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 // Introduction:

 //

 // The RedefineClasses() API is used to change the definition of one or

 // more classes. While the API supports redefining more than one class

 // in a single call, in general, the API is discussed in the context of

 // changing the definition of a single current class to a single new

 // class. For clarity, the current class is will always be called

 // "the_class" and the new class will always be called "scratch_class".

 //

 // The name "the_class" is used because there is only one structure

 // that represents a specific class; redefinition does not replace the

 // structure, but instead replaces parts of the structure. The name

 // "scratch_class" is used because the structure that represents the

 // new definition of a specific class is simply used to carry around

 // the parts of the new definition until they are used to replace the

 // appropriate parts in the_class. Once redefinition of a class is

 // complete, scratch_class is thrown away.

 //

 //

 // Implementation Overview:

 //

 // The RedefineClasses() API is mostly a wrapper around the VM op that

 // does the real work. The work is split in varying degrees between

 // doit_prologue(), doit() and doit_epilogue().

 //

 // 1) doit_prologue() is called by the JavaThread on the way to a

 //    safepoint. It does parameter verification and loads scratch_class

 //    which involves:

 //    - parsing the incoming class definition using the_class' class

 //      loader and security context

 //    - linking scratch_class

 //    - merging constant pools and rewriting bytecodes as needed

 //      for the merged constant pool

 //    - verifying the bytecodes in scratch_class

 //    - setting up the constant pool cache and rewriting bytecodes

 //      as needed to use the cache

 //    - finally, scratch_class is compared to the_class to verify

 //      that it is a valid replacement class

 //    - if everything is good, then scratch_class is saved in an

 //      instance field in the VM operation for the doit() call

 //

 //    Note: A JavaThread must do the above work.

 //

 // 2) doit() is called by the VMThread during a safepoint. It installs

 //    the new class definition(s) which involves:

 //    - retrieving the scratch_class from the instance field in the

 //      VM operation

 //    - house keeping (flushing breakpoints and caches, deoptimizing

 //      dependent compiled code)

 //    - replacing parts in the_class with parts from scratch_class

 //    - adding weak reference(s) 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.

 //    - telling the SystemDictionary to notice our changes

 //

 //    Note: the above work must be done by the VMThread to be safe.

 //

 // 3) doit_epilogue() is called by the JavaThread after the VM op

 //    is finished and the safepoint is done. It simply cleans up

 //    memory allocated in doit_prologue() and used in doit().

 //

 //

 // Constant Pool Details:

 //

 // When the_class is redefined, we cannot just replace the constant

 // pool in the_class with the constant pool from scratch_class because

 // that could confuse obsolete methods that may still be running.

 // Instead, the constant pool from the_class, old_cp, is merged with

 // the constant pool from scratch_class, scratch_cp. The resulting

 // constant pool, merge_cp, replaces old_cp in the_class.

 //

 // The key part of any merging algorithm is the entry comparison

 // function so we have to know the types of entries in a constant pool

 // in order to merge two of them together. Constant pools can contain

 // up to 12 different kinds of entries; the JVM_CONSTANT_Unicode entry

 // is not presently used so we only have to worry about the other 11

 // entry types. For the purposes of constant pool merging, it is

 // helpful to know that the 11 entry types fall into 3 different

 // subtypes: "direct", "indirect" and "double-indirect".

 //

 // Direct CP entries contain data and do not contain references to

 // other CP entries. The following are direct CP entries:

 //     JVM_CONSTANT_{Double,Float,Integer,Long,Utf8}

 //

 // Indirect CP entries contain 1 or 2 references to a direct CP entry

 // and no other data. The following are indirect CP entries:

 //     JVM_CONSTANT_{Class,NameAndType,String}

 //

 // Double-indirect CP entries contain two references to indirect CP

 // entries and no other data. The following are double-indirect CP

 // entries:

 //     JVM_CONSTANT_{Fieldref,InterfaceMethodref,Methodref}

 //

 // When comparing entries between two constant pools, the entry types

 // are compared first and if they match, then further comparisons are

 // made depending on the entry subtype. Comparing direct CP entries is

 // simply a matter of comparing the data associated with each entry.

 // Comparing both indirect and double-indirect CP entries requires

 // recursion.

 //

 // Fortunately, the recursive combinations are limited because indirect

 // CP entries can only refer to direct CP entries and double-indirect

 // CP entries can only refer to indirect CP entries. The following is

 // an example illustration of the deepest set of indirections needed to

 // access the data associated with a JVM_CONSTANT_Fieldref entry:

 //

 //     JVM_CONSTANT_Fieldref {

 //         class_index => JVM_CONSTANT_Class {

 //             name_index => JVM_CONSTANT_Utf8 {

 //                 <data-1>

 //             }

 //         }

 //         name_and_type_index => JVM_CONSTANT_NameAndType {

 //             name_index => JVM_CONSTANT_Utf8 {

 //                 <data-2>

 //             }

 //             descriptor_index => JVM_CONSTANT_Utf8 {

 //                 <data-3>

 //             }

 //         }

 //     }

 //

 // The above illustration is not a data structure definition for any

 // computer language. The curly braces ('{' and '}') are meant to

 // delimit the context of the "fields" in the CP entry types shown.

 // Each indirection from the JVM_CONSTANT_Fieldref entry is shown via

 // "=>", e.g., the class_index is used to indirectly reference a

 // JVM_CONSTANT_Class entry where the name_index is used to indirectly

 // reference a JVM_CONSTANT_Utf8 entry which contains the interesting

 // <data-1>. In order to understand a JVM_CONSTANT_Fieldref entry, we

 // have to do a total of 5 indirections just to get to the CP entries

 // that contain the interesting pieces of data and then we have to

 // fetch the three pieces of data. This means we have to do a total of

 // (5 + 3) * 2 == 16 dereferences to compare two JVM_CONSTANT_Fieldref

 // entries.

 //

 // Here is the indirection, data and dereference count for each entry

 // type:

 //

 //    JVM_CONSTANT_Class               1 indir, 1 data, 2 derefs

 //    JVM_CONSTANT_Double              0 indir, 1 data, 1 deref

 //    JVM_CONSTANT_Fieldref            2 indir, 3 data, 8 derefs

 //    JVM_CONSTANT_Float               0 indir, 1 data, 1 deref

 //    JVM_CONSTANT_Integer             0 indir, 1 data, 1 deref

 //    JVM_CONSTANT_InterfaceMethodref  2 indir, 3 data, 8 derefs

 //    JVM_CONSTANT_Long                0 indir, 1 data, 1 deref

 //    JVM_CONSTANT_Methodref           2 indir, 3 data, 8 derefs

 //    JVM_CONSTANT_NameAndType         1 indir, 2 data, 4 derefs

 //    JVM_CONSTANT_String              1 indir, 1 data, 2 derefs

 //    JVM_CONSTANT_Utf8                0 indir, 1 data, 1 deref

 //

 // So different subtypes of CP entries require different amounts of

 // work for a proper comparison.

 //

 // Now that we've talked about the different entry types and how to

 // compare them we need to get back to merging. This is not a merge in

 // the "sort -u" sense or even in the "sort" sense. When we merge two

 // constant pools, we copy all the entries from old_cp to merge_cp,

 // preserving entry order. Next we append all the unique entries from

 // scratch_cp to merge_cp and we track the index changes from the

 // location in scratch_cp to the possibly new location in merge_cp.

 // When we are done, any obsolete code that is still running that

 // uses old_cp should not be able to observe any difference if it

 // were to use merge_cp. As for the new code in scratch_class, it is

 // modified to use the appropriate index values in merge_cp before it

 // is used to replace the code in the_class.

 //

 // There is one small complication in copying the entries from old_cp

 // to merge_cp. Two of the CP entry types are special in that they are

 // lazily resolved. Before explaining the copying complication, we need

 // to digress into CP entry resolution.

 //

 // JVM_CONSTANT_Class and JVM_CONSTANT_String entries are present in

 // the class file, but are not stored in memory as such until they are

 // resolved. The entries are not resolved unless they are used because

 // resolution is expensive. During class file parsing the entries are

 // initially stored in memory as JVM_CONSTANT_ClassIndex and

 // JVM_CONSTANT_StringIndex entries. These special CP entry types

 // indicate that the JVM_CONSTANT_Class and JVM_CONSTANT_String entries

 // have been parsed, but the index values in the entries have not been

 // validated. After the entire constant pool has been parsed, the index

 // values can be validated and then the entries are converted into

 // JVM_CONSTANT_UnresolvedClass and JVM_CONSTANT_UnresolvedString

 // entries. During this conversion process, the UTF8 values that are

 // indirectly referenced by the JVM_CONSTANT_ClassIndex and

 // JVM_CONSTANT_StringIndex entries are changed into symbolOops and the

 // entries are modified to refer to the symbolOops. This optimization

 // eliminates one level of indirection for those two CP entry types and

 // gets the entries ready for verification. During class file parsing

 // it is also possible for JVM_CONSTANT_UnresolvedString entries to be

 // resolved into JVM_CONSTANT_String entries. Verification expects to

 // find JVM_CONSTANT_UnresolvedClass and either JVM_CONSTANT_String or

 // JVM_CONSTANT_UnresolvedString entries and not JVM_CONSTANT_Class

 // entries.

 //

 // Now we can get back to the copying complication. When we copy

 // entries from old_cp to merge_cp, we have to revert any

 // JVM_CONSTANT_Class entries to JVM_CONSTANT_UnresolvedClass entries

 // or verification will fail.

 //

 // It is important to explicitly state that the merging algorithm

 // effectively unresolves JVM_CONSTANT_Class entries that were in the

 // old_cp when they are changed into JVM_CONSTANT_UnresolvedClass

 // entries in the merge_cp. This is done both to make verification

 // happy and to avoid adding more brittleness between RedefineClasses

 // and the constant pool cache. By allowing the constant pool cache

 // implementation to (re)resolve JVM_CONSTANT_UnresolvedClass entries

 // into JVM_CONSTANT_Class entries, we avoid having to embed knowledge

 // about those algorithms in RedefineClasses.

 //

 // Appending unique entries from scratch_cp to merge_cp is straight

 // forward for direct CP entries and most indirect CP entries. For the

 // indirect CP entry type JVM_CONSTANT_NameAndType and for the double-

 // indirect CP entry types, the presence of more than one piece of

 // interesting data makes appending the entries more complicated.

 //

 // For the JVM_CONSTANT_{Double,Float,Integer,Long,Utf8} entry types,

 // the entry is simply copied from scratch_cp to the end of merge_cp.

 // If the index in scratch_cp is different than the destination index

 // in merge_cp, then the change in index value is tracked.

 //

 // Note: the above discussion for the direct CP entries also applies

 // to the JVM_CONSTANT_Unresolved{Class,String} entry types.

 //

 // For the JVM_CONSTANT_{Class,String} entry types, since there is only

 // one data element at the end of the recursion, we know that we have

 // either one or two unique entries. If the JVM_CONSTANT_Utf8 entry is

 // unique then it is appended to merge_cp before the current entry.

 // If the JVM_CONSTANT_Utf8 entry is not unique, then the current entry

 // is updated to refer to the duplicate entry in merge_cp before it is

 // appended to merge_cp. Again, any changes in index values are tracked

 // as needed.

 //

 // Note: the above discussion for JVM_CONSTANT_{Class,String} entry

 // types is theoretical. Since those entry types have already been

 // optimized into JVM_CONSTANT_Unresolved{Class,String} entry types,

 // they are handled as direct CP entries.

 //

 // For the JVM_CONSTANT_NameAndType entry type, since there are two

 // data elements at the end of the recursions, we know that we have

 // between one and three unique entries. Any unique JVM_CONSTANT_Utf8

 // entries are appended to merge_cp before the current entry. For any

 // JVM_CONSTANT_Utf8 entries that are not unique, the current entry is

 // updated to refer to the duplicate entry in merge_cp before it is

 // appended to merge_cp. Again, any changes in index values are tracked

 // as needed.

 //

 // For the JVM_CONSTANT_{Fieldref,InterfaceMethodref,Methodref} entry

 // types, since there are two indirect CP entries and three data

 // elements at the end of the recursions, we know that we have between

 // one and six unique entries. See the JVM_CONSTANT_Fieldref diagram

 // above for an example of all six entries. The uniqueness algorithm

 // for the JVM_CONSTANT_Class and JVM_CONSTANT_NameAndType entries is

 // covered above. Any unique entries are appended to merge_cp before

 // the current entry. For any entries that are not unique, the current

 // entry is updated to refer to the duplicate entry in merge_cp before

 // it is appended to merge_cp. Again, any changes in index values are

 // tracked as needed.

 //

 //

 // Other Details:

 //

 // Details for other parts of RedefineClasses need to be written.

 // This is a placeholder section.

 //

 //

 // Open Issues (in no particular order):

 //

 // - How do we serialize the RedefineClasses() API without deadlocking?

 //

 // - SystemDictionary::parse_stream() was called with a NULL protection

 //   domain since the initial version. This has been changed to pass

 //   the_class->protection_domain(). This change has been tested with

 //   all NSK tests and nothing broke, but what will adding it now break

 //   in ways that we don't test?

 //

 // - GenerateOopMap::rewrite_load_or_store() has a comment in its

 //   (indirect) use of the Relocator class that the max instruction

 //   size is 4 bytes. goto_w and jsr_w are 5 bytes and wide/iinc is

 //   6 bytes. Perhaps Relocator only needs a 4 byte buffer to do

 //   what it does to the bytecodes. More investigation is needed.

 //

 // - java.lang.Object methods can be called on arrays. This is

 //   implemented via the arrayKlassOop vtable which we don't

 //   update. For example, if we redefine java.lang.Object.toString(),

 //   then the new version of the method will not be called for array

 //   objects.

 //

 // - How do we know if redefine_single_class() and the guts of

 //   instanceKlass are out of sync? I don't think this can be

 //   automated, but we should probably order the work in

 //   redefine_single_class() to match the order of field

 //   definitions in instanceKlass. We also need to add some

 //   comments about keeping things in sync.

 //

 // - set_new_constant_pool() is huge and we should consider refactoring

 //   it into smaller chunks of work.

 //

 // - The exception table update code in set_new_constant_pool() defines

 //   const values that are also defined in a local context elsewhere.

 //   The same literal values are also used in elsewhere. We need to

 //   coordinate a cleanup of these constants with Runtime.

 //

 class VM_RedefineClasses: public VM_Operation {

  private:

   // These static fields are needed by SystemDictionary::classes_do()

   // facility and the adjust_cpool_cache_and_vtable() helper:

   static objArrayOop     _old_methods;

   static objArrayOop     _new_methods;

   static methodOop*      _matching_old_methods;

   static methodOop*      _matching_new_methods;

   static methodOop*      _deleted_methods;

   static methodOop*      _added_methods;

   static int             _matching_methods_length;

   static int             _deleted_methods_length;

   static int             _added_methods_length;

   static klassOop        _the_class_oop;

   // The instance fields are used to pass information from

   // doit_prologue() to doit() and doit_epilogue().

   jint                        _class_count;

   const jvmtiClassDefinition *_class_defs;  // ptr to _class_count defs

   // This operation is used by both RedefineClasses and

   // RetransformClasses.  Indicate which.

   JvmtiClassLoadKind          _class_load_kind;

   // _index_map_count is just an optimization for knowing if

   // _index_map_p contains any entries.

   int                         _index_map_count;

   intArray *                  _index_map_p;

   // ptr to _class_count scratch_classes

   instanceKlassHandle *       _scratch_classes;

   jvmtiError                  _res;

   // Performance measurement support. These timers do not cover all

   // the work done for JVM/TI RedefineClasses() but they do cover

   // the heavy lifting.

   elapsedTimer  _timer_rsc_phase1;

   elapsedTimer  _timer_rsc_phase2;

   elapsedTimer  _timer_vm_op_prologue;

   // These routines are roughly in call order unless otherwise noted.

   // Load the caller's new class definition(s) into _scratch_classes.

   // Constant pool merging work is done here as needed. Also calls

   // compare_and_normalize_class_versions() to verify the class

   // definition(s).

   jvmtiError load_new_class_versions(TRAPS);

   // Verify that the caller provided class definition(s) that meet

   // the restrictions of RedefineClasses. Normalize the order of

   // overloaded methods as needed.

   jvmtiError compare_and_normalize_class_versions(

     instanceKlassHandle the_class, instanceKlassHandle scratch_class);

   // Swap annotations[i] with annotations[j]

   // Used by compare_and_normalize_class_versions() when normalizing

   // overloaded methods or changing idnum as when adding or deleting methods.

   void swap_all_method_annotations(int i, int j, instanceKlassHandle scratch_class);

   // Figure out which new methods match old methods in name and signature,

   // which methods have been added, and which are no longer present

   void compute_added_deleted_matching_methods();

   // Change jmethodIDs to point to the new methods

   void update_jmethod_ids();

   // In addition to marking methods as obsolete, this routine

   // records which methods are EMCP (Equivalent Module Constant

   // Pool) in the emcp_methods BitMap and returns the number of

   // EMCP methods via emcp_method_count_p. This information is

   // used when information about the previous version of the_class

   // is squirreled away.

   void check_methods_and_mark_as_obsolete(BitMap *emcp_methods,

          int * emcp_method_count_p);

   void transfer_old_native_function_registrations(instanceKlassHandle the_class);

   // 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.

   static void adjust_cpool_cache_and_vtable(klassOop k_oop, oop loader, TRAPS);

   // Install the redefinition of a class

   void redefine_single_class(jclass the_jclass,

     instanceKlassHandle scratch_class, TRAPS);

   // Increment the classRedefinedCount field in the specific instanceKlass

   // and in all direct and indirect subclasses.

   void increment_class_counter(instanceKlass *ik, TRAPS);

   // Support for constant pool merging (these routines are in alpha

   // order):

   void append_entry(constantPoolHandle scratch_cp, int scratch_i,

     constantPoolHandle *merge_cp_p, int *merge_cp_length_p, TRAPS);

   int find_new_index(int old_index);

   bool is_unresolved_class_mismatch(constantPoolHandle cp1, int index1,

     constantPoolHandle cp2, int index2);

   bool is_unresolved_string_mismatch(constantPoolHandle cp1, int index1,

     constantPoolHandle cp2, int index2);

   void map_index(constantPoolHandle scratch_cp, int old_index, int new_index);

   bool merge_constant_pools(constantPoolHandle old_cp,

     constantPoolHandle scratch_cp, constantPoolHandle *merge_cp_p,

     int *merge_cp_length_p, TRAPS);

   jvmtiError merge_cp_and_rewrite(instanceKlassHandle the_class,

     instanceKlassHandle scratch_class, TRAPS);

   u2 rewrite_cp_ref_in_annotation_data(

     typeArrayHandle annotations_typeArray, int &byte_i_ref,

     const char * trace_mesg, TRAPS);

   bool rewrite_cp_refs(instanceKlassHandle scratch_class, TRAPS);

   bool rewrite_cp_refs_in_annotation_struct(

     typeArrayHandle class_annotations, int &byte_i_ref, TRAPS);

   bool rewrite_cp_refs_in_annotations_typeArray(

     typeArrayHandle annotations_typeArray, int &byte_i_ref, TRAPS);

   bool rewrite_cp_refs_in_class_annotations(

     instanceKlassHandle scratch_class, TRAPS);

   bool rewrite_cp_refs_in_element_value(

     typeArrayHandle class_annotations, int &byte_i_ref, TRAPS);

   bool rewrite_cp_refs_in_fields_annotations(

     instanceKlassHandle scratch_class, TRAPS);

   void rewrite_cp_refs_in_method(methodHandle method,

     methodHandle * new_method_p, TRAPS);

   bool rewrite_cp_refs_in_methods(instanceKlassHandle scratch_class, TRAPS);

   bool rewrite_cp_refs_in_methods_annotations(

     instanceKlassHandle scratch_class, TRAPS);

   bool rewrite_cp_refs_in_methods_default_annotations(

     instanceKlassHandle scratch_class, TRAPS);

   bool rewrite_cp_refs_in_methods_parameter_annotations(

     instanceKlassHandle scratch_class, TRAPS);

   void rewrite_cp_refs_in_stack_map_table(methodHandle method, TRAPS);

   void rewrite_cp_refs_in_verification_type_info(

          address& stackmap_addr_ref, address stackmap_end, u2 frame_i,

          u1 frame_size, TRAPS);

   void set_new_constant_pool(instanceKlassHandle scratch_class,

     constantPoolHandle scratch_cp, int scratch_cp_length, bool shrink, TRAPS);

   void flush_dependent_code(instanceKlassHandle k_h, TRAPS);

   static void check_class(klassOop k_oop, oop initiating_loader, TRAPS) PRODUCT_RETURN;

   static void dump_methods()   PRODUCT_RETURN;

  public:

   VM_RedefineClasses(jint class_count,

                      const jvmtiClassDefinition *class_defs,

                      JvmtiClassLoadKind class_load_kind);

   VMOp_Type type() const { return VMOp_RedefineClasses; }

   bool doit_prologue();

   void doit();

   void doit_epilogue();

   bool allow_nested_vm_operations() const        { return true; }

   jvmtiError check_error()                       { return _res; }

   // Modifiable test must be shared between IsModifiableClass query

   // and redefine implementation

   static bool is_modifiable_class(oop klass_mirror);

 };