1 /*
   2  * Copyright (c) 1997, 2024, 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 "precompiled.hpp"
  26 #include "cds/archiveHeapLoader.hpp"
  27 #include "cds/cdsConfig.hpp"
  28 #include "cds/heapShared.hpp"
  29 #include "classfile/classLoader.hpp"
  30 #include "classfile/classLoaderData.inline.hpp"
  31 #include "classfile/classLoaderDataGraph.inline.hpp"
  32 #include "classfile/javaClasses.inline.hpp"
  33 #include "classfile/moduleEntry.hpp"
  34 #include "classfile/systemDictionary.hpp"
  35 #include "classfile/systemDictionaryShared.hpp"
  36 #include "classfile/vmClasses.hpp"
  37 #include "classfile/vmSymbols.hpp"
  38 #include "gc/shared/collectedHeap.inline.hpp"
  39 #include "jvm_io.h"
  40 #include "logging/log.hpp"
  41 #include "memory/metadataFactory.hpp"
  42 #include "memory/metaspaceClosure.hpp"
  43 #include "memory/oopFactory.hpp"
  44 #include "memory/resourceArea.hpp"
  45 #include "memory/universe.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 _access_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     _access_flags.set_is_cloneable_fast();
  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   if (UseSecondarySupersTable) {
 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::search_secondary_supers(Klass* k) const {
 167   // Put some extra logic here out-of-line, before the search proper.
 168   // This cuts down the size of the inline method.
 169 
 170   // This is necessary, since I am never in my own secondary_super list.
 171   if (this == k)
 172     return true;
 173   // Scan the array-of-objects for a match
 174   int cnt = secondary_supers()->length();
 175   for (int i = 0; i < cnt; i++) {
 176     if (secondary_supers()->at(i) == k) {
 177       ((Klass*)this)->set_secondary_super_cache(k);
 178       return true;
 179     }
 180   }
 181   return false;
 182 }
 183 
 184 // Return self, except for abstract classes with exactly 1
 185 // implementor.  Then return the 1 concrete implementation.
 186 Klass *Klass::up_cast_abstract() {
 187   Klass *r = this;
 188   while( r->is_abstract() ) {   // Receiver is abstract?
 189     Klass *s = r->subklass();   // Check for exactly 1 subklass
 190     if (s == nullptr || s->next_sibling() != nullptr) // Oops; wrong count; give up
 191       return this;              // Return 'this' as a no-progress flag
 192     r = s;                    // Loop till find concrete class
 193   }
 194   return r;                   // Return the 1 concrete class
 195 }
 196 
 197 // Find LCA in class hierarchy
 198 Klass *Klass::LCA( Klass *k2 ) {
 199   Klass *k1 = this;
 200   while( 1 ) {
 201     if( k1->is_subtype_of(k2) ) return k2;
 202     if( k2->is_subtype_of(k1) ) return k1;
 203     k1 = k1->super();
 204     k2 = k2->super();
 205   }
 206 }
 207 
 208 
 209 void Klass::check_valid_for_instantiation(bool throwError, TRAPS) {
 210   ResourceMark rm(THREAD);
 211   THROW_MSG(throwError ? vmSymbols::java_lang_InstantiationError()
 212             : vmSymbols::java_lang_InstantiationException(), external_name());
 213 }
 214 
 215 
 216 void Klass::copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS) {
 217   ResourceMark rm(THREAD);
 218   assert(s != nullptr, "Throw NPE!");
 219   THROW_MSG(vmSymbols::java_lang_ArrayStoreException(),
 220             err_msg("arraycopy: source type %s is not an array", s->klass()->external_name()));
 221 }
 222 
 223 
 224 void Klass::initialize(TRAPS) {
 225   ShouldNotReachHere();
 226 }
 227 
 228 Klass* Klass::find_field(Symbol* name, Symbol* sig, fieldDescriptor* fd) const {
 229 #ifdef ASSERT
 230   tty->print_cr("Error: find_field called on a klass oop."
 231                 " Likely error: reflection method does not correctly"
 232                 " wrap return value in a mirror object.");
 233 #endif
 234   ShouldNotReachHere();
 235   return nullptr;
 236 }
 237 
 238 Method* Klass::uncached_lookup_method(const Symbol* name, const Symbol* signature,
 239                                       OverpassLookupMode overpass_mode,
 240                                       PrivateLookupMode private_mode) const {
 241 #ifdef ASSERT
 242   tty->print_cr("Error: uncached_lookup_method called on a klass oop."
 243                 " Likely error: reflection method does not correctly"
 244                 " wrap return value in a mirror object.");
 245 #endif
 246   ShouldNotReachHere();
 247   return nullptr;
 248 }
 249 
 250 void* Klass::operator new(size_t size, ClassLoaderData* loader_data, size_t word_size, TRAPS) throw() {
 251   return Metaspace::allocate(loader_data, word_size, MetaspaceObj::ClassType, THREAD);
 252 }
 253 
 254 Klass::Klass() : _kind(UnknownKlassKind) {
 255   assert(CDSConfig::is_dumping_static_archive() || CDSConfig::is_using_archive(), "only for cds");
 256 }
 257 
 258 // "Normal" instantiation is preceded by a MetaspaceObj allocation
 259 // which zeros out memory - calloc equivalent.
 260 // The constructor is also used from CppVtableCloner,
 261 // which doesn't zero out the memory before calling the constructor.
 262 Klass::Klass(KlassKind kind) : _kind(kind),
 263                            _shared_class_path_index(-1) {
 264   CDS_ONLY(_shared_class_flags = 0;)
 265   CDS_JAVA_HEAP_ONLY(_archived_mirror_index = -1;)
 266   _primary_supers[0] = this;
 267   set_super_check_offset(in_bytes(primary_supers_offset()));
 268 }
 269 
 270 jint Klass::array_layout_helper(BasicType etype) {
 271   assert(etype >= T_BOOLEAN && etype <= T_OBJECT, "valid etype");
 272   // Note that T_ARRAY is not allowed here.
 273   int  hsize = arrayOopDesc::base_offset_in_bytes(etype);
 274   int  esize = type2aelembytes(etype);
 275   bool isobj = (etype == T_OBJECT);
 276   int  tag   =  isobj ? _lh_array_tag_obj_value : _lh_array_tag_type_value;
 277   int lh = array_layout_helper(tag, hsize, etype, exact_log2(esize));
 278 
 279   assert(lh < (int)_lh_neutral_value, "must look like an array layout");
 280   assert(layout_helper_is_array(lh), "correct kind");
 281   assert(layout_helper_is_objArray(lh) == isobj, "correct kind");
 282   assert(layout_helper_is_typeArray(lh) == !isobj, "correct kind");
 283   assert(layout_helper_header_size(lh) == hsize, "correct decode");
 284   assert(layout_helper_element_type(lh) == etype, "correct decode");
 285   assert(1 << layout_helper_log2_element_size(lh) == esize, "correct decode");
 286 
 287   return lh;
 288 }
 289 
 290 bool Klass::can_be_primary_super_slow() const {
 291   if (super() == nullptr)
 292     return true;
 293   else if (super()->super_depth() >= primary_super_limit()-1)
 294     return false;
 295   else
 296     return true;
 297 }
 298 
 299 void Klass::set_secondary_supers(Array<Klass*>* secondaries) {
 300   assert(!UseSecondarySupersTable || secondaries == nullptr, "");
 301   set_secondary_supers(secondaries, SECONDARY_SUPERS_BITMAP_EMPTY);
 302 }
 303 
 304 void Klass::set_secondary_supers(Array<Klass*>* secondaries, uintx bitmap) {
 305 #ifdef ASSERT
 306   if (UseSecondarySupersTable && secondaries != nullptr) {
 307     uintx real_bitmap = compute_secondary_supers_bitmap(secondaries);
 308     assert(bitmap == real_bitmap, "must be");
 309   }
 310 #endif
 311   _bitmap = bitmap;
 312   _secondary_supers = secondaries;
 313 
 314   if (secondaries != nullptr) {
 315     LogMessage(class, load) msg;
 316     NonInterleavingLogStream log {LogLevel::Debug, msg};
 317     if (log.is_enabled()) {
 318       ResourceMark rm;
 319       log.print_cr("set_secondary_supers: hash_slot: %d; klass: %s", hash_slot(), external_name());
 320       print_secondary_supers_on(&log);
 321     }
 322   }
 323 }
 324 
 325 // Hashed secondary superclasses
 326 //
 327 // We use a compressed 64-entry hash table with linear probing. We
 328 // start by creating a hash table in the usual way, followed by a pass
 329 // that removes all the null entries. To indicate which entries would
 330 // have been null we use a bitmap that contains a 1 in each position
 331 // where an entry is present, 0 otherwise. This bitmap also serves as
 332 // a kind of Bloom filter, which in many cases allows us quickly to
 333 // eliminate the possibility that something is a member of a set of
 334 // secondaries.
 335 uintx Klass::hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite) {
 336   const int length = secondaries->length();
 337 
 338   if (length == 0) {
 339     return SECONDARY_SUPERS_BITMAP_EMPTY;
 340   }
 341 
 342   if (length == 1) {
 343     int hash_slot = secondaries->at(0)->hash_slot();
 344     return uintx(1) << hash_slot;
 345   }
 346 
 347   // For performance reasons we don't use a hashed table unless there
 348   // are at least two empty slots in it. If there were only one empty
 349   // slot it'd take a long time to create the table and the resulting
 350   // search would be no faster than linear probing.
 351   if (length > SECONDARY_SUPERS_TABLE_SIZE - 2) {
 352     return SECONDARY_SUPERS_BITMAP_FULL;
 353   }
 354 
 355   {
 356     PerfTraceTime ptt(ClassLoader::perf_secondary_hash_time());
 357 
 358     ResourceMark rm;
 359     uintx bitmap = SECONDARY_SUPERS_BITMAP_EMPTY;
 360     auto hashed_secondaries = new GrowableArray<Klass*>(SECONDARY_SUPERS_TABLE_SIZE,
 361                                                         SECONDARY_SUPERS_TABLE_SIZE, nullptr);
 362 
 363     for (int j = 0; j < length; j++) {
 364       Klass* k = secondaries->at(j);
 365       hash_insert(k, hashed_secondaries, bitmap);
 366     }
 367 
 368     // Pack the hashed secondaries array by copying it into the
 369     // secondaries array, sans nulls, if modification is allowed.
 370     // Otherwise, validate the order.
 371     int i = 0;
 372     for (int slot = 0; slot < SECONDARY_SUPERS_TABLE_SIZE; slot++) {
 373       bool has_element = ((bitmap >> slot) & 1) != 0;
 374       assert(has_element == (hashed_secondaries->at(slot) != nullptr), "");
 375       if (has_element) {
 376         Klass* k = hashed_secondaries->at(slot);
 377         if (rewrite) {
 378           secondaries->at_put(i, k);
 379         } else if (secondaries->at(i) != k) {
 380           assert(false, "broken secondary supers hash table");
 381           return SECONDARY_SUPERS_BITMAP_FULL;
 382         }
 383         i++;
 384       }
 385     }
 386     assert(i == secondaries->length(), "mismatch");
 387 
 388     return bitmap;
 389   }
 390 }
 391 
 392 void Klass::hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap) {
 393   assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 394 
 395   int dist = 0;
 396   for (int slot = klass->hash_slot(); true; slot = (slot + 1) & SECONDARY_SUPERS_TABLE_MASK) {
 397     Klass* existing = secondaries->at(slot);
 398     assert(((bitmap >> slot) & 1) == (existing != nullptr), "mismatch");
 399     if (existing == nullptr) { // no conflict
 400       secondaries->at_put(slot, klass);
 401       bitmap |= uintx(1) << slot;
 402       assert(bitmap != SECONDARY_SUPERS_BITMAP_FULL, "");
 403       return;
 404     } else {
 405       // Use Robin Hood hashing to minimize the worst case search.
 406       // Also, every permutation of the insertion sequence produces
 407       // the same final Robin Hood hash table, provided that a
 408       // consistent tie breaker is used.
 409       int existing_dist = (slot - existing->hash_slot()) & SECONDARY_SUPERS_TABLE_MASK;
 410       if (existing_dist < dist
 411           // This tie breaker ensures that the hash order is maintained.
 412           || ((existing_dist == dist)
 413               && (uintptr_t(existing) < uintptr_t(klass)))) {
 414         Klass* tmp = secondaries->at(slot);
 415         secondaries->at_put(slot, klass);
 416         klass = tmp;
 417         dist = existing_dist;
 418       }
 419       ++dist;
 420     }
 421   }
 422 }
 423 
 424 Array<Klass*>* Klass::pack_secondary_supers(ClassLoaderData* loader_data,
 425                                             GrowableArray<Klass*>* primaries,
 426                                             GrowableArray<Klass*>* secondaries,
 427                                             uintx& bitmap, TRAPS) {
 428   int new_length = primaries->length() + secondaries->length();
 429   Array<Klass*>* secondary_supers = MetadataFactory::new_array<Klass*>(loader_data, new_length, CHECK_NULL);
 430 
 431   // Combine the two arrays into a metadata object to pack the array.
 432   // The primaries are added in the reverse order, then the secondaries.
 433   int fill_p = primaries->length();
 434   for (int j = 0; j < fill_p; j++) {
 435     secondary_supers->at_put(j, primaries->pop());  // add primaries in reverse order.
 436   }
 437   for( int j = 0; j < secondaries->length(); j++ ) {
 438     secondary_supers->at_put(j+fill_p, secondaries->at(j));  // add secondaries on the end.
 439   }
 440 #ifdef ASSERT
 441   // We must not copy any null placeholders left over from bootstrap.
 442   for (int j = 0; j < secondary_supers->length(); j++) {
 443     assert(secondary_supers->at(j) != nullptr, "correct bootstrapping order");
 444   }
 445 #endif
 446 
 447   if (UseSecondarySupersTable) {
 448     bitmap = hash_secondary_supers(secondary_supers, /*rewrite=*/true); // rewrites freshly allocated array
 449   } else {
 450     bitmap = SECONDARY_SUPERS_BITMAP_EMPTY;
 451   }
 452   return secondary_supers;
 453 }
 454 
 455 uintx Klass::compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers) {
 456   return hash_secondary_supers(secondary_supers, /*rewrite=*/false); // no rewrites allowed
 457 }
 458 
 459 uint8_t Klass::compute_home_slot(Klass* k, uintx bitmap) {
 460   uint8_t hash = k->hash_slot();
 461   if (hash > 0) {
 462     return population_count(bitmap << (SECONDARY_SUPERS_TABLE_SIZE - hash));
 463   }
 464   return 0;
 465 }
 466 
 467 
 468 void Klass::initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS) {
 469   if (k == nullptr) {
 470     set_super(nullptr);
 471     _primary_supers[0] = this;
 472     assert(super_depth() == 0, "Object must already be initialized properly");
 473   } else if (k != super() || k == vmClasses::Object_klass()) {
 474     assert(super() == nullptr || super() == vmClasses::Object_klass(),
 475            "initialize this only once to a non-trivial value");
 476     set_super(k);
 477     Klass* sup = k;
 478     int sup_depth = sup->super_depth();
 479     juint my_depth  = MIN2(sup_depth + 1, (int)primary_super_limit());
 480     if (!can_be_primary_super_slow())
 481       my_depth = primary_super_limit();
 482     for (juint i = 0; i < my_depth; i++) {
 483       _primary_supers[i] = sup->_primary_supers[i];
 484     }
 485     Klass* *super_check_cell;
 486     if (my_depth < primary_super_limit()) {
 487       _primary_supers[my_depth] = this;
 488       super_check_cell = &_primary_supers[my_depth];
 489     } else {
 490       // Overflow of the primary_supers array forces me to be secondary.
 491       super_check_cell = &_secondary_super_cache;
 492     }
 493     set_super_check_offset(u4((address)super_check_cell - (address) this));
 494 
 495 #ifdef ASSERT
 496     {
 497       juint j = super_depth();
 498       assert(j == my_depth, "computed accessor gets right answer");
 499       Klass* t = this;
 500       while (!t->can_be_primary_super()) {
 501         t = t->super();
 502         j = t->super_depth();
 503       }
 504       for (juint j1 = j+1; j1 < primary_super_limit(); j1++) {
 505         assert(primary_super_of_depth(j1) == nullptr, "super list padding");
 506       }
 507       while (t != nullptr) {
 508         assert(primary_super_of_depth(j) == t, "super list initialization");
 509         t = t->super();
 510         --j;
 511       }
 512       assert(j == (juint)-1, "correct depth count");
 513     }
 514 #endif
 515   }
 516 
 517   if (secondary_supers() == nullptr) {
 518 
 519     // Now compute the list of secondary supertypes.
 520     // Secondaries can occasionally be on the super chain,
 521     // if the inline "_primary_supers" array overflows.
 522     int extras = 0;
 523     Klass* p;
 524     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 525       ++extras;
 526     }
 527 
 528     ResourceMark rm(THREAD);  // need to reclaim GrowableArrays allocated below
 529 
 530     // Compute the "real" non-extra secondaries.
 531     GrowableArray<Klass*>* secondaries = compute_secondary_supers(extras, transitive_interfaces);
 532     if (secondaries == nullptr) {
 533       // secondary_supers set by compute_secondary_supers
 534       return;
 535     }
 536 
 537     GrowableArray<Klass*>* primaries = new GrowableArray<Klass*>(extras);
 538 
 539     for (p = super(); !(p == nullptr || p->can_be_primary_super()); p = p->super()) {
 540       int i;                    // Scan for overflow primaries being duplicates of 2nd'arys
 541 
 542       // This happens frequently for very deeply nested arrays: the
 543       // primary superclass chain overflows into the secondary.  The
 544       // secondary list contains the element_klass's secondaries with
 545       // an extra array dimension added.  If the element_klass's
 546       // secondary list already contains some primary overflows, they
 547       // (with the extra level of array-ness) will collide with the
 548       // normal primary superclass overflows.
 549       for( i = 0; i < secondaries->length(); i++ ) {
 550         if( secondaries->at(i) == p )
 551           break;
 552       }
 553       if( i < secondaries->length() )
 554         continue;               // It's a dup, don't put it in
 555       primaries->push(p);
 556     }
 557     // Combine the two arrays into a metadata object to pack the array.
 558     uintx bitmap = 0;
 559     Array<Klass*>* s2 = pack_secondary_supers(class_loader_data(), primaries, secondaries, bitmap, CHECK);
 560     set_secondary_supers(s2, bitmap);
 561   }
 562 }
 563 
 564 GrowableArray<Klass*>* Klass::compute_secondary_supers(int num_extra_slots,
 565                                                        Array<InstanceKlass*>* transitive_interfaces) {
 566   assert(num_extra_slots == 0, "override for complex klasses");
 567   assert(transitive_interfaces == nullptr, "sanity");
 568   set_secondary_supers(Universe::the_empty_klass_array(), Universe::the_empty_klass_bitmap());
 569   return nullptr;
 570 }
 571 
 572 
 573 // superklass links
 574 InstanceKlass* Klass::superklass() const {
 575   assert(super() == nullptr || super()->is_instance_klass(), "must be instance klass");
 576   return _super == nullptr ? nullptr : InstanceKlass::cast(_super);
 577 }
 578 
 579 // subklass links.  Used by the compiler (and vtable initialization)
 580 // May be cleaned concurrently, so must use the Compile_lock.
 581 // The log parameter is for clean_weak_klass_links to report unlinked classes.
 582 Klass* Klass::subklass(bool log) const {
 583   // Need load_acquire on the _subklass, because it races with inserts that
 584   // publishes freshly initialized data.
 585   for (Klass* chain = Atomic::load_acquire(&_subklass);
 586        chain != nullptr;
 587        // Do not need load_acquire on _next_sibling, because inserts never
 588        // create _next_sibling edges to dead data.
 589        chain = Atomic::load(&chain->_next_sibling))
 590   {
 591     if (chain->is_loader_alive()) {
 592       return chain;
 593     } else if (log) {
 594       if (log_is_enabled(Trace, class, unload)) {
 595         ResourceMark rm;
 596         log_trace(class, unload)("unlinking class (subclass): %s", chain->external_name());
 597       }
 598     }
 599   }
 600   return nullptr;
 601 }
 602 
 603 Klass* Klass::next_sibling(bool log) const {
 604   // Do not need load_acquire on _next_sibling, because inserts never
 605   // create _next_sibling edges to dead data.
 606   for (Klass* chain = Atomic::load(&_next_sibling);
 607        chain != nullptr;
 608        chain = Atomic::load(&chain->_next_sibling)) {
 609     // Only return alive klass, there may be stale klass
 610     // in this chain if cleaned concurrently.
 611     if (chain->is_loader_alive()) {
 612       return chain;
 613     } else if (log) {
 614       if (log_is_enabled(Trace, class, unload)) {
 615         ResourceMark rm;
 616         log_trace(class, unload)("unlinking class (sibling): %s", chain->external_name());
 617       }
 618     }
 619   }
 620   return nullptr;
 621 }
 622 
 623 void Klass::set_subklass(Klass* s) {
 624   assert(s != this, "sanity check");
 625   Atomic::release_store(&_subklass, s);
 626 }
 627 
 628 void Klass::set_next_sibling(Klass* s) {
 629   assert(s != this, "sanity check");
 630   // Does not need release semantics. If used by cleanup, it will link to
 631   // already safely published data, and if used by inserts, will be published
 632   // safely using cmpxchg.
 633   Atomic::store(&_next_sibling, s);
 634 }
 635 
 636 void Klass::append_to_sibling_list() {
 637   if (Universe::is_fully_initialized()) {
 638     assert_locked_or_safepoint(Compile_lock);
 639   }
 640   debug_only(verify();)
 641   // add ourselves to superklass' subklass list
 642   InstanceKlass* super = superklass();
 643   if (super == nullptr) return;     // special case: class Object
 644   assert((!super->is_interface()    // interfaces cannot be supers
 645           && (super->superklass() == nullptr || !is_interface())),
 646          "an interface can only be a subklass of Object");
 647 
 648   // Make sure there is no stale subklass head
 649   super->clean_subklass();
 650 
 651   for (;;) {
 652     Klass* prev_first_subklass = Atomic::load_acquire(&_super->_subklass);
 653     if (prev_first_subklass != nullptr) {
 654       // set our sibling to be the superklass' previous first subklass
 655       assert(prev_first_subklass->is_loader_alive(), "May not attach not alive klasses");
 656       set_next_sibling(prev_first_subklass);
 657     }
 658     // Note that the prev_first_subklass is always alive, meaning no sibling_next links
 659     // are ever created to not alive klasses. This is an important invariant of the lock-free
 660     // cleaning protocol, that allows us to safely unlink dead klasses from the sibling list.
 661     if (Atomic::cmpxchg(&super->_subklass, prev_first_subklass, this) == prev_first_subklass) {
 662       return;
 663     }
 664   }
 665   debug_only(verify();)
 666 }
 667 
 668 void Klass::clean_subklass() {
 669   for (;;) {
 670     // Need load_acquire, due to contending with concurrent inserts
 671     Klass* subklass = Atomic::load_acquire(&_subklass);
 672     if (subklass == nullptr || subklass->is_loader_alive()) {
 673       return;
 674     }
 675     // Try to fix _subklass until it points at something not dead.
 676     Atomic::cmpxchg(&_subklass, subklass, subklass->next_sibling());
 677   }
 678 }
 679 
 680 void Klass::clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses) {
 681   if (!ClassUnloading || !unloading_occurred) {
 682     return;
 683   }
 684 
 685   Klass* root = vmClasses::Object_klass();
 686   Stack<Klass*, mtGC> stack;
 687 
 688   stack.push(root);
 689   while (!stack.is_empty()) {
 690     Klass* current = stack.pop();
 691 
 692     assert(current->is_loader_alive(), "just checking, this should be live");
 693 
 694     // Find and set the first alive subklass
 695     Klass* sub = current->subklass(true);
 696     current->clean_subklass();
 697     if (sub != nullptr) {
 698       stack.push(sub);
 699     }
 700 
 701     // Find and set the first alive sibling
 702     Klass* sibling = current->next_sibling(true);
 703     current->set_next_sibling(sibling);
 704     if (sibling != nullptr) {
 705       stack.push(sibling);
 706     }
 707 
 708     // Clean the implementors list and method data.
 709     if (clean_alive_klasses && current->is_instance_klass()) {
 710       InstanceKlass* ik = InstanceKlass::cast(current);
 711       ik->clean_weak_instanceklass_links();
 712 
 713       // JVMTI RedefineClasses creates previous versions that are not in
 714       // the class hierarchy, so process them here.
 715       while ((ik = ik->previous_versions()) != nullptr) {
 716         ik->clean_weak_instanceklass_links();
 717       }
 718     }
 719   }
 720 }
 721 
 722 void Klass::metaspace_pointers_do(MetaspaceClosure* it) {
 723   if (log_is_enabled(Trace, cds)) {
 724     ResourceMark rm;
 725     log_trace(cds)("Iter(Klass): %p (%s)", this, external_name());
 726   }
 727 
 728   it->push(&_name);
 729   it->push(&_secondary_supers);
 730   for (int i = 0; i < _primary_super_limit; i++) {
 731     it->push(&_primary_supers[i]);
 732   }
 733   it->push(&_super);
 734   if (!CDSConfig::is_dumping_archive()) {
 735     // If dumping archive, these may point to excluded classes. There's no need
 736     // to follow these pointers anyway, as they will be set to null in
 737     // remove_unshareable_info().
 738     it->push((Klass**)&_subklass);
 739     it->push((Klass**)&_next_sibling);
 740     it->push(&_next_link);
 741   }
 742 
 743   vtableEntry* vt = start_of_vtable();
 744   for (int i=0; i<vtable_length(); i++) {
 745     it->push(vt[i].method_addr());
 746   }
 747 }
 748 
 749 #if INCLUDE_CDS
 750 void Klass::remove_unshareable_info() {
 751   assert(CDSConfig::is_dumping_archive(),
 752           "only called during CDS dump time");
 753   JFR_ONLY(REMOVE_ID(this);)
 754   if (log_is_enabled(Trace, cds, unshareable)) {
 755     ResourceMark rm;
 756     log_trace(cds, unshareable)("remove: %s", external_name());
 757   }
 758 
 759   // _secondary_super_cache may be updated by an is_subtype_of() call
 760   // while ArchiveBuilder is copying metaspace objects. Let's reset it to
 761   // null and let it be repopulated at runtime.
 762   set_secondary_super_cache(nullptr);
 763 
 764   set_subklass(nullptr);
 765   set_next_sibling(nullptr);
 766   set_next_link(nullptr);
 767 
 768   // Null out class_loader_data because we don't share that yet.
 769   set_class_loader_data(nullptr);
 770   set_is_shared();
 771 
 772   // FIXME: validation in Klass::hash_secondary_supers() may fail for shared klasses.
 773   // Even though the bitmaps always match, the canonical order of elements in the table
 774   // is not guaranteed to stay the same (see tie breaker during Robin Hood hashing in Klass::hash_insert).
 775   //assert(compute_secondary_supers_bitmap(secondary_supers()) == _bitmap, "broken table");
 776 }
 777 
 778 void Klass::remove_java_mirror() {
 779   assert(CDSConfig::is_dumping_archive(), "sanity");
 780   if (log_is_enabled(Trace, cds, unshareable)) {
 781     ResourceMark rm;
 782     log_trace(cds, unshareable)("remove java_mirror: %s", external_name());
 783   }
 784   // Just null out the mirror.  The class_loader_data() no longer exists.
 785   clear_java_mirror_handle();
 786 }
 787 
 788 void Klass::restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS) {
 789   assert(is_klass(), "ensure C++ vtable is restored");
 790   assert(is_shared(), "must be set");
 791   JFR_ONLY(RESTORE_ID(this);)
 792   if (log_is_enabled(Trace, cds, unshareable)) {
 793     ResourceMark rm(THREAD);
 794     oop class_loader = loader_data->class_loader();
 795     log_trace(cds, unshareable)("restore: %s with class loader: %s", external_name(),
 796       class_loader != nullptr ? class_loader->klass()->external_name() : "boot");
 797   }
 798 
 799   // If an exception happened during CDS restore, some of these fields may already be
 800   // set.  We leave the class on the CLD list, even if incomplete so that we don't
 801   // modify the CLD list outside a safepoint.
 802   if (class_loader_data() == nullptr) {
 803     set_class_loader_data(loader_data);
 804 
 805     // Add to class loader list first before creating the mirror
 806     // (same order as class file parsing)
 807     loader_data->add_class(this);
 808   }
 809 
 810   Handle loader(THREAD, loader_data->class_loader());
 811   ModuleEntry* module_entry = nullptr;
 812   Klass* k = this;
 813   if (k->is_objArray_klass()) {
 814     k = ObjArrayKlass::cast(k)->bottom_klass();
 815   }
 816   // Obtain klass' module.
 817   if (k->is_instance_klass()) {
 818     InstanceKlass* ik = (InstanceKlass*) k;
 819     module_entry = ik->module();
 820   } else {
 821     module_entry = ModuleEntryTable::javabase_moduleEntry();
 822   }
 823   // Obtain java.lang.Module, if available
 824   Handle module_handle(THREAD, ((module_entry != nullptr) ? module_entry->module() : (oop)nullptr));
 825 
 826   if (this->has_archived_mirror_index()) {
 827     ResourceMark rm(THREAD);
 828     log_debug(cds, mirror)("%s has raw archived mirror", external_name());
 829     if (ArchiveHeapLoader::is_in_use()) {
 830       bool present = java_lang_Class::restore_archived_mirror(this, loader, module_handle,
 831                                                               protection_domain,
 832                                                               CHECK);
 833       if (present) {
 834         return;
 835       }
 836     }
 837 
 838     // No archived mirror data
 839     log_debug(cds, mirror)("No archived mirror data for %s", external_name());
 840     clear_java_mirror_handle();
 841     this->clear_archived_mirror_index();
 842   }
 843 
 844   // Only recreate it if not present.  A previous attempt to restore may have
 845   // gotten an OOM later but keep the mirror if it was created.
 846   if (java_mirror() == nullptr) {
 847     ResourceMark rm(THREAD);
 848     log_trace(cds, mirror)("Recreate mirror for %s", external_name());
 849     java_lang_Class::create_mirror(this, loader, module_handle, protection_domain, Handle(), CHECK);
 850   }
 851 }
 852 #endif // INCLUDE_CDS
 853 
 854 #if INCLUDE_CDS_JAVA_HEAP
 855 oop Klass::archived_java_mirror() {
 856   assert(has_archived_mirror_index(), "must have archived mirror");
 857   return HeapShared::get_root(_archived_mirror_index);
 858 }
 859 
 860 void Klass::clear_archived_mirror_index() {
 861   if (_archived_mirror_index >= 0) {
 862     HeapShared::clear_root(_archived_mirror_index);
 863   }
 864   _archived_mirror_index = -1;
 865 }
 866 
 867 // No GC barrier
 868 void Klass::set_archived_java_mirror(int mirror_index) {
 869   assert(CDSConfig::is_dumping_heap(), "sanity");
 870   _archived_mirror_index = mirror_index;
 871 }
 872 #endif // INCLUDE_CDS_JAVA_HEAP
 873 
 874 void Klass::check_array_allocation_length(int length, int max_length, TRAPS) {
 875   if (length > max_length) {
 876     if (!THREAD->is_in_internal_oome_mark()) {
 877       report_java_out_of_memory("Requested array size exceeds VM limit");
 878       JvmtiExport::post_array_size_exhausted();
 879       THROW_OOP(Universe::out_of_memory_error_array_size());
 880     } else {
 881       THROW_OOP(Universe::out_of_memory_error_java_heap_without_backtrace());
 882     }
 883   } else if (length < 0) {
 884     THROW_MSG(vmSymbols::java_lang_NegativeArraySizeException(), err_msg("%d", length));
 885   }
 886 }
 887 
 888 // Replace the last '+' char with '/'.
 889 static char* convert_hidden_name_to_java(Symbol* name) {
 890   size_t name_len = name->utf8_length();
 891   char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 892   name->as_klass_external_name(result, (int)name_len + 1);
 893   for (int index = (int)name_len; index > 0; index--) {
 894     if (result[index] == '+') {
 895       result[index] = JVM_SIGNATURE_SLASH;
 896       break;
 897     }
 898   }
 899   return result;
 900 }
 901 
 902 // In product mode, this function doesn't have virtual function calls so
 903 // there might be some performance advantage to handling InstanceKlass here.
 904 const char* Klass::external_name() const {
 905   if (is_instance_klass()) {
 906     const InstanceKlass* ik = static_cast<const InstanceKlass*>(this);
 907     if (ik->is_hidden()) {
 908       char* result = convert_hidden_name_to_java(name());
 909       return result;
 910     }
 911   } else if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 912     char* result = convert_hidden_name_to_java(name());
 913     return result;
 914   }
 915   if (name() == nullptr)  return "<unknown>";
 916   return name()->as_klass_external_name();
 917 }
 918 
 919 const char* Klass::signature_name() const {
 920   if (name() == nullptr)  return "<unknown>";
 921   if (is_objArray_klass() && ObjArrayKlass::cast(this)->bottom_klass()->is_hidden()) {
 922     size_t name_len = name()->utf8_length();
 923     char* result = NEW_RESOURCE_ARRAY(char, name_len + 1);
 924     name()->as_C_string(result, (int)name_len + 1);
 925     for (int index = (int)name_len; index > 0; index--) {
 926       if (result[index] == '+') {
 927         result[index] = JVM_SIGNATURE_DOT;
 928         break;
 929       }
 930     }
 931     return result;
 932   }
 933   return name()->as_C_string();
 934 }
 935 
 936 const char* Klass::external_kind() const {
 937   if (is_interface()) return "interface";
 938   if (is_abstract()) return "abstract class";
 939   return "class";
 940 }
 941 
 942 // Unless overridden, jvmti_class_status has no flags set.
 943 jint Klass::jvmti_class_status() const {
 944   return 0;
 945 }
 946 
 947 
 948 // Printing
 949 
 950 void Klass::print_on(outputStream* st) const {
 951   ResourceMark rm;
 952   // print title
 953   st->print("%s", internal_name());
 954   print_address_on(st);
 955   st->cr();
 956 }
 957 
 958 #define BULLET  " - "
 959 
 960 // Caller needs ResourceMark
 961 void Klass::oop_print_on(oop obj, outputStream* st) {
 962   // print title
 963   st->print_cr("%s ", internal_name());
 964   obj->print_address_on(st);
 965 
 966   if (WizardMode) {
 967      // print header
 968      obj->mark().print_on(st);
 969      st->cr();
 970   }
 971 
 972   // print class
 973   st->print(BULLET"klass: ");
 974   obj->klass()->print_value_on(st);
 975   st->cr();
 976 }
 977 
 978 void Klass::oop_print_value_on(oop obj, outputStream* st) {
 979   // print title
 980   ResourceMark rm;              // Cannot print in debug mode without this
 981   st->print("%s", internal_name());
 982   obj->print_address_on(st);
 983 }
 984 
 985 // Verification
 986 
 987 void Klass::verify_on(outputStream* st) {
 988 
 989   // This can be expensive, but it is worth checking that this klass is actually
 990   // in the CLD graph but not in production.
 991   assert(Metaspace::contains((address)this), "Should be");
 992 
 993   guarantee(this->is_klass(),"should be klass");
 994 
 995   if (super() != nullptr) {
 996     guarantee(super()->is_klass(), "should be klass");
 997   }
 998   if (secondary_super_cache() != nullptr) {
 999     Klass* ko = secondary_super_cache();
1000     guarantee(ko->is_klass(), "should be klass");
1001   }
1002   for ( uint i = 0; i < primary_super_limit(); i++ ) {
1003     Klass* ko = _primary_supers[i];
1004     if (ko != nullptr) {
1005       guarantee(ko->is_klass(), "should be klass");
1006     }
1007   }
1008 
1009   if (java_mirror_no_keepalive() != nullptr) {
1010     guarantee(java_lang_Class::is_instance(java_mirror_no_keepalive()), "should be instance");
1011   }
1012 }
1013 
1014 void Klass::oop_verify_on(oop obj, outputStream* st) {
1015   guarantee(oopDesc::is_oop(obj),  "should be oop");
1016   guarantee(obj->klass()->is_klass(), "klass field is not a klass");
1017 }
1018 
1019 bool Klass::is_valid(Klass* k) {
1020   if (!is_aligned(k, sizeof(MetaWord))) return false;
1021   if ((size_t)k < os::min_page_size()) return false;
1022 
1023   if (!os::is_readable_range(k, k + 1)) return false;
1024   if (!Metaspace::contains(k)) return false;
1025 
1026   if (!Symbol::is_valid(k->name())) return false;
1027   return ClassLoaderDataGraph::is_valid(k->class_loader_data());
1028 }
1029 
1030 Method* Klass::method_at_vtable(int index)  {
1031 #ifndef PRODUCT
1032   assert(index >= 0, "valid vtable index");
1033   if (DebugVtables) {
1034     verify_vtable_index(index);
1035   }
1036 #endif
1037   return start_of_vtable()[index].method();
1038 }
1039 
1040 
1041 #ifndef PRODUCT
1042 
1043 bool Klass::verify_vtable_index(int i) {
1044   int limit = vtable_length()/vtableEntry::size();
1045   assert(i >= 0 && i < limit, "index %d out of bounds %d", i, limit);
1046   return true;
1047 }
1048 
1049 #endif // PRODUCT
1050 
1051 // Caller needs ResourceMark
1052 // joint_in_module_of_loader provides an optimization if 2 classes are in
1053 // the same module to succinctly print out relevant information about their
1054 // module name and class loader's name_and_id for error messages.
1055 // Format:
1056 //   <fully-qualified-external-class-name1> and <fully-qualified-external-class-name2>
1057 //                      are in module <module-name>[@<version>]
1058 //                      of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1059 const char* Klass::joint_in_module_of_loader(const Klass* class2, bool include_parent_loader) const {
1060   assert(module() == class2->module(), "classes do not have the same module");
1061   const char* class1_name = external_name();
1062   size_t len = strlen(class1_name) + 1;
1063 
1064   const char* class2_description = class2->class_in_module_of_loader(true, include_parent_loader);
1065   len += strlen(class2_description);
1066 
1067   len += strlen(" and ");
1068 
1069   char* joint_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1070 
1071   // Just return the FQN if error when allocating string
1072   if (joint_description == nullptr) {
1073     return class1_name;
1074   }
1075 
1076   jio_snprintf(joint_description, len, "%s and %s",
1077                class1_name,
1078                class2_description);
1079 
1080   return joint_description;
1081 }
1082 
1083 // Caller needs ResourceMark
1084 // class_in_module_of_loader provides a standard way to include
1085 // relevant information about a class, such as its module name as
1086 // well as its class loader's name_and_id, in error messages and logging.
1087 // Format:
1088 //   <fully-qualified-external-class-name> is in module <module-name>[@<version>]
1089 //                                         of loader <loader-name_and_id>[, parent loader <parent-loader-name_and_id>]
1090 const char* Klass::class_in_module_of_loader(bool use_are, bool include_parent_loader) const {
1091   // 1. fully qualified external name of class
1092   const char* klass_name = external_name();
1093   size_t len = strlen(klass_name) + 1;
1094 
1095   // 2. module name + @version
1096   const char* module_name = "";
1097   const char* version = "";
1098   bool has_version = false;
1099   bool module_is_named = false;
1100   const char* module_name_phrase = "";
1101   const Klass* bottom_klass = is_objArray_klass() ?
1102                                 ObjArrayKlass::cast(this)->bottom_klass() : this;
1103   if (bottom_klass->is_instance_klass()) {
1104     ModuleEntry* module = InstanceKlass::cast(bottom_klass)->module();
1105     if (module->is_named()) {
1106       module_is_named = true;
1107       module_name_phrase = "module ";
1108       module_name = module->name()->as_C_string();
1109       len += strlen(module_name);
1110       // Use version if exists and is not a jdk module
1111       if (module->should_show_version()) {
1112         has_version = true;
1113         version = module->version()->as_C_string();
1114         // Include stlen(version) + 1 for the "@"
1115         len += strlen(version) + 1;
1116       }
1117     } else {
1118       module_name = UNNAMED_MODULE;
1119       len += UNNAMED_MODULE_LEN;
1120     }
1121   } else {
1122     // klass is an array of primitives, module is java.base
1123     module_is_named = true;
1124     module_name_phrase = "module ";
1125     module_name = JAVA_BASE_NAME;
1126     len += JAVA_BASE_NAME_LEN;
1127   }
1128 
1129   // 3. class loader's name_and_id
1130   ClassLoaderData* cld = class_loader_data();
1131   assert(cld != nullptr, "class_loader_data should not be null");
1132   const char* loader_name_and_id = cld->loader_name_and_id();
1133   len += strlen(loader_name_and_id);
1134 
1135   // 4. include parent loader information
1136   const char* parent_loader_phrase = "";
1137   const char* parent_loader_name_and_id = "";
1138   if (include_parent_loader &&
1139       !cld->is_builtin_class_loader_data()) {
1140     oop parent_loader = java_lang_ClassLoader::parent(class_loader());
1141     ClassLoaderData *parent_cld = ClassLoaderData::class_loader_data_or_null(parent_loader);
1142     // The parent loader's ClassLoaderData could be null if it is
1143     // a delegating class loader that has never defined a class.
1144     // In this case the loader's name must be obtained via the parent loader's oop.
1145     if (parent_cld == nullptr) {
1146       oop cl_name_and_id = java_lang_ClassLoader::nameAndId(parent_loader);
1147       if (cl_name_and_id != nullptr) {
1148         parent_loader_name_and_id = java_lang_String::as_utf8_string(cl_name_and_id);
1149       }
1150     } else {
1151       parent_loader_name_and_id = parent_cld->loader_name_and_id();
1152     }
1153     parent_loader_phrase = ", parent loader ";
1154     len += strlen(parent_loader_phrase) + strlen(parent_loader_name_and_id);
1155   }
1156 
1157   // Start to construct final full class description string
1158   len += ((use_are) ? strlen(" are in ") : strlen(" is in "));
1159   len += strlen(module_name_phrase) + strlen(" of loader ");
1160 
1161   char* class_description = NEW_RESOURCE_ARRAY_RETURN_NULL(char, len);
1162 
1163   // Just return the FQN if error when allocating string
1164   if (class_description == nullptr) {
1165     return klass_name;
1166   }
1167 
1168   jio_snprintf(class_description, len, "%s %s in %s%s%s%s of loader %s%s%s",
1169                klass_name,
1170                (use_are) ? "are" : "is",
1171                module_name_phrase,
1172                module_name,
1173                (has_version) ? "@" : "",
1174                (has_version) ? version : "",
1175                loader_name_and_id,
1176                parent_loader_phrase,
1177                parent_loader_name_and_id);
1178 
1179   return class_description;
1180 }
1181 
1182 class LookupStats : StackObj {
1183  private:
1184   uint _no_of_samples;
1185   uint _worst;
1186   uint _worst_count;
1187   uint _average;
1188   uint _best;
1189   uint _best_count;
1190  public:
1191   LookupStats() : _no_of_samples(0), _worst(0), _worst_count(0), _average(0), _best(INT_MAX), _best_count(0) {}
1192 
1193   ~LookupStats() {
1194     assert(_best <= _worst || _no_of_samples == 0, "sanity");
1195   }
1196 
1197   void sample(uint value) {
1198     ++_no_of_samples;
1199     _average += value;
1200 
1201     if (_worst < value) {
1202       _worst = value;
1203       _worst_count = 1;
1204     } else if (_worst == value) {
1205       ++_worst_count;
1206     }
1207 
1208     if (_best > value) {
1209       _best = value;
1210       _best_count = 1;
1211     } else if (_best == value) {
1212       ++_best_count;
1213     }
1214   }
1215 
1216   void print_on(outputStream* st) const {
1217     st->print("best: %2d (%4.1f%%)", _best, (100.0 * _best_count) / _no_of_samples);
1218     if (_best_count < _no_of_samples) {
1219       st->print("; average: %4.1f; worst: %2d (%4.1f%%)",
1220                 (1.0 * _average) / _no_of_samples,
1221                 _worst, (100.0 * _worst_count) / _no_of_samples);
1222     }
1223   }
1224 };
1225 
1226 static void print_positive_lookup_stats(Array<Klass*>* secondary_supers, uintx bitmap, outputStream* st) {
1227   int num_of_supers = secondary_supers->length();
1228 
1229   LookupStats s;
1230   for (int i = 0; i < num_of_supers; i++) {
1231     Klass* secondary_super = secondary_supers->at(i);
1232     int home_slot = Klass::compute_home_slot(secondary_super, bitmap);
1233     uint score = 1 + ((i - home_slot) & Klass::SECONDARY_SUPERS_TABLE_MASK);
1234     s.sample(score);
1235   }
1236   st->print("positive_lookup: "); s.print_on(st);
1237 }
1238 
1239 static uint compute_distance_to_nearest_zero(int slot, uintx bitmap) {
1240   assert(~bitmap != 0, "no zeroes");
1241   uintx start = rotate_right(bitmap, slot);
1242   return count_trailing_zeros(~start);
1243 }
1244 
1245 static void print_negative_lookup_stats(uintx bitmap, outputStream* st) {
1246   LookupStats s;
1247   for (int slot = 0; slot < Klass::SECONDARY_SUPERS_TABLE_SIZE; slot++) {
1248     uint score = compute_distance_to_nearest_zero(slot, bitmap);
1249     s.sample(score);
1250   }
1251   st->print("negative_lookup: "); s.print_on(st);
1252 }
1253 
1254 void Klass::print_secondary_supers_on(outputStream* st) const {
1255   if (secondary_supers() != nullptr) {
1256     if (UseSecondarySupersTable) {
1257       st->print("  - "); st->print("%d elements;", _secondary_supers->length());
1258       st->print_cr(" bitmap: " UINTX_FORMAT_X_0 ";", _bitmap);
1259       if (_bitmap != SECONDARY_SUPERS_BITMAP_EMPTY &&
1260           _bitmap != SECONDARY_SUPERS_BITMAP_FULL) {
1261         st->print("  - "); print_positive_lookup_stats(secondary_supers(), _bitmap, st); st->cr();
1262         st->print("  - "); print_negative_lookup_stats(_bitmap, st); st->cr();
1263       }
1264     }
1265   } else {
1266     st->print("null");
1267   }
1268 }
1269 
1270 void Klass::on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg) {
1271   ResourceMark rm;
1272   super->print();
1273   sub->print();
1274   fatal("%s: %s implements %s: is_subtype_of: %d; linear_search: %d; table_lookup: %d",
1275         msg, sub->external_name(), super->external_name(),
1276         sub->is_subtype_of(super), linear_result, table_result);
1277 }