // Now compute the list of secondary supertypes.
 562     // Secondaries can occasionally be on the super chain,
 563     // if the inline "_primary_supers" array overflows.
 564     int extras = 0;
 565     Klass* p;
 566     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 567       ++extras;
 568     }
 569 
 570     ResourceMark rm(THREAD);  // need to reclaim GrowableArrays allocated below
 571 
 572     // Compute the "real" non-extra secondaries.
 573     GrowableArray<Klass*>* secondaries = compute_secondary_supers(extras, transitive_interfaces);
 574     if (secondaries == nullptr) {
 575       // secondary_supers set by compute_secondary_supers
 576       return;
 577     }
 578 
 579     GrowableArray<Klass*>* primaries = new GrowableArray<Klass*>(extras);
 580 
 581     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 582       int i;                    // Scan for overflow primaries being duplicates of 2nd'arys
 583 
 584       // This happens frequently for very deeply nested arrays: the
 585       // primary superclass chain overflows into the secondary.  The
 586       // secondary list contains the element_klass's secondaries with
 587       // an extra array dimension added.  If the element_klass's
 588       // secondary list already contains some primary overflows, they
 589       // (with the extra level of array-ness) will collide with the
 590       // normal primary superclass overflows.
 591       for( i = 0; i < secondaries->length(); i++ ) {
 592         if( secondaries->at(i) == p )
 593           break;
 594       }
 595       if( i < secondaries->length() )
 596         continue;               // It's a dup, don't put it in
 597       primaries->push(p);
 598     }
 599     // Combine the two arrays into a metadata object to pack the array.
 600     uintx bitmap = 0;
 601     Array<Klass*>* s2 = pack_secondary_supers(class_loader_data(), primaries, secondaries, bitmap, CHECK);
 602     set_secondary_supers(s2, bitmap);
 603   }
 604 }
 605 
 606 GrowableArray<Klass*>* Klass::compute_secondary_supers(int num_extra_slots,
 607                                                        Array<InstanceKlass*>* transitive_interfaces) {
 608   assert(num_extra_slots == 0, "override for complex klasses");
 609   assert(transitive_interfaces == nullptr, "sanity");
 610   set_secondary_supers(Universe::the_empty_klass_array(), Universe::the_empty_klass_bitmap());
 611   return nullptr;
 612 }
 613 
 614 
 615 // superklass links
 616 InstanceKlass* Klass::superklass() const {
 617   assert(super() == nullptr || super()->is_instance_klass(), "must be instance klass");
 618   return _super == nullptr ? nullptr : InstanceKlass::cast(_super);
 619 }
 620 
 621 // subklass links.  Used by the compiler (and vtable initialization)
 622 // May be cleaned concurrently, so must use the Compile_lock.
 623 // The log parameter is for clean_weak_klass_links to report unlinked classes.
 624 Klass* Klass::subklass(bool log) const {
 625   // Need load_acquire on the _subklass, because it races with inserts that
 626   // publishes freshly initialized data.
 627   for (Klass* chain = Atomic::load_acquire(&_subklass);
 628        chain != nullptr;
 629        // Do not need load_acquire on _next_sibling, because inserts never
 630        // create _next_sibling edges to dead data.
 631        chain = Atomic::load(&chain->_next_sibling))
 632   {
 633     if (chain->is_loader_alive()) {
 634       return chain;
 635     } else if (log) {
 636       if (log_is_enabled(Trace, class, unload)) {
 637         ResourceMark rm;
 638         log_trace(class, unload)("unlinking class (subclass): %s", chain->external_name());
 639       }
 640     }
 641   }
 642   return nullptr;
 643 }
 644 
 645 Klass* Klass::next_sibling(bool log) const {
 646   // Do not need load_acquire on _next_sibling, because inserts never
 647   // create _next_sibling edges to dead data.
 648   for (Klass* chain = Atomic::load(&_next_sibling);
 649        chain != nullptr;
 650        chain = Atomic::load(&chain->_next_sibling)) {
 651     // Only return alive klass, there may be stale klass
 652     // in this chain if cleaned concurrently.
 653     if (chain->is_loader_alive()) {
 654       return chain;
 655     } else if (log) {
 656       if (log_is_enabled(Trace, class, unload)) {
 657         ResourceMark rm;
 658         log_trace(class, unload)("unlinking class (sibling): %s", chain->external_name());
 659       }
 660     }
 661   }
 662   return nullptr;
 663 }
 664 
 665 void Klass::set_subklass(Klass* s) {
 666   assert(s != this, "sanity check");
 667   Atomic::release_store(&_subklass, s);
 668 }
 669 
 670 void Klass::set_next_sibling(Klass* s) {
 671   assert(s != this, "sanity check");
 672   // Does not need release semantics. If used by cleanup, it will link to
 673   // already safely published data, and if used by inserts, will be published
 674   // safely using cmpxchg.
 675   Atomic::store(&_next_sibling, s);
 676 }
 677 
 678 void Klass::append_to_sibling_list() {
 679   if (Universe::is_fully_initialized()) {
 680     assert_locked_or_safepoint(Compile_lock);
 681   }
 682   DEBUG_ONLY(verify();)
 683   // add ourselves to superklass' subklass list
 684   InstanceKlass* super = superklass();
 685   if (super == nullptr) return;     // special case: class Object
 686   assert((!super->is_interface()    // interfaces cannot be supers
 687           && (super->superklass() == nullptr || !is_interface())),
 688          "an interface can only be a subklass of Object");
 689 
 690   // Make sure there is no stale subklass head
 691   super->clean_subklass();
 692 
 693   for (;;) {
 694     Klass* prev_first_subklass = Atomic::load_acquire(&_super->_subklass);
 695     if (prev_first_subklass != nullptr) {
 696       // set our sibling to be the superklass' previous first subklass
 697       assert(prev_first_subklass->is_loader_alive(), "May not attach not alive klasses");
 698       set_next_sibling(prev_first_subklass);
 699     }
 700     // Note that the prev_first_subklass is always alive, meaning no sibling_next links
 701     // are ever created to not alive klasses. This is an important invariant of the lock-free
 702     // cleaning protocol, that allows us to safely unlink dead klasses from the sibling list.
 703     if (Atomic::cmpxchg(&super->_subklass, prev_first_subklass, this) == prev_first_subklass) {
 704       return;
 705     }
 706   }
 707   DEBUG_ONLY(verify();)
 708 }
 709 
 710 void Klass::clean_subklass() {
 711   for (;;) {
 712     // Need load_acquire, due to contending with concurrent inserts
 713     Klass* subklass = Atomic::load_acquire(&_subklass);
 714     if (subklass == nullptr || subklass->is_loader_alive()) {
 715       return;
 716     }
 717     // Try to fix _subklass until it points at something not dead.
 718     Atomic::cmpxchg(&_subklass, subklass, subklass->next_sibling());
 719   }
 720 }
 721 
 722 void Klass::clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses) {
 723   if (!ClassUnloading || !unloading_occurred) {
 724     return;
 725   }
 726 
 727   Klass* root = vmClasses::Object_klass();
 728   Stack<Klass*, mtGC> stack;
 729 
 730   stack.push(root);
 731   while (!stack.is_empty()) {
 732     Klass* current = stack.pop();
 733 
 734     assert(current->is_loader_alive(), "just checking, this should be live");
 735 
 736     // Find and set the first alive subklass
 737     Klass* sub = current->subklass(true);
 738     current->clean_subklass();
 739     if (sub != nullptr) {
 740       stack.push(sub);
 741     }
 742 
 743     // Find and set the first alive sibling
 744     Klass* sibling = current->next_sibling(true);
 745     current->set_next_sibling(sibling);
 746     if (sibling != nullptr) {
 747       stack.push(sibling);
 748     }
 749 
 750     // Clean the implementors list and method data.
 751     if (clean_alive_klasses && current->is_instance_klass()) {
 752       InstanceKlass* ik = InstanceKlass::cast(current);
 753       clean_weak_instanceklass_links(ik);
 754     }
 755   }
 756 }
 757 
 758 void Klass::clean_weak_instanceklass_links(InstanceKlass* ik) {
 759   ik->clean_weak_instanceklass_links();
 760   // JVMTI RedefineClasses creates previous versions that are not in
 761   // the class hierarchy, so process them here.
 762   while ((ik = ik->previous_versions()) != nullptr) {
 763     ik->clean_weak_instanceklass_links();
 764   }
 765 }
 766 
 767 void Klass::metaspace_pointers_do(MetaspaceClosure* it) {
 768   if (log_is_enabled(Trace, aot)) {
 769     ResourceMark rm;
 770     log_trace(aot)("Iter(Klass): %p (%s)", this, external_name());
 771   }
 772 
 773   it->push(&_name);
 774   it->push(&_secondary_supers);
 775   for (int i = 0; i < _primary_super_limit; i++) {
 776     it->push(&_primary_supers[i]);
 777   }
 778   it->push(&_super);
 779   if (!CDSConfig::is_dumping_archive()) {
 780     // If dumping archive, these may point to excluded classes. There's no need
 781     // to follow these pointers anyway, as they will be set to null in
 782     // remove_unshareable_info().
 783     it->push((Klass**)&_subklass);
 784     it->push((Klass**)&_next_sibling);
 785     it->push(&_next_link);
 786   }
 787 
 788   vtableEntry* vt = start_of_vtable();
 789   for (int i=0; i<vtable_length(); i++) {
 790     it->push(vt[i].method_addr());
 791   }
 792 }
 793 
 794 #if INCLUDE_CDS
 795 void Klass::remove_unshareable_info() {
 796   assert(CDSConfig::is_dumping_archive(),
 797           "only called during CDS dump time");
 798   JFR_ONLY(REMOVE_ID(this);)
 799   if (log_is_enabled(Trace, aot, unshareable)) {
 800     ResourceMark rm;
 801     log_trace(aot, unshareable)("remove: %s", external_name());
 802   }
 803 
 804   // _secondary_super_cache may be updated by an is_subtype_of() call
 805   // while ArchiveBuilder is copying metaspace objects. Let's reset it to
 806   // null and let it be repopulated at runtime.
 807   set_secondary_super_cache(nullptr);
 808 
 809   set_subklass(nullptr);
 810   set_next_sibling(nullptr);
 811   set_next_link(nullptr);
 812 
 813   // Null out class_loader_data because we don't share that yet.
 814   set_class_loader_data(nullptr);
 815   set_is_shared();
 816 
 817   if (CDSConfig::is_dumping_classic_static_archive()) {
 818     // "Classic" static archives are required to have deterministic contents.
 819     // The elements in _secondary_supers are addresses in the ArchiveBuilder
 820     // output buffer, so they should have deterministic values. If we rehash
 821     // _secondary_supers, its elements will appear in a deterministic order.
 822     //
 823     // Note that the bitmap is guaranteed to be deterministic, regardless of the
 824     // actual addresses of the elements in _secondary_supers. So rehashing shouldn't
 825     // change it.
 826     uintx bitmap = hash_secondary_supers(secondary_supers(), true);
 827     assert(bitmap == _secondary_supers_bitmap, "bitmap should not be changed due to rehashing");
 828   }
 829 }
 830 
 831 void Klass::remove_java_mirror() {
 832   assert(CDSConfig::is_dumping_archive(), "sanity");
 833   if (log_is_enabled(Trace, aot, unshareable)) {
 834     ResourceMark rm;
 835     log_trace(aot, unshareable)("remove java_mirror: %s", external_name());
 836   }
 837 
 838 #if INCLUDE_CDS_JAVA_HEAP
 839   _archived_mirror_index = -1;
 840   if (CDSConfig::is_dumping_heap()) {
 841     Klass* src_k = ArchiveBuilder::current()->get_source_addr(this);
 842     oop orig_mirror = src_k->java_mirror();
 843     if (orig_mirror == nullptr) {
 844       assert(CDSConfig::is_dumping_final_static_archive(), "sanity");
 845       if (is_instance_klass()) {
 846         assert(InstanceKlass::cast(this)->defined_by_other_loaders(), "sanity");
 847       } else {
 848         precond(is_objArray_klass());
 849         Klass *k = ObjArrayKlass::cast(this)->bottom_klass();
 850         precond(k->is_instance_klass());
 851         assert(InstanceKlass::cast(k)->defined_by_other_loaders(), "sanity");
 852       }
 853     } else {
 854       oop scratch_mirror = HeapShared::scratch_java_mirror(orig_mirror);
 855       if (scratch_mirror != nullptr) {
 856         _archived_mirror_index = HeapShared::append_root(scratch_mirror);
 857       }
 858     }
 859   }
 860 #endif
 861 
 862   // Just null out the mirror.  The class_loader_data() no longer exists.
 863   clear_java_mirror_handle();
 864 }
 865 
 866 void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS) {
 867   assert(is_klass(), "ensure C++ vtable is restored");
 868   assert(is_shared(), "must be set");
 869   assert(secondary_supers()->length() >= (int)population_count(_secondary_supers_bitmap), "must be");
 870   JFR_ONLY(RESTORE_ID(this);)
 871   if (log_is_enabled(Trace, aot, unshareable)) {
 872     ResourceMark rm(THREAD);
 873     oop class_loader = loader_data->class_loader();
 874     log_trace(aot, unshareable)("restore: %s with class loader: %s", external_name(),
 875       class_loader != nullptr ? class_loader->klass()->external_name() : "boot");
 876   }
 877 
 878   // If an exception happened during CDS restore, some of these fields may already be
 879   // set.  We leave the class on the CLD list, even if incomplete so that we don't
 880   // modify the CLD list outside a safepoint.
 881   if (class_loader_data() == nullptr) {
 882     set_class_loader_data(loader_data);
 883 
 884     // Add to class loader list first before creating the mirror
 885     // (same order as class file parsing)
 886     loader_data->add_class(this);
 887   }
 888 
 889   Handle loader(THREAD, loader_data->class_loader());
 890   ModuleEntry* module_entry = nullptr;
 891   Klass* k = this;
 892   if (k->is_objArray_klass()) {
 893     k = ObjArrayKlass::cast(k)->bottom_klass();
 894   }
 895   // Obtain klass' module.
 896   if (k->is_instance_klass()) {
 897     InstanceKlass* ik = (InstanceKlass*) k;
 898     module_entry = ik->module();
 899   } else {
 900     module_entry = ModuleEntryTable::javabase_moduleEntry();
 901   }
 902   // Obtain java.lang.Module, if available
 903   Handle module_handle(THREAD, ((module_entry != nullptr) ? module_entry->module_oop() : (oop)nullptr));
 904 
 905   if (this->has_archived_mirror_index()) {
 906     ResourceMark rm(THREAD);
 907     log_debug(aot, mirror)("%s has raw archived mirror", external_name());
 908     if (ArchiveHeapLoader::is_in_use()) {
 909       bool present = java_lang_Class::restore_archived_mirror(this, loader, module_handle,
 910                                                               protection_domain,
 911                                                               CHECK);
 912       if (present) {
 913         return;
 914       }
 915     }
 916 
 917     // No archived mirror data
 918     log_debug(aot, mirror)("No archived mirror data for %s", external_name());
 919     clear_java_mirror_handle();
 920     this->clear_archived_mirror_index();
 921   }
 922 
 923   // Only recreate it if not present.  A previous attempt to restore may have
 924   // gotten an OOM later but keep the mirror if it was created.
 925   if (java_mirror() == nullptr) {
 926     ResourceMark rm(THREAD);
 927     log_trace(aot, mirror)("Recreate mirror for %s", external_name());
 928     java_lang_Class::create_mirror(this, loader, module_handle, protection_domain, Handle(), CHECK);
 929   }
 930 }
 931 #endif // INCLUDE_CDS
 932 
 933 #if INCLUDE_CDS_JAVA_HEAP
 934 oop Klass::archived_java_mirror() {
 935   assert(has_archived_mirror_index(), "must have archived mirror");
 936   return HeapShared::get_root(_archived_mirror_index);
 937 }
 938 
 939 void Klass::clear_archived_mirror_index() {
 940   if (_archived_mirror_index >= 0) {
 941     HeapShared::clear_root(_archived_mirror_index);
 942   }
 943   _archived_mirror_index = -1;
 944 }
 945 #endif // INCLUDE_CDS_JAVA_HEAP
 946 
 947 void Klass::check_array_allocation_length(int length, int max_length, TRAPS) {
 948   if (length > max_length) {
 949     if (!THREAD->is_in_internal_oome_mark()) {
 950       report_java_out_of_memory("Requested array size exceeds VM limit");
 951       JvmtiExport::post_array_size_exhausted();
 952       THROW_OOP(Universe::out_of_memory_error_array_size());
 953     } else {
 954       THROW_OOP(Universe::out_of_memory_error_java_heap_without_backtrace());
 955     }
 956   } else if (length < 0) {
 957     THROW_MSG(vmSymbols::java_lang_NegativeArraySizeException(), err_msg("%d", length));
 958   }
 959 }
 960 
 961 // Replace the last '+' char with '/'.
 962 static char* convert_hidden_name_to_java(Symbol* name) {
 963   size_t name_len = name->utf8_length();
 964   char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 965   name->as_klass_external_name(result, (int)name_len + 1);
 966   for (int index = (int)name_len; index > 0; index--) {
 967     if (result[index] == '+') {
 968       result[index] = JVM_SIGNATURE_SLASH;
 969       break;
 970     }
 971   }
 972   return result;
 973 }
 974 
 975 // In product mode, this function doesn't have virtual function calls so
 976 // there might be some performance advantage to handling InstanceKlass here.
 977 const char* Klass::external_name() const {
 978   if (is_instance_klass()) {
 979     const InstanceKlass* ik = static_cast<const InstanceKlass*>(this);
 980     if (ik->is_hidden()) {
 981       char* result = convert_hidden_name_to_java(name());
 982       return result;
 983     }
 984   } else if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 985     char* result = convert_hidden_name_to_java(name());
 986     return result;
 987   }
 988   if (name() == nullptr)  return "<unknown>";
 989   return name()->as_klass_external_name();
 990 }
 991 
 992 const char* Klass::signature_name() const {
 993   if (name() == nullptr)  return "<unknown>";
 994   if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 995     size_t name_len = name()->utf8_length();
 996     char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 997     name()->as_C_string(result, (int)name_len + 1);
 998     for (int index = (int)name_len; index > 0; index--) {
 999       if (result[index] == '+') {
1000         result[index] = JVM_SIGNATURE_DOT;
1001         break;
1002       }
1003     }
1004     return result;
1005   }
1006   return name()->as_C_string();
1007 }
1008 
1009 const char* Klass::external_kind() const {
1010   if (is_interface()) return "interface";
1011   if (is_abstract()) return "abstract class";
1012   return "class";
1013 }
1014 
1015 // Unless overridden, jvmti_class_status has no flags set.
1016 jint Klass::jvmti_class_status() const {
1017   return 0;
1018 }
1019 
1020 
1021 // Printing
1022 
1023 void Klass::print_on(outputStream* st) const {
1024   ResourceMark rm;
1025   // print title
1026   st->print("%s", internal_name());
1027   print_address_on(st);
1028   st->cr();
1029 }
1030 
1031 #define BULLET  " - "
1032 
1033 // Caller needs ResourceMark
1034 void Klass::oop_print_on(oop obj, outputStream* st) {
1035   // print title
1036   st->print_cr("%s ", internal_name());
1037   obj->print_address_on(st);
1038 
1039   if (WizardMode) {
1040      // print header
1041      obj->mark().print_on(st);
1042      st->cr();
1043      if (UseCompactObjectHeaders) {
1044        st->print(BULLET"prototype_header: " INTPTR_FORMAT, _prototype_header.value());
1045        st->cr();
1046      }
1047   }
1048 
1049   // print class
1050   st->print(BULLET"klass: ");
1051   obj->klass()->print_value_on(st);
1052   st->print(BULLET"flags: "); _misc_flags.print_on(st); st->cr();
1053   st->cr();
1054 }
1055 
1056 void Klass::oop_print_value_on(oop obj, outputStream* st) {
1057   // print title
1058   ResourceMark rm;              // Cannot print in debug mode without this
1059   st->print("%s", internal_name());
1060   obj->print_address_on(st);
1061 }
1062 
1063 // Verification
1064 
1065 void Klass::verify_on(outputStream* st) {
1066 
1067   // This can be expensive, but it is worth checking that this klass is actually
1068   // in the CLD graph but not in production.
1069 #ifdef ASSERT
1070   if (UseCompressedClassPointers && needs_narrow_id()) {
1071     // Stricter checks for both correct alignment and placement
1072     CompressedKlassPointers::check_encodable(this);
1073   } else {
1074     assert(Metaspace::contains((address)this), "Should be");
1075   }
1076 #endif // ASSERT
1077 
1078   guarantee(this->is_klass(),"should be klass");
1079 
1080   if (super() != nullptr) {
1081     guarantee(super()->is_klass(), "should be klass");
1082   }
1083   if (secondary_super_cache() != nullptr) {
1084     Klass* ko = secondary_super_cache();
1085     guarantee(ko->is_klass(), "should be klass");
1086   }
1087   for ( uint i = 0; i < primary_super_limit(); i++ ) {
1088     Klass* ko = _primary_supers[i];
1089     if (ko != nullptr) {
1090       guarantee(ko->is_klass(), "should be klass");
1091     }
1092   }
1093 
1094   if (java_mirror_no_keepalive() != nullptr) {
1095     guarantee(java_lang_Class::is_instance(java_mirror_no_keepalive()), "should be instance");
1096   }
1097 }
1098 
1099 void Klass::oop_verify_on(oop obj, outputStream* st) {
1100   guarantee(oopDesc::is_oop(obj),  "should be oop");
1101   guarantee(obj->klass()->is_klass(), "klass field is not a klass");
1102 }
1103 
1104 // Note: this function is called with an address that may or may not be a Klass.
1105 // The point is not to assert it is but to check if it could be.
1106 bool Klass::is_valid(Klass* k) {
1107   if (!is_aligned(k, sizeof(MetaWord))) return false;
1108   if ((size_t)k < os::min_page_size()) return false;
1109 
1110   if (!os::is_readable_range(k, k + 1)) return false;
1111   if (!Metaspace::contains(k)) return false;
1112 
1113   if (!Symbol::is_valid(k->name())) return false;
1114   return ClassLoaderDataGraph::is_valid(k->class_loader_data());
1115 }
1116 
1117 Method* Klass::method_at_vtable(int index)  {
1118 #ifndef PRODUCT
1119   assert(index >= 0, "valid vtable index");
1120   if (DebugVtables) {
1121     verify_vtable_index(index);
1122   }
1123 #endif
1124   return start_of_vtable()[index].method();
1125 }
1126 
1127 
1128 #ifndef PRODUCT
1129 
1130 bool Klass::verify_vtable_index(int i) {
1131   int limit = vtable_length()/vtableEntry::size();
1132   assert(i >= 0 && i < limit, "index %d out of bounds %d", i, limit);
1133   return true;
1134 }
1135 
1136 #endif // PRODUCT
1137 
1138 // Caller needs ResourceMark
1139 // joint_in_module_of_loader provides an optimization if 2 classes are in
1140 // the same module to succinctly print out relevant information about their
1141 // module name and class loader's name_and_id for error messages.
1142 // Format:
1143 //   <fully-qualified-external-class-name1> and <fully-qualified-external-class-name2>
1144 //                      are in module <module-name>[@<version>]
1145 //                      of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1146 const char* Klass::joint_in_module_of_loader(const Klass* class2, bool include_parent_loader) const {
1147   assert(module() == class2->module(), "classes do not have the same module");
1148   const char* class1_name = external_name();
1149   size_t len = strlen(class1_name) + 1;
1150 
1151   const char* class2_description = class2->class_in_module_of_loader(true, include_parent_loader);
1152   len += strlen(class2_description);
1153 
1154   len += strlen(" and ");
1155 
1156   char* joint_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1157 
1158   // Just return the FQN if error when allocating string
1159   if (joint_description == nullptr) {
1160     return class1_name;
1161   }
1162 
1163   jio_snprintf(joint_description, len, "%s and %s",
1164                class1_name,
1165                class2_description);
1166 
1167   return joint_description;
1168 }
1169 
1170 // Caller needs ResourceMark
1171 // class_in_module_of_loader provides a standard way to include
1172 // relevant information about a class, such as its module name as
1173 // well as its class loader's name_and_id, in error messages and logging.
1174 // Format:
1175 //   <fully-qualified-external-class-name> is in module <module-name>[@<version>]
1176 //                                         of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1177 const char* Klass::class_in_module_of_loader(bool use_are, bool include_parent_loader) const {
1178   // 1. fully qualified external name of class
1179   const char* klass_name = external_name();
1180   size_t len = strlen(klass_name) + 1;
1181 
1182   // 2. module name + @version
1183   const char* module_name = "";
1184   const char* version = "";
1185   bool has_version = false;
1186   bool module_is_named = false;
1187   const char* module_name_phrase = "";
1188   const Klass* bottom_klass = is_objArray_klass() ?
1189                                 ObjArrayKlass::cast(this)->bottom_klass() : this;
1190   if (bottom_klass->is_instance_klass()) {
1191     ModuleEntry* module = InstanceKlass::cast(bottom_klass)->module();
1192     if (module->is_named()) {
1193       module_is_named = true;
1194       module_name_phrase = "module ";
1195       module_name = module->name()->as_C_string();
1196       len += strlen(module_name);
1197       // Use version if exists and is not a jdk module
1198       if (module->should_show_version()) {
1199         has_version = true;
1200         version = module->version()->as_C_string();
1201         // Include stlen(version) + 1 for the "@"
1202         len += strlen(version) + 1;
1203       }
1204     } else {
1205       module_name = UNNAMED_MODULE;
1206       len += UNNAMED_MODULE_LEN;
1207     }
1208   } else {
1209     // klass is an array of primitives, module is java.base
1210     module_is_named = true;
1211     module_name_phrase = "module ";
1212     module_name = JAVA_BASE_NAME;
1213     len += JAVA_BASE_NAME_LEN;
1214   }
1215 
1216   // 3. class loader's name_and_id
1217   ClassLoaderData* cld = class_loader_data();
1218   assert(cld != nullptr, "class_loader_data should not be null");
1219   const char* loader_name_and_id = cld->loader_name_and_id();
1220   len += strlen(loader_name_and_id);
1221 
1222   // 4. include parent loader information
1223   const char* parent_loader_phrase = "";
1224   const char* parent_loader_name_and_id = "";
1225   if (include_parent_loader &&
1226       !cld->is_builtin_class_loader_data()) {
1227     oop parent_loader = java_lang_ClassLoader::parent(class_loader());
1228     ClassLoaderData *parent_cld = ClassLoaderData::class_loader_data_or_null(parent_loader);
1229     // The parent loader's ClassLoaderData could be null if it is
1230     // a delegating class loader that has never defined a class.
1231     // In this case the loader's name must be obtained via the parent loader's oop.
1232     if (parent_cld == nullptr) {
1233       oop cl_name_and_id = java_lang_ClassLoader::nameAndId(parent_loader);
1234       if (cl_name_and_id != nullptr) {
1235         parent_loader_name_and_id = java_lang_String::as_utf8_string(cl_name_and_id);
1236       }
1237     } else {
1238       parent_loader_name_and_id = parent_cld->loader_name_and_id();
1239     }
1240     parent_loader_phrase = ", parent loader ";
1241     len += strlen(parent_loader_phrase) + strlen(parent_loader_name_and_id);
1242   }
1243 
1244   // Start to construct final full class description string
1245   len += ((use_are) ? strlen(" are in ") : strlen(" is in "));
1246   len += strlen(module_name_phrase) + strlen(" of loader ");
1247 
1248   char* class_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1249 
1250   // Just return the FQN if error when allocating string
1251   if (class_description == nullptr) {
1252     return klass_name;
1253   }
1254 
1255   jio_snprintf(class_description, len, "%s %s in %s%s%s%s of loader %s%s%s",
1256                klass_name,
1257                (use_are) ? "are" : "is",
1258                module_name_phrase,
1259                module_name,
1260                (has_version) ? "@" : "",
1261                (has_version) ? version : "",
1262                loader_name_and_id,
1263                parent_loader_phrase,
1264                parent_loader_name_and_id);
1265 
1266   return class_description;
1267 }
1268 
1269 class LookupStats : StackObj {
1270  private:
1271   uint _no_of_samples;
1272   uint _worst;
1273   uint _worst_count;
1274   uint _average;
1275   uint _best;
1276   uint _best_count;
1277  public:
1278   LookupStats() : _no_of_samples(0), _worst(0), _worst_count(0), _average(0), _best(INT_MAX), _best_count(0) {}
1279 
1280   ~LookupStats() {
1281     assert(_best <= _worst || _no_of_samples == 0, "sanity");
1282   }
1283 
1284   void sample(uint value) {
1285     ++_no_of_samples;
1286     _average += value;
1287 
1288     if (_worst < value) {
1289       _worst = value;
1290       _worst_count = 1;
1291     } else if (_worst == value) {
1292       ++_worst_count;
1293     }
1294 
1295     if (_best > value) {
1296       _best = value;
1297       _best_count = 1;
1298     } else if (_best == value) {
1299       ++_best_count;
1300     }
1301   }
1302 
1303   void print_on(outputStream* st) const {
1304     st->print("best: %2d (%4.1f%%)", _best, (100.0 * _best_count) / _no_of_samples);
1305     if (_best_count < _no_of_samples) {
1306       st->print("; average: %4.1f; worst: %2d (%4.1f%%)",
1307                 (1.0 * _average) / _no_of_samples,
1308                 _worst, (100.0 * _worst_count) / _no_of_samples);
1309     }
1310   }
1311 };
1312 
1313 static void print_positive_lookup_stats(Array<Klass*>* secondary_supers, uintx bitmap, outputStream* st) {
1314   int num_of_supers = secondary_supers->length();
1315 
1316   LookupStats s;
1317   for (int i = 0; i < num_of_supers; i++) {
1318     Klass* secondary_super = secondary_supers->at(i);
1319     int home_slot = Klass::compute_home_slot(secondary_super, bitmap);
1320     uint score = 1 + ((i - home_slot) & Klass::SECONDARY_SUPERS_TABLE_MASK);
1321     s.sample(score);
1322   }
1323   st->print("positive_lookup: "); s.print_on(st);
1324 }
1325 
1326 static uint compute_distance_to_nearest_zero(int slot, uintx bitmap) {
1327   assert(~bitmap != 0, "no zeroes");
1328   uintx start = rotate_right(bitmap, slot);
1329   return count_trailing_zeros(~start);
1330 }
1331 
1332 static void print_negative_lookup_stats(uintx bitmap, outputStream* st) {
1333   LookupStats s;
1334   for (int slot = 0; slot < Klass::SECONDARY_SUPERS_TABLE_SIZE; slot++) {
1335     uint score = compute_distance_to_nearest_zero(slot, bitmap);
1336     s.sample(score);
1337   }
1338   st->print("negative_lookup: "); s.print_on(st);
1339 }
1340 
1341 void Klass::print_secondary_supers_on(outputStream* st) const {
1342   if (secondary_supers() != nullptr) {
1343     st->print("  - "); st->print("%d elements;", _secondary_supers->length());
1344     st->print_cr(" bitmap: " UINTX_FORMAT_X_0, _secondary_supers_bitmap);
1345     if (_secondary_supers_bitmap != SECONDARY_SUPERS_BITMAP_EMPTY &&
1346         _secondary_supers_bitmap != SECONDARY_SUPERS_BITMAP_FULL) {
1347       st->print("  - "); print_positive_lookup_stats(secondary_supers(),
1348                                                      _secondary_supers_bitmap, st); st->cr();
1349       st->print("  - "); print_negative_lookup_stats(_secondary_supers_bitmap, st); st->cr();
1350     }
1351   } else {
1352     st->print("null");
1353   }
1354 }
1355 
1356 void Klass::on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg) {
1357   ResourceMark rm;
1358   super->print();
1359   sub->print();
1360   fatal("%s: %s implements %s: linear_search: %d; table_lookup: %d",
1361         msg, sub->external_name(), super->external_name(), linear_result, table_result);
1362 }
1363 
1364 static int expanded = 0;
1365 static int not_expanded = 0;
1366 static NumberSeq seq = NumberSeq();
1367 
1368 bool Klass::expand_for_hash(oop obj, markWord m) const {
1369   assert(UseCompactObjectHeaders, "only with compact i-hash");
1370   {
1371     ResourceMark rm;
1372     assert((size_t)hash_offset_in_bytes(obj,m ) <= (obj->base_size_given_klass(m, this) * HeapWordSize), "hash offset must be eq or lt base size: hash offset: %d, base size: %zu, class-name: %s", hash_offset_in_bytes(obj, m), obj->base_size_given_klass(m, this) * HeapWordSize, external_name());
1373   }
1374   return obj->base_size_given_klass(m, this) * HeapWordSize - hash_offset_in_bytes(obj, m) < (int)sizeof(uint32_t);
1375 }