1 /*
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  24 
  25 #ifndef SHARE_VM_PRIMS_JVMTIREDEFINECLASSES_HPP
  26 #define SHARE_VM_PRIMS_JVMTIREDEFINECLASSES_HPP
  27 
  28 #include "jvmtifiles/jvmtiEnv.hpp"
  29 #include "memory/oopFactory.hpp"
  30 #include "memory/resourceArea.hpp"
  31 #include "oops/objArrayKlass.hpp"
  32 #include "oops/objArrayOop.hpp"
  33 #include "runtime/vm_operations.hpp"
  34 
  35 // Introduction:
  36 //
  37 // The RedefineClasses() API is used to change the definition of one or
  38 // more classes. While the API supports redefining more than one class
  39 // in a single call, in general, the API is discussed in the context of
  40 // changing the definition of a single current class to a single new
  41 // class. For clarity, the current class is will always be called
  42 // "the_class" and the new class will always be called "scratch_class".
  43 //
  44 // The name "the_class" is used because there is only one structure
  45 // that represents a specific class; redefinition does not replace the
  46 // structure, but instead replaces parts of the structure. The name
  47 // "scratch_class" is used because the structure that represents the
  48 // new definition of a specific class is simply used to carry around
  49 // the parts of the new definition until they are used to replace the
  50 // appropriate parts in the_class. Once redefinition of a class is
  51 // complete, scratch_class is thrown away.
  52 //
  53 //
  54 // Implementation Overview:
  55 //
  56 // The RedefineClasses() API is mostly a wrapper around the VM op that
  57 // does the real work. The work is split in varying degrees between
  58 // doit_prologue(), doit() and doit_epilogue().
  59 //
  60 // 1) doit_prologue() is called by the JavaThread on the way to a
  61 //    safepoint. It does parameter verification and loads scratch_class
  62 //    which involves:
  63 //    - parsing the incoming class definition using the_class' class
  64 //      loader and security context
  65 //    - linking scratch_class
  66 //    - merging constant pools and rewriting bytecodes as needed
  67 //      for the merged constant pool
  68 //    - verifying the bytecodes in scratch_class
  69 //    - setting up the constant pool cache and rewriting bytecodes
  70 //      as needed to use the cache
  71 //    - finally, scratch_class is compared to the_class to verify
  72 //      that it is a valid replacement class
  73 //    - if everything is good, then scratch_class is saved in an
  74 //      instance field in the VM operation for the doit() call
  75 //
  76 //    Note: A JavaThread must do the above work.
  77 //
  78 // 2) doit() is called by the VMThread during a safepoint. It installs
  79 //    the new class definition(s) which involves:
  80 //    - retrieving the scratch_class from the instance field in the
  81 //      VM operation
  82 //    - house keeping (flushing breakpoints and caches, deoptimizing
  83 //      dependent compiled code)
  84 //    - replacing parts in the_class with parts from scratch_class
  85 //    - adding weak reference(s) to track the obsolete but interesting
  86 //      parts of the_class
  87 //    - adjusting constant pool caches and vtables in other classes
  88 //      that refer to methods in the_class. These adjustments use the
  89 //      ClassLoaderDataGraph::classes_do() facility which only allows
  90 //      a helper method to be specified. The interesting parameters
  91 //      that we would like to pass to the helper method are saved in
  92 //      static global fields in the VM operation.
  93 //    - telling the SystemDictionary to notice our changes
  94 //
  95 //    Note: the above work must be done by the VMThread to be safe.
  96 //
  97 // 3) doit_epilogue() is called by the JavaThread after the VM op
  98 //    is finished and the safepoint is done. It simply cleans up
  99 //    memory allocated in doit_prologue() and used in doit().
 100 //
 101 //
 102 // Constant Pool Details:
 103 //
 104 // When the_class is redefined, we cannot just replace the constant
 105 // pool in the_class with the constant pool from scratch_class because
 106 // that could confuse obsolete methods that may still be running.
 107 // Instead, the constant pool from the_class, old_cp, is merged with
 108 // the constant pool from scratch_class, scratch_cp. The resulting
 109 // constant pool, merge_cp, replaces old_cp in the_class.
 110 //
 111 // The key part of any merging algorithm is the entry comparison
 112 // function so we have to know the types of entries in a constant pool
 113 // in order to merge two of them together. Constant pools can contain
 114 // up to 12 different kinds of entries; the JVM_CONSTANT_Unicode entry
 115 // is not presently used so we only have to worry about the other 11
 116 // entry types. For the purposes of constant pool merging, it is
 117 // helpful to know that the 11 entry types fall into 3 different
 118 // subtypes: "direct", "indirect" and "double-indirect".
 119 //
 120 // Direct CP entries contain data and do not contain references to
 121 // other CP entries. The following are direct CP entries:
 122 //     JVM_CONSTANT_{Double,Float,Integer,Long,Utf8}
 123 //
 124 // Indirect CP entries contain 1 or 2 references to a direct CP entry
 125 // and no other data. The following are indirect CP entries:
 126 //     JVM_CONSTANT_{Class,NameAndType,String}
 127 //
 128 // Double-indirect CP entries contain two references to indirect CP
 129 // entries and no other data. The following are double-indirect CP
 130 // entries:
 131 //     JVM_CONSTANT_{Fieldref,InterfaceMethodref,Methodref}
 132 //
 133 // When comparing entries between two constant pools, the entry types
 134 // are compared first and if they match, then further comparisons are
 135 // made depending on the entry subtype. Comparing direct CP entries is
 136 // simply a matter of comparing the data associated with each entry.
 137 // Comparing both indirect and double-indirect CP entries requires
 138 // recursion.
 139 //
 140 // Fortunately, the recursive combinations are limited because indirect
 141 // CP entries can only refer to direct CP entries and double-indirect
 142 // CP entries can only refer to indirect CP entries. The following is
 143 // an example illustration of the deepest set of indirections needed to
 144 // access the data associated with a JVM_CONSTANT_Fieldref entry:
 145 //
 146 //     JVM_CONSTANT_Fieldref {
 147 //         class_index => JVM_CONSTANT_Class {
 148 //             name_index => JVM_CONSTANT_Utf8 {
 149 //                 <data-1>
 150 //             }
 151 //         }
 152 //         name_and_type_index => JVM_CONSTANT_NameAndType {
 153 //             name_index => JVM_CONSTANT_Utf8 {
 154 //                 <data-2>
 155 //             }
 156 //             descriptor_index => JVM_CONSTANT_Utf8 {
 157 //                 <data-3>
 158 //             }
 159 //         }
 160 //     }
 161 //
 162 // The above illustration is not a data structure definition for any
 163 // computer language. The curly braces ('{' and '}') are meant to
 164 // delimit the context of the "fields" in the CP entry types shown.
 165 // Each indirection from the JVM_CONSTANT_Fieldref entry is shown via
 166 // "=>", e.g., the class_index is used to indirectly reference a
 167 // JVM_CONSTANT_Class entry where the name_index is used to indirectly
 168 // reference a JVM_CONSTANT_Utf8 entry which contains the interesting
 169 // <data-1>. In order to understand a JVM_CONSTANT_Fieldref entry, we
 170 // have to do a total of 5 indirections just to get to the CP entries
 171 // that contain the interesting pieces of data and then we have to
 172 // fetch the three pieces of data. This means we have to do a total of
 173 // (5 + 3) * 2 == 16 dereferences to compare two JVM_CONSTANT_Fieldref
 174 // entries.
 175 //
 176 // Here is the indirection, data and dereference count for each entry
 177 // type:
 178 //
 179 //    JVM_CONSTANT_Class               1 indir, 1 data, 2 derefs
 180 //    JVM_CONSTANT_Double              0 indir, 1 data, 1 deref
 181 //    JVM_CONSTANT_Fieldref            2 indir, 3 data, 8 derefs
 182 //    JVM_CONSTANT_Float               0 indir, 1 data, 1 deref
 183 //    JVM_CONSTANT_Integer             0 indir, 1 data, 1 deref
 184 //    JVM_CONSTANT_InterfaceMethodref  2 indir, 3 data, 8 derefs
 185 //    JVM_CONSTANT_Long                0 indir, 1 data, 1 deref
 186 //    JVM_CONSTANT_Methodref           2 indir, 3 data, 8 derefs
 187 //    JVM_CONSTANT_NameAndType         1 indir, 2 data, 4 derefs
 188 //    JVM_CONSTANT_String              1 indir, 1 data, 2 derefs
 189 //    JVM_CONSTANT_Utf8                0 indir, 1 data, 1 deref
 190 //
 191 // So different subtypes of CP entries require different amounts of
 192 // work for a proper comparison.
 193 //
 194 // Now that we've talked about the different entry types and how to
 195 // compare them we need to get back to merging. This is not a merge in
 196 // the "sort -u" sense or even in the "sort" sense. When we merge two
 197 // constant pools, we copy all the entries from old_cp to merge_cp,
 198 // preserving entry order. Next we append all the unique entries from
 199 // scratch_cp to merge_cp and we track the index changes from the
 200 // location in scratch_cp to the possibly new location in merge_cp.
 201 // When we are done, any obsolete code that is still running that
 202 // uses old_cp should not be able to observe any difference if it
 203 // were to use merge_cp. As for the new code in scratch_class, it is
 204 // modified to use the appropriate index values in merge_cp before it
 205 // is used to replace the code in the_class.
 206 //
 207 // There is one small complication in copying the entries from old_cp
 208 // to merge_cp. Two of the CP entry types are special in that they are
 209 // lazily resolved. Before explaining the copying complication, we need
 210 // to digress into CP entry resolution.
 211 //
 212 // JVM_CONSTANT_Class entries are present in the class file, but are not
 213 // stored in memory as such until they are resolved. The entries are not
 214 // resolved unless they are used because resolution is expensive. During class
 215 // file parsing the entries are initially stored in memory as
 216 // JVM_CONSTANT_ClassIndex and JVM_CONSTANT_StringIndex entries. These special
 217 // CP entry types indicate that the JVM_CONSTANT_Class and JVM_CONSTANT_String
 218 // entries have been parsed, but the index values in the entries have not been
 219 // validated. After the entire constant pool has been parsed, the index
 220 // values can be validated and then the entries are converted into
 221 // JVM_CONSTANT_UnresolvedClass and JVM_CONSTANT_String
 222 // entries. During this conversion process, the UTF8 values that are
 223 // indirectly referenced by the JVM_CONSTANT_ClassIndex and
 224 // JVM_CONSTANT_StringIndex entries are changed into Symbol*s and the
 225 // entries are modified to refer to the Symbol*s. This optimization
 226 // eliminates one level of indirection for those two CP entry types and
 227 // gets the entries ready for verification.  Verification expects to
 228 // find JVM_CONSTANT_UnresolvedClass but not JVM_CONSTANT_Class entries.
 229 //
 230 // Now we can get back to the copying complication. When we copy
 231 // entries from old_cp to merge_cp, we have to revert any
 232 // JVM_CONSTANT_Class entries to JVM_CONSTANT_UnresolvedClass entries
 233 // or verification will fail.
 234 //
 235 // It is important to explicitly state that the merging algorithm
 236 // effectively unresolves JVM_CONSTANT_Class entries that were in the
 237 // old_cp when they are changed into JVM_CONSTANT_UnresolvedClass
 238 // entries in the merge_cp. This is done both to make verification
 239 // happy and to avoid adding more brittleness between RedefineClasses
 240 // and the constant pool cache. By allowing the constant pool cache
 241 // implementation to (re)resolve JVM_CONSTANT_UnresolvedClass entries
 242 // into JVM_CONSTANT_Class entries, we avoid having to embed knowledge
 243 // about those algorithms in RedefineClasses.
 244 //
 245 // Appending unique entries from scratch_cp to merge_cp is straight
 246 // forward for direct CP entries and most indirect CP entries. For the
 247 // indirect CP entry type JVM_CONSTANT_NameAndType and for the double-
 248 // indirect CP entry types, the presence of more than one piece of
 249 // interesting data makes appending the entries more complicated.
 250 //
 251 // For the JVM_CONSTANT_{Double,Float,Integer,Long,Utf8} entry types,
 252 // the entry is simply copied from scratch_cp to the end of merge_cp.
 253 // If the index in scratch_cp is different than the destination index
 254 // in merge_cp, then the change in index value is tracked.
 255 //
 256 // Note: the above discussion for the direct CP entries also applies
 257 // to the JVM_CONSTANT_UnresolvedClass entry types.
 258 //
 259 // For the JVM_CONSTANT_Class entry types, since there is only
 260 // one data element at the end of the recursion, we know that we have
 261 // either one or two unique entries. If the JVM_CONSTANT_Utf8 entry is
 262 // unique then it is appended to merge_cp before the current entry.
 263 // If the JVM_CONSTANT_Utf8 entry is not unique, then the current entry
 264 // is updated to refer to the duplicate entry in merge_cp before it is
 265 // appended to merge_cp. Again, any changes in index values are tracked
 266 // as needed.
 267 //
 268 // Note: the above discussion for JVM_CONSTANT_Class entry
 269 // types is theoretical. Since those entry types have already been
 270 // optimized into JVM_CONSTANT_UnresolvedClass entry types,
 271 // they are handled as direct CP entries.
 272 //
 273 // For the JVM_CONSTANT_NameAndType entry type, since there are two
 274 // data elements at the end of the recursions, we know that we have
 275 // between one and three unique entries. Any unique JVM_CONSTANT_Utf8
 276 // entries are appended to merge_cp before the current entry. For any
 277 // JVM_CONSTANT_Utf8 entries that are not unique, the current entry is
 278 // updated to refer to the duplicate entry in merge_cp before it is
 279 // appended to merge_cp. Again, any changes in index values are tracked
 280 // as needed.
 281 //
 282 // For the JVM_CONSTANT_{Fieldref,InterfaceMethodref,Methodref} entry
 283 // types, since there are two indirect CP entries and three data
 284 // elements at the end of the recursions, we know that we have between
 285 // one and six unique entries. See the JVM_CONSTANT_Fieldref diagram
 286 // above for an example of all six entries. The uniqueness algorithm
 287 // for the JVM_CONSTANT_Class and JVM_CONSTANT_NameAndType entries is
 288 // covered above. Any unique entries are appended to merge_cp before
 289 // the current entry. For any entries that are not unique, the current
 290 // entry is updated to refer to the duplicate entry in merge_cp before
 291 // it is appended to merge_cp. Again, any changes in index values are
 292 // tracked as needed.
 293 //
 294 //
 295 // Other Details:
 296 //
 297 // Details for other parts of RedefineClasses need to be written.
 298 // This is a placeholder section.
 299 //
 300 //
 301 // Open Issues (in no particular order):
 302 //
 303 // - How do we serialize the RedefineClasses() API without deadlocking?
 304 //
 305 // - SystemDictionary::parse_stream() was called with a NULL protection
 306 //   domain since the initial version. This has been changed to pass
 307 //   the_class->protection_domain(). This change has been tested with
 308 //   all NSK tests and nothing broke, but what will adding it now break
 309 //   in ways that we don't test?
 310 //
 311 // - GenerateOopMap::rewrite_load_or_store() has a comment in its
 312 //   (indirect) use of the Relocator class that the max instruction
 313 //   size is 4 bytes. goto_w and jsr_w are 5 bytes and wide/iinc is
 314 //   6 bytes. Perhaps Relocator only needs a 4 byte buffer to do
 315 //   what it does to the bytecodes. More investigation is needed.
 316 //
 317 // - How do we know if redefine_single_class() and the guts of
 318 //   InstanceKlass are out of sync? I don't think this can be
 319 //   automated, but we should probably order the work in
 320 //   redefine_single_class() to match the order of field
 321 //   definitions in InstanceKlass. We also need to add some
 322 //   comments about keeping things in sync.
 323 //
 324 // - set_new_constant_pool() is huge and we should consider refactoring
 325 //   it into smaller chunks of work.
 326 //
 327 // - The exception table update code in set_new_constant_pool() defines
 328 //   const values that are also defined in a local context elsewhere.
 329 //   The same literal values are also used in elsewhere. We need to
 330 //   coordinate a cleanup of these constants with Runtime.
 331 //
 332 
 333 struct JvmtiCachedClassFileData {
 334   jint length;
 335   unsigned char data[1];
 336 };
 337 
 338 class VM_RedefineClasses: public VM_Operation {
 339  private:
 340   // These static fields are needed by ClassLoaderDataGraph::classes_do()
 341   // facility and the AdjustCpoolCacheAndVtable helper:
 342   static Array<Method*>* _old_methods;
 343   static Array<Method*>* _new_methods;
 344   static Method**      _matching_old_methods;
 345   static Method**      _matching_new_methods;
 346   static Method**      _deleted_methods;
 347   static Method**      _added_methods;
 348   static int             _matching_methods_length;
 349   static int             _deleted_methods_length;
 350   static int             _added_methods_length;
 351   static Klass*          _the_class;
 352 
 353   // The instance fields are used to pass information from
 354   // doit_prologue() to doit() and doit_epilogue().
 355   jint                        _class_count;
 356   const jvmtiClassDefinition *_class_defs;  // ptr to _class_count defs
 357 
 358   // This operation is used by both RedefineClasses and
 359   // RetransformClasses.  Indicate which.
 360   JvmtiClassLoadKind          _class_load_kind;
 361 
 362   // _index_map_count is just an optimization for knowing if
 363   // _index_map_p contains any entries.
 364   int                         _index_map_count;
 365   intArray *                  _index_map_p;
 366 
 367   // _operands_index_map_count is just an optimization for knowing if
 368   // _operands_index_map_p contains any entries.
 369   int                         _operands_cur_length;
 370   int                         _operands_index_map_count;
 371   intArray *                  _operands_index_map_p;
 372 
 373   // ptr to _class_count scratch_classes
 374   InstanceKlass**             _scratch_classes;
 375   jvmtiError                  _res;
 376 
 377   // Set if any of the InstanceKlasses have entries in the ResolvedMethodTable
 378   // to avoid walking after redefinition if the redefined classes do not
 379   // have any entries.
 380   bool _any_class_has_resolved_methods;
 381 
 382   // Performance measurement support. These timers do not cover all
 383   // the work done for JVM/TI RedefineClasses() but they do cover
 384   // the heavy lifting.
 385   elapsedTimer  _timer_rsc_phase1;
 386   elapsedTimer  _timer_rsc_phase2;
 387   elapsedTimer  _timer_vm_op_prologue;
 388 
 389   // These routines are roughly in call order unless otherwise noted.
 390 
 391   // Load the caller's new class definition(s) into _scratch_classes.
 392   // Constant pool merging work is done here as needed. Also calls
 393   // compare_and_normalize_class_versions() to verify the class
 394   // definition(s).
 395   jvmtiError load_new_class_versions(TRAPS);
 396 
 397   // Verify that the caller provided class definition(s) that meet
 398   // the restrictions of RedefineClasses. Normalize the order of
 399   // overloaded methods as needed.
 400   jvmtiError compare_and_normalize_class_versions(
 401     InstanceKlass* the_class, InstanceKlass* scratch_class);
 402 
 403   // Figure out which new methods match old methods in name and signature,
 404   // which methods have been added, and which are no longer present
 405   void compute_added_deleted_matching_methods();
 406 
 407   // Change jmethodIDs to point to the new methods
 408   void update_jmethod_ids();
 409 
 410   // In addition to marking methods as old and/or obsolete, this routine
 411   // counts the number of methods that are EMCP (Equivalent Module Constant Pool).
 412   int check_methods_and_mark_as_obsolete();
 413   void transfer_old_native_function_registrations(InstanceKlass* the_class);
 414 
 415   // Install the redefinition of a class
 416   void redefine_single_class(jclass the_jclass,
 417     InstanceKlass* scratch_class_oop, TRAPS);
 418 
 419   void swap_annotations(InstanceKlass* new_class,
 420                         InstanceKlass* scratch_class);
 421 
 422   // Increment the classRedefinedCount field in the specific InstanceKlass
 423   // and in all direct and indirect subclasses.
 424   void increment_class_counter(InstanceKlass *ik, TRAPS);
 425 
 426   // Support for constant pool merging (these routines are in alpha order):
 427   void append_entry(const constantPoolHandle& scratch_cp, int scratch_i,
 428     constantPoolHandle *merge_cp_p, int *merge_cp_length_p, TRAPS);
 429   void append_operand(const constantPoolHandle& scratch_cp, int scratch_bootstrap_spec_index,
 430     constantPoolHandle *merge_cp_p, int *merge_cp_length_p, TRAPS);
 431   void finalize_operands_merge(const constantPoolHandle& merge_cp, TRAPS);
 432   int find_or_append_indirect_entry(const constantPoolHandle& scratch_cp, int scratch_i,
 433     constantPoolHandle *merge_cp_p, int *merge_cp_length_p, TRAPS);
 434   int find_or_append_operand(const constantPoolHandle& scratch_cp, int scratch_bootstrap_spec_index,
 435     constantPoolHandle *merge_cp_p, int *merge_cp_length_p, TRAPS);
 436   int find_new_index(int old_index);
 437   int find_new_operand_index(int old_bootstrap_spec_index);
 438   bool is_unresolved_class_mismatch(const constantPoolHandle& cp1, int index1,
 439     const constantPoolHandle& cp2, int index2);
 440   void map_index(const constantPoolHandle& scratch_cp, int old_index, int new_index);
 441   void map_operand_index(int old_bootstrap_spec_index, int new_bootstrap_spec_index);
 442   bool merge_constant_pools(const constantPoolHandle& old_cp,
 443     const constantPoolHandle& scratch_cp, constantPoolHandle *merge_cp_p,
 444     int *merge_cp_length_p, TRAPS);
 445   jvmtiError merge_cp_and_rewrite(InstanceKlass* the_class,
 446     InstanceKlass* scratch_class, TRAPS);
 447   u2 rewrite_cp_ref_in_annotation_data(
 448     AnnotationArray* annotations_typeArray, int &byte_i_ref,
 449     const char * trace_mesg, TRAPS);
 450   bool rewrite_cp_refs(InstanceKlass* scratch_class, TRAPS);
 451   bool rewrite_cp_refs_in_annotation_struct(
 452     AnnotationArray* class_annotations, int &byte_i_ref, TRAPS);
 453   bool rewrite_cp_refs_in_annotations_typeArray(
 454     AnnotationArray* annotations_typeArray, int &byte_i_ref, TRAPS);
 455   bool rewrite_cp_refs_in_class_annotations(
 456     InstanceKlass* scratch_class, TRAPS);
 457   bool rewrite_cp_refs_in_element_value(
 458     AnnotationArray* class_annotations, int &byte_i_ref, TRAPS);
 459   bool rewrite_cp_refs_in_type_annotations_typeArray(
 460     AnnotationArray* type_annotations_typeArray, int &byte_i_ref,
 461     const char * location_mesg, TRAPS);
 462   bool rewrite_cp_refs_in_type_annotation_struct(
 463     AnnotationArray* type_annotations_typeArray, int &byte_i_ref,
 464     const char * location_mesg, TRAPS);
 465   bool skip_type_annotation_target(
 466     AnnotationArray* type_annotations_typeArray, int &byte_i_ref,
 467     const char * location_mesg, TRAPS);
 468   bool skip_type_annotation_type_path(
 469     AnnotationArray* type_annotations_typeArray, int &byte_i_ref, TRAPS);
 470   bool rewrite_cp_refs_in_fields_annotations(
 471     InstanceKlass* scratch_class, TRAPS);
 472   bool rewrite_cp_refs_in_nest_attributes(InstanceKlass* scratch_class);
 473   void rewrite_cp_refs_in_method(methodHandle method,
 474     methodHandle * new_method_p, TRAPS);
 475   bool rewrite_cp_refs_in_methods(InstanceKlass* scratch_class, TRAPS);
 476   bool rewrite_cp_refs_in_methods_annotations(
 477     InstanceKlass* scratch_class, TRAPS);
 478   bool rewrite_cp_refs_in_methods_default_annotations(
 479     InstanceKlass* scratch_class, TRAPS);
 480   bool rewrite_cp_refs_in_methods_parameter_annotations(
 481     InstanceKlass* scratch_class, TRAPS);
 482   bool rewrite_cp_refs_in_class_type_annotations(
 483     InstanceKlass* scratch_class, TRAPS);
 484   bool rewrite_cp_refs_in_fields_type_annotations(
 485     InstanceKlass* scratch_class, TRAPS);
 486   bool rewrite_cp_refs_in_methods_type_annotations(
 487     InstanceKlass* scratch_class, TRAPS);
 488   void rewrite_cp_refs_in_stack_map_table(const methodHandle& method, TRAPS);
 489   void rewrite_cp_refs_in_verification_type_info(
 490          address& stackmap_addr_ref, address stackmap_end, u2 frame_i,
 491          u1 frame_size, TRAPS);
 492   void set_new_constant_pool(ClassLoaderData* loader_data,
 493          InstanceKlass* scratch_class,
 494          constantPoolHandle scratch_cp, int scratch_cp_length, TRAPS);
 495 
 496   void flush_dependent_code(InstanceKlass* ik, TRAPS);
 497 
 498   // lock classes to redefine since constant pool merging isn't thread safe.
 499   void lock_classes();
 500   void unlock_classes();
 501 
 502   static void dump_methods();
 503 
 504   // Check that there are no old or obsolete methods
 505   class CheckClass : public KlassClosure {
 506     Thread* _thread;
 507    public:
 508     CheckClass(Thread* t) : _thread(t) {}
 509     void do_klass(Klass* k);
 510   };
 511 
 512   // Unevolving classes may point to methods of the_class directly
 513   // from their constant pool caches, itables, and/or vtables. We
 514   // use the ClassLoaderDataGraph::classes_do() facility and this helper
 515   // to fix up these pointers.
 516   class AdjustCpoolCacheAndVtable : public KlassClosure {
 517     Thread* _thread;
 518    public:
 519     AdjustCpoolCacheAndVtable(Thread* t) : _thread(t) {}
 520     void do_klass(Klass* k);
 521   };
 522 
 523   // Clean MethodData out
 524   class MethodDataCleaner : public KlassClosure {
 525    public:
 526     MethodDataCleaner() {}
 527     void do_klass(Klass* k);
 528   };
 529  public:
 530   VM_RedefineClasses(jint class_count,
 531                      const jvmtiClassDefinition *class_defs,
 532                      JvmtiClassLoadKind class_load_kind);
 533   VMOp_Type type() const { return VMOp_RedefineClasses; }
 534   bool doit_prologue();
 535   void doit();
 536   void doit_epilogue();
 537 
 538   bool allow_nested_vm_operations() const        { return true; }
 539   jvmtiError check_error()                       { return _res; }
 540 
 541   // Modifiable test must be shared between IsModifiableClass query
 542   // and redefine implementation
 543   static bool is_modifiable_class(oop klass_mirror);
 544 
 545   static jint get_cached_class_file_len(JvmtiCachedClassFileData *cache) {
 546     return cache == NULL ? 0 : cache->length;
 547   }
 548   static unsigned char * get_cached_class_file_bytes(JvmtiCachedClassFileData *cache) {
 549     return cache == NULL ? NULL : cache->data;
 550   }
 551 
 552   // Error printing
 553   void print_on_error(outputStream* st) const;
 554 };
 555 #endif // SHARE_VM_PRIMS_JVMTIREDEFINECLASSES_HPP