1 /*
  2  * Copyright (c) 1997, 2025, 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
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 24 
 25 #ifndef SHARE_OOPS_KLASS_HPP
 26 #define SHARE_OOPS_KLASS_HPP
 27 
 28 #include "oops/klassFlags.hpp"
 29 #include "oops/markWord.hpp"
 30 #include "oops/metadata.hpp"
 31 #include "oops/oop.hpp"
 32 #include "oops/oopHandle.hpp"
 33 #include "utilities/accessFlags.hpp"
 34 #include "utilities/macros.hpp"
 35 #if INCLUDE_JFR
 36 #include "jfr/support/jfrTraceIdExtension.hpp"
 37 #endif
 38 
 39 //
 40 // A Klass provides:
 41 //  1: language level class object (method dictionary etc.)
 42 //  2: provide vm dispatch behavior for the object
 43 // Both functions are combined into one C++ class.
 44 
 45 // One reason for the oop/klass dichotomy in the implementation is
 46 // that we don't want a C++ vtbl pointer in every object.  Thus,
 47 // normal oops don't have any virtual functions.  Instead, they
 48 // forward all "virtual" functions to their klass, which does have
 49 // a vtbl and does the C++ dispatch depending on the object's
 50 // actual type.  (See oop.inline.hpp for some of the forwarding code.)
 51 // ALL FUNCTIONS IMPLEMENTING THIS DISPATCH ARE PREFIXED WITH "oop_"!
 52 
 53 // Forward declarations.
 54 template <class T> class Array;
 55 template <class T> class GrowableArray;
 56 class ClassLoaderData;
 57 class fieldDescriptor;
 58 class klassVtable;
 59 class ModuleEntry;
 60 class PackageEntry;
 61 class vtableEntry;
 62 
 63 class Klass : public Metadata {
 64 
 65   friend class VMStructs;
 66   friend class JVMCIVMStructs;
 67  public:
 68   // Klass Kinds for all subclasses of Klass
 69    enum KlassKind : u2
 70    {
 71      InstanceKlassKind,
 72      InlineKlassKind,
 73      InstanceRefKlassKind,
 74      InstanceMirrorKlassKind,
 75      InstanceClassLoaderKlassKind,
 76      InstanceStackChunkKlassKind,
 77      TypeArrayKlassKind,
 78      ObjArrayKlassKind,
 79      RefArrayKlassKind,
 80      FlatArrayKlassKind,
 81      UnknownKlassKind
 82    };
 83 
 84    static const uint KLASS_KIND_COUNT = FlatArrayKlassKind + 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   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
128                                 // Some flags created by the JVM, not in the class file itself,
129                                 // are in _misc_flags below.
130   KlassFlags  _misc_flags;
131 
132   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
133   // and _primary_supers all help make fast subtype checks.  See big discussion
134   // in doc/server_compiler/checktype.txt
135   //
136   // Where to look to observe a supertype (it is &_secondary_super_cache for
137   // secondary supers, else is &_primary_supers[depth()].
138   juint       _super_check_offset;
139 
140   // Class name.  Instance classes: java/lang/String, etc.  Array classes: [I,
141   // [Ljava/lang/String;, etc.  Set to zero for all other kinds of classes.
142   Symbol*     _name;
143 
144   // Cache of last observed secondary supertype
145   Klass*      _secondary_super_cache;
146   // Array of all secondary supertypes
147   Array<Klass*>* _secondary_supers;
148   // Ordered list of all primary supertypes
149   Klass*      _primary_supers[_primary_super_limit];
150   // java/lang/Class instance mirroring this class
151   OopHandle   _java_mirror;
152   // Superclass
153   Klass*      _super;
154   // First subclass (null if none); _subklass->next_sibling() is next one
155   Klass* volatile _subklass;
156   // Sibling link (or null); links all subklasses of a klass
157   Klass* volatile _next_sibling;
158 
159   // All klasses loaded by a class loader are chained through these links
160   Klass*      _next_link;
161 
162   // The VM's representation of the ClassLoader used to load this class.
163   // Provide access the corresponding instance java.lang.ClassLoader.
164   ClassLoaderData* _class_loader_data;
165 
166   markWord _prototype_header;   // Used to initialize objects' header
167 
168   // Bitmap and hash code used by hashed secondary supers.
169   uintx    _secondary_supers_bitmap;
170   uint8_t  _hash_slot;
171 
172 private:
173   // This is an index into AOTClassLocationConfig::class_locations(), to
174   // indicate the AOTClassLocation where this class is loaded from during
175   // dump time. If a class is not loaded from the AOT cache, this field is
176   // -1.
177   s2 _shared_class_path_index;
178 
179 #if INCLUDE_CDS
180   // Various attributes for shared classes. Should be zero for a non-shared class.
181   u2     _shared_class_flags;
182   enum CDSSharedClassFlags {
183     _is_shared_class                       = 1 << 0,  // shadows MetaspaceObj::is_shared
184     _archived_lambda_proxy_is_available    = 1 << 1,
185     _has_value_based_class_annotation      = 1 << 2,
186     _verified_at_dump_time                 = 1 << 3,
187     _has_archived_enum_objs                = 1 << 4,
188     // This class was not loaded from a classfile in the module image
189     // or classpath.
190     _is_generated_shared_class             = 1 << 5,
191     // archived mirror already initialized by AOT-cache assembly: no further need to call <clinit>
192     _has_aot_initialized_mirror            = 1 << 6,
193     // If this class has been aot-inititalized, do we need to call its runtimeSetup()
194     // method during the production run?
195     _is_runtime_setup_required             = 1 << 7,
196   };
197 #endif
198 
199   int _vtable_len;              // vtable length. This field may be read very often when we
200                                 // have lots of itable dispatches (e.g., lambdas and streams).
201                                 // Keep it away from the beginning of a Klass to avoid cacheline
202                                 // contention that may happen when a nearby object is modified.
203 
204   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
205 
206 public:
207 
208   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
209 
210 protected:
211 
212   Klass(KlassKind kind, markWord prototype_header = markWord::prototype());
213   Klass();
214 
215  public:
216   int kind() { return _kind; }
217 
218   enum class DefaultsLookupMode { find, skip };
219   enum class OverpassLookupMode { find, skip };
220   enum class StaticLookupMode   { find, skip };
221   enum class PrivateLookupMode  { find, skip };
222 
223   virtual bool is_klass() const { return true; }
224 
225   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
226   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
227   // If this is not what your code expects, you're probably looking for Klass::java_super().
228   Klass* super() const               { return _super; }
229   void set_super(Klass* k)           { _super = k; }
230 
231   // initializes _super link, _primary_supers & _secondary_supers arrays
232   void initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS);
233 
234   // klass-specific helper for initializing _secondary_supers
235   virtual GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
236                                                           Array<InstanceKlass*>* transitive_interfaces);
237 
238   // java_super is the Java-level super type as specified by Class.getSuperClass.
239   virtual InstanceKlass* java_super() const  { return nullptr; }
240 
241   juint    super_check_offset() const  { return _super_check_offset; }
242   void set_super_check_offset(juint o) { _super_check_offset = o; }
243 
244   Klass* secondary_super_cache() const     { return _secondary_super_cache; }
245   void set_secondary_super_cache(Klass* k) { _secondary_super_cache = k; }
246 
247   Array<Klass*>* secondary_supers() const { return _secondary_supers; }
248   void set_secondary_supers(Array<Klass*>* k, uintx bitmap);
249 
250   uint8_t hash_slot() const { return _hash_slot; }
251 
252   // Return the element of the _super chain of the given depth.
253   // If there is no such element, return either null or this.
254   Klass* primary_super_of_depth(juint i) const {
255     assert(i < primary_super_limit(), "oob");
256     Klass* super = _primary_supers[i];
257     assert(super == nullptr || super->super_depth() == i, "correct display");
258     return super;
259   }
260 
261   // Can this klass be a primary super?  False for interfaces and arrays of
262   // interfaces.  False also for arrays or classes with long super chains.
263   bool can_be_primary_super() const {
264     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
265     return super_check_offset() != secondary_offset;
266   }
267   virtual bool can_be_primary_super_slow() const;
268 
269   // Returns number of primary supers; may be a number in the inclusive range [0, primary_super_limit].
270   juint super_depth() const {
271     if (!can_be_primary_super()) {
272       return primary_super_limit();
273     } else {
274       juint d = (super_check_offset() - in_bytes(primary_supers_offset())) / sizeof(Klass*);
275       assert(d < primary_super_limit(), "oob");
276       assert(_primary_supers[d] == this, "proper init");
277       return d;
278     }
279   }
280 
281   // java mirror
282   oop java_mirror() const;
283   oop java_mirror_no_keepalive() const;
284   void set_java_mirror(Handle m);
285 
286   oop archived_java_mirror() NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
287 
288   // Temporary mirror switch used by RedefineClasses
289   OopHandle java_mirror_handle() const { return _java_mirror; }
290   void swap_java_mirror_handle(OopHandle& mirror) { _java_mirror.swap(mirror); }
291 
292   // Set java mirror OopHandle to null for CDS
293   // This leaves the OopHandle in the CLD, but that's ok, you can't release them.
294   void clear_java_mirror_handle() { _java_mirror = OopHandle(); }
295 
296   // size helper
297   int layout_helper() const            { return _layout_helper; }
298   void set_layout_helper(int lh)       { _layout_helper = lh; }
299 
300   // Note: for instances layout_helper() may include padding.
301   // Use InstanceKlass::contains_field_offset to classify field offsets.
302 
303   // sub/superklass links
304   Klass* subklass(bool log = false) const;
305   Klass* next_sibling(bool log = false) const;
306 
307   InstanceKlass* superklass() const;
308   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
309 
310   void set_next_link(Klass* k) { _next_link = k; }
311   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
312   Klass** next_link_addr() { return &_next_link; }
313 
314   // class loader data
315   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
316   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
317 
318   s2 shared_classpath_index() const   {
319     return _shared_class_path_index;
320   };
321 
322   void set_shared_classpath_index(s2 index) {
323     _shared_class_path_index = index;
324   };
325 
326   bool has_archived_mirror_index() const {
327     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
328     NOT_CDS_JAVA_HEAP(return false);
329   }
330 
331   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
332 
333   void set_lambda_proxy_is_available() {
334     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
335   }
336   void clear_lambda_proxy_is_available() {
337     CDS_ONLY(_shared_class_flags &= (u2)(~_archived_lambda_proxy_is_available);)
338   }
339   bool lambda_proxy_is_available() const {
340     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
341     NOT_CDS(return false;)
342   }
343 
344   void set_has_value_based_class_annotation() {
345     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
346   }
347   void clear_has_value_based_class_annotation() {
348     CDS_ONLY(_shared_class_flags &= (u2)(~_has_value_based_class_annotation);)
349   }
350   bool has_value_based_class_annotation() const {
351     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
352     NOT_CDS(return false;)
353   }
354 
355   void set_verified_at_dump_time() {
356     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
357   }
358   bool verified_at_dump_time() const {
359     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
360     NOT_CDS(return false;)
361   }
362 
363   void set_has_archived_enum_objs() {
364     CDS_ONLY(_shared_class_flags |= _has_archived_enum_objs;)
365   }
366   bool has_archived_enum_objs() const {
367     CDS_ONLY(return (_shared_class_flags & _has_archived_enum_objs) != 0;)
368     NOT_CDS(return false;)
369   }
370 
371   void set_is_generated_shared_class() {
372     CDS_ONLY(_shared_class_flags |= _is_generated_shared_class;)
373   }
374   bool is_generated_shared_class() const {
375     CDS_ONLY(return (_shared_class_flags & _is_generated_shared_class) != 0;)
376     NOT_CDS(return false;)
377   }
378 
379   void set_has_aot_initialized_mirror() {
380     CDS_ONLY(_shared_class_flags |= _has_aot_initialized_mirror;)
381   }
382   bool has_aot_initialized_mirror() const {
383     CDS_ONLY(return (_shared_class_flags & _has_aot_initialized_mirror) != 0;)
384     NOT_CDS(return false;)
385   }
386 
387   void set_is_runtime_setup_required() {
388     assert(has_aot_initialized_mirror(), "sanity");
389     CDS_ONLY(_shared_class_flags |= _is_runtime_setup_required;)
390   }
391   bool is_runtime_setup_required() const {
392     CDS_ONLY(return (_shared_class_flags & _is_runtime_setup_required) != 0;)
393     NOT_CDS(return false;)
394   }
395 
396   bool is_shared() const                { // shadows MetaspaceObj::is_shared)()
397     CDS_ONLY(return (_shared_class_flags & _is_shared_class) != 0;)
398     NOT_CDS(return false;)
399   }
400 
401   void set_is_shared() {
402     CDS_ONLY(_shared_class_flags |= _is_shared_class;)
403   }
404 
405   // Obtain the module or package for this class
406   virtual ModuleEntry* module() const = 0;
407   virtual PackageEntry* package() const = 0;
408 
409  protected:                                // internal accessors
410   void     set_subklass(Klass* s);
411   void     set_next_sibling(Klass* s);
412 
413  private:
414   static uint8_t compute_hash_slot(Symbol* s);
415   static void  hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap);
416   static uintx hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite);
417 
418   bool search_secondary_supers(Klass* k) const;
419   bool lookup_secondary_supers_table(Klass *k) const;
420   bool linear_search_secondary_supers(const Klass* k) const;
421   bool fallback_search_secondary_supers(const Klass* k, int index, uintx rotated_bitmap) const;
422 
423  public:
424   // Secondary supers table support
425   static Array<Klass*>* pack_secondary_supers(ClassLoaderData* loader_data,
426                                               GrowableArray<Klass*>* primaries,
427                                               GrowableArray<Klass*>* secondaries,
428                                               uintx& bitmap,
429                                               TRAPS);
430 
431   static uintx   compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers);
432   static uint8_t compute_home_slot(Klass* k, uintx bitmap);
433 
434   static constexpr int SECONDARY_SUPERS_TABLE_SIZE = sizeof(_secondary_supers_bitmap) * 8;
435   static constexpr int SECONDARY_SUPERS_TABLE_MASK = SECONDARY_SUPERS_TABLE_SIZE - 1;
436 
437   static constexpr uintx SECONDARY_SUPERS_BITMAP_EMPTY    = 0;
438   static constexpr uintx SECONDARY_SUPERS_BITMAP_FULL     = ~(uintx)0;
439 
440   // Compiler support
441   static ByteSize super_offset()                 { return byte_offset_of(Klass, _super); }
442   static ByteSize super_check_offset_offset()    { return byte_offset_of(Klass, _super_check_offset); }
443   static ByteSize primary_supers_offset()        { return byte_offset_of(Klass, _primary_supers); }
444   static ByteSize secondary_super_cache_offset() { return byte_offset_of(Klass, _secondary_super_cache); }
445   static ByteSize secondary_supers_offset()      { return byte_offset_of(Klass, _secondary_supers); }
446   static ByteSize java_mirror_offset()           { return byte_offset_of(Klass, _java_mirror); }
447   static ByteSize class_loader_data_offset()     { return byte_offset_of(Klass, _class_loader_data); }
448   static ByteSize layout_helper_offset()         { return byte_offset_of(Klass, _layout_helper); }
449   static ByteSize access_flags_offset()          { return byte_offset_of(Klass, _access_flags); }
450 #if INCLUDE_JVMCI
451   static ByteSize subklass_offset()              { return byte_offset_of(Klass, _subklass); }
452   static ByteSize next_sibling_offset()          { return byte_offset_of(Klass, _next_sibling); }
453 #endif
454   static ByteSize secondary_supers_bitmap_offset()
455                                                  { return byte_offset_of(Klass, _secondary_supers_bitmap); }
456   static ByteSize hash_slot_offset()             { return byte_offset_of(Klass, _hash_slot); }
457   static ByteSize misc_flags_offset()            { return byte_offset_of(Klass, _misc_flags._flags); }
458 
459   // Unpacking layout_helper:
460   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
461   static const int _lh_instance_slow_path_bit  = 0x01;
462   static const int _lh_log2_element_size_shift = BitsPerByte*0;
463   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
464   static const int _lh_element_type_shift      = BitsPerByte*1;
465   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
466   static const int _lh_header_size_shift       = BitsPerByte*2;
467   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
468   static const int _lh_array_tag_bits          = 4;
469   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
470 
471   static const unsigned int _lh_array_tag_type_value = 0Xfffffffc;
472   static const unsigned int _lh_array_tag_flat_value = 0Xfffffffa;
473   static const unsigned int _lh_array_tag_ref_value  = 0Xfffffff8;
474 
475   // null-free array flag bit under the array tag bits, shift one more to get array tag value
476   static const int _lh_null_free_shift = _lh_array_tag_shift - 1;
477   static const int _lh_null_free_mask  = 1;
478 
479   static const jint _lh_array_tag_flat_value_bit_inplace = (jint) (1 << (_lh_array_tag_shift + 1));
480 
481   static int layout_helper_size_in_bytes(jint lh) {
482     assert(lh > (jint)_lh_neutral_value, "must be instance");
483     return (int) lh & ~_lh_instance_slow_path_bit;
484   }
485   static bool layout_helper_needs_slow_path(jint lh) {
486     assert(lh > (jint)_lh_neutral_value, "must be instance");
487     return (lh & _lh_instance_slow_path_bit) != 0;
488   }
489   static bool layout_helper_is_instance(jint lh) {
490     return (jint)lh > (jint)_lh_neutral_value;
491   }
492   static bool layout_helper_is_array(jint lh) {
493     return (jint)lh < (jint)_lh_neutral_value;
494   }
495   static bool layout_helper_is_typeArray(jint lh) {
496     return (juint) _lh_array_tag_type_value == (juint)(lh >> _lh_array_tag_shift);
497   }
498   static bool layout_helper_is_refArray(jint lh) {
499     return (juint)_lh_array_tag_ref_value == (juint)(lh >> _lh_array_tag_shift);
500   }
501   static bool layout_helper_is_flatArray(jint lh) {
502     return (juint)_lh_array_tag_flat_value == (juint)(lh >> _lh_array_tag_shift);
503   }
504   static bool layout_helper_is_null_free(jint lh) {
505     assert(layout_helper_is_flatArray(lh) || layout_helper_is_refArray(lh), "must be array of inline types");
506     return ((lh >> _lh_null_free_shift) & _lh_null_free_mask);
507   }
508   static jint layout_helper_set_null_free(jint lh) {
509     lh |= (_lh_null_free_mask << _lh_null_free_shift);
510     assert(layout_helper_is_null_free(lh), "Bad encoding");
511     return lh;
512   }
513   static int layout_helper_header_size(jint lh) {
514     assert(lh < (jint)_lh_neutral_value, "must be array");
515     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
516     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
517     return hsize;
518   }
519   static BasicType layout_helper_element_type(jint lh) {
520     assert(lh < (jint)_lh_neutral_value, "must be array");
521     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
522     assert((btvalue >= T_BOOLEAN && btvalue <= T_OBJECT) || btvalue == T_FLAT_ELEMENT, "sanity");
523     return (BasicType) btvalue;
524   }
525 
526   // Want a pattern to quickly diff against layout header in register
527   // find something less clever!
528   static int layout_helper_boolean_diffbit() {
529     jint zlh = array_layout_helper(T_BOOLEAN);
530     jint blh = array_layout_helper(T_BYTE);
531     assert(zlh != blh, "array layout helpers must differ");
532     int diffbit = 1;
533     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
534       diffbit <<= 1;
535       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
536     }
537     return diffbit;
538   }
539 
540   static int layout_helper_log2_element_size(jint lh) {
541     assert(lh < (jint)_lh_neutral_value, "must be array");
542     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
543     assert(layout_helper_element_type(lh) == T_FLAT_ELEMENT || l2esz <= LogBytesPerLong,
544            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
545     return l2esz;
546   }
547   static jint array_layout_helper(jint tag, bool null_free, int hsize, BasicType etype, int log2_esize) {
548     return (tag        << _lh_array_tag_shift)
549       |    ((null_free ? 1 : 0) <<  _lh_null_free_shift)
550       |    (hsize      << _lh_header_size_shift)
551       |    ((int)etype << _lh_element_type_shift)
552       |    (log2_esize << _lh_log2_element_size_shift);
553   }
554   static jint instance_layout_helper(jint size, bool slow_path_flag) {
555     return (size << LogBytesPerWord)
556       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
557   }
558   static int layout_helper_to_size_helper(jint lh) {
559     assert(lh > (jint)_lh_neutral_value, "must be instance");
560     // Note that the following expression discards _lh_instance_slow_path_bit.
561     return lh >> LogBytesPerWord;
562   }
563   // Out-of-line version computes everything based on the etype:
564   static jint array_layout_helper(BasicType etype);
565 
566   // What is the maximum number of primary superclasses any klass can have?
567   static juint primary_super_limit()         { return _primary_super_limit; }
568 
569   // vtables
570   klassVtable vtable() const;
571   int vtable_length() const { return _vtable_len; }
572 
573   // subclass check
574   bool is_subclass_of(const Klass* k) const;
575 
576   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
577   bool is_subtype_of(Klass* k) const;
578 
579 public:
580   // Find LCA in class hierarchy
581   Klass *LCA( Klass *k );
582 
583   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
584   // if not, throw either an Error or an Exception.
585   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
586 
587   // array copying
588   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
589 
590   // tells if the class should be initialized
591   virtual bool should_be_initialized() const    { return false; }
592   // initializes the klass
593   virtual void initialize(TRAPS);
594   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
595   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
596                                          OverpassLookupMode overpass_mode,
597                                          PrivateLookupMode = PrivateLookupMode::find) const;
598  public:
599   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
600     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
601   }
602 
603   // array class with specific rank
604   virtual ArrayKlass* array_klass(int rank, TRAPS) = 0;
605 
606   // array class with this klass as element type
607   virtual ArrayKlass* array_klass(TRAPS) = 0;
608 
609   // These will return null instead of allocating on the heap:
610   virtual ArrayKlass* array_klass_or_null(int rank) = 0;
611   virtual ArrayKlass* array_klass_or_null() = 0;
612 
613   virtual oop protection_domain() const = 0;
614 
615   oop class_loader() const;
616 
617   inline oop klass_holder() const;
618 
619   inline void keep_alive() const;
620 
621  protected:
622 
623   // Error handling when length > max_length or length < 0
624   static void check_array_allocation_length(int length, int max_length, TRAPS);
625 
626   void set_vtable_length(int len) { _vtable_len= len; }
627 
628   vtableEntry* start_of_vtable() const;
629 #if INCLUDE_CDS
630   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
631 #endif
632  public:
633   Method* method_at_vtable(int index);
634 
635   static ByteSize vtable_start_offset();
636   static ByteSize vtable_length_offset() {
637     return byte_offset_of(Klass, _vtable_len);
638   }
639 
640 #if INCLUDE_CDS
641   // CDS support - remove and restore oops from metadata. Oops are not shared.
642   virtual void remove_unshareable_info();
643   virtual void remove_java_mirror();
644 
645   bool is_unshareable_info_restored() const {
646     assert(is_shared(), "use this for shared classes only");
647     if (has_archived_mirror_index()) {
648       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
649       return false;
650     } else if (_java_mirror.is_empty()) {
651       return false;
652     } else {
653       return true;
654     }
655   }
656 #endif // INCLUDE_CDS
657 
658  public:
659   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
660   // These functions describe behavior for the oop not the KLASS.
661 
662   // actual oop size of obj in memory in word size.
663   virtual size_t oop_size(oop obj) const = 0;
664 
665   // Size of klass in word size.
666   virtual int size() const = 0;
667 
668   // Returns the Java name for a class (Resource allocated)
669   // For arrays, this returns the name of the element with a leading '['.
670   // For classes, this returns the name with the package separators
671   //     turned into '.'s.
672   const char* external_name() const;
673   // Returns the name for a class (Resource allocated) as the class
674   // would appear in a signature.
675   // For arrays, this returns the name of the element with a leading '['.
676   // For classes, this returns the name with a leading 'L' and a trailing ';'
677   //     and the package separators as '/'.
678   virtual const char* signature_name() const;
679 
680   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
681   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
682 
683   // Returns "interface", "abstract class" or "class".
684   const char* external_kind() const;
685 
686   // type testing operations
687 #ifdef ASSERT
688  protected:
689   virtual bool is_instance_klass_slow()     const { return false; }
690   virtual bool is_array_klass_slow()        const { return false; }
691   virtual bool is_objArray_klass_slow()     const { return false; }
692   virtual bool is_refArray_klass_slow()     const { return false; }
693   virtual bool is_typeArray_klass_slow()    const { return false; }
694   virtual bool is_flatArray_klass_slow()    const { return false; }
695 #endif // ASSERT
696   // current implementation uses this method even in non debug builds
697   virtual bool is_inline_klass_slow()       const { return false; }
698  public:
699 
700   // Fast non-virtual versions
701   #ifndef ASSERT
702   #define assert_same_query(xval, xcheck) xval
703   #else
704  private:
705   static bool assert_same_query(bool xval, bool xslow) {
706     assert(xval == xslow, "slow and fast queries agree");
707     return xval;
708   }
709  public:
710   #endif
711 
712   bool is_instance_klass()              const { return assert_same_query(_kind <= InstanceStackChunkKlassKind, is_instance_klass_slow()); }
713   bool is_inline_klass()                const { return assert_same_query(_kind == InlineKlassKind, is_inline_klass_slow()); }
714   bool is_reference_instance_klass()    const { return _kind == InstanceRefKlassKind; }
715   bool is_mirror_instance_klass()       const { return _kind == InstanceMirrorKlassKind; }
716   bool is_class_loader_instance_klass() const { return _kind == InstanceClassLoaderKlassKind; }
717   bool is_array_klass()                 const { return assert_same_query( _kind >= TypeArrayKlassKind, is_array_klass_slow()); }
718   bool is_stack_chunk_instance_klass()  const { return _kind == InstanceStackChunkKlassKind; }
719   bool is_flatArray_klass()             const { return assert_same_query( _kind == FlatArrayKlassKind, is_flatArray_klass_slow()); }
720   bool is_objArray_klass()              const { return assert_same_query( _kind == ObjArrayKlassKind || _kind == RefArrayKlassKind || _kind == FlatArrayKlassKind,  is_objArray_klass_slow()); }
721   bool is_refArray_klass()              const { return assert_same_query( _kind == RefArrayKlassKind, is_refArray_klass_slow()); }
722   bool is_typeArray_klass()             const { return assert_same_query( _kind == TypeArrayKlassKind, is_typeArray_klass_slow()); }
723   bool is_refined_objArray_klass()      const { return is_refArray_klass() || is_flatArray_klass(); }
724   #undef assert_same_query
725 
726   inline bool is_null_free_array_klass() const { return !is_typeArray_klass() && layout_helper_is_null_free(layout_helper()); }
727 
728   // Access flags
729   AccessFlags access_flags() const         { return _access_flags;  }
730   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
731 
732   bool is_public() const                { return _access_flags.is_public(); }
733   bool is_final() const                 { return _access_flags.is_final(); }
734   bool is_interface() const             { return _access_flags.is_interface(); }
735   bool is_abstract() const              { return _access_flags.is_abstract(); }
736   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
737   bool is_identity_class() const        { assert(is_instance_klass(), "only for instanceKlass"); return _access_flags.is_identity_class(); }
738   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
739   bool has_finalizer() const            { return _misc_flags.has_finalizer(); }
740   void set_has_finalizer()              { _misc_flags.set_has_finalizer(true); }
741   bool is_hidden() const                { return _misc_flags.is_hidden_class(); }
742   void set_is_hidden()                  { _misc_flags.set_is_hidden_class(true); }
743   bool is_value_based() const           { return _misc_flags.is_value_based_class(); }
744   void set_is_value_based()             { _misc_flags.set_is_value_based_class(true); }
745 
746   klass_flags_t misc_flags() const      { return _misc_flags.value(); }
747 
748   inline bool is_non_strong_hidden() const;
749 
750   bool is_cloneable() const;
751   void set_is_cloneable();
752 
753   static inline markWord make_prototype_header(const Klass* kls, markWord prototype = markWord::prototype());
754   inline markWord prototype_header() const;
755   inline void set_prototype_header(markWord header);
756   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
757   static inline markWord default_prototype_header(Klass* k);
758 
759   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
760 
761   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
762   virtual MetaspaceObj::Type type() const { return ClassType; }
763 
764   inline bool is_loader_alive() const;
765   inline bool is_loader_present_and_alive() const;
766 
767   void clean_subklass();
768 
769   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
770   static void clean_subklass_tree() {
771     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
772   }
773 
774   // Return self, except for abstract classes with exactly 1
775   // implementor.  Then return the 1 concrete implementation.
776   Klass *up_cast_abstract();
777 
778   // klass name
779   Symbol* name() const                   { return _name; }
780   void set_name(Symbol* n);
781 
782   virtual void release_C_heap_structures(bool release_constant_pool = true);
783 
784  public:
785   // Get modifier flags from Java mirror cache.
786   int modifier_flags() const;
787 
788   // Compute modifier flags from the original data. This also allows
789   // accessing flags when Java mirror is already dead, e.g. during class
790   // unloading.
791   virtual u2 compute_modifier_flags() const = 0;
792 
793   // JVMTI support
794   virtual jint jvmti_class_status() const;
795 
796   // Printing
797   virtual void print_on(outputStream* st) const;
798 
799   virtual void oop_print_value_on(oop obj, outputStream* st);
800   virtual void oop_print_on      (oop obj, outputStream* st);
801 
802   void print_secondary_supers_on(outputStream* st) const;
803 
804   virtual const char* internal_name() const = 0;
805 
806   // Verification
807   virtual void verify_on(outputStream* st);
808   void verify() { verify_on(tty); }
809 
810 #ifndef PRODUCT
811   bool verify_vtable_index(int index);
812 #endif
813 
814   virtual void oop_verify_on(oop obj, outputStream* st);
815 
816   // for error reporting
817   static bool is_valid(Klass* k);
818 
819   static void on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg);
820 
821   // Returns true if this Klass needs to be addressable via narrow Klass ID.
822   inline bool needs_narrow_id() const;
823 
824 };
825 
826 #endif // SHARE_OOPS_KLASS_HPP