1 /*
  2  * Copyright (c) 1997, 2024, 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.
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 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 //
 41 // A Klass provides:
 42 //  1: language level class object (method dictionary etc.)
 43 //  2: provide vm dispatch behavior for the object
 44 // Both functions are combined into one C++ class.
 45 
 46 // One reason for the oop/klass dichotomy in the implementation is
 47 // that we don't want a C++ vtbl pointer in every object.  Thus,
 48 // normal oops don't have any virtual functions.  Instead, they
 49 // forward all "virtual" functions to their klass, which does have
 50 // a vtbl and does the C++ dispatch depending on the object's
 51 // actual type.  (See oop.inline.hpp for some of the forwarding code.)
 52 // ALL FUNCTIONS IMPLEMENTING THIS DISPATCH ARE PREFIXED WITH "oop_"!
 53 
 54 // Forward declarations.
 55 template <class T> class Array;
 56 template <class T> class GrowableArray;
 57 class ClassLoaderData;
 58 class fieldDescriptor;
 59 class klassVtable;
 60 class ModuleEntry;
 61 class PackageEntry;
 62 class ParCompactionManager;
 63 class PSPromotionManager;
 64 class vtableEntry;
 65 
 66 class Klass : public Metadata {
 67   friend class VMStructs;
 68   friend class JVMCIVMStructs;
 69  public:
 70   // Klass Kinds for all subclasses of Klass
 71   enum KlassKind {
 72     InstanceKlassKind,
 73     InlineKlassKind,
 74     InstanceRefKlassKind,
 75     InstanceMirrorKlassKind,
 76     InstanceClassLoaderKlassKind,
 77     InstanceStackChunkKlassKind,
 78     TypeArrayKlassKind,
 79     FlatArrayKlassKind,
 80     ObjArrayKlassKind,
 81     UnknownKlassKind
 82   };
 83 
 84   static const uint KLASS_KIND_COUNT = ObjArrayKlassKind + 1;
 85  protected:
 86 
 87   // If you add a new field that points to any metaspace object, you
 88   // must add this field to Klass::metaspace_pointers_do().
 89 
 90   // note: put frequently-used fields together at start of klass structure
 91   // for better cache behavior (may not make much of a difference but sure won't hurt)
 92   enum { _primary_super_limit = 8 };
 93 
 94   // The "layout helper" is a combined descriptor of object layout.
 95   // For klasses which are neither instance nor array, the value is zero.
 96   //
 97   // For instances, layout helper is a positive number, the instance size.
 98   // This size is already passed through align_object_size and scaled to bytes.
 99   // The low order bit is set if instances of this class cannot be
100   // allocated using the fastpath.
101   //
102   // For arrays, layout helper is a negative number, containing four
103   // distinct bytes, as follows:
104   //    MSB:[tag, hsz, ebt, log2(esz)]:LSB
105   // where:
106   //    tag is 0x80 if the elements are oops, 0xC0 if non-oops, 0xA0 if value types
107   //    hsz is array header size in bytes (i.e., offset of first element)
108   //    ebt is the BasicType of the elements
109   //    esz is the element size in bytes
110   // This packed word is arranged so as to be quickly unpacked by the
111   // various fast paths that use the various subfields.
112   //
113   // The esz bits can be used directly by a SLL instruction, without masking.
114   //
115   // Note that the array-kind tag looks like 0x00 for instance klasses,
116   // since their length in bytes is always less than 24Mb.
117   //
118   // Final note:  This comes first, immediately after C++ vtable,
119   // because it is frequently queried.
120   jint        _layout_helper;
121 
122   // Klass kind used to resolve the runtime type of the instance.
123   //  - Used to implement devirtualized oop closure dispatching.
124   //  - Various type checking in the JVM
125   const KlassKind _kind;
126 
127   // Processed access flags, for use by Class.getModifiers.
128   jint        _modifier_flags;
129 
130   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
131   // and _primary_supers all help make fast subtype checks.  See big discussion
132   // in doc/server_compiler/checktype.txt
133   //
134   // Where to look to observe a supertype (it is &_secondary_super_cache for
135   // secondary supers, else is &_primary_supers[depth()].
136   juint       _super_check_offset;
137 
138   // Class name.  Instance classes: java/lang/String, etc.  Array classes: [I,
139   // [Ljava/lang/String;, etc.  Set to zero for all other kinds of classes.
140   Symbol*     _name;
141 
142   // Cache of last observed secondary supertype
143   Klass*      _secondary_super_cache;
144   // Array of all secondary supertypes
145   Array<Klass*>* _secondary_supers;
146   // Ordered list of all primary supertypes
147   Klass*      _primary_supers[_primary_super_limit];
148   // java/lang/Class instance mirroring this class
149   OopHandle   _java_mirror;
150   // Superclass
151   Klass*      _super;
152   // First subclass (null if none); _subklass->next_sibling() is next one
153   Klass* volatile _subklass;
154   // Sibling link (or null); links all subklasses of a klass
155   Klass* volatile _next_sibling;
156 
157   // All klasses loaded by a class loader are chained through these links
158   Klass*      _next_link;
159 
160   // The VM's representation of the ClassLoader used to load this class.
161   // Provide access the corresponding instance java.lang.ClassLoader.
162   ClassLoaderData* _class_loader_data;
163 
164   // Bitmap and hash code used by hashed secondary supers.
165   uintx    _bitmap;
166   uint8_t  _hash_slot;
167 
168   static uint8_t compute_hash_slot(Symbol* s);
169 
170   int _vtable_len;              // vtable length. This field may be read very often when we
171                                 // have lots of itable dispatches (e.g., lambdas and streams).
172                                 // Keep it away from the beginning of a Klass to avoid cacheline
173                                 // contention that may happen when a nearby object is modified.
174   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
175 
176   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
177 
178   markWord _prototype_header;  // inline type and inline array mark patterns
179 private:
180   // This is an index into FileMapHeader::_shared_path_table[], to
181   // associate this class with the JAR file where it's loaded from during
182   // dump time. If a class is not loaded from the shared archive, this field is
183   // -1.
184   s2 _shared_class_path_index;
185 
186 #if INCLUDE_CDS
187   // Various attributes for shared classes. Should be zero for a non-shared class.
188   u2     _shared_class_flags;
189   enum CDSSharedClassFlags {
190     _is_shared_class                       = 1 << 0,  // shadows MetaspaceObj::is_shared
191     _archived_lambda_proxy_is_available    = 1 << 1,
192     _has_value_based_class_annotation      = 1 << 2,
193     _verified_at_dump_time                 = 1 << 3,
194     _has_archived_enum_objs                = 1 << 4,
195     // This class was not loaded from a classfile in the module image
196     // or classpath.
197     _is_generated_shared_class             = 1 << 5
198   };
199 #endif
200 
201   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
202 
203 protected:
204 
205   Klass(KlassKind kind);
206   Klass();
207 
208   void* operator new(size_t size, ClassLoaderData* loader_data, size_t word_size, TRAPS) throw();
209 
210  public:
211   int kind() { return _kind; }
212 
213   enum class DefaultsLookupMode { find, skip };
214   enum class OverpassLookupMode { find, skip };
215   enum class StaticLookupMode   { find, skip };
216   enum class PrivateLookupMode  { find, skip };
217 
218   virtual bool is_klass() const { return true; }
219 
220   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
221   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
222   // If this is not what your code expects, you're probably looking for Klass::java_super().
223   Klass* super() const               { return _super; }
224   void set_super(Klass* k)           { _super = k; }
225 
226   // initializes _super link, _primary_supers & _secondary_supers arrays
227   void initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS);
228 
229   // klass-specific helper for initializing _secondary_supers
230   virtual GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
231                                                           Array<InstanceKlass*>* transitive_interfaces);
232 
233   // java_super is the Java-level super type as specified by Class.getSuperClass.
234   virtual InstanceKlass* java_super() const  { return nullptr; }
235 
236   juint    super_check_offset() const  { return _super_check_offset; }
237   void set_super_check_offset(juint o) { _super_check_offset = o; }
238 
239   Klass* secondary_super_cache() const     { return _secondary_super_cache; }
240   void set_secondary_super_cache(Klass* k) { _secondary_super_cache = k; }
241 
242   Array<Klass*>* secondary_supers() const { return _secondary_supers; }
243   void set_secondary_supers(Array<Klass*>* k);
244   void set_secondary_supers(Array<Klass*>* k, uintx bitmap);
245 
246   uint8_t hash_slot() const { return _hash_slot; }
247 
248   // Return the element of the _super chain of the given depth.
249   // If there is no such element, return either null or this.
250   Klass* primary_super_of_depth(juint i) const {
251     assert(i < primary_super_limit(), "oob");
252     Klass* super = _primary_supers[i];
253     assert(super == nullptr || super->super_depth() == i, "correct display");
254     return super;
255   }
256 
257   // Can this klass be a primary super?  False for interfaces and arrays of
258   // interfaces.  False also for arrays or classes with long super chains.
259   bool can_be_primary_super() const {
260     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
261     return super_check_offset() != secondary_offset;
262   }
263   virtual bool can_be_primary_super_slow() const;
264 
265   // Returns number of primary supers; may be a number in the inclusive range [0, primary_super_limit].
266   juint super_depth() const {
267     if (!can_be_primary_super()) {
268       return primary_super_limit();
269     } else {
270       juint d = (super_check_offset() - in_bytes(primary_supers_offset())) / sizeof(Klass*);
271       assert(d < primary_super_limit(), "oob");
272       assert(_primary_supers[d] == this, "proper init");
273       return d;
274     }
275   }
276 
277   // java mirror
278   oop java_mirror() const;
279   oop java_mirror_no_keepalive() const;
280   void set_java_mirror(Handle m);
281 
282   oop archived_java_mirror() NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
283   void set_archived_java_mirror(int mirror_index) NOT_CDS_JAVA_HEAP_RETURN;
284 
285   // Temporary mirror switch used by RedefineClasses
286   OopHandle java_mirror_handle() const { return _java_mirror; }
287   void swap_java_mirror_handle(OopHandle& mirror) { _java_mirror.swap(mirror); }
288 
289   // Set java mirror OopHandle to null for CDS
290   // This leaves the OopHandle in the CLD, but that's ok, you can't release them.
291   void clear_java_mirror_handle() { _java_mirror = OopHandle(); }
292 
293   // modifier flags
294   jint modifier_flags() const          { return _modifier_flags; }
295   void set_modifier_flags(jint flags)  { _modifier_flags = flags; }
296 
297   // size helper
298   int layout_helper() const            { return _layout_helper; }
299   void set_layout_helper(int lh)       { _layout_helper = lh; }
300 
301   // Note: for instances layout_helper() may include padding.
302   // Use InstanceKlass::contains_field_offset to classify field offsets.
303 
304   // sub/superklass links
305   Klass* subklass(bool log = false) const;
306   Klass* next_sibling(bool log = false) const;
307 
308   InstanceKlass* superklass() const;
309   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
310 
311   void set_next_link(Klass* k) { _next_link = k; }
312   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
313   Klass** next_link_addr() { return &_next_link; }
314 
315   // class loader data
316   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
317   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
318 
319   s2 shared_classpath_index() const   {
320     return _shared_class_path_index;
321   };
322 
323   void set_shared_classpath_index(s2 index) {
324     _shared_class_path_index = index;
325   };
326 
327   bool has_archived_mirror_index() const {
328     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
329     NOT_CDS_JAVA_HEAP(return false);
330   }
331 
332   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
333 
334   void set_lambda_proxy_is_available() {
335     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
336   }
337   void clear_lambda_proxy_is_available() {
338     CDS_ONLY(_shared_class_flags &= (u2)(~_archived_lambda_proxy_is_available);)
339   }
340   bool lambda_proxy_is_available() const {
341     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
342     NOT_CDS(return false;)
343   }
344 
345   void set_has_value_based_class_annotation() {
346     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
347   }
348   void clear_has_value_based_class_annotation() {
349     CDS_ONLY(_shared_class_flags &= (u2)(~_has_value_based_class_annotation);)
350   }
351   bool has_value_based_class_annotation() const {
352     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
353     NOT_CDS(return false;)
354   }
355 
356   void set_verified_at_dump_time() {
357     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
358   }
359   bool verified_at_dump_time() const {
360     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
361     NOT_CDS(return false;)
362   }
363 
364   void set_has_archived_enum_objs() {
365     CDS_ONLY(_shared_class_flags |= _has_archived_enum_objs;)
366   }
367   bool has_archived_enum_objs() const {
368     CDS_ONLY(return (_shared_class_flags & _has_archived_enum_objs) != 0;)
369     NOT_CDS(return false;)
370   }
371 
372   void set_is_generated_shared_class() {
373     CDS_ONLY(_shared_class_flags |= _is_generated_shared_class;)
374   }
375   bool is_generated_shared_class() const {
376     CDS_ONLY(return (_shared_class_flags & _is_generated_shared_class) != 0;)
377     NOT_CDS(return false;)
378   }
379 
380   bool is_shared() const                { // shadows MetaspaceObj::is_shared)()
381     CDS_ONLY(return (_shared_class_flags & _is_shared_class) != 0;)
382     NOT_CDS(return false;)
383   }
384 
385   void set_is_shared() {
386     CDS_ONLY(_shared_class_flags |= _is_shared_class;)
387   }
388 
389   // Obtain the module or package for this class
390   virtual ModuleEntry* module() const = 0;
391   virtual PackageEntry* package() const = 0;
392 
393  protected:                                // internal accessors
394   void     set_subklass(Klass* s);
395   void     set_next_sibling(Klass* s);
396 
397  private:
398   static void  hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap);
399   static uintx hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite);
400 
401  public:
402   // Secondary supers table support
403   static Array<Klass*>* pack_secondary_supers(ClassLoaderData* loader_data,
404                                               GrowableArray<Klass*>* primaries,
405                                               GrowableArray<Klass*>* secondaries,
406                                               uintx& bitmap,
407                                               TRAPS);
408 
409   static uintx   compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers);
410   static uint8_t compute_home_slot(Klass* k, uintx bitmap);
411 
412   static constexpr int SECONDARY_SUPERS_TABLE_SIZE = sizeof(_bitmap) * 8;
413   static constexpr int SECONDARY_SUPERS_TABLE_MASK = SECONDARY_SUPERS_TABLE_SIZE - 1;
414 
415   static constexpr uintx SECONDARY_SUPERS_BITMAP_EMPTY    = 0;
416   static constexpr uintx SECONDARY_SUPERS_BITMAP_FULL     = ~(uintx)0;
417 
418   // Compiler support
419   static ByteSize super_offset()                 { return byte_offset_of(Klass, _super); }
420   static ByteSize super_check_offset_offset()    { return byte_offset_of(Klass, _super_check_offset); }
421   static ByteSize primary_supers_offset()        { return byte_offset_of(Klass, _primary_supers); }
422   static ByteSize secondary_super_cache_offset() { return byte_offset_of(Klass, _secondary_super_cache); }
423   static ByteSize secondary_supers_offset()      { return byte_offset_of(Klass, _secondary_supers); }
424   static ByteSize java_mirror_offset()           { return byte_offset_of(Klass, _java_mirror); }
425   static ByteSize class_loader_data_offset()     { return byte_offset_of(Klass, _class_loader_data); }
426   static ByteSize modifier_flags_offset()        { return byte_offset_of(Klass, _modifier_flags); }
427   static ByteSize layout_helper_offset()         { return byte_offset_of(Klass, _layout_helper); }
428   static ByteSize access_flags_offset()          { return byte_offset_of(Klass, _access_flags); }
429 #if INCLUDE_JVMCI
430   static ByteSize subklass_offset()              { return byte_offset_of(Klass, _subklass); }
431   static ByteSize next_sibling_offset()          { return byte_offset_of(Klass, _next_sibling); }
432 #endif
433   static ByteSize bitmap_offset()                { return byte_offset_of(Klass, _bitmap); }
434 
435   // Unpacking layout_helper:
436   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
437   static const int _lh_instance_slow_path_bit  = 0x01;
438   static const int _lh_log2_element_size_shift = BitsPerByte*0;
439   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
440   static const int _lh_element_type_shift      = BitsPerByte*1;
441   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
442   static const int _lh_header_size_shift       = BitsPerByte*2;
443   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
444   static const int _lh_array_tag_bits          = 3;
445   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
446 
447   static const unsigned int _lh_array_tag_type_value = 0Xfffffffc;
448   static const unsigned int _lh_array_tag_vt_value   = 0Xfffffffd;
449   static const unsigned int _lh_array_tag_obj_value  = 0Xfffffffe;
450 
451   // null-free array flag bit under the array tag bits, shift one more to get array tag value
452   static const int _lh_null_free_shift = _lh_array_tag_shift - 1;
453   static const int _lh_null_free_mask  = 1;
454 
455   static const jint _lh_array_tag_flat_value_bit_inplace = (jint) (1 << _lh_array_tag_shift);
456 
457   static int layout_helper_size_in_bytes(jint lh) {
458     assert(lh > (jint)_lh_neutral_value, "must be instance");
459     return (int) lh & ~_lh_instance_slow_path_bit;
460   }
461   static bool layout_helper_needs_slow_path(jint lh) {
462     assert(lh > (jint)_lh_neutral_value, "must be instance");
463     return (lh & _lh_instance_slow_path_bit) != 0;
464   }
465   static bool layout_helper_is_instance(jint lh) {
466     return (jint)lh > (jint)_lh_neutral_value;
467   }
468   static bool layout_helper_is_array(jint lh) {
469     return (jint)lh < (jint)_lh_neutral_value;
470   }
471   static bool layout_helper_is_typeArray(jint lh) {
472     return (juint) _lh_array_tag_type_value == (juint)(lh >> _lh_array_tag_shift);
473   }
474   static bool layout_helper_is_objArray(jint lh) {
475     return (juint)_lh_array_tag_obj_value == (juint)(lh >> _lh_array_tag_shift);
476   }
477   static bool layout_helper_is_flatArray(jint lh) {
478     return (juint)_lh_array_tag_vt_value == (juint)(lh >> _lh_array_tag_shift);
479   }
480   static bool layout_helper_is_null_free(jint lh) {
481     assert(layout_helper_is_flatArray(lh) || layout_helper_is_objArray(lh), "must be array of inline types");
482     return ((lh >> _lh_null_free_shift) & _lh_null_free_mask);
483   }
484   static jint layout_helper_set_null_free(jint lh) {
485     lh |= (_lh_null_free_mask << _lh_null_free_shift);
486     assert(layout_helper_is_null_free(lh), "Bad encoding");
487     return lh;
488   }
489   static int layout_helper_header_size(jint lh) {
490     assert(lh < (jint)_lh_neutral_value, "must be array");
491     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
492     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
493     return hsize;
494   }
495   static BasicType layout_helper_element_type(jint lh) {
496     assert(lh < (jint)_lh_neutral_value, "must be array");
497     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
498     assert((btvalue >= T_BOOLEAN && btvalue <= T_OBJECT) || btvalue == T_PRIMITIVE_OBJECT, "sanity");
499     return (BasicType) btvalue;
500   }
501 
502   // Want a pattern to quickly diff against layout header in register
503   // find something less clever!
504   static int layout_helper_boolean_diffbit() {
505     jint zlh = array_layout_helper(T_BOOLEAN);
506     jint blh = array_layout_helper(T_BYTE);
507     assert(zlh != blh, "array layout helpers must differ");
508     int diffbit = 1;
509     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
510       diffbit <<= 1;
511       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
512     }
513     return diffbit;
514   }
515 
516   static int layout_helper_log2_element_size(jint lh) {
517     assert(lh < (jint)_lh_neutral_value, "must be array");
518     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
519     assert(layout_helper_element_type(lh) == T_PRIMITIVE_OBJECT || l2esz <= LogBytesPerLong,
520            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
521     return l2esz;
522   }
523   static jint array_layout_helper(jint tag, bool null_free, int hsize, BasicType etype, int log2_esize) {
524     return (tag        << _lh_array_tag_shift)
525       |    ((null_free ? 1 : 0) <<  _lh_null_free_shift)
526       |    (hsize      << _lh_header_size_shift)
527       |    ((int)etype << _lh_element_type_shift)
528       |    (log2_esize << _lh_log2_element_size_shift);
529   }
530   static jint instance_layout_helper(jint size, bool slow_path_flag) {
531     return (size << LogBytesPerWord)
532       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
533   }
534   static int layout_helper_to_size_helper(jint lh) {
535     assert(lh > (jint)_lh_neutral_value, "must be instance");
536     // Note that the following expression discards _lh_instance_slow_path_bit.
537     return lh >> LogBytesPerWord;
538   }
539   // Out-of-line version computes everything based on the etype:
540   static jint array_layout_helper(BasicType etype);
541 
542   // What is the maximum number of primary superclasses any klass can have?
543   static juint primary_super_limit()         { return _primary_super_limit; }
544 
545   // vtables
546   klassVtable vtable() const;
547   int vtable_length() const { return _vtable_len; }
548 
549   // subclass check
550   bool is_subclass_of(const Klass* k) const;
551   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
552   bool is_subtype_of(Klass* k) const {
553     juint    off = k->super_check_offset();
554     Klass* sup = *(Klass**)( (address)this + off );
555     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
556     if (sup == k) {
557       return true;
558     } else if (off != secondary_offset) {
559       return false;
560     } else {
561       return search_secondary_supers(k);
562     }
563   }
564 
565   bool search_secondary_supers(Klass* k) const;
566 
567   // Find LCA in class hierarchy
568   Klass *LCA( Klass *k );
569 
570   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
571   // if not, throw either an Error or an Exception.
572   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
573 
574   // array copying
575   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
576 
577   // tells if the class should be initialized
578   virtual bool should_be_initialized() const    { return false; }
579   // initializes the klass
580   virtual void initialize(TRAPS);
581   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
582   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
583                                          OverpassLookupMode overpass_mode,
584                                          PrivateLookupMode = PrivateLookupMode::find) const;
585  public:
586   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
587     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
588   }
589 
590   // array class with specific rank
591   virtual ArrayKlass* array_klass(int rank, TRAPS) = 0;
592 
593   // array class with this klass as element type
594   virtual ArrayKlass* array_klass(TRAPS) = 0;
595 
596   // These will return null instead of allocating on the heap:
597   virtual ArrayKlass* array_klass_or_null(int rank) = 0;
598   virtual ArrayKlass* array_klass_or_null() = 0;
599 
600   virtual oop protection_domain() const = 0;
601 
602   oop class_loader() const;
603 
604   inline oop klass_holder() const;
605 
606  protected:
607 
608   // Error handling when length > max_length or length < 0
609   static void check_array_allocation_length(int length, int max_length, TRAPS);
610 
611   void set_vtable_length(int len) { _vtable_len= len; }
612 
613   vtableEntry* start_of_vtable() const;
614 #if INCLUDE_CDS
615   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
616 #endif
617  public:
618   Method* method_at_vtable(int index);
619 
620   static ByteSize vtable_start_offset();
621   static ByteSize vtable_length_offset() {
622     return byte_offset_of(Klass, _vtable_len);
623   }
624 
625 #if INCLUDE_CDS
626   // CDS support - remove and restore oops from metadata. Oops are not shared.
627   virtual void remove_unshareable_info();
628   virtual void remove_java_mirror();
629 
630   bool is_unshareable_info_restored() const {
631     assert(is_shared(), "use this for shared classes only");
632     if (has_archived_mirror_index()) {
633       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
634       return false;
635     } else if (_java_mirror.is_empty()) {
636       return false;
637     } else {
638       return true;
639     }
640   }
641 #endif // INCLUDE_CDS
642 
643  public:
644   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
645   // These functions describe behavior for the oop not the KLASS.
646 
647   // actual oop size of obj in memory in word size.
648   virtual size_t oop_size(oop obj) const = 0;
649 
650   // Size of klass in word size.
651   virtual int size() const = 0;
652 
653   // Returns the Java name for a class (Resource allocated)
654   // For arrays, this returns the name of the element with a leading '['.
655   // For classes, this returns the name with the package separators
656   //     turned into '.'s.
657   const char* external_name() const;
658   // Returns the name for a class (Resource allocated) as the class
659   // would appear in a signature.
660   // For arrays, this returns the name of the element with a leading '['.
661   // For classes, this returns the name with a leading 'L' and a trailing ';'
662   //     and the package separators as '/'.
663   virtual const char* signature_name() const;
664 
665   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
666   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
667 
668   // Returns "interface", "abstract class" or "class".
669   const char* external_kind() const;
670 
671   // type testing operations
672 #ifdef ASSERT
673  protected:
674   virtual bool is_instance_klass_slow()     const { return false; }
675   virtual bool is_array_klass_slow()        const { return false; }
676   virtual bool is_objArray_klass_slow()     const { return false; }
677   virtual bool is_typeArray_klass_slow()    const { return false; }
678   virtual bool is_flatArray_klass_slow()    const { return false; }
679 #endif // ASSERT
680   // current implementation uses this method even in non debug builds
681   virtual bool is_inline_klass_slow()       const { return false; }
682  public:
683 
684   // Fast non-virtual versions
685   #ifndef ASSERT
686   #define assert_same_query(xval, xcheck) xval
687   #else
688  private:
689   static bool assert_same_query(bool xval, bool xslow) {
690     assert(xval == xslow, "slow and fast queries agree");
691     return xval;
692   }
693  public:
694   #endif
695 
696   bool is_instance_klass()              const { return assert_same_query(_kind <= InstanceStackChunkKlassKind, is_instance_klass_slow()); }
697   bool is_inline_klass()                const { return assert_same_query(_kind == InlineKlassKind, is_inline_klass_slow()); }
698   bool is_reference_instance_klass()    const { return _kind == InstanceRefKlassKind; }
699   bool is_mirror_instance_klass()       const { return _kind == InstanceMirrorKlassKind; }
700   bool is_class_loader_instance_klass() const { return _kind == InstanceClassLoaderKlassKind; }
701   bool is_array_klass()                 const { return assert_same_query( _kind >= TypeArrayKlassKind, is_array_klass_slow()); }
702   bool is_stack_chunk_instance_klass()  const { return _kind == InstanceStackChunkKlassKind; }
703   bool is_flatArray_klass()             const { return assert_same_query( _kind == FlatArrayKlassKind, is_flatArray_klass_slow()); }
704   bool is_objArray_klass()              const { return assert_same_query( _kind == ObjArrayKlassKind,  is_objArray_klass_slow()); }
705   bool is_typeArray_klass()             const { return assert_same_query( _kind == TypeArrayKlassKind, is_typeArray_klass_slow()); }
706   #undef assert_same_query
707 
708   inline bool is_null_free_array_klass()      const { return layout_helper_is_null_free(layout_helper()); }
709 
710   // Access flags
711   AccessFlags access_flags() const         { return _access_flags;  }
712   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
713 
714   bool is_public() const                { return _access_flags.is_public(); }
715   bool is_final() const                 { return _access_flags.is_final(); }
716   bool is_interface() const             { return _access_flags.is_interface(); }
717   bool is_abstract() const              { return _access_flags.is_abstract(); }
718   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
719   bool is_identity_class() const        { return _access_flags.is_identity_class(); }
720   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
721   bool has_finalizer() const            { return _access_flags.has_finalizer(); }
722   void set_has_finalizer()              { _access_flags.set_has_finalizer(); }
723   bool is_hidden() const                { return access_flags().is_hidden_class(); }
724   void set_is_hidden()                  { _access_flags.set_is_hidden_class(); }
725   bool is_value_based()                 { return _access_flags.is_value_based_class(); }
726   void set_is_value_based()             { _access_flags.set_is_value_based_class(); }
727 
728   inline bool is_non_strong_hidden() const;
729 
730   bool is_cloneable() const;
731   void set_is_cloneable();
732 
733   // inline types and inline type array patterns
734   markWord prototype_header() const {
735     return _prototype_header;
736   }
737   static inline markWord default_prototype_header(Klass* k) {
738     return (k == nullptr) ? markWord::prototype() : k->prototype_header();
739   }
740 
741   inline void set_prototype_header(markWord header);
742   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
743 
744   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
745 
746   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
747   virtual MetaspaceObj::Type type() const { return ClassType; }
748 
749   inline bool is_loader_alive() const;
750 
751   void clean_subklass();
752 
753   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
754   static void clean_subklass_tree() {
755     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
756   }
757 
758   // Return self, except for abstract classes with exactly 1
759   // implementor.  Then return the 1 concrete implementation.
760   Klass *up_cast_abstract();
761 
762   // klass name
763   Symbol* name() const                   { return _name; }
764   void set_name(Symbol* n);
765 
766   virtual void release_C_heap_structures(bool release_constant_pool = true);
767 
768  public:
769   virtual jint compute_modifier_flags() const = 0;
770 
771   // JVMTI support
772   virtual jint jvmti_class_status() const;
773 
774   // Printing
775   virtual void print_on(outputStream* st) const;
776 
777   virtual void oop_print_value_on(oop obj, outputStream* st);
778   virtual void oop_print_on      (oop obj, outputStream* st);
779 
780   void print_secondary_supers_on(outputStream* st) const;
781 
782   virtual const char* internal_name() const = 0;
783 
784   // Verification
785   virtual void verify_on(outputStream* st);
786   void verify() { verify_on(tty); }
787 
788 #ifndef PRODUCT
789   bool verify_vtable_index(int index);
790 #endif
791 
792   virtual void oop_verify_on(oop obj, outputStream* st);
793 
794   // for error reporting
795   static bool is_valid(Klass* k);
796 
797   static void on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg);
798 };
799 
800 #endif // SHARE_OOPS_KLASS_HPP