Quelle  jvmtiRedefineClasses.cpp   Sprache: C

/*
 * Copyright (c) 2003, 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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#include "precompiled.hpp"
#include "cds/metaspaceShared.hpp"
#include "classfile/classFileStream.hpp"
#include "classfile/classLoaderDataGraph.hpp"
#include "classfile/classLoadInfo.hpp"
#include "classfile/javaClasses.inline.hpp"
#include "classfile/metadataOnStackMark.hpp"
#include "classfile/symbolTable.hpp"
#include "classfile/klassFactory.hpp"
#include "classfile/verifier.hpp"
#include "classfile/vmClasses.hpp"
#include "classfile/vmSymbols.hpp"
#include "code/codeCache.hpp"
#include "compiler/compileBroker.hpp"
#include "interpreter/oopMapCache.hpp"
#include "interpreter/rewriter.hpp"
#include "jfr/jfrEvents.hpp"
#include "logging/logStream.hpp"
#include "memory/metadataFactory.hpp"
#include "memory/resourceArea.hpp"
#include "memory/universe.hpp"
#include "oops/annotations.hpp"
#include "oops/constantPool.hpp"
#include "oops/fieldStreams.inline.hpp"
#include "oops/klass.inline.hpp"
#include "oops/klassVtable.hpp"
#include "oops/oop.inline.hpp"
#include "oops/recordComponent.hpp"
#include "prims/jvmtiImpl.hpp"
#include "prims/jvmtiRedefineClasses.hpp"
#include "prims/jvmtiThreadState.inline.hpp"
#include "prims/resolvedMethodTable.hpp"
#include "prims/methodComparator.hpp"
#include "runtime/atomic.hpp"
#include "runtime/deoptimization.hpp"
#include "runtime/handles.inline.hpp"
#include "runtime/jniHandles.inline.hpp"
#include "runtime/relocator.hpp"
#include "runtime/safepointVerifiers.hpp"
#include "utilities/bitMap.inline.hpp"
#include "utilities/events.hpp"

Array<Method*>* VM_RedefineClasses::_old_methods = NULL;
Array<Method*>* VM_RedefineClasses::_new_methods = NULL;
Method**  VM_RedefineClasses::_matching_old_methods = NULL;
Method**  VM_RedefineClasses::_matching_new_methods = NULL;
Method**  VM_RedefineClasses::_deleted_methods      = NULL;
Method**  VM_RedefineClasses::_added_methods        = NULL;
int       VM_RedefineClasses::_matching_methods_length = 0;
int       VM_RedefineClasses::_deleted_methods_length  = 0;
int       VM_RedefineClasses::_added_methods_length    = 0;

// This flag is global as the constructor does not reset it:
bool      VM_RedefineClasses::_has_redefined_Object = false;
u8        VM_RedefineClasses::_id_counter = 0;

VM_RedefineClasses::VM_RedefineClasses(jint class_count,
                                       const jvmtiClassDefinition *class_defs,
                                       JvmtiClassLoadKind class_load_kind) {
  _class_count = class_count;
  _class_defs = class_defs;
  _class_load_kind = class_load_kind;
  _any_class_has_resolved_methods = false;
  _res = JVMTI_ERROR_NONE;
  _the_class = NULL;
  _id = next_id();
}

static inline InstanceKlass* get_ik(jclass def) {
  oop mirror = JNIHandles::resolve_non_null(def);
  return InstanceKlass::cast(java_lang_Class::as_Klass(mirror));
}

// If any of the classes are being redefined, wait
// Parallel constant pool merging leads to indeterminate constant pools.
void VM_RedefineClasses::lock_classes() {
  JvmtiThreadState *state = JvmtiThreadState::state_for(JavaThread::current());
  GrowableArray<Klass*>* redef_classes = state->get_classes_being_redefined();

  MonitorLocker ml(RedefineClasses_lock);

  if (redef_classes == NULL) {
    redef_classes = new (mtClass) GrowableArray<Klass*>(1, mtClass);
    state->set_classes_being_redefined(redef_classes);
  }

  bool has_redefined;
  do {
    has_redefined = false;
    // Go through classes each time until none are being redefined. Skip
    // the ones that are being redefined by this thread currently. Class file
    // load hook event may trigger new class redefine when we are redefining
    // a class (after lock_classes()).
    for (int i = 0; i < _class_count; i++) {
      InstanceKlass* ik = get_ik(_class_defs[i].klass);
      // Check if we are currently redefining the class in this thread already.
      if (redef_classes->contains(ik)) {
        assert(ik->is_being_redefined(), "sanity");
      } else {
        if (ik->is_being_redefined()) {
          ml.wait();
          has_redefined = true;
          break;  // for loop
        }
      }
    }
  } while (has_redefined);

  for (int i = 0; i < _class_count; i++) {
    InstanceKlass* ik = get_ik(_class_defs[i].klass);
    redef_classes->push(ik); // Add to the _classes_being_redefined list
    ik->set_is_being_redefined(true);
  }
  ml.notify_all();
}

void VM_RedefineClasses::unlock_classes() {
  JvmtiThreadState *state = JvmtiThreadState::state_for(JavaThread::current());
  GrowableArray<Klass*>* redef_classes = state->get_classes_being_redefined();
  assert(redef_classes != NULL, "_classes_being_redefined is not allocated");

  MonitorLocker ml(RedefineClasses_lock);

  for (int i = _class_count - 1; i >= 0; i--) {
    InstanceKlass* def_ik = get_ik(_class_defs[i].klass);
    if (redef_classes->length() > 0) {
      // Remove the class from _classes_being_redefined list
      Klass* k = redef_classes->pop();
      assert(def_ik == k, "unlocking wrong class");
    }
    assert(def_ik->is_being_redefined(),
           "should be being redefined to get here");

    // Unlock after we finish all redefines for this class within
    // the thread. Same class can be pushed to the list multiple
    // times (not more than once by each recursive redefinition).
    if (!redef_classes->contains(def_ik)) {
      def_ik->set_is_being_redefined(false);
    }
  }
  ml.notify_all();
}

bool VM_RedefineClasses::doit_prologue() {
  if (_class_count == 0) {
    _res = JVMTI_ERROR_NONE;
    return false;
  }
  if (_class_defs == NULL) {
    _res = JVMTI_ERROR_NULL_POINTER;
    return false;
  }

  for (int i = 0; i < _class_count; i++) {
    if (_class_defs[i].klass == NULL) {
      _res = JVMTI_ERROR_INVALID_CLASS;
      return false;
    }
    if (_class_defs[i].class_byte_count == 0) {
      _res = JVMTI_ERROR_INVALID_CLASS_FORMAT;
      return false;
    }
    if (_class_defs[i].class_bytes == NULL) {
      _res = JVMTI_ERROR_NULL_POINTER;
      return false;
    }

    oop mirror = JNIHandles::resolve_non_null(_class_defs[i].klass);
    // classes for primitives, arrays, and hidden classes
    // cannot be redefined.
    if (!is_modifiable_class(mirror)) {
      _res = JVMTI_ERROR_UNMODIFIABLE_CLASS;
      return false;
    }
  }

  // Start timer after all the sanity checks; not quite accurate, but
  // better than adding a bunch of stop() calls.
  if (log_is_enabled(Info, redefine, class, timer)) {
    _timer_vm_op_prologue.start();
  }

  lock_classes();
  // We first load new class versions in the prologue, because somewhere down the
  // call chain it is required that the current thread is a Java thread.
  _res = load_new_class_versions();
  if (_res != JVMTI_ERROR_NONE) {
    // free any successfully created classes, since none are redefined
    for (int i = 0; i < _class_count; i++) {
      if (_scratch_classes[i] != NULL) {
        ClassLoaderData* cld = _scratch_classes[i]->class_loader_data();
        // Free the memory for this class at class unloading time.  Not before
        // because CMS might think this is still live.
        InstanceKlass* ik = get_ik(_class_defs[i].klass);
        if (ik->get_cached_class_file() == _scratch_classes[i]->get_cached_class_file()) {
          // Don't double-free cached_class_file copied from the original class if error.
          _scratch_classes[i]->set_cached_class_file(NULL);
        }
        cld->add_to_deallocate_list(InstanceKlass::cast(_scratch_classes[i]));
      }
    }
    // Free os::malloc allocated memory in load_new_class_version.
    os::free(_scratch_classes);
    _timer_vm_op_prologue.stop();
    unlock_classes();
    return false;
  }

  _timer_vm_op_prologue.stop();
  return true;
}

void VM_RedefineClasses::doit() {
  Thread* current = Thread::current();

  if (log_is_enabled(Info, redefine, class, timer)) {
    _timer_vm_op_doit.start();
  }

#if INCLUDE_CDS
  if (UseSharedSpaces) {
    // Sharing is enabled so we remap the shared readonly space to
    // shared readwrite, private just in case we need to redefine
    // a shared class. We do the remap during the doit() phase of
    // the safepoint to be safer.
    if (!MetaspaceShared::remap_shared_readonly_as_readwrite()) {
      log_info(redefine, class, load)("failed to remap shared readonly space to readwrite, private");
      _res = JVMTI_ERROR_INTERNAL;
      _timer_vm_op_doit.stop();
      return;
    }
  }
#endif

  // Mark methods seen on stack and everywhere else so old methods are not
  // cleaned up if they're on the stack.
  MetadataOnStackMark md_on_stack(/*walk_all_metadata*/true, /*redefinition_walk*/true);
  HandleMark hm(current);   // make sure any handles created are deleted
                            // before the stack walk again.

  for (int i = 0; i < _class_count; i++) {
    redefine_single_class(current, _class_defs[i].klass, _scratch_classes[i]);
  }

  // Flush all compiled code that depends on the classes redefined.
  flush_dependent_code();

  // Adjust constantpool caches and vtables for all classes
  // that reference methods of the evolved classes.
  // Have to do this after all classes are redefined and all methods that
  // are redefined are marked as old.
  AdjustAndCleanMetadata adjust_and_clean_metadata(current);
  ClassLoaderDataGraph::classes_do(&adjust_and_clean_metadata);

  // JSR-292 support
  if (_any_class_has_resolved_methods) {
    bool trace_name_printed = false;
    ResolvedMethodTable::adjust_method_entries(&trace_name_printed);
  }

  // Increment flag indicating that some invariants are no longer true.
  // See jvmtiExport.hpp for detailed explanation.
  JvmtiExport::increment_redefinition_count();

  // check_class() is optionally called for product bits, but is
  // always called for non-product bits.
#ifdef PRODUCT
  if (log_is_enabled(Trace, redefine, class, obsolete, metadata)) {
#endif
    log_trace(redefine, class, obsolete, metadata)("calling check_class");
    CheckClass check_class(current);
    ClassLoaderDataGraph::classes_do(&check_class);
#ifdef PRODUCT
  }
#endif

  // Clean up any metadata now unreferenced while MetadataOnStackMark is set.
  ClassLoaderDataGraph::clean_deallocate_lists(false);

  _timer_vm_op_doit.stop();
}

void VM_RedefineClasses::doit_epilogue() {
  unlock_classes();

  // Free os::malloc allocated memory.
  os::free(_scratch_classes);

  // Reset the_class to null for error printing.
  _the_class = NULL;

  if (log_is_enabled(Info, redefine, class, timer)) {
    // Used to have separate timers for "doit" and "all", but the timer
    // overhead skewed the measurements.
    julong doit_time = _timer_vm_op_doit.milliseconds();
    julong all_time = _timer_vm_op_prologue.milliseconds() + doit_time;

    log_info(redefine, class, timer)
      ("vm_op: all=" JULONG_FORMAT " prologue=" JULONG_FORMAT " doit=" JULONG_FORMAT,
       all_time, (julong)_timer_vm_op_prologue.milliseconds(), doit_time);
    log_info(redefine, class, timer)
      ("redefine_single_class: phase1=" JULONG_FORMAT " phase2=" JULONG_FORMAT,
       (julong)_timer_rsc_phase1.milliseconds(), (julong)_timer_rsc_phase2.milliseconds());
  }
}

bool VM_RedefineClasses::is_modifiable_class(oop klass_mirror) {
  // classes for primitives cannot be redefined
  if (java_lang_Class::is_primitive(klass_mirror)) {
    return false;
  }
  Klass* k = java_lang_Class::as_Klass(klass_mirror);
  // classes for arrays cannot be redefined
  if (k == NULL || !k->is_instance_klass()) {
    return false;
  }

  // Cannot redefine or retransform a hidden class.
  if (InstanceKlass::cast(k)->is_hidden()) {
    return false;
  }
  return true;
}

// Append the current entry at scratch_i in scratch_cp to *merge_cp_p
// where the end of *merge_cp_p is specified by *merge_cp_length_p. For
// direct CP entries, there is just the current entry to append. For
// indirect and double-indirect CP entries, there are zero or more
// referenced CP entries along with the current entry to append.
// Indirect and double-indirect CP entries are handled by recursive
// calls to append_entry() as needed. The referenced CP entries are
// always appended to *merge_cp_p before the referee CP entry. These
// referenced CP entries may already exist in *merge_cp_p in which case
// there is nothing extra to append and only the current entry is
// appended.
void VM_RedefineClasses::append_entry(const constantPoolHandle& scratch_cp,
       int scratch_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {

  // append is different depending on entry tag type
  switch (scratch_cp->tag_at(scratch_i).value()) {

    // The old verifier is implemented outside the VM. It loads classes,
    // but does not resolve constant pool entries directly so we never
    // see Class entries here with the old verifier. Similarly the old
    // verifier does not like Class entries in the input constant pool.
    // The split-verifier is implemented in the VM so it can optionally
    // and directly resolve constant pool entries to load classes. The
    // split-verifier can accept either Class entries or UnresolvedClass
    // entries in the input constant pool. We revert the appended copy
    // back to UnresolvedClass so that either verifier will be happy
    // with the constant pool entry.
    //
    // this is an indirect CP entry so it needs special handling
    case JVM_CONSTANT_Class:
    case JVM_CONSTANT_UnresolvedClass:
    {
      int name_i = scratch_cp->klass_name_index_at(scratch_i);
      int new_name_i = find_or_append_indirect_entry(scratch_cp, name_i, merge_cp_p,
                                                     merge_cp_length_p);

      if (new_name_i != name_i) {
        log_trace(redefine, class, constantpool)
          ("Class entry@%d name_index change: %d to %d",
           *merge_cp_length_p, name_i, new_name_i);
      }

      (*merge_cp_p)->temp_unresolved_klass_at_put(*merge_cp_length_p, new_name_i);
      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // these are direct CP entries so they can be directly appended,
    // but double and long take two constant pool entries
    case JVM_CONSTANT_Double:  // fall through
    case JVM_CONSTANT_Long:
    {
      ConstantPool::copy_entry_to(scratch_cp, scratch_i, *merge_cp_p, *merge_cp_length_p);

      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p) += 2;
    } break;

    // these are direct CP entries so they can be directly appended
    case JVM_CONSTANT_Float:   // fall through
    case JVM_CONSTANT_Integer: // fall through
    case JVM_CONSTANT_Utf8:    // fall through

    // This was an indirect CP entry, but it has been changed into
    // Symbol*s so this entry can be directly appended.
    case JVM_CONSTANT_String:      // fall through
    {
      ConstantPool::copy_entry_to(scratch_cp, scratch_i, *merge_cp_p, *merge_cp_length_p);

      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // this is an indirect CP entry so it needs special handling
    case JVM_CONSTANT_NameAndType:
    {
      int name_ref_i = scratch_cp->name_ref_index_at(scratch_i);
      int new_name_ref_i = find_or_append_indirect_entry(scratch_cp, name_ref_i, merge_cp_p,
                                                         merge_cp_length_p);

      int signature_ref_i = scratch_cp->signature_ref_index_at(scratch_i);
      int new_signature_ref_i = find_or_append_indirect_entry(scratch_cp, signature_ref_i,
                                                              merge_cp_p, merge_cp_length_p);

      // If the referenced entries already exist in *merge_cp_p, then
      // both new_name_ref_i and new_signature_ref_i will both be 0.
      // In that case, all we are appending is the current entry.
      if (new_name_ref_i != name_ref_i) {
        log_trace(redefine, class, constantpool)
          ("NameAndType entry@%d name_ref_index change: %d to %d",
           *merge_cp_length_p, name_ref_i, new_name_ref_i);
      }
      if (new_signature_ref_i != signature_ref_i) {
        log_trace(redefine, class, constantpool)
          ("NameAndType entry@%d signature_ref_index change: %d to %d",
           *merge_cp_length_p, signature_ref_i, new_signature_ref_i);
      }

      (*merge_cp_p)->name_and_type_at_put(*merge_cp_length_p,
        new_name_ref_i, new_signature_ref_i);
      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // this is a double-indirect CP entry so it needs special handling
    case JVM_CONSTANT_Fieldref:           // fall through
    case JVM_CONSTANT_InterfaceMethodref: // fall through
    case JVM_CONSTANT_Methodref:
    {
      int klass_ref_i = scratch_cp->uncached_klass_ref_index_at(scratch_i);
      int new_klass_ref_i = find_or_append_indirect_entry(scratch_cp, klass_ref_i,
                                                          merge_cp_p, merge_cp_length_p);

      int name_and_type_ref_i = scratch_cp->uncached_name_and_type_ref_index_at(scratch_i);
      int new_name_and_type_ref_i = find_or_append_indirect_entry(scratch_cp, name_and_type_ref_i,
                                                          merge_cp_p, merge_cp_length_p);

      const char *entry_name = NULL;
      switch (scratch_cp->tag_at(scratch_i).value()) {
      case JVM_CONSTANT_Fieldref:
        entry_name = "Fieldref";
        (*merge_cp_p)->field_at_put(*merge_cp_length_p, new_klass_ref_i,
          new_name_and_type_ref_i);
        break;
      case JVM_CONSTANT_InterfaceMethodref:
        entry_name = "IFMethodref";
        (*merge_cp_p)->interface_method_at_put(*merge_cp_length_p,
          new_klass_ref_i, new_name_and_type_ref_i);
        break;
      case JVM_CONSTANT_Methodref:
        entry_name = "Methodref";
        (*merge_cp_p)->method_at_put(*merge_cp_length_p, new_klass_ref_i,
          new_name_and_type_ref_i);
        break;
      default:
        guarantee(false, "bad switch");
        break;
      }

      if (klass_ref_i != new_klass_ref_i) {
        log_trace(redefine, class, constantpool)
          ("%s entry@%d class_index changed: %d to %d", entry_name, *merge_cp_length_p, klass_ref_i, new_klass_ref_i);
      }
      if (name_and_type_ref_i != new_name_and_type_ref_i) {
        log_trace(redefine, class, constantpool)
          ("%s entry@%d name_and_type_index changed: %d to %d",
           entry_name, *merge_cp_length_p, name_and_type_ref_i, new_name_and_type_ref_i);
      }

      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // this is an indirect CP entry so it needs special handling
    case JVM_CONSTANT_MethodType:
    {
      int ref_i = scratch_cp->method_type_index_at(scratch_i);
      int new_ref_i = find_or_append_indirect_entry(scratch_cp, ref_i, merge_cp_p,
                                                    merge_cp_length_p);
      if (new_ref_i != ref_i) {
        log_trace(redefine, class, constantpool)
          ("MethodType entry@%d ref_index change: %d to %d", *merge_cp_length_p, ref_i, new_ref_i);
      }
      (*merge_cp_p)->method_type_index_at_put(*merge_cp_length_p, new_ref_i);
      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // this is an indirect CP entry so it needs special handling
    case JVM_CONSTANT_MethodHandle:
    {
      int ref_kind = scratch_cp->method_handle_ref_kind_at(scratch_i);
      int ref_i = scratch_cp->method_handle_index_at(scratch_i);
      int new_ref_i = find_or_append_indirect_entry(scratch_cp, ref_i, merge_cp_p,
                                                    merge_cp_length_p);
      if (new_ref_i != ref_i) {
        log_trace(redefine, class, constantpool)
          ("MethodHandle entry@%d ref_index change: %d to %d", *merge_cp_length_p, ref_i, new_ref_i);
      }
      (*merge_cp_p)->method_handle_index_at_put(*merge_cp_length_p, ref_kind, new_ref_i);
      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // this is an indirect CP entry so it needs special handling
    case JVM_CONSTANT_Dynamic:  // fall through
    case JVM_CONSTANT_InvokeDynamic:
    {
      // Index of the bootstrap specifier in the operands array
      int old_bs_i = scratch_cp->bootstrap_methods_attribute_index(scratch_i);
      int new_bs_i = find_or_append_operand(scratch_cp, old_bs_i, merge_cp_p,
                                            merge_cp_length_p);
      // The bootstrap method NameAndType_info index
      int old_ref_i = scratch_cp->bootstrap_name_and_type_ref_index_at(scratch_i);
      int new_ref_i = find_or_append_indirect_entry(scratch_cp, old_ref_i, merge_cp_p,
                                                    merge_cp_length_p);
      if (new_bs_i != old_bs_i) {
        log_trace(redefine, class, constantpool)
          ("Dynamic entry@%d bootstrap_method_attr_index change: %d to %d",
           *merge_cp_length_p, old_bs_i, new_bs_i);
      }
      if (new_ref_i != old_ref_i) {
        log_trace(redefine, class, constantpool)
          ("Dynamic entry@%d name_and_type_index change: %d to %d", *merge_cp_length_p, old_ref_i, new_ref_i);
      }

      if (scratch_cp->tag_at(scratch_i).is_dynamic_constant())
        (*merge_cp_p)->dynamic_constant_at_put(*merge_cp_length_p, new_bs_i, new_ref_i);
      else
        (*merge_cp_p)->invoke_dynamic_at_put(*merge_cp_length_p, new_bs_i, new_ref_i);
      if (scratch_i != *merge_cp_length_p) {
        // The new entry in *merge_cp_p is at a different index than
        // the new entry in scratch_cp so we need to map the index values.
        map_index(scratch_cp, scratch_i, *merge_cp_length_p);
      }
      (*merge_cp_length_p)++;
    } break;

    // At this stage, Class or UnresolvedClass could be in scratch_cp, but not
    // ClassIndex
    case JVM_CONSTANT_ClassIndex: // fall through

    // Invalid is used as the tag for the second constant pool entry
    // occupied by JVM_CONSTANT_Double or JVM_CONSTANT_Long. It should
    // not be seen by itself.
    case JVM_CONSTANT_Invalid: // fall through

    // At this stage, String could be here, but not StringIndex
    case JVM_CONSTANT_StringIndex: // fall through

    // At this stage JVM_CONSTANT_UnresolvedClassInError should not be
    // here
    case JVM_CONSTANT_UnresolvedClassInError: // fall through

    default:
    {
      // leave a breadcrumb
      jbyte bad_value = scratch_cp->tag_at(scratch_i).value();
      ShouldNotReachHere();
    } break;
  } // end switch tag value
} // end append_entry()


int VM_RedefineClasses::find_or_append_indirect_entry(const constantPoolHandle& ;scratch_cp,
      int ref_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {

  int new_ref_i = ref_i;
  bool match = (ref_i < *merge_cp_length_p) &&
               scratch_cp->compare_entry_to(ref_i, *merge_cp_p, ref_i);

  if (!match) {
    // forward reference in *merge_cp_p or not a direct match
    int found_i = scratch_cp->find_matching_entry(ref_i, *merge_cp_p);
    if (found_i != 0) {
      guarantee(found_i != ref_i, "compare_entry_to() and find_matching_entry() do not agree");
      // Found a matching entry somewhere else in *merge_cp_p so just need a mapping entry.
      new_ref_i = found_i;
      map_index(scratch_cp, ref_i, found_i);
    } else {
      // no match found so we have to append this entry to *merge_cp_p
      append_entry(scratch_cp, ref_i, merge_cp_p, merge_cp_length_p);
      // The above call to append_entry() can only append one entry
      // so the post call query of *merge_cp_length_p is only for
      // the sake of consistency.
      new_ref_i = *merge_cp_length_p - 1;
    }
  }

  return new_ref_i;
} // end find_or_append_indirect_entry()


// Append a bootstrap specifier into the merge_cp operands that is semantically equal
// to the scratch_cp operands bootstrap specifier passed by the old_bs_i index.
// Recursively append new merge_cp entries referenced by the new bootstrap specifier.
void VM_RedefineClasses::append_operand(const constantPoolHandle& scratch_cp, int old_bs_i,
       constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {

  int old_ref_i = scratch_cp->operand_bootstrap_method_ref_index_at(old_bs_i);
  int new_ref_i = find_or_append_indirect_entry(scratch_cp, old_ref_i, merge_cp_p,
                                                merge_cp_length_p);
  if (new_ref_i != old_ref_i) {
    log_trace(redefine, class, constantpool)
      ("operands entry@%d bootstrap method ref_index change: %d to %d", _operands_cur_length, old_ref_i, new_ref_i);
  }

  Array<u2>* merge_ops = (*merge_cp_p)->operands();
  int new_bs_i = _operands_cur_length;
  // We have _operands_cur_length == 0 when the merge_cp operands is empty yet.
  // However, the operand_offset_at(0) was set in the extend_operands() call.
  int new_base = (new_bs_i == 0) ? (*merge_cp_p)->operand_offset_at(0)
                                 : (*merge_cp_p)->operand_next_offset_at(new_bs_i - 1);
  int argc     = scratch_cp->operand_argument_count_at(old_bs_i);

  ConstantPool::operand_offset_at_put(merge_ops, _operands_cur_length, new_base);
  merge_ops->at_put(new_base++, new_ref_i);
  merge_ops->at_put(new_base++, argc);

  for (int i = 0; i < argc; i++) {
    int old_arg_ref_i = scratch_cp->operand_argument_index_at(old_bs_i, i);
    int new_arg_ref_i = find_or_append_indirect_entry(scratch_cp, old_arg_ref_i, merge_cp_p,
                                                      merge_cp_length_p);
    merge_ops->at_put(new_base++, new_arg_ref_i);
    if (new_arg_ref_i != old_arg_ref_i) {
      log_trace(redefine, class, constantpool)
        ("operands entry@%d bootstrap method argument ref_index change: %d to %d",
         _operands_cur_length, old_arg_ref_i, new_arg_ref_i);
    }
  }
  if (old_bs_i != _operands_cur_length) {
    // The bootstrap specifier in *merge_cp_p is at a different index than
    // that in scratch_cp so we need to map the index values.
    map_operand_index(old_bs_i, new_bs_i);
  }
  _operands_cur_length++;
} // end append_operand()


int VM_RedefineClasses::find_or_append_operand(const constantPoolHandle& scratch_cp,
      int old_bs_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p) {

  int new_bs_i = old_bs_i; // bootstrap specifier index
  bool match = (old_bs_i < _operands_cur_length) &&
               scratch_cp->compare_operand_to(old_bs_i, *merge_cp_p, old_bs_i);

  if (!match) {
    // forward reference in *merge_cp_p or not a direct match
    int found_i = scratch_cp->find_matching_operand(old_bs_i, *merge_cp_p,
                                                    _operands_cur_length);
    if (found_i != -1) {
      guarantee(found_i != old_bs_i, "compare_operand_to() and find_matching_operand() disagree");
      // found a matching operand somewhere else in *merge_cp_p so just need a mapping
      new_bs_i = found_i;
      map_operand_index(old_bs_i, found_i);
    } else {
      // no match found so we have to append this bootstrap specifier to *merge_cp_p
      append_operand(scratch_cp, old_bs_i, merge_cp_p, merge_cp_length_p);
      new_bs_i = _operands_cur_length - 1;
    }
  }
  return new_bs_i;
} // end find_or_append_operand()


void VM_RedefineClasses::finalize_operands_merge(const constantPoolHandle& merge_cp, TRAPS) {
  if (merge_cp->operands() == NULL) {
    return;
  }
  // Shrink the merge_cp operands
  merge_cp->shrink_operands(_operands_cur_length, CHECK);

  if (log_is_enabled(Trace, redefine, class, constantpool)) {
    // don't want to loop unless we are tracing
    int count = 0;
    for (int i = 1; i < _operands_index_map_p->length(); i++) {
      int value = _operands_index_map_p->at(i);
      if (value != -1) {
        log_trace(redefine, class, constantpool)("operands_index_map[%d]: old=%d new=%d", count, i, value);
        count++;
      }
    }
  }
  // Clean-up
  _operands_index_map_p = NULL;
  _operands_cur_length = 0;
  _operands_index_map_count = 0;
} // end finalize_operands_merge()

// Symbol* comparator for qsort
// The caller must have an active ResourceMark.
static int symcmp(const void* a, const void* b) {
  char* astr = (*(Symbol**)a)->as_C_string();
  char* bstr = (*(Symbol**)b)->as_C_string();
  return strcmp(astr, bstr);
}

// The caller must have an active ResourceMark.
static jvmtiError check_attribute_arrays(const char* attr_name,
           InstanceKlass* the_class, InstanceKlass* scratch_class,
           Array<u2>* the_array, Array<u2>* scr_array) {
  bool the_array_exists = the_array != Universe::the_empty_short_array();
  bool scr_array_exists = scr_array != Universe::the_empty_short_array();

  int array_len = the_array->length();
  if (the_array_exists && scr_array_exists) {
    if (array_len != scr_array->length()) {
      log_trace(redefine, class)
        ("redefined class %s attribute change error: %s len=%d changed to len=%d",
         the_class->external_name(), attr_name, array_len, scr_array->length());
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
    }

    // The order of entries in the attribute array is not specified so we
    // have to explicitly check for the same contents. We do this by copying
    // the referenced symbols into their own arrays, sorting them and then
    // comparing each element pair.

    Symbol** the_syms = NEW_RESOURCE_ARRAY_RETURN_NULL(Symbol*, array_len);
    Symbol** scr_syms = NEW_RESOURCE_ARRAY_RETURN_NULL(Symbol*, array_len);

    if (the_syms == NULL || scr_syms == NULL) {
      return JVMTI_ERROR_OUT_OF_MEMORY;
    }

    for (int i = 0; i < array_len; i++) {
      int the_cp_index = the_array->at(i);
      int scr_cp_index = scr_array->at(i);
      the_syms[i] = the_class->constants()->klass_name_at(the_cp_index);
      scr_syms[i] = scratch_class->constants()->klass_name_at(scr_cp_index);
    }

    qsort(the_syms, array_len, sizeof(Symbol*), symcmp);
    qsort(scr_syms, array_len, sizeof(Symbol*), symcmp);

    for (int i = 0; i < array_len; i++) {
      if (the_syms[i] != scr_syms[i]) {
        log_info(redefine, class)
          ("redefined class %s attribute change error: %s[%d]: %s changed to %s",
           the_class->external_name(), attr_name, i,
           the_syms[i]->as_C_string(), scr_syms[i]->as_C_string());
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
      }
    }
  } else if (the_array_exists ^ scr_array_exists) {
    const char* action_str = (the_array_exists) ? "removed" : "added";
    log_info(redefine, class)
      ("redefined class %s attribute change error: %s attribute %s",
       the_class->external_name(), attr_name, action_str);
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
  }
  return JVMTI_ERROR_NONE;
}

static jvmtiError check_nest_attributes(InstanceKlass* the_class,
                                        InstanceKlass* scratch_class) {
  // Check whether the class NestHost attribute has been changed.
  Thread* thread = Thread::current();
  ResourceMark rm(thread);
  u2 the_nest_host_idx = the_class->nest_host_index();
  u2 scr_nest_host_idx = scratch_class->nest_host_index();

  if (the_nest_host_idx != 0 && scr_nest_host_idx != 0) {
    Symbol* the_sym = the_class->constants()->klass_name_at(the_nest_host_idx);
    Symbol* scr_sym = scratch_class->constants()->klass_name_at(scr_nest_host_idx);
    if (the_sym != scr_sym) {
      log_info(redefine, class, nestmates)
        ("redefined class %s attribute change error: NestHost class: %s replaced with: %s",
         the_class->external_name(), the_sym->as_C_string(), scr_sym->as_C_string());
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
    }
  } else if ((the_nest_host_idx == 0) ^ (scr_nest_host_idx == 0)) {
    const char* action_str = (the_nest_host_idx != 0) ? "removed" : "added";
    log_info(redefine, class, nestmates)
      ("redefined class %s attribute change error: NestHost attribute %s",
       the_class->external_name(), action_str);
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
  }

  // Check whether the class NestMembers attribute has been changed.
  return check_attribute_arrays("NestMembers",
                                the_class, scratch_class,
                                the_class->nest_members(),
                                scratch_class->nest_members());
}

// Return an error status if the class Record attribute was changed.
static jvmtiError check_record_attribute(InstanceKlass* the_class, InstanceKlass* scratch_class) {
  // Get lists of record components.
  Array<RecordComponent*>* the_record = the_class->record_components();
  Array<RecordComponent*>* scr_record = scratch_class->record_components();
  bool the_record_exists = the_record != NULL;
  bool scr_record_exists = scr_record != NULL;

  if (the_record_exists && scr_record_exists) {
    int the_num_components = the_record->length();
    int scr_num_components = scr_record->length();
    if (the_num_components != scr_num_components) {
      log_info(redefine, class, record)
        ("redefined class %s attribute change error: Record num_components=%d changed to num_components=%d",
         the_class->external_name(), the_num_components, scr_num_components);
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
    }

    // Compare each field in each record component.
    ConstantPool* the_cp =  the_class->constants();
    ConstantPool* scr_cp =  scratch_class->constants();
    for (int x = 0; x < the_num_components; x++) {
      RecordComponent* the_component = the_record->at(x);
      RecordComponent* scr_component = scr_record->at(x);
      const Symbol* const the_name = the_cp->symbol_at(the_component->name_index());
      const Symbol* const scr_name = scr_cp->symbol_at(scr_component->name_index());
      const Symbol* const the_descr = the_cp->symbol_at(the_component->descriptor_index());
      const Symbol* const scr_descr = scr_cp->symbol_at(scr_component->descriptor_index());
      if (the_name != scr_name || the_descr != scr_descr) {
        log_info(redefine, class, record)
          ("redefined class %s attribute change error: Record name_index, descriptor_index, and/or attributes_count changed",
           the_class->external_name());
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
      }

      int the_gen_sig = the_component->generic_signature_index();
      int scr_gen_sig = scr_component->generic_signature_index();
      const Symbol* const the_gen_sig_sym = (the_gen_sig == 0 ? NULL :
        the_cp->symbol_at(the_component->generic_signature_index()));
      const Symbol* const scr_gen_sig_sym = (scr_gen_sig == 0 ? NULL :
        scr_cp->symbol_at(scr_component->generic_signature_index()));
      if (the_gen_sig_sym != scr_gen_sig_sym) {
        log_info(redefine, class, record)
          ("redefined class %s attribute change error: Record generic_signature attribute changed",
           the_class->external_name());
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
      }

      // It's okay if a record component's annotations were changed.
    }

  } else if (the_record_exists ^ scr_record_exists) {
    const char* action_str = (the_record_exists) ? "removed" : "added";
    log_info(redefine, class, record)
      ("redefined class %s attribute change error: Record attribute %s",
       the_class->external_name(), action_str);
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_ATTRIBUTE_CHANGED;
  }

  return JVMTI_ERROR_NONE;
}


static jvmtiError check_permitted_subclasses_attribute(InstanceKlass* the_class,
                                                       InstanceKlass* scratch_class) {
  Thread* thread = Thread::current();
  ResourceMark rm(thread);

  // Check whether the class PermittedSubclasses attribute has been changed.
  return check_attribute_arrays("PermittedSubclasses",
                                the_class, scratch_class,
                                the_class->permitted_subclasses(),
                                scratch_class->permitted_subclasses());
}

static bool can_add_or_delete(Method* m) {
      // Compatibility mode
  return (AllowRedefinitionToAddDeleteMethods &&
          (m->is_private() && (m->is_static() || m->is_final())));
}

jvmtiError VM_RedefineClasses::compare_and_normalize_class_versions(
             InstanceKlass* the_class,
             InstanceKlass* scratch_class) {
  int i;

  // Check superclasses, or rather their names, since superclasses themselves can be
  // requested to replace.
  // Check for NULL superclass first since this might be java.lang.Object
  if (the_class->super() != scratch_class->super() &&
      (the_class->super() == NULL || scratch_class->super() == NULL ||
       the_class->super()->name() !=
       scratch_class->super()->name())) {
    log_info(redefine, class, normalize)
      ("redefined class %s superclass change error: superclass changed from %s to %s.",
       the_class->external_name(),
       the_class->super() == NULL ? "NULL" : the_class->super()->external_name(),
       scratch_class->super() == NULL ? "NULL" : scratch_class->super()->external_name());
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
  }

  // Check if the number, names and order of directly implemented interfaces are the same.
  // I think in principle we should just check if the sets of names of directly implemented
  // interfaces are the same, i.e. the order of declaration (which, however, if changed in the
  // .java file, also changes in .class file) should not matter. However, comparing sets is
  // technically a bit more difficult, and, more importantly, I am not sure at present that the
  // order of interfaces does not matter on the implementation level, i.e. that the VM does not
  // rely on it somewhere.
  Array<InstanceKlass*>* k_interfaces = the_class->local_interfaces();
  Array<InstanceKlass*>* k_new_interfaces = scratch_class->local_interfaces();
  int n_intfs = k_interfaces->length();
  if (n_intfs != k_new_interfaces->length()) {
    log_info(redefine, class, normalize)
      ("redefined class %s interfaces change error: number of implemented interfaces changed from %d to %d.",
       the_class->external_name(), n_intfs, k_new_interfaces->length());
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
  }
  for (i = 0; i < n_intfs; i++) {
    if (k_interfaces->at(i)->name() !=
        k_new_interfaces->at(i)->name()) {
      log_info(redefine, class, normalize)
          ("redefined class %s interfaces change error: interface changed from %s to %s.",
           the_class->external_name(),
           k_interfaces->at(i)->external_name(), k_new_interfaces->at(i)->external_name());
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
    }
  }

  // Check whether class is in the error init state.
  if (the_class->is_in_error_state()) {
    log_info(redefine, class, normalize)
      ("redefined class %s is in error init state.", the_class->external_name());
    // TBD #5057930: special error code is needed in 1.6
    return JVMTI_ERROR_INVALID_CLASS;
  }

  // Check whether the nest-related attributes have been changed.
  jvmtiError err = check_nest_attributes(the_class, scratch_class);
  if (err != JVMTI_ERROR_NONE) {
    return err;
  }

  // Check whether the Record attribute has been changed.
  err = check_record_attribute(the_class, scratch_class);
  if (err != JVMTI_ERROR_NONE) {
    return err;
  }

  // Check whether the PermittedSubclasses attribute has been changed.
  err = check_permitted_subclasses_attribute(the_class, scratch_class);
  if (err != JVMTI_ERROR_NONE) {
    return err;
  }

  // Check whether class modifiers are the same.
  jushort old_flags = (jushort) the_class->access_flags().get_flags();
  jushort new_flags = (jushort) scratch_class->access_flags().get_flags();
  if (old_flags != new_flags) {
    log_info(redefine, class, normalize)
        ("redefined class %s modifiers change error: modifiers changed from %d to %d.",
         the_class->external_name(), old_flags, new_flags);
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_CLASS_MODIFIERS_CHANGED;
  }

  // Check if the number, names, types and order of fields declared in these classes
  // are the same.
  JavaFieldStream old_fs(the_class);
  JavaFieldStream new_fs(scratch_class);
  for (; !old_fs.done() && !new_fs.done(); old_fs.next(), new_fs.next()) {
    // name and signature
    Symbol* name_sym1 = the_class->constants()->symbol_at(old_fs.name_index());
    Symbol* sig_sym1 = the_class->constants()->symbol_at(old_fs.signature_index());
    Symbol* name_sym2 = scratch_class->constants()->symbol_at(new_fs.name_index());
    Symbol* sig_sym2 = scratch_class->constants()->symbol_at(new_fs.signature_index());
    if (name_sym1 != name_sym2 || sig_sym1 != sig_sym2) {
      log_info(redefine, class, normalize)
          ("redefined class %s fields change error: field %s %s changed to %s %s.",
           the_class->external_name(),
           sig_sym1->as_C_string(), name_sym1->as_C_string(),
           sig_sym2->as_C_string(), name_sym2->as_C_string());
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
    }
    // offset
    if (old_fs.offset() != new_fs.offset()) {
      log_info(redefine, class, normalize)
          ("redefined class %s field %s change error: offset changed from %d to %d.",
           the_class->external_name(), name_sym2->as_C_string(), old_fs.offset(), new_fs.offset());
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
    }
    // access
    old_flags = old_fs.access_flags().as_short();
    new_flags = new_fs.access_flags().as_short();
    if ((old_flags ^ new_flags) & JVM_RECOGNIZED_FIELD_MODIFIERS) {
      log_info(redefine, class, normalize)
          ("redefined class %s field %s change error: modifiers changed from %d to %d.",
           the_class->external_name(), name_sym2->as_C_string(), old_flags, new_flags);
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
    }
  }

  // If both streams aren't done then we have a differing number of
  // fields.
  if (!old_fs.done() || !new_fs.done()) {
    const char* action = old_fs.done() ? "added" : "deleted";
    log_info(redefine, class, normalize)
        ("redefined class %s fields change error: some fields were %s.",
         the_class->external_name(), action);
    return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
  }

  // Do a parallel walk through the old and new methods. Detect
  // cases where they match (exist in both), have been added in
  // the new methods, or have been deleted (exist only in the
  // old methods).  The class file parser places methods in order
  // by method name, but does not order overloaded methods by
  // signature.  In order to determine what fate befell the methods,
  // this code places the overloaded new methods that have matching
  // old methods in the same order as the old methods and places
  // new overloaded methods at the end of overloaded methods of
  // that name. The code for this order normalization is adapted
  // from the algorithm used in InstanceKlass::find_method().
  // Since we are swapping out of order entries as we find them,
  // we only have to search forward through the overloaded methods.
  // Methods which are added and have the same name as an existing
  // method (but different signature) will be put at the end of
  // the methods with that name, and the name mismatch code will
  // handle them.
  Array<Method*>* k_old_methods(the_class->methods());
  Array<Method*>* k_new_methods(scratch_class->methods());
  int n_old_methods = k_old_methods->length();
  int n_new_methods = k_new_methods->length();
  Thread* thread = Thread::current();

  int ni = 0;
  int oi = 0;
  while (true) {
    Method* k_old_method;
    Method* k_new_method;
    enum { matched, added, deleted, undetermined } method_was = undetermined;

    if (oi >= n_old_methods) {
      if (ni >= n_new_methods) {
        break; // we've looked at everything, done
      }
      // New method at the end
      k_new_method = k_new_methods->at(ni);
      method_was = added;
    } else if (ni >= n_new_methods) {
      // Old method, at the end, is deleted
      k_old_method = k_old_methods->at(oi);
      method_was = deleted;
    } else {
      // There are more methods in both the old and new lists
      k_old_method = k_old_methods->at(oi);
      k_new_method = k_new_methods->at(ni);
      if (k_old_method->name() != k_new_method->name()) {
        // Methods are sorted by method name, so a mismatch means added
        // or deleted
        if (k_old_method->name()->fast_compare(k_new_method->name()) > 0) {
          method_was = added;
        } else {
          method_was = deleted;
        }
      } else if (k_old_method->signature() == k_new_method->signature()) {
        // Both the name and signature match
        method_was = matched;
      } else {
        // The name matches, but the signature doesn't, which means we have to
        // search forward through the new overloaded methods.
        int nj;  // outside the loop for post-loop check
        for (nj = ni + 1; nj < n_new_methods; nj++) {
          Method* m = k_new_methods->at(nj);
          if (k_old_method->name() != m->name()) {
            // reached another method name so no more overloaded methods
            method_was = deleted;
            break;
          }
          if (k_old_method->signature() == m->signature()) {
            // found a match so swap the methods
            k_new_methods->at_put(ni, m);
            k_new_methods->at_put(nj, k_new_method);
            k_new_method = m;
            method_was = matched;
            break;
          }
        }

        if (nj >= n_new_methods) {
          // reached the end without a match; so method was deleted
          method_was = deleted;
        }
      }
    }

    switch (method_was) {
    case matched:
      // methods match, be sure modifiers do too
      old_flags = (jushort) k_old_method->access_flags().get_flags();
      new_flags = (jushort) k_new_method->access_flags().get_flags();
      if ((old_flags ^ new_flags) & ~(JVM_ACC_NATIVE)) {
        log_info(redefine, class, normalize)
          ("redefined class %s method %s modifiers error: modifiers changed from %d to %d",
           the_class->external_name(), k_old_method->name_and_sig_as_C_string(), old_flags, new_flags);
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_MODIFIERS_CHANGED;
      }
      {
        u2 new_num = k_new_method->method_idnum();
        u2 old_num = k_old_method->method_idnum();
        if (new_num != old_num) {
          Method* idnum_owner = scratch_class->method_with_idnum(old_num);
          if (idnum_owner != NULL) {
            // There is already a method assigned this idnum -- switch them
            // Take current and original idnum from the new_method
            idnum_owner->set_method_idnum(new_num);
            idnum_owner->set_orig_method_idnum(k_new_method->orig_method_idnum());
          }
          // Take current and original idnum from the old_method
          k_new_method->set_method_idnum(old_num);
          k_new_method->set_orig_method_idnum(k_old_method->orig_method_idnum());
          if (thread->has_pending_exception()) {
            return JVMTI_ERROR_OUT_OF_MEMORY;
          }
        }
      }
      log_trace(redefine, class, normalize)
        ("Method matched: new: %s [%d] == old: %s [%d]",
         k_new_method->name_and_sig_as_C_string(), ni, k_old_method->name_and_sig_as_C_string(), oi);
      // advance to next pair of methods
      ++oi;
      ++ni;
      break;
    case added:
      // method added, see if it is OK
      if (!can_add_or_delete(k_new_method)) {
        log_info(redefine, class, normalize)
          ("redefined class %s methods error: added method: %s [%d]",
           the_class->external_name(), k_new_method->name_and_sig_as_C_string(), ni);
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_ADDED;
      }
      {
        u2 num = the_class->next_method_idnum();
        if (num == ConstMethod::UNSET_IDNUM) {
          // cannot add any more methods
          log_info(redefine, class, normalize)
            ("redefined class %s methods error: can't create ID for new method %s [%d]",
             the_class->external_name(), k_new_method->name_and_sig_as_C_string(), ni);
          return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_ADDED;
        }
        u2 new_num = k_new_method->method_idnum();
        Method* idnum_owner = scratch_class->method_with_idnum(num);
        if (idnum_owner != NULL) {
          // There is already a method assigned this idnum -- switch them
          // Take current and original idnum from the new_method
          idnum_owner->set_method_idnum(new_num);
          idnum_owner->set_orig_method_idnum(k_new_method->orig_method_idnum());
        }
        k_new_method->set_method_idnum(num);
        k_new_method->set_orig_method_idnum(num);
        if (thread->has_pending_exception()) {
          return JVMTI_ERROR_OUT_OF_MEMORY;
        }
      }
      log_trace(redefine, class, normalize)
        ("Method added: new: %s [%d]", k_new_method->name_and_sig_as_C_string(), ni);
      ++ni; // advance to next new method
      break;
    case deleted:
      // method deleted, see if it is OK
      if (!can_add_or_delete(k_old_method)) {
        log_info(redefine, class, normalize)
          ("redefined class %s methods error: deleted method %s [%d]",
           the_class->external_name(), k_old_method->name_and_sig_as_C_string(), oi);
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_DELETED;
      }
      log_trace(redefine, class, normalize)
        ("Method deleted: old: %s [%d]", k_old_method->name_and_sig_as_C_string(), oi);
      ++oi; // advance to next old method
      break;
    default:
      ShouldNotReachHere();
    }
  }

  return JVMTI_ERROR_NONE;
}


// Find new constant pool index value for old constant pool index value
// by searching the index map. Returns zero (0) if there is no mapped
// value for the old constant pool index.
int VM_RedefineClasses::find_new_index(int old_index) {
  if (_index_map_count == 0) {
    // map is empty so nothing can be found
    return 0;
  }

  if (old_index < 1 || old_index >= _index_map_p->length()) {
    // The old_index is out of range so it is not mapped. This should
    // not happen in regular constant pool merging use, but it can
    // happen if a corrupt annotation is processed.
    return 0;
  }

  int value = _index_map_p->at(old_index);
  if (value == -1) {
    // the old_index is not mapped
    return 0;
  }

  return value;
} // end find_new_index()


// Find new bootstrap specifier index value for old bootstrap specifier index
// value by searching the index map. Returns unused index (-1) if there is
// no mapped value for the old bootstrap specifier index.
int VM_RedefineClasses::find_new_operand_index(int old_index) {
  if (_operands_index_map_count == 0) {
    // map is empty so nothing can be found
    return -1;
  }

  if (old_index == -1 || old_index >= _operands_index_map_p->length()) {
    // The old_index is out of range so it is not mapped.
    // This should not happen in regular constant pool merging use.
    return -1;
  }

  int value = _operands_index_map_p->at(old_index);
  if (value == -1) {
    // the old_index is not mapped
    return -1;
  }

  return value;
} // end find_new_operand_index()


// Returns true if the current mismatch is due to a resolved/unresolved
// class pair. Otherwise, returns false.
bool VM_RedefineClasses::is_unresolved_class_mismatch(const constantPoolHandle& ;cp1,
       int index1, const constantPoolHandle& cp2, int index2) {

  jbyte t1 = cp1->tag_at(index1).value();
  if (t1 != JVM_CONSTANT_Class && t1 != JVM_CONSTANT_UnresolvedClass) {
    return false;  // wrong entry type; not our special case
  }

  jbyte t2 = cp2->tag_at(index2).value();
  if (t2 != JVM_CONSTANT_Class && t2 != JVM_CONSTANT_UnresolvedClass) {
    return false;  // wrong entry type; not our special case
  }

  if (t1 == t2) {
    return false;  // not a mismatch; not our special case
  }

  char *s1 = cp1->klass_name_at(index1)->as_C_string();
  char *s2 = cp2->klass_name_at(index2)->as_C_string();
  if (strcmp(s1, s2) != 0) {
    return false;  // strings don't match; not our special case
  }

  return true;  // made it through the gauntlet; this is our special case
} // end is_unresolved_class_mismatch()


// The bug 6214132 caused the verification to fail.
// 1. What's done in RedefineClasses() before verification:
//  a) A reference to the class being redefined (_the_class) and a
//     reference to new version of the class (_scratch_class) are
//     saved here for use during the bytecode verification phase of
//     RedefineClasses.
//  b) The _java_mirror field from _the_class is copied to the
//     _java_mirror field in _scratch_class. This means that a jclass
//     returned for _the_class or _scratch_class will refer to the
//     same Java mirror. The verifier will see the "one true mirror"
//     for the class being verified.
// 2. See comments in JvmtiThreadState for what is done during verification.

class RedefineVerifyMark : public StackObj {
 private:
  JvmtiThreadState* _state;
  Klass*            _scratch_class;
  OopHandle         _scratch_mirror;

 public:

  RedefineVerifyMark(Klass* the_class, Klass* scratch_class,
                     JvmtiThreadState* state) : _state(state), _scratch_class(scratch_class)
  {
    _state->set_class_versions_map(the_class, scratch_class);
    _scratch_mirror = the_class->java_mirror_handle();  // this is a copy that is swapped
    _scratch_class->swap_java_mirror_handle(_scratch_mirror);
  }

  ~RedefineVerifyMark() {
    // Restore the scratch class's mirror, so when scratch_class is removed
    // the correct mirror pointing to it can be cleared.
    _scratch_class->swap_java_mirror_handle(_scratch_mirror);
    _state->clear_class_versions_map();
  }
};


jvmtiError VM_RedefineClasses::load_new_class_versions() {

  // For consistency allocate memory using os::malloc wrapper.
  _scratch_classes = (InstanceKlass**)
    os::malloc(sizeof(InstanceKlass*) * _class_count, mtClass);
  if (_scratch_classes == NULL) {
    return JVMTI_ERROR_OUT_OF_MEMORY;
  }
  // Zero initialize the _scratch_classes array.
  for (int i = 0; i < _class_count; i++) {
    _scratch_classes[i] = NULL;
  }

  JavaThread* current = JavaThread::current();
  ResourceMark rm(current);

  JvmtiThreadState *state = JvmtiThreadState::state_for(current);
  // state can only be NULL if the current thread is exiting which
  // should not happen since we're trying to do a RedefineClasses
  guarantee(state != NULL, "exiting thread calling load_new_class_versions");
  for (int i = 0; i < _class_count; i++) {
    // Create HandleMark so that any handles created while loading new class
    // versions are deleted. Constant pools are deallocated while merging
    // constant pools
    HandleMark hm(current);
    InstanceKlass* the_class = get_ik(_class_defs[i].klass);

    log_debug(redefine, class, load)
      ("loading name=%s kind=%d (avail_mem=" UINT64_FORMAT "K)",
       the_class->external_name(), _class_load_kind, os::available_memory() >> 10);

    ClassFileStream st((u1*)_class_defs[i].class_bytes,
                       _class_defs[i].class_byte_count,
                       "__VM_RedefineClasses__",
                       ClassFileStream::verify);

    // Set redefined class handle in JvmtiThreadState class.
    // This redefined class is sent to agent event handler for class file
    // load hook event.
    state->set_class_being_redefined(the_class, _class_load_kind);

    JavaThread* THREAD = current; // For exception macros.
    ExceptionMark em(THREAD);
    Handle protection_domain(THREAD, the_class->protection_domain());
    ClassLoadInfo cl_info(protection_domain);
    // Parse and create a class from the bytes, but this class isn't added
    // to the dictionary, so do not call resolve_from_stream.
    InstanceKlass* scratch_class = KlassFactory::create_from_stream(&st,
                                                      the_class->name(),
                                                      the_class->class_loader_data(),
                                                      cl_info,
                                                      THREAD);

    // Clear class_being_redefined just to be sure.
    state->clear_class_being_redefined();

    // TODO: if this is retransform, and nothing changed we can skip it

    // Need to clean up allocated InstanceKlass if there's an error so assign
    // the result here. Caller deallocates all the scratch classes in case of
    // an error.
    _scratch_classes[i] = scratch_class;

    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      log_info(redefine, class, load, exceptions)("create_from_stream exception: '%s'", ex_name->as_C_string());
      CLEAR_PENDING_EXCEPTION;

      if (ex_name == vmSymbols::java_lang_UnsupportedClassVersionError()) {
        return JVMTI_ERROR_UNSUPPORTED_VERSION;
      } else if (ex_name == vmSymbols::java_lang_ClassFormatError()) {
        return JVMTI_ERROR_INVALID_CLASS_FORMAT;
      } else if (ex_name == vmSymbols::java_lang_ClassCircularityError()) {
        return JVMTI_ERROR_CIRCULAR_CLASS_DEFINITION;
      } else if (ex_name == vmSymbols::java_lang_NoClassDefFoundError()) {
        // The message will be "XXX (wrong name: YYY)"
        return JVMTI_ERROR_NAMES_DONT_MATCH;
      } else if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
        return JVMTI_ERROR_OUT_OF_MEMORY;
      } else {  // Just in case more exceptions can be thrown..
        return JVMTI_ERROR_FAILS_VERIFICATION;
      }
    }

    // Ensure class is linked before redefine
    if (!the_class->is_linked()) {
      the_class->link_class(THREAD);
      if (HAS_PENDING_EXCEPTION) {
        Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
        oop message = java_lang_Throwable::message(PENDING_EXCEPTION);
        if (message != NULL) {
          char* ex_msg = java_lang_String::as_utf8_string(message);
          log_info(redefine, class, load, exceptions)("link_class exception: '%s %s'",
                   ex_name->as_C_string(), ex_msg);
        } else {
          log_info(redefine, class, load, exceptions)("link_class exception: '%s'",
                   ex_name->as_C_string());
        }
        CLEAR_PENDING_EXCEPTION;
        if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
          return JVMTI_ERROR_OUT_OF_MEMORY;
        } else if (ex_name == vmSymbols::java_lang_NoClassDefFoundError()) {
          return JVMTI_ERROR_INVALID_CLASS;
        } else {
          return JVMTI_ERROR_INTERNAL;
        }
      }
    }

    // Do the validity checks in compare_and_normalize_class_versions()
    // before verifying the byte codes. By doing these checks first, we
    // limit the number of functions that require redirection from
    // the_class to scratch_class. In particular, we don't have to
    // modify JNI GetSuperclass() and thus won't change its performance.
    jvmtiError res = compare_and_normalize_class_versions(the_class,
                       scratch_class);
    if (res != JVMTI_ERROR_NONE) {
      return res;
    }

    // verify what the caller passed us
    {
      // The bug 6214132 caused the verification to fail.
      // Information about the_class and scratch_class is temporarily
      // recorded into jvmtiThreadState. This data is used to redirect
      // the_class to scratch_class in the JVM_* functions called by the
      // verifier. Please, refer to jvmtiThreadState.hpp for the detailed
      // description.
      RedefineVerifyMark rvm(the_class, scratch_class, state);
      Verifier::verify(scratch_class, true, THREAD);
    }

    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      log_info(redefine, class, load, exceptions)("verify_byte_codes exception: '%s'", ex_name->as_C_string());
      CLEAR_PENDING_EXCEPTION;
      if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
        return JVMTI_ERROR_OUT_OF_MEMORY;
      } else {
        // tell the caller the bytecodes are bad
        return JVMTI_ERROR_FAILS_VERIFICATION;
      }
    }

    res = merge_cp_and_rewrite(the_class, scratch_class, THREAD);
    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      log_info(redefine, class, load, exceptions)("merge_cp_and_rewrite exception: '%s'", ex_name->as_C_string());
      CLEAR_PENDING_EXCEPTION;
      if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
        return JVMTI_ERROR_OUT_OF_MEMORY;
      } else {
        return JVMTI_ERROR_INTERNAL;
      }
    }

#ifdef ASSERT
    {
      // verify what we have done during constant pool merging
      {
        RedefineVerifyMark rvm(the_class, scratch_class, state);
        Verifier::verify(scratch_class, true, THREAD);
      }

      if (HAS_PENDING_EXCEPTION) {
        Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
        log_info(redefine, class, load, exceptions)
          ("verify_byte_codes post merge-CP exception: '%s'", ex_name->as_C_string());
        CLEAR_PENDING_EXCEPTION;
        if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
          return JVMTI_ERROR_OUT_OF_MEMORY;
        } else {
          // tell the caller that constant pool merging screwed up
          return JVMTI_ERROR_INTERNAL;
        }
      }
    }
#endif // ASSERT

    Rewriter::rewrite(scratch_class, THREAD);
    if (!HAS_PENDING_EXCEPTION) {
      scratch_class->link_methods(THREAD);
    }
    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      log_info(redefine, class, load, exceptions)
        ("Rewriter::rewrite or link_methods exception: '%s'", ex_name->as_C_string());
      CLEAR_PENDING_EXCEPTION;
      if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
        return JVMTI_ERROR_OUT_OF_MEMORY;
      } else {
        return JVMTI_ERROR_INTERNAL;
      }
    }

    log_debug(redefine, class, load)
      ("loaded name=%s (avail_mem=" UINT64_FORMAT "K)", the_class->external_name(), os::available_memory() >> 10);
  }

  return JVMTI_ERROR_NONE;
}


// Map old_index to new_index as needed. scratch_cp is only needed
// for log calls.
void VM_RedefineClasses::map_index(const constantPoolHandle& scratch_cp,
       int old_index, int new_index) {
  if (find_new_index(old_index) != 0) {
    // old_index is already mapped
    return;
  }

  if (old_index == new_index) {
    // no mapping is needed
    return;
  }

  _index_map_p->at_put(old_index, new_index);
  _index_map_count++;

--> --------------------

--> maximum size reached

--> --------------------