1 /*
   2  * Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #include "cds/cdsConfig.hpp"
  26 #include "cds/metaspaceShared.hpp"
  27 #include "classfile/classFileStream.hpp"
  28 #include "classfile/classLoaderDataGraph.hpp"
  29 #include "classfile/classLoadInfo.hpp"
  30 #include "classfile/javaClasses.inline.hpp"
  31 #include "classfile/metadataOnStackMark.hpp"
  32 #include "classfile/symbolTable.hpp"
  33 #include "classfile/klassFactory.hpp"
  34 #include "classfile/verifier.hpp"
  35 #include "classfile/vmClasses.hpp"
  36 #include "classfile/vmSymbols.hpp"
  37 #include "code/codeCache.hpp"
  38 #include "compiler/compileBroker.hpp"
  39 #include "interpreter/oopMapCache.hpp"
  40 #include "interpreter/rewriter.hpp"
  41 #include "jfr/jfrEvents.hpp"
  42 #include "logging/logStream.hpp"
  43 #include "memory/metadataFactory.hpp"
  44 #include "memory/resourceArea.hpp"
  45 #include "memory/universe.hpp"
  46 #include "oops/annotations.hpp"
  47 #include "oops/constantPool.hpp"
  48 #include "oops/fieldStreams.inline.hpp"
  49 #include "oops/klass.inline.hpp"
  50 #include "oops/klassVtable.hpp"
  51 #include "oops/method.hpp"
  52 #include "oops/oop.inline.hpp"
  53 #include "oops/recordComponent.hpp"
  54 #include "prims/jvmtiImpl.hpp"
  55 #include "prims/jvmtiRedefineClasses.hpp"
  56 #include "prims/jvmtiThreadState.inline.hpp"
  57 #include "prims/resolvedMethodTable.hpp"
  58 #include "prims/methodComparator.hpp"
  59 #include "runtime/atomic.hpp"
  60 #include "runtime/deoptimization.hpp"
  61 #include "runtime/handles.inline.hpp"
  62 #include "runtime/jniHandles.inline.hpp"
  63 #include "runtime/relocator.hpp"
  64 #include "runtime/safepointVerifiers.hpp"
  65 #include "utilities/bitMap.inline.hpp"
  66 #include "utilities/checkedCast.hpp"
  67 #include "utilities/events.hpp"
  68 #include "utilities/macros.hpp"
  69 
  70 Array<Method*>* VM_RedefineClasses::_old_methods = nullptr;
  71 Array<Method*>* VM_RedefineClasses::_new_methods = nullptr;
  72 Method**  VM_RedefineClasses::_matching_old_methods = nullptr;
  73 Method**  VM_RedefineClasses::_matching_new_methods = nullptr;
  74 Method**  VM_RedefineClasses::_deleted_methods      = nullptr;
  75 Method**  VM_RedefineClasses::_added_methods        = nullptr;
  76 int       VM_RedefineClasses::_matching_methods_length = 0;
  77 int       VM_RedefineClasses::_deleted_methods_length  = 0;
  78 int       VM_RedefineClasses::_added_methods_length    = 0;
  79 
  80 // This flag is global as the constructor does not reset it:
  81 bool      VM_RedefineClasses::_has_redefined_Object = false;
  82 u8        VM_RedefineClasses::_id_counter = 0;
  83 
  84 VM_RedefineClasses::VM_RedefineClasses(jint class_count,
  85                                        const jvmtiClassDefinition *class_defs,
  86                                        JvmtiClassLoadKind class_load_kind) {
  87   _class_count = class_count;
  88   _class_defs = class_defs;
  89   _class_load_kind = class_load_kind;
  90   _any_class_has_resolved_methods = false;
  91   _res = JVMTI_ERROR_NONE;
  92   _the_class = nullptr;
  93   _id = next_id();
  94 }
  95 
  96 static inline InstanceKlass* get_ik(jclass def) {
  97   oop mirror = JNIHandles::resolve_non_null(def);
  98   return InstanceKlass::cast(java_lang_Class::as_Klass(mirror));
  99 }
 100 
 101 // If any of the classes are being redefined, wait
 102 // Parallel constant pool merging leads to indeterminate constant pools.
 103 void VM_RedefineClasses::lock_classes() {
 104   JvmtiThreadState *state = JvmtiThreadState::state_for(JavaThread::current());
 105   GrowableArray<Klass*>* redef_classes = state->get_classes_being_redefined();
 106 
 107   MonitorLocker ml(RedefineClasses_lock);
 108 
 109   if (redef_classes == nullptr) {
 110     redef_classes = new (mtClass) GrowableArray<Klass*>(1, mtClass);
 111     state->set_classes_being_redefined(redef_classes);
 112   }
 113 
 114   bool has_redefined;
 115   do {
 116     has_redefined = false;
 117     // Go through classes each time until none are being redefined. Skip
 118     // the ones that are being redefined by this thread currently. Class file
 119     // load hook event may trigger new class redefine when we are redefining
 120     // a class (after lock_classes()).
 121     for (int i = 0; i < _class_count; i++) {
 122       InstanceKlass* ik = get_ik(_class_defs[i].klass);
 123       // Check if we are currently redefining the class in this thread already.
 124       if (redef_classes->contains(ik)) {
 125         assert(ik->is_being_redefined(), "sanity");
 126       } else {
 127         if (ik->is_being_redefined()) {
 128           ml.wait();
 129           has_redefined = true;
 130           break;  // for loop
 131         }
 132       }
 133     }
 134   } while (has_redefined);
 135 
 136   for (int i = 0; i < _class_count; i++) {
 137     InstanceKlass* ik = get_ik(_class_defs[i].klass);
 138     redef_classes->push(ik); // Add to the _classes_being_redefined list
 139     ik->set_is_being_redefined(true);
 140   }
 141   ml.notify_all();
 142 }
 143 
 144 void VM_RedefineClasses::unlock_classes() {
 145   JvmtiThreadState *state = JvmtiThreadState::state_for(JavaThread::current());
 146   GrowableArray<Klass*>* redef_classes = state->get_classes_being_redefined();
 147   assert(redef_classes != nullptr, "_classes_being_redefined is not allocated");
 148 
 149   MonitorLocker ml(RedefineClasses_lock);
 150 
 151   for (int i = _class_count - 1; i >= 0; i--) {
 152     InstanceKlass* def_ik = get_ik(_class_defs[i].klass);
 153     if (redef_classes->length() > 0) {
 154       // Remove the class from _classes_being_redefined list
 155       Klass* k = redef_classes->pop();
 156       assert(def_ik == k, "unlocking wrong class");
 157     }
 158     assert(def_ik->is_being_redefined(),
 159            "should be being redefined to get here");
 160 
 161     // Unlock after we finish all redefines for this class within
 162     // the thread. Same class can be pushed to the list multiple
 163     // times (not more than once by each recursive redefinition).
 164     if (!redef_classes->contains(def_ik)) {
 165       def_ik->set_is_being_redefined(false);
 166     }
 167   }
 168   ml.notify_all();
 169 }
 170 
 171 bool VM_RedefineClasses::doit_prologue() {
 172   if (_class_count == 0) {
 173     _res = JVMTI_ERROR_NONE;
 174     return false;
 175   }
 176   if (_class_defs == nullptr) {
 177     _res = JVMTI_ERROR_NULL_POINTER;
 178     return false;
 179   }
 180 
 181   for (int i = 0; i < _class_count; i++) {
 182     if (_class_defs[i].klass == nullptr) {
 183       _res = JVMTI_ERROR_INVALID_CLASS;
 184       return false;
 185     }
 186     if (_class_defs[i].class_byte_count == 0) {
 187       _res = JVMTI_ERROR_INVALID_CLASS_FORMAT;
 188       return false;
 189     }
 190     if (_class_defs[i].class_bytes == nullptr) {
 191       _res = JVMTI_ERROR_NULL_POINTER;
 192       return false;
 193     }
 194 
 195     oop mirror = JNIHandles::resolve_non_null(_class_defs[i].klass);
 196     // classes for primitives, arrays, and hidden classes
 197     // cannot be redefined.
 198     if (!is_modifiable_class(mirror)) {
 199       _res = JVMTI_ERROR_UNMODIFIABLE_CLASS;
 200       return false;
 201     }
 202   }
 203 
 204   // Start timer after all the sanity checks; not quite accurate, but
 205   // better than adding a bunch of stop() calls.
 206   if (log_is_enabled(Info, redefine, class, timer)) {
 207     _timer_vm_op_prologue.start();
 208   }
 209 
 210   lock_classes();
 211   // We first load new class versions in the prologue, because somewhere down the
 212   // call chain it is required that the current thread is a Java thread.
 213   _res = load_new_class_versions();
 214   if (_res != JVMTI_ERROR_NONE) {
 215     // free any successfully created classes, since none are redefined
 216     for (int i = 0; i < _class_count; i++) {
 217       if (_scratch_classes[i] != nullptr) {
 218         ClassLoaderData* cld = _scratch_classes[i]->class_loader_data();
 219         // Free the memory for this class at class unloading time.  Not before
 220         // because CMS might think this is still live.
 221         InstanceKlass* ik = get_ik(_class_defs[i].klass);
 222         if (ik->get_cached_class_file() == _scratch_classes[i]->get_cached_class_file()) {
 223           // Don't double-free cached_class_file copied from the original class if error.
 224           _scratch_classes[i]->set_cached_class_file(nullptr);
 225         }
 226         cld->add_to_deallocate_list(InstanceKlass::cast(_scratch_classes[i]));
 227       }
 228     }
 229     // Free os::malloc allocated memory in load_new_class_version.
 230     os::free(_scratch_classes);
 231     _timer_vm_op_prologue.stop();
 232     unlock_classes();
 233     return false;
 234   }
 235 
 236   _timer_vm_op_prologue.stop();
 237   return true;
 238 }
 239 
 240 void VM_RedefineClasses::doit() {
 241   Thread* current = Thread::current();
 242 
 243   if (log_is_enabled(Info, redefine, class, timer)) {
 244     _timer_vm_op_doit.start();
 245   }
 246 
 247 #if INCLUDE_CDS
 248   if (CDSConfig::is_using_archive()) {
 249     // Sharing is enabled so we remap the shared readonly space to
 250     // shared readwrite, private just in case we need to redefine
 251     // a shared class. We do the remap during the doit() phase of
 252     // the safepoint to be safer.
 253     if (!MetaspaceShared::remap_shared_readonly_as_readwrite()) {
 254       log_info(redefine, class, load)("failed to remap shared readonly space to readwrite, private");
 255       _res = JVMTI_ERROR_INTERNAL;
 256       _timer_vm_op_doit.stop();
 257       return;
 258     }
 259   }
 260 #endif
 261 
 262   // Mark methods seen on stack and everywhere else so old methods are not
 263   // cleaned up if they're on the stack.
 264   MetadataOnStackMark md_on_stack(/*walk_all_metadata*/true, /*redefinition_walk*/true);
 265   HandleMark hm(current);   // make sure any handles created are deleted
 266                             // before the stack walk again.
 267 
 268   for (int i = 0; i < _class_count; i++) {
 269     redefine_single_class(current, _class_defs[i].klass, _scratch_classes[i]);
 270   }
 271 
 272   // Flush all compiled code that depends on the classes redefined.
 273   flush_dependent_code();
 274 
 275   // Adjust constantpool caches and vtables for all classes
 276   // that reference methods of the evolved classes.
 277   // Have to do this after all classes are redefined and all methods that
 278   // are redefined are marked as old.
 279   AdjustAndCleanMetadata adjust_and_clean_metadata(current);
 280   ClassLoaderDataGraph::classes_do(&adjust_and_clean_metadata);
 281 
 282   // JSR-292 support
 283   if (_any_class_has_resolved_methods) {
 284     bool trace_name_printed = false;
 285     ResolvedMethodTable::adjust_method_entries(&trace_name_printed);
 286   }
 287 
 288   // Increment flag indicating that some invariants are no longer true.
 289   // See jvmtiExport.hpp for detailed explanation.
 290   JvmtiExport::increment_redefinition_count();
 291 
 292   // check_class() is optionally called for product bits, but is
 293   // always called for non-product bits.
 294 #ifdef PRODUCT
 295   if (log_is_enabled(Trace, redefine, class, obsolete, metadata)) {
 296 #endif
 297     log_trace(redefine, class, obsolete, metadata)("calling check_class");
 298     CheckClass check_class(current);
 299     ClassLoaderDataGraph::classes_do(&check_class);
 300 #ifdef PRODUCT
 301   }
 302 #endif
 303 
 304   // Clean up any metadata now unreferenced while MetadataOnStackMark is set.
 305   ClassLoaderDataGraph::clean_deallocate_lists(false);
 306 
 307   _timer_vm_op_doit.stop();
 308 }
 309 
 310 void VM_RedefineClasses::doit_epilogue() {
 311   unlock_classes();
 312 
 313   // Free os::malloc allocated memory.
 314   os::free(_scratch_classes);
 315 
 316   // Reset the_class to null for error printing.
 317   _the_class = nullptr;
 318 
 319   if (log_is_enabled(Info, redefine, class, timer)) {
 320     // Used to have separate timers for "doit" and "all", but the timer
 321     // overhead skewed the measurements.
 322     julong doit_time = _timer_vm_op_doit.milliseconds();
 323     julong all_time = _timer_vm_op_prologue.milliseconds() + doit_time;
 324 
 325     log_info(redefine, class, timer)
 326       ("vm_op: all=" JULONG_FORMAT "  prologue=" JULONG_FORMAT "  doit=" JULONG_FORMAT,
 327        all_time, (julong)_timer_vm_op_prologue.milliseconds(), doit_time);
 328     log_info(redefine, class, timer)
 329       ("redefine_single_class: phase1=" JULONG_FORMAT "  phase2=" JULONG_FORMAT,
 330        (julong)_timer_rsc_phase1.milliseconds(), (julong)_timer_rsc_phase2.milliseconds());
 331   }
 332 }
 333 
 334 bool VM_RedefineClasses::is_modifiable_class(oop klass_mirror) {
 335   // classes for primitives cannot be redefined
 336   if (java_lang_Class::is_primitive(klass_mirror)) {
 337     return false;
 338   }
 339   Klass* k = java_lang_Class::as_Klass(klass_mirror);
 340   // classes for arrays cannot be redefined
 341   if (k == nullptr || !k->is_instance_klass()) {
 342     return false;
 343   }
 344 
 345   // Cannot redefine or retransform a hidden class.
 346   if (InstanceKlass::cast(k)->is_hidden()) {
 347     return false;
 348   }
 349   if (InstanceKlass::cast(k) == vmClasses::Continuation_klass()) {
 350     // Don't redefine Continuation class. See 8302779.
 351     return false;
 352   }
 353   return true;
 354 }
 355 
 356 // Append the current entry at scratch_i in scratch_cp to *merge_cp_p
 357 // where the end of *merge_cp_p is specified by *merge_cp_length_p. For
 358 // direct CP entries, there is just the current entry to append. For
 359 // indirect and double-indirect CP entries, there are zero or more
 360 // referenced CP entries along with the current entry to append.
 361 // Indirect and double-indirect CP entries are handled by recursive
 362 // calls to append_entry() as needed. The referenced CP entries are
 363 // always appended to *merge_cp_p before the referee CP entry. These
 364 // referenced CP entries may already exist in *merge_cp_p in which case
 365 // there is nothing extra to append and only the current entry is
 366 // appended.
 367 void VM_RedefineClasses::append_entry(const constantPoolHandle& scratch_cp,
 368        int scratch_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {
 369 
 370   // append is different depending on entry tag type
 371   switch (scratch_cp->tag_at(scratch_i).value()) {
 372 
 373     // The old verifier is implemented outside the VM. It loads classes,
 374     // but does not resolve constant pool entries directly so we never
 375     // see Class entries here with the old verifier. Similarly the old
 376     // verifier does not like Class entries in the input constant pool.
 377     // The split-verifier is implemented in the VM so it can optionally
 378     // and directly resolve constant pool entries to load classes. The
 379     // split-verifier can accept either Class entries or UnresolvedClass
 380     // entries in the input constant pool. We revert the appended copy
 381     // back to UnresolvedClass so that either verifier will be happy
 382     // with the constant pool entry.
 383     //
 384     // this is an indirect CP entry so it needs special handling
 385     case JVM_CONSTANT_Class:
 386     case JVM_CONSTANT_UnresolvedClass:
 387     {
 388       int name_i = scratch_cp->klass_name_index_at(scratch_i);
 389       int new_name_i = find_or_append_indirect_entry(scratch_cp, name_i, merge_cp_p,
 390                                                      merge_cp_length_p);
 391 
 392       if (new_name_i != name_i) {
 393         log_trace(redefine, class, constantpool)
 394           ("Class entry@%d name_index change: %d to %d",
 395            *merge_cp_length_p, name_i, new_name_i);
 396       }
 397 
 398       (*merge_cp_p)->temp_unresolved_klass_at_put(*merge_cp_length_p, new_name_i);
 399       if (scratch_i != *merge_cp_length_p) {
 400         // The new entry in *merge_cp_p is at a different index than
 401         // the new entry in scratch_cp so we need to map the index values.
 402         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 403       }
 404       (*merge_cp_length_p)++;
 405     } break;
 406 
 407     // these are direct CP entries so they can be directly appended,
 408     // but double and long take two constant pool entries
 409     case JVM_CONSTANT_Double:  // fall through
 410     case JVM_CONSTANT_Long:
 411     {
 412       ConstantPool::copy_entry_to(scratch_cp, scratch_i, *merge_cp_p, *merge_cp_length_p);
 413 
 414       if (scratch_i != *merge_cp_length_p) {
 415         // The new entry in *merge_cp_p is at a different index than
 416         // the new entry in scratch_cp so we need to map the index values.
 417         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 418       }
 419       (*merge_cp_length_p) += 2;
 420     } break;
 421 
 422     // these are direct CP entries so they can be directly appended
 423     case JVM_CONSTANT_Float:   // fall through
 424     case JVM_CONSTANT_Integer: // fall through
 425     case JVM_CONSTANT_Utf8:    // fall through
 426 
 427     // This was an indirect CP entry, but it has been changed into
 428     // Symbol*s so this entry can be directly appended.
 429     case JVM_CONSTANT_String:      // fall through
 430     {
 431       ConstantPool::copy_entry_to(scratch_cp, scratch_i, *merge_cp_p, *merge_cp_length_p);
 432 
 433       if (scratch_i != *merge_cp_length_p) {
 434         // The new entry in *merge_cp_p is at a different index than
 435         // the new entry in scratch_cp so we need to map the index values.
 436         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 437       }
 438       (*merge_cp_length_p)++;
 439     } break;
 440 
 441     // this is an indirect CP entry so it needs special handling
 442     case JVM_CONSTANT_NameAndType:
 443     {
 444       int name_ref_i = scratch_cp->name_ref_index_at(scratch_i);
 445       int new_name_ref_i = find_or_append_indirect_entry(scratch_cp, name_ref_i, merge_cp_p,
 446                                                          merge_cp_length_p);
 447 
 448       int signature_ref_i = scratch_cp->signature_ref_index_at(scratch_i);
 449       int new_signature_ref_i = find_or_append_indirect_entry(scratch_cp, signature_ref_i,
 450                                                               merge_cp_p, merge_cp_length_p);
 451 
 452       // If the referenced entries already exist in *merge_cp_p, then
 453       // both new_name_ref_i and new_signature_ref_i will both be 0.
 454       // In that case, all we are appending is the current entry.
 455       if (new_name_ref_i != name_ref_i) {
 456         log_trace(redefine, class, constantpool)
 457           ("NameAndType entry@%d name_ref_index change: %d to %d",
 458            *merge_cp_length_p, name_ref_i, new_name_ref_i);
 459       }
 460       if (new_signature_ref_i != signature_ref_i) {
 461         log_trace(redefine, class, constantpool)
 462           ("NameAndType entry@%d signature_ref_index change: %d to %d",
 463            *merge_cp_length_p, signature_ref_i, new_signature_ref_i);
 464       }
 465 
 466       (*merge_cp_p)->name_and_type_at_put(*merge_cp_length_p,
 467         new_name_ref_i, new_signature_ref_i);
 468       if (scratch_i != *merge_cp_length_p) {
 469         // The new entry in *merge_cp_p is at a different index than
 470         // the new entry in scratch_cp so we need to map the index values.
 471         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 472       }
 473       (*merge_cp_length_p)++;
 474     } break;
 475 
 476     // this is a double-indirect CP entry so it needs special handling
 477     case JVM_CONSTANT_Fieldref:           // fall through
 478     case JVM_CONSTANT_InterfaceMethodref: // fall through
 479     case JVM_CONSTANT_Methodref:
 480     {
 481       int klass_ref_i = scratch_cp->uncached_klass_ref_index_at(scratch_i);
 482       int new_klass_ref_i = find_or_append_indirect_entry(scratch_cp, klass_ref_i,
 483                                                           merge_cp_p, merge_cp_length_p);
 484 
 485       int name_and_type_ref_i = scratch_cp->uncached_name_and_type_ref_index_at(scratch_i);
 486       int new_name_and_type_ref_i = find_or_append_indirect_entry(scratch_cp, name_and_type_ref_i,
 487                                                           merge_cp_p, merge_cp_length_p);
 488 
 489       const char *entry_name = nullptr;
 490       switch (scratch_cp->tag_at(scratch_i).value()) {
 491       case JVM_CONSTANT_Fieldref:
 492         entry_name = "Fieldref";
 493         (*merge_cp_p)->field_at_put(*merge_cp_length_p, new_klass_ref_i,
 494           new_name_and_type_ref_i);
 495         break;
 496       case JVM_CONSTANT_InterfaceMethodref:
 497         entry_name = "IFMethodref";
 498         (*merge_cp_p)->interface_method_at_put(*merge_cp_length_p,
 499           new_klass_ref_i, new_name_and_type_ref_i);
 500         break;
 501       case JVM_CONSTANT_Methodref:
 502         entry_name = "Methodref";
 503         (*merge_cp_p)->method_at_put(*merge_cp_length_p, new_klass_ref_i,
 504           new_name_and_type_ref_i);
 505         break;
 506       default:
 507         guarantee(false, "bad switch");
 508         break;
 509       }
 510 
 511       if (klass_ref_i != new_klass_ref_i) {
 512         log_trace(redefine, class, constantpool)
 513           ("%s entry@%d class_index changed: %d to %d", entry_name, *merge_cp_length_p, klass_ref_i, new_klass_ref_i);
 514       }
 515       if (name_and_type_ref_i != new_name_and_type_ref_i) {
 516         log_trace(redefine, class, constantpool)
 517           ("%s entry@%d name_and_type_index changed: %d to %d",
 518            entry_name, *merge_cp_length_p, name_and_type_ref_i, new_name_and_type_ref_i);
 519       }
 520 
 521       if (scratch_i != *merge_cp_length_p) {
 522         // The new entry in *merge_cp_p is at a different index than
 523         // the new entry in scratch_cp so we need to map the index values.
 524         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 525       }
 526       (*merge_cp_length_p)++;
 527     } break;
 528 
 529     // this is an indirect CP entry so it needs special handling
 530     case JVM_CONSTANT_MethodType:
 531     {
 532       int ref_i = scratch_cp->method_type_index_at(scratch_i);
 533       int new_ref_i = find_or_append_indirect_entry(scratch_cp, ref_i, merge_cp_p,
 534                                                     merge_cp_length_p);
 535       if (new_ref_i != ref_i) {
 536         log_trace(redefine, class, constantpool)
 537           ("MethodType entry@%d ref_index change: %d to %d", *merge_cp_length_p, ref_i, new_ref_i);
 538       }
 539       (*merge_cp_p)->method_type_index_at_put(*merge_cp_length_p, new_ref_i);
 540       if (scratch_i != *merge_cp_length_p) {
 541         // The new entry in *merge_cp_p is at a different index than
 542         // the new entry in scratch_cp so we need to map the index values.
 543         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 544       }
 545       (*merge_cp_length_p)++;
 546     } break;
 547 
 548     // this is an indirect CP entry so it needs special handling
 549     case JVM_CONSTANT_MethodHandle:
 550     {
 551       int ref_kind = scratch_cp->method_handle_ref_kind_at(scratch_i);
 552       int ref_i = scratch_cp->method_handle_index_at(scratch_i);
 553       int new_ref_i = find_or_append_indirect_entry(scratch_cp, ref_i, merge_cp_p,
 554                                                     merge_cp_length_p);
 555       if (new_ref_i != ref_i) {
 556         log_trace(redefine, class, constantpool)
 557           ("MethodHandle entry@%d ref_index change: %d to %d", *merge_cp_length_p, ref_i, new_ref_i);
 558       }
 559       (*merge_cp_p)->method_handle_index_at_put(*merge_cp_length_p, ref_kind, new_ref_i);
 560       if (scratch_i != *merge_cp_length_p) {
 561         // The new entry in *merge_cp_p is at a different index than
 562         // the new entry in scratch_cp so we need to map the index values.
 563         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 564       }
 565       (*merge_cp_length_p)++;
 566     } break;
 567 
 568     // this is an indirect CP entry so it needs special handling
 569     case JVM_CONSTANT_Dynamic:  // fall through
 570     case JVM_CONSTANT_InvokeDynamic:
 571     {
 572       // Index of the bootstrap specifier in the operands array
 573       int old_bs_i = scratch_cp->bootstrap_methods_attribute_index(scratch_i);
 574       int new_bs_i = find_or_append_operand(scratch_cp, old_bs_i, merge_cp_p,
 575                                             merge_cp_length_p);
 576       // The bootstrap method NameAndType_info index
 577       int old_ref_i = scratch_cp->bootstrap_name_and_type_ref_index_at(scratch_i);
 578       int new_ref_i = find_or_append_indirect_entry(scratch_cp, old_ref_i, merge_cp_p,
 579                                                     merge_cp_length_p);
 580       if (new_bs_i != old_bs_i) {
 581         log_trace(redefine, class, constantpool)
 582           ("Dynamic entry@%d bootstrap_method_attr_index change: %d to %d",
 583            *merge_cp_length_p, old_bs_i, new_bs_i);
 584       }
 585       if (new_ref_i != old_ref_i) {
 586         log_trace(redefine, class, constantpool)
 587           ("Dynamic entry@%d name_and_type_index change: %d to %d", *merge_cp_length_p, old_ref_i, new_ref_i);
 588       }
 589 
 590       if (scratch_cp->tag_at(scratch_i).is_dynamic_constant())
 591         (*merge_cp_p)->dynamic_constant_at_put(*merge_cp_length_p, new_bs_i, new_ref_i);
 592       else
 593         (*merge_cp_p)->invoke_dynamic_at_put(*merge_cp_length_p, new_bs_i, new_ref_i);
 594       if (scratch_i != *merge_cp_length_p) {
 595         // The new entry in *merge_cp_p is at a different index than
 596         // the new entry in scratch_cp so we need to map the index values.
 597         map_index(scratch_cp, scratch_i, *merge_cp_length_p);
 598       }
 599       (*merge_cp_length_p)++;
 600     } break;
 601 
 602     // At this stage, Class or UnresolvedClass could be in scratch_cp, but not
 603     // ClassIndex
 604     case JVM_CONSTANT_ClassIndex: // fall through
 605 
 606     // Invalid is used as the tag for the second constant pool entry
 607     // occupied by JVM_CONSTANT_Double or JVM_CONSTANT_Long. It should
 608     // not be seen by itself.
 609     case JVM_CONSTANT_Invalid: // fall through
 610 
 611     // At this stage, String could be here, but not StringIndex
 612     case JVM_CONSTANT_StringIndex: // fall through
 613 
 614     // At this stage JVM_CONSTANT_UnresolvedClassInError should not be
 615     // here
 616     case JVM_CONSTANT_UnresolvedClassInError: // fall through
 617 
 618     default:
 619     {
 620       // leave a breadcrumb
 621       jbyte bad_value = scratch_cp->tag_at(scratch_i).value();
 622       ShouldNotReachHere();
 623     } break;
 624   } // end switch tag value
 625 } // end append_entry()
 626 
 627 
 628 u2 VM_RedefineClasses::find_or_append_indirect_entry(const constantPoolHandle& scratch_cp,
 629       int ref_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {
 630 
 631   int new_ref_i = ref_i;
 632   bool match = (ref_i < *merge_cp_length_p) &&
 633                scratch_cp->compare_entry_to(ref_i, *merge_cp_p, ref_i);
 634 
 635   if (!match) {
 636     // forward reference in *merge_cp_p or not a direct match
 637     int found_i = scratch_cp->find_matching_entry(ref_i, *merge_cp_p);
 638     if (found_i != 0) {
 639       guarantee(found_i != ref_i, "compare_entry_to() and find_matching_entry() do not agree");
 640       // Found a matching entry somewhere else in *merge_cp_p so just need a mapping entry.
 641       new_ref_i = found_i;
 642       map_index(scratch_cp, ref_i, found_i);
 643     } else {
 644       // no match found so we have to append this entry to *merge_cp_p
 645       append_entry(scratch_cp, ref_i, merge_cp_p, merge_cp_length_p);
 646       // The above call to append_entry() can only append one entry
 647       // so the post call query of *merge_cp_length_p is only for
 648       // the sake of consistency.
 649       new_ref_i = *merge_cp_length_p - 1;
 650     }
 651   }
 652 
 653   // constant pool indices are u2, unless the merged constant pool overflows which
 654   // we don't check for.
 655   return checked_cast<u2>(new_ref_i);
 656 } // end find_or_append_indirect_entry()
 657 
 658 
 659 // Append a bootstrap specifier into the merge_cp operands that is semantically equal
 660 // to the scratch_cp operands bootstrap specifier passed by the old_bs_i index.
 661 // Recursively append new merge_cp entries referenced by the new bootstrap specifier.
 662 void VM_RedefineClasses::append_operand(const constantPoolHandle& scratch_cp, int old_bs_i,
 663        constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {
 664 
 665   u2 old_ref_i = scratch_cp->operand_bootstrap_method_ref_index_at(old_bs_i);
 666   u2 new_ref_i = find_or_append_indirect_entry(scratch_cp, old_ref_i, merge_cp_p,
 667                                                merge_cp_length_p);
 668   if (new_ref_i != old_ref_i) {
 669     log_trace(redefine, class, constantpool)
 670       ("operands entry@%d bootstrap method ref_index change: %d to %d", _operands_cur_length, old_ref_i, new_ref_i);
 671   }
 672 
 673   Array<u2>* merge_ops = (*merge_cp_p)->operands();
 674   int new_bs_i = _operands_cur_length;
 675   // We have _operands_cur_length == 0 when the merge_cp operands is empty yet.
 676   // However, the operand_offset_at(0) was set in the extend_operands() call.
 677   int new_base = (new_bs_i == 0) ? (*merge_cp_p)->operand_offset_at(0)
 678                                  : (*merge_cp_p)->operand_next_offset_at(new_bs_i - 1);
 679   u2 argc      = scratch_cp->operand_argument_count_at(old_bs_i);
 680 
 681   ConstantPool::operand_offset_at_put(merge_ops, _operands_cur_length, new_base);
 682   merge_ops->at_put(new_base++, new_ref_i);
 683   merge_ops->at_put(new_base++, argc);
 684 
 685   for (int i = 0; i < argc; i++) {
 686     u2 old_arg_ref_i = scratch_cp->operand_argument_index_at(old_bs_i, i);
 687     u2 new_arg_ref_i = find_or_append_indirect_entry(scratch_cp, old_arg_ref_i, merge_cp_p,
 688                                                      merge_cp_length_p);
 689     merge_ops->at_put(new_base++, new_arg_ref_i);
 690     if (new_arg_ref_i != old_arg_ref_i) {
 691       log_trace(redefine, class, constantpool)
 692         ("operands entry@%d bootstrap method argument ref_index change: %d to %d",
 693          _operands_cur_length, old_arg_ref_i, new_arg_ref_i);
 694     }
 695   }
 696   if (old_bs_i != _operands_cur_length) {
 697     // The bootstrap specifier in *merge_cp_p is at a different index than
 698     // that in scratch_cp so we need to map the index values.
 699     map_operand_index(old_bs_i, new_bs_i);
 700   }
 701   _operands_cur_length++;
 702 } // end append_operand()
 703 
 704 
 705 int VM_RedefineClasses::find_or_append_operand(const constantPoolHandle& scratch_cp,
 706       int old_bs_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {
 707 
 708   int new_bs_i = old_bs_i; // bootstrap specifier index
 709   bool match = (old_bs_i < _operands_cur_length) &&
 710                scratch_cp->compare_operand_to(old_bs_i, *merge_cp_p, old_bs_i);
 711 
 712   if (!match) {
 713     // forward reference in *merge_cp_p or not a direct match
 714     int found_i = scratch_cp->find_matching_operand(old_bs_i, *merge_cp_p,
 715                                                     _operands_cur_length);
 716     if (found_i != -1) {
 717       guarantee(found_i != old_bs_i, "compare_operand_to() and find_matching_operand() disagree");
 718       // found a matching operand somewhere else in *merge_cp_p so just need a mapping
 719       new_bs_i = found_i;
 720       map_operand_index(old_bs_i, found_i);
 721     } else {
 722       // no match found so we have to append this bootstrap specifier to *merge_cp_p
 723       append_operand(scratch_cp, old_bs_i, merge_cp_p, merge_cp_length_p);
 724       new_bs_i = _operands_cur_length - 1;
 725     }
 726   }
 727   return new_bs_i;
 728 } // end find_or_append_operand()
 729 
 730 
 731 void VM_RedefineClasses::finalize_operands_merge(const constantPoolHandle& merge_cp, TRAPS) {
 732   if (merge_cp->operands() == nullptr) {
 733     return;
 734   }
 735   // Shrink the merge_cp operands
 736   merge_cp->shrink_operands(_operands_cur_length, CHECK);
 737 
 738   if (log_is_enabled(Trace, redefine, class, constantpool)) {
 739     // don't want to loop unless we are tracing
 740     int count = 0;
 741     for (int i = 1; i < _operands_index_map_p->length(); i++) {
 742       int value = _operands_index_map_p->at(i);
 743       if (value != -1) {
 744         log_trace(redefine, class, constantpool)("operands_index_map[%d]: old=%d new=%d", count, i, value);
 745         count++;
 746       }
 747     }
 748   }
 749   // Clean-up
 750   _operands_index_map_p = nullptr;
 751   _operands_cur_length = 0;
 752   _operands_index_map_count = 0;
 753 } // end finalize_operands_merge()
 754 
 755 // Symbol* comparator for qsort
 756 // The caller must have an active ResourceMark.
 757 static int symcmp(const void* a, const void* b) {
 758   char* astr = (*(Symbol**)a)->as_C_string();
 759   char* bstr = (*(Symbol**)b)->as_C_string();
 760   return strcmp(astr, bstr);
 761 }
 762 
 763 // The caller must have an active ResourceMark.
 764 static jvmtiError check_attribute_arrays(const char* attr_name,
 765            InstanceKlass* the_class, InstanceKlass* scratch_class,
 766            Array<u2>* the_array, Array<u2>* scr_array) {
 767   bool the_array_exists = the_array != Universe::the_empty_short_array();
 768   bool scr_array_exists = scr_array != Universe::the_empty_short_array();
 769 
 770   int array_len = the_array->length();
 771   if (the_array_exists && scr_array_exists) {
 772     if (array_len != scr_array->length()) {
 773       log_trace(redefine, class)
 774         ("redefined class %s attribute change error: %s len=%d changed to len=%d",
 775          the_class->external_name(), attr_name, array_len, scr_array->length());
 776       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 777     }
 778 
 779     // The order of entries in the attribute array is not specified so we
 780     // have to explicitly check for the same contents. We do this by copying
 781     // the referenced symbols into their own arrays, sorting them and then
 782     // comparing each element pair.
 783 
 784     Symbol** the_syms = NEW_RESOURCE_ARRAY_RETURN_NULL(Symbol*, array_len);
 785     Symbol** scr_syms = NEW_RESOURCE_ARRAY_RETURN_NULL(Symbol*, array_len);
 786 
 787     if (the_syms == nullptr || scr_syms == nullptr) {
 788       return JVMTI_ERROR_OUT_OF_MEMORY;
 789     }
 790 
 791     for (int i = 0; i < array_len; i++) {
 792       int the_cp_index = the_array->at(i);
 793       int scr_cp_index = scr_array->at(i);
 794       the_syms[i] = the_class->constants()->klass_name_at(the_cp_index);
 795       scr_syms[i] = scratch_class->constants()->klass_name_at(scr_cp_index);
 796     }
 797 
 798     qsort(the_syms, array_len, sizeof(Symbol*), symcmp);
 799     qsort(scr_syms, array_len, sizeof(Symbol*), symcmp);
 800 
 801     for (int i = 0; i < array_len; i++) {
 802       if (the_syms[i] != scr_syms[i]) {
 803         log_info(redefine, class)
 804           ("redefined class %s attribute change error: %s[%d]: %s changed to %s",
 805            the_class->external_name(), attr_name, i,
 806            the_syms[i]->as_C_string(), scr_syms[i]->as_C_string());
 807         return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 808       }
 809     }
 810   } else if (the_array_exists ^ scr_array_exists) {
 811     const char* action_str = (the_array_exists) ? "removed" : "added";
 812     log_info(redefine, class)
 813       ("redefined class %s attribute change error: %s attribute %s",
 814        the_class->external_name(), attr_name, action_str);
 815     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 816   }
 817   return JVMTI_ERROR_NONE;
 818 }
 819 
 820 static jvmtiError check_nest_attributes(InstanceKlass* the_class,
 821                                         InstanceKlass* scratch_class) {
 822   // Check whether the class NestHost attribute has been changed.
 823   Thread* thread = Thread::current();
 824   ResourceMark rm(thread);
 825   u2 the_nest_host_idx = the_class->nest_host_index();
 826   u2 scr_nest_host_idx = scratch_class->nest_host_index();
 827 
 828   if (the_nest_host_idx != 0 && scr_nest_host_idx != 0) {
 829     Symbol* the_sym = the_class->constants()->klass_name_at(the_nest_host_idx);
 830     Symbol* scr_sym = scratch_class->constants()->klass_name_at(scr_nest_host_idx);
 831     if (the_sym != scr_sym) {
 832       log_info(redefine, class, nestmates)
 833         ("redefined class %s attribute change error: NestHost class: %s replaced with: %s",
 834          the_class->external_name(), the_sym->as_C_string(), scr_sym->as_C_string());
 835       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 836     }
 837   } else if ((the_nest_host_idx == 0) ^ (scr_nest_host_idx == 0)) {
 838     const char* action_str = (the_nest_host_idx != 0) ? "removed" : "added";
 839     log_info(redefine, class, nestmates)
 840       ("redefined class %s attribute change error: NestHost attribute %s",
 841        the_class->external_name(), action_str);
 842     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 843   }
 844 
 845   // Check whether the class NestMembers attribute has been changed.
 846   return check_attribute_arrays("NestMembers",
 847                                 the_class, scratch_class,
 848                                 the_class->nest_members(),
 849                                 scratch_class->nest_members());
 850 }
 851 
 852 // Return an error status if the class Record attribute was changed.
 853 static jvmtiError check_record_attribute(InstanceKlass* the_class, InstanceKlass* scratch_class) {
 854   // Get lists of record components.
 855   Array<RecordComponent*>* the_record = the_class->record_components();
 856   Array<RecordComponent*>* scr_record = scratch_class->record_components();
 857   bool the_record_exists = the_record != nullptr;
 858   bool scr_record_exists = scr_record != nullptr;
 859 
 860   if (the_record_exists && scr_record_exists) {
 861     int the_num_components = the_record->length();
 862     int scr_num_components = scr_record->length();
 863     if (the_num_components != scr_num_components) {
 864       log_info(redefine, class, record)
 865         ("redefined class %s attribute change error: Record num_components=%d changed to num_components=%d",
 866          the_class->external_name(), the_num_components, scr_num_components);
 867       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 868     }
 869 
 870     // Compare each field in each record component.
 871     ConstantPool* the_cp =  the_class->constants();
 872     ConstantPool* scr_cp =  scratch_class->constants();
 873     for (int x = 0; x < the_num_components; x++) {
 874       RecordComponent* the_component = the_record->at(x);
 875       RecordComponent* scr_component = scr_record->at(x);
 876       const Symbol* const the_name = the_cp->symbol_at(the_component->name_index());
 877       const Symbol* const scr_name = scr_cp->symbol_at(scr_component->name_index());
 878       const Symbol* const the_descr = the_cp->symbol_at(the_component->descriptor_index());
 879       const Symbol* const scr_descr = scr_cp->symbol_at(scr_component->descriptor_index());
 880       if (the_name != scr_name || the_descr != scr_descr) {
 881         log_info(redefine, class, record)
 882           ("redefined class %s attribute change error: Record name_index, descriptor_index, and/or attributes_count changed",
 883            the_class->external_name());
 884         return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 885       }
 886 
 887       int the_gen_sig = the_component->generic_signature_index();
 888       int scr_gen_sig = scr_component->generic_signature_index();
 889       const Symbol* const the_gen_sig_sym = (the_gen_sig == 0 ? nullptr :
 890         the_cp->symbol_at(the_component->generic_signature_index()));
 891       const Symbol* const scr_gen_sig_sym = (scr_gen_sig == 0 ? nullptr :
 892         scr_cp->symbol_at(scr_component->generic_signature_index()));
 893       if (the_gen_sig_sym != scr_gen_sig_sym) {
 894         log_info(redefine, class, record)
 895           ("redefined class %s attribute change error: Record generic_signature attribute changed",
 896            the_class->external_name());
 897         return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 898       }
 899 
 900       // It's okay if a record component's annotations were changed.
 901     }
 902 
 903   } else if (the_record_exists ^ scr_record_exists) {
 904     const char* action_str = (the_record_exists) ? "removed" : "added";
 905     log_info(redefine, class, record)
 906       ("redefined class %s attribute change error: Record attribute %s",
 907        the_class->external_name(), action_str);
 908     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
 909   }
 910 
 911   return JVMTI_ERROR_NONE;
 912 }
 913 
 914 
 915 static jvmtiError check_permitted_subclasses_attribute(InstanceKlass* the_class,
 916                                                        InstanceKlass* scratch_class) {
 917   Thread* thread = Thread::current();
 918   ResourceMark rm(thread);
 919 
 920   // Check whether the class PermittedSubclasses attribute has been changed.
 921   return check_attribute_arrays("PermittedSubclasses",
 922                                 the_class, scratch_class,
 923                                 the_class->permitted_subclasses(),
 924                                 scratch_class->permitted_subclasses());
 925 }
 926 
 927 static bool can_add_or_delete(Method* m) {
 928       // Compatibility mode
 929   return (AllowRedefinitionToAddDeleteMethods &&
 930           (m->is_private() && (m->is_static() || m->is_final())));
 931 }
 932 
 933 jvmtiError VM_RedefineClasses::compare_and_normalize_class_versions(
 934              InstanceKlass* the_class,
 935              InstanceKlass* scratch_class) {
 936   int i;
 937 
 938   // Check superclasses, or rather their names, since superclasses themselves can be
 939   // requested to replace.
 940   // Check for null superclass first since this might be java.lang.Object
 941   if (the_class->super() != scratch_class->super() &&
 942       (the_class->super() == nullptr || scratch_class->super() == nullptr ||
 943        the_class->super()->name() !=
 944        scratch_class->super()->name())) {
 945     log_info(redefine, class, normalize)
 946       ("redefined class %s superclass change error: superclass changed from %s to %s.",
 947        the_class->external_name(),
 948        the_class->super() == nullptr ? "null" : the_class->super()->external_name(),
 949        scratch_class->super() == nullptr ? "null" : scratch_class->super()->external_name());
 950     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
 951   }
 952 
 953   // Check if the number, names and order of directly implemented interfaces are the same.
 954   // I think in principle we should just check if the sets of names of directly implemented
 955   // interfaces are the same, i.e. the order of declaration (which, however, if changed in the
 956   // .java file, also changes in .class file) should not matter. However, comparing sets is
 957   // technically a bit more difficult, and, more importantly, I am not sure at present that the
 958   // order of interfaces does not matter on the implementation level, i.e. that the VM does not
 959   // rely on it somewhere.
 960   Array<InstanceKlass*>* k_interfaces = the_class->local_interfaces();
 961   Array<InstanceKlass*>* k_new_interfaces = scratch_class->local_interfaces();
 962   int n_intfs = k_interfaces->length();
 963   if (n_intfs != k_new_interfaces->length()) {
 964     log_info(redefine, class, normalize)
 965       ("redefined class %s interfaces change error: number of implemented interfaces changed from %d to %d.",
 966        the_class->external_name(), n_intfs, k_new_interfaces->length());
 967     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
 968   }
 969   for (i = 0; i < n_intfs; i++) {
 970     if (k_interfaces->at(i)->name() !=
 971         k_new_interfaces->at(i)->name()) {
 972       log_info(redefine, class, normalize)
 973           ("redefined class %s interfaces change error: interface changed from %s to %s.",
 974            the_class->external_name(),
 975            k_interfaces->at(i)->external_name(), k_new_interfaces->at(i)->external_name());
 976       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
 977     }
 978   }
 979 
 980   // Check whether class is in the error init state.
 981   if (the_class->is_in_error_state()) {
 982     log_info(redefine, class, normalize)
 983       ("redefined class %s is in error init state.", the_class->external_name());
 984     // TBD #5057930: special error code is needed in 1.6
 985     return JVMTI_ERROR_INVALID_CLASS;
 986   }
 987 
 988   // Check whether the nest-related attributes have been changed.
 989   jvmtiError err = check_nest_attributes(the_class, scratch_class);
 990   if (err != JVMTI_ERROR_NONE) {
 991     return err;
 992   }
 993 
 994   // Check whether the Record attribute has been changed.
 995   err = check_record_attribute(the_class, scratch_class);
 996   if (err != JVMTI_ERROR_NONE) {
 997     return err;
 998   }
 999 
1000   // Check whether the PermittedSubclasses attribute has been changed.
1001   err = check_permitted_subclasses_attribute(the_class, scratch_class);
1002   if (err != JVMTI_ERROR_NONE) {
1003     return err;
1004   }
1005 
1006   // Check whether class modifiers are the same.
1007   u2 old_flags = the_class->access_flags().as_class_flags();
1008   u2 new_flags = scratch_class->access_flags().as_class_flags();
1009   if (old_flags != new_flags) {
1010     log_info(redefine, class, normalize)
1011         ("redefined class %s modifiers change error: modifiers changed from %d to %d.",
1012          the_class->external_name(), old_flags, new_flags);
1013     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_MODIFIERS_CHANGED;
1014   }
1015 
1016   // Check if the number, names, types and order of fields declared in these classes
1017   // are the same.
1018   JavaFieldStream old_fs(the_class);
1019   JavaFieldStream new_fs(scratch_class);
1020   for (; !old_fs.done() && !new_fs.done(); old_fs.next(), new_fs.next()) {
1021     // name and signature
1022     Symbol* name_sym1 = the_class->constants()->symbol_at(old_fs.name_index());
1023     Symbol* sig_sym1 = the_class->constants()->symbol_at(old_fs.signature_index());
1024     Symbol* name_sym2 = scratch_class->constants()->symbol_at(new_fs.name_index());
1025     Symbol* sig_sym2 = scratch_class->constants()->symbol_at(new_fs.signature_index());
1026     if (name_sym1 != name_sym2 || sig_sym1 != sig_sym2) {
1027       log_info(redefine, class, normalize)
1028           ("redefined class %s fields change error: field %s %s changed to %s %s.",
1029            the_class->external_name(),
1030            sig_sym1->as_C_string(), name_sym1->as_C_string(),
1031            sig_sym2->as_C_string(), name_sym2->as_C_string());
1032       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
1033     }
1034     // offset
1035     if (old_fs.offset() != new_fs.offset()) {
1036       log_info(redefine, class, normalize)
1037           ("redefined class %s field %s change error: offset changed from %d to %d.",
1038            the_class->external_name(), name_sym2->as_C_string(), old_fs.offset(), new_fs.offset());
1039       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
1040     }
1041     // access
1042     old_flags = old_fs.access_flags().as_field_flags();
1043     new_flags = new_fs.access_flags().as_field_flags();
1044     if (old_flags != new_flags) {
1045       log_info(redefine, class, normalize)
1046           ("redefined class %s field %s change error: modifiers changed from %d to %d.",
1047            the_class->external_name(), name_sym2->as_C_string(), old_flags, new_flags);
1048       return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
1049     }
1050   }
1051 
1052   // If both streams aren't done then we have a differing number of
1053   // fields.
1054   if (!old_fs.done() || !new_fs.done()) {
1055     const char* action = old_fs.done() ? "added" : "deleted";
1056     log_info(redefine, class, normalize)
1057         ("redefined class %s fields change error: some fields were %s.",
1058          the_class->external_name(), action);
1059     return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
1060   }
1061 
1062   // Do a parallel walk through the old and new methods. Detect
1063   // cases where they match (exist in both), have been added in
1064   // the new methods, or have been deleted (exist only in the
1065   // old methods).  The class file parser places methods in order
1066   // by method name, but does not order overloaded methods by
1067   // signature.  In order to determine what fate befell the methods,
1068   // this code places the overloaded new methods that have matching
1069   // old methods in the same order as the old methods and places
1070   // new overloaded methods at the end of overloaded methods of
1071   // that name. The code for this order normalization is adapted
1072   // from the algorithm used in InstanceKlass::find_method().
1073   // Since we are swapping out of order entries as we find them,
1074   // we only have to search forward through the overloaded methods.
1075   // Methods which are added and have the same name as an existing
1076   // method (but different signature) will be put at the end of
1077   // the methods with that name, and the name mismatch code will
1078   // handle them.
1079   Array<Method*>* k_old_methods(the_class->methods());
1080   Array<Method*>* k_new_methods(scratch_class->methods());
1081   int n_old_methods = k_old_methods->length();
1082   int n_new_methods = k_new_methods->length();
1083   Thread* thread = Thread::current();
1084 
1085   int ni = 0;
1086   int oi = 0;
1087   while (true) {
1088     Method* k_old_method;
1089     Method* k_new_method;
1090     enum { matched, added, deleted, undetermined } method_was = undetermined;
1091 
1092     if (oi >= n_old_methods) {
1093       if (ni >= n_new_methods) {
1094         break; // we've looked at everything, done
1095       }
1096       // New method at the end
1097       k_new_method = k_new_methods->at(ni);
1098       method_was = added;
1099     } else if (ni >= n_new_methods) {
1100       // Old method, at the end, is deleted
1101       k_old_method = k_old_methods->at(oi);
1102       method_was = deleted;
1103     } else {
1104       // There are more methods in both the old and new lists
1105       k_old_method = k_old_methods->at(oi);
1106       k_new_method = k_new_methods->at(ni);
1107       if (k_old_method->name() != k_new_method->name()) {
1108         // Methods are sorted by method name, so a mismatch means added
1109         // or deleted
1110         if (k_old_method->name()->fast_compare(k_new_method->name()) > 0) {
1111           method_was = added;
1112         } else {
1113           method_was = deleted;
1114         }
1115       } else if (k_old_method->signature() == k_new_method->signature()) {
1116         // Both the name and signature match
1117         method_was = matched;
1118       } else {
1119         // The name matches, but the signature doesn't, which means we have to
1120         // search forward through the new overloaded methods.
1121         int nj;  // outside the loop for post-loop check
1122         for (nj = ni + 1; nj < n_new_methods; nj++) {
1123           Method* m = k_new_methods->at(nj);
1124           if (k_old_method->name() != m->name()) {
1125             // reached another method name so no more overloaded methods
1126             method_was = deleted;
1127             break;
1128           }
1129           if (k_old_method->signature() == m->signature()) {
1130             // found a match so swap the methods
1131             k_new_methods->at_put(ni, m);
1132             k_new_methods->at_put(nj, k_new_method);
1133             k_new_method = m;
1134             method_was = matched;
1135             break;
1136           }
1137         }
1138 
1139         if (nj >= n_new_methods) {
1140           // reached the end without a match; so method was deleted
1141           method_was = deleted;
1142         }
1143       }
1144     }
1145 
1146     switch (method_was) {
1147     case matched:
1148       // methods match, be sure modifiers do too
1149       old_flags = k_old_method->access_flags().as_method_flags();
1150       new_flags = k_new_method->access_flags().as_method_flags();
1151       if ((old_flags ^ new_flags) & ~(JVM_ACC_NATIVE)) {
1152         log_info(redefine, class, normalize)
1153           ("redefined class %s  method %s modifiers error: modifiers changed from %d to %d",
1154            the_class->external_name(), k_old_method->name_and_sig_as_C_string(), old_flags, new_flags);
1155         return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_MODIFIERS_CHANGED;
1156       }
1157       {
1158         u2 new_num = k_new_method->method_idnum();
1159         u2 old_num = k_old_method->method_idnum();
1160         if (new_num != old_num) {
1161           Method* idnum_owner = scratch_class->method_with_idnum(old_num);
1162           if (idnum_owner != nullptr) {
1163             // There is already a method assigned this idnum -- switch them
1164             // Take current and original idnum from the new_method
1165             idnum_owner->set_method_idnum(new_num);
1166             idnum_owner->set_orig_method_idnum(k_new_method->orig_method_idnum());
1167           }
1168           // Take current and original idnum from the old_method
1169           k_new_method->set_method_idnum(old_num);
1170           k_new_method->set_orig_method_idnum(k_old_method->orig_method_idnum());
1171           if (thread->has_pending_exception()) {
1172             return JVMTI_ERROR_OUT_OF_MEMORY;
1173           }
1174         }
1175       }
1176       JFR_ONLY(k_new_method->copy_trace_flags(k_old_method->trace_flags());)
1177       log_trace(redefine, class, normalize)
1178         ("Method matched: new: %s [%d] == old: %s [%d]",
1179          k_new_method->name_and_sig_as_C_string(), ni, k_old_method->name_and_sig_as_C_string(), oi);
1180       // advance to next pair of methods
1181       ++oi;
1182       ++ni;
1183       break;
1184     case added:
1185       // method added, see if it is OK
1186       if (!can_add_or_delete(k_new_method)) {
1187         log_info(redefine, class, normalize)
1188           ("redefined class %s methods error: added method: %s [%d]",
1189            the_class->external_name(), k_new_method->name_and_sig_as_C_string(), ni);
1190         return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_ADDED;
1191       }
1192       {
1193         u2 num = the_class->next_method_idnum();
1194         if (num == ConstMethod::UNSET_IDNUM) {
1195           // cannot add any more methods
1196           log_info(redefine, class, normalize)
1197             ("redefined class %s methods error: can't create ID for new method %s [%d]",
1198              the_class->external_name(), k_new_method->name_and_sig_as_C_string(), ni);
1199           return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_ADDED;
1200         }
1201         u2 new_num = k_new_method->method_idnum();
1202         Method* idnum_owner = scratch_class->method_with_idnum(num);
1203         if (idnum_owner != nullptr) {
1204           // There is already a method assigned this idnum -- switch them
1205           // Take current and original idnum from the new_method
1206           idnum_owner->set_method_idnum(new_num);
1207           idnum_owner->set_orig_method_idnum(k_new_method->orig_method_idnum());
1208         }
1209         k_new_method->set_method_idnum(num);
1210         k_new_method->set_orig_method_idnum(num);
1211         if (thread->has_pending_exception()) {
1212           return JVMTI_ERROR_OUT_OF_MEMORY;
1213         }
1214       }
1215       log_trace(redefine, class, normalize)
1216         ("Method added: new: %s [%d]", k_new_method->name_and_sig_as_C_string(), ni);
1217       ++ni; // advance to next new method
1218       break;
1219     case deleted:
1220       // method deleted, see if it is OK
1221       if (!can_add_or_delete(k_old_method)) {
1222         log_info(redefine, class, normalize)
1223           ("redefined class %s methods error: deleted method %s [%d]",
1224            the_class->external_name(), k_old_method->name_and_sig_as_C_string(), oi);
1225         return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_DELETED;
1226       }
1227       log_trace(redefine, class, normalize)
1228         ("Method deleted: old: %s [%d]", k_old_method->name_and_sig_as_C_string(), oi);
1229       ++oi; // advance to next old method
1230       break;
1231     default:
1232       ShouldNotReachHere();
1233     }
1234   }
1235 
1236   return JVMTI_ERROR_NONE;
1237 }
1238 
1239 
1240 // Find new constant pool index value for old constant pool index value
1241 // by searching the index map. Returns zero (0) if there is no mapped
1242 // value for the old constant pool index.
1243 u2 VM_RedefineClasses::find_new_index(int old_index) {
1244   if (_index_map_count == 0) {
1245     // map is empty so nothing can be found
1246     return 0;
1247   }
1248 
1249   if (old_index < 1 || old_index >= _index_map_p->length()) {
1250     // The old_index is out of range so it is not mapped. This should
1251     // not happen in regular constant pool merging use, but it can
1252     // happen if a corrupt annotation is processed.
1253     return 0;
1254   }
1255 
1256   int value = _index_map_p->at(old_index);
1257   if (value == -1) {
1258     // the old_index is not mapped
1259     return 0;
1260   }
1261 
1262   // constant pool indices are u2, unless the merged constant pool overflows which
1263   // we don't check for.
1264   return checked_cast<u2>(value);
1265 } // end find_new_index()
1266 
1267 
1268 // Find new bootstrap specifier index value for old bootstrap specifier index
1269 // value by searching the index map. Returns unused index (-1) if there is
1270 // no mapped value for the old bootstrap specifier index.
1271 int VM_RedefineClasses::find_new_operand_index(int old_index) {
1272   if (_operands_index_map_count == 0) {
1273     // map is empty so nothing can be found
1274     return -1;
1275   }
1276 
1277   if (old_index == -1 || old_index >= _operands_index_map_p->length()) {
1278     // The old_index is out of range so it is not mapped.
1279     // This should not happen in regular constant pool merging use.
1280     return -1;
1281   }
1282 
1283   int value = _operands_index_map_p->at(old_index);
1284   if (value == -1) {
1285     // the old_index is not mapped
1286     return -1;
1287   }
1288 
1289   return value;
1290 } // end find_new_operand_index()
1291 
1292 
1293 // The bug 6214132 caused the verification to fail.
1294 // 1. What's done in RedefineClasses() before verification:
1295 //  a) A reference to the class being redefined (_the_class) and a
1296 //     reference to new version of the class (_scratch_class) are
1297 //     saved here for use during the bytecode verification phase of
1298 //     RedefineClasses.
1299 //  b) The _java_mirror field from _the_class is copied to the
1300 //     _java_mirror field in _scratch_class. This means that a jclass
1301 //     returned for _the_class or _scratch_class will refer to the
1302 //     same Java mirror. The verifier will see the "one true mirror"
1303 //     for the class being verified.
1304 // 2. See comments in JvmtiThreadState for what is done during verification.
1305 
1306 class RedefineVerifyMark : public StackObj {
1307  private:
1308   JvmtiThreadState* _state;
1309   Klass*            _scratch_class;
1310   OopHandle         _scratch_mirror;
1311 
1312  public:
1313 
1314   RedefineVerifyMark(Klass* the_class, Klass* scratch_class,
1315                      JvmtiThreadState* state) : _state(state), _scratch_class(scratch_class)
1316   {
1317     _state->set_class_versions_map(the_class, scratch_class);
1318     _scratch_mirror = the_class->java_mirror_handle();  // this is a copy that is swapped
1319     _scratch_class->swap_java_mirror_handle(_scratch_mirror);
1320   }
1321 
1322   ~RedefineVerifyMark() {
1323     // Restore the scratch class's mirror, so when scratch_class is removed
1324     // the correct mirror pointing to it can be cleared.
1325     _scratch_class->swap_java_mirror_handle(_scratch_mirror);
1326     _state->clear_class_versions_map();
1327   }
1328 };
1329 
1330 
1331 jvmtiError VM_RedefineClasses::load_new_class_versions() {
1332 
1333   // For consistency allocate memory using os::malloc wrapper.
1334   _scratch_classes = (InstanceKlass**)
1335     os::malloc(sizeof(InstanceKlass*) * _class_count, mtClass);
1336   if (_scratch_classes == nullptr) {
1337     return JVMTI_ERROR_OUT_OF_MEMORY;
1338   }
1339   // Zero initialize the _scratch_classes array.
1340   for (int i = 0; i < _class_count; i++) {
1341     _scratch_classes[i] = nullptr;
1342   }
1343 
1344   JavaThread* current = JavaThread::current();
1345   ResourceMark rm(current);
1346 
1347   JvmtiThreadState *state = JvmtiThreadState::state_for(current);
1348   // state can only be null if the current thread is exiting which
1349   // should not happen since we're trying to do a RedefineClasses
1350   guarantee(state != nullptr, "exiting thread calling load_new_class_versions");
1351   for (int i = 0; i < _class_count; i++) {
1352     // Create HandleMark so that any handles created while loading new class
1353     // versions are deleted. Constant pools are deallocated while merging
1354     // constant pools
1355     HandleMark hm(current);
1356     InstanceKlass* the_class = get_ik(_class_defs[i].klass);
1357 
1358     log_debug(redefine, class, load)
1359       ("loading name=%s kind=%d (avail_mem=" UINT64_FORMAT "K)",
1360        the_class->external_name(), _class_load_kind, os::available_memory() >> 10);
1361 
1362     ClassFileStream st((u1*)_class_defs[i].class_bytes,
1363                        _class_defs[i].class_byte_count,
1364                        "__VM_RedefineClasses__");
1365 
1366     // Set redefined class handle in JvmtiThreadState class.
1367     // This redefined class is sent to agent event handler for class file
1368     // load hook event.
1369     state->set_class_being_redefined(the_class, _class_load_kind);
1370 
1371     JavaThread* THREAD = current; // For exception macros.
1372     ExceptionMark em(THREAD);
1373     Handle protection_domain(THREAD, the_class->protection_domain());
1374     ClassLoadInfo cl_info(protection_domain);
1375     // Parse and create a class from the bytes, but this class isn't added
1376     // to the dictionary, so do not call resolve_from_stream.
1377     InstanceKlass* scratch_class = KlassFactory::create_from_stream(&st,
1378                                                       the_class->name(),
1379                                                       the_class->class_loader_data(),
1380                                                       cl_info,
1381                                                       THREAD);
1382 
1383     // Clear class_being_redefined just to be sure.
1384     state->clear_class_being_redefined();
1385 
1386     // TODO: if this is retransform, and nothing changed we can skip it
1387 
1388     // Need to clean up allocated InstanceKlass if there's an error so assign
1389     // the result here. Caller deallocates all the scratch classes in case of
1390     // an error.
1391     _scratch_classes[i] = scratch_class;
1392 
1393     if (HAS_PENDING_EXCEPTION) {
1394       Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
1395       log_info(redefine, class, load, exceptions)("create_from_stream exception: '%s'", ex_name->as_C_string());
1396       CLEAR_PENDING_EXCEPTION;
1397 
1398       if (ex_name == vmSymbols::java_lang_UnsupportedClassVersionError()) {
1399         return JVMTI_ERROR_UNSUPPORTED_VERSION;
1400       } else if (ex_name == vmSymbols::java_lang_ClassFormatError()) {
1401         return JVMTI_ERROR_INVALID_CLASS_FORMAT;
1402       } else if (ex_name == vmSymbols::java_lang_ClassCircularityError()) {
1403         return JVMTI_ERROR_CIRCULAR_CLASS_DEFINITION;
1404       } else if (ex_name == vmSymbols::java_lang_NoClassDefFoundError()) {
1405         // The message will be "XXX (wrong name: YYY)"
1406         return JVMTI_ERROR_NAMES_DONT_MATCH;
1407       } else if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
1408         return JVMTI_ERROR_OUT_OF_MEMORY;
1409       } else {  // Just in case more exceptions can be thrown..
1410         return JVMTI_ERROR_FAILS_VERIFICATION;
1411       }
1412     }
1413 
1414     // Ensure class is linked before redefine
1415     if (!the_class->is_linked()) {
1416       the_class->link_class(THREAD);
1417       if (HAS_PENDING_EXCEPTION) {
1418         Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
1419         oop message = java_lang_Throwable::message(PENDING_EXCEPTION);
1420         if (message != nullptr) {
1421           char* ex_msg = java_lang_String::as_utf8_string(message);
1422           log_info(redefine, class, load, exceptions)("link_class exception: '%s %s'",
1423                    ex_name->as_C_string(), ex_msg);
1424         } else {
1425           log_info(redefine, class, load, exceptions)("link_class exception: '%s'",
1426                    ex_name->as_C_string());
1427         }
1428         CLEAR_PENDING_EXCEPTION;
1429         if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
1430           return JVMTI_ERROR_OUT_OF_MEMORY;
1431         } else if (ex_name == vmSymbols::java_lang_NoClassDefFoundError()) {
1432           return JVMTI_ERROR_INVALID_CLASS;
1433         } else {
1434           return JVMTI_ERROR_INTERNAL;
1435         }
1436       }
1437     }
1438 
1439     // Do the validity checks in compare_and_normalize_class_versions()
1440     // before verifying the byte codes. By doing these checks first, we
1441     // limit the number of functions that require redirection from
1442     // the_class to scratch_class. In particular, we don't have to
1443     // modify JNI GetSuperclass() and thus won't change its performance.
1444     jvmtiError res = compare_and_normalize_class_versions(the_class,
1445                        scratch_class);
1446     if (res != JVMTI_ERROR_NONE) {
1447       return res;
1448     }
1449 
1450     // verify what the caller passed us
1451     {
1452       // The bug 6214132 caused the verification to fail.
1453       // Information about the_class and scratch_class is temporarily
1454       // recorded into jvmtiThreadState. This data is used to redirect
1455       // the_class to scratch_class in the JVM_* functions called by the
1456       // verifier. Please, refer to jvmtiThreadState.hpp for the detailed
1457       // description.
1458       RedefineVerifyMark rvm(the_class, scratch_class, state);
1459       Verifier::verify(scratch_class, true, THREAD);
1460     }
1461 
1462     if (HAS_PENDING_EXCEPTION) {
1463       Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
1464       log_info(redefine, class, load, exceptions)("verify_byte_codes exception: '%s'", ex_name->as_C_string());
1465       CLEAR_PENDING_EXCEPTION;
1466       if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
1467         return JVMTI_ERROR_OUT_OF_MEMORY;
1468       } else {
1469         // tell the caller the bytecodes are bad
1470         return JVMTI_ERROR_FAILS_VERIFICATION;
1471       }
1472     }
1473 
1474     res = merge_cp_and_rewrite(the_class, scratch_class, THREAD);
1475     if (HAS_PENDING_EXCEPTION) {
1476       Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
1477       log_info(redefine, class, load, exceptions)("merge_cp_and_rewrite exception: '%s'", ex_name->as_C_string());
1478       CLEAR_PENDING_EXCEPTION;
1479       if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
1480         return JVMTI_ERROR_OUT_OF_MEMORY;
1481       } else {
1482         return JVMTI_ERROR_INTERNAL;
1483       }
1484     }
1485 
1486 #ifdef ASSERT
1487     {
1488       // verify what we have done during constant pool merging
1489       {
1490         RedefineVerifyMark rvm(the_class, scratch_class, state);
1491         Verifier::verify(scratch_class, true, THREAD);
1492       }
1493 
1494       if (HAS_PENDING_EXCEPTION) {
1495         Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
1496         log_info(redefine, class, load, exceptions)
1497           ("verify_byte_codes post merge-CP exception: '%s'", ex_name->as_C_string());
1498         CLEAR_PENDING_EXCEPTION;
1499         if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
1500           return JVMTI_ERROR_OUT_OF_MEMORY;
1501         } else {
1502           // tell the caller that constant pool merging screwed up
1503           return JVMTI_ERROR_INTERNAL;
1504         }
1505       }
1506     }
1507 #endif // ASSERT
1508 
1509     Rewriter::rewrite(scratch_class, THREAD);
1510     if (!HAS_PENDING_EXCEPTION) {
1511       scratch_class->link_methods(THREAD);
1512     }
1513     if (HAS_PENDING_EXCEPTION) {
1514       Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
1515       log_info(redefine, class, load, exceptions)
1516         ("Rewriter::rewrite or link_methods exception: '%s'", ex_name->as_C_string());
1517       CLEAR_PENDING_EXCEPTION;
1518       if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
1519         return JVMTI_ERROR_OUT_OF_MEMORY;
1520       } else {
1521         return JVMTI_ERROR_INTERNAL;
1522       }
1523     }
1524 
1525     log_debug(redefine, class, load)
1526       ("loaded name=%s (avail_mem=" UINT64_FORMAT "K)", the_class->external_name(), os::available_memory() >> 10);
1527   }
1528 
1529   return JVMTI_ERROR_NONE;
1530 }
1531 
1532 
1533 // Map old_index to new_index as needed. scratch_cp is only needed
1534 // for log calls.
1535 void VM_RedefineClasses::map_index(const constantPoolHandle& scratch_cp,
1536        int old_index, int new_index) {
1537   if (find_new_index(old_index) != 0) {
1538     // old_index is already mapped
1539     return;
1540   }
1541 
1542   if (old_index == new_index) {
1543     // no mapping is needed
1544     return;
1545   }
1546 
1547   _index_map_p->at_put(old_index, new_index);
1548   _index_map_count++;
1549 
1550   log_trace(redefine, class, constantpool)
1551     ("mapped tag %d at index %d to %d", scratch_cp->tag_at(old_index).value(), old_index, new_index);
1552 } // end map_index()
1553 
1554 
1555 // Map old_index to new_index as needed.
1556 void VM_RedefineClasses::map_operand_index(int old_index, int new_index) {
1557   if (find_new_operand_index(old_index) != -1) {
1558     // old_index is already mapped
1559     return;
1560   }
1561 
1562   if (old_index == new_index) {
1563     // no mapping is needed
1564     return;
1565   }
1566 
1567   _operands_index_map_p->at_put(old_index, new_index);
1568   _operands_index_map_count++;
1569 
1570   log_trace(redefine, class, constantpool)("mapped bootstrap specifier at index %d to %d", old_index, new_index);
1571 } // end map_index()
1572 
1573 
1574 // Merge old_cp and scratch_cp and return the results of the merge via
1575 // merge_cp_p. The number of entries in *merge_cp_p is returned via
1576 // merge_cp_length_p. The entries in old_cp occupy the same locations
1577 // in *merge_cp_p. Also creates a map of indices from entries in
1578 // scratch_cp to the corresponding entry in *merge_cp_p. Index map
1579 // entries are only created for entries in scratch_cp that occupy a
1580 // different location in *merged_cp_p.
1581 bool VM_RedefineClasses::merge_constant_pools(const constantPoolHandle& old_cp,
1582        const constantPoolHandle& scratch_cp, constantPoolHandle *merge_cp_p,
1583        int *merge_cp_length_p, TRAPS) {
1584 
1585   if (merge_cp_p == nullptr) {
1586     assert(false, "caller must provide scratch constantPool");
1587     return false; // robustness
1588   }
1589   if (merge_cp_length_p == nullptr) {
1590     assert(false, "caller must provide scratch CP length");
1591     return false; // robustness
1592   }
1593   // Worst case we need old_cp->length() + scratch_cp()->length(),
1594   // but the caller might be smart so make sure we have at least
1595   // the minimum.
1596   if ((*merge_cp_p)->length() < old_cp->length()) {
1597     assert(false, "merge area too small");
1598     return false; // robustness
1599   }
1600 
1601   log_info(redefine, class, constantpool)("old_cp_len=%d, scratch_cp_len=%d", old_cp->length(), scratch_cp->length());
1602 
1603   {
1604     // Pass 0:
1605     // The old_cp is copied to *merge_cp_p; this means that any code
1606     // using old_cp does not have to change. This work looks like a
1607     // perfect fit for ConstantPool*::copy_cp_to(), but we need to
1608     // handle one special case:
1609     // - revert JVM_CONSTANT_Class to JVM_CONSTANT_UnresolvedClass
1610     // This will make verification happy.
1611 
1612     int old_i;  // index into old_cp
1613 
1614     // index zero (0) is not used in constantPools
1615     for (old_i = 1; old_i < old_cp->length(); old_i++) {
1616       // leave debugging crumb
1617       jbyte old_tag = old_cp->tag_at(old_i).value();
1618       switch (old_tag) {
1619       case JVM_CONSTANT_Class:
1620       case JVM_CONSTANT_UnresolvedClass:
1621         // revert the copy to JVM_CONSTANT_UnresolvedClass
1622         // May be resolving while calling this so do the same for
1623         // JVM_CONSTANT_UnresolvedClass (klass_name_at() deals with transition)
1624         (*merge_cp_p)->temp_unresolved_klass_at_put(old_i,
1625           old_cp->klass_name_index_at(old_i));
1626         break;
1627 
1628       case JVM_CONSTANT_Double:
1629       case JVM_CONSTANT_Long:
1630         // just copy the entry to *merge_cp_p, but double and long take
1631         // two constant pool entries
1632         ConstantPool::copy_entry_to(old_cp, old_i, *merge_cp_p, old_i);
1633         old_i++;
1634         break;
1635 
1636       default:
1637         // just copy the entry to *merge_cp_p
1638         ConstantPool::copy_entry_to(old_cp, old_i, *merge_cp_p, old_i);
1639         break;
1640       }
1641     } // end for each old_cp entry
1642 
1643     ConstantPool::copy_operands(old_cp, *merge_cp_p, CHECK_false);
1644     (*merge_cp_p)->extend_operands(scratch_cp, CHECK_false);
1645 
1646     // We don't need to sanity check that *merge_cp_length_p is within
1647     // *merge_cp_p bounds since we have the minimum on-entry check above.
1648     (*merge_cp_length_p) = old_i;
1649   }
1650 
1651   // merge_cp_len should be the same as old_cp->length() at this point
1652   // so this trace message is really a "warm-and-breathing" message.
1653   log_debug(redefine, class, constantpool)("after pass 0: merge_cp_len=%d", *merge_cp_length_p);
1654 
1655   int scratch_i;  // index into scratch_cp
1656   {
1657     // Pass 1a:
1658     // Compare scratch_cp entries to the old_cp entries that we have
1659     // already copied to *merge_cp_p. In this pass, we are eliminating
1660     // exact duplicates (matching entry at same index) so we only
1661     // compare entries in the common indice range.
1662     int increment = 1;
1663     int pass1a_length = MIN2(old_cp->length(), scratch_cp->length());
1664     for (scratch_i = 1; scratch_i < pass1a_length; scratch_i += increment) {
1665       switch (scratch_cp->tag_at(scratch_i).value()) {
1666       case JVM_CONSTANT_Double:
1667       case JVM_CONSTANT_Long:
1668         // double and long take two constant pool entries
1669         increment = 2;
1670         break;
1671 
1672       default:
1673         increment = 1;
1674         break;
1675       }
1676 
1677       bool match = scratch_cp->compare_entry_to(scratch_i, *merge_cp_p, scratch_i);
1678       if (match) {
1679         // found a match at the same index so nothing more to do
1680         continue;
1681       }
1682 
1683       int found_i = scratch_cp->find_matching_entry(scratch_i, *merge_cp_p);
1684       if (found_i != 0) {
1685         guarantee(found_i != scratch_i,
1686           "compare_entry_to() and find_matching_entry() do not agree");
1687 
1688         // Found a matching entry somewhere else in *merge_cp_p so
1689         // just need a mapping entry.
1690         map_index(scratch_cp, scratch_i, found_i);
1691         continue;
1692       }
1693 
1694       // No match found so we have to append this entry and any unique
1695       // referenced entries to *merge_cp_p.
1696       append_entry(scratch_cp, scratch_i, merge_cp_p, merge_cp_length_p);
1697     }
1698   }
1699 
1700   log_debug(redefine, class, constantpool)
1701     ("after pass 1a: merge_cp_len=%d, scratch_i=%d, index_map_len=%d",
1702      *merge_cp_length_p, scratch_i, _index_map_count);
1703 
1704   if (scratch_i < scratch_cp->length()) {
1705     // Pass 1b:
1706     // old_cp is smaller than scratch_cp so there are entries in
1707     // scratch_cp that we have not yet processed. We take care of
1708     // those now.
1709     int increment = 1;
1710     for (; scratch_i < scratch_cp->length(); scratch_i += increment) {
1711       switch (scratch_cp->tag_at(scratch_i).value()) {
1712       case JVM_CONSTANT_Double:
1713       case JVM_CONSTANT_Long:
1714         // double and long take two constant pool entries
1715         increment = 2;
1716         break;
1717 
1718       default:
1719         increment = 1;
1720         break;
1721       }
1722 
1723       int found_i =
1724         scratch_cp->find_matching_entry(scratch_i, *merge_cp_p);
1725       if (found_i != 0) {
1726         // Found a matching entry somewhere else in *merge_cp_p so
1727         // just need a mapping entry.
1728         map_index(scratch_cp, scratch_i, found_i);
1729         continue;
1730       }
1731 
1732       // No match found so we have to append this entry and any unique
1733       // referenced entries to *merge_cp_p.
1734       append_entry(scratch_cp, scratch_i, merge_cp_p, merge_cp_length_p);
1735     }
1736 
1737     log_debug(redefine, class, constantpool)
1738       ("after pass 1b: merge_cp_len=%d, scratch_i=%d, index_map_len=%d",
1739        *merge_cp_length_p, scratch_i, _index_map_count);
1740   }
1741   finalize_operands_merge(*merge_cp_p, CHECK_false);
1742 
1743   return true;
1744 } // end merge_constant_pools()
1745 
1746 
1747 // Scoped object to clean up the constant pool(s) created for merging
1748 class MergeCPCleaner {
1749   ClassLoaderData*   _loader_data;
1750   ConstantPool*      _cp;
1751   ConstantPool*      _scratch_cp;
1752  public:
1753   MergeCPCleaner(ClassLoaderData* loader_data, ConstantPool* merge_cp) :
1754                  _loader_data(loader_data), _cp(merge_cp), _scratch_cp(nullptr) {}
1755   ~MergeCPCleaner() {
1756     _loader_data->add_to_deallocate_list(_cp);
1757     if (_scratch_cp != nullptr) {
1758       _loader_data->add_to_deallocate_list(_scratch_cp);
1759     }
1760   }
1761   void add_scratch_cp(ConstantPool* scratch_cp) { _scratch_cp = scratch_cp; }
1762 };
1763 
1764 // Merge constant pools between the_class and scratch_class and
1765 // potentially rewrite bytecodes in scratch_class to use the merged
1766 // constant pool.
1767 jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
1768              InstanceKlass* the_class, InstanceKlass* scratch_class,
1769              TRAPS) {
1770   // worst case merged constant pool length is old and new combined
1771   int merge_cp_length = the_class->constants()->length()
1772         + scratch_class->constants()->length();
1773 
1774   // Constant pools are not easily reused so we allocate a new one
1775   // each time.
1776   // merge_cp is created unsafe for concurrent GC processing.  It
1777   // should be marked safe before discarding it. Even though
1778   // garbage,  if it crosses a card boundary, it may be scanned
1779   // in order to find the start of the first complete object on the card.
1780   ClassLoaderData* loader_data = the_class->class_loader_data();
1781   ConstantPool* merge_cp_oop =
1782     ConstantPool::allocate(loader_data,
1783                            merge_cp_length,
1784                            CHECK_(JVMTI_ERROR_OUT_OF_MEMORY));
1785   MergeCPCleaner cp_cleaner(loader_data, merge_cp_oop);
1786 
1787   HandleMark hm(THREAD);  // make sure handles are cleared before
1788                           // MergeCPCleaner clears out merge_cp_oop
1789   constantPoolHandle merge_cp(THREAD, merge_cp_oop);
1790 
1791   // Get constants() from the old class because it could have been rewritten
1792   // while we were at a safepoint allocating a new constant pool.
1793   constantPoolHandle old_cp(THREAD, the_class->constants());
1794   constantPoolHandle scratch_cp(THREAD, scratch_class->constants());
1795 
1796   // If the length changed, the class was redefined out from under us. Return
1797   // an error.
1798   if (merge_cp_length != the_class->constants()->length()
1799          + scratch_class->constants()->length()) {
1800     return JVMTI_ERROR_INTERNAL;
1801   }
1802 
1803   // Update the version number of the constant pools (may keep scratch_cp)
1804   merge_cp->increment_and_save_version(old_cp->version());
1805   scratch_cp->increment_and_save_version(old_cp->version());
1806 
1807   ResourceMark rm(THREAD);
1808   _index_map_count = 0;
1809   _index_map_p = new intArray(scratch_cp->length(), scratch_cp->length(), -1);
1810 
1811   _operands_cur_length = ConstantPool::operand_array_length(old_cp->operands());
1812   _operands_index_map_count = 0;
1813   int operands_index_map_len = ConstantPool::operand_array_length(scratch_cp->operands());
1814   _operands_index_map_p = new intArray(operands_index_map_len, operands_index_map_len, -1);
1815 
1816   // reference to the cp holder is needed for copy_operands()
1817   merge_cp->set_pool_holder(scratch_class);
1818   bool result = merge_constant_pools(old_cp, scratch_cp, &merge_cp,
1819                   &merge_cp_length, THREAD);
1820   merge_cp->set_pool_holder(nullptr);
1821 
1822   if (!result) {
1823     // The merge can fail due to memory allocation failure or due
1824     // to robustness checks.
1825     return JVMTI_ERROR_INTERNAL;
1826   }
1827 
1828   // ensure merged constant pool size does not overflow u2
1829   if (merge_cp_length > 0xFFFF) {
1830     log_warning(redefine, class, constantpool)("Merged constant pool overflow: %d entries", merge_cp_length);
1831     return JVMTI_ERROR_INTERNAL;
1832   }
1833 
1834   // Set dynamic constants attribute from the original CP.
1835   if (old_cp->has_dynamic_constant()) {
1836     scratch_cp->set_has_dynamic_constant();
1837   }
1838 
1839   log_info(redefine, class, constantpool)("merge_cp_len=%d, index_map_len=%d", merge_cp_length, _index_map_count);
1840 
1841   if (_index_map_count == 0) {
1842     // there is nothing to map between the new and merged constant pools
1843 
1844     // Copy attributes from scratch_cp to merge_cp
1845     merge_cp->copy_fields(scratch_cp());
1846 
1847     if (old_cp->length() == scratch_cp->length()) {
1848       // The old and new constant pools are the same length and the
1849       // index map is empty. This means that the three constant pools
1850       // are equivalent (but not the same). Unfortunately, the new
1851       // constant pool has not gone through link resolution nor have
1852       // the new class bytecodes gone through constant pool cache
1853       // rewriting so we can't use the old constant pool with the new
1854       // class.
1855 
1856       // toss the merged constant pool at return
1857     } else if (old_cp->length() < scratch_cp->length()) {
1858       // The old constant pool has fewer entries than the new constant
1859       // pool and the index map is empty. This means the new constant
1860       // pool is a superset of the old constant pool. However, the old
1861       // class bytecodes have already gone through constant pool cache
1862       // rewriting so we can't use the new constant pool with the old
1863       // class.
1864 
1865       // toss the merged constant pool at return
1866     } else {
1867       // The old constant pool has more entries than the new constant
1868       // pool and the index map is empty. This means that both the old
1869       // and merged constant pools are supersets of the new constant
1870       // pool.
1871 
1872       // Replace the new constant pool with a shrunken copy of the
1873       // merged constant pool
1874       set_new_constant_pool(loader_data, scratch_class, merge_cp, merge_cp_length,
1875                             CHECK_(JVMTI_ERROR_OUT_OF_MEMORY));
1876       // The new constant pool replaces scratch_cp so have cleaner clean it up.
1877       // It can't be cleaned up while there are handles to it.
1878       cp_cleaner.add_scratch_cp(scratch_cp());
1879     }
1880   } else {
1881     if (log_is_enabled(Trace, redefine, class, constantpool)) {
1882       // don't want to loop unless we are tracing
1883       int count = 0;
1884       for (int i = 1; i < _index_map_p->length(); i++) {
1885         int value = _index_map_p->at(i);
1886 
1887         if (value != -1) {
1888           log_trace(redefine, class, constantpool)("index_map[%d]: old=%d new=%d", count, i, value);
1889           count++;
1890         }
1891       }
1892     }
1893 
1894     // We have entries mapped between the new and merged constant pools
1895     // so we have to rewrite some constant pool references.
1896     if (!rewrite_cp_refs(scratch_class)) {
1897       return JVMTI_ERROR_INTERNAL;
1898     }
1899 
1900     // Copy attributes from scratch_cp to merge_cp (should be done after rewrite_cp_refs())
1901     merge_cp->copy_fields(scratch_cp());
1902 
1903     // Replace the new constant pool with a shrunken copy of the
1904     // merged constant pool so now the rewritten bytecodes have
1905     // valid references; the previous new constant pool will get
1906     // GCed.
1907     set_new_constant_pool(loader_data, scratch_class, merge_cp, merge_cp_length,
1908                           CHECK_(JVMTI_ERROR_OUT_OF_MEMORY));
1909     // The new constant pool replaces scratch_cp so have cleaner clean it up.
1910     // It can't be cleaned up while there are handles to it.
1911     cp_cleaner.add_scratch_cp(scratch_cp());
1912   }
1913 
1914   return JVMTI_ERROR_NONE;
1915 } // end merge_cp_and_rewrite()
1916 
1917 
1918 // Rewrite constant pool references in klass scratch_class.
1919 bool VM_RedefineClasses::rewrite_cp_refs(InstanceKlass* scratch_class) {
1920 
1921   // rewrite constant pool references in the nest attributes:
1922   if (!rewrite_cp_refs_in_nest_attributes(scratch_class)) {
1923     // propagate failure back to caller
1924     return false;
1925   }
1926 
1927   // rewrite constant pool references in the Record attribute:
1928   if (!rewrite_cp_refs_in_record_attribute(scratch_class)) {
1929     // propagate failure back to caller
1930     return false;
1931   }
1932 
1933   // rewrite constant pool references in the PermittedSubclasses attribute:
1934   if (!rewrite_cp_refs_in_permitted_subclasses_attribute(scratch_class)) {
1935     // propagate failure back to caller
1936     return false;
1937   }
1938 
1939   // rewrite constant pool references in the methods:
1940   if (!rewrite_cp_refs_in_methods(scratch_class)) {
1941     // propagate failure back to caller
1942     return false;
1943   }
1944 
1945   // rewrite constant pool references in the class_annotations:
1946   if (!rewrite_cp_refs_in_class_annotations(scratch_class)) {
1947     // propagate failure back to caller
1948     return false;
1949   }
1950 
1951   // rewrite constant pool references in the fields_annotations:
1952   if (!rewrite_cp_refs_in_fields_annotations(scratch_class)) {
1953     // propagate failure back to caller
1954     return false;
1955   }
1956 
1957   // rewrite constant pool references in the methods_annotations:
1958   if (!rewrite_cp_refs_in_methods_annotations(scratch_class)) {
1959     // propagate failure back to caller
1960     return false;
1961   }
1962 
1963   // rewrite constant pool references in the methods_parameter_annotations:
1964   if (!rewrite_cp_refs_in_methods_parameter_annotations(scratch_class)) {
1965     // propagate failure back to caller
1966     return false;
1967   }
1968 
1969   // rewrite constant pool references in the methods_default_annotations:
1970   if (!rewrite_cp_refs_in_methods_default_annotations(scratch_class)) {
1971     // propagate failure back to caller
1972     return false;
1973   }
1974 
1975   // rewrite constant pool references in the class_type_annotations:
1976   if (!rewrite_cp_refs_in_class_type_annotations(scratch_class)) {
1977     // propagate failure back to caller
1978     return false;
1979   }
1980 
1981   // rewrite constant pool references in the fields_type_annotations:
1982   if (!rewrite_cp_refs_in_fields_type_annotations(scratch_class)) {
1983     // propagate failure back to caller
1984     return false;
1985   }
1986 
1987   // rewrite constant pool references in the methods_type_annotations:
1988   if (!rewrite_cp_refs_in_methods_type_annotations(scratch_class)) {
1989     // propagate failure back to caller
1990     return false;
1991   }
1992 
1993   // There can be type annotations in the Code part of a method_info attribute.
1994   // These annotations are not accessible, even by reflection.
1995   // Currently they are not even parsed by the ClassFileParser.
1996   // If runtime access is added they will also need to be rewritten.
1997 
1998   // rewrite source file name index:
1999   u2 source_file_name_idx = scratch_class->source_file_name_index();
2000   if (source_file_name_idx != 0) {
2001     u2 new_source_file_name_idx = find_new_index(source_file_name_idx);
2002     if (new_source_file_name_idx != 0) {
2003       scratch_class->set_source_file_name_index(new_source_file_name_idx);
2004     }
2005   }
2006 
2007   // rewrite class generic signature index:
2008   u2 generic_signature_index = scratch_class->generic_signature_index();
2009   if (generic_signature_index != 0) {
2010     u2 new_generic_signature_index = find_new_index(generic_signature_index);
2011     if (new_generic_signature_index != 0) {
2012       scratch_class->set_generic_signature_index(new_generic_signature_index);
2013     }
2014   }
2015 
2016   return true;
2017 } // end rewrite_cp_refs()
2018 
2019 // Rewrite constant pool references in the NestHost and NestMembers attributes.
2020 bool VM_RedefineClasses::rewrite_cp_refs_in_nest_attributes(
2021        InstanceKlass* scratch_class) {
2022 
2023   u2 cp_index = scratch_class->nest_host_index();
2024   if (cp_index != 0) {
2025     scratch_class->set_nest_host_index(find_new_index(cp_index));
2026   }
2027   Array<u2>* nest_members = scratch_class->nest_members();
2028   for (int i = 0; i < nest_members->length(); i++) {
2029     u2 cp_index = nest_members->at(i);
2030     nest_members->at_put(i, find_new_index(cp_index));
2031   }
2032   return true;
2033 }
2034 
2035 // Rewrite constant pool references in the Record attribute.
2036 bool VM_RedefineClasses::rewrite_cp_refs_in_record_attribute(InstanceKlass* scratch_class) {
2037   Array<RecordComponent*>* components = scratch_class->record_components();
2038   if (components != nullptr) {
2039     for (int i = 0; i < components->length(); i++) {
2040       RecordComponent* component = components->at(i);
2041       u2 cp_index = component->name_index();
2042       component->set_name_index(find_new_index(cp_index));
2043       cp_index = component->descriptor_index();
2044       component->set_descriptor_index(find_new_index(cp_index));
2045       cp_index = component->generic_signature_index();
2046       if (cp_index != 0) {
2047         component->set_generic_signature_index(find_new_index(cp_index));
2048       }
2049 
2050       AnnotationArray* annotations = component->annotations();
2051       if (annotations != nullptr && annotations->length() != 0) {
2052         int byte_i = 0;  // byte index into annotations
2053         if (!rewrite_cp_refs_in_annotations_typeArray(annotations, byte_i)) {
2054           log_debug(redefine, class, annotation)("bad record_component_annotations at %d", i);
2055           // propagate failure back to caller
2056           return false;
2057         }
2058       }
2059 
2060       AnnotationArray* type_annotations = component->type_annotations();
2061       if (type_annotations != nullptr && type_annotations->length() != 0) {
2062         int byte_i = 0;  // byte index into annotations
2063         if (!rewrite_cp_refs_in_annotations_typeArray(type_annotations, byte_i)) {
2064           log_debug(redefine, class, annotation)("bad record_component_type_annotations at %d", i);
2065           // propagate failure back to caller
2066           return false;
2067         }
2068       }
2069     }
2070   }
2071   return true;
2072 }
2073 
2074 // Rewrite constant pool references in the PermittedSubclasses attribute.
2075 bool VM_RedefineClasses::rewrite_cp_refs_in_permitted_subclasses_attribute(
2076        InstanceKlass* scratch_class) {
2077 
2078   Array<u2>* permitted_subclasses = scratch_class->permitted_subclasses();
2079   assert(permitted_subclasses != nullptr, "unexpected null permitted_subclasses");
2080   for (int i = 0; i < permitted_subclasses->length(); i++) {
2081     u2 cp_index = permitted_subclasses->at(i);
2082     permitted_subclasses->at_put(i, find_new_index(cp_index));
2083   }
2084   return true;
2085 }
2086 
2087 // Rewrite constant pool references in the methods.
2088 bool VM_RedefineClasses::rewrite_cp_refs_in_methods(InstanceKlass* scratch_class) {
2089 
2090   Array<Method*>* methods = scratch_class->methods();
2091 
2092   if (methods == nullptr || methods->length() == 0) {
2093     // no methods so nothing to do
2094     return true;
2095   }
2096 
2097   JavaThread* THREAD = JavaThread::current(); // For exception macros.
2098   ExceptionMark em(THREAD);
2099 
2100   // rewrite constant pool references in the methods:
2101   for (int i = methods->length() - 1; i >= 0; i--) {
2102     methodHandle method(THREAD, methods->at(i));
2103     methodHandle new_method;
2104     rewrite_cp_refs_in_method(method, &new_method, THREAD);
2105     if (!new_method.is_null()) {
2106       // the method has been replaced so save the new method version
2107       // even in the case of an exception.  original method is on the
2108       // deallocation list.
2109       methods->at_put(i, new_method());
2110     }
2111     if (HAS_PENDING_EXCEPTION) {
2112       Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
2113       log_info(redefine, class, load, exceptions)("rewrite_cp_refs_in_method exception: '%s'", ex_name->as_C_string());
2114       // Need to clear pending exception here as the super caller sets
2115       // the JVMTI_ERROR_INTERNAL if the returned value is false.
2116       CLEAR_PENDING_EXCEPTION;
2117       return false;
2118     }
2119   }
2120 
2121   return true;
2122 }
2123 
2124 
2125 // Rewrite constant pool references in the specific method. This code
2126 // was adapted from Rewriter::rewrite_method().
2127 void VM_RedefineClasses::rewrite_cp_refs_in_method(methodHandle method,
2128        methodHandle *new_method_p, TRAPS) {
2129 
2130   *new_method_p = methodHandle();  // default is no new method
2131 
2132   // We cache a pointer to the bytecodes here in code_base. If GC
2133   // moves the Method*, then the bytecodes will also move which
2134   // will likely cause a crash. We create a NoSafepointVerifier
2135   // object to detect whether we pass a possible safepoint in this
2136   // code block.
2137   NoSafepointVerifier nsv;
2138 
2139   // Bytecodes and their length
2140   address code_base = method->code_base();
2141   int code_length = method->code_size();
2142 
2143   int bc_length;
2144   for (int bci = 0; bci < code_length; bci += bc_length) {
2145     address bcp = code_base + bci;
2146     Bytecodes::Code c = (Bytecodes::Code)(*bcp);
2147 
2148     bc_length = Bytecodes::length_for(c);
2149     if (bc_length == 0) {
2150       // More complicated bytecodes report a length of zero so
2151       // we have to try again a slightly different way.
2152       bc_length = Bytecodes::length_at(method(), bcp);
2153     }
2154 
2155     assert(bc_length != 0, "impossible bytecode length");
2156 
2157     switch (c) {
2158       case Bytecodes::_ldc:
2159       {
2160         u1 cp_index = *(bcp + 1);
2161         u2 new_index = find_new_index(cp_index);
2162 
2163         if (StressLdcRewrite && new_index == 0) {
2164           // If we are stressing ldc -> ldc_w rewriting, then we
2165           // always need a new_index value.
2166           new_index = cp_index;
2167         }
2168         if (new_index != 0) {
2169           // the original index is mapped so we have more work to do
2170           if (!StressLdcRewrite && new_index <= max_jubyte) {
2171             // The new value can still use ldc instead of ldc_w
2172             // unless we are trying to stress ldc -> ldc_w rewriting
2173             log_trace(redefine, class, constantpool)
2174               ("%s@" INTPTR_FORMAT " old=%d, new=%d", Bytecodes::name(c), p2i(bcp), cp_index, new_index);
2175             // We checked that new_index fits in a u1 so this cast is safe
2176             *(bcp + 1) = (u1)new_index;
2177           } else {
2178             log_trace(redefine, class, constantpool)
2179               ("%s->ldc_w@" INTPTR_FORMAT " old=%d, new=%d", Bytecodes::name(c), p2i(bcp), cp_index, new_index);
2180             // the new value needs ldc_w instead of ldc
2181             u_char inst_buffer[4]; // max instruction size is 4 bytes
2182             bcp = (address)inst_buffer;
2183             // construct new instruction sequence
2184             *bcp = Bytecodes::_ldc_w;
2185             bcp++;
2186             // Rewriter::rewrite_method() does not rewrite ldc -> ldc_w.
2187             // See comment below for difference between put_Java_u2()
2188             // and put_native_u2().
2189             Bytes::put_Java_u2(bcp, new_index);
2190 
2191             Relocator rc(method, nullptr /* no RelocatorListener needed */);
2192             methodHandle m;
2193             {
2194               PauseNoSafepointVerifier pnsv(&nsv);
2195 
2196               // ldc is 2 bytes and ldc_w is 3 bytes
2197               m = rc.insert_space_at(bci, 3, inst_buffer, CHECK);
2198             }
2199 
2200             // return the new method so that the caller can update
2201             // the containing class
2202             *new_method_p = method = m;
2203             // switch our bytecode processing loop from the old method
2204             // to the new method
2205             code_base = method->code_base();
2206             code_length = method->code_size();
2207             bcp = code_base + bci;
2208             c = (Bytecodes::Code)(*bcp);
2209             bc_length = Bytecodes::length_for(c);
2210             assert(bc_length != 0, "sanity check");
2211           } // end we need ldc_w instead of ldc
2212         } // end if there is a mapped index
2213       } break;
2214 
2215       // these bytecodes have a two-byte constant pool index
2216       case Bytecodes::_anewarray      : // fall through
2217       case Bytecodes::_checkcast      : // fall through
2218       case Bytecodes::_getfield       : // fall through
2219       case Bytecodes::_getstatic      : // fall through
2220       case Bytecodes::_instanceof     : // fall through
2221       case Bytecodes::_invokedynamic  : // fall through
2222       case Bytecodes::_invokeinterface: // fall through
2223       case Bytecodes::_invokespecial  : // fall through
2224       case Bytecodes::_invokestatic   : // fall through
2225       case Bytecodes::_invokevirtual  : // fall through
2226       case Bytecodes::_ldc_w          : // fall through
2227       case Bytecodes::_ldc2_w         : // fall through
2228       case Bytecodes::_multianewarray : // fall through
2229       case Bytecodes::_new            : // fall through
2230       case Bytecodes::_putfield       : // fall through
2231       case Bytecodes::_putstatic      :
2232       {
2233         address p = bcp + 1;
2234         int cp_index = Bytes::get_Java_u2(p);
2235         u2 new_index = find_new_index(cp_index);
2236         if (new_index != 0) {
2237           // the original index is mapped so update w/ new value
2238           log_trace(redefine, class, constantpool)
2239             ("%s@" INTPTR_FORMAT " old=%d, new=%d", Bytecodes::name(c),p2i(bcp), cp_index, new_index);
2240           // Rewriter::rewrite_method() uses put_native_u2() in this
2241           // situation because it is reusing the constant pool index
2242           // location for a native index into the ConstantPoolCache.
2243           // Since we are updating the constant pool index prior to
2244           // verification and ConstantPoolCache initialization, we
2245           // need to keep the new index in Java byte order.
2246           Bytes::put_Java_u2(p, new_index);
2247         }
2248       } break;
2249       default:
2250         break;
2251     }
2252   } // end for each bytecode
2253 } // end rewrite_cp_refs_in_method()
2254 
2255 
2256 // Rewrite constant pool references in the class_annotations field.
2257 bool VM_RedefineClasses::rewrite_cp_refs_in_class_annotations(InstanceKlass* scratch_class) {
2258 
2259   AnnotationArray* class_annotations = scratch_class->class_annotations();
2260   if (class_annotations == nullptr || class_annotations->length() == 0) {
2261     // no class_annotations so nothing to do
2262     return true;
2263   }
2264 
2265   log_debug(redefine, class, annotation)("class_annotations length=%d", class_annotations->length());
2266 
2267   int byte_i = 0;  // byte index into class_annotations
2268   return rewrite_cp_refs_in_annotations_typeArray(class_annotations, byte_i);
2269 }
2270 
2271 
2272 // Rewrite constant pool references in an annotations typeArray. This
2273 // "structure" is adapted from the RuntimeVisibleAnnotations_attribute
2274 // that is described in section 4.8.15 of the 2nd-edition of the VM spec:
2275 //
2276 // annotations_typeArray {
2277 //   u2 num_annotations;
2278 //   annotation annotations[num_annotations];
2279 // }
2280 //
2281 bool VM_RedefineClasses::rewrite_cp_refs_in_annotations_typeArray(
2282        AnnotationArray* annotations_typeArray, int &byte_i_ref) {
2283 
2284   if ((byte_i_ref + 2) > annotations_typeArray->length()) {
2285     // not enough room for num_annotations field
2286     log_debug(redefine, class, annotation)("length() is too small for num_annotations field");
2287     return false;
2288   }
2289 
2290   u2 num_annotations = Bytes::get_Java_u2((address)
2291                          annotations_typeArray->adr_at(byte_i_ref));
2292   byte_i_ref += 2;
2293 
2294   log_debug(redefine, class, annotation)("num_annotations=%d", num_annotations);
2295 
2296   int calc_num_annotations = 0;
2297   for (; calc_num_annotations < num_annotations; calc_num_annotations++) {
2298     if (!rewrite_cp_refs_in_annotation_struct(annotations_typeArray, byte_i_ref)) {
2299       log_debug(redefine, class, annotation)("bad annotation_struct at %d", calc_num_annotations);
2300       // propagate failure back to caller
2301       return false;
2302     }
2303   }
2304   assert(num_annotations == calc_num_annotations, "sanity check");
2305 
2306   return true;
2307 } // end rewrite_cp_refs_in_annotations_typeArray()
2308 
2309 
2310 // Rewrite constant pool references in the annotation struct portion of
2311 // an annotations_typeArray. This "structure" is from section 4.8.15 of
2312 // the 2nd-edition of the VM spec:
2313 //
2314 // struct annotation {
2315 //   u2 type_index;
2316 //   u2 num_element_value_pairs;
2317 //   {
2318 //     u2 element_name_index;
2319 //     element_value value;
2320 //   } element_value_pairs[num_element_value_pairs];
2321 // }
2322 //
2323 bool VM_RedefineClasses::rewrite_cp_refs_in_annotation_struct(
2324        AnnotationArray* annotations_typeArray, int &byte_i_ref) {
2325   if ((byte_i_ref + 2 + 2) > annotations_typeArray->length()) {
2326     // not enough room for smallest annotation_struct
2327     log_debug(redefine, class, annotation)("length() is too small for annotation_struct");
2328     return false;
2329   }
2330 
2331   u2 type_index = rewrite_cp_ref_in_annotation_data(annotations_typeArray,
2332                     byte_i_ref, "type_index");
2333 
2334   u2 num_element_value_pairs = Bytes::get_Java_u2((address)
2335                                  annotations_typeArray->adr_at(byte_i_ref));
2336   byte_i_ref += 2;
2337 
2338   log_debug(redefine, class, annotation)
2339     ("type_index=%d  num_element_value_pairs=%d", type_index, num_element_value_pairs);
2340 
2341   int calc_num_element_value_pairs = 0;
2342   for (; calc_num_element_value_pairs < num_element_value_pairs;
2343        calc_num_element_value_pairs++) {
2344     if ((byte_i_ref + 2) > annotations_typeArray->length()) {
2345       // not enough room for another element_name_index, let alone
2346       // the rest of another component
2347       log_debug(redefine, class, annotation)("length() is too small for element_name_index");
2348       return false;
2349     }
2350 
2351     u2 element_name_index = rewrite_cp_ref_in_annotation_data(
2352                               annotations_typeArray, byte_i_ref,
2353                               "element_name_index");
2354 
2355     log_debug(redefine, class, annotation)("element_name_index=%d", element_name_index);
2356 
2357     if (!rewrite_cp_refs_in_element_value(annotations_typeArray, byte_i_ref)) {
2358       log_debug(redefine, class, annotation)("bad element_value at %d", calc_num_element_value_pairs);
2359       // propagate failure back to caller
2360       return false;
2361     }
2362   } // end for each component
2363   assert(num_element_value_pairs == calc_num_element_value_pairs,
2364     "sanity check");
2365 
2366   return true;
2367 } // end rewrite_cp_refs_in_annotation_struct()
2368 
2369 
2370 // Rewrite a constant pool reference at the current position in
2371 // annotations_typeArray if needed. Returns the original constant
2372 // pool reference if a rewrite was not needed or the new constant
2373 // pool reference if a rewrite was needed.
2374 u2 VM_RedefineClasses::rewrite_cp_ref_in_annotation_data(
2375      AnnotationArray* annotations_typeArray, int &byte_i_ref,
2376      const char * trace_mesg) {
2377 
2378   address cp_index_addr = (address)
2379     annotations_typeArray->adr_at(byte_i_ref);
2380   u2 old_cp_index = Bytes::get_Java_u2(cp_index_addr);
2381   u2 new_cp_index = find_new_index(old_cp_index);
2382   if (new_cp_index != 0) {
2383     log_debug(redefine, class, annotation)("mapped old %s=%d", trace_mesg, old_cp_index);
2384     Bytes::put_Java_u2(cp_index_addr, new_cp_index);
2385     old_cp_index = new_cp_index;
2386   }
2387   byte_i_ref += 2;
2388   return old_cp_index;
2389 }
2390 
2391 
2392 // Rewrite constant pool references in the element_value portion of an
2393 // annotations_typeArray. This "structure" is from section 4.8.15.1 of
2394 // the 2nd-edition of the VM spec:
2395 //
2396 // struct element_value {
2397 //   u1 tag;
2398 //   union {
2399 //     u2 const_value_index;
2400 //     {
2401 //       u2 type_name_index;
2402 //       u2 const_name_index;
2403 //     } enum_const_value;
2404 //     u2 class_info_index;
2405 //     annotation annotation_value;
2406 //     struct {
2407 //       u2 num_values;
2408 //       element_value values[num_values];
2409 //     } array_value;
2410 //   } value;
2411 // }
2412 //
2413 bool VM_RedefineClasses::rewrite_cp_refs_in_element_value(
2414        AnnotationArray* annotations_typeArray, int &byte_i_ref) {
2415 
2416   if ((byte_i_ref + 1) > annotations_typeArray->length()) {
2417     // not enough room for a tag let alone the rest of an element_value
2418     log_debug(redefine, class, annotation)("length() is too small for a tag");
2419     return false;
2420   }
2421 
2422   u1 tag = annotations_typeArray->at(byte_i_ref);
2423   byte_i_ref++;
2424   log_debug(redefine, class, annotation)("tag='%c'", tag);
2425 
2426   switch (tag) {
2427     // These BaseType tag values are from Table 4.2 in VM spec:
2428     case JVM_SIGNATURE_BYTE:
2429     case JVM_SIGNATURE_CHAR:
2430     case JVM_SIGNATURE_DOUBLE:
2431     case JVM_SIGNATURE_FLOAT:
2432     case JVM_SIGNATURE_INT:
2433     case JVM_SIGNATURE_LONG:
2434     case JVM_SIGNATURE_SHORT:
2435     case JVM_SIGNATURE_BOOLEAN:
2436 
2437     // The remaining tag values are from Table 4.8 in the 2nd-edition of
2438     // the VM spec:
2439     case 's':
2440     {
2441       // For the above tag values (including the BaseType values),
2442       // value.const_value_index is right union field.
2443 
2444       if ((byte_i_ref + 2) > annotations_typeArray->length()) {
2445         // not enough room for a const_value_index
2446         log_debug(redefine, class, annotation)("length() is too small for a const_value_index");
2447         return false;
2448       }
2449 
2450       u2 const_value_index = rewrite_cp_ref_in_annotation_data(
2451                                annotations_typeArray, byte_i_ref,
2452                                "const_value_index");
2453 
2454       log_debug(redefine, class, annotation)("const_value_index=%d", const_value_index);
2455     } break;
2456 
2457     case 'e':
2458     {
2459       // for the above tag value, value.enum_const_value is right union field
2460 
2461       if ((byte_i_ref + 4) > annotations_typeArray->length()) {
2462         // not enough room for a enum_const_value
2463         log_debug(redefine, class, annotation)("length() is too small for a enum_const_value");
2464         return false;
2465       }
2466 
2467       u2 type_name_index = rewrite_cp_ref_in_annotation_data(
2468                              annotations_typeArray, byte_i_ref,
2469                              "type_name_index");
2470 
2471       u2 const_name_index = rewrite_cp_ref_in_annotation_data(
2472                               annotations_typeArray, byte_i_ref,
2473                               "const_name_index");
2474 
2475       log_debug(redefine, class, annotation)
2476         ("type_name_index=%d  const_name_index=%d", type_name_index, const_name_index);
2477     } break;
2478 
2479     case 'c':
2480     {
2481       // for the above tag value, value.class_info_index is right union field
2482 
2483       if ((byte_i_ref + 2) > annotations_typeArray->length()) {
2484         // not enough room for a class_info_index
2485         log_debug(redefine, class, annotation)("length() is too small for a class_info_index");
2486         return false;
2487       }
2488 
2489       u2 class_info_index = rewrite_cp_ref_in_annotation_data(
2490                               annotations_typeArray, byte_i_ref,
2491                               "class_info_index");
2492 
2493       log_debug(redefine, class, annotation)("class_info_index=%d", class_info_index);
2494     } break;
2495 
2496     case '@':
2497       // For the above tag value, value.attr_value is the right union
2498       // field. This is a nested annotation.
2499       if (!rewrite_cp_refs_in_annotation_struct(annotations_typeArray, byte_i_ref)) {
2500         // propagate failure back to caller
2501         return false;
2502       }
2503       break;
2504 
2505     case JVM_SIGNATURE_ARRAY:
2506     {
2507       if ((byte_i_ref + 2) > annotations_typeArray->length()) {
2508         // not enough room for a num_values field
2509         log_debug(redefine, class, annotation)("length() is too small for a num_values field");
2510         return false;
2511       }
2512 
2513       // For the above tag value, value.array_value is the right union
2514       // field. This is an array of nested element_value.
2515       u2 num_values = Bytes::get_Java_u2((address)
2516                         annotations_typeArray->adr_at(byte_i_ref));
2517       byte_i_ref += 2;
2518       log_debug(redefine, class, annotation)("num_values=%d", num_values);
2519 
2520       int calc_num_values = 0;
2521       for (; calc_num_values < num_values; calc_num_values++) {
2522         if (!rewrite_cp_refs_in_element_value(annotations_typeArray, byte_i_ref)) {
2523           log_debug(redefine, class, annotation)("bad nested element_value at %d", calc_num_values);
2524           // propagate failure back to caller
2525           return false;
2526         }
2527       }
2528       assert(num_values == calc_num_values, "sanity check");
2529     } break;
2530 
2531     default:
2532       log_debug(redefine, class, annotation)("bad tag=0x%x", tag);
2533       return false;
2534   } // end decode tag field
2535 
2536   return true;
2537 } // end rewrite_cp_refs_in_element_value()
2538 
2539 
2540 // Rewrite constant pool references in a fields_annotations field.
2541 bool VM_RedefineClasses::rewrite_cp_refs_in_fields_annotations(
2542        InstanceKlass* scratch_class) {
2543 
2544   Array<AnnotationArray*>* fields_annotations = scratch_class->fields_annotations();
2545 
2546   if (fields_annotations == nullptr || fields_annotations->length() == 0) {
2547     // no fields_annotations so nothing to do
2548     return true;
2549   }
2550 
2551   log_debug(redefine, class, annotation)("fields_annotations length=%d", fields_annotations->length());
2552 
2553   for (int i = 0; i < fields_annotations->length(); i++) {
2554     AnnotationArray* field_annotations = fields_annotations->at(i);
2555     if (field_annotations == nullptr || field_annotations->length() == 0) {
2556       // this field does not have any annotations so skip it
2557       continue;
2558     }
2559 
2560     int byte_i = 0;  // byte index into field_annotations
2561     if (!rewrite_cp_refs_in_annotations_typeArray(field_annotations, byte_i)) {
2562       log_debug(redefine, class, annotation)("bad field_annotations at %d", i);
2563       // propagate failure back to caller
2564       return false;
2565     }
2566   }
2567 
2568   return true;
2569 } // end rewrite_cp_refs_in_fields_annotations()
2570 
2571 
2572 // Rewrite constant pool references in a methods_annotations field.
2573 bool VM_RedefineClasses::rewrite_cp_refs_in_methods_annotations(
2574        InstanceKlass* scratch_class) {
2575 
2576   for (int i = 0; i < scratch_class->methods()->length(); i++) {
2577     Method* m = scratch_class->methods()->at(i);
2578     AnnotationArray* method_annotations = m->constMethod()->method_annotations();
2579 
2580     if (method_annotations == nullptr || method_annotations->length() == 0) {
2581       // this method does not have any annotations so skip it
2582       continue;
2583     }
2584 
2585     int byte_i = 0;  // byte index into method_annotations
2586     if (!rewrite_cp_refs_in_annotations_typeArray(method_annotations, byte_i)) {
2587       log_debug(redefine, class, annotation)("bad method_annotations at %d", i);
2588       // propagate failure back to caller
2589       return false;
2590     }
2591   }
2592 
2593   return true;
2594 } // end rewrite_cp_refs_in_methods_annotations()
2595 
2596 
2597 // Rewrite constant pool references in a methods_parameter_annotations
2598 // field. This "structure" is adapted from the
2599 // RuntimeVisibleParameterAnnotations_attribute described in section
2600 // 4.8.17 of the 2nd-edition of the VM spec:
2601 //
2602 // methods_parameter_annotations_typeArray {
2603 //   u1 num_parameters;
2604 //   {
2605 //     u2 num_annotations;
2606 //     annotation annotations[num_annotations];
2607 //   } parameter_annotations[num_parameters];
2608 // }
2609 //
2610 bool VM_RedefineClasses::rewrite_cp_refs_in_methods_parameter_annotations(
2611        InstanceKlass* scratch_class) {
2612 
2613   for (int i = 0; i < scratch_class->methods()->length(); i++) {
2614     Method* m = scratch_class->methods()->at(i);
2615     AnnotationArray* method_parameter_annotations = m->constMethod()->parameter_annotations();
2616     if (method_parameter_annotations == nullptr
2617         || method_parameter_annotations->length() == 0) {
2618       // this method does not have any parameter annotations so skip it
2619       continue;
2620     }
2621 
2622     if (method_parameter_annotations->length() < 1) {
2623       // not enough room for a num_parameters field
2624       log_debug(redefine, class, annotation)("length() is too small for a num_parameters field at %d", i);
2625       return false;
2626     }
2627 
2628     int byte_i = 0;  // byte index into method_parameter_annotations
2629 
2630     u1 num_parameters = method_parameter_annotations->at(byte_i);
2631     byte_i++;
2632 
2633     log_debug(redefine, class, annotation)("num_parameters=%d", num_parameters);
2634 
2635     int calc_num_parameters = 0;
2636     for (; calc_num_parameters < num_parameters; calc_num_parameters++) {
2637       if (!rewrite_cp_refs_in_annotations_typeArray(method_parameter_annotations, byte_i)) {
2638         log_debug(redefine, class, annotation)("bad method_parameter_annotations at %d", calc_num_parameters);
2639         // propagate failure back to caller
2640         return false;
2641       }
2642     }
2643     assert(num_parameters == calc_num_parameters, "sanity check");
2644   }
2645 
2646   return true;
2647 } // end rewrite_cp_refs_in_methods_parameter_annotations()
2648 
2649 
2650 // Rewrite constant pool references in a methods_default_annotations
2651 // field. This "structure" is adapted from the AnnotationDefault_attribute
2652 // that is described in section 4.8.19 of the 2nd-edition of the VM spec:
2653 //
2654 // methods_default_annotations_typeArray {
2655 //   element_value default_value;
2656 // }
2657 //
2658 bool VM_RedefineClasses::rewrite_cp_refs_in_methods_default_annotations(
2659        InstanceKlass* scratch_class) {
2660 
2661   for (int i = 0; i < scratch_class->methods()->length(); i++) {
2662     Method* m = scratch_class->methods()->at(i);
2663     AnnotationArray* method_default_annotations = m->constMethod()->default_annotations();
2664     if (method_default_annotations == nullptr
2665         || method_default_annotations->length() == 0) {
2666       // this method does not have any default annotations so skip it
2667       continue;
2668     }
2669 
2670     int byte_i = 0;  // byte index into method_default_annotations
2671 
2672     if (!rewrite_cp_refs_in_element_value(
2673            method_default_annotations, byte_i)) {
2674       log_debug(redefine, class, annotation)("bad default element_value at %d", i);
2675       // propagate failure back to caller
2676       return false;
2677     }
2678   }
2679 
2680   return true;
2681 } // end rewrite_cp_refs_in_methods_default_annotations()
2682 
2683 
2684 // Rewrite constant pool references in a class_type_annotations field.
2685 bool VM_RedefineClasses::rewrite_cp_refs_in_class_type_annotations(
2686        InstanceKlass* scratch_class) {
2687 
2688   AnnotationArray* class_type_annotations = scratch_class->class_type_annotations();
2689   if (class_type_annotations == nullptr || class_type_annotations->length() == 0) {
2690     // no class_type_annotations so nothing to do
2691     return true;
2692   }
2693 
2694   log_debug(redefine, class, annotation)("class_type_annotations length=%d", class_type_annotations->length());
2695 
2696   int byte_i = 0;  // byte index into class_type_annotations
2697   return rewrite_cp_refs_in_type_annotations_typeArray(class_type_annotations,
2698       byte_i, "ClassFile");
2699 } // end rewrite_cp_refs_in_class_type_annotations()
2700 
2701 
2702 // Rewrite constant pool references in a fields_type_annotations field.
2703 bool VM_RedefineClasses::rewrite_cp_refs_in_fields_type_annotations(InstanceKlass* scratch_class) {
2704 
2705   Array<AnnotationArray*>* fields_type_annotations = scratch_class->fields_type_annotations();
2706   if (fields_type_annotations == nullptr || fields_type_annotations->length() == 0) {
2707     // no fields_type_annotations so nothing to do
2708     return true;
2709   }
2710 
2711   log_debug(redefine, class, annotation)("fields_type_annotations length=%d", fields_type_annotations->length());
2712 
2713   for (int i = 0; i < fields_type_annotations->length(); i++) {
2714     AnnotationArray* field_type_annotations = fields_type_annotations->at(i);
2715     if (field_type_annotations == nullptr || field_type_annotations->length() == 0) {
2716       // this field does not have any annotations so skip it
2717       continue;
2718     }
2719 
2720     int byte_i = 0;  // byte index into field_type_annotations
2721     if (!rewrite_cp_refs_in_type_annotations_typeArray(field_type_annotations,
2722            byte_i, "field_info")) {
2723       log_debug(redefine, class, annotation)("bad field_type_annotations at %d", i);
2724       // propagate failure back to caller
2725       return false;
2726     }
2727   }
2728 
2729   return true;
2730 } // end rewrite_cp_refs_in_fields_type_annotations()
2731 
2732 
2733 // Rewrite constant pool references in a methods_type_annotations field.
2734 bool VM_RedefineClasses::rewrite_cp_refs_in_methods_type_annotations(
2735        InstanceKlass* scratch_class) {
2736 
2737   for (int i = 0; i < scratch_class->methods()->length(); i++) {
2738     Method* m = scratch_class->methods()->at(i);
2739     AnnotationArray* method_type_annotations = m->constMethod()->type_annotations();
2740 
2741     if (method_type_annotations == nullptr || method_type_annotations->length() == 0) {
2742       // this method does not have any annotations so skip it
2743       continue;
2744     }
2745 
2746     log_debug(redefine, class, annotation)("methods type_annotations length=%d", method_type_annotations->length());
2747 
2748     int byte_i = 0;  // byte index into method_type_annotations
2749     if (!rewrite_cp_refs_in_type_annotations_typeArray(method_type_annotations,
2750            byte_i, "method_info")) {
2751       log_debug(redefine, class, annotation)("bad method_type_annotations at %d", i);
2752       // propagate failure back to caller
2753       return false;
2754     }
2755   }
2756 
2757   return true;
2758 } // end rewrite_cp_refs_in_methods_type_annotations()
2759 
2760 
2761 // Rewrite constant pool references in a type_annotations
2762 // field. This "structure" is adapted from the
2763 // RuntimeVisibleTypeAnnotations_attribute described in
2764 // section 4.7.20 of the Java SE 8 Edition of the VM spec:
2765 //
2766 // type_annotations_typeArray {
2767 //   u2              num_annotations;
2768 //   type_annotation annotations[num_annotations];
2769 // }
2770 //
2771 bool VM_RedefineClasses::rewrite_cp_refs_in_type_annotations_typeArray(
2772        AnnotationArray* type_annotations_typeArray, int &byte_i_ref,
2773        const char * location_mesg) {
2774 
2775   if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
2776     // not enough room for num_annotations field
2777     log_debug(redefine, class, annotation)("length() is too small for num_annotations field");
2778     return false;
2779   }
2780 
2781   u2 num_annotations = Bytes::get_Java_u2((address)
2782                          type_annotations_typeArray->adr_at(byte_i_ref));
2783   byte_i_ref += 2;
2784 
2785   log_debug(redefine, class, annotation)("num_type_annotations=%d", num_annotations);
2786 
2787   int calc_num_annotations = 0;
2788   for (; calc_num_annotations < num_annotations; calc_num_annotations++) {
2789     if (!rewrite_cp_refs_in_type_annotation_struct(type_annotations_typeArray,
2790            byte_i_ref, location_mesg)) {
2791       log_debug(redefine, class, annotation)("bad type_annotation_struct at %d", calc_num_annotations);
2792       // propagate failure back to caller
2793       return false;
2794     }
2795   }
2796   assert(num_annotations == calc_num_annotations, "sanity check");
2797 
2798   if (byte_i_ref != type_annotations_typeArray->length()) {
2799     log_debug(redefine, class, annotation)
2800       ("read wrong amount of bytes at end of processing type_annotations_typeArray (%d of %d bytes were read)",
2801        byte_i_ref, type_annotations_typeArray->length());
2802     return false;
2803   }
2804 
2805   return true;
2806 } // end rewrite_cp_refs_in_type_annotations_typeArray()
2807 
2808 
2809 // Rewrite constant pool references in a type_annotation
2810 // field. This "structure" is adapted from the
2811 // RuntimeVisibleTypeAnnotations_attribute described in
2812 // section 4.7.20 of the Java SE 8 Edition of the VM spec:
2813 //
2814 // type_annotation {
2815 //   u1 target_type;
2816 //   union {
2817 //     type_parameter_target;
2818 //     supertype_target;
2819 //     type_parameter_bound_target;
2820 //     empty_target;
2821 //     method_formal_parameter_target;
2822 //     throws_target;
2823 //     localvar_target;
2824 //     catch_target;
2825 //     offset_target;
2826 //     type_argument_target;
2827 //   } target_info;
2828 //   type_path target_path;
2829 //   annotation anno;
2830 // }
2831 //
2832 bool VM_RedefineClasses::rewrite_cp_refs_in_type_annotation_struct(
2833        AnnotationArray* type_annotations_typeArray, int &byte_i_ref,
2834        const char * location_mesg) {
2835 
2836   if (!skip_type_annotation_target(type_annotations_typeArray,
2837          byte_i_ref, location_mesg)) {
2838     return false;
2839   }
2840 
2841   if (!skip_type_annotation_type_path(type_annotations_typeArray, byte_i_ref)) {
2842     return false;
2843   }
2844 
2845   if (!rewrite_cp_refs_in_annotation_struct(type_annotations_typeArray, byte_i_ref)) {
2846     return false;
2847   }
2848 
2849   return true;
2850 } // end rewrite_cp_refs_in_type_annotation_struct()
2851 
2852 
2853 // Read, verify and skip over the target_type and target_info part
2854 // so that rewriting can continue in the later parts of the struct.
2855 //
2856 // u1 target_type;
2857 // union {
2858 //   type_parameter_target;
2859 //   supertype_target;
2860 //   type_parameter_bound_target;
2861 //   empty_target;
2862 //   method_formal_parameter_target;
2863 //   throws_target;
2864 //   localvar_target;
2865 //   catch_target;
2866 //   offset_target;
2867 //   type_argument_target;
2868 // } target_info;
2869 //
2870 bool VM_RedefineClasses::skip_type_annotation_target(
2871        AnnotationArray* type_annotations_typeArray, int &byte_i_ref,
2872        const char * location_mesg) {
2873 
2874   if ((byte_i_ref + 1) > type_annotations_typeArray->length()) {
2875     // not enough room for a target_type let alone the rest of a type_annotation
2876     log_debug(redefine, class, annotation)("length() is too small for a target_type");
2877     return false;
2878   }
2879 
2880   u1 target_type = type_annotations_typeArray->at(byte_i_ref);
2881   byte_i_ref += 1;
2882   log_debug(redefine, class, annotation)("target_type=0x%.2x", target_type);
2883   log_debug(redefine, class, annotation)("location=%s", location_mesg);
2884 
2885   // Skip over target_info
2886   switch (target_type) {
2887     case 0x00:
2888     // kind: type parameter declaration of generic class or interface
2889     // location: ClassFile
2890     case 0x01:
2891     // kind: type parameter declaration of generic method or constructor
2892     // location: method_info
2893 
2894     {
2895       // struct:
2896       // type_parameter_target {
2897       //   u1 type_parameter_index;
2898       // }
2899       //
2900       if ((byte_i_ref + 1) > type_annotations_typeArray->length()) {
2901         log_debug(redefine, class, annotation)("length() is too small for a type_parameter_target");
2902         return false;
2903       }
2904 
2905       u1 type_parameter_index = type_annotations_typeArray->at(byte_i_ref);
2906       byte_i_ref += 1;
2907 
2908       log_debug(redefine, class, annotation)("type_parameter_target: type_parameter_index=%d", type_parameter_index);
2909     } break;
2910 
2911     case 0x10:
2912     // kind: type in extends clause of class or interface declaration
2913     //       or in implements clause of interface declaration
2914     // location: ClassFile
2915 
2916     {
2917       // struct:
2918       // supertype_target {
2919       //   u2 supertype_index;
2920       // }
2921       //
2922       if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
2923         log_debug(redefine, class, annotation)("length() is too small for a supertype_target");
2924         return false;
2925       }
2926 
2927       u2 supertype_index = Bytes::get_Java_u2((address)
2928                              type_annotations_typeArray->adr_at(byte_i_ref));
2929       byte_i_ref += 2;
2930 
2931       log_debug(redefine, class, annotation)("supertype_target: supertype_index=%d", supertype_index);
2932     } break;
2933 
2934     case 0x11:
2935     // kind: type in bound of type parameter declaration of generic class or interface
2936     // location: ClassFile
2937     case 0x12:
2938     // kind: type in bound of type parameter declaration of generic method or constructor
2939     // location: method_info
2940 
2941     {
2942       // struct:
2943       // type_parameter_bound_target {
2944       //   u1 type_parameter_index;
2945       //   u1 bound_index;
2946       // }
2947       //
2948       if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
2949         log_debug(redefine, class, annotation)("length() is too small for a type_parameter_bound_target");
2950         return false;
2951       }
2952 
2953       u1 type_parameter_index = type_annotations_typeArray->at(byte_i_ref);
2954       byte_i_ref += 1;
2955       u1 bound_index = type_annotations_typeArray->at(byte_i_ref);
2956       byte_i_ref += 1;
2957 
2958       log_debug(redefine, class, annotation)
2959         ("type_parameter_bound_target: type_parameter_index=%d, bound_index=%d", type_parameter_index, bound_index);
2960     } break;
2961 
2962     case 0x13:
2963     // kind: type in field declaration
2964     // location: field_info
2965     case 0x14:
2966     // kind: return type of method, or type of newly constructed object
2967     // location: method_info
2968     case 0x15:
2969     // kind: receiver type of method or constructor
2970     // location: method_info
2971 
2972     {
2973       // struct:
2974       // empty_target {
2975       // }
2976       //
2977       log_debug(redefine, class, annotation)("empty_target");
2978     } break;
2979 
2980     case 0x16:
2981     // kind: type in formal parameter declaration of method, constructor, or lambda expression
2982     // location: method_info
2983 
2984     {
2985       // struct:
2986       // formal_parameter_target {
2987       //   u1 formal_parameter_index;
2988       // }
2989       //
2990       if ((byte_i_ref + 1) > type_annotations_typeArray->length()) {
2991         log_debug(redefine, class, annotation)("length() is too small for a formal_parameter_target");
2992         return false;
2993       }
2994 
2995       u1 formal_parameter_index = type_annotations_typeArray->at(byte_i_ref);
2996       byte_i_ref += 1;
2997 
2998       log_debug(redefine, class, annotation)
2999         ("formal_parameter_target: formal_parameter_index=%d", formal_parameter_index);
3000     } break;
3001 
3002     case 0x17:
3003     // kind: type in throws clause of method or constructor
3004     // location: method_info
3005 
3006     {
3007       // struct:
3008       // throws_target {
3009       //   u2 throws_type_index
3010       // }
3011       //
3012       if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
3013         log_debug(redefine, class, annotation)("length() is too small for a throws_target");
3014         return false;
3015       }
3016 
3017       u2 throws_type_index = Bytes::get_Java_u2((address)
3018                                type_annotations_typeArray->adr_at(byte_i_ref));
3019       byte_i_ref += 2;
3020 
3021       log_debug(redefine, class, annotation)("throws_target: throws_type_index=%d", throws_type_index);
3022     } break;
3023 
3024     case 0x40:
3025     // kind: type in local variable declaration
3026     // location: Code
3027     case 0x41:
3028     // kind: type in resource variable declaration
3029     // location: Code
3030 
3031     {
3032       // struct:
3033       // localvar_target {
3034       //   u2 table_length;
3035       //   struct {
3036       //     u2 start_pc;
3037       //     u2 length;
3038       //     u2 index;
3039       //   } table[table_length];
3040       // }
3041       //
3042       if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
3043         // not enough room for a table_length let alone the rest of a localvar_target
3044         log_debug(redefine, class, annotation)("length() is too small for a localvar_target table_length");
3045         return false;
3046       }
3047 
3048       u2 table_length = Bytes::get_Java_u2((address)
3049                           type_annotations_typeArray->adr_at(byte_i_ref));
3050       byte_i_ref += 2;
3051 
3052       log_debug(redefine, class, annotation)("localvar_target: table_length=%d", table_length);
3053 
3054       int table_struct_size = 2 + 2 + 2; // 3 u2 variables per table entry
3055       int table_size = table_length * table_struct_size;
3056 
3057       if ((byte_i_ref + table_size) > type_annotations_typeArray->length()) {
3058         // not enough room for a table
3059         log_debug(redefine, class, annotation)("length() is too small for a table array of length %d", table_length);
3060         return false;
3061       }
3062 
3063       // Skip over table
3064       byte_i_ref += table_size;
3065     } break;
3066 
3067     case 0x42:
3068     // kind: type in exception parameter declaration
3069     // location: Code
3070 
3071     {
3072       // struct:
3073       // catch_target {
3074       //   u2 exception_table_index;
3075       // }
3076       //
3077       if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
3078         log_debug(redefine, class, annotation)("length() is too small for a catch_target");
3079         return false;
3080       }
3081 
3082       u2 exception_table_index = Bytes::get_Java_u2((address)
3083                                    type_annotations_typeArray->adr_at(byte_i_ref));
3084       byte_i_ref += 2;
3085 
3086       log_debug(redefine, class, annotation)("catch_target: exception_table_index=%d", exception_table_index);
3087     } break;
3088 
3089     case 0x43:
3090     // kind: type in instanceof expression
3091     // location: Code
3092     case 0x44:
3093     // kind: type in new expression
3094     // location: Code
3095     case 0x45:
3096     // kind: type in method reference expression using ::new
3097     // location: Code
3098     case 0x46:
3099     // kind: type in method reference expression using ::Identifier
3100     // location: Code
3101 
3102     {
3103       // struct:
3104       // offset_target {
3105       //   u2 offset;
3106       // }
3107       //
3108       if ((byte_i_ref + 2) > type_annotations_typeArray->length()) {
3109         log_debug(redefine, class, annotation)("length() is too small for a offset_target");
3110         return false;
3111       }
3112 
3113       u2 offset = Bytes::get_Java_u2((address)
3114                     type_annotations_typeArray->adr_at(byte_i_ref));
3115       byte_i_ref += 2;
3116 
3117       log_debug(redefine, class, annotation)("offset_target: offset=%d", offset);
3118     } break;
3119 
3120     case 0x47:
3121     // kind: type in cast expression
3122     // location: Code
3123     case 0x48:
3124     // kind: type argument for generic constructor in new expression or
3125     //       explicit constructor invocation statement
3126     // location: Code
3127     case 0x49:
3128     // kind: type argument for generic method in method invocation expression
3129     // location: Code
3130     case 0x4A:
3131     // kind: type argument for generic constructor in method reference expression using ::new
3132     // location: Code
3133     case 0x4B:
3134     // kind: type argument for generic method in method reference expression using ::Identifier
3135     // location: Code
3136 
3137     {
3138       // struct:
3139       // type_argument_target {
3140       //   u2 offset;
3141       //   u1 type_argument_index;
3142       // }
3143       //
3144       if ((byte_i_ref + 3) > type_annotations_typeArray->length()) {
3145         log_debug(redefine, class, annotation)("length() is too small for a type_argument_target");
3146         return false;
3147       }
3148 
3149       u2 offset = Bytes::get_Java_u2((address)
3150                     type_annotations_typeArray->adr_at(byte_i_ref));
3151       byte_i_ref += 2;
3152       u1 type_argument_index = type_annotations_typeArray->at(byte_i_ref);
3153       byte_i_ref += 1;
3154 
3155       log_debug(redefine, class, annotation)
3156         ("type_argument_target: offset=%d, type_argument_index=%d", offset, type_argument_index);
3157     } break;
3158 
3159     default:
3160       log_debug(redefine, class, annotation)("unknown target_type");
3161 #ifdef ASSERT
3162       ShouldNotReachHere();
3163 #endif
3164       return false;
3165   }
3166 
3167   return true;
3168 } // end skip_type_annotation_target()
3169 
3170 
3171 // Read, verify and skip over the type_path part so that rewriting
3172 // can continue in the later parts of the struct.
3173 //
3174 // type_path {
3175 //   u1 path_length;
3176 //   {
3177 //     u1 type_path_kind;
3178 //     u1 type_argument_index;
3179 //   } path[path_length];
3180 // }
3181 //
3182 bool VM_RedefineClasses::skip_type_annotation_type_path(
3183        AnnotationArray* type_annotations_typeArray, int &byte_i_ref) {
3184 
3185   if ((byte_i_ref + 1) > type_annotations_typeArray->length()) {
3186     // not enough room for a path_length let alone the rest of the type_path
3187     log_debug(redefine, class, annotation)("length() is too small for a type_path");
3188     return false;
3189   }
3190 
3191   u1 path_length = type_annotations_typeArray->at(byte_i_ref);
3192   byte_i_ref += 1;
3193 
3194   log_debug(redefine, class, annotation)("type_path: path_length=%d", path_length);
3195 
3196   int calc_path_length = 0;
3197   for (; calc_path_length < path_length; calc_path_length++) {
3198     if ((byte_i_ref + 1 + 1) > type_annotations_typeArray->length()) {
3199       // not enough room for a path
3200       log_debug(redefine, class, annotation)
3201         ("length() is too small for path entry %d of %d", calc_path_length, path_length);
3202       return false;
3203     }
3204 
3205     u1 type_path_kind = type_annotations_typeArray->at(byte_i_ref);
3206     byte_i_ref += 1;
3207     u1 type_argument_index = type_annotations_typeArray->at(byte_i_ref);
3208     byte_i_ref += 1;
3209 
3210     log_debug(redefine, class, annotation)
3211       ("type_path: path[%d]: type_path_kind=%d, type_argument_index=%d",
3212        calc_path_length, type_path_kind, type_argument_index);
3213 
3214     if (type_path_kind > 3 || (type_path_kind != 3 && type_argument_index != 0)) {
3215       // not enough room for a path
3216       log_debug(redefine, class, annotation)("inconsistent type_path values");
3217       return false;
3218     }
3219   }
3220   assert(path_length == calc_path_length, "sanity check");
3221 
3222   return true;
3223 } // end skip_type_annotation_type_path()
3224 
3225 
3226 // Rewrite constant pool references in the method's stackmap table.
3227 // These "structures" are adapted from the StackMapTable_attribute that
3228 // is described in section 4.8.4 of the 6.0 version of the VM spec
3229 // (dated 2005.10.26):
3230 // file:///net/quincunx.sfbay/export/gbracha/ClassFile-Java6.pdf
3231 //
3232 // stack_map {
3233 //   u2 number_of_entries;
3234 //   stack_map_frame entries[number_of_entries];
3235 // }
3236 //
3237 void VM_RedefineClasses::rewrite_cp_refs_in_stack_map_table(
3238        const methodHandle& method) {
3239 
3240   if (!method->has_stackmap_table()) {
3241     return;
3242   }
3243 
3244   AnnotationArray* stackmap_data = method->stackmap_data();
3245   address stackmap_p = (address)stackmap_data->adr_at(0);
3246   address stackmap_end = stackmap_p + stackmap_data->length();
3247 
3248   assert(stackmap_p + 2 <= stackmap_end, "no room for number_of_entries");
3249   u2 number_of_entries = Bytes::get_Java_u2(stackmap_p);
3250   stackmap_p += 2;
3251 
3252   log_debug(redefine, class, stackmap)("number_of_entries=%u", number_of_entries);
3253 
3254   // walk through each stack_map_frame
3255   u2 calc_number_of_entries = 0;
3256   for (; calc_number_of_entries < number_of_entries; calc_number_of_entries++) {
3257     // The stack_map_frame structure is a u1 frame_type followed by
3258     // 0 or more bytes of data:
3259     //
3260     // union stack_map_frame {
3261     //   same_frame;
3262     //   same_locals_1_stack_item_frame;
3263     //   same_locals_1_stack_item_frame_extended;
3264     //   chop_frame;
3265     //   same_frame_extended;
3266     //   append_frame;
3267     //   full_frame;
3268     // }
3269 
3270     assert(stackmap_p + 1 <= stackmap_end, "no room for frame_type");
3271     u1 frame_type = *stackmap_p;
3272     stackmap_p++;
3273 
3274     // same_frame {
3275     //   u1 frame_type = SAME; /* 0-63 */
3276     // }
3277     if (frame_type <= 63) {
3278       // nothing more to do for same_frame
3279     }
3280 
3281     // same_locals_1_stack_item_frame {
3282     //   u1 frame_type = SAME_LOCALS_1_STACK_ITEM; /* 64-127 */
3283     //   verification_type_info stack[1];
3284     // }
3285     else if (frame_type >= 64 && frame_type <= 127) {
3286       rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
3287         calc_number_of_entries, frame_type);
3288     }
3289 
3290     // reserved for future use
3291     else if (frame_type >= 128 && frame_type <= 246) {
3292       // nothing more to do for reserved frame_types
3293     }
3294 
3295     // same_locals_1_stack_item_frame_extended {
3296     //   u1 frame_type = SAME_LOCALS_1_STACK_ITEM_EXTENDED; /* 247 */
3297     //   u2 offset_delta;
3298     //   verification_type_info stack[1];
3299     // }
3300     else if (frame_type == 247) {
3301       stackmap_p += 2;
3302       rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
3303         calc_number_of_entries, frame_type);
3304     }
3305 
3306     // chop_frame {
3307     //   u1 frame_type = CHOP; /* 248-250 */
3308     //   u2 offset_delta;
3309     // }
3310     else if (frame_type >= 248 && frame_type <= 250) {
3311       stackmap_p += 2;
3312     }
3313 
3314     // same_frame_extended {
3315     //   u1 frame_type = SAME_FRAME_EXTENDED; /* 251*/
3316     //   u2 offset_delta;
3317     // }
3318     else if (frame_type == 251) {
3319       stackmap_p += 2;
3320     }
3321 
3322     // append_frame {
3323     //   u1 frame_type = APPEND; /* 252-254 */
3324     //   u2 offset_delta;
3325     //   verification_type_info locals[frame_type - 251];
3326     // }
3327     else if (frame_type >= 252 && frame_type <= 254) {
3328       assert(stackmap_p + 2 <= stackmap_end,
3329         "no room for offset_delta");
3330       stackmap_p += 2;
3331       u1 len = frame_type - 251;
3332       for (u1 i = 0; i < len; i++) {
3333         rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
3334           calc_number_of_entries, frame_type);
3335       }
3336     }
3337 
3338     // full_frame {
3339     //   u1 frame_type = FULL_FRAME; /* 255 */
3340     //   u2 offset_delta;
3341     //   u2 number_of_locals;
3342     //   verification_type_info locals[number_of_locals];
3343     //   u2 number_of_stack_items;
3344     //   verification_type_info stack[number_of_stack_items];
3345     // }
3346     else if (frame_type == 255) {
3347       assert(stackmap_p + 2 + 2 <= stackmap_end,
3348         "no room for smallest full_frame");
3349       stackmap_p += 2;
3350 
3351       u2 number_of_locals = Bytes::get_Java_u2(stackmap_p);
3352       stackmap_p += 2;
3353 
3354       for (u2 locals_i = 0; locals_i < number_of_locals; locals_i++) {
3355         rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
3356           calc_number_of_entries, frame_type);
3357       }
3358 
3359       // Use the largest size for the number_of_stack_items, but only get
3360       // the right number of bytes.
3361       u2 number_of_stack_items = Bytes::get_Java_u2(stackmap_p);
3362       stackmap_p += 2;
3363 
3364       for (u2 stack_i = 0; stack_i < number_of_stack_items; stack_i++) {
3365         rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
3366           calc_number_of_entries, frame_type);
3367       }
3368     }
3369   } // end while there is a stack_map_frame
3370   assert(number_of_entries == calc_number_of_entries, "sanity check");
3371 } // end rewrite_cp_refs_in_stack_map_table()
3372 
3373 
3374 // Rewrite constant pool references in the verification type info
3375 // portion of the method's stackmap table. These "structures" are
3376 // adapted from the StackMapTable_attribute that is described in
3377 // section 4.8.4 of the 6.0 version of the VM spec (dated 2005.10.26):
3378 // file:///net/quincunx.sfbay/export/gbracha/ClassFile-Java6.pdf
3379 //
3380 // The verification_type_info structure is a u1 tag followed by 0 or
3381 // more bytes of data:
3382 //
3383 // union verification_type_info {
3384 //   Top_variable_info;
3385 //   Integer_variable_info;
3386 //   Float_variable_info;
3387 //   Long_variable_info;
3388 //   Double_variable_info;
3389 //   Null_variable_info;
3390 //   UninitializedThis_variable_info;
3391 //   Object_variable_info;
3392 //   Uninitialized_variable_info;
3393 // }
3394 //
3395 void VM_RedefineClasses::rewrite_cp_refs_in_verification_type_info(
3396        address& stackmap_p_ref, address stackmap_end, u2 frame_i,
3397        u1 frame_type) {
3398 
3399   assert(stackmap_p_ref + 1 <= stackmap_end, "no room for tag");
3400   u1 tag = *stackmap_p_ref;
3401   stackmap_p_ref++;
3402 
3403   switch (tag) {
3404   // Top_variable_info {
3405   //   u1 tag = ITEM_Top; /* 0 */
3406   // }
3407   // verificationType.hpp has zero as ITEM_Bogus instead of ITEM_Top
3408   case 0:  // fall through
3409 
3410   // Integer_variable_info {
3411   //   u1 tag = ITEM_Integer; /* 1 */
3412   // }
3413   case ITEM_Integer:  // fall through
3414 
3415   // Float_variable_info {
3416   //   u1 tag = ITEM_Float; /* 2 */
3417   // }
3418   case ITEM_Float:  // fall through
3419 
3420   // Double_variable_info {
3421   //   u1 tag = ITEM_Double; /* 3 */
3422   // }
3423   case ITEM_Double:  // fall through
3424 
3425   // Long_variable_info {
3426   //   u1 tag = ITEM_Long; /* 4 */
3427   // }
3428   case ITEM_Long:  // fall through
3429 
3430   // Null_variable_info {
3431   //   u1 tag = ITEM_Null; /* 5 */
3432   // }
3433   case ITEM_Null:  // fall through
3434 
3435   // UninitializedThis_variable_info {
3436   //   u1 tag = ITEM_UninitializedThis; /* 6 */
3437   // }
3438   case ITEM_UninitializedThis:
3439     // nothing more to do for the above tag types
3440     break;
3441 
3442   // Object_variable_info {
3443   //   u1 tag = ITEM_Object; /* 7 */
3444   //   u2 cpool_index;
3445   // }
3446   case ITEM_Object:
3447   {
3448     assert(stackmap_p_ref + 2 <= stackmap_end, "no room for cpool_index");
3449     u2 cpool_index = Bytes::get_Java_u2(stackmap_p_ref);
3450     u2 new_cp_index = find_new_index(cpool_index);
3451     if (new_cp_index != 0) {
3452       log_debug(redefine, class, stackmap)("mapped old cpool_index=%d", cpool_index);
3453       Bytes::put_Java_u2(stackmap_p_ref, new_cp_index);
3454       cpool_index = new_cp_index;
3455     }
3456     stackmap_p_ref += 2;
3457 
3458     log_debug(redefine, class, stackmap)
3459       ("frame_i=%u, frame_type=%u, cpool_index=%d", frame_i, frame_type, cpool_index);
3460   } break;
3461 
3462   // Uninitialized_variable_info {
3463   //   u1 tag = ITEM_Uninitialized; /* 8 */
3464   //   u2 offset;
3465   // }
3466   case ITEM_Uninitialized:
3467     assert(stackmap_p_ref + 2 <= stackmap_end, "no room for offset");
3468     stackmap_p_ref += 2;
3469     break;
3470 
3471   default:
3472     log_debug(redefine, class, stackmap)("frame_i=%u, frame_type=%u, bad tag=0x%x", frame_i, frame_type, tag);
3473     ShouldNotReachHere();
3474     break;
3475   } // end switch (tag)
3476 } // end rewrite_cp_refs_in_verification_type_info()
3477 
3478 
3479 // Change the constant pool associated with klass scratch_class to scratch_cp.
3480 // scratch_cp_length elements are copied from scratch_cp to a smaller constant pool
3481 // and the smaller constant pool is associated with scratch_class.
3482 void VM_RedefineClasses::set_new_constant_pool(
3483        ClassLoaderData* loader_data,
3484        InstanceKlass* scratch_class, constantPoolHandle scratch_cp,
3485        int scratch_cp_length, TRAPS) {
3486   assert(scratch_cp->length() >= scratch_cp_length, "sanity check");
3487 
3488   // scratch_cp is a merged constant pool and has enough space for a
3489   // worst case merge situation. We want to associate the minimum
3490   // sized constant pool with the klass to save space.
3491   ConstantPool* cp = ConstantPool::allocate(loader_data, scratch_cp_length, CHECK);
3492   constantPoolHandle smaller_cp(THREAD, cp);
3493 
3494   // preserve version() value in the smaller copy
3495   int version = scratch_cp->version();
3496   assert(version != 0, "sanity check");
3497   smaller_cp->set_version(version);
3498 
3499   // attach klass to new constant pool
3500   // reference to the cp holder is needed for copy_operands()
3501   smaller_cp->set_pool_holder(scratch_class);
3502 
3503   smaller_cp->copy_fields(scratch_cp());
3504 
3505   scratch_cp->copy_cp_to(1, scratch_cp_length - 1, smaller_cp, 1, THREAD);
3506   if (HAS_PENDING_EXCEPTION) {
3507     // Exception is handled in the caller
3508     loader_data->add_to_deallocate_list(smaller_cp());
3509     return;
3510   }
3511   scratch_cp = smaller_cp;
3512 
3513   // attach new constant pool to klass
3514   scratch_class->set_constants(scratch_cp());
3515   scratch_cp->initialize_unresolved_klasses(loader_data, CHECK);
3516 
3517   int i;  // for portability
3518 
3519   // update each field in klass to use new constant pool indices as needed
3520   int java_fields;
3521   int injected_fields;
3522   bool update_required = false;
3523   GrowableArray<FieldInfo>* fields = FieldInfoStream::create_FieldInfoArray(scratch_class->fieldinfo_stream(), &java_fields, &injected_fields);
3524   for (int i = 0; i < java_fields; i++) {
3525     FieldInfo* fi = fields->adr_at(i);
3526     jshort cur_index = fi->name_index();
3527     jshort new_index = find_new_index(cur_index);
3528     if (new_index != 0) {
3529       log_trace(redefine, class, constantpool)("field-name_index change: %d to %d", cur_index, new_index);
3530       fi->set_name_index(new_index);
3531       update_required = true;
3532     }
3533     cur_index = fi->signature_index();
3534     new_index = find_new_index(cur_index);
3535     if (new_index != 0) {
3536       log_trace(redefine, class, constantpool)("field-signature_index change: %d to %d", cur_index, new_index);
3537       fi->set_signature_index(new_index);
3538       update_required = true;
3539     }
3540     cur_index = fi->initializer_index();
3541     new_index = find_new_index(cur_index);
3542     if (new_index != 0) {
3543       log_trace(redefine, class, constantpool)("field-initval_index change: %d to %d", cur_index, new_index);
3544       fi->set_initializer_index(new_index);
3545       update_required = true;
3546     }
3547     cur_index = fi->generic_signature_index();
3548     new_index = find_new_index(cur_index);
3549     if (new_index != 0) {
3550       log_trace(redefine, class, constantpool)("field-generic_signature change: %d to %d", cur_index, new_index);
3551       fi->set_generic_signature_index(new_index);
3552       update_required = true;
3553     }
3554   }
3555   if (update_required) {
3556     Array<u1>* old_stream = scratch_class->fieldinfo_stream();
3557     assert(fields->length() == (java_fields + injected_fields), "Must be");
3558     Array<u1>* new_fis = FieldInfoStream::create_FieldInfoStream(fields, java_fields, injected_fields, scratch_class->class_loader_data(), CHECK);
3559     scratch_class->set_fieldinfo_stream(new_fis);
3560     MetadataFactory::free_array<u1>(scratch_class->class_loader_data(), old_stream);
3561   }
3562 
3563   // Update constant pool indices in the inner classes info to use
3564   // new constant indices as needed. The inner classes info is a
3565   // quadruple:
3566   // (inner_class_info, outer_class_info, inner_name, inner_access_flags)
3567   InnerClassesIterator iter(scratch_class);
3568   for (; !iter.done(); iter.next()) {
3569     int cur_index = iter.inner_class_info_index();
3570     if (cur_index == 0) {
3571       continue;  // JVM spec. allows null inner class refs so skip it
3572     }
3573     u2 new_index = find_new_index(cur_index);
3574     if (new_index != 0) {
3575       log_trace(redefine, class, constantpool)("inner_class_info change: %d to %d", cur_index, new_index);
3576       iter.set_inner_class_info_index(new_index);
3577     }
3578     cur_index = iter.outer_class_info_index();
3579     new_index = find_new_index(cur_index);
3580     if (new_index != 0) {
3581       log_trace(redefine, class, constantpool)("outer_class_info change: %d to %d", cur_index, new_index);
3582       iter.set_outer_class_info_index(new_index);
3583     }
3584     cur_index = iter.inner_name_index();
3585     new_index = find_new_index(cur_index);
3586     if (new_index != 0) {
3587       log_trace(redefine, class, constantpool)("inner_name change: %d to %d", cur_index, new_index);
3588       iter.set_inner_name_index(new_index);
3589     }
3590   } // end for each inner class
3591 
3592   // Attach each method in klass to the new constant pool and update
3593   // to use new constant pool indices as needed:
3594   Array<Method*>* methods = scratch_class->methods();
3595   for (i = methods->length() - 1; i >= 0; i--) {
3596     methodHandle method(THREAD, methods->at(i));
3597     method->set_constants(scratch_cp());
3598 
3599     u2 new_index = find_new_index(method->name_index());
3600     if (new_index != 0) {
3601       log_trace(redefine, class, constantpool)
3602         ("method-name_index change: %d to %d", method->name_index(), new_index);
3603       method->set_name_index(new_index);
3604     }
3605     new_index = find_new_index(method->signature_index());
3606     if (new_index != 0) {
3607       log_trace(redefine, class, constantpool)
3608         ("method-signature_index change: %d to %d", method->signature_index(), new_index);
3609       method->set_signature_index(new_index);
3610     }
3611     new_index = find_new_index(method->generic_signature_index());
3612     if (new_index != 0) {
3613       log_trace(redefine, class, constantpool)
3614         ("method-generic_signature_index change: %d to %d", method->generic_signature_index(), new_index);
3615       method->constMethod()->set_generic_signature_index(new_index);
3616     }
3617 
3618     // Update constant pool indices in the method's checked exception
3619     // table to use new constant indices as needed.
3620     int cext_length = method->checked_exceptions_length();
3621     if (cext_length > 0) {
3622       CheckedExceptionElement * cext_table =
3623         method->checked_exceptions_start();
3624       for (int j = 0; j < cext_length; j++) {
3625         int cur_index = cext_table[j].class_cp_index;
3626         int new_index = find_new_index(cur_index);
3627         if (new_index != 0) {
3628           log_trace(redefine, class, constantpool)("cext-class_cp_index change: %d to %d", cur_index, new_index);
3629           cext_table[j].class_cp_index = (u2)new_index;
3630         }
3631       } // end for each checked exception table entry
3632     } // end if there are checked exception table entries
3633 
3634     // Update each catch type index in the method's exception table
3635     // to use new constant pool indices as needed. The exception table
3636     // holds quadruple entries of the form:
3637     //   (beg_bci, end_bci, handler_bci, klass_index)
3638 
3639     ExceptionTable ex_table(method());
3640     int ext_length = ex_table.length();
3641 
3642     for (int j = 0; j < ext_length; j ++) {
3643       int cur_index = ex_table.catch_type_index(j);
3644       u2 new_index = find_new_index(cur_index);
3645       if (new_index != 0) {
3646         log_trace(redefine, class, constantpool)("ext-klass_index change: %d to %d", cur_index, new_index);
3647         ex_table.set_catch_type_index(j, new_index);
3648       }
3649     } // end for each exception table entry
3650 
3651     // Update constant pool indices in the method's local variable
3652     // table to use new constant indices as needed. The local variable
3653     // table hold sextuple entries of the form:
3654     // (start_pc, length, name_index, descriptor_index, signature_index, slot)
3655     int lvt_length = method->localvariable_table_length();
3656     if (lvt_length > 0) {
3657       LocalVariableTableElement * lv_table =
3658         method->localvariable_table_start();
3659       for (int j = 0; j < lvt_length; j++) {
3660         int cur_index = lv_table[j].name_cp_index;
3661         int new_index = find_new_index(cur_index);
3662         if (new_index != 0) {
3663           log_trace(redefine, class, constantpool)("lvt-name_cp_index change: %d to %d", cur_index, new_index);
3664           lv_table[j].name_cp_index = (u2)new_index;
3665         }
3666         cur_index = lv_table[j].descriptor_cp_index;
3667         new_index = find_new_index(cur_index);
3668         if (new_index != 0) {
3669           log_trace(redefine, class, constantpool)("lvt-descriptor_cp_index change: %d to %d", cur_index, new_index);
3670           lv_table[j].descriptor_cp_index = (u2)new_index;
3671         }
3672         cur_index = lv_table[j].signature_cp_index;
3673         new_index = find_new_index(cur_index);
3674         if (new_index != 0) {
3675           log_trace(redefine, class, constantpool)("lvt-signature_cp_index change: %d to %d", cur_index, new_index);
3676           lv_table[j].signature_cp_index = (u2)new_index;
3677         }
3678       } // end for each local variable table entry
3679     } // end if there are local variable table entries
3680 
3681     // Update constant pool indices in the method's method_parameters.
3682     int mp_length = method->method_parameters_length();
3683     if (mp_length > 0) {
3684       MethodParametersElement* elem = method->method_parameters_start();
3685       for (int j = 0; j < mp_length; j++) {
3686         const int cp_index = elem[j].name_cp_index;
3687         const int new_cp_index = find_new_index(cp_index);
3688         if (new_cp_index != 0) {
3689           elem[j].name_cp_index = (u2)new_cp_index;
3690         }
3691       }
3692     }
3693 
3694     rewrite_cp_refs_in_stack_map_table(method);
3695   } // end for each method
3696 } // end set_new_constant_pool()
3697 
3698 
3699 // Unevolving classes may point to methods of the_class directly
3700 // from their constant pool caches, itables, and/or vtables. We
3701 // use the ClassLoaderDataGraph::classes_do() facility and this helper
3702 // to fix up these pointers.  MethodData also points to old methods and
3703 // must be cleaned.
3704 
3705 // Adjust cpools and vtables closure
3706 void VM_RedefineClasses::AdjustAndCleanMetadata::do_klass(Klass* k) {
3707 
3708   // This is a very busy routine. We don't want too much tracing
3709   // printed out.
3710   bool trace_name_printed = false;
3711 
3712   // If the class being redefined is java.lang.Object, we need to fix all
3713   // array class vtables also. The _has_redefined_Object flag is global.
3714   // Once the java.lang.Object has been redefined (by the current or one
3715   // of the previous VM_RedefineClasses operations) we have to always
3716   // adjust method entries for array classes.
3717   if (k->is_array_klass() && _has_redefined_Object) {
3718     k->vtable().adjust_method_entries(&trace_name_printed);
3719 
3720   } else if (k->is_instance_klass()) {
3721     HandleMark hm(_thread);
3722     InstanceKlass *ik = InstanceKlass::cast(k);
3723 
3724     // Clean MethodData of this class's methods so they don't refer to
3725     // old methods that are no longer running.
3726     Array<Method*>* methods = ik->methods();
3727     int num_methods = methods->length();
3728     for (int index = 0; index < num_methods; ++index) {
3729       if (methods->at(index)->method_data() != nullptr) {
3730         methods->at(index)->method_data()->clean_weak_method_links();
3731       }
3732     }
3733 
3734     // Adjust all vtables, default methods and itables, to clean out old methods.
3735     ResourceMark rm(_thread);
3736     if (ik->vtable_length() > 0) {
3737       ik->vtable().adjust_method_entries(&trace_name_printed);
3738       ik->adjust_default_methods(&trace_name_printed);
3739     }
3740 
3741     if (ik->itable_length() > 0) {
3742       ik->itable().adjust_method_entries(&trace_name_printed);
3743     }
3744 
3745     // The constant pools in other classes (other_cp) can refer to
3746     // old methods.  We have to update method information in
3747     // other_cp's cache. If other_cp has a previous version, then we
3748     // have to repeat the process for each previous version. The
3749     // constant pool cache holds the Method*s for non-virtual
3750     // methods and for virtual, final methods.
3751     //
3752     // Special case: if the current class is being redefined by the current
3753     // VM_RedefineClasses operation, then new_cp has already been attached
3754     // to the_class and old_cp has already been added as a previous version.
3755     // The new_cp doesn't have any cached references to old methods so it
3756     // doesn't need to be updated and we could optimize by skipping it.
3757     // However, the current class can be marked as being redefined by another
3758     // VM_RedefineClasses operation which has already executed its doit_prologue
3759     // and needs cpcache method entries adjusted. For simplicity, the cpcache
3760     // update is done unconditionally. It should result in doing nothing for
3761     // classes being redefined by the current VM_RedefineClasses operation.
3762     // Method entries in the previous version(s) are adjusted as well.
3763     ConstantPoolCache* cp_cache;
3764 
3765     // this klass' constant pool cache may need adjustment
3766     ConstantPool* other_cp = ik->constants();
3767     cp_cache = other_cp->cache();
3768     if (cp_cache != nullptr) {
3769       cp_cache->adjust_method_entries(&trace_name_printed);
3770     }
3771 
3772     // the previous versions' constant pool caches may need adjustment
3773     for (InstanceKlass* pv_node = ik->previous_versions();
3774          pv_node != nullptr;
3775          pv_node = pv_node->previous_versions()) {
3776       cp_cache = pv_node->constants()->cache();
3777       if (cp_cache != nullptr) {
3778         cp_cache->adjust_method_entries(&trace_name_printed);
3779       }
3780     }
3781   }
3782 }
3783 
3784 void VM_RedefineClasses::update_jmethod_ids() {
3785   for (int j = 0; j < _matching_methods_length; ++j) {
3786     Method* old_method = _matching_old_methods[j];
3787     jmethodID jmid = old_method->find_jmethod_id_or_null();
3788     if (jmid != nullptr) {
3789       // There is a jmethodID, change it to point to the new method
3790       Method* new_method = _matching_new_methods[j];
3791       Method::change_method_associated_with_jmethod_id(jmid, new_method);
3792       assert(Method::resolve_jmethod_id(jmid) == _matching_new_methods[j],
3793              "should be replaced");
3794     }
3795   }
3796 }
3797 
3798 int VM_RedefineClasses::check_methods_and_mark_as_obsolete() {
3799   int emcp_method_count = 0;
3800   int obsolete_count = 0;
3801   int old_index = 0;
3802   for (int j = 0; j < _matching_methods_length; ++j, ++old_index) {
3803     Method* old_method = _matching_old_methods[j];
3804     Method* new_method = _matching_new_methods[j];
3805     Method* old_array_method;
3806 
3807     // Maintain an old_index into the _old_methods array by skipping
3808     // deleted methods
3809     while ((old_array_method = _old_methods->at(old_index)) != old_method) {
3810       ++old_index;
3811     }
3812 
3813     if (MethodComparator::methods_EMCP(old_method, new_method)) {
3814       // The EMCP definition from JSR-163 requires the bytecodes to be
3815       // the same with the exception of constant pool indices which may
3816       // differ. However, the constants referred to by those indices
3817       // must be the same.
3818       //
3819       // We use methods_EMCP() for comparison since constant pool
3820       // merging can remove duplicate constant pool entries that were
3821       // present in the old method and removed from the rewritten new
3822       // method. A faster binary comparison function would consider the
3823       // old and new methods to be different when they are actually
3824       // EMCP.
3825       //
3826       // The old and new methods are EMCP and you would think that we
3827       // could get rid of one of them here and now and save some space.
3828       // However, the concept of EMCP only considers the bytecodes and
3829       // the constant pool entries in the comparison. Other things,
3830       // e.g., the line number table (LNT) or the local variable table
3831       // (LVT) don't count in the comparison. So the new (and EMCP)
3832       // method can have a new LNT that we need so we can't just
3833       // overwrite the new method with the old method.
3834       //
3835       // When this routine is called, we have already attached the new
3836       // methods to the_class so the old methods are effectively
3837       // overwritten. However, if an old method is still executing,
3838       // then the old method cannot be collected until sometime after
3839       // the old method call has returned. So the overwriting of old
3840       // methods by new methods will save us space except for those
3841       // (hopefully few) old methods that are still executing.
3842       //
3843       // A method refers to a ConstMethod* and this presents another
3844       // possible avenue to space savings. The ConstMethod* in the
3845       // new method contains possibly new attributes (LNT, LVT, etc).
3846       // At first glance, it seems possible to save space by replacing
3847       // the ConstMethod* in the old method with the ConstMethod*
3848       // from the new method. The old and new methods would share the
3849       // same ConstMethod* and we would save the space occupied by
3850       // the old ConstMethod*. However, the ConstMethod* contains
3851       // a back reference to the containing method. Sharing the
3852       // ConstMethod* between two methods could lead to confusion in
3853       // the code that uses the back reference. This would lead to
3854       // brittle code that could be broken in non-obvious ways now or
3855       // in the future.
3856       //
3857       // Another possibility is to copy the ConstMethod* from the new
3858       // method to the old method and then overwrite the new method with
3859       // the old method. Since the ConstMethod* contains the bytecodes
3860       // for the method embedded in the oop, this option would change
3861       // the bytecodes out from under any threads executing the old
3862       // method and make the thread's bcp invalid. Since EMCP requires
3863       // that the bytecodes be the same modulo constant pool indices, it
3864       // is straight forward to compute the correct new bcp in the new
3865       // ConstMethod* from the old bcp in the old ConstMethod*. The
3866       // time consuming part would be searching all the frames in all
3867       // of the threads to find all of the calls to the old method.
3868       //
3869       // It looks like we will have to live with the limited savings
3870       // that we get from effectively overwriting the old methods
3871       // when the new methods are attached to the_class.
3872 
3873       // Count number of methods that are EMCP.  The method will be marked
3874       // old but not obsolete if it is EMCP.
3875       emcp_method_count++;
3876 
3877       // An EMCP method is _not_ obsolete. An obsolete method has a
3878       // different jmethodID than the current method. An EMCP method
3879       // has the same jmethodID as the current method. Having the
3880       // same jmethodID for all EMCP versions of a method allows for
3881       // a consistent view of the EMCP methods regardless of which
3882       // EMCP method you happen to have in hand. For example, a
3883       // breakpoint set in one EMCP method will work for all EMCP
3884       // versions of the method including the current one.
3885     } else {
3886       // mark obsolete methods as such
3887       old_method->set_is_obsolete();
3888       obsolete_count++;
3889 
3890       // obsolete methods need a unique idnum so they become new entries in
3891       // the jmethodID cache in InstanceKlass
3892       assert(old_method->method_idnum() == new_method->method_idnum(), "must match");
3893       u2 num = InstanceKlass::cast(_the_class)->next_method_idnum();
3894       if (num != ConstMethod::UNSET_IDNUM) {
3895         old_method->set_method_idnum(num);
3896       }
3897 
3898       // With tracing we try not to "yack" too much. The position of
3899       // this trace assumes there are fewer obsolete methods than
3900       // EMCP methods.
3901       if (log_is_enabled(Trace, redefine, class, obsolete, mark)) {
3902         ResourceMark rm;
3903         log_trace(redefine, class, obsolete, mark)
3904           ("mark %s(%s) as obsolete", old_method->name()->as_C_string(), old_method->signature()->as_C_string());
3905       }
3906     }
3907     old_method->set_is_old();
3908   }
3909   for (int i = 0; i < _deleted_methods_length; ++i) {
3910     Method* old_method = _deleted_methods[i];
3911 
3912     assert(!old_method->has_vtable_index(),
3913            "cannot delete methods with vtable entries");;
3914 
3915     // Mark all deleted methods as old, obsolete and deleted
3916     old_method->set_is_deleted();
3917     old_method->set_is_old();
3918     old_method->set_is_obsolete();
3919     ++obsolete_count;
3920     // With tracing we try not to "yack" too much. The position of
3921     // this trace assumes there are fewer obsolete methods than
3922     // EMCP methods.
3923     if (log_is_enabled(Trace, redefine, class, obsolete, mark)) {
3924       ResourceMark rm;
3925       log_trace(redefine, class, obsolete, mark)
3926         ("mark deleted %s(%s) as obsolete", old_method->name()->as_C_string(), old_method->signature()->as_C_string());
3927     }
3928   }
3929   assert((emcp_method_count + obsolete_count) == _old_methods->length(),
3930     "sanity check");
3931   log_trace(redefine, class, obsolete, mark)("EMCP_cnt=%d, obsolete_cnt=%d", emcp_method_count, obsolete_count);
3932   return emcp_method_count;
3933 }
3934 
3935 // This internal class transfers the native function registration from old methods
3936 // to new methods.  It is designed to handle both the simple case of unchanged
3937 // native methods and the complex cases of native method prefixes being added and/or
3938 // removed.
3939 // It expects only to be used during the VM_RedefineClasses op (a safepoint).
3940 //
3941 // This class is used after the new methods have been installed in "the_class".
3942 //
3943 // So, for example, the following must be handled.  Where 'm' is a method and
3944 // a number followed by an underscore is a prefix.
3945 //
3946 //                                      Old Name    New Name
3947 // Simple transfer to new method        m       ->  m
3948 // Add prefix                           m       ->  1_m
3949 // Remove prefix                        1_m     ->  m
3950 // Simultaneous add of prefixes         m       ->  3_2_1_m
3951 // Simultaneous removal of prefixes     3_2_1_m ->  m
3952 // Simultaneous add and remove          1_m     ->  2_m
3953 // Same, caused by prefix removal only  3_2_1_m ->  3_2_m
3954 //
3955 class TransferNativeFunctionRegistration {
3956  private:
3957   InstanceKlass* the_class;
3958   int prefix_count;
3959   char** prefixes;
3960 
3961   // Recursively search the binary tree of possibly prefixed method names.
3962   // Iteration could be used if all agents were well behaved. Full tree walk is
3963   // more resilent to agents not cleaning up intermediate methods.
3964   // Branch at each depth in the binary tree is:
3965   //    (1) without the prefix.
3966   //    (2) with the prefix.
3967   // where 'prefix' is the prefix at that 'depth' (first prefix, second prefix,...)
3968   Method* search_prefix_name_space(int depth, char* name_str, size_t name_len,
3969                                      Symbol* signature) {
3970     TempNewSymbol name_symbol = SymbolTable::probe(name_str, (int)name_len);
3971     if (name_symbol != nullptr) {
3972       Method* method = the_class->lookup_method(name_symbol, signature);
3973       if (method != nullptr) {
3974         // Even if prefixed, intermediate methods must exist.
3975         if (method->is_native()) {
3976           // Wahoo, we found a (possibly prefixed) version of the method, return it.
3977           return method;
3978         }
3979         if (depth < prefix_count) {
3980           // Try applying further prefixes (other than this one).
3981           method = search_prefix_name_space(depth+1, name_str, name_len, signature);
3982           if (method != nullptr) {
3983             return method; // found
3984           }
3985 
3986           // Try adding this prefix to the method name and see if it matches
3987           // another method name.
3988           char* prefix = prefixes[depth];
3989           size_t prefix_len = strlen(prefix);
3990           size_t trial_len = name_len + prefix_len;
3991           char* trial_name_str = NEW_RESOURCE_ARRAY(char, trial_len + 1);
3992           strcpy(trial_name_str, prefix);
3993           strcat(trial_name_str, name_str);
3994           method = search_prefix_name_space(depth+1, trial_name_str, trial_len,
3995                                             signature);
3996           if (method != nullptr) {
3997             // If found along this branch, it was prefixed, mark as such
3998             method->set_is_prefixed_native();
3999             return method; // found
4000           }
4001         }
4002       }
4003     }
4004     return nullptr;  // This whole branch bore nothing
4005   }
4006 
4007   // Return the method name with old prefixes stripped away.
4008   char* method_name_without_prefixes(Method* method) {
4009     Symbol* name = method->name();
4010     char* name_str = name->as_utf8();
4011 
4012     // Old prefixing may be defunct, strip prefixes, if any.
4013     for (int i = prefix_count-1; i >= 0; i--) {
4014       char* prefix = prefixes[i];
4015       size_t prefix_len = strlen(prefix);
4016       if (strncmp(prefix, name_str, prefix_len) == 0) {
4017         name_str += prefix_len;
4018       }
4019     }
4020     return name_str;
4021   }
4022 
4023   // Strip any prefixes off the old native method, then try to find a
4024   // (possibly prefixed) new native that matches it.
4025   Method* strip_and_search_for_new_native(Method* method) {
4026     ResourceMark rm;
4027     char* name_str = method_name_without_prefixes(method);
4028     return search_prefix_name_space(0, name_str, strlen(name_str),
4029                                     method->signature());
4030   }
4031 
4032  public:
4033 
4034   // Construct a native method transfer processor for this class.
4035   TransferNativeFunctionRegistration(InstanceKlass* _the_class) {
4036     assert(SafepointSynchronize::is_at_safepoint(), "sanity check");
4037 
4038     the_class = _the_class;
4039     prefixes = JvmtiExport::get_all_native_method_prefixes(&prefix_count);
4040   }
4041 
4042   // Attempt to transfer any of the old or deleted methods that are native
4043   void transfer_registrations(Method** old_methods, int methods_length) {
4044     for (int j = 0; j < methods_length; j++) {
4045       Method* old_method = old_methods[j];
4046 
4047       if (old_method->is_native() && old_method->has_native_function()) {
4048         Method* new_method = strip_and_search_for_new_native(old_method);
4049         if (new_method != nullptr) {
4050           // Actually set the native function in the new method.
4051           // Redefine does not send events (except CFLH), certainly not this
4052           // behind the scenes re-registration.
4053           new_method->set_native_function(old_method->native_function(),
4054                               !Method::native_bind_event_is_interesting);
4055         }
4056       }
4057     }
4058   }
4059 };
4060 
4061 // Don't lose the association between a native method and its JNI function.
4062 void VM_RedefineClasses::transfer_old_native_function_registrations(InstanceKlass* the_class) {
4063   TransferNativeFunctionRegistration transfer(the_class);
4064   transfer.transfer_registrations(_deleted_methods, _deleted_methods_length);
4065   transfer.transfer_registrations(_matching_old_methods, _matching_methods_length);
4066 }
4067 
4068 // Deoptimize all compiled code that depends on the classes redefined.
4069 //
4070 // If the can_redefine_classes capability is obtained in the onload
4071 // phase or 'AlwaysRecordEvolDependencies' is true, then the compiler has
4072 // recorded all dependencies from startup. In that case we need only
4073 // deoptimize and throw away all compiled code that depends on the class.
4074 //
4075 // If can_redefine_classes is obtained sometime after the onload phase
4076 // (and 'AlwaysRecordEvolDependencies' is false) then the dependency
4077 // information may be incomplete. In that case the first call to
4078 // RedefineClasses causes all compiled code to be thrown away. As
4079 // can_redefine_classes has been obtained then all future compilations will
4080 // record dependencies so second and subsequent calls to RedefineClasses
4081 // need only throw away code that depends on the class.
4082 //
4083 
4084 void VM_RedefineClasses::flush_dependent_code() {
4085   assert(SafepointSynchronize::is_at_safepoint(), "sanity check");
4086   assert(JvmtiExport::all_dependencies_are_recorded() || !AlwaysRecordEvolDependencies, "sanity check");
4087 
4088   DeoptimizationScope deopt_scope;
4089 
4090   // This is the first redefinition, mark all the nmethods for deoptimization
4091   if (!JvmtiExport::all_dependencies_are_recorded()) {
4092     CodeCache::mark_all_nmethods_for_evol_deoptimization(&deopt_scope);
4093     log_debug(redefine, class, nmethod)("Marked all nmethods for deopt");
4094   } else {
4095     CodeCache::mark_dependents_for_evol_deoptimization(&deopt_scope);
4096     log_debug(redefine, class, nmethod)("Marked dependent nmethods for deopt");
4097   }
4098 
4099   deopt_scope.deoptimize_marked();
4100 
4101   // From now on we know that the dependency information is complete
4102   JvmtiExport::set_all_dependencies_are_recorded(true);
4103 }
4104 
4105 void VM_RedefineClasses::compute_added_deleted_matching_methods() {
4106   Method* old_method;
4107   Method* new_method;
4108 
4109   _matching_old_methods = NEW_RESOURCE_ARRAY(Method*, _old_methods->length());
4110   _matching_new_methods = NEW_RESOURCE_ARRAY(Method*, _old_methods->length());
4111   _added_methods        = NEW_RESOURCE_ARRAY(Method*, _new_methods->length());
4112   _deleted_methods      = NEW_RESOURCE_ARRAY(Method*, _old_methods->length());
4113 
4114   _matching_methods_length = 0;
4115   _deleted_methods_length  = 0;
4116   _added_methods_length    = 0;
4117 
4118   int nj = 0;
4119   int oj = 0;
4120   while (true) {
4121     if (oj >= _old_methods->length()) {
4122       if (nj >= _new_methods->length()) {
4123         break; // we've looked at everything, done
4124       }
4125       // New method at the end
4126       new_method = _new_methods->at(nj);
4127       _added_methods[_added_methods_length++] = new_method;
4128       ++nj;
4129     } else if (nj >= _new_methods->length()) {
4130       // Old method, at the end, is deleted
4131       old_method = _old_methods->at(oj);
4132       _deleted_methods[_deleted_methods_length++] = old_method;
4133       ++oj;
4134     } else {
4135       old_method = _old_methods->at(oj);
4136       new_method = _new_methods->at(nj);
4137       if (old_method->name() == new_method->name()) {
4138         if (old_method->signature() == new_method->signature()) {
4139           _matching_old_methods[_matching_methods_length  ] = old_method;
4140           _matching_new_methods[_matching_methods_length++] = new_method;
4141           ++nj;
4142           ++oj;
4143         } else {
4144           // added overloaded have already been moved to the end,
4145           // so this is a deleted overloaded method
4146           _deleted_methods[_deleted_methods_length++] = old_method;
4147           ++oj;
4148         }
4149       } else { // names don't match
4150         if (old_method->name()->fast_compare(new_method->name()) > 0) {
4151           // new method
4152           _added_methods[_added_methods_length++] = new_method;
4153           ++nj;
4154         } else {
4155           // deleted method
4156           _deleted_methods[_deleted_methods_length++] = old_method;
4157           ++oj;
4158         }
4159       }
4160     }
4161   }
4162   assert(_matching_methods_length + _deleted_methods_length == _old_methods->length(), "sanity");
4163   assert(_matching_methods_length + _added_methods_length == _new_methods->length(), "sanity");
4164 }
4165 
4166 
4167 void VM_RedefineClasses::swap_annotations(InstanceKlass* the_class,
4168                                           InstanceKlass* scratch_class) {
4169   // Swap annotation fields values
4170   Annotations* old_annotations = the_class->annotations();
4171   the_class->set_annotations(scratch_class->annotations());
4172   scratch_class->set_annotations(old_annotations);
4173 }
4174 
4175 
4176 // Install the redefinition of a class:
4177 //    - house keeping (flushing breakpoints and caches, deoptimizing
4178 //      dependent compiled code)
4179 //    - replacing parts in the_class with parts from scratch_class
4180 //    - adding a weak reference to track the obsolete but interesting
4181 //      parts of the_class
4182 //    - adjusting constant pool caches and vtables in other classes
4183 //      that refer to methods in the_class. These adjustments use the
4184 //      ClassLoaderDataGraph::classes_do() facility which only allows
4185 //      a helper method to be specified. The interesting parameters
4186 //      that we would like to pass to the helper method are saved in
4187 //      static global fields in the VM operation.
4188 void VM_RedefineClasses::redefine_single_class(Thread* current, jclass the_jclass,
4189                                                InstanceKlass* scratch_class) {
4190 
4191   HandleMark hm(current);   // make sure handles from this call are freed
4192 
4193   if (log_is_enabled(Info, redefine, class, timer)) {
4194     _timer_rsc_phase1.start();
4195   }
4196 
4197   InstanceKlass* the_class = get_ik(the_jclass);
4198 
4199   // Set a flag to control and optimize adjusting method entries
4200   _has_redefined_Object |= the_class == vmClasses::Object_klass();
4201 
4202   // Remove all breakpoints in methods of this class
4203   JvmtiBreakpoints& jvmti_breakpoints = JvmtiCurrentBreakpoints::get_jvmti_breakpoints();
4204   jvmti_breakpoints.clearall_in_class_at_safepoint(the_class);
4205 
4206   _old_methods = the_class->methods();
4207   _new_methods = scratch_class->methods();
4208   _the_class = the_class;
4209   compute_added_deleted_matching_methods();
4210   update_jmethod_ids();
4211 
4212   _any_class_has_resolved_methods = the_class->has_resolved_methods() || _any_class_has_resolved_methods;
4213 
4214   // Attach new constant pool to the original klass. The original
4215   // klass still refers to the old constant pool (for now).
4216   scratch_class->constants()->set_pool_holder(the_class);
4217 
4218 #if 0
4219   // In theory, with constant pool merging in place we should be able
4220   // to save space by using the new, merged constant pool in place of
4221   // the old constant pool(s). By "pool(s)" I mean the constant pool in
4222   // the klass version we are replacing now and any constant pool(s) in
4223   // previous versions of klass. Nice theory, doesn't work in practice.
4224   // When this code is enabled, even simple programs throw NullPointer
4225   // exceptions. I'm guessing that this is caused by some constant pool
4226   // cache difference between the new, merged constant pool and the
4227   // constant pool that was just being used by the klass. I'm keeping
4228   // this code around to archive the idea, but the code has to remain
4229   // disabled for now.
4230 
4231   // Attach each old method to the new constant pool. This can be
4232   // done here since we are past the bytecode verification and
4233   // constant pool optimization phases.
4234   for (int i = _old_methods->length() - 1; i >= 0; i--) {
4235     Method* method = _old_methods->at(i);
4236     method->set_constants(scratch_class->constants());
4237   }
4238 
4239   // NOTE: this doesn't work because you can redefine the same class in two
4240   // threads, each getting their own constant pool data appended to the
4241   // original constant pool.  In order for the new methods to work when they
4242   // become old methods, they need to keep their updated copy of the constant pool.
4243 
4244   {
4245     // walk all previous versions of the klass
4246     InstanceKlass *ik = the_class;
4247     PreviousVersionWalker pvw(ik);
4248     do {
4249       ik = pvw.next_previous_version();
4250       if (ik != nullptr) {
4251 
4252         // attach previous version of klass to the new constant pool
4253         ik->set_constants(scratch_class->constants());
4254 
4255         // Attach each method in the previous version of klass to the
4256         // new constant pool
4257         Array<Method*>* prev_methods = ik->methods();
4258         for (int i = prev_methods->length() - 1; i >= 0; i--) {
4259           Method* method = prev_methods->at(i);
4260           method->set_constants(scratch_class->constants());
4261         }
4262       }
4263     } while (ik != nullptr);
4264   }
4265 #endif
4266 
4267   // Replace methods and constantpool
4268   the_class->set_methods(_new_methods);
4269   scratch_class->set_methods(_old_methods);     // To prevent potential GCing of the old methods,
4270                                           // and to be able to undo operation easily.
4271 
4272   Array<int>* old_ordering = the_class->method_ordering();
4273   the_class->set_method_ordering(scratch_class->method_ordering());
4274   scratch_class->set_method_ordering(old_ordering);
4275 
4276   ConstantPool* old_constants = the_class->constants();
4277   the_class->set_constants(scratch_class->constants());
4278   scratch_class->set_constants(old_constants);  // See the previous comment.
4279 #if 0
4280   // We are swapping the guts of "the new class" with the guts of "the
4281   // class". Since the old constant pool has just been attached to "the
4282   // new class", it seems logical to set the pool holder in the old
4283   // constant pool also. However, doing this will change the observable
4284   // class hierarchy for any old methods that are still executing. A
4285   // method can query the identity of its "holder" and this query uses
4286   // the method's constant pool link to find the holder. The change in
4287   // holding class from "the class" to "the new class" can confuse
4288   // things.
4289   //
4290   // Setting the old constant pool's holder will also cause
4291   // verification done during vtable initialization below to fail.
4292   // During vtable initialization, the vtable's class is verified to be
4293   // a subtype of the method's holder. The vtable's class is "the
4294   // class" and the method's holder is gotten from the constant pool
4295   // link in the method itself. For "the class"'s directly implemented
4296   // methods, the method holder is "the class" itself (as gotten from
4297   // the new constant pool). The check works fine in this case. The
4298   // check also works fine for methods inherited from super classes.
4299   //
4300   // Miranda methods are a little more complicated. A miranda method is
4301   // provided by an interface when the class implementing the interface
4302   // does not provide its own method.  These interfaces are implemented
4303   // internally as an InstanceKlass. These special instanceKlasses
4304   // share the constant pool of the class that "implements" the
4305   // interface. By sharing the constant pool, the method holder of a
4306   // miranda method is the class that "implements" the interface. In a
4307   // non-redefine situation, the subtype check works fine. However, if
4308   // the old constant pool's pool holder is modified, then the check
4309   // fails because there is no class hierarchy relationship between the
4310   // vtable's class and "the new class".
4311 
4312   old_constants->set_pool_holder(scratch_class());
4313 #endif
4314 
4315   // track number of methods that are EMCP for add_previous_version() call below
4316   int emcp_method_count = check_methods_and_mark_as_obsolete();
4317   transfer_old_native_function_registrations(the_class);
4318 
4319   if (scratch_class->get_cached_class_file() != the_class->get_cached_class_file()) {
4320     // 1. the_class doesn't have a cache yet, scratch_class does have a cache.
4321     // 2. The same class can be present twice in the scratch classes list or there
4322     // are multiple concurrent RetransformClasses calls on different threads.
4323     // the_class and scratch_class have the same cached bytes, but different buffers.
4324     // In such cases we need to deallocate one of the buffers.
4325     // 3. RedefineClasses and the_class has cached bytes from a previous transformation.
4326     // In the case we need to use class bytes from scratch_class.
4327     if (the_class->get_cached_class_file() != nullptr) {
4328       os::free(the_class->get_cached_class_file());
4329     }
4330     the_class->set_cached_class_file(scratch_class->get_cached_class_file());
4331   }
4332 
4333   // null out in scratch class to not delete twice.  The class to be redefined
4334   // always owns these bytes.
4335   scratch_class->set_cached_class_file(nullptr);
4336 
4337   // Replace inner_classes
4338   Array<u2>* old_inner_classes = the_class->inner_classes();
4339   the_class->set_inner_classes(scratch_class->inner_classes());
4340   scratch_class->set_inner_classes(old_inner_classes);
4341 
4342   // Initialize the vtable and interface table after
4343   // methods have been rewritten
4344   // no exception should happen here since we explicitly
4345   // do not check loader constraints.
4346   // compare_and_normalize_class_versions has already checked:
4347   //  - classloaders unchanged, signatures unchanged
4348   //  - all instanceKlasses for redefined classes reused & contents updated
4349   the_class->vtable().initialize_vtable();
4350   the_class->itable().initialize_itable();
4351 
4352   // Update jmethodID cache if present.
4353   the_class->update_methods_jmethod_cache();
4354 
4355   // Copy the "source debug extension" attribute from new class version
4356   the_class->set_source_debug_extension(
4357     scratch_class->source_debug_extension(),
4358     scratch_class->source_debug_extension() == nullptr ? 0 :
4359     (int)strlen(scratch_class->source_debug_extension()));
4360 
4361   // Use of javac -g could be different in the old and the new
4362   if (scratch_class->has_localvariable_table() !=
4363       the_class->has_localvariable_table()) {
4364     the_class->set_has_localvariable_table(scratch_class->has_localvariable_table());
4365   }
4366 
4367   swap_annotations(the_class, scratch_class);
4368 
4369   // Replace minor version number of class file
4370   u2 old_minor_version = the_class->constants()->minor_version();
4371   the_class->constants()->set_minor_version(scratch_class->constants()->minor_version());
4372   scratch_class->constants()->set_minor_version(old_minor_version);
4373 
4374   // Replace major version number of class file
4375   u2 old_major_version = the_class->constants()->major_version();
4376   the_class->constants()->set_major_version(scratch_class->constants()->major_version());
4377   scratch_class->constants()->set_major_version(old_major_version);
4378 
4379   // Replace CP indexes for class and name+type of enclosing method
4380   u2 old_class_idx  = the_class->enclosing_method_class_index();
4381   u2 old_method_idx = the_class->enclosing_method_method_index();
4382   the_class->set_enclosing_method_indices(
4383     scratch_class->enclosing_method_class_index(),
4384     scratch_class->enclosing_method_method_index());
4385   scratch_class->set_enclosing_method_indices(old_class_idx, old_method_idx);
4386 
4387   if (!the_class->has_been_redefined()) {
4388     the_class->set_has_been_redefined();
4389   }
4390 
4391   // Scratch class is unloaded but still needs cleaning, and skipping for CDS.
4392   scratch_class->set_is_scratch_class();
4393 
4394   // keep track of previous versions of this class
4395   the_class->add_previous_version(scratch_class, emcp_method_count);
4396 
4397   _timer_rsc_phase1.stop();
4398   if (log_is_enabled(Info, redefine, class, timer)) {
4399     _timer_rsc_phase2.start();
4400   }
4401 
4402   if (the_class->oop_map_cache() != nullptr) {
4403     // Flush references to any obsolete methods from the oop map cache
4404     // so that obsolete methods are not pinned.
4405     the_class->oop_map_cache()->flush_obsolete_entries();
4406   }
4407 
4408   increment_class_counter(the_class);
4409 
4410   if (EventClassRedefinition::is_enabled()) {
4411     EventClassRedefinition event;
4412     event.set_classModificationCount(java_lang_Class::classRedefinedCount(the_class->java_mirror()));
4413     event.set_redefinedClass(the_class);
4414     event.set_redefinitionId(_id);
4415     event.commit();
4416   }
4417 
4418   {
4419     ResourceMark rm(current);
4420     // increment the classRedefinedCount field in the_class and in any
4421     // direct and indirect subclasses of the_class
4422     log_info(redefine, class, load)
4423       ("redefined name=%s, count=%d (avail_mem=" UINT64_FORMAT "K)",
4424        the_class->external_name(), java_lang_Class::classRedefinedCount(the_class->java_mirror()), os::available_memory() >> 10);
4425     Events::log_redefinition(current, "redefined class name=%s, count=%d",
4426                              the_class->external_name(),
4427                              java_lang_Class::classRedefinedCount(the_class->java_mirror()));
4428 
4429   }
4430   _timer_rsc_phase2.stop();
4431 
4432 } // end redefine_single_class()
4433 
4434 
4435 // Increment the classRedefinedCount field in the specific InstanceKlass
4436 // and in all direct and indirect subclasses.
4437 void VM_RedefineClasses::increment_class_counter(InstanceKlass* ik) {
4438   for (ClassHierarchyIterator iter(ik); !iter.done(); iter.next()) {
4439     // Only update instanceKlasses
4440     Klass* sub = iter.klass();
4441     if (sub->is_instance_klass()) {
4442       oop class_mirror = InstanceKlass::cast(sub)->java_mirror();
4443       Klass* class_oop = java_lang_Class::as_Klass(class_mirror);
4444       int new_count = java_lang_Class::classRedefinedCount(class_mirror) + 1;
4445       java_lang_Class::set_classRedefinedCount(class_mirror, new_count);
4446 
4447       if (class_oop != _the_class) {
4448         // _the_class count is printed at end of redefine_single_class()
4449         log_debug(redefine, class, subclass)("updated count in subclass=%s to %d", ik->external_name(), new_count);
4450       }
4451     }
4452   }
4453 }
4454 
4455 void VM_RedefineClasses::CheckClass::do_klass(Klass* k) {
4456   bool no_old_methods = true;  // be optimistic
4457 
4458   // Both array and instance classes have vtables.
4459   // a vtable should never contain old or obsolete methods
4460   ResourceMark rm(_thread);
4461   if (k->vtable_length() > 0 &&
4462       !k->vtable().check_no_old_or_obsolete_entries()) {
4463     if (log_is_enabled(Trace, redefine, class, obsolete, metadata)) {
4464       log_trace(redefine, class, obsolete, metadata)
4465         ("klassVtable::check_no_old_or_obsolete_entries failure -- OLD or OBSOLETE method found -- class: %s",
4466          k->signature_name());
4467       k->vtable().dump_vtable();
4468     }
4469     no_old_methods = false;
4470   }
4471 
4472   if (k->is_instance_klass()) {
4473     HandleMark hm(_thread);
4474     InstanceKlass *ik = InstanceKlass::cast(k);
4475 
4476     // an itable should never contain old or obsolete methods
4477     if (ik->itable_length() > 0 &&
4478         !ik->itable().check_no_old_or_obsolete_entries()) {
4479       if (log_is_enabled(Trace, redefine, class, obsolete, metadata)) {
4480         log_trace(redefine, class, obsolete, metadata)
4481           ("klassItable::check_no_old_or_obsolete_entries failure -- OLD or OBSOLETE method found -- class: %s",
4482            ik->signature_name());
4483         ik->itable().dump_itable();
4484       }
4485       no_old_methods = false;
4486     }
4487 
4488     // the constant pool cache should never contain non-deleted old or obsolete methods
4489     if (ik->constants() != nullptr &&
4490         ik->constants()->cache() != nullptr &&
4491         !ik->constants()->cache()->check_no_old_or_obsolete_entries()) {
4492       if (log_is_enabled(Trace, redefine, class, obsolete, metadata)) {
4493         log_trace(redefine, class, obsolete, metadata)
4494           ("cp-cache::check_no_old_or_obsolete_entries failure -- OLD or OBSOLETE method found -- class: %s",
4495            ik->signature_name());
4496         ik->constants()->cache()->dump_cache();
4497       }
4498       no_old_methods = false;
4499     }
4500   }
4501 
4502   // print and fail guarantee if old methods are found.
4503   if (!no_old_methods) {
4504     if (log_is_enabled(Trace, redefine, class, obsolete, metadata)) {
4505       dump_methods();
4506     } else {
4507       log_trace(redefine, class)("Use the '-Xlog:redefine+class*:' option "
4508         "to see more info about the following guarantee() failure.");
4509     }
4510     guarantee(false, "OLD and/or OBSOLETE method(s) found");
4511   }
4512 }
4513 
4514 u8 VM_RedefineClasses::next_id() {
4515   while (true) {
4516     u8 id = _id_counter;
4517     u8 next_id = id + 1;
4518     u8 result = Atomic::cmpxchg(&_id_counter, id, next_id);
4519     if (result == id) {
4520       return next_id;
4521     }
4522   }
4523 }
4524 
4525 void VM_RedefineClasses::dump_methods() {
4526   int j;
4527   log_trace(redefine, class, dump)("_old_methods --");
4528   for (j = 0; j < _old_methods->length(); ++j) {
4529     LogStreamHandle(Trace, redefine, class, dump) log_stream;
4530     Method* m = _old_methods->at(j);
4531     log_stream.print("%4d  (%5d)  ", j, m->vtable_index());
4532     m->access_flags().print_on(&log_stream);
4533     log_stream.print(" --  ");
4534     m->print_name(&log_stream);
4535     log_stream.cr();
4536   }
4537   log_trace(redefine, class, dump)("_new_methods --");
4538   for (j = 0; j < _new_methods->length(); ++j) {
4539     LogStreamHandle(Trace, redefine, class, dump) log_stream;
4540     Method* m = _new_methods->at(j);
4541     log_stream.print("%4d  (%5d)  ", j, m->vtable_index());
4542     m->access_flags().print_on(&log_stream);
4543     log_stream.print(" --  ");
4544     m->print_name(&log_stream);
4545     log_stream.cr();
4546   }
4547   log_trace(redefine, class, dump)("_matching_methods --");
4548   for (j = 0; j < _matching_methods_length; ++j) {
4549     LogStreamHandle(Trace, redefine, class, dump) log_stream;
4550     Method* m = _matching_old_methods[j];
4551     log_stream.print("%4d  (%5d)  ", j, m->vtable_index());
4552     m->access_flags().print_on(&log_stream);
4553     log_stream.print(" --  ");
4554     m->print_name();
4555     log_stream.cr();
4556 
4557     m = _matching_new_methods[j];
4558     log_stream.print("      (%5d)  ", m->vtable_index());
4559     m->access_flags().print_on(&log_stream);
4560     log_stream.cr();
4561   }
4562   log_trace(redefine, class, dump)("_deleted_methods --");
4563   for (j = 0; j < _deleted_methods_length; ++j) {
4564     LogStreamHandle(Trace, redefine, class, dump) log_stream;
4565     Method* m = _deleted_methods[j];
4566     log_stream.print("%4d  (%5d)  ", j, m->vtable_index());
4567     m->access_flags().print_on(&log_stream);
4568     log_stream.print(" --  ");
4569     m->print_name(&log_stream);
4570     log_stream.cr();
4571   }
4572   log_trace(redefine, class, dump)("_added_methods --");
4573   for (j = 0; j < _added_methods_length; ++j) {
4574     LogStreamHandle(Trace, redefine, class, dump) log_stream;
4575     Method* m = _added_methods[j];
4576     log_stream.print("%4d  (%5d)  ", j, m->vtable_index());
4577     m->access_flags().print_on(&log_stream);
4578     log_stream.print(" --  ");
4579     m->print_name(&log_stream);
4580     log_stream.cr();
4581   }
4582 }
4583 
4584 void VM_RedefineClasses::print_on_error(outputStream* st) const {
4585   VM_Operation::print_on_error(st);
4586   if (_the_class != nullptr) {
4587     ResourceMark rm;
4588     st->print_cr(", redefining class %s", _the_class->external_name());
4589   }
4590 }