1 /*
  2  * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #ifndef SHARE_OOPS_KLASS_HPP
 26 #define SHARE_OOPS_KLASS_HPP
 27 
 28 #include "memory/iterator.hpp"
 29 #include "memory/memRegion.hpp"
 30 #include "oops/markWord.hpp"
 31 #include "oops/metadata.hpp"
 32 #include "oops/oop.hpp"
 33 #include "oops/oopHandle.hpp"
 34 #include "utilities/accessFlags.hpp"
 35 #include "utilities/macros.hpp"
 36 #if INCLUDE_JFR
 37 #include "jfr/support/jfrTraceIdExtension.hpp"
 38 #endif
 39 
 40 // Klass IDs for all subclasses of Klass
 41 enum KlassID {
 42   InstanceKlassID,
 43   InstanceRefKlassID,
 44   InstanceMirrorKlassID,
 45   InstanceClassLoaderKlassID,
 46   TypeArrayKlassID,
 47   FlatArrayKlassID,
 48   ObjArrayKlassID
 49 };
 50 
 51 const uint KLASS_ID_COUNT = 7;
 52 
 53 //
 54 // A Klass provides:
 55 //  1: language level class object (method dictionary etc.)
 56 //  2: provide vm dispatch behavior for the object
 57 // Both functions are combined into one C++ class.
 58 
 59 // One reason for the oop/klass dichotomy in the implementation is
 60 // that we don't want a C++ vtbl pointer in every object.  Thus,
 61 // normal oops don't have any virtual functions.  Instead, they
 62 // forward all "virtual" functions to their klass, which does have
 63 // a vtbl and does the C++ dispatch depending on the object's
 64 // actual type.  (See oop.inline.hpp for some of the forwarding code.)
 65 // ALL FUNCTIONS IMPLEMENTING THIS DISPATCH ARE PREFIXED WITH "oop_"!
 66 
 67 // Forward declarations.
 68 template <class T> class Array;
 69 template <class T> class GrowableArray;
 70 class ClassLoaderData;
 71 class fieldDescriptor;
 72 class klassVtable;
 73 class ModuleEntry;
 74 class PackageEntry;
 75 class ParCompactionManager;
 76 class PSPromotionManager;
 77 class vtableEntry;
 78 
 79 class Klass : public Metadata {
 80   friend class VMStructs;
 81   friend class JVMCIVMStructs;
 82  protected:
 83   // If you add a new field that points to any metaspace object, you
 84   // must add this field to Klass::metaspace_pointers_do().
 85 
 86   // note: put frequently-used fields together at start of klass structure
 87   // for better cache behavior (may not make much of a difference but sure won't hurt)
 88   enum { _primary_super_limit = 8 };
 89 
 90   // The "layout helper" is a combined descriptor of object layout.
 91   // For klasses which are neither instance nor array, the value is zero.
 92   //
 93   // For instances, layout helper is a positive number, the instance size.
 94   // This size is already passed through align_object_size and scaled to bytes.
 95   // The low order bit is set if instances of this class cannot be
 96   // allocated using the fastpath.
 97   //
 98   // For arrays, layout helper is a negative number, containing four
 99   // distinct bytes, as follows:
100   //    MSB:[tag, hsz, ebt, log2(esz)]:LSB
101   // where:
102   //    tag is 0x80 if the elements are oops, 0xC0 if non-oops, 0xA0 if value types
103   //    hsz is array header size in bytes (i.e., offset of first element)
104   //    ebt is the BasicType of the elements
105   //    esz is the element size in bytes
106   // This packed word is arranged so as to be quickly unpacked by the
107   // various fast paths that use the various subfields.
108   //
109   // The esz bits can be used directly by a SLL instruction, without masking.
110   //
111   // Note that the array-kind tag looks like 0x00 for instance klasses,
112   // since their length in bytes is always less than 24Mb.
113   //
114   // Final note:  This comes first, immediately after C++ vtable,
115   // because it is frequently queried.
116   jint        _layout_helper;
117 
118   // Klass identifier used to implement devirtualized oop closure dispatching.
119   const KlassID _id;
120 
121   // vtable length
122   int _vtable_len;
123 
124   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
125   // and _primary_supers all help make fast subtype checks.  See big discussion
126   // in doc/server_compiler/checktype.txt
127   //
128   // Where to look to observe a supertype (it is &_secondary_super_cache for
129   // secondary supers, else is &_primary_supers[depth()].
130   juint       _super_check_offset;
131 
132   // Class name.  Instance classes: java/lang/String, etc.  Array classes: [I,
133   // [Ljava/lang/String;, etc.  Set to zero for all other kinds of classes.
134   Symbol*     _name;
135 
136   // Cache of last observed secondary supertype
137   Klass*      _secondary_super_cache;
138   // Array of all secondary supertypes
139   Array<Klass*>* _secondary_supers;
140   // Ordered list of all primary supertypes
141   Klass*      _primary_supers[_primary_super_limit];
142   // java/lang/Class instance mirroring this class
143   OopHandle   _java_mirror;
144   // Superclass
145   Klass*      _super;
146   // First subclass (NULL if none); _subklass->next_sibling() is next one
147   Klass* volatile _subklass;
148   // Sibling link (or NULL); links all subklasses of a klass
149   Klass* volatile _next_sibling;
150 
151   // All klasses loaded by a class loader are chained through these links
152   Klass*      _next_link;
153 
154   // The VM's representation of the ClassLoader used to load this class.
155   // Provide access the corresponding instance java.lang.ClassLoader.
156   ClassLoaderData* _class_loader_data;
157 
158   jint        _modifier_flags;  // Processed access flags, for use by Class.getModifiers.
159   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
160 
161   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
162 
163   markWord _prototype_header;  // inline type and inline array mark patterns
164 private:
165   // This is an index into FileMapHeader::_shared_path_table[], to
166   // associate this class with the JAR file where it's loaded from during
167   // dump time. If a class is not loaded from the shared archive, this field is
168   // -1.
169   jshort _shared_class_path_index;
170 
171 #if INCLUDE_CDS
172   // Flags of the current shared class.
173   u2     _shared_class_flags;
174   enum {
175     _archived_lambda_proxy_is_available = 2,
176     _has_value_based_class_annotation = 4,
177     _verified_at_dump_time = 8
178   };
179 #endif
180 
181   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
182 
183 protected:
184 
185   // Constructor
186   Klass(KlassID id);
187   Klass() : _id(KlassID(-1)) { assert(DumpSharedSpaces || UseSharedSpaces, "only for cds"); }
188 
189   void* operator new(size_t size, ClassLoaderData* loader_data, size_t word_size, TRAPS) throw();
190 
191  public:
192   int id() { return _id; }
193 
194   enum class DefaultsLookupMode { find, skip };
195   enum class OverpassLookupMode { find, skip };
196   enum class StaticLookupMode   { find, skip };
197   enum class PrivateLookupMode  { find, skip };
198 
199   virtual bool is_klass() const { return true; }
200 
201   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
202   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
203   // If this is not what your code expects, you're probably looking for Klass::java_super().
204   Klass* super() const               { return _super; }
205   void set_super(Klass* k)           { _super = k; }
206 
207   // initializes _super link, _primary_supers & _secondary_supers arrays
208   void initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS);
209 
210   // klass-specific helper for initializing _secondary_supers
211   virtual GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
212                                                           Array<InstanceKlass*>* transitive_interfaces);
213 
214   // java_super is the Java-level super type as specified by Class.getSuperClass.
215   virtual InstanceKlass* java_super() const  { return NULL; }
216 
217   juint    super_check_offset() const  { return _super_check_offset; }
218   void set_super_check_offset(juint o) { _super_check_offset = o; }
219 
220   Klass* secondary_super_cache() const     { return _secondary_super_cache; }
221   void set_secondary_super_cache(Klass* k) { _secondary_super_cache = k; }
222 
223   Array<Klass*>* secondary_supers() const { return _secondary_supers; }
224   void set_secondary_supers(Array<Klass*>* k) { _secondary_supers = k; }
225 
226   // Return the element of the _super chain of the given depth.
227   // If there is no such element, return either NULL or this.
228   Klass* primary_super_of_depth(juint i) const {
229     assert(i < primary_super_limit(), "oob");
230     Klass* super = _primary_supers[i];
231     assert(super == NULL || super->super_depth() == i, "correct display");
232     return super;
233   }
234 
235   // Can this klass be a primary super?  False for interfaces and arrays of
236   // interfaces.  False also for arrays or classes with long super chains.
237   bool can_be_primary_super() const {
238     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
239     return super_check_offset() != secondary_offset;
240   }
241   virtual bool can_be_primary_super_slow() const;
242 
243   // Returns number of primary supers; may be a number in the inclusive range [0, primary_super_limit].
244   juint super_depth() const {
245     if (!can_be_primary_super()) {
246       return primary_super_limit();
247     } else {
248       juint d = (super_check_offset() - in_bytes(primary_supers_offset())) / sizeof(Klass*);
249       assert(d < primary_super_limit(), "oob");
250       assert(_primary_supers[d] == this, "proper init");
251       return d;
252     }
253   }
254 
255   // java mirror
256   oop java_mirror() const;
257   oop java_mirror_no_keepalive() const;
258   void set_java_mirror(Handle m);
259 
260   oop archived_java_mirror() NOT_CDS_JAVA_HEAP_RETURN_(NULL);
261   void set_archived_java_mirror(oop m) NOT_CDS_JAVA_HEAP_RETURN;
262 
263   // Temporary mirror switch used by RedefineClasses
264   void replace_java_mirror(oop mirror);
265 
266   // Set java mirror OopHandle to NULL for CDS
267   // This leaves the OopHandle in the CLD, but that's ok, you can't release them.
268   void clear_java_mirror_handle() { _java_mirror = OopHandle(); }
269 
270   // modifier flags
271   jint modifier_flags() const          { return _modifier_flags; }
272   void set_modifier_flags(jint flags)  { _modifier_flags = flags; }
273 
274   // size helper
275   int layout_helper() const            { return _layout_helper; }
276   void set_layout_helper(int lh)       { _layout_helper = lh; }
277 
278   // Note: for instances layout_helper() may include padding.
279   // Use InstanceKlass::contains_field_offset to classify field offsets.
280 
281   // sub/superklass links
282   Klass* subklass(bool log = false) const;
283   Klass* next_sibling(bool log = false) const;
284 
285   InstanceKlass* superklass() const;
286   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
287 
288   void set_next_link(Klass* k) { _next_link = k; }
289   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
290   Klass** next_link_addr() { return &_next_link; }
291 
292   // class loader data
293   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
294   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
295 
296   int shared_classpath_index() const   {
297     return _shared_class_path_index;
298   };
299 
300   void set_shared_classpath_index(int index) {
301     _shared_class_path_index = index;
302   };
303 
304   bool has_archived_mirror_index() const {
305     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
306     NOT_CDS_JAVA_HEAP(return false);
307   }
308 
309   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
310 
311   void set_lambda_proxy_is_available() {
312     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
313   }
314   void clear_lambda_proxy_is_available() {
315     CDS_ONLY(_shared_class_flags &= ~_archived_lambda_proxy_is_available;)
316   }
317   bool lambda_proxy_is_available() const {
318     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
319     NOT_CDS(return false;)
320   }
321 
322   void set_has_value_based_class_annotation() {
323     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
324   }
325   void clear_has_value_based_class_annotation() {
326     CDS_ONLY(_shared_class_flags &= ~_has_value_based_class_annotation;)
327   }
328   bool has_value_based_class_annotation() const {
329     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
330     NOT_CDS(return false;)
331   }
332 
333   void set_verified_at_dump_time() {
334     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
335   }
336   bool verified_at_dump_time() const {
337     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
338     NOT_CDS(return false;)
339   }
340 
341 
342   // Obtain the module or package for this class
343   virtual ModuleEntry* module() const = 0;
344   virtual PackageEntry* package() const = 0;
345 
346  protected:                                // internal accessors
347   void     set_subklass(Klass* s);
348   void     set_next_sibling(Klass* s);
349 
350  public:
351 
352   // Compiler support
353   static ByteSize super_offset()                 { return in_ByteSize(offset_of(Klass, _super)); }
354   static ByteSize super_check_offset_offset()    { return in_ByteSize(offset_of(Klass, _super_check_offset)); }
355   static ByteSize primary_supers_offset()        { return in_ByteSize(offset_of(Klass, _primary_supers)); }
356   static ByteSize secondary_super_cache_offset() { return in_ByteSize(offset_of(Klass, _secondary_super_cache)); }
357   static ByteSize secondary_supers_offset()      { return in_ByteSize(offset_of(Klass, _secondary_supers)); }
358   static ByteSize java_mirror_offset()           { return in_ByteSize(offset_of(Klass, _java_mirror)); }
359   static ByteSize class_loader_data_offset()     { return in_ByteSize(offset_of(Klass, _class_loader_data)); }
360   static ByteSize modifier_flags_offset()        { return in_ByteSize(offset_of(Klass, _modifier_flags)); }
361   static ByteSize layout_helper_offset()         { return in_ByteSize(offset_of(Klass, _layout_helper)); }
362   static ByteSize access_flags_offset()          { return in_ByteSize(offset_of(Klass, _access_flags)); }
363 
364   // Unpacking layout_helper:
365   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
366   static const int _lh_instance_slow_path_bit  = 0x01;
367   static const int _lh_log2_element_size_shift = BitsPerByte*0;
368   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
369   static const int _lh_element_type_shift      = BitsPerByte*1;
370   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
371   static const int _lh_header_size_shift       = BitsPerByte*2;
372   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
373   static const int _lh_array_tag_bits          = 3;
374   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
375 
376   static const unsigned int _lh_array_tag_type_value = 0Xfffffffc;
377   static const unsigned int _lh_array_tag_vt_value   = 0Xfffffffd;
378   static const unsigned int _lh_array_tag_obj_value  = 0Xfffffffe;
379 
380   // null-free array flag bit under the array tag bits, shift one more to get array tag value
381   static const int _lh_null_free_shift = _lh_array_tag_shift - 1;
382   static const int _lh_null_free_mask  = 1;
383 
384   static const jint _lh_array_tag_vt_value_bit_inplace = (jint) (1 << _lh_array_tag_shift);
385   static const jint _lh_null_free_bit_inplace = (jint) (_lh_null_free_mask << _lh_null_free_shift);
386 
387   static int layout_helper_size_in_bytes(jint lh) {
388     assert(lh > (jint)_lh_neutral_value, "must be instance");
389     return (int) lh & ~_lh_instance_slow_path_bit;
390   }
391   static bool layout_helper_needs_slow_path(jint lh) {
392     assert(lh > (jint)_lh_neutral_value, "must be instance");
393     return (lh & _lh_instance_slow_path_bit) != 0;
394   }
395   static bool layout_helper_is_instance(jint lh) {
396     return (jint)lh > (jint)_lh_neutral_value;
397   }
398   static bool layout_helper_is_array(jint lh) {
399     return (jint)lh < (jint)_lh_neutral_value;
400   }
401   static bool layout_helper_is_typeArray(jint lh) {
402     return (juint) _lh_array_tag_type_value == (juint)(lh >> _lh_array_tag_shift);
403   }
404   static bool layout_helper_is_objArray(jint lh) {
405     return (juint)_lh_array_tag_obj_value == (juint)(lh >> _lh_array_tag_shift);
406   }
407   static bool layout_helper_is_flatArray(jint lh) {
408     return (juint)_lh_array_tag_vt_value == (juint)(lh >> _lh_array_tag_shift);
409   }
410   static bool layout_helper_is_null_free(jint lh) {
411     assert(layout_helper_is_flatArray(lh) || layout_helper_is_objArray(lh), "must be array of inline types");
412     return ((lh >> _lh_null_free_shift) & _lh_null_free_mask);
413   }
414   static jint layout_helper_set_null_free(jint lh) {
415     lh |= (_lh_null_free_mask << _lh_null_free_shift);
416     assert(layout_helper_is_null_free(lh), "Bad encoding");
417     return lh;
418   }
419   static int layout_helper_header_size(jint lh) {
420     assert(lh < (jint)_lh_neutral_value, "must be array");
421     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
422     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
423     return hsize;
424   }
425   static BasicType layout_helper_element_type(jint lh) {
426     assert(lh < (jint)_lh_neutral_value, "must be array");
427     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
428     assert((btvalue >= T_BOOLEAN && btvalue <= T_OBJECT) || btvalue == T_INLINE_TYPE, "sanity");
429     return (BasicType) btvalue;
430   }
431 
432   // Want a pattern to quickly diff against layout header in register
433   // find something less clever!
434   static int layout_helper_boolean_diffbit() {
435     jint zlh = array_layout_helper(T_BOOLEAN);
436     jint blh = array_layout_helper(T_BYTE);
437     assert(zlh != blh, "array layout helpers must differ");
438     int diffbit = 1;
439     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
440       diffbit <<= 1;
441       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
442     }
443     return diffbit;
444   }
445 
446   static int layout_helper_log2_element_size(jint lh) {
447     assert(lh < (jint)_lh_neutral_value, "must be array");
448     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
449     assert(layout_helper_element_type(lh) == T_INLINE_TYPE || l2esz <= LogBytesPerLong,
450            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
451     return l2esz;
452   }
453   static jint array_layout_helper(jint tag, bool null_free, int hsize, BasicType etype, int log2_esize) {
454     return (tag        << _lh_array_tag_shift)
455       |    ((null_free ? 1 : 0) <<  _lh_null_free_shift)
456       |    (hsize      << _lh_header_size_shift)
457       |    ((int)etype << _lh_element_type_shift)
458       |    (log2_esize << _lh_log2_element_size_shift);
459   }
460   static jint instance_layout_helper(jint size, bool slow_path_flag) {
461     return (size << LogBytesPerWord)
462       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
463   }
464   static int layout_helper_to_size_helper(jint lh) {
465     assert(lh > (jint)_lh_neutral_value, "must be instance");
466     // Note that the following expression discards _lh_instance_slow_path_bit.
467     return lh >> LogBytesPerWord;
468   }
469   // Out-of-line version computes everything based on the etype:
470   static jint array_layout_helper(BasicType etype);
471 
472   // What is the maximum number of primary superclasses any klass can have?
473   static juint primary_super_limit()         { return _primary_super_limit; }
474 
475   // vtables
476   klassVtable vtable() const;
477   int vtable_length() const { return _vtable_len; }
478 
479   // subclass check
480   bool is_subclass_of(const Klass* k) const;
481   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
482   bool is_subtype_of(Klass* k) const {
483     juint    off = k->super_check_offset();
484     Klass* sup = *(Klass**)( (address)this + off );
485     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
486     if (sup == k) {
487       return true;
488     } else if (off != secondary_offset) {
489       return false;
490     } else {
491       return search_secondary_supers(k);
492     }
493   }
494 
495   bool search_secondary_supers(Klass* k) const;
496 
497   // Find LCA in class hierarchy
498   Klass *LCA( Klass *k );
499 
500   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
501   // if not, throw either an Error or an Exception.
502   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
503 
504   // array copying
505   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
506 
507   // tells if the class should be initialized
508   virtual bool should_be_initialized() const    { return false; }
509   // initializes the klass
510   virtual void initialize(TRAPS);
511   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
512   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
513                                          OverpassLookupMode overpass_mode,
514                                          PrivateLookupMode = PrivateLookupMode::find) const;
515  public:
516   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
517     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
518   }
519 
520   // array class with specific rank
521   virtual Klass* array_klass(int rank, TRAPS) = 0;
522 
523   // array class with this klass as element type
524   virtual Klass* array_klass(TRAPS) = 0;
525 
526   // These will return NULL instead of allocating on the heap:
527   virtual Klass* array_klass_or_null(int rank) = 0;
528   virtual Klass* array_klass_or_null() = 0;
529 
530   virtual oop protection_domain() const = 0;
531 
532   oop class_loader() const;
533 
534   inline oop klass_holder() const;
535 
536  protected:
537 
538   // Error handling when length > max_length or length < 0
539   static void check_array_allocation_length(int length, int max_length, TRAPS);
540 
541   void set_vtable_length(int len) { _vtable_len= len; }
542 
543   vtableEntry* start_of_vtable() const;
544   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
545  public:
546   Method* method_at_vtable(int index);
547 
548   static ByteSize vtable_start_offset();
549   static ByteSize vtable_length_offset() {
550     return byte_offset_of(Klass, _vtable_len);
551   }
552 
553   // CDS support - remove and restore oops from metadata. Oops are not shared.
554   virtual void remove_unshareable_info();
555   virtual void remove_java_mirror();
556 
557   bool is_unshareable_info_restored() const {
558     assert(is_shared(), "use this for shared classes only");
559     if (has_archived_mirror_index()) {
560       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
561       return false;
562     } else if (_java_mirror.ptr_raw() == NULL) {
563       return false;
564     } else {
565       return true;
566     }
567   }
568 
569  public:
570   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
571   // These functions describe behavior for the oop not the KLASS.
572 
573   // actual oop size of obj in memory
574   virtual int oop_size(oop obj) const = 0;
575 
576   // Size of klass in word size.
577   virtual int size() const = 0;
578 
579   // Returns the Java name for a class (Resource allocated)
580   // For arrays, this returns the name of the element with a leading '['.
581   // For classes, this returns the name with the package separators
582   //     turned into '.'s.
583   const char* external_name() const;
584   // Returns the name for a class (Resource allocated) as the class
585   // would appear in a signature.
586   // For arrays, this returns the name of the element with a leading '['.
587   // For classes, this returns the name with a leading 'L' and a trailing ';'
588   //     and the package separators as '/'.
589   virtual const char* signature_name() const;
590 
591   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
592   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
593 
594   // Returns "interface", "abstract class" or "class".
595   const char* external_kind() const;
596 
597   // type testing operations
598 #ifdef ASSERT
599  protected:
600   virtual bool is_instance_klass_slow()     const { return false; }
601   virtual bool is_array_klass_slow()        const { return false; }
602   virtual bool is_objArray_klass_slow()     const { return false; }
603   virtual bool is_typeArray_klass_slow()    const { return false; }
604   virtual bool is_flatArray_klass_slow()    const { return false; }
605 #endif // ASSERT
606   // current implementation uses this method even in non debug builds
607   virtual bool is_inline_klass_slow()       const { return false; }
608  public:
609 
610   // Fast non-virtual versions
611   #ifndef ASSERT
612   #define assert_same_query(xval, xcheck) xval
613   #else
614  private:
615   static bool assert_same_query(bool xval, bool xslow) {
616     assert(xval == xslow, "slow and fast queries agree");
617     return xval;
618   }
619  public:
620   #endif
621   inline  bool is_instance_klass()            const { return assert_same_query(
622                                                       layout_helper_is_instance(layout_helper()),
623                                                       is_instance_klass_slow()); }
624   inline  bool is_array_klass()               const { return assert_same_query(
625                                                     layout_helper_is_array(layout_helper()),
626                                                     is_array_klass_slow()); }
627   inline  bool is_objArray_klass()            const { return assert_same_query(
628                                                     layout_helper_is_objArray(layout_helper()),
629                                                     is_objArray_klass_slow()); }
630   inline  bool is_typeArray_klass()           const { return assert_same_query(
631                                                     layout_helper_is_typeArray(layout_helper()),
632                                                     is_typeArray_klass_slow()); }
633   inline  bool is_inline_klass()              const { return is_inline_klass_slow(); } //temporary hack
634   inline  bool is_flatArray_klass()           const { return assert_same_query(
635                                                     layout_helper_is_flatArray(layout_helper()),
636                                                     is_flatArray_klass_slow()); }
637 
638   #undef assert_same_query
639 
640   inline bool is_null_free_array_klass()      const { return layout_helper_is_null_free(layout_helper()); }
641 
642   // Access flags
643   AccessFlags access_flags() const         { return _access_flags;  }
644   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
645 
646   bool is_public() const                { return _access_flags.is_public(); }
647   bool is_final() const                 { return _access_flags.is_final(); }
648   bool is_interface() const             { return _access_flags.is_interface(); }
649   bool is_abstract() const              { return _access_flags.is_abstract(); }
650   bool is_super() const                 { return _access_flags.is_super(); }
651   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
652   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
653   bool has_finalizer() const            { return _access_flags.has_finalizer(); }
654   bool has_final_method() const         { return _access_flags.has_final_method(); }
655   void set_has_finalizer()              { _access_flags.set_has_finalizer(); }
656   void set_has_final_method()           { _access_flags.set_has_final_method(); }
657   bool has_vanilla_constructor() const  { return _access_flags.has_vanilla_constructor(); }
658   void set_has_vanilla_constructor()    { _access_flags.set_has_vanilla_constructor(); }
659   bool has_miranda_methods () const     { return access_flags().has_miranda_methods(); }
660   void set_has_miranda_methods()        { _access_flags.set_has_miranda_methods(); }
661   bool is_shared() const                { return access_flags().is_shared_class(); } // shadows MetaspaceObj::is_shared)()
662   void set_is_shared()                  { _access_flags.set_is_shared_class(); }
663   bool is_hidden() const                { return access_flags().is_hidden_class(); }
664   void set_is_hidden()                  { _access_flags.set_is_hidden_class(); }
665   bool is_value_based()                 { return _access_flags.is_value_based_class(); }
666   void set_is_value_based()             { _access_flags.set_is_value_based_class(); }
667 
668   inline bool is_non_strong_hidden() const;
669 
670   bool is_cloneable() const;
671   void set_is_cloneable();
672 
673   // inline types and inline type array patterns
674   markWord prototype_header() const {
675     return _prototype_header;
676   }
677   static inline markWord default_prototype_header(Klass* k) {
678     return (k == NULL) ? markWord::prototype() : k->prototype_header();
679   }
680 
681   inline void set_prototype_header(markWord header);
682   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
683 
684   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
685 
686   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
687   virtual MetaspaceObj::Type type() const { return ClassType; }
688 
689   inline bool is_loader_alive() const;
690 
691   void clean_subklass();
692 
693   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
694   static void clean_subklass_tree() {
695     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
696   }
697 
698   virtual void array_klasses_do(void f(Klass* k)) {}
699 
700   // Return self, except for abstract classes with exactly 1
701   // implementor.  Then return the 1 concrete implementation.
702   Klass *up_cast_abstract();
703 
704   // klass name
705   Symbol* name() const                   { return _name; }
706   void set_name(Symbol* n);
707 
708   virtual void release_C_heap_structures();
709 
710  public:
711   virtual jint compute_modifier_flags() const = 0;
712 
713   // JVMTI support
714   virtual jint jvmti_class_status() const;
715 
716   // Printing
717   virtual void print_on(outputStream* st) const;
718 
719   virtual void oop_print_value_on(oop obj, outputStream* st);
720   virtual void oop_print_on      (oop obj, outputStream* st);
721 
722   virtual const char* internal_name() const = 0;
723 
724   // Verification
725   virtual void verify_on(outputStream* st);
726   void verify() { verify_on(tty); }
727 
728 #ifndef PRODUCT
729   bool verify_vtable_index(int index);
730 #endif
731 
732   virtual void oop_verify_on(oop obj, outputStream* st);
733 
734   // for error reporting
735   static bool is_valid(Klass* k);
736 };
737 
738 #endif // SHARE_OOPS_KLASS_HPP