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
 21  * questions.
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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     InstanceKlassKind,
 71     InstanceRefKlassKind,
 72     InstanceMirrorKlassKind,
 73     InstanceClassLoaderKlassKind,
 74     InstanceStackChunkKlassKind,
 75     TypeArrayKlassKind,
 76     ObjArrayKlassKind,
 77     UnknownKlassKind
 78   };
 79 
 80   static const uint KLASS_KIND_COUNT = ObjArrayKlassKind + 1;
 81  protected:
 82 
 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
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 kind used to resolve the runtime type of the instance.
119   //  - Used to implement devirtualized oop closure dispatching.
120   //  - Various type checking in the JVM
121   const KlassKind _kind;
122 
123   AccessFlags _access_flags;    // Access flags. The class/interface distinction is stored here.
124                                 // Some flags created by the JVM, not in the class file itself,
125                                 // are in _misc_flags below.
126   // Processed access flags, for use by Class.getModifiers.
127   u2          _modifier_flags;
128 
129   KlassFlags  _misc_flags;
130 
131   // The fields _super_check_offset, _secondary_super_cache, _secondary_supers
132   // and _primary_supers all help make fast subtype checks.  See big discussion
133   // in doc/server_compiler/checktype.txt
134   //
135   // Where to look to observe a supertype (it is &_secondary_super_cache for
136   // secondary supers, else is &_primary_supers[depth()].
137   juint       _super_check_offset;
138 
139   // Class name.  Instance classes: java/lang/String, etc.  Array classes: [I,
140   // [Ljava/lang/String;, etc.  Set to zero for all other kinds of classes.
141   Symbol*     _name;
142 
143   // Cache of last observed secondary supertype
144   Klass*      _secondary_super_cache;
145   // Array of all secondary supertypes
146   Array<Klass*>* _secondary_supers;
147   // Ordered list of all primary supertypes
148   Klass*      _primary_supers[_primary_super_limit];
149   // java/lang/Class instance mirroring this class
150   OopHandle   _java_mirror;
151   // Superclass
152   Klass*      _super;
153   // First subclass (null if none); _subklass->next_sibling() is next one
154   Klass* volatile _subklass;
155   // Sibling link (or null); links all subklasses of a klass
156   Klass* volatile _next_sibling;
157 
158   // All klasses loaded by a class loader are chained through these links
159   Klass*      _next_link;
160 
161   // The VM's representation of the ClassLoader used to load this class.
162   // Provide access the corresponding instance java.lang.ClassLoader.
163   ClassLoaderData* _class_loader_data;
164 
165   markWord _prototype_header;   // Used to initialize objects' header
166 
167   // Bitmap and hash code used by hashed secondary supers.
168   uintx    _secondary_supers_bitmap;
169   uint8_t  _hash_slot;
170 
171 private:
172   // This is an index into FileMapHeader::_shared_path_table[], to
173   // associate this class with the JAR file where it's loaded from during
174   // dump time. If a class is not loaded from the shared archive, this field is
175   // -1.
176   s2 _shared_class_path_index;
177 
178 #if INCLUDE_CDS
179   // Various attributes for shared classes. Should be zero for a non-shared class.
180   u2     _shared_class_flags;
181   enum CDSSharedClassFlags {
182     _is_shared_class                       = 1 << 0,  // shadows MetaspaceObj::is_shared
183     _archived_lambda_proxy_is_available    = 1 << 1,
184     _has_value_based_class_annotation      = 1 << 2,
185     _verified_at_dump_time                 = 1 << 3,
186     _has_archived_enum_objs                = 1 << 4,
187     // This class was not loaded from a classfile in the module image
188     // or classpath.
189     _is_generated_shared_class             = 1 << 5,
190     // archived mirror already initialized by AOT-cache assembly: no further need to call <clinit>
191     _has_aot_initialized_mirror            = 1 << 6,
192     // If this class has been aot-inititalized, do we need to call its runtimeSetup()
193     // method during the production run?
194     _is_runtime_setup_required             = 1 << 7,
195   };
196 #endif
197 
198   int _vtable_len;              // vtable length. This field may be read very often when we
199                                 // have lots of itable dispatches (e.g., lambdas and streams).
200                                 // Keep it away from the beginning of a Klass to avoid cacheline
201                                 // contention that may happen when a nearby object is modified.
202 
203   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
204 
205 public:
206 
207   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
208 
209 protected:
210 
211   Klass(KlassKind kind);
212   Klass();
213 
214  public:
215   int kind() { return _kind; }
216 
217   enum class DefaultsLookupMode { find, skip };
218   enum class OverpassLookupMode { find, skip };
219   enum class StaticLookupMode   { find, skip };
220   enum class PrivateLookupMode  { find, skip };
221 
222   virtual bool is_klass() const { return true; }
223 
224   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
225   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
226   // If this is not what your code expects, you're probably looking for Klass::java_super().
227   Klass* super() const               { return _super; }
228   void set_super(Klass* k)           { _super = k; }
229 
230   // initializes _super link, _primary_supers & _secondary_supers arrays
231   void initialize_supers(Klass* k, Array<InstanceKlass*>* transitive_interfaces, TRAPS);
232 
233   // klass-specific helper for initializing _secondary_supers
234   virtual GrowableArray<Klass*>* compute_secondary_supers(int num_extra_slots,
235                                                           Array<InstanceKlass*>* transitive_interfaces);
236 
237   // java_super is the Java-level super type as specified by Class.getSuperClass.
238   virtual InstanceKlass* java_super() const  { return nullptr; }
239 
240   juint    super_check_offset() const  { return _super_check_offset; }
241   void set_super_check_offset(juint o) { _super_check_offset = o; }
242 
243   Klass* secondary_super_cache() const     { return _secondary_super_cache; }
244   void set_secondary_super_cache(Klass* k) { _secondary_super_cache = k; }
245 
246   Array<Klass*>* secondary_supers() const { return _secondary_supers; }
247   void set_secondary_supers(Array<Klass*>* k, uintx bitmap);
248 
249   uint8_t hash_slot() const { return _hash_slot; }
250 
251   // Return the element of the _super chain of the given depth.
252   // If there is no such element, return either null or this.
253   Klass* primary_super_of_depth(juint i) const {
254     assert(i < primary_super_limit(), "oob");
255     Klass* super = _primary_supers[i];
256     assert(super == nullptr || super->super_depth() == i, "correct display");
257     return super;
258   }
259 
260   // Can this klass be a primary super?  False for interfaces and arrays of
261   // interfaces.  False also for arrays or classes with long super chains.
262   bool can_be_primary_super() const {
263     const juint secondary_offset = in_bytes(secondary_super_cache_offset());
264     return super_check_offset() != secondary_offset;
265   }
266   virtual bool can_be_primary_super_slow() const;
267 
268   // Returns number of primary supers; may be a number in the inclusive range [0, primary_super_limit].
269   juint super_depth() const {
270     if (!can_be_primary_super()) {
271       return primary_super_limit();
272     } else {
273       juint d = (super_check_offset() - in_bytes(primary_supers_offset())) / sizeof(Klass*);
274       assert(d < primary_super_limit(), "oob");
275       assert(_primary_supers[d] == this, "proper init");
276       return d;
277     }
278   }
279 
280   // java mirror
281   oop java_mirror() const;
282   oop java_mirror_no_keepalive() const;
283   void set_java_mirror(Handle m);
284 
285   oop archived_java_mirror() NOT_CDS_JAVA_HEAP_RETURN_(nullptr);
286 
287   // Temporary mirror switch used by RedefineClasses
288   OopHandle java_mirror_handle() const { return _java_mirror; }
289   void swap_java_mirror_handle(OopHandle& mirror) { _java_mirror.swap(mirror); }
290 
291   // Set java mirror OopHandle to null for CDS
292   // This leaves the OopHandle in the CLD, but that's ok, you can't release them.
293   void clear_java_mirror_handle() { _java_mirror = OopHandle(); }
294 
295   // modifier flags
296   u2 modifier_flags() const          { return _modifier_flags; }
297   void set_modifier_flags(u2 flags)  { _modifier_flags = flags; }
298 
299   // size helper
300   int layout_helper() const            { return _layout_helper; }
301   void set_layout_helper(int lh)       { _layout_helper = lh; }
302 
303   // Note: for instances layout_helper() may include padding.
304   // Use InstanceKlass::contains_field_offset to classify field offsets.
305 
306   // sub/superklass links
307   Klass* subklass(bool log = false) const;
308   Klass* next_sibling(bool log = false) const;
309 
310   InstanceKlass* superklass() const;
311   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
312 
313   void set_next_link(Klass* k) { _next_link = k; }
314   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
315   Klass** next_link_addr() { return &_next_link; }
316 
317   // class loader data
318   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
319   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
320 
321   s2 shared_classpath_index() const   {
322     return _shared_class_path_index;
323   };
324 
325   void set_shared_classpath_index(s2 index) {
326     _shared_class_path_index = index;
327   };
328 
329   bool has_archived_mirror_index() const {
330     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
331     NOT_CDS_JAVA_HEAP(return false);
332   }
333 
334   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
335 
336   void set_lambda_proxy_is_available() {
337     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
338   }
339   void clear_lambda_proxy_is_available() {
340     CDS_ONLY(_shared_class_flags &= (u2)(~_archived_lambda_proxy_is_available);)
341   }
342   bool lambda_proxy_is_available() const {
343     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
344     NOT_CDS(return false;)
345   }
346 
347   void set_has_value_based_class_annotation() {
348     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
349   }
350   void clear_has_value_based_class_annotation() {
351     CDS_ONLY(_shared_class_flags &= (u2)(~_has_value_based_class_annotation);)
352   }
353   bool has_value_based_class_annotation() const {
354     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
355     NOT_CDS(return false;)
356   }
357 
358   void set_verified_at_dump_time() {
359     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
360   }
361   bool verified_at_dump_time() const {
362     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
363     NOT_CDS(return false;)
364   }
365 
366   void set_has_archived_enum_objs() {
367     CDS_ONLY(_shared_class_flags |= _has_archived_enum_objs;)
368   }
369   bool has_archived_enum_objs() const {
370     CDS_ONLY(return (_shared_class_flags & _has_archived_enum_objs) != 0;)
371     NOT_CDS(return false;)
372   }
373 
374   void set_is_generated_shared_class() {
375     CDS_ONLY(_shared_class_flags |= _is_generated_shared_class;)
376   }
377   bool is_generated_shared_class() const {
378     CDS_ONLY(return (_shared_class_flags & _is_generated_shared_class) != 0;)
379     NOT_CDS(return false;)
380   }
381 
382   void set_has_aot_initialized_mirror() {
383     CDS_ONLY(_shared_class_flags |= _has_aot_initialized_mirror;)
384   }
385   bool has_aot_initialized_mirror() const {
386     CDS_ONLY(return (_shared_class_flags & _has_aot_initialized_mirror) != 0;)
387     NOT_CDS(return false;)
388   }
389 
390   void set_is_runtime_setup_required() {
391     assert(has_aot_initialized_mirror(), "sanity");
392     CDS_ONLY(_shared_class_flags |= _is_runtime_setup_required;)
393   }
394   bool is_runtime_setup_required() const {
395     CDS_ONLY(return (_shared_class_flags & _is_runtime_setup_required) != 0;)
396     NOT_CDS(return false;)
397   }
398 
399   bool is_shared() const                { // shadows MetaspaceObj::is_shared)()
400     CDS_ONLY(return (_shared_class_flags & _is_shared_class) != 0;)
401     NOT_CDS(return false;)
402   }
403 
404   void set_is_shared() {
405     CDS_ONLY(_shared_class_flags |= _is_shared_class;)
406   }
407 
408   // Obtain the module or package for this class
409   virtual ModuleEntry* module() const = 0;
410   virtual PackageEntry* package() const = 0;
411 
412  protected:                                // internal accessors
413   void     set_subklass(Klass* s);
414   void     set_next_sibling(Klass* s);
415 
416  private:
417   static uint8_t compute_hash_slot(Symbol* s);
418   static void  hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap);
419   static uintx hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite);
420 
421   bool search_secondary_supers(Klass* k) const;
422   bool lookup_secondary_supers_table(Klass *k) const;
423   bool linear_search_secondary_supers(const Klass* k) const;
424   bool fallback_search_secondary_supers(const Klass* k, int index, uintx rotated_bitmap) const;
425 
426  public:
427   // Secondary supers table support
428   static Array<Klass*>* pack_secondary_supers(ClassLoaderData* loader_data,
429                                               GrowableArray<Klass*>* primaries,
430                                               GrowableArray<Klass*>* secondaries,
431                                               uintx& bitmap,
432                                               TRAPS);
433 
434   static uintx   compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers);
435   static uint8_t compute_home_slot(Klass* k, uintx bitmap);
436 
437   static constexpr int SECONDARY_SUPERS_TABLE_SIZE = sizeof(_secondary_supers_bitmap) * 8;
438   static constexpr int SECONDARY_SUPERS_TABLE_MASK = SECONDARY_SUPERS_TABLE_SIZE - 1;
439 
440   static constexpr uintx SECONDARY_SUPERS_BITMAP_EMPTY    = 0;
441   static constexpr uintx SECONDARY_SUPERS_BITMAP_FULL     = ~(uintx)0;
442 
443   // Compiler support
444   static ByteSize super_offset()                 { return byte_offset_of(Klass, _super); }
445   static ByteSize super_check_offset_offset()    { return byte_offset_of(Klass, _super_check_offset); }
446   static ByteSize primary_supers_offset()        { return byte_offset_of(Klass, _primary_supers); }
447   static ByteSize secondary_super_cache_offset() { return byte_offset_of(Klass, _secondary_super_cache); }
448   static ByteSize secondary_supers_offset()      { return byte_offset_of(Klass, _secondary_supers); }
449   static ByteSize java_mirror_offset()           { return byte_offset_of(Klass, _java_mirror); }
450   static ByteSize class_loader_data_offset()     { return byte_offset_of(Klass, _class_loader_data); }
451   static ByteSize modifier_flags_offset()        { return byte_offset_of(Klass, _modifier_flags); }
452   static ByteSize layout_helper_offset()         { return byte_offset_of(Klass, _layout_helper); }
453   static ByteSize access_flags_offset()          { return byte_offset_of(Klass, _access_flags); }
454 #if INCLUDE_JVMCI
455   static ByteSize subklass_offset()              { return byte_offset_of(Klass, _subklass); }
456   static ByteSize next_sibling_offset()          { return byte_offset_of(Klass, _next_sibling); }
457 #endif
458   static ByteSize secondary_supers_bitmap_offset()
459                                                  { return byte_offset_of(Klass, _secondary_supers_bitmap); }
460   static ByteSize hash_slot_offset()             { return byte_offset_of(Klass, _hash_slot); }
461   static ByteSize misc_flags_offset()            { return byte_offset_of(Klass, _misc_flags._flags); }
462 
463   // Unpacking layout_helper:
464   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
465   static const int _lh_instance_slow_path_bit  = 0x01;
466   static const int _lh_log2_element_size_shift = BitsPerByte*0;
467   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
468   static const int _lh_element_type_shift      = BitsPerByte*1;
469   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
470   static const int _lh_header_size_shift       = BitsPerByte*2;
471   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
472   static const int _lh_array_tag_bits          = 2;
473   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
474   static const int _lh_array_tag_obj_value     = ~0x01;   // 0x80000000 >> 30
475 
476   static const unsigned int _lh_array_tag_type_value = 0Xffffffff; // ~0x00,  // 0xC0000000 >> 30
477 
478   static int layout_helper_size_in_bytes(jint lh) {
479     assert(lh > (jint)_lh_neutral_value, "must be instance");
480     return (int) lh & ~_lh_instance_slow_path_bit;
481   }
482   static bool layout_helper_needs_slow_path(jint lh) {
483     assert(lh > (jint)_lh_neutral_value, "must be instance");
484     return (lh & _lh_instance_slow_path_bit) != 0;
485   }
486   static bool layout_helper_is_instance(jint lh) {
487     return (jint)lh > (jint)_lh_neutral_value;
488   }
489   static bool layout_helper_is_array(jint lh) {
490     return (jint)lh < (jint)_lh_neutral_value;
491   }
492   static bool layout_helper_is_typeArray(jint lh) {
493     // _lh_array_tag_type_value == (lh >> _lh_array_tag_shift);
494     return (juint)lh >= (juint)(_lh_array_tag_type_value << _lh_array_tag_shift);
495   }
496   static bool layout_helper_is_objArray(jint lh) {
497     // _lh_array_tag_obj_value == (lh >> _lh_array_tag_shift);
498     return (jint)lh < (jint)(_lh_array_tag_type_value << _lh_array_tag_shift);
499   }
500   static int layout_helper_header_size(jint lh) {
501     assert(lh < (jint)_lh_neutral_value, "must be array");
502     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
503     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
504     return hsize;
505   }
506   static BasicType layout_helper_element_type(jint lh) {
507     assert(lh < (jint)_lh_neutral_value, "must be array");
508     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
509     assert(btvalue >= T_BOOLEAN && btvalue <= T_OBJECT, "sanity");
510     return (BasicType) btvalue;
511   }
512 
513   // Want a pattern to quickly diff against layout header in register
514   // find something less clever!
515   static int layout_helper_boolean_diffbit() {
516     jint zlh = array_layout_helper(T_BOOLEAN);
517     jint blh = array_layout_helper(T_BYTE);
518     assert(zlh != blh, "array layout helpers must differ");
519     int diffbit = 1;
520     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
521       diffbit <<= 1;
522       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
523     }
524     return diffbit;
525   }
526 
527   static int layout_helper_log2_element_size(jint lh) {
528     assert(lh < (jint)_lh_neutral_value, "must be array");
529     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
530     assert(l2esz <= LogBytesPerLong,
531            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
532     return l2esz;
533   }
534   static jint array_layout_helper(jint tag, int hsize, BasicType etype, int log2_esize) {
535     return (tag        << _lh_array_tag_shift)
536       |    (hsize      << _lh_header_size_shift)
537       |    ((int)etype << _lh_element_type_shift)
538       |    (log2_esize << _lh_log2_element_size_shift);
539   }
540   static jint instance_layout_helper(jint size, bool slow_path_flag) {
541     return (size << LogBytesPerWord)
542       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
543   }
544   static int layout_helper_to_size_helper(jint lh) {
545     assert(lh > (jint)_lh_neutral_value, "must be instance");
546     // Note that the following expression discards _lh_instance_slow_path_bit.
547     return lh >> LogBytesPerWord;
548   }
549   // Out-of-line version computes everything based on the etype:
550   static jint array_layout_helper(BasicType etype);
551 
552   // What is the maximum number of primary superclasses any klass can have?
553   static juint primary_super_limit()         { return _primary_super_limit; }
554 
555   // vtables
556   klassVtable vtable() const;
557   int vtable_length() const { return _vtable_len; }
558 
559   // subclass check
560   bool is_subclass_of(const Klass* k) const;
561 
562   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
563   bool is_subtype_of(Klass* k) const;
564 
565 public:
566   // Find LCA in class hierarchy
567   Klass *LCA( Klass *k );
568 
569   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
570   // if not, throw either an Error or an Exception.
571   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
572 
573   // array copying
574   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
575 
576   // tells if the class should be initialized
577   virtual bool should_be_initialized() const    { return false; }
578   // initializes the klass
579   virtual void initialize(TRAPS);
580   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
581   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
582                                          OverpassLookupMode overpass_mode,
583                                          PrivateLookupMode = PrivateLookupMode::find) const;
584  public:
585   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
586     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
587   }
588 
589   // array class with specific rank
590   virtual ArrayKlass* array_klass(int rank, TRAPS) = 0;
591 
592   // array class with this klass as element type
593   virtual ArrayKlass* array_klass(TRAPS) = 0;
594 
595   // These will return null instead of allocating on the heap:
596   virtual ArrayKlass* array_klass_or_null(int rank) = 0;
597   virtual ArrayKlass* array_klass_or_null() = 0;
598 
599   virtual oop protection_domain() const = 0;
600 
601   oop class_loader() const;
602 
603   inline oop klass_holder() const;
604 
605   inline void keep_alive() const;
606 
607  protected:
608 
609   // Error handling when length > max_length or length < 0
610   static void check_array_allocation_length(int length, int max_length, TRAPS);
611 
612   void set_vtable_length(int len) { _vtable_len= len; }
613 
614   vtableEntry* start_of_vtable() const;
615 #if INCLUDE_CDS
616   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
617 #endif
618  public:
619   Method* method_at_vtable(int index);
620 
621   static ByteSize vtable_start_offset();
622   static ByteSize vtable_length_offset() {
623     return byte_offset_of(Klass, _vtable_len);
624   }
625 
626 #if INCLUDE_CDS
627   // CDS support - remove and restore oops from metadata. Oops are not shared.
628   virtual void remove_unshareable_info();
629   virtual void remove_java_mirror();
630 
631   bool is_unshareable_info_restored() const {
632     assert(is_shared(), "use this for shared classes only");
633     if (has_archived_mirror_index()) {
634       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
635       return false;
636     } else if (_java_mirror.is_empty()) {
637       return false;
638     } else {
639       return true;
640     }
641   }
642 #endif // INCLUDE_CDS
643 
644  public:
645   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
646   // These functions describe behavior for the oop not the KLASS.
647 
648   // actual oop size of obj in memory in word size.
649   virtual size_t oop_size(oop obj) const = 0;
650 
651   // Size of klass in word size.
652   virtual int size() const = 0;
653 
654   // Returns the Java name for a class (Resource allocated)
655   // For arrays, this returns the name of the element with a leading '['.
656   // For classes, this returns the name with the package separators
657   //     turned into '.'s.
658   const char* external_name() const;
659   // Returns the name for a class (Resource allocated) as the class
660   // would appear in a signature.
661   // For arrays, this returns the name of the element with a leading '['.
662   // For classes, this returns the name with a leading 'L' and a trailing ';'
663   //     and the package separators as '/'.
664   virtual const char* signature_name() const;
665 
666   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
667   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
668 
669   // Returns "interface", "abstract class" or "class".
670   const char* external_kind() const;
671 
672   // type testing operations
673 #ifdef ASSERT
674  protected:
675   virtual bool is_instance_klass_slow()     const { return false; }
676   virtual bool is_array_klass_slow()        const { return false; }
677   virtual bool is_objArray_klass_slow()     const { return false; }
678   virtual bool is_typeArray_klass_slow()    const { return false; }
679 #endif // ASSERT
680  public:
681 
682   // Fast non-virtual versions
683   #ifndef ASSERT
684   #define assert_same_query(xval, xcheck) xval
685   #else
686  private:
687   static bool assert_same_query(bool xval, bool xslow) {
688     assert(xval == xslow, "slow and fast queries agree");
689     return xval;
690   }
691  public:
692   #endif
693 
694   bool is_instance_klass()              const { return assert_same_query(_kind <= InstanceStackChunkKlassKind, is_instance_klass_slow()); }
695   // Other is anything that is not one of the more specialized kinds of InstanceKlass.
696   bool is_other_instance_klass()        const { return _kind == InstanceKlassKind; }
697   bool is_reference_instance_klass()    const { return _kind == InstanceRefKlassKind; }
698   bool is_mirror_instance_klass()       const { return _kind == InstanceMirrorKlassKind; }
699   bool is_class_loader_instance_klass() const { return _kind == InstanceClassLoaderKlassKind; }
700   bool is_array_klass()                 const { return assert_same_query( _kind >= TypeArrayKlassKind, is_array_klass_slow()); }
701   bool is_stack_chunk_instance_klass()  const { return _kind == InstanceStackChunkKlassKind; }
702   bool is_objArray_klass()              const { return assert_same_query( _kind == ObjArrayKlassKind,  is_objArray_klass_slow()); }
703   bool is_typeArray_klass()             const { return assert_same_query( _kind == TypeArrayKlassKind, is_typeArray_klass_slow()); }
704   #undef assert_same_query
705 
706   // Access flags
707   AccessFlags access_flags() const         { return _access_flags;  }
708   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
709 
710   bool is_public() const                { return _access_flags.is_public(); }
711   bool is_final() const                 { return _access_flags.is_final(); }
712   bool is_interface() const             { return _access_flags.is_interface(); }
713   bool is_abstract() const              { return _access_flags.is_abstract(); }
714   bool is_super() const                 { return _access_flags.is_super(); }
715   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
716   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
717   bool has_finalizer() const            { return _misc_flags.has_finalizer(); }
718   void set_has_finalizer()              { _misc_flags.set_has_finalizer(true); }
719   bool is_hidden() const                { return _misc_flags.is_hidden_class(); }
720   void set_is_hidden()                  { _misc_flags.set_is_hidden_class(true); }
721   bool is_value_based() const           { return _misc_flags.is_value_based_class(); }
722   void set_is_value_based()             { _misc_flags.set_is_value_based_class(true); }
723 
724   klass_flags_t misc_flags() const      { return _misc_flags.value(); }
725 
726   inline bool is_non_strong_hidden() const;
727 
728   bool is_cloneable() const;
729   void set_is_cloneable();
730 
731   inline markWord prototype_header() const;
732   inline void set_prototype_header(markWord header);
733   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
734 
735   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
736 
737   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
738   virtual MetaspaceObj::Type type() const { return ClassType; }
739 
740   inline bool is_loader_alive() const;
741 
742   void clean_subklass();
743 
744   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
745   static void clean_subklass_tree() {
746     clean_weak_klass_links(/*unloading_occurred*/ true , /* clean_alive_klasses */ false);
747   }
748 
749   // Return self, except for abstract classes with exactly 1
750   // implementor.  Then return the 1 concrete implementation.
751   Klass *up_cast_abstract();
752 
753   // klass name
754   Symbol* name() const                   { return _name; }
755   void set_name(Symbol* n);
756 
757   virtual void release_C_heap_structures(bool release_constant_pool = true);
758 
759  public:
760   virtual u2 compute_modifier_flags() const = 0;
761 
762   // JVMTI support
763   virtual jint jvmti_class_status() const;
764 
765   // Printing
766   virtual void print_on(outputStream* st) const;
767 
768   virtual void oop_print_value_on(oop obj, outputStream* st);
769   virtual void oop_print_on      (oop obj, outputStream* st);
770 
771   void print_secondary_supers_on(outputStream* st) const;
772 
773   virtual const char* internal_name() const = 0;
774 
775   // Verification
776   virtual void verify_on(outputStream* st);
777   void verify() { verify_on(tty); }
778 
779 #ifndef PRODUCT
780   bool verify_vtable_index(int index);
781 #endif
782 
783   virtual void oop_verify_on(oop obj, outputStream* st);
784 
785   // for error reporting
786   static bool is_valid(Klass* k);
787 
788   static void on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg);
789 
790   // Returns true if this Klass needs to be addressable via narrow Klass ID.
791   inline bool needs_narrow_id() const;
792 
793 };
794 
795 #endif // SHARE_OOPS_KLASS_HPP