jvmtiRedefineClasses.cpp

/*
 * Copyright (c) 2003, 2012, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

#include "precompiled.hpp"
#include "classfile/systemDictionary.hpp"
#include "classfile/verifier.hpp"
#include "code/codeCache.hpp"
#include "compiler/compileBroker.hpp"
#include "interpreter/oopMapCache.hpp"
#include "interpreter/rewriter.hpp"
#include "memory/gcLocker.hpp"
#include "memory/metadataFactory.hpp"
#include "memory/metaspaceShared.hpp"
#include "memory/universe.inline.hpp"
#include "oops/fieldStreams.hpp"
#include "oops/klassVtable.hpp"
#include "prims/jvmtiImpl.hpp"
#include "prims/jvmtiRedefineClasses.hpp"
#include "prims/methodComparator.hpp"
#include "runtime/deoptimization.hpp"
#include "runtime/relocator.hpp"
#include "utilities/bitMap.inline.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;
Klass*      VM_RedefineClasses::_the_class_oop = NULL;


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;
  _res = JVMTI_ERROR_NONE;
}

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;
    }
  }

  // Start timer after all the sanity checks; not quite accurate, but
  // better than adding a bunch of stop() calls.
  RC_TIMER_START(_timer_vm_op_prologue);

  // 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(Thread::current());
  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.
        cld->add_to_deallocate_list((InstanceKlass*)_scratch_classes[i]);
      }
    }
    // Free os::malloc allocated memory in load_new_class_version.
    os::free(_scratch_classes);
    RC_TIMER_STOP(_timer_vm_op_prologue);
    return false;
  }

  RC_TIMER_STOP(_timer_vm_op_prologue);
  return true;
}

// Keep track of marked on-stack metadata so it can be cleared.
GrowableArray<Metadata*>* _marked_objects = NULL;
NOT_PRODUCT(bool MetadataOnStackMark::_is_active = false;)

// Walk metadata on the stack and mark it so that redefinition doesn't delete
// it.  Class unloading also walks the previous versions and might try to
// delete it, so this class is used by class unloading also.
MetadataOnStackMark::MetadataOnStackMark() {
  assert(SafepointSynchronize::is_at_safepoint(), "sanity check");
  NOT_PRODUCT(_is_active = true;)
  if (_marked_objects == NULL) {
    _marked_objects = new (ResourceObj::C_HEAP, mtClass) GrowableArray<Metadata*>(1000, true);
  }
  Threads::metadata_do(Metadata::mark_on_stack);
  CodeCache::alive_nmethods_do(nmethod::mark_on_stack);
  CompileBroker::mark_on_stack();
}

MetadataOnStackMark::~MetadataOnStackMark() {
  assert(SafepointSynchronize::is_at_safepoint(), "sanity check");
  // Unmark everything that was marked.   Can't do the same walk because
  // redefine classes messes up the code cache so the set of methods
  // might not be the same.
  for (int i = 0; i< _marked_objects->length(); i++) {
    _marked_objects->at(i)->set_on_stack(false);
  }
  _marked_objects->clear();   // reuse growable array for next time.
  NOT_PRODUCT(_is_active = false;)
}

// Record which objects are marked so we can unmark the same objects.
void MetadataOnStackMark::record(Metadata* m) {
  assert(_is_active, "metadata on stack marking is active");
  _marked_objects->push(m);
}


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

  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()) {
      RC_TRACE_WITH_THREAD(0x00000001, thread,
        ("failed to remap shared readonly space to readwrite, private"));
      _res = JVMTI_ERROR_INTERNAL;
      return;
    }
  }

  // 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;
  HandleMark hm(thread);   // make sure any handles created are deleted
                           // before the stack walk again.

  for (int i = 0; i < _class_count; i++) {
    redefine_single_class(_class_defs[i].klass, _scratch_classes[i], thread);
    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.
    cld->add_to_deallocate_list((InstanceKlass*)_scratch_classes[i]);
    _scratch_classes[i] = NULL;
  }

  // Disable any dependent concurrent compilations
  SystemDictionary::notice_modification();

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

#ifdef ASSERT
  SystemDictionary::classes_do(check_class, thread);
#endif
}

void VM_RedefineClasses::doit_epilogue() {
  // Free os::malloc allocated memory.
  os::free(_scratch_classes);

  if (RC_TRACE_ENABLED(0x00000004)) {
    // Used to have separate timers for "doit" and "all", but the timer
    // overhead skewed the measurements.
    jlong doit_time = _timer_rsc_phase1.milliseconds() +
                      _timer_rsc_phase2.milliseconds();
    jlong all_time = _timer_vm_op_prologue.milliseconds() + doit_time;

    RC_TRACE(0x00000004, ("vm_op: all=" UINT64_FORMAT
      "  prologue=" UINT64_FORMAT "  doit=" UINT64_FORMAT, all_time,
      _timer_vm_op_prologue.milliseconds(), doit_time));
    RC_TRACE(0x00000004,
      ("redefine_single_class: phase1=" UINT64_FORMAT "  phase2=" UINT64_FORMAT,
       _timer_rsc_phase1.milliseconds(), _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* the_class_oop = java_lang_Class::as_Klass(klass_mirror);
  // classes for arrays cannot be redefined
  if (the_class_oop == NULL || !the_class_oop->oop_is_instance()) {
    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(constantPoolHandle scratch_cp,
       int scratch_i, constantPoolHandle *merge_cp_p, int *merge_cp_length_p,
       TRAPS) {

  // 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.
    case JVM_CONSTANT_Class:
    {
      // revert the copy to JVM_CONSTANT_UnresolvedClass
      (*merge_cp_p)->unresolved_klass_at_put(*merge_cp_length_p,
        scratch_cp->klass_name_at(scratch_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,
        THREAD);

      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

    // These were indirect CP entries, but they have been changed into
    // Symbol*s so these entries can be directly appended.
    case JVM_CONSTANT_UnresolvedClass:  // fall through
    {
      ConstantPool::copy_entry_to(scratch_cp, scratch_i, *merge_cp_p, *merge_cp_length_p,
        THREAD);

      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 = 0;
      bool match = (name_ref_i < *merge_cp_length_p) &&
        scratch_cp->compare_entry_to(name_ref_i, *merge_cp_p, name_ref_i,
          THREAD);
      if (!match) {
        // forward reference in *merge_cp_p or not a direct match

        int found_i = scratch_cp->find_matching_entry(name_ref_i, *merge_cp_p,
          THREAD);
        if (found_i != 0) {
          guarantee(found_i != name_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_name_ref_i = found_i;
          map_index(scratch_cp, name_ref_i, found_i);
        } else {
          // no match found so we have to append this entry to *merge_cp_p
          append_entry(scratch_cp, name_ref_i, merge_cp_p, merge_cp_length_p,
            THREAD);
          // 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_name_ref_i = *merge_cp_length_p - 1;
        }
      }

      int signature_ref_i = scratch_cp->signature_ref_index_at(scratch_i);
      int new_signature_ref_i = 0;
      match = (signature_ref_i < *merge_cp_length_p) &&
        scratch_cp->compare_entry_to(signature_ref_i, *merge_cp_p,
          signature_ref_i, THREAD);
      if (!match) {
        // forward reference in *merge_cp_p or not a direct match

        int found_i = scratch_cp->find_matching_entry(signature_ref_i,
          *merge_cp_p, THREAD);
        if (found_i != 0) {
          guarantee(found_i != signature_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_signature_ref_i = found_i;
          map_index(scratch_cp, signature_ref_i, found_i);
        } else {
          // no match found so we have to append this entry to *merge_cp_p
          append_entry(scratch_cp, signature_ref_i, merge_cp_p,
            merge_cp_length_p, THREAD);
          // 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_signature_ref_i = *merge_cp_length_p - 1;
        }
      }

      // 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 == 0) {
        new_name_ref_i = name_ref_i;
      } else {
        RC_TRACE(0x00080000,
          ("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 == 0) {
        new_signature_ref_i = signature_ref_i;
      } else {
        RC_TRACE(0x00080000,
          ("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 = 0;
      bool match = (klass_ref_i < *merge_cp_length_p) &&
        scratch_cp->compare_entry_to(klass_ref_i, *merge_cp_p, klass_ref_i,
          THREAD);
      if (!match) {
        // forward reference in *merge_cp_p or not a direct match

        int found_i = scratch_cp->find_matching_entry(klass_ref_i, *merge_cp_p,
          THREAD);
        if (found_i != 0) {
          guarantee(found_i != klass_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_klass_ref_i = found_i;
          map_index(scratch_cp, klass_ref_i, found_i);
        } else {
          // no match found so we have to append this entry to *merge_cp_p
          append_entry(scratch_cp, klass_ref_i, merge_cp_p, merge_cp_length_p,
            THREAD);
          // 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. Without the optimization where we
          // use JVM_CONSTANT_UnresolvedClass, then up to two entries
          // could be appended.
          new_klass_ref_i = *merge_cp_length_p - 1;
        }
      }

      int name_and_type_ref_i =
        scratch_cp->uncached_name_and_type_ref_index_at(scratch_i);
      int new_name_and_type_ref_i = 0;
      match = (name_and_type_ref_i < *merge_cp_length_p) &&
        scratch_cp->compare_entry_to(name_and_type_ref_i, *merge_cp_p,
          name_and_type_ref_i, THREAD);
      if (!match) {
        // forward reference in *merge_cp_p or not a direct match

        int found_i = scratch_cp->find_matching_entry(name_and_type_ref_i,
          *merge_cp_p, THREAD);
        if (found_i != 0) {
          guarantee(found_i != name_and_type_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_name_and_type_ref_i = found_i;
          map_index(scratch_cp, name_and_type_ref_i, found_i);
        } else {
          // no match found so we have to append this entry to *merge_cp_p
          append_entry(scratch_cp, name_and_type_ref_i, merge_cp_p,
            merge_cp_length_p, THREAD);
          // The above call to append_entry() can append more than
          // one entry so the post call query of *merge_cp_length_p
          // is required in order to get the right index for the
          // JVM_CONSTANT_NameAndType entry.
          new_name_and_type_ref_i = *merge_cp_length_p - 1;
        }
      }

      // If the referenced entries already exist in *merge_cp_p, then
      // both new_klass_ref_i and new_name_and_type_ref_i will both be
      // 0. In that case, all we are appending is the current entry.
      if (new_klass_ref_i == 0) {
        new_klass_ref_i = klass_ref_i;
      }
      if (new_name_and_type_ref_i == 0) {
        new_name_and_type_ref_i = name_and_type_ref_i;
      }

      const char *entry_name;
      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) {
        RC_TRACE(0x00080000, ("%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) {
        RC_TRACE(0x00080000,
          ("%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;

    // At this stage, Class or UnresolvedClass could be here, 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()


void VM_RedefineClasses::swap_all_method_annotations(int i, int j, instanceKlassHandle scratch_class, TRAPS) {
  AnnotationArray* save;

  Annotations* sca = scratch_class->annotations();
  if (sca == NULL) return;

  save = sca->get_method_annotations_of(i);
  sca->set_method_annotations_of(scratch_class, i, sca->get_method_annotations_of(j), CHECK);
  sca->set_method_annotations_of(scratch_class, j, save, CHECK);

  save = sca->get_method_parameter_annotations_of(i);
  sca->set_method_parameter_annotations_of(scratch_class, i, sca->get_method_parameter_annotations_of(j), CHECK);
  sca->set_method_parameter_annotations_of(scratch_class, j, save, CHECK);

  save = sca->get_method_default_annotations_of(i);
  sca->set_method_default_annotations_of(scratch_class, i, sca->get_method_default_annotations_of(j), CHECK);
  sca->set_method_default_annotations_of(scratch_class, j, save, CHECK);
}


jvmtiError VM_RedefineClasses::compare_and_normalize_class_versions(
             instanceKlassHandle the_class,
             instanceKlassHandle 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())) {
    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<Klass*>* k_interfaces = the_class->local_interfaces();
  Array<Klass*>* k_new_interfaces = scratch_class->local_interfaces();
  int n_intfs = k_interfaces->length();
  if (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()) {
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_HIERARCHY_CHANGED;
    }
  }

  // Check whether class is in the error init state.
  if (the_class->is_in_error_state()) {
    // TBD #5057930: special error code is needed in 1.6
    return JVMTI_ERROR_INVALID_CLASS;
  }

  // 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) {
    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()) {
    // 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) {
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
    }
    // offset
    if (old_fs.offset() != new_fs.offset()) {
      return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_SCHEMA_CHANGED;
    }
    // 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) {
      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()) {
    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)) {
        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
            idnum_owner->set_method_idnum(new_num);
          }
          k_new_method->set_method_idnum(old_num);
          swap_all_method_annotations(old_num, new_num, scratch_class, thread);
           if (thread->has_pending_exception()) {
             return JVMTI_ERROR_OUT_OF_MEMORY;
           }
        }
      }
      RC_TRACE(0x00008000, ("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
      new_flags = (jushort) k_new_method->access_flags().get_flags();
      if ((new_flags & JVM_ACC_PRIVATE) == 0
           // hack: private should be treated as final, but alas
          || (new_flags & (JVM_ACC_FINAL|JVM_ACC_STATIC)) == 0
         ) {
        // new methods must be private
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_ADDED;
      }
      {
        u2 num = the_class->next_method_idnum();
        if (num == ConstMethod::UNSET_IDNUM) {
          // cannot add any more methods
          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
          idnum_owner->set_method_idnum(new_num);
        }
        k_new_method->set_method_idnum(num);
        swap_all_method_annotations(new_num, num, scratch_class, thread);
        if (thread->has_pending_exception()) {
          return JVMTI_ERROR_OUT_OF_MEMORY;
        }
      }
      RC_TRACE(0x00008000, ("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
      old_flags = (jushort) k_old_method->access_flags().get_flags();
      if ((old_flags & JVM_ACC_PRIVATE) == 0
           // hack: private should be treated as final, but alas
          || (old_flags & (JVM_ACC_FINAL|JVM_ACC_STATIC)) == 0
         ) {
        // deleted methods must be private
        return JVMTI_ERROR_UNSUPPORTED_REDEFINITION_METHOD_DELETED;
      }
      RC_TRACE(0x00008000, ("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 seaching 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()


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


jvmtiError VM_RedefineClasses::load_new_class_versions(TRAPS) {

  // For consistency allocate memory using os::malloc wrapper.
  _scratch_classes = (Klass**)
    os::malloc(sizeof(Klass*) * _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;
  }

  ResourceMark rm(THREAD);

  JvmtiThreadState *state = JvmtiThreadState::state_for(JavaThread::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(THREAD);

    oop mirror = JNIHandles::resolve_non_null(_class_defs[i].klass);
    // classes for primitives cannot be redefined
    if (!is_modifiable_class(mirror)) {
      return JVMTI_ERROR_UNMODIFIABLE_CLASS;
    }
    Klass* the_class_oop = java_lang_Class::as_Klass(mirror);
    instanceKlassHandle the_class = instanceKlassHandle(THREAD, the_class_oop);
    Symbol*  the_class_sym = the_class->name();

    // RC_TRACE_WITH_THREAD macro has an embedded ResourceMark
    RC_TRACE_WITH_THREAD(0x00000001, THREAD,
      ("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, (char *)"__VM_RedefineClasses__");

    // Parse the stream.
    Handle the_class_loader(THREAD, the_class->class_loader());
    Handle protection_domain(THREAD, the_class->protection_domain());
    // 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);

    Klass* k = SystemDictionary::parse_stream(the_class_sym,
                                                the_class_loader,
                                                protection_domain,
                                                &st,
                                                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

    instanceKlassHandle scratch_class (THREAD, k);

    // 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] = k;

    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      // RC_TRACE_WITH_THREAD macro has an embedded ResourceMark
      RC_TRACE_WITH_THREAD(0x00000002, THREAD, ("parse_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();
        // RC_TRACE_WITH_THREAD macro has an embedded ResourceMark
        RC_TRACE_WITH_THREAD(0x00000002, THREAD, ("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 {
          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, Verifier::ThrowException, true, THREAD);
    }

    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      // RC_TRACE_WITH_THREAD macro has an embedded ResourceMark
      RC_TRACE_WITH_THREAD(0x00000002, THREAD,
        ("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 (res != JVMTI_ERROR_NONE) {
      return res;
    }

    if (VerifyMergedCPBytecodes) {
      // verify what we have done during constant pool merging
      {
        RedefineVerifyMark rvm(&the_class, &scratch_class, state);
        Verifier::verify(scratch_class, Verifier::ThrowException, true, THREAD);
      }

      if (HAS_PENDING_EXCEPTION) {
        Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
        // RC_TRACE_WITH_THREAD macro has an embedded ResourceMark
        RC_TRACE_WITH_THREAD(0x00000002, THREAD,
          ("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;
        }
      }
    }

    Rewriter::rewrite(scratch_class, THREAD);
    if (!HAS_PENDING_EXCEPTION) {
      Rewriter::relocate_and_link(scratch_class, THREAD);
    }
    if (HAS_PENDING_EXCEPTION) {
      Symbol* ex_name = PENDING_EXCEPTION->klass()->name();
      CLEAR_PENDING_EXCEPTION;
      if (ex_name == vmSymbols::java_lang_OutOfMemoryError()) {
        return JVMTI_ERROR_OUT_OF_MEMORY;
      } else {
        return JVMTI_ERROR_INTERNAL;
      }
    }

    // RC_TRACE_WITH_THREAD macro has an embedded ResourceMark
    RC_TRACE_WITH_THREAD(0x00000001, THREAD,
      ("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 RC_TRACE() calls.
void VM_RedefineClasses::map_index(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++;

  RC_TRACE(0x00040000, ("mapped tag %d at index %d to %d",
    scratch_cp->tag_at(old_index).value(), old_index, new_index));
} // end map_index()


// Merge old_cp and scratch_cp and return the results of the merge via
// merge_cp_p. The number of entries in *merge_cp_p is returned via
// merge_cp_length_p. The entries in old_cp occupy the same locations
// in *merge_cp_p. Also creates a map of indices from entries in
// scratch_cp to the corresponding entry in *merge_cp_p. Index map
// entries are only created for entries in scratch_cp that occupy a
// different location in *merged_cp_p.
bool VM_RedefineClasses::merge_constant_pools(constantPoolHandle old_cp,
       constantPoolHandle scratch_cp, constantPoolHandle *merge_cp_p,
       int *merge_cp_length_p, TRAPS) {

  if (merge_cp_p == NULL) {
    assert(false, "caller must provide scratch constantPool");
    return false; // robustness
  }
  if (merge_cp_length_p == NULL) {
    assert(false, "caller must provide scratch CP length");
    return false; // robustness
  }
  // Worst case we need old_cp->length() + scratch_cp()->length(),
  // but the caller might be smart so make sure we have at least
  // the minimum.
  if ((*merge_cp_p)->length() < old_cp->length()) {
    assert(false, "merge area too small");
    return false; // robustness
  }

  RC_TRACE_WITH_THREAD(0x00010000, THREAD,
    ("old_cp_len=%d, scratch_cp_len=%d", old_cp->length(),
    scratch_cp->length()));

  {
    // Pass 0:
    // The old_cp is copied to *merge_cp_p; this means that any code
    // using old_cp does not have to change. This work looks like a
    // perfect fit for ConstantPool*::copy_cp_to(), but we need to
    // handle one special case:
    // - revert JVM_CONSTANT_Class to JVM_CONSTANT_UnresolvedClass
    // This will make verification happy.

    int old_i;  // index into old_cp

    // index zero (0) is not used in constantPools
    for (old_i = 1; old_i < old_cp->length(); old_i++) {
      // leave debugging crumb
      jbyte old_tag = old_cp->tag_at(old_i).value();
      switch (old_tag) {
      case JVM_CONSTANT_Class:
      case JVM_CONSTANT_UnresolvedClass:
        // revert the copy to JVM_CONSTANT_UnresolvedClass
        // May be resolving while calling this so do the same for
        // JVM_CONSTANT_UnresolvedClass (klass_name_at() deals with transition)
        (*merge_cp_p)->unresolved_klass_at_put(old_i,
          old_cp->klass_name_at(old_i));
        break;

      case JVM_CONSTANT_Double:
      case JVM_CONSTANT_Long:
        // just copy the entry to *merge_cp_p, but double and long take
        // two constant pool entries
        ConstantPool::copy_entry_to(old_cp, old_i, *merge_cp_p, old_i, CHECK_0);
        old_i++;
        break;

      default:
        // just copy the entry to *merge_cp_p
        ConstantPool::copy_entry_to(old_cp, old_i, *merge_cp_p, old_i, CHECK_0);
        break;
      }
    } // end for each old_cp entry

    // We don't need to sanity check that *merge_cp_length_p is within
    // *merge_cp_p bounds since we have the minimum on-entry check above.
    (*merge_cp_length_p) = old_i;
  }

  // merge_cp_len should be the same as old_cp->length() at this point
  // so this trace message is really a "warm-and-breathing" message.
  RC_TRACE_WITH_THREAD(0x00020000, THREAD,
    ("after pass 0: merge_cp_len=%d", *merge_cp_length_p));

  int scratch_i;  // index into scratch_cp
  {
    // Pass 1a:
    // Compare scratch_cp entries to the old_cp entries that we have
    // already copied to *merge_cp_p. In this pass, we are eliminating
    // exact duplicates (matching entry at same index) so we only
    // compare entries in the common indice range.
    int increment = 1;
    int pass1a_length = MIN2(old_cp->length(), scratch_cp->length());
    for (scratch_i = 1; scratch_i < pass1a_length; scratch_i += increment) {
      switch (scratch_cp->tag_at(scratch_i).value()) {
      case JVM_CONSTANT_Double:
      case JVM_CONSTANT_Long:
        // double and long take two constant pool entries
        increment = 2;
        break;

      default:
        increment = 1;
        break;
      }

      bool match = scratch_cp->compare_entry_to(scratch_i, *merge_cp_p,
        scratch_i, CHECK_0);
      if (match) {
        // found a match at the same index so nothing more to do
        continue;
      } else if (is_unresolved_class_mismatch(scratch_cp, scratch_i,
                                              *merge_cp_p, scratch_i)) {
        // The mismatch in compare_entry_to() above is because of a
        // resolved versus unresolved class entry at the same index
        // with the same string value. Since Pass 0 reverted any
        // class entries to unresolved class entries in *merge_cp_p,
        // we go with the unresolved class entry.
        continue;
      }

      int found_i = scratch_cp->find_matching_entry(scratch_i, *merge_cp_p,
        CHECK_0);
      if (found_i != 0) {
        guarantee(found_i != scratch_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.
        map_index(scratch_cp, scratch_i, found_i);
        continue;
      }

      // The find_matching_entry() call above could fail to find a match
      // due to a resolved versus unresolved class or string entry situation
      // like we solved above with the is_unresolved_*_mismatch() calls.
      // However, we would have to call is_unresolved_*_mismatch() over
      // all of *merge_cp_p (potentially) and that doesn't seem to be
      // worth the time.

      // No match found so we have to append this entry and any unique
      // referenced entries to *merge_cp_p.
      append_entry(scratch_cp, scratch_i, merge_cp_p, merge_cp_length_p,
        CHECK_0);
    }
  }

  RC_TRACE_WITH_THREAD(0x00020000, THREAD,
    ("after pass 1a: merge_cp_len=%d, scratch_i=%d, index_map_len=%d",
    *merge_cp_length_p, scratch_i, _index_map_count));

  if (scratch_i < scratch_cp->length()) {
    // Pass 1b:
    // old_cp is smaller than scratch_cp so there are entries in
    // scratch_cp that we have not yet processed. We take care of
    // those now.
    int increment = 1;
    for (; scratch_i < scratch_cp->length(); scratch_i += increment) {
      switch (scratch_cp->tag_at(scratch_i).value()) {
      case JVM_CONSTANT_Double:
      case JVM_CONSTANT_Long:
        // double and long take two constant pool entries
        increment = 2;
        break;

      default:
        increment = 1;
        break;
      }

      int found_i =
        scratch_cp->find_matching_entry(scratch_i, *merge_cp_p, CHECK_0);
      if (found_i != 0) {
        // Found a matching entry somewhere else in *merge_cp_p so
        // just need a mapping entry.
        map_index(scratch_cp, scratch_i, found_i);
        continue;
      }

      // No match found so we have to append this entry and any unique
      // referenced entries to *merge_cp_p.
      append_entry(scratch_cp, scratch_i, merge_cp_p, merge_cp_length_p,
        CHECK_0);
    }

    RC_TRACE_WITH_THREAD(0x00020000, THREAD,
      ("after pass 1b: merge_cp_len=%d, scratch_i=%d, index_map_len=%d",
      *merge_cp_length_p, scratch_i, _index_map_count));
  }

  return true;
} // end merge_constant_pools()


// Scoped object to clean up the constant pool(s) created for merging
class MergeCPCleaner {
  ClassLoaderData*   _loader_data;
  ConstantPool*      _cp;
  ConstantPool*      _scratch_cp;
 public:
  MergeCPCleaner(ClassLoaderData* loader_data, ConstantPool* merge_cp) :
                 _loader_data(loader_data), _cp(merge_cp), _scratch_cp(NULL) {}
  ~MergeCPCleaner() {
    _loader_data->add_to_deallocate_list(_cp);
    if (_scratch_cp != NULL) {
      _loader_data->add_to_deallocate_list(_scratch_cp);
    }
  }
  void add_scratch_cp(ConstantPool* scratch_cp) { _scratch_cp = scratch_cp; }
};

// Merge constant pools between the_class and scratch_class and
// potentially rewrite bytecodes in scratch_class to use the merged
// constant pool.
jvmtiError VM_RedefineClasses::merge_cp_and_rewrite(
             instanceKlassHandle the_class, instanceKlassHandle scratch_class,
             TRAPS) {
  // worst case merged constant pool length is old and new combined
  int merge_cp_length = the_class->constants()->length()
        + scratch_class->constants()->length();

  // Constant pools are not easily reused so we allocate a new one
  // each time.
  // merge_cp is created unsafe for concurrent GC processing.  It
  // should be marked safe before discarding it. Even though
  // garbage,  if it crosses a card boundary, it may be scanned
  // in order to find the start of the first complete object on the card.
  ClassLoaderData* loader_data = the_class->class_loader_data();
  ConstantPool* merge_cp_oop =
    ConstantPool::allocate(loader_data,
                                  merge_cp_length,
                                  THREAD);
  MergeCPCleaner cp_cleaner(loader_data, merge_cp_oop);

  HandleMark hm(THREAD);  // make sure handles are cleared before
                          // MergeCPCleaner clears out merge_cp_oop
  constantPoolHandle merge_cp(THREAD, merge_cp_oop);

  // Get constants() from the old class because it could have been rewritten
  // while we were at a safepoint allocating a new constant pool.
  constantPoolHandle old_cp(THREAD, the_class->constants());
  constantPoolHandle scratch_cp(THREAD, scratch_class->constants());

  // If the length changed, the class was redefined out from under us. Return
  // an error.
  if (merge_cp_length != the_class->constants()->length()
         + scratch_class->constants()->length()) {
    return JVMTI_ERROR_INTERNAL;
  }

  int orig_length = old_cp->orig_length();
  if (orig_length == 0) {
    // This old_cp is an actual original constant pool. We save
    // the original length in the merged constant pool so that
    // merge_constant_pools() can be more efficient. If a constant
    // pool has a non-zero orig_length() value, then that constant
    // pool was created by a merge operation in RedefineClasses.
    merge_cp->set_orig_length(old_cp->length());
  } else {
    // This old_cp is a merged constant pool from a previous
    // RedefineClasses() calls so just copy the orig_length()
    // value.
    merge_cp->set_orig_length(old_cp->orig_length());
  }

  ResourceMark rm(THREAD);
  _index_map_count = 0;
  _index_map_p = new intArray(scratch_cp->length(), -1);

  bool result = merge_constant_pools(old_cp, scratch_cp, &merge_cp,
                  &merge_cp_length, THREAD);
  if (!result) {
    // The merge can fail due to memory allocation failure or due
    // to robustness checks.
    return JVMTI_ERROR_INTERNAL;
  }

  RC_TRACE_WITH_THREAD(0x00010000, THREAD,
    ("merge_cp_len=%d, index_map_len=%d", merge_cp_length, _index_map_count));

  if (_index_map_count == 0) {
    // there is nothing to map between the new and merged constant pools

    if (old_cp->length() == scratch_cp->length()) {
      // The old and new constant pools are the same length and the
      // index map is empty. This means that the three constant pools
      // are equivalent (but not the same). Unfortunately, the new
      // constant pool has not gone through link resolution nor have
      // the new class bytecodes gone through constant pool cache
      // rewriting so we can't use the old constant pool with the new
      // class.

      // toss the merged constant pool at return
    } else if (old_cp->length() < scratch_cp->length()) {
      // The old constant pool has fewer entries than the new constant
      // pool and the index map is empty. This means the new constant
      // pool is a superset of the old constant pool. However, the old
      // class bytecodes have already gone through constant pool cache
      // rewriting so we can't use the new constant pool with the old
      // class.

      // toss the merged constant pool at return
    } else {
      // The old constant pool has more entries than the new constant
      // pool and the index map is empty. This means that both the old
      // and merged constant pools are supersets of the new constant
      // pool.

      // Replace the new constant pool with a shrunken copy of the
      // merged constant pool
      set_new_constant_pool(loader_data, scratch_class, merge_cp, merge_cp_length, THREAD);
      // The new constant pool replaces scratch_cp so have cleaner clean it up.
      // It can't be cleaned up while there are handles to it.
      cp_cleaner.add_scratch_cp(scratch_cp());
    }
  } else {
    if (RC_TRACE_ENABLED(0x00040000)) {
      // don't want to loop unless we are tracing
      int count = 0;
      for (int i = 1; i < _index_map_p->length(); i++) {
        int value = _index_map_p->at(i);

        if (value != -1) {
          RC_TRACE_WITH_THREAD(0x00040000, THREAD,
            ("index_map[%d]: old=%d new=%d", count, i, value));
          count++;
        }
      }
    }

    // We have entries mapped between the new and merged constant pools
    // so we have to rewrite some constant pool references.
    if (!rewrite_cp_refs(scratch_class, THREAD)) {
      return JVMTI_ERROR_INTERNAL;
    }

    // Replace the new constant pool with a shrunken copy of the
    // merged constant pool so now the rewritten bytecodes have
    // valid references; the previous new constant pool will get
    // GCed.
    set_new_constant_pool(loader_data, scratch_class, merge_cp, merge_cp_length, THREAD);
    // The new constant pool replaces scratch_cp so have cleaner clean it up.
    // It can't be cleaned up while there are handles to it.
    cp_cleaner.add_scratch_cp(scratch_cp());
  }

  return JVMTI_ERROR_NONE;
} // end merge_cp_and_rewrite()


// Rewrite constant pool references in klass scratch_class.
bool VM_RedefineClasses::rewrite_cp_refs(instanceKlassHandle scratch_class,
       TRAPS) {

  // rewrite constant pool references in the methods:
  if (!rewrite_cp_refs_in_methods(scratch_class, THREAD)) {
    // propagate failure back to caller
    return false;
  }

  // rewrite constant pool references in the class_annotations:
  if (!rewrite_cp_refs_in_class_annotations(scratch_class, THREAD)) {
    // propagate failure back to caller
    return false;
  }

  // rewrite constant pool references in the fields_annotations:
  if (!rewrite_cp_refs_in_fields_annotations(scratch_class, THREAD)) {
    // propagate failure back to caller
    return false;
  }

  // rewrite constant pool references in the methods_annotations:
  if (!rewrite_cp_refs_in_methods_annotations(scratch_class, THREAD)) {
    // propagate failure back to caller
    return false;
  }

  // rewrite constant pool references in the methods_parameter_annotations:
  if (!rewrite_cp_refs_in_methods_parameter_annotations(scratch_class,
         THREAD)) {
    // propagate failure back to caller
    return false;
  }

  // rewrite constant pool references in the methods_default_annotations:
  if (!rewrite_cp_refs_in_methods_default_annotations(scratch_class,
         THREAD)) {
    // propagate failure back to caller
    return false;
  }

  return true;
} // end rewrite_cp_refs()


// Rewrite constant pool references in the methods.
bool VM_RedefineClasses::rewrite_cp_refs_in_methods(
       instanceKlassHandle scratch_class, TRAPS) {

  Array<Method*>* methods = scratch_class->methods();

  if (methods == NULL || methods->length() == 0) {
    // no methods so nothing to do
    return true;
  }

  // rewrite constant pool references in the methods:
  for (int i = methods->length() - 1; i >= 0; i--) {
    methodHandle method(THREAD, methods->at(i));
    methodHandle new_method;
    rewrite_cp_refs_in_method(method, &new_method, CHECK_false);
    if (!new_method.is_null()) {
      // the method has been replaced so save the new method version
      methods->at_put(i, new_method());
    }
  }

  return true;
}


// Rewrite constant pool references in the specific method. This code
// was adapted from Rewriter::rewrite_method().
void VM_RedefineClasses::rewrite_cp_refs_in_method(methodHandle method,
       methodHandle *new_method_p, TRAPS) {

  *new_method_p = methodHandle();  // default is no new method

  // We cache a pointer to the bytecodes here in code_base. If GC
  // moves the Method*, then the bytecodes will also move which
  // will likely cause a crash. We create a No_Safepoint_Verifier
  // object to detect whether we pass a possible safepoint in this
  // code block.
  No_Safepoint_Verifier nsv;

  // Bytecodes and their length
  address code_base = method->code_base();
  int code_length = method->code_size();

  int bc_length;
  for (int bci = 0; bci < code_length; bci += bc_length) {
    address bcp = code_base + bci;
    Bytecodes::Code c = (Bytecodes::Code)(*bcp);

    bc_length = Bytecodes::length_for(c);
    if (bc_length == 0) {
      // More complicated bytecodes report a length of zero so
      // we have to try again a slightly different way.
      bc_length = Bytecodes::length_at(method(), bcp);
    }

    assert(bc_length != 0, "impossible bytecode length");

    switch (c) {
      case Bytecodes::_ldc:
      {
        int cp_index = *(bcp + 1);
        int new_index = find_new_index(cp_index);

        if (StressLdcRewrite && new_index == 0) {
          // If we are stressing ldc -> ldc_w rewriting, then we
          // always need a new_index value.
          new_index = cp_index;
        }
        if (new_index != 0) {
          // the original index is mapped so we have more work to do
          if (!StressLdcRewrite && new_index <= max_jubyte) {
            // The new value can still use ldc instead of ldc_w
            // unless we are trying to stress ldc -> ldc_w rewriting
            RC_TRACE_WITH_THREAD(0x00080000, THREAD,
              ("%s@" INTPTR_FORMAT " old=%d, new=%d", Bytecodes::name(c),
              bcp, cp_index, new_index));
            *(bcp + 1) = new_index;
          } else {
            RC_TRACE_WITH_THREAD(0x00080000, THREAD,
              ("%s->ldc_w@" INTPTR_FORMAT " old=%d, new=%d",
              Bytecodes::name(c), bcp, cp_index, new_index));
            // the new value needs ldc_w instead of ldc
            u_char inst_buffer[4]; // max instruction size is 4 bytes
            bcp = (address)inst_buffer;
            // construct new instruction sequence
            *bcp = Bytecodes::_ldc_w;
            bcp++;
            // Rewriter::rewrite_method() does not rewrite ldc -> ldc_w.
            // See comment below for difference between put_Java_u2()
            // and put_native_u2().
            Bytes::put_Java_u2(bcp, new_index);

            Relocator rc(method, NULL /* no RelocatorListener needed */);
            methodHandle m;
            {
              Pause_No_Safepoint_Verifier pnsv(&nsv);

              // ldc is 2 bytes and ldc_w is 3 bytes
              m = rc.insert_space_at(bci, 3, inst_buffer, THREAD);
              if (m.is_null() || HAS_PENDING_EXCEPTION) {
                guarantee(false, "insert_space_at() failed");
              }
            }

            // return the new method so that the caller can update
            // the containing class
            *new_method_p = method = m;
            // switch our bytecode processing loop from the old method
            // to the new method
            code_base = method->code_base();
            code_length = method->code_size();
            bcp = code_base + bci;
            c = (Bytecodes::Code)(*bcp);
            bc_length = Bytecodes::length_for(c);
            assert(bc_length != 0, "sanity check");
          } // end we need ldc_w instead of ldc
        } // end if there is a mapped index
      } break;

      // these bytecodes have a two-byte constant pool index
      case Bytecodes::_anewarray      : // fall through
      case Bytecodes::_checkcast      : // fall through
      case Bytecodes::_getfield       : // fall through
      case Bytecodes::_getstatic      : // fall through
      case Bytecodes::_instanceof     : // fall through
      case Bytecodes::_invokeinterface: // fall through
      case Bytecodes::_invokespecial  : // fall through
      case Bytecodes::_invokestatic   : // fall through
      case Bytecodes::_invokevirtual  : // fall through
      case Bytecodes::_ldc_w          : // fall through
      case Bytecodes::_ldc2_w         : // fall through
      case Bytecodes::_multianewarray : // fall through
      case Bytecodes::_new            : // fall through
      case Bytecodes::_putfield       : // fall through
      case Bytecodes::_putstatic      :
      {
        address p = bcp + 1;
        int cp_index = Bytes::get_Java_u2(p);
        int new_index = find_new_index(cp_index);
        if (new_index != 0) {
          // the original index is mapped so update w/ new value
          RC_TRACE_WITH_THREAD(0x00080000, THREAD,
            ("%s@" INTPTR_FORMAT " old=%d, new=%d", Bytecodes::name(c),
            bcp, cp_index, new_index));
          // Rewriter::rewrite_method() uses put_native_u2() in this
          // situation because it is reusing the constant pool index
          // location for a native index into the constantPoolCache.
          // Since we are updating the constant pool index prior to
          // verification and constantPoolCache initialization, we
          // need to keep the new index in Java byte order.
          Bytes::put_Java_u2(p, new_index);
        }
      } break;
    }
  } // end for each bytecode
} // end rewrite_cp_refs_in_method()


// Rewrite constant pool references in the class_annotations field.
bool VM_RedefineClasses::rewrite_cp_refs_in_class_annotations(
       instanceKlassHandle scratch_class, TRAPS) {

  AnnotationArray* class_annotations = scratch_class->class_annotations();
  if (class_annotations == NULL || class_annotations->length() == 0) {
    // no class_annotations so nothing to do
    return true;
  }

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("class_annotations length=%d", class_annotations->length()));

  int byte_i = 0;  // byte index into class_annotations
  return rewrite_cp_refs_in_annotations_typeArray(class_annotations, byte_i,
           THREAD);
}


// Rewrite constant pool references in an annotations typeArray. This
// "structure" is adapted from the RuntimeVisibleAnnotations_attribute
// that is described in section 4.8.15 of the 2nd-edition of the VM spec:
//
// annotations_typeArray {
//   u2 num_annotations;
//   annotation annotations[num_annotations];
// }
//
bool VM_RedefineClasses::rewrite_cp_refs_in_annotations_typeArray(
       AnnotationArray* annotations_typeArray, int &byte_i_ref, TRAPS) {

  if ((byte_i_ref + 2) > annotations_typeArray->length()) {
    // not enough room for num_annotations field
    RC_TRACE_WITH_THREAD(0x02000000, THREAD,
      ("length() is too small for num_annotations field"));
    return false;
  }

  u2 num_annotations = Bytes::get_Java_u2((address)
                         annotations_typeArray->adr_at(byte_i_ref));
  byte_i_ref += 2;

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("num_annotations=%d", num_annotations));

  int calc_num_annotations = 0;
  for (; calc_num_annotations < num_annotations; calc_num_annotations++) {
    if (!rewrite_cp_refs_in_annotation_struct(annotations_typeArray,
           byte_i_ref, THREAD)) {
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("bad annotation_struct at %d", calc_num_annotations));
      // propagate failure back to caller
      return false;
    }
  }
  assert(num_annotations == calc_num_annotations, "sanity check");

  return true;
} // end rewrite_cp_refs_in_annotations_typeArray()


// Rewrite constant pool references in the annotation struct portion of
// an annotations_typeArray. This "structure" is from section 4.8.15 of
// the 2nd-edition of the VM spec:
//
// struct annotation {
//   u2 type_index;
//   u2 num_element_value_pairs;
//   {
//     u2 element_name_index;
//     element_value value;
//   } element_value_pairs[num_element_value_pairs];
// }
//
bool VM_RedefineClasses::rewrite_cp_refs_in_annotation_struct(
       AnnotationArray* annotations_typeArray, int &byte_i_ref, TRAPS) {
  if ((byte_i_ref + 2 + 2) > annotations_typeArray->length()) {
    // not enough room for smallest annotation_struct
    RC_TRACE_WITH_THREAD(0x02000000, THREAD,
      ("length() is too small for annotation_struct"));
    return false;
  }

  u2 type_index = rewrite_cp_ref_in_annotation_data(annotations_typeArray,
                    byte_i_ref, "mapped old type_index=%d", THREAD);

  u2 num_element_value_pairs = Bytes::get_Java_u2((address)
                                 annotations_typeArray->adr_at(byte_i_ref));
  byte_i_ref += 2;

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("type_index=%d  num_element_value_pairs=%d", type_index,
    num_element_value_pairs));

  int calc_num_element_value_pairs = 0;
  for (; calc_num_element_value_pairs < num_element_value_pairs;
       calc_num_element_value_pairs++) {
    if ((byte_i_ref + 2) > annotations_typeArray->length()) {
      // not enough room for another element_name_index, let alone
      // the rest of another component
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("length() is too small for element_name_index"));
      return false;
    }

    u2 element_name_index = rewrite_cp_ref_in_annotation_data(
                              annotations_typeArray, byte_i_ref,
                              "mapped old element_name_index=%d", THREAD);

    RC_TRACE_WITH_THREAD(0x02000000, THREAD,
      ("element_name_index=%d", element_name_index));

    if (!rewrite_cp_refs_in_element_value(annotations_typeArray,
           byte_i_ref, THREAD)) {
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("bad element_value at %d", calc_num_element_value_pairs));
      // propagate failure back to caller
      return false;
    }
  } // end for each component
  assert(num_element_value_pairs == calc_num_element_value_pairs,
    "sanity check");

  return true;
} // end rewrite_cp_refs_in_annotation_struct()


// Rewrite a constant pool reference at the current position in
// annotations_typeArray if needed. Returns the original constant
// pool reference if a rewrite was not needed or the new constant
// pool reference if a rewrite was needed.
u2 VM_RedefineClasses::rewrite_cp_ref_in_annotation_data(
     AnnotationArray* annotations_typeArray, int &byte_i_ref,
     const char * trace_mesg, TRAPS) {

  address cp_index_addr = (address)
    annotations_typeArray->adr_at(byte_i_ref);
  u2 old_cp_index = Bytes::get_Java_u2(cp_index_addr);
  u2 new_cp_index = find_new_index(old_cp_index);
  if (new_cp_index != 0) {
    RC_TRACE_WITH_THREAD(0x02000000, THREAD, (trace_mesg, old_cp_index));
    Bytes::put_Java_u2(cp_index_addr, new_cp_index);
    old_cp_index = new_cp_index;
  }
  byte_i_ref += 2;
  return old_cp_index;
}


// Rewrite constant pool references in the element_value portion of an
// annotations_typeArray. This "structure" is from section 4.8.15.1 of
// the 2nd-edition of the VM spec:
//
// struct element_value {
//   u1 tag;
//   union {
//     u2 const_value_index;
//     {
//       u2 type_name_index;
//       u2 const_name_index;
//     } enum_const_value;
//     u2 class_info_index;
//     annotation annotation_value;
//     struct {
//       u2 num_values;
//       element_value values[num_values];
//     } array_value;
//   } value;
// }
//
bool VM_RedefineClasses::rewrite_cp_refs_in_element_value(
       AnnotationArray* annotations_typeArray, int &byte_i_ref, TRAPS) {

  if ((byte_i_ref + 1) > annotations_typeArray->length()) {
    // not enough room for a tag let alone the rest of an element_value
    RC_TRACE_WITH_THREAD(0x02000000, THREAD,
      ("length() is too small for a tag"));
    return false;
  }

  u1 tag = annotations_typeArray->at(byte_i_ref);
  byte_i_ref++;
  RC_TRACE_WITH_THREAD(0x02000000, THREAD, ("tag='%c'", tag));

  switch (tag) {
    // These BaseType tag values are from Table 4.2 in VM spec:
    case 'B':  // byte
    case 'C':  // char
    case 'D':  // double
    case 'F':  // float
    case 'I':  // int
    case 'J':  // long
    case 'S':  // short
    case 'Z':  // boolean

    // The remaining tag values are from Table 4.8 in the 2nd-edition of
    // the VM spec:
    case 's':
    {
      // For the above tag values (including the BaseType values),
      // value.const_value_index is right union field.

      if ((byte_i_ref + 2) > annotations_typeArray->length()) {
        // not enough room for a const_value_index
        RC_TRACE_WITH_THREAD(0x02000000, THREAD,
          ("length() is too small for a const_value_index"));
        return false;
      }

      u2 const_value_index = rewrite_cp_ref_in_annotation_data(
                               annotations_typeArray, byte_i_ref,
                               "mapped old const_value_index=%d", THREAD);

      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("const_value_index=%d", const_value_index));
    } break;

    case 'e':
    {
      // for the above tag value, value.enum_const_value is right union field

      if ((byte_i_ref + 4) > annotations_typeArray->length()) {
        // not enough room for a enum_const_value
        RC_TRACE_WITH_THREAD(0x02000000, THREAD,
          ("length() is too small for a enum_const_value"));
        return false;
      }

      u2 type_name_index = rewrite_cp_ref_in_annotation_data(
                             annotations_typeArray, byte_i_ref,
                             "mapped old type_name_index=%d", THREAD);

      u2 const_name_index = rewrite_cp_ref_in_annotation_data(
                              annotations_typeArray, byte_i_ref,
                              "mapped old const_name_index=%d", THREAD);

      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("type_name_index=%d  const_name_index=%d", type_name_index,
        const_name_index));
    } break;

    case 'c':
    {
      // for the above tag value, value.class_info_index is right union field

      if ((byte_i_ref + 2) > annotations_typeArray->length()) {
        // not enough room for a class_info_index
        RC_TRACE_WITH_THREAD(0x02000000, THREAD,
          ("length() is too small for a class_info_index"));
        return false;
      }

      u2 class_info_index = rewrite_cp_ref_in_annotation_data(
                              annotations_typeArray, byte_i_ref,
                              "mapped old class_info_index=%d", THREAD);

      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("class_info_index=%d", class_info_index));
    } break;

    case '@':
      // For the above tag value, value.attr_value is the right union
      // field. This is a nested annotation.
      if (!rewrite_cp_refs_in_annotation_struct(annotations_typeArray,
             byte_i_ref, THREAD)) {
        // propagate failure back to caller
        return false;
      }
      break;

    case '[':
    {
      if ((byte_i_ref + 2) > annotations_typeArray->length()) {
        // not enough room for a num_values field
        RC_TRACE_WITH_THREAD(0x02000000, THREAD,
          ("length() is too small for a num_values field"));
        return false;
      }

      // For the above tag value, value.array_value is the right union
      // field. This is an array of nested element_value.
      u2 num_values = Bytes::get_Java_u2((address)
                        annotations_typeArray->adr_at(byte_i_ref));
      byte_i_ref += 2;
      RC_TRACE_WITH_THREAD(0x02000000, THREAD, ("num_values=%d", num_values));

      int calc_num_values = 0;
      for (; calc_num_values < num_values; calc_num_values++) {
        if (!rewrite_cp_refs_in_element_value(
               annotations_typeArray, byte_i_ref, THREAD)) {
          RC_TRACE_WITH_THREAD(0x02000000, THREAD,
            ("bad nested element_value at %d", calc_num_values));
          // propagate failure back to caller
          return false;
        }
      }
      assert(num_values == calc_num_values, "sanity check");
    } break;

    default:
      RC_TRACE_WITH_THREAD(0x02000000, THREAD, ("bad tag=0x%x", tag));
      return false;
  } // end decode tag field

  return true;
} // end rewrite_cp_refs_in_element_value()


// Rewrite constant pool references in a fields_annotations field.
bool VM_RedefineClasses::rewrite_cp_refs_in_fields_annotations(
       instanceKlassHandle scratch_class, TRAPS) {

  Annotations* sca = scratch_class->annotations();
  if (sca == NULL) return true;

  Array<AnnotationArray*>* fields_annotations = sca->fields_annotations();

  if (fields_annotations == NULL || fields_annotations->length() == 0) {
    // no fields_annotations so nothing to do
    return true;
  }

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("fields_annotations length=%d", fields_annotations->length()));

  for (int i = 0; i < fields_annotations->length(); i++) {
    AnnotationArray* field_annotations = fields_annotations->at(i);
    if (field_annotations == NULL || field_annotations->length() == 0) {
      // this field does not have any annotations so skip it
      continue;
    }

    int byte_i = 0;  // byte index into field_annotations
    if (!rewrite_cp_refs_in_annotations_typeArray(field_annotations, byte_i,
           THREAD)) {
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("bad field_annotations at %d", i));
      // propagate failure back to caller
      return false;
    }
  }

  return true;
} // end rewrite_cp_refs_in_fields_annotations()


// Rewrite constant pool references in a methods_annotations field.
bool VM_RedefineClasses::rewrite_cp_refs_in_methods_annotations(
       instanceKlassHandle scratch_class, TRAPS) {

  Annotations* sca = scratch_class->annotations();
  if (sca == NULL) return true;

  Array<AnnotationArray*>* methods_annotations = sca->methods_annotations();

  if (methods_annotations == NULL || methods_annotations->length() == 0) {
    // no methods_annotations so nothing to do
    return true;
  }

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("methods_annotations length=%d", methods_annotations->length()));

  for (int i = 0; i < methods_annotations->length(); i++) {
    AnnotationArray* method_annotations = methods_annotations->at(i);
    if (method_annotations == NULL || method_annotations->length() == 0) {
      // this method does not have any annotations so skip it
      continue;
    }

    int byte_i = 0;  // byte index into method_annotations
    if (!rewrite_cp_refs_in_annotations_typeArray(method_annotations, byte_i,
           THREAD)) {
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("bad method_annotations at %d", i));
      // propagate failure back to caller
      return false;
    }
  }

  return true;
} // end rewrite_cp_refs_in_methods_annotations()


// Rewrite constant pool references in a methods_parameter_annotations
// field. This "structure" is adapted from the
// RuntimeVisibleParameterAnnotations_attribute described in section
// 4.8.17 of the 2nd-edition of the VM spec:
//
// methods_parameter_annotations_typeArray {
//   u1 num_parameters;
//   {
//     u2 num_annotations;
//     annotation annotations[num_annotations];
//   } parameter_annotations[num_parameters];
// }
//
bool VM_RedefineClasses::rewrite_cp_refs_in_methods_parameter_annotations(
       instanceKlassHandle scratch_class, TRAPS) {

  Annotations* sca = scratch_class->annotations();
  if (sca == NULL) return true;

  Array<AnnotationArray*>* methods_parameter_annotations =
    sca->methods_parameter_annotations();

  if (methods_parameter_annotations == NULL
      || methods_parameter_annotations->length() == 0) {
    // no methods_parameter_annotations so nothing to do
    return true;
  }

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("methods_parameter_annotations length=%d",
    methods_parameter_annotations->length()));

  for (int i = 0; i < methods_parameter_annotations->length(); i++) {
    AnnotationArray* method_parameter_annotations = methods_parameter_annotations->at(i);
    if (method_parameter_annotations == NULL
        || method_parameter_annotations->length() == 0) {
      // this method does not have any parameter annotations so skip it
      continue;
    }

    if (method_parameter_annotations->length() < 1) {
      // not enough room for a num_parameters field
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("length() is too small for a num_parameters field at %d", i));
      return false;
    }

    int byte_i = 0;  // byte index into method_parameter_annotations

    u1 num_parameters = method_parameter_annotations->at(byte_i);
    byte_i++;

    RC_TRACE_WITH_THREAD(0x02000000, THREAD,
      ("num_parameters=%d", num_parameters));

    int calc_num_parameters = 0;
    for (; calc_num_parameters < num_parameters; calc_num_parameters++) {
      if (!rewrite_cp_refs_in_annotations_typeArray(
             method_parameter_annotations, byte_i, THREAD)) {
        RC_TRACE_WITH_THREAD(0x02000000, THREAD,
          ("bad method_parameter_annotations at %d", calc_num_parameters));
        // propagate failure back to caller
        return false;
      }
    }
    assert(num_parameters == calc_num_parameters, "sanity check");
  }

  return true;
} // end rewrite_cp_refs_in_methods_parameter_annotations()


// Rewrite constant pool references in a methods_default_annotations
// field. This "structure" is adapted from the AnnotationDefault_attribute
// that is described in section 4.8.19 of the 2nd-edition of the VM spec:
//
// methods_default_annotations_typeArray {
//   element_value default_value;
// }
//
bool VM_RedefineClasses::rewrite_cp_refs_in_methods_default_annotations(
       instanceKlassHandle scratch_class, TRAPS) {

  Annotations* sca = scratch_class->annotations();
  if (sca == NULL) return true;

  Array<AnnotationArray*>* methods_default_annotations =
    sca->methods_default_annotations();

  if (methods_default_annotations == NULL
      || methods_default_annotations->length() == 0) {
    // no methods_default_annotations so nothing to do
    return true;
  }

  RC_TRACE_WITH_THREAD(0x02000000, THREAD,
    ("methods_default_annotations length=%d",
    methods_default_annotations->length()));

  for (int i = 0; i < methods_default_annotations->length(); i++) {
    AnnotationArray* method_default_annotations = methods_default_annotations->at(i);
    if (method_default_annotations == NULL
        || method_default_annotations->length() == 0) {
      // this method does not have any default annotations so skip it
      continue;
    }

    int byte_i = 0;  // byte index into method_default_annotations

    if (!rewrite_cp_refs_in_element_value(
           method_default_annotations, byte_i, THREAD)) {
      RC_TRACE_WITH_THREAD(0x02000000, THREAD,
        ("bad default element_value at %d", i));
      // propagate failure back to caller
      return false;
    }
  }

  return true;
} // end rewrite_cp_refs_in_methods_default_annotations()


// Rewrite constant pool references in the method's stackmap table.
// These "structures" are adapted from the StackMapTable_attribute that
// is described in section 4.8.4 of the 6.0 version of the VM spec
// (dated 2005.10.26):
// file:///net/quincunx.sfbay/export/gbracha/ClassFile-Java6.pdf
//
// stack_map {
//   u2 number_of_entries;
//   stack_map_frame entries[number_of_entries];
// }
//
void VM_RedefineClasses::rewrite_cp_refs_in_stack_map_table(
       methodHandle method, TRAPS) {

  if (!method->has_stackmap_table()) {
    return;
  }

  AnnotationArray* stackmap_data = method->stackmap_data();
  address stackmap_p = (address)stackmap_data->adr_at(0);
  address stackmap_end = stackmap_p + stackmap_data->length();

  assert(stackmap_p + 2 <= stackmap_end, "no room for number_of_entries");
  u2 number_of_entries = Bytes::get_Java_u2(stackmap_p);
  stackmap_p += 2;

  RC_TRACE_WITH_THREAD(0x04000000, THREAD,
    ("number_of_entries=%u", number_of_entries));

  // walk through each stack_map_frame
  u2 calc_number_of_entries = 0;
  for (; calc_number_of_entries < number_of_entries; calc_number_of_entries++) {
    // The stack_map_frame structure is a u1 frame_type followed by
    // 0 or more bytes of data:
    //
    // union stack_map_frame {
    //   same_frame;
    //   same_locals_1_stack_item_frame;
    //   same_locals_1_stack_item_frame_extended;
    //   chop_frame;
    //   same_frame_extended;
    //   append_frame;
    //   full_frame;
    // }

    assert(stackmap_p + 1 <= stackmap_end, "no room for frame_type");
    // The Linux compiler does not like frame_type to be u1 or u2. It
    // issues the following warning for the first if-statement below:
    //
    // "warning: comparison is always true due to limited range of data type"
    //
    u4 frame_type = *stackmap_p;
    stackmap_p++;

    // same_frame {
    //   u1 frame_type = SAME; /* 0-63 */
    // }
    if (frame_type >= 0 && frame_type <= 63) {
      // nothing more to do for same_frame
    }

    // same_locals_1_stack_item_frame {
    //   u1 frame_type = SAME_LOCALS_1_STACK_ITEM; /* 64-127 */
    //   verification_type_info stack[1];
    // }
    else if (frame_type >= 64 && frame_type <= 127) {
      rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
        calc_number_of_entries, frame_type, THREAD);
    }

    // reserved for future use
    else if (frame_type >= 128 && frame_type <= 246) {
      // nothing more to do for reserved frame_types
    }

    // same_locals_1_stack_item_frame_extended {
    //   u1 frame_type = SAME_LOCALS_1_STACK_ITEM_EXTENDED; /* 247 */
    //   u2 offset_delta;
    //   verification_type_info stack[1];
    // }
    else if (frame_type == 247) {
      stackmap_p += 2;
      rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
        calc_number_of_entries, frame_type, THREAD);
    }

    // chop_frame {
    //   u1 frame_type = CHOP; /* 248-250 */
    //   u2 offset_delta;
    // }
    else if (frame_type >= 248 && frame_type <= 250) {
      stackmap_p += 2;
    }

    // same_frame_extended {
    //   u1 frame_type = SAME_FRAME_EXTENDED; /* 251*/
    //   u2 offset_delta;
    // }
    else if (frame_type == 251) {
      stackmap_p += 2;
    }

    // append_frame {
    //   u1 frame_type = APPEND; /* 252-254 */
    //   u2 offset_delta;
    //   verification_type_info locals[frame_type - 251];
    // }
    else if (frame_type >= 252 && frame_type <= 254) {
      assert(stackmap_p + 2 <= stackmap_end,
        "no room for offset_delta");
      stackmap_p += 2;
      u1 len = frame_type - 251;
      for (u1 i = 0; i < len; i++) {
        rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
          calc_number_of_entries, frame_type, THREAD);
      }
    }

    // full_frame {
    //   u1 frame_type = FULL_FRAME; /* 255 */
    //   u2 offset_delta;
    //   u2 number_of_locals;
    //   verification_type_info locals[number_of_locals];
    //   u2 number_of_stack_items;
    //   verification_type_info stack[number_of_stack_items];
    // }
    else if (frame_type == 255) {
      assert(stackmap_p + 2 + 2 <= stackmap_end,
        "no room for smallest full_frame");
      stackmap_p += 2;

      u2 number_of_locals = Bytes::get_Java_u2(stackmap_p);
      stackmap_p += 2;

      for (u2 locals_i = 0; locals_i < number_of_locals; locals_i++) {
        rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
          calc_number_of_entries, frame_type, THREAD);
      }

      // Use the largest size for the number_of_stack_items, but only get
      // the right number of bytes.
      u2 number_of_stack_items = Bytes::get_Java_u2(stackmap_p);
      stackmap_p += 2;

      for (u2 stack_i = 0; stack_i < number_of_stack_items; stack_i++) {
        rewrite_cp_refs_in_verification_type_info(stackmap_p, stackmap_end,
          calc_number_of_entries, frame_type, THREAD);
      }
    }
  } // end while there is a stack_map_frame
  assert(number_of_entries == calc_number_of_entries, "sanity check");
} // end rewrite_cp_refs_in_stack_map_table()


// Rewrite constant pool references in the verification type info
// portion of the method's stackmap table. These "structures" are
// adapted from the StackMapTable_attribute that is described in
// section 4.8.4 of the 6.0 version of the VM spec (dated 2005.10.26):
// file:///net/quincunx.sfbay/export/gbracha/ClassFile-Java6.pdf
//
// The verification_type_info structure is a u1 tag followed by 0 or
// more bytes of data:
//
// union verification_type_info {
//   Top_variable_info;
//   Integer_variable_info;
//   Float_variable_info;
//   Long_variable_info;
//   Double_variable_info;
//   Null_variable_info;
//   UninitializedThis_variable_info;
//   Object_variable_info;
//   Uninitialized_variable_info;
// }
//
void VM_RedefineClasses::rewrite_cp_refs_in_verification_type_info(
       address& stackmap_p_ref, address stackmap_end, u2 frame_i,
       u1 frame_type, TRAPS) {

  assert(stackmap_p_ref + 1 <= stackmap_end, "no room for tag");
  u1 tag = *stackmap_p_ref;
  stackmap_p_ref++;

  switch (tag) {
  // Top_variable_info {
  //   u1 tag = ITEM_Top; /* 0 */
  // }
  // verificationType.hpp has zero as ITEM_Bogus instead of ITEM_Top
  case 0:  // fall through

  // Integer_variable_info {
  //   u1 tag = ITEM_Integer; /* 1 */
  // }
  case ITEM_Integer:  // fall through

  // Float_variable_info {
  //   u1 tag = ITEM_Float; /* 2 */
  // }
  case ITEM_Float:  // fall through

  // Double_variable_info {
  //   u1 tag = ITEM_Double; /* 3 */
  // }
  case ITEM_Double:  // fall through

  // Long_variable_info {
  //   u1 tag = ITEM_Long; /* 4 */
  // }
  case ITEM_Long:  // fall through

  // Null_variable_info {
  //   u1 tag = ITEM_Null; /* 5 */
  // }
  case ITEM_Null:  // fall through

  // UninitializedThis_variable_info {
  //   u1 tag = ITEM_UninitializedThis; /* 6 */
  // }
  case ITEM_UninitializedThis:
    // nothing more to do for the above tag types
    break;

  // Object_variable_info {
  //   u1 tag = ITEM_Object; /* 7 */
  //   u2 cpool_index;
  // }
  case ITEM_Object:
  {
    assert(stackmap_p_ref + 2 <= stackmap_end, "no room for cpool_index");
    u2 cpool_index = Bytes::get_Java_u2(stackmap_p_ref);
    u2 new_cp_index = find_new_index(cpool_index);
    if (new_cp_index != 0) {
      RC_TRACE_WITH_THREAD(0x04000000, THREAD,
        ("mapped old cpool_index=%d", cpool_index));
      Bytes::put_Java_u2(stackmap_p_ref, new_cp_index);
      cpool_index = new_cp_index;
    }
    stackmap_p_ref += 2;

    RC_TRACE_WITH_THREAD(0x04000000, THREAD,
      ("frame_i=%u, frame_type=%u, cpool_index=%d", frame_i,
      frame_type, cpool_index));
  } break;

  // Uninitialized_variable_info {
  //   u1 tag = ITEM_Uninitialized; /* 8 */
  //   u2 offset;
  // }
  case ITEM_Uninitialized:
    assert(stackmap_p_ref + 2 <= stackmap_end, "no room for offset");
    stackmap_p_ref += 2;
    break;

  default:
    RC_TRACE_WITH_THREAD(0x04000000, THREAD,
      ("frame_i=%u, frame_type=%u, bad tag=0x%x", frame_i, frame_type, tag));
    ShouldNotReachHere();
    break;
  } // end switch (tag)
} // end rewrite_cp_refs_in_verification_type_info()


// Change the constant pool associated with klass scratch_class to
// scratch_cp. If shrink is true, then scratch_cp_length elements
// are copied from scratch_cp to a smaller constant pool and the
// smaller constant pool is associated with scratch_class.
void VM_RedefineClasses::set_new_constant_pool(
       ClassLoaderData* loader_data,
       instanceKlassHandle scratch_class, constantPoolHandle scratch_cp,
       int scratch_cp_length, TRAPS) {
  assert(scratch_cp->length() >= scratch_cp_length, "sanity check");

    // scratch_cp is a merged constant pool and has enough space for a
    // worst case merge situation. We want to associate the minimum
    // sized constant pool with the klass to save space.
    constantPoolHandle smaller_cp(THREAD,
    ConstantPool::allocate(loader_data, scratch_cp_length,
                                   THREAD));
    // preserve orig_length() value in the smaller copy
    int orig_length = scratch_cp->orig_length();
    assert(orig_length != 0, "sanity check");
    smaller_cp->set_orig_length(orig_length);
    scratch_cp->copy_cp_to(1, scratch_cp_length - 1, smaller_cp, 1, THREAD);
    scratch_cp = smaller_cp;

  // attach new constant pool to klass
  scratch_cp->set_pool_holder(scratch_class());

  // attach klass to new constant pool
  scratch_class->set_constants(scratch_cp());

  int i;  // for portability

  // update each field in klass to use new constant pool indices as needed
  for (JavaFieldStream fs(scratch_class); !fs.done(); fs.next()) {
    jshort cur_index = fs.name_index();
    jshort new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("field-name_index change: %d to %d", cur_index, new_index));
      fs.set_name_index(new_index);
    }
    cur_index = fs.signature_index();
    new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("field-signature_index change: %d to %d", cur_index, new_index));
      fs.set_signature_index(new_index);
    }
    cur_index = fs.initval_index();
    new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("field-initval_index change: %d to %d", cur_index, new_index));
      fs.set_initval_index(new_index);
    }
    cur_index = fs.generic_signature_index();
    new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("field-generic_signature change: %d to %d", cur_index, new_index));
      fs.set_generic_signature_index(new_index);
    }
  } // end for each field

  // Update constant pool indices in the inner classes info to use
  // new constant indices as needed. The inner classes info is a
  // quadruple:
  // (inner_class_info, outer_class_info, inner_name, inner_access_flags)
  InnerClassesIterator iter(scratch_class);
  for (; !iter.done(); iter.next()) {
    int cur_index = iter.inner_class_info_index();
    if (cur_index == 0) {
      continue;  // JVM spec. allows null inner class refs so skip it
    }
    int new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("inner_class_info change: %d to %d", cur_index, new_index));
      iter.set_inner_class_info_index(new_index);
    }
    cur_index = iter.outer_class_info_index();
    new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("outer_class_info change: %d to %d", cur_index, new_index));
      iter.set_outer_class_info_index(new_index);
    }
    cur_index = iter.inner_name_index();
    new_index = find_new_index(cur_index);
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("inner_name change: %d to %d", cur_index, new_index));
      iter.set_inner_name_index(new_index);
    }
  } // end for each inner class

  // Attach each method in klass to the new constant pool and update
  // to use new constant pool indices as needed:
  Array<Method*>* methods = scratch_class->methods();
  for (i = methods->length() - 1; i >= 0; i--) {
    methodHandle method(THREAD, methods->at(i));
    method->set_constants(scratch_cp());

    int new_index = find_new_index(method->name_index());
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("method-name_index change: %d to %d", method->name_index(),
        new_index));
      method->set_name_index(new_index);
    }
    new_index = find_new_index(method->signature_index());
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("method-signature_index change: %d to %d",
        method->signature_index(), new_index));
      method->set_signature_index(new_index);
    }
    new_index = find_new_index(method->generic_signature_index());
    if (new_index != 0) {
      RC_TRACE_WITH_THREAD(0x00080000, THREAD,
        ("method-generic_signature_index change: %d to %d",
        method->generic_signature_index(), new_index));
      method->set_generic_signature_index(new_index);
    }

    // Update constant pool indices in the method's checked exception
    // table to use new constant indices as needed.
    int cext_length = method->checked_exceptions_length();
    if (cext_length > 0) {
      CheckedExceptionElement * cext_table =
        method->checked_exceptions_start();
      for (int j = 0; j < cext_length; j++) {
        int cur_index = cext_table[j].class_cp_index;
        int new_index = find_new_index(cur_index);
        if (new_index != 0) {
          RC_TRACE_WITH_THREAD(0x00080000, THREAD,
            ("cext-class_cp_index change: %d to %d", cur_index, new_index));
          cext_table[j].class_cp_index = (u2)new_index;
        }
      } // end for each checked exception table entry
    } // end if there are checked exception table entries

    // Update each catch type index in the method's exception table
    // to use new constant pool indices as needed. The exception table
    // holds quadruple entries of the form:
    //   (beg_bci, end_bci, handler_bci, klass_index)

    ExceptionTable ex_table(method());
    int ext_length = ex_table.length();

    for (int j = 0; j < ext_length; j ++) {
      int cur_index = ex_table.catch_type_index(j);
      int new_index = find_new_index(cur_index);
      if (new_index != 0) {
        RC_TRACE_WITH_THREAD(0x00080000, THREAD,
          ("ext-klass_index change: %d to %d", cur_index, new_index));
        ex_table.set_catch_type_index(j, new_index);
      }
    } // end for each exception table entry

    // Update constant pool indices in the method's local variable
    // table to use new constant indices as needed. The local variable
    // table hold sextuple entries of the form:
    // (start_pc, length, name_index, descriptor_index, signature_index, slot)
    int lvt_length = method->localvariable_table_length();
    if (lvt_length > 0) {
      LocalVariableTableElement * lv_table =
        method->localvariable_table_start();
      for (int j = 0; j < lvt_length; j++) {
        int cur_index = lv_table[j].name_cp_index;
        int new_index = find_new_index(cur_index);
        if (new_index != 0) {
          RC_TRACE_WITH_THREAD(0x00080000, THREAD,
            ("lvt-name_cp_index change: %d to %d", cur_index, new_index));
          lv_table[j].name_cp_index = (u2)new_index;
        }
        cur_index = lv_table[j].descriptor_cp_index;
        new_index = find_new_index(cur_index);
        if (new_index != 0) {
          RC_TRACE_WITH_THREAD(0x00080000, THREAD,
            ("lvt-descriptor_cp_index change: %d to %d", cur_index,
            new_index));
          lv_table[j].descriptor_cp_index = (u2)new_index;
        }
        cur_index = lv_table[j].signature_cp_index;
        new_index = find_new_index(cur_index);
        if (new_index != 0) {
          RC_TRACE_WITH_THREAD(0x00080000, THREAD,
            ("lvt-signature_cp_index change: %d to %d", cur_index, new_index));
          lv_table[j].signature_cp_index = (u2)new_index;
        }
      } // end for each local variable table entry
    } // end if there are local variable table entries

    rewrite_cp_refs_in_stack_map_table(method, THREAD);
  } // end for each method
} // end set_new_constant_pool()


void VM_RedefineClasses::adjust_array_vtable(Klass* k_oop) {
  ArrayKlass* ak = ArrayKlass::cast(k_oop);
  bool trace_name_printed = false;
  ak->vtable()->adjust_method_entries(_matching_old_methods,
                                      _matching_new_methods,
                                      _matching_methods_length,
                                      &trace_name_printed);
}

// Unevolving classes may point to methods of the_class directly
// from their constant pool caches, itables, and/or vtables. We
// use the SystemDictionary::classes_do() facility and this helper
// to fix up these pointers.
//
// Note: We currently don't support updating the vtable in
// arrayKlassOops. See Open Issues in jvmtiRedefineClasses.hpp.
void VM_RedefineClasses::adjust_cpool_cache_and_vtable(Klass* k_oop,
       ClassLoaderData* initiating_loader,
       TRAPS) {
  Klass *k = k_oop;
  if (k->oop_is_instance()) {
    HandleMark hm(THREAD);
    InstanceKlass *ik = (InstanceKlass *) k;

    // HotSpot specific optimization! HotSpot does not currently
    // support delegation from the bootstrap class loader to a
    // user-defined class loader. This means that if the bootstrap
    // class loader is the initiating class loader, then it will also
    // be the defining class loader. This also means that classes
    // loaded by the bootstrap class loader cannot refer to classes
    // loaded by a user-defined class loader. Note: a user-defined
    // class loader can delegate to the bootstrap class loader.
    //
    // If the current class being redefined has a user-defined class
    // loader as its defining class loader, then we can skip all
    // classes loaded by the bootstrap class loader.
    bool is_user_defined =
           InstanceKlass::cast(_the_class_oop)->class_loader() != NULL;
    if (is_user_defined && ik->class_loader() == NULL) {
      return;
    }

    // If the class being redefined is java.lang.Object, we need to fix all
    // array class vtables also
    if (_the_class_oop == SystemDictionary::Object_klass()) {
      ik->array_klasses_do(adjust_array_vtable);
    }

    // This is a very busy routine. We don't want too much tracing
    // printed out.
    bool trace_name_printed = false;

    // Very noisy: only enable this call if you are trying to determine
    // that a specific class gets found by this routine.
    // RC_TRACE macro has an embedded ResourceMark
    // RC_TRACE_WITH_THREAD(0x00100000, THREAD,
    //   ("adjust check: name=%s", ik->external_name()));
    // trace_name_printed = true;

    // Fix the vtable embedded in the_class and subclasses of the_class,
    // if one exists. We discard scratch_class and we don't keep an
    // InstanceKlass around to hold obsolete methods so we don't have
    // any other InstanceKlass embedded vtables to update. The vtable
    // holds the Method*s for virtual (but not final) methods.
    if (ik->vtable_length() > 0 && ik->is_subtype_of(_the_class_oop)) {
      // ik->vtable() creates a wrapper object; rm cleans it up
      ResourceMark rm(THREAD);
      ik->vtable()->adjust_method_entries(_matching_old_methods,
                                          _matching_new_methods,
                                          _matching_methods_length,
                                          &trace_name_printed);
    }

    // If the current class has an itable and we are either redefining an
    // interface or if the current class is a subclass of the_class, then
    // we potentially have to fix the itable. If we are redefining an
    // interface, then we have to call adjust_method_entries() for
    // every InstanceKlass that has an itable since there isn't a
    // subclass relationship between an interface and an InstanceKlass.
    if (ik->itable_length() > 0 && (_the_class_oop->is_interface()
        || ik->is_subclass_of(_the_class_oop))) {
      // ik->itable() creates a wrapper object; rm cleans it up
      ResourceMark rm(THREAD);
      ik->itable()->adjust_method_entries(_matching_old_methods,
                                          _matching_new_methods,
                                          _matching_methods_length,
                                          &trace_name_printed);
    }

    // The constant pools in other classes (other_cp) can refer to
    // methods in the_class. We have to update method information in
    // other_cp's cache. If other_cp has a previous version, then we
    // have to repeat the process for each previous version. The
    // constant pool cache holds the Method*s for non-virtual
    // methods and for virtual, final methods.
    //
    // Special case: if the current class is the_class, then new_cp
    // has already been attached to the_class and old_cp has already
    // been added as a previous version. The new_cp doesn't have any
    // cached references to old methods so it doesn't need to be
    // updated. We can simply start with the previous version(s) in
    // that case.
    constantPoolHandle other_cp;
    ConstantPoolCache* cp_cache;

    if (k_oop != _the_class_oop) {
      // this klass' constant pool cache may need adjustment
      other_cp = constantPoolHandle(ik->constants());
      cp_cache = other_cp->cache();
      if (cp_cache != NULL) {
        cp_cache->adjust_method_entries(_matching_old_methods,
                                        _matching_new_methods,
                                        _matching_methods_length,
                                        &trace_name_printed);
      }
    }
    {
      ResourceMark rm(THREAD);
      // PreviousVersionInfo objects returned via PreviousVersionWalker
      // contain a GrowableArray of handles. We have to clean up the
      // GrowableArray _after_ the PreviousVersionWalker destructor
      // has destroyed the handles.
      {
        // the previous versions' constant pool caches may need adjustment
        PreviousVersionWalker pvw(ik);
        for (PreviousVersionInfo * pv_info = pvw.next_previous_version();
             pv_info != NULL; pv_info = pvw.next_previous_version()) {
          other_cp = pv_info->prev_constant_pool_handle();
          cp_cache = other_cp->cache();
          if (cp_cache != NULL) {
            cp_cache->adjust_method_entries(_matching_old_methods,
                                            _matching_new_methods,
                                            _matching_methods_length,
                                            &trace_name_printed);
          }
        }
      } // pvw is cleaned up
    } // rm is cleaned up
  }
}

void VM_RedefineClasses::update_jmethod_ids() {
  for (int j = 0; j < _matching_methods_length; ++j) {
    Method* old_method = _matching_old_methods[j];
    jmethodID jmid = old_method->find_jmethod_id_or_null();
    if (jmid != NULL) {
      // There is a jmethodID, change it to point to the new method
      methodHandle new_method_h(_matching_new_methods[j]);
      Method::change_method_associated_with_jmethod_id(jmid, new_method_h());
      assert(Method::resolve_jmethod_id(jmid) == _matching_new_methods[j],
             "should be replaced");
    }
  }
}

void VM_RedefineClasses::check_methods_and_mark_as_obsolete(
       BitMap *emcp_methods, int * emcp_method_count_p) {
  *emcp_method_count_p = 0;
  int obsolete_count = 0;
  int old_index = 0;
  for (int j = 0; j < _matching_methods_length; ++j, ++old_index) {
    Method* old_method = _matching_old_methods[j];
    Method* new_method = _matching_new_methods[j];
    Method* old_array_method;

    // Maintain an old_index into the _old_methods array by skipping
    // deleted methods
    while ((old_array_method = _old_methods->at(old_index)) != old_method) {
      ++old_index;
    }

    if (MethodComparator::methods_EMCP(old_method, new_method)) {
      // The EMCP definition from JSR-163 requires the bytecodes to be
      // the same with the exception of constant pool indices which may
      // differ. However, the constants referred to by those indices
      // must be the same.
      //
      // We use methods_EMCP() for comparison since constant pool
      // merging can remove duplicate constant pool entries that were
      // present in the old method and removed from the rewritten new
      // method. A faster binary comparison function would consider the
      // old and new methods to be different when they are actually
      // EMCP.
      //
      // The old and new methods are EMCP and you would think that we
      // could get rid of one of them here and now and save some space.
      // However, the concept of EMCP only considers the bytecodes and
      // the constant pool entries in the comparison. Other things,
      // e.g., the line number table (LNT) or the local variable table
      // (LVT) don't count in the comparison. So the new (and EMCP)
      // method can have a new LNT that we need so we can't just
      // overwrite the new method with the old method.
      //
      // When this routine is called, we have already attached the new
      // methods to the_class so the old methods are effectively
      // overwritten. However, if an old method is still executing,
      // then the old method cannot be collected until sometime after
      // the old method call has returned. So the overwriting of old
      // methods by new methods will save us space except for those
      // (hopefully few) old methods that are still executing.
      //
      // A method refers to a ConstMethod* and this presents another
      // possible avenue to space savings. The ConstMethod* in the
      // new method contains possibly new attributes (LNT, LVT, etc).
      // At first glance, it seems possible to save space by replacing
      // the ConstMethod* in the old method with the ConstMethod*
      // from the new method. The old and new methods would share the
      // same ConstMethod* and we would save the space occupied by
      // the old ConstMethod*. However, the ConstMethod* contains
      // a back reference to the containing method. Sharing the
      // ConstMethod* between two methods could lead to confusion in
      // the code that uses the back reference. This would lead to
      // brittle code that could be broken in non-obvious ways now or
      // in the future.
      //
      // Another possibility is to copy the ConstMethod* from the new
      // method to the old method and then overwrite the new method with
      // the old method. Since the ConstMethod* contains the bytecodes
      // for the method embedded in the oop, this option would change
      // the bytecodes out from under any threads executing the old
      // method and make the thread's bcp invalid. Since EMCP requires
      // that the bytecodes be the same modulo constant pool indices, it
      // is straight forward to compute the correct new bcp in the new
      // ConstMethod* from the old bcp in the old ConstMethod*. The
      // time consuming part would be searching all the frames in all
      // of the threads to find all of the calls to the old method.
      //
      // It looks like we will have to live with the limited savings
      // that we get from effectively overwriting the old methods
      // when the new methods are attached to the_class.

      // track which methods are EMCP for add_previous_version() call
      emcp_methods->set_bit(old_index);
      (*emcp_method_count_p)++;

      // An EMCP method is _not_ obsolete. An obsolete method has a
      // different jmethodID than the current method. An EMCP method
      // has the same jmethodID as the current method. Having the
      // same jmethodID for all EMCP versions of a method allows for
      // a consistent view of the EMCP methods regardless of which
      // EMCP method you happen to have in hand. For example, a
      // breakpoint set in one EMCP method will work for all EMCP
      // versions of the method including the current one.
    } else {
      // mark obsolete methods as such
      old_method->set_is_obsolete();
      obsolete_count++;

      // obsolete methods need a unique idnum
      u2 num = InstanceKlass::cast(_the_class_oop)->next_method_idnum();
      if (num != ConstMethod::UNSET_IDNUM) {
//      u2 old_num = old_method->method_idnum();
        old_method->set_method_idnum(num);
// TO DO: attach obsolete annotations to obsolete method's new idnum
      }
      // With tracing we try not to "yack" too much. The position of
      // this trace assumes there are fewer obsolete methods than
      // EMCP methods.
      RC_TRACE(0x00000100, ("mark %s(%s) as obsolete",
        old_method->name()->as_C_string(),
        old_method->signature()->as_C_string()));
    }
    old_method->set_is_old();
  }
  for (int i = 0; i < _deleted_methods_length; ++i) {
    Method* old_method = _deleted_methods[i];

    assert(old_method->vtable_index() < 0,
           "cannot delete methods with vtable entries");;

    // Mark all deleted methods as old and obsolete
    old_method->set_is_old();
    old_method->set_is_obsolete();
    ++obsolete_count;
    // With tracing we try not to "yack" too much. The position of
    // this trace assumes there are fewer obsolete methods than
    // EMCP methods.
    RC_TRACE(0x00000100, ("mark deleted %s(%s) as obsolete",
                          old_method->name()->as_C_string(),
                          old_method->signature()->as_C_string()));
  }
  assert((*emcp_method_count_p + obsolete_count) == _old_methods->length(),
    "sanity check");
  RC_TRACE(0x00000100, ("EMCP_cnt=%d, obsolete_cnt=%d", *emcp_method_count_p,
    obsolete_count));
}

// This internal class transfers the native function registration from old methods
// to new methods.  It is designed to handle both the simple case of unchanged
// native methods and the complex cases of native method prefixes being added and/or
// removed.
// It expects only to be used during the VM_RedefineClasses op (a safepoint).
//
// This class is used after the new methods have been installed in "the_class".
//
// So, for example, the following must be handled.  Where 'm' is a method and
// a number followed by an underscore is a prefix.
//
//                                      Old Name    New Name
// Simple transfer to new method        m       ->  m
// Add prefix                           m       ->  1_m
// Remove prefix                        1_m     ->  m
// Simultaneous add of prefixes         m       ->  3_2_1_m
// Simultaneous removal of prefixes     3_2_1_m ->  m
// Simultaneous add and remove          1_m     ->  2_m
// Same, caused by prefix removal only  3_2_1_m ->  3_2_m
//
class TransferNativeFunctionRegistration {
 private:
  instanceKlassHandle the_class;
  int prefix_count;
  char** prefixes;

  // Recursively search the binary tree of possibly prefixed method names.
  // Iteration could be used if all agents were well behaved. Full tree walk is
  // more resilent to agents not cleaning up intermediate methods.
  // Branch at each depth in the binary tree is:
  //    (1) without the prefix.
  //    (2) with the prefix.
  // where 'prefix' is the prefix at that 'depth' (first prefix, second prefix,...)
  Method* search_prefix_name_space(int depth, char* name_str, size_t name_len,
                                     Symbol* signature) {
    TempNewSymbol name_symbol = SymbolTable::probe(name_str, (int)name_len);
    if (name_symbol != NULL) {
      Method* method = the_class()->lookup_method(name_symbol, signature);
      if (method != NULL) {
        // Even if prefixed, intermediate methods must exist.
        if (method->is_native()) {
          // Wahoo, we found a (possibly prefixed) version of the method, return it.
          return method;
        }
        if (depth < prefix_count) {
          // Try applying further prefixes (other than this one).
          method = search_prefix_name_space(depth+1, name_str, name_len, signature);
          if (method != NULL) {
            return method; // found
          }

          // Try adding this prefix to the method name and see if it matches
          // another method name.
          char* prefix = prefixes[depth];
          size_t prefix_len = strlen(prefix);
          size_t trial_len = name_len + prefix_len;
          char* trial_name_str = NEW_RESOURCE_ARRAY(char, trial_len + 1);
          strcpy(trial_name_str, prefix);
          strcat(trial_name_str, name_str);
          method = search_prefix_name_space(depth+1, trial_name_str, trial_len,
                                            signature);
          if (method != NULL) {
            // If found along this branch, it was prefixed, mark as such
            method->set_is_prefixed_native();
            return method; // found
          }
        }
      }
    }
    return NULL;  // This whole branch bore nothing
  }

  // Return the method name with old prefixes stripped away.
  char* method_name_without_prefixes(Method* method) {
    Symbol* name = method->name();
    char* name_str = name->as_utf8();

    // Old prefixing may be defunct, strip prefixes, if any.
    for (int i = prefix_count-1; i >= 0; i--) {
      char* prefix = prefixes[i];
      size_t prefix_len = strlen(prefix);
      if (strncmp(prefix, name_str, prefix_len) == 0) {
        name_str += prefix_len;
      }
    }
    return name_str;
  }

  // Strip any prefixes off the old native method, then try to find a
  // (possibly prefixed) new native that matches it.
  Method* strip_and_search_for_new_native(Method* method) {
    ResourceMark rm;
    char* name_str = method_name_without_prefixes(method);
    return search_prefix_name_space(0, name_str, strlen(name_str),
                                    method->signature());
  }

 public:

  // Construct a native method transfer processor for this class.
  TransferNativeFunctionRegistration(instanceKlassHandle _the_class) {
    assert(SafepointSynchronize::is_at_safepoint(), "sanity check");

    the_class = _the_class;
    prefixes = JvmtiExport::get_all_native_method_prefixes(&prefix_count);
  }

  // Attempt to transfer any of the old or deleted methods that are native
  void transfer_registrations(Method** old_methods, int methods_length) {
    for (int j = 0; j < methods_length; j++) {
      Method* old_method = old_methods[j];

      if (old_method->is_native() && old_method->has_native_function()) {
        Method* new_method = strip_and_search_for_new_native(old_method);
        if (new_method != NULL) {
          // Actually set the native function in the new method.
          // Redefine does not send events (except CFLH), certainly not this
          // behind the scenes re-registration.
          new_method->set_native_function(old_method->native_function(),
                              !Method::native_bind_event_is_interesting);
        }
      }
    }
  }
};

// Don't lose the association between a native method and its JNI function.
void VM_RedefineClasses::transfer_old_native_function_registrations(instanceKlassHandle the_class) {
  TransferNativeFunctionRegistration transfer(the_class);
  transfer.transfer_registrations(_deleted_methods, _deleted_methods_length);
  transfer.transfer_registrations(_matching_old_methods, _matching_methods_length);
}

// Deoptimize all compiled code that depends on this class.
//
// If the can_redefine_classes capability is obtained in the onload
// phase then the compiler has recorded all dependencies from startup.
// In that case we need only deoptimize and throw away all compiled code
// that depends on the class.
//
// If can_redefine_classes is obtained sometime after the onload
// phase then the dependency information may be incomplete. In that case
// the first call to RedefineClasses causes all compiled code to be
// thrown away. As can_redefine_classes has been obtained then
// all future compilations will record dependencies so second and
// subsequent calls to RedefineClasses need only throw away code
// that depends on the class.
//
void VM_RedefineClasses::flush_dependent_code(instanceKlassHandle k_h, TRAPS) {
  assert_locked_or_safepoint(Compile_lock);

  // All dependencies have been recorded from startup or this is a second or
  // subsequent use of RedefineClasses
  if (JvmtiExport::all_dependencies_are_recorded()) {
    Universe::flush_evol_dependents_on(k_h);
  } else {
    CodeCache::mark_all_nmethods_for_deoptimization();

    ResourceMark rm(THREAD);
    DeoptimizationMarker dm;

    // Deoptimize all activations depending on marked nmethods
    Deoptimization::deoptimize_dependents();

    // Make the dependent methods not entrant (in VM_Deoptimize they are made zombies)
    CodeCache::make_marked_nmethods_not_entrant();

    // From now on we know that the dependency information is complete
    JvmtiExport::set_all_dependencies_are_recorded(true);
  }
}

void VM_RedefineClasses::compute_added_deleted_matching_methods() {
  Method* old_method;
  Method* new_method;

  _matching_old_methods = NEW_RESOURCE_ARRAY(Method*, _old_methods->length());
  _matching_new_methods = NEW_RESOURCE_ARRAY(Method*, _old_methods->length());
  _added_methods        = NEW_RESOURCE_ARRAY(Method*, _new_methods->length());
  _deleted_methods      = NEW_RESOURCE_ARRAY(Method*, _old_methods->length());

  _matching_methods_length = 0;
  _deleted_methods_length  = 0;
  _added_methods_length    = 0;

  int nj = 0;
  int oj = 0;
  while (true) {
    if (oj >= _old_methods->length()) {
      if (nj >= _new_methods->length()) {
        break; // we've looked at everything, done
      }
      // New method at the end
      new_method = _new_methods->at(nj);
      _added_methods[_added_methods_length++] = new_method;
      ++nj;
    } else if (nj >= _new_methods->length()) {
      // Old method, at the end, is deleted
      old_method = _old_methods->at(oj);
      _deleted_methods[_deleted_methods_length++] = old_method;
      ++oj;
    } else {
      old_method = _old_methods->at(oj);
      new_method = _new_methods->at(nj);
      if (old_method->name() == new_method->name()) {
        if (old_method->signature() == new_method->signature()) {
          _matching_old_methods[_matching_methods_length  ] = old_method;
          _matching_new_methods[_matching_methods_length++] = new_method;
          ++nj;
          ++oj;
        } else {
          // added overloaded have already been moved to the end,
          // so this is a deleted overloaded method
          _deleted_methods[_deleted_methods_length++] = old_method;
          ++oj;
        }
      } else { // names don't match
        if (old_method->name()->fast_compare(new_method->name()) > 0) {
          // new method
          _added_methods[_added_methods_length++] = new_method;
          ++nj;
        } else {
          // deleted method
          _deleted_methods[_deleted_methods_length++] = old_method;
          ++oj;
        }
      }
    }
  }
  assert(_matching_methods_length + _deleted_methods_length == _old_methods->length(), "sanity");
  assert(_matching_methods_length + _added_methods_length == _new_methods->length(), "sanity");
}



// Install the redefinition of a class:
//    - house keeping (flushing breakpoints and caches, deoptimizing
//      dependent compiled code)
//    - replacing parts in the_class with parts from scratch_class
//    - adding a weak reference to track the obsolete but interesting
//      parts of the_class
//    - adjusting constant pool caches and vtables in other classes
//      that refer to methods in the_class. These adjustments use the
//      SystemDictionary::classes_do() facility which only allows
//      a helper method to be specified. The interesting parameters
//      that we would like to pass to the helper method are saved in
//      static global fields in the VM operation.
void VM_RedefineClasses::redefine_single_class(jclass the_jclass,
       Klass* scratch_class_oop, TRAPS) {

  HandleMark hm(THREAD);   // make sure handles from this call are freed
  RC_TIMER_START(_timer_rsc_phase1);

  instanceKlassHandle scratch_class(scratch_class_oop);

  oop the_class_mirror = JNIHandles::resolve_non_null(the_jclass);
  Klass* the_class_oop = java_lang_Class::as_Klass(the_class_mirror);
  instanceKlassHandle the_class = instanceKlassHandle(THREAD, the_class_oop);

#ifndef JVMTI_KERNEL
  // Remove all breakpoints in methods of this class
  JvmtiBreakpoints& jvmti_breakpoints = JvmtiCurrentBreakpoints::get_jvmti_breakpoints();
  jvmti_breakpoints.clearall_in_class_at_safepoint(the_class_oop);
#endif // !JVMTI_KERNEL

  if (the_class_oop == Universe::reflect_invoke_cache()->klass()) {
    // We are redefining java.lang.reflect.Method. Method.invoke() is
    // cached and users of the cache care about each active version of
    // the method so we have to track this previous version.
    // Do this before methods get switched
    Universe::reflect_invoke_cache()->add_previous_version(
      the_class->method_with_idnum(Universe::reflect_invoke_cache()->method_idnum()));
  }

  // Deoptimize all compiled code that depends on this class
  flush_dependent_code(the_class, THREAD);

  _old_methods = the_class->methods();
  _new_methods = scratch_class->methods();
  _the_class_oop = the_class_oop;
  compute_added_deleted_matching_methods();
  update_jmethod_ids();

  // Attach new constant pool to the original klass. The original
  // klass still refers to the old constant pool (for now).
  scratch_class->constants()->set_pool_holder(the_class());

#if 0
  // In theory, with constant pool merging in place we should be able
  // to save space by using the new, merged constant pool in place of
  // the old constant pool(s). By "pool(s)" I mean the constant pool in
  // the klass version we are replacing now and any constant pool(s) in
  // previous versions of klass. Nice theory, doesn't work in practice.
  // When this code is enabled, even simple programs throw NullPointer
  // exceptions. I'm guessing that this is caused by some constant pool
  // cache difference between the new, merged constant pool and the
  // constant pool that was just being used by the klass. I'm keeping
  // this code around to archive the idea, but the code has to remain
  // disabled for now.

  // Attach each old method to the new constant pool. This can be
  // done here since we are past the bytecode verification and
  // constant pool optimization phases.
  for (int i = _old_methods->length() - 1; i >= 0; i--) {
    Method* method = _old_methods->at(i);
    method->set_constants(scratch_class->constants());
  }

  {
    // walk all previous versions of the klass
    InstanceKlass *ik = (InstanceKlass *)the_class();
    PreviousVersionWalker pvw(ik);
    instanceKlassHandle ikh;
    do {
      ikh = pvw.next_previous_version();
      if (!ikh.is_null()) {
        ik = ikh();

        // attach previous version of klass to the new constant pool
        ik->set_constants(scratch_class->constants());

        // Attach each method in the previous version of klass to the
        // new constant pool
        Array<Method*>* prev_methods = ik->methods();
        for (int i = prev_methods->length() - 1; i >= 0; i--) {
          Method* method = prev_methods->at(i);
          method->set_constants(scratch_class->constants());
        }
      }
    } while (!ikh.is_null());
  }
#endif

  // Replace methods and constantpool
  the_class->set_methods(_new_methods);
  scratch_class->set_methods(_old_methods);     // To prevent potential GCing of the old methods,
                                          // and to be able to undo operation easily.

  ConstantPool* old_constants = the_class->constants();
  the_class->set_constants(scratch_class->constants());
  scratch_class->set_constants(old_constants);  // See the previous comment.
#if 0
  // We are swapping the guts of "the new class" with the guts of "the
  // class". Since the old constant pool has just been attached to "the
  // new class", it seems logical to set the pool holder in the old
  // constant pool also. However, doing this will change the observable
  // class hierarchy for any old methods that are still executing. A
  // method can query the identity of its "holder" and this query uses
  // the method's constant pool link to find the holder. The change in
  // holding class from "the class" to "the new class" can confuse
  // things.
  //
  // Setting the old constant pool's holder will also cause
  // verification done during vtable initialization below to fail.
  // During vtable initialization, the vtable's class is verified to be
  // a subtype of the method's holder. The vtable's class is "the
  // class" and the method's holder is gotten from the constant pool
  // link in the method itself. For "the class"'s directly implemented
  // methods, the method holder is "the class" itself (as gotten from
  // the new constant pool). The check works fine in this case. The
  // check also works fine for methods inherited from super classes.
  //
  // Miranda methods are a little more complicated. A miranda method is
  // provided by an interface when the class implementing the interface
  // does not provide its own method.  These interfaces are implemented
  // internally as an InstanceKlass. These special instanceKlasses
  // share the constant pool of the class that "implements" the
  // interface. By sharing the constant pool, the method holder of a
  // miranda method is the class that "implements" the interface. In a
  // non-redefine situation, the subtype check works fine. However, if
  // the old constant pool's pool holder is modified, then the check
  // fails because there is no class hierarchy relationship between the
  // vtable's class and "the new class".

  old_constants->set_pool_holder(scratch_class());
#endif

  // track which methods are EMCP for add_previous_version() call below
  BitMap emcp_methods(_old_methods->length());
  int emcp_method_count = 0;
  emcp_methods.clear();  // clears 0..(length() - 1)
  check_methods_and_mark_as_obsolete(&emcp_methods, &emcp_method_count);
  transfer_old_native_function_registrations(the_class);

  // The class file bytes from before any retransformable agents mucked
  // with them was cached on the scratch class, move to the_class.
  // Note: we still want to do this if nothing needed caching since it
  // should get cleared in the_class too.
  if (the_class->get_cached_class_file_bytes() == 0) {
    // the_class doesn't have a cache yet so copy it
    the_class->set_cached_class_file(
      scratch_class->get_cached_class_file_bytes(),
      scratch_class->get_cached_class_file_len());
  }
#ifndef PRODUCT
  else {
    assert(the_class->get_cached_class_file_bytes() ==
      scratch_class->get_cached_class_file_bytes(), "cache ptrs must match");
    assert(the_class->get_cached_class_file_len() ==
      scratch_class->get_cached_class_file_len(), "cache lens must match");
  }
#endif

  // Replace inner_classes
  Array<u2>* old_inner_classes = the_class->inner_classes();
  the_class->set_inner_classes(scratch_class->inner_classes());
  scratch_class->set_inner_classes(old_inner_classes);

  // Initialize the vtable and interface table after
  // methods have been rewritten
  {
    ResourceMark rm(THREAD);
    // no exception should happen here since we explicitly
    // do not check loader constraints.
    // compare_and_normalize_class_versions has already checked:
    //  - classloaders unchanged, signatures unchanged
    //  - all instanceKlasses for redefined classes reused & contents updated
    the_class->vtable()->initialize_vtable(false, THREAD);
    the_class->itable()->initialize_itable(false, THREAD);
    assert(!HAS_PENDING_EXCEPTION || (THREAD->pending_exception()->is_a(SystemDictionary::ThreadDeath_klass())), "redefine exception");
  }

  // Leave arrays of jmethodIDs and itable index cache unchanged

  // Copy the "source file name" attribute from new class version
  the_class->set_source_file_name(scratch_class->source_file_name());

  // Copy the "source debug extension" attribute from new class version
  the_class->set_source_debug_extension(
    scratch_class->source_debug_extension(),
    scratch_class->source_debug_extension() == NULL ? 0 :
    (int)strlen(scratch_class->source_debug_extension()));

  // Use of javac -g could be different in the old and the new
  if (scratch_class->access_flags().has_localvariable_table() !=
      the_class->access_flags().has_localvariable_table()) {

    AccessFlags flags = the_class->access_flags();
    if (scratch_class->access_flags().has_localvariable_table()) {
      flags.set_has_localvariable_table();
    } else {
      flags.clear_has_localvariable_table();
    }
    the_class->set_access_flags(flags);
  }

  // Replace annotation fields value
  Annotations* old_annotations = the_class->annotations();
  the_class->set_annotations(scratch_class->annotations());
  scratch_class->set_annotations(old_annotations);

  // Replace minor version number of class file
  u2 old_minor_version = the_class->minor_version();
  the_class->set_minor_version(scratch_class->minor_version());
  scratch_class->set_minor_version(old_minor_version);

  // Replace major version number of class file
  u2 old_major_version = the_class->major_version();
  the_class->set_major_version(scratch_class->major_version());
  scratch_class->set_major_version(old_major_version);

  // Replace CP indexes for class and name+type of enclosing method
  u2 old_class_idx  = the_class->enclosing_method_class_index();
  u2 old_method_idx = the_class->enclosing_method_method_index();
  the_class->set_enclosing_method_indices(
    scratch_class->enclosing_method_class_index(),
    scratch_class->enclosing_method_method_index());
  scratch_class->set_enclosing_method_indices(old_class_idx, old_method_idx);

  // keep track of previous versions of this class
  the_class->add_previous_version(scratch_class, &emcp_methods,
    emcp_method_count);

  RC_TIMER_STOP(_timer_rsc_phase1);
  RC_TIMER_START(_timer_rsc_phase2);

  // Adjust constantpool caches and vtables for all classes
  // that reference methods of the evolved class.
  SystemDictionary::classes_do(adjust_cpool_cache_and_vtable, THREAD);

  // Fix Resolution Error table also to remove old constant pools
  SystemDictionary::delete_resolution_error(old_constants);

  if (the_class->oop_map_cache() != NULL) {
    // Flush references to any obsolete methods from the oop map cache
    // so that obsolete methods are not pinned.
    the_class->oop_map_cache()->flush_obsolete_entries();
  }

  // increment the classRedefinedCount field in the_class and in any
  // direct and indirect subclasses of the_class
  increment_class_counter((InstanceKlass *)the_class(), THREAD);

  // RC_TRACE macro has an embedded ResourceMark
  RC_TRACE_WITH_THREAD(0x00000001, THREAD,
    ("redefined name=%s, count=%d (avail_mem=" UINT64_FORMAT "K)",
    the_class->external_name(),
    java_lang_Class::classRedefinedCount(the_class_mirror),
    os::available_memory() >> 10));

  RC_TIMER_STOP(_timer_rsc_phase2);
} // end redefine_single_class()


// Increment the classRedefinedCount field in the specific InstanceKlass
// and in all direct and indirect subclasses.
void VM_RedefineClasses::increment_class_counter(InstanceKlass *ik, TRAPS) {
  oop class_mirror = ik->java_mirror();
  Klass* class_oop = java_lang_Class::as_Klass(class_mirror);
  int new_count = java_lang_Class::classRedefinedCount(class_mirror) + 1;
  java_lang_Class::set_classRedefinedCount(class_mirror, new_count);

  if (class_oop != _the_class_oop) {
    // _the_class_oop count is printed at end of redefine_single_class()
    RC_TRACE_WITH_THREAD(0x00000008, THREAD,
      ("updated count in subclass=%s to %d", ik->external_name(), new_count));
  }

  for (Klass *subk = ik->subklass(); subk != NULL;
       subk = subk->next_sibling()) {
    if (subk->oop_is_instance()) {
      // Only update instanceKlasses
      InstanceKlass *subik = (InstanceKlass*)subk;
      // recursively do subclasses of the current subclass
      increment_class_counter(subik, THREAD);
    }
  }
}

#ifndef PRODUCT
void VM_RedefineClasses::check_class(Klass* k_oop,
                                     ClassLoaderData* initiating_loader,
                                     TRAPS) {
  Klass *k = k_oop;
  if (k->oop_is_instance()) {
    HandleMark hm(THREAD);
    InstanceKlass *ik = (InstanceKlass *) k;

    if (ik->vtable_length() > 0) {
      ResourceMark rm(THREAD);
      if (!ik->vtable()->check_no_old_entries()) {
        tty->print_cr("klassVtable::check_no_old_entries failure -- OLD method found -- class: %s", ik->signature_name());
        ik->vtable()->dump_vtable();
        assert(false, "OLD method found");
      }
    }
    if (ik->itable_length() > 0) {
      ResourceMark rm(THREAD);
      if (!ik->itable()->check_no_old_entries()) {
        tty->print_cr("klassItable::check_no_old_entries failure -- OLD method found -- class: %s", ik->signature_name());
        assert(false, "OLD method found");
      }
    }
    // Check that the constant pool cache has no deleted entries.
    if (ik->constants() != NULL &&
        ik->constants()->cache() != NULL &&
       !ik->constants()->cache()->check_no_old_entries()) {
      tty->print_cr("klassVtable::check_no_old_entries failure -- OLD method found -- class: %s", ik->signature_name());
      assert(false, "OLD method found");
    }
  }
}

void VM_RedefineClasses::dump_methods() {
        int j;
        tty->print_cr("_old_methods --");
        for (j = 0; j < _old_methods->length(); ++j) {
          Method* m = _old_methods->at(j);
          tty->print("%4d  (%5d)  ", j, m->vtable_index());
          m->access_flags().print_on(tty);
          tty->print(" --  ");
          m->print_name(tty);
          tty->cr();
        }
        tty->print_cr("_new_methods --");
        for (j = 0; j < _new_methods->length(); ++j) {
          Method* m = _new_methods->at(j);
          tty->print("%4d  (%5d)  ", j, m->vtable_index());
          m->access_flags().print_on(tty);
          tty->print(" --  ");
          m->print_name(tty);
          tty->cr();
        }
        tty->print_cr("_matching_(old/new)_methods --");
        for (j = 0; j < _matching_methods_length; ++j) {
          Method* m = _matching_old_methods[j];
          tty->print("%4d  (%5d)  ", j, m->vtable_index());
          m->access_flags().print_on(tty);
          tty->print(" --  ");
          m->print_name(tty);
          tty->cr();
          m = _matching_new_methods[j];
          tty->print("      (%5d)  ", m->vtable_index());
          m->access_flags().print_on(tty);
          tty->cr();
        }
        tty->print_cr("_deleted_methods --");
        for (j = 0; j < _deleted_methods_length; ++j) {
          Method* m = _deleted_methods[j];
          tty->print("%4d  (%5d)  ", j, m->vtable_index());
          m->access_flags().print_on(tty);
          tty->print(" --  ");
          m->print_name(tty);
          tty->cr();
        }
        tty->print_cr("_added_methods --");
        for (j = 0; j < _added_methods_length; ++j) {
          Method* m = _added_methods[j];
          tty->print("%4d  (%5d)  ", j, m->vtable_index());
          m->access_flags().print_on(tty);
          tty->print(" --  ");
          m->print_name(tty);
          tty->cr();
        }
}
#endif