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    {
 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     _in_aot_cache                          = 1 << 0,
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   };
194 #endif
195 
196   int _vtable_len;              // vtable length. This field may be read very often when we
197                                 // have lots of itable dispatches (e.g., lambdas and streams).
198                                 // Keep it away from the beginning of a Klass to avoid cacheline
199                                 // contention that may happen when a nearby object is modified.
200 
201   CDS_JAVA_HEAP_ONLY(int _archived_mirror_index;)
202 
203 public:
204 
205   JFR_ONLY(DEFINE_TRACE_ID_FIELD;)
206 
207 protected:
208 
209   Klass(KlassKind kind, markWord prototype_header = markWord::prototype());
210   Klass();
211 
212  public:
213   int kind() { return _kind; }
214 
215   enum class DefaultsLookupMode { find, skip };
216   enum class OverpassLookupMode { find, skip };
217   enum class StaticLookupMode   { find, skip };
218   enum class PrivateLookupMode  { find, skip };
219 
220   virtual bool is_klass() const { return true; }
221 
222   // super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
223   // to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
224   // If this is not what your code expects, you're probably looking for:
225   // - Klass::java_super() - if you have a Klass*
226   // - InstanceKlass::super() - if you have an InstanceKlass* ik, ik->super() returns InstanceKlass*.
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   // size helper
296   int layout_helper() const            { return _layout_helper; }
297   void set_layout_helper(int lh)       { _layout_helper = lh; }
298 
299   // Note: for instances layout_helper() may include padding.
300   // Use InstanceKlass::contains_field_offset to classify field offsets.
301 
302   // sub/superklass links
303   Klass* subklass(bool log = false) const;
304   Klass* next_sibling(bool log = false) const;
305 
306   void append_to_sibling_list();           // add newly created receiver to superklass' subklass list
307 
308   void set_next_link(Klass* k) { _next_link = k; }
309   Klass* next_link() const { return _next_link; }   // The next klass defined by the class loader.
310   Klass** next_link_addr() { return &_next_link; }
311 
312   // class loader data
313   ClassLoaderData* class_loader_data() const               { return _class_loader_data; }
314   void set_class_loader_data(ClassLoaderData* loader_data) {  _class_loader_data = loader_data; }
315 
316   s2 shared_classpath_index() const   {
317     return _shared_class_path_index;
318   };
319 
320   void set_shared_classpath_index(s2 index) {
321     _shared_class_path_index = index;
322   };
323 
324   bool has_archived_mirror_index() const {
325     CDS_JAVA_HEAP_ONLY(return _archived_mirror_index >= 0;)
326     NOT_CDS_JAVA_HEAP(return false);
327   }
328 
329   void clear_archived_mirror_index() NOT_CDS_JAVA_HEAP_RETURN;
330 
331   void set_lambda_proxy_is_available() {
332     CDS_ONLY(_shared_class_flags |= _archived_lambda_proxy_is_available;)
333   }
334   void clear_lambda_proxy_is_available() {
335     CDS_ONLY(_shared_class_flags &= (u2)(~_archived_lambda_proxy_is_available);)
336   }
337   bool lambda_proxy_is_available() const {
338     CDS_ONLY(return (_shared_class_flags & _archived_lambda_proxy_is_available) != 0;)
339     NOT_CDS(return false;)
340   }
341 
342   void set_has_value_based_class_annotation() {
343     CDS_ONLY(_shared_class_flags |= _has_value_based_class_annotation;)
344   }
345   void clear_has_value_based_class_annotation() {
346     CDS_ONLY(_shared_class_flags &= (u2)(~_has_value_based_class_annotation);)
347   }
348   bool has_value_based_class_annotation() const {
349     CDS_ONLY(return (_shared_class_flags & _has_value_based_class_annotation) != 0;)
350     NOT_CDS(return false;)
351   }
352 
353   void set_verified_at_dump_time() {
354     CDS_ONLY(_shared_class_flags |= _verified_at_dump_time;)
355   }
356   bool verified_at_dump_time() const {
357     CDS_ONLY(return (_shared_class_flags & _verified_at_dump_time) != 0;)
358     NOT_CDS(return false;)
359   }
360 
361   void set_has_archived_enum_objs() {
362     CDS_ONLY(_shared_class_flags |= _has_archived_enum_objs;)
363   }
364   bool has_archived_enum_objs() const {
365     CDS_ONLY(return (_shared_class_flags & _has_archived_enum_objs) != 0;)
366     NOT_CDS(return false;)
367   }
368 
369   void set_is_generated_shared_class() {
370     CDS_ONLY(_shared_class_flags |= _is_generated_shared_class;)
371   }
372   bool is_generated_shared_class() const {
373     CDS_ONLY(return (_shared_class_flags & _is_generated_shared_class) != 0;)
374     NOT_CDS(return false;)
375   }
376 
377   void set_has_aot_initialized_mirror() {
378     CDS_ONLY(_shared_class_flags |= _has_aot_initialized_mirror;)
379   }
380   bool has_aot_initialized_mirror() const {
381     CDS_ONLY(return (_shared_class_flags & _has_aot_initialized_mirror) != 0;)
382     NOT_CDS(return false;)
383   }
384 
385   bool in_aot_cache() const                { // shadows MetaspaceObj::in_aot_cache)()
386     CDS_ONLY(return (_shared_class_flags & _in_aot_cache) != 0;)
387     NOT_CDS(return false;)
388   }
389 
390   void set_in_aot_cache() {
391     CDS_ONLY(_shared_class_flags |= _in_aot_cache;)
392   }
393 
394   // Obtain the module or package for this class
395   virtual ModuleEntry* module() const = 0;
396   virtual PackageEntry* package() const = 0;
397 
398  protected:                                // internal accessors
399   void     set_subklass(Klass* s);
400   void     set_next_sibling(Klass* s);
401 
402  private:
403   static uint8_t compute_hash_slot(Symbol* s);
404   static void  hash_insert(Klass* klass, GrowableArray<Klass*>* secondaries, uintx& bitmap);
405   static uintx hash_secondary_supers(Array<Klass*>* secondaries, bool rewrite);
406 
407   bool search_secondary_supers(Klass* k) const;
408   bool lookup_secondary_supers_table(Klass *k) const;
409   bool linear_search_secondary_supers(const Klass* k) const;
410   bool fallback_search_secondary_supers(const Klass* k, int index, uintx rotated_bitmap) const;
411 
412  public:
413   // Secondary supers table support
414   static Array<Klass*>* pack_secondary_supers(ClassLoaderData* loader_data,
415                                               GrowableArray<Klass*>* primaries,
416                                               GrowableArray<Klass*>* secondaries,
417                                               uintx& bitmap,
418                                               TRAPS);
419 
420   static uintx   compute_secondary_supers_bitmap(Array<Klass*>* secondary_supers);
421   static uint8_t compute_home_slot(Klass* k, uintx bitmap);
422 
423   static constexpr int SECONDARY_SUPERS_TABLE_SIZE = sizeof(_secondary_supers_bitmap) * 8;
424   static constexpr int SECONDARY_SUPERS_TABLE_MASK = SECONDARY_SUPERS_TABLE_SIZE - 1;
425 
426   static constexpr uintx SECONDARY_SUPERS_BITMAP_EMPTY    = 0;
427   static constexpr uintx SECONDARY_SUPERS_BITMAP_FULL     = ~(uintx)0;
428 
429   // Compiler support
430   static ByteSize super_offset()                 { return byte_offset_of(Klass, _super); }
431   static ByteSize super_check_offset_offset()    { return byte_offset_of(Klass, _super_check_offset); }
432   static ByteSize primary_supers_offset()        { return byte_offset_of(Klass, _primary_supers); }
433   static ByteSize secondary_super_cache_offset() { return byte_offset_of(Klass, _secondary_super_cache); }
434   static ByteSize secondary_supers_offset()      { return byte_offset_of(Klass, _secondary_supers); }
435   static ByteSize java_mirror_offset()           { return byte_offset_of(Klass, _java_mirror); }
436   static ByteSize class_loader_data_offset()     { return byte_offset_of(Klass, _class_loader_data); }
437   static ByteSize layout_helper_offset()         { return byte_offset_of(Klass, _layout_helper); }
438   static ByteSize access_flags_offset()          { return byte_offset_of(Klass, _access_flags); }
439 #if INCLUDE_JVMCI
440   static ByteSize subklass_offset()              { return byte_offset_of(Klass, _subklass); }
441   static ByteSize next_sibling_offset()          { return byte_offset_of(Klass, _next_sibling); }
442 #endif
443   static ByteSize secondary_supers_bitmap_offset()
444                                                  { return byte_offset_of(Klass, _secondary_supers_bitmap); }
445   static ByteSize hash_slot_offset()             { return byte_offset_of(Klass, _hash_slot); }
446   static ByteSize misc_flags_offset()            { return byte_offset_of(Klass, _misc_flags._flags); }
447 
448   // Unpacking layout_helper:
449   static const int _lh_neutral_value           = 0;  // neutral non-array non-instance value
450   static const int _lh_instance_slow_path_bit  = 0x01;
451   static const int _lh_log2_element_size_shift = BitsPerByte*0;
452   static const int _lh_log2_element_size_mask  = BitsPerLong-1;
453   static const int _lh_element_type_shift      = BitsPerByte*1;
454   static const int _lh_element_type_mask       = right_n_bits(BitsPerByte);  // shifted mask
455   static const int _lh_header_size_shift       = BitsPerByte*2;
456   static const int _lh_header_size_mask        = right_n_bits(BitsPerByte);  // shifted mask
457   static const int _lh_array_tag_bits          = 4;
458   static const int _lh_array_tag_shift         = BitsPerInt - _lh_array_tag_bits;
459 
460   static const unsigned int _lh_array_tag_type_value = 0Xfffffffc;
461   static const unsigned int _lh_array_tag_flat_value = 0Xfffffffa;
462   static const unsigned int _lh_array_tag_ref_value  = 0Xfffffff8;
463 
464   // null-free array flag bit under the array tag bits, shift one more to get array tag value
465   static const int _lh_null_free_shift = _lh_array_tag_shift - 1;
466   static const int _lh_null_free_mask  = 1;
467 
468   static const jint _lh_array_tag_flat_value_bit_inplace = (jint) (1 << (_lh_array_tag_shift + 1));
469 
470   static int layout_helper_size_in_bytes(jint lh) {
471     assert(lh > (jint)_lh_neutral_value, "must be instance");
472     return (int) lh & ~_lh_instance_slow_path_bit;
473   }
474   static bool layout_helper_needs_slow_path(jint lh) {
475     assert(lh > (jint)_lh_neutral_value, "must be instance");
476     return (lh & _lh_instance_slow_path_bit) != 0;
477   }
478   static bool layout_helper_is_instance(jint lh) {
479     return (jint)lh > (jint)_lh_neutral_value;
480   }
481   static bool layout_helper_is_array(jint lh) {
482     return (jint)lh < (jint)_lh_neutral_value;
483   }
484   static bool layout_helper_is_typeArray(jint lh) {
485     return (juint) _lh_array_tag_type_value == (juint)(lh >> _lh_array_tag_shift);
486   }
487   static bool layout_helper_is_refArray(jint lh) {
488     return (juint)_lh_array_tag_ref_value == (juint)(lh >> _lh_array_tag_shift);
489   }
490   static bool layout_helper_is_flatArray(jint lh) {
491     return (juint)_lh_array_tag_flat_value == (juint)(lh >> _lh_array_tag_shift);
492   }
493   static bool layout_helper_is_null_free(jint lh) {
494     assert(layout_helper_is_flatArray(lh) || layout_helper_is_refArray(lh), "must be array of inline types");
495     return ((lh >> _lh_null_free_shift) & _lh_null_free_mask);
496   }
497   static jint layout_helper_set_null_free(jint lh) {
498     lh |= (_lh_null_free_mask << _lh_null_free_shift);
499     assert(layout_helper_is_null_free(lh), "Bad encoding");
500     return lh;
501   }
502   static int layout_helper_header_size(jint lh) {
503     assert(lh < (jint)_lh_neutral_value, "must be array");
504     int hsize = (lh >> _lh_header_size_shift) & _lh_header_size_mask;
505     assert(hsize > 0 && hsize < (int)sizeof(oopDesc)*3, "sanity");
506     return hsize;
507   }
508   static BasicType layout_helper_element_type(jint lh) {
509     assert(lh < (jint)_lh_neutral_value, "must be array");
510     int btvalue = (lh >> _lh_element_type_shift) & _lh_element_type_mask;
511     assert((btvalue >= T_BOOLEAN && btvalue <= T_OBJECT) || btvalue == T_FLAT_ELEMENT, "sanity");
512     return (BasicType) btvalue;
513   }
514 
515   // Want a pattern to quickly diff against layout header in register
516   // find something less clever!
517   static int layout_helper_boolean_diffbit() {
518     jint zlh = array_layout_helper(T_BOOLEAN);
519     jint blh = array_layout_helper(T_BYTE);
520     assert(zlh != blh, "array layout helpers must differ");
521     int diffbit = 1;
522     while ((diffbit & (zlh ^ blh)) == 0 && (diffbit & zlh) == 0) {
523       diffbit <<= 1;
524       assert(diffbit != 0, "make sure T_BOOLEAN has a different bit than T_BYTE");
525     }
526     return diffbit;
527   }
528 
529   static int layout_helper_log2_element_size(jint lh) {
530     assert(lh < (jint)_lh_neutral_value, "must be array");
531     int l2esz = (lh >> _lh_log2_element_size_shift) & _lh_log2_element_size_mask;
532     assert(layout_helper_element_type(lh) == T_FLAT_ELEMENT || l2esz <= LogBytesPerLong,
533            "sanity. l2esz: 0x%x for lh: 0x%x", (uint)l2esz, (uint)lh);
534     return l2esz;
535   }
536   static jint array_layout_helper(jint tag, bool null_free, int hsize, BasicType etype, int log2_esize) {
537     return (tag        << _lh_array_tag_shift)
538       |    ((null_free ? 1 : 0) <<  _lh_null_free_shift)
539       |    (hsize      << _lh_header_size_shift)
540       |    ((int)etype << _lh_element_type_shift)
541       |    (log2_esize << _lh_log2_element_size_shift);
542   }
543   static jint instance_layout_helper(jint size, bool slow_path_flag) {
544     return (size << LogBytesPerWord)
545       |    (slow_path_flag ? _lh_instance_slow_path_bit : 0);
546   }
547   static int layout_helper_to_size_helper(jint lh) {
548     assert(lh > (jint)_lh_neutral_value, "must be instance");
549     // Note that the following expression discards _lh_instance_slow_path_bit.
550     return lh >> LogBytesPerWord;
551   }
552   // Out-of-line version computes everything based on the etype:
553   static jint array_layout_helper(BasicType etype);
554 
555   // What is the maximum number of primary superclasses any klass can have?
556   static juint primary_super_limit()         { return _primary_super_limit; }
557 
558   // vtables
559   klassVtable vtable() const;
560   int vtable_length() const { return _vtable_len; }
561 
562   // subclass check
563   bool is_subclass_of(const Klass* k) const;
564 
565   // subtype check: true if is_subclass_of, or if k is interface and receiver implements it
566   bool is_subtype_of(Klass* k) const;
567 
568 public:
569   // Find LCA in class hierarchy
570   Klass *LCA( Klass *k );
571 
572   // Check whether reflection/jni/jvm code is allowed to instantiate this class;
573   // if not, throw either an Error or an Exception.
574   virtual void check_valid_for_instantiation(bool throwError, TRAPS);
575 
576   // array copying
577   virtual void  copy_array(arrayOop s, int src_pos, arrayOop d, int dst_pos, int length, TRAPS);
578 
579   // tells if the class should be initialized
580   virtual bool should_be_initialized() const    { return false; }
581   // initializes the klass
582   virtual void initialize(TRAPS);
583   virtual Klass* find_field(Symbol* name, Symbol* signature, fieldDescriptor* fd) const;
584   virtual Method* uncached_lookup_method(const Symbol* name, const Symbol* signature,
585                                          OverpassLookupMode overpass_mode,
586                                          PrivateLookupMode = PrivateLookupMode::find) const;
587  public:
588   Method* lookup_method(const Symbol* name, const Symbol* signature) const {
589     return uncached_lookup_method(name, signature, OverpassLookupMode::find);
590   }
591 
592   // array class with specific rank
593   virtual ArrayKlass* array_klass(int rank, TRAPS) = 0;
594 
595   // array class with this klass as element type
596   virtual ArrayKlass* array_klass(TRAPS) = 0;
597 
598   // These will return null instead of allocating on the heap:
599   virtual ArrayKlass* array_klass_or_null(int rank) = 0;
600   virtual ArrayKlass* array_klass_or_null() = 0;
601 
602   virtual oop protection_domain() const = 0;
603 
604   oop class_loader() const;
605 
606   inline oop klass_holder() const;
607 
608   inline void keep_alive() const;
609 
610  protected:
611 
612   // Error handling when length > max_length or length < 0
613   static void check_array_allocation_length(int length, int max_length, TRAPS);
614 
615   void set_vtable_length(int len) { _vtable_len= len; }
616 
617   vtableEntry* start_of_vtable() const;
618 #if INCLUDE_CDS
619   void restore_unshareable_info(ClassLoaderData* loader_data, Handle protection_domain, TRAPS);
620 #endif
621  public:
622   Method* method_at_vtable(int index);
623 
624   static ByteSize vtable_start_offset();
625   static ByteSize vtable_length_offset() {
626     return byte_offset_of(Klass, _vtable_len);
627   }
628 
629 #if INCLUDE_CDS
630   // CDS support - remove and restore oops from metadata. Oops are not shared.
631   virtual void remove_unshareable_info();
632   virtual void remove_java_mirror();
633 
634   bool is_unshareable_info_restored() const {
635     assert(in_aot_cache(), "use this for shared classes only");
636     if (has_archived_mirror_index()) {
637       // _java_mirror is not a valid OopHandle but rather an encoded reference in the shared heap
638       return false;
639     } else if (_java_mirror.is_empty()) {
640       return false;
641     } else {
642       return true;
643     }
644   }
645 #endif // INCLUDE_CDS
646 
647  public:
648   // ALL FUNCTIONS BELOW THIS POINT ARE DISPATCHED FROM AN OOP
649   // These functions describe behavior for the oop not the KLASS.
650 
651   // actual oop size of obj in memory in word size.
652   virtual size_t oop_size(oop obj) const = 0;
653 
654   // Size of klass in word size.
655   virtual int size() const = 0;
656 
657   // Returns the Java name for a class (Resource allocated)
658   // For arrays, this returns the name of the element with a leading '['.
659   // For classes, this returns the name with the package separators
660   //     turned into '.'s.
661   const char* external_name() const;
662   // Returns the name for a class (Resource allocated) as the class
663   // would appear in a signature.
664   // For arrays, this returns the name of the element with a leading '['.
665   // For classes, this returns the name with a leading 'L' and a trailing ';'
666   //     and the package separators as '/'.
667   virtual const char* signature_name() const;
668 
669   const char* joint_in_module_of_loader(const Klass* class2, bool include_parent_loader = false) const;
670   const char* class_in_module_of_loader(bool use_are = false, bool include_parent_loader = false) const;
671 
672   // Returns "interface", "abstract class" or "class".
673   const char* external_kind() const;
674 
675   // type testing operations
676 #ifdef ASSERT
677  protected:
678   virtual bool is_instance_klass_slow()     const { return false; }
679   virtual bool is_array_klass_slow()        const { return false; }
680   virtual bool is_objArray_klass_slow()     const { return false; }
681   virtual bool is_refArray_klass_slow()     const { return false; }
682   virtual bool is_typeArray_klass_slow()    const { return false; }
683   virtual bool is_flatArray_klass_slow()    const { return false; }
684 #endif // ASSERT
685   // current implementation uses this method even in non debug builds
686   virtual bool is_inline_klass_slow()       const { return false; }
687  public:
688 
689   // Fast non-virtual versions
690   #ifndef ASSERT
691   #define assert_same_query(xval, xcheck) xval
692   #else
693  private:
694   static bool assert_same_query(bool xval, bool xslow) {
695     assert(xval == xslow, "slow and fast queries agree");
696     return xval;
697   }
698  public:
699   #endif
700 
701   bool is_instance_klass()              const { return assert_same_query(_kind <= InstanceStackChunkKlassKind, is_instance_klass_slow()); }
702   bool is_inline_klass()                const { return assert_same_query(_kind == InlineKlassKind, is_inline_klass_slow()); }
703   bool is_reference_instance_klass()    const { return _kind == InstanceRefKlassKind; }
704   bool is_mirror_instance_klass()       const { return _kind == InstanceMirrorKlassKind; }
705   bool is_class_loader_instance_klass() const { return _kind == InstanceClassLoaderKlassKind; }
706   bool is_array_klass()                 const { return assert_same_query( _kind >= TypeArrayKlassKind, is_array_klass_slow()); }
707   bool is_stack_chunk_instance_klass()  const { return _kind == InstanceStackChunkKlassKind; }
708   bool is_flatArray_klass()             const { return assert_same_query( _kind == FlatArrayKlassKind, is_flatArray_klass_slow()); }
709   bool is_objArray_klass()              const { return assert_same_query( _kind == ObjArrayKlassKind || _kind == RefArrayKlassKind || _kind == FlatArrayKlassKind,  is_objArray_klass_slow()); }
710   bool is_refArray_klass()              const { return assert_same_query( _kind == RefArrayKlassKind, is_refArray_klass_slow()); }
711   bool is_typeArray_klass()             const { return assert_same_query( _kind == TypeArrayKlassKind, is_typeArray_klass_slow()); }
712   bool is_refined_objArray_klass()      const { return is_refArray_klass() || is_flatArray_klass(); }
713   #undef assert_same_query
714 
715   inline bool is_null_free_array_klass() const { return !is_typeArray_klass() && layout_helper_is_null_free(layout_helper()); }
716 
717   // Access flags
718   AccessFlags access_flags() const         { return _access_flags;  }
719   void set_access_flags(AccessFlags flags) { _access_flags = flags; }
720 
721   bool is_public() const                { return _access_flags.is_public(); }
722   bool is_final() const                 { return _access_flags.is_final(); }
723   bool is_interface() const             { return _access_flags.is_interface(); }
724   bool is_abstract() const              { return _access_flags.is_abstract(); }
725   bool is_synthetic() const             { return _access_flags.is_synthetic(); }
726   bool is_identity_class() const        { assert(is_instance_klass(), "only for instanceKlass"); return _access_flags.is_identity_class(); }
727   void set_is_synthetic()               { _access_flags.set_is_synthetic(); }
728   bool has_finalizer() const            { return _misc_flags.has_finalizer(); }
729   void set_has_finalizer()              { _misc_flags.set_has_finalizer(true); }
730   bool is_hidden() const                { return _misc_flags.is_hidden_class(); }
731   void set_is_hidden()                  { _misc_flags.set_is_hidden_class(true); }
732   bool is_value_based() const           { return _misc_flags.is_value_based_class(); }
733   void set_is_value_based()             { _misc_flags.set_is_value_based_class(true); }
734 
735   klass_flags_t misc_flags() const      { return _misc_flags.value(); }
736 
737   inline bool is_non_strong_hidden() const;
738 
739   bool is_cloneable() const;
740   void set_is_cloneable();
741 
742   static inline markWord make_prototype_header(const Klass* kls, markWord prototype = markWord::prototype());
743   inline markWord prototype_header() const;
744   inline void set_prototype_header(markWord header);
745   static ByteSize prototype_header_offset() { return in_ByteSize(offset_of(Klass, _prototype_header)); }
746   inline void set_prototype_header_klass(narrowKlass klass);
747 
748   JFR_ONLY(DEFINE_TRACE_ID_METHODS;)
749 
750   virtual void metaspace_pointers_do(MetaspaceClosure* iter);
751   virtual MetaspaceObj::Type type() const { return ClassType; }
752 
753   inline bool is_loader_alive() const;
754   inline bool is_loader_present_and_alive() const;
755 
756   void clean_subklass();
757 
758   // Clean out unnecessary weak klass links from the whole klass hierarchy.
759   static void clean_weak_klass_links(bool unloading_occurred, bool clean_alive_klasses = true);
760   // Clean out unnecessary weak klass links from the given InstanceKlass.
761   static void clean_weak_instanceklass_links(InstanceKlass* ik);
762 
763   // Return self, except for abstract classes with exactly 1
764   // implementor.  Then return the 1 concrete implementation.
765   Klass *up_cast_abstract();
766 
767   // klass name
768   Symbol* name() const                   { return _name; }
769   void set_name(Symbol* n);
770 
771   virtual void release_C_heap_structures(bool release_constant_pool = true);
772 
773  public:
774   // Get modifier flags from Java mirror cache.
775   int modifier_flags() const;
776 
777   // Compute modifier flags from the original data. This also allows
778   // accessing flags when Java mirror is already dead, e.g. during class
779   // unloading.
780   virtual u2 compute_modifier_flags() const = 0;
781 
782   // JVMTI support
783   virtual jint jvmti_class_status() const;
784 
785   // Printing
786   virtual void print_on(outputStream* st) const;
787 
788   virtual void oop_print_value_on(oop obj, outputStream* st);
789   virtual void oop_print_on      (oop obj, outputStream* st);
790 
791   void print_secondary_supers_on(outputStream* st) const;
792 
793   virtual const char* internal_name() const = 0;
794 
795   // Verification
796   virtual void verify_on(outputStream* st);
797   void verify() { verify_on(tty); }
798 
799 #ifndef PRODUCT
800   bool verify_vtable_index(int index);
801 #endif
802 
803   virtual void oop_verify_on(oop obj, outputStream* st);
804 
805   // for error reporting
806   static bool is_valid(Klass* k);
807 
808   static void on_secondary_supers_verification_failure(Klass* super, Klass* sub, bool linear_result, bool table_result, const char* msg);
809 
810   // Returns true if this Klass needs to be addressable via narrow Klass ID.
811   inline bool needs_narrow_id() const;
812 
813 };
814 
815 #endif // SHARE_OOPS_KLASS_HPP