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