1 /*
  2  * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
  3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  4  *
  5  * This code is free software; you can redistribute it and/or modify it
  6  * under the terms of the GNU General Public License version 2 only, as
  7  * published by the Free Software Foundation.
  8  *
  9  * This code is distributed in the hope that it will be useful, but WITHOUT
 10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 12  * version 2 for more details (a copy is included in the LICENSE file that
 13  * accompanied this code).
 14  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 18  *
 19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 20  * or visit www.oracle.com if you need additional information or have any
 21  * questions.
 22  *
 23  */
 24 
 25 #include "precompiled.hpp"
 26 #include "classfile/moduleEntry.hpp"
 27 #include "classfile/packageEntry.hpp"
 28 #include "classfile/symbolTable.hpp"
 29 #include "classfile/vmClasses.hpp"
 30 #include "classfile/vmSymbols.hpp"
 31 #include "gc/shared/collectedHeap.inline.hpp"
 32 #include "memory/iterator.inline.hpp"
 33 #include "memory/metadataFactory.hpp"
 34 #include "memory/metaspaceClosure.hpp"
 35 #include "memory/oopFactory.hpp"
 36 #include "memory/resourceArea.hpp"
 37 #include "memory/universe.hpp"
 38 #include "oops/arrayKlass.inline.hpp"
 39 #include "oops/instanceKlass.hpp"
 40 #include "oops/klass.inline.hpp"
 41 #include "oops/objArrayKlass.inline.hpp"
 42 #include "oops/objArrayOop.inline.hpp"
 43 #include "oops/oop.inline.hpp"
 44 #include "oops/symbol.hpp"
 45 #include "runtime/handles.inline.hpp"
 46 #include "runtime/mutexLocker.hpp"
 47 #include "utilities/macros.hpp"
 48 
 49 ObjArrayKlass* ObjArrayKlass::allocate(ClassLoaderData* loader_data, int n,
 50                                        Klass* k, Symbol* name, bool null_free,
 51                                        TRAPS) {
 52   assert(ObjArrayKlass::header_size() <= InstanceKlass::header_size(),
 53       "array klasses must be same size as InstanceKlass");
 54 
 55   int size = ArrayKlass::static_size(ObjArrayKlass::header_size());
 56 
 57   return new (loader_data, size, THREAD) ObjArrayKlass(n, k, name, null_free);
 58 }
 59 
 60 ObjArrayKlass* ObjArrayKlass::allocate_objArray_klass(ClassLoaderData* loader_data,
 61                                                       int n, Klass* element_klass,
 62                                                       bool null_free, bool qdesc, TRAPS) {
 63   assert(!null_free || (n == 1 && element_klass->is_inline_klass() && qdesc), "null-free unsupported");
 64 
 65   // Eagerly allocate the direct array supertype.
 66   Klass* super_klass = NULL;
 67   if (!Universe::is_bootstrapping() || vmClasses::Object_klass_loaded()) {
 68     Klass* element_super = element_klass->super();
 69     if (element_super != NULL) {
 70       // The element type has a direct super.  E.g., String[] has direct super of Object[].
 71       if (null_free) {
 72         super_klass = element_klass->array_klass_or_null();
 73       } else {
 74         super_klass = element_super->array_klass_or_null();
 75       }
 76       bool supers_exist = super_klass != NULL;
 77       // Also, see if the element has secondary supertypes.
 78       // We need an array type for each.
 79       const Array<Klass*>* element_supers = element_klass->secondary_supers();
 80       for( int i = element_supers->length()-1; i >= 0; i-- ) {
 81         Klass* elem_super = element_supers->at(i);
 82         if (elem_super->array_klass_or_null() == NULL) {
 83           supers_exist = false;
 84           break;
 85         }
 86       }
 87       if (null_free) {
 88         if (element_klass->array_klass_or_null() == NULL) {
 89           supers_exist = false;
 90         }
 91       }
 92       if (!supers_exist) {
 93         // Oops.  Not allocated yet.  Back out, allocate it, and retry.
 94         Klass* ek = NULL;
 95         {
 96           MutexUnlocker mu(MultiArray_lock);
 97           if (null_free) {
 98             element_klass->array_klass(CHECK_NULL);
 99           } else {
100             element_super->array_klass(CHECK_NULL);
101           }
102           for( int i = element_supers->length()-1; i >= 0; i-- ) {
103             Klass* elem_super = element_supers->at(i);
104             elem_super->array_klass(CHECK_NULL);
105           }
106           // Now retry from the beginning
107           if (null_free) {
108             ek = InlineKlass::cast(element_klass)->null_free_inline_array_klass(CHECK_NULL);
109           } else {
110             ek = element_klass->array_klass(n, CHECK_NULL);
111           }
112         }  // re-lock
113         return ObjArrayKlass::cast(ek);
114       }
115     } else {
116       // The element type is already Object.  Object[] has direct super of Object.
117       super_klass = vmClasses::Object_klass();
118     }
119   }
120 
121   // Create type name for klass.
122   Symbol* name = ArrayKlass::create_element_klass_array_name(element_klass, qdesc, CHECK_NULL);
123 
124   // Initialize instance variables
125   ObjArrayKlass* oak = ObjArrayKlass::allocate(loader_data, n, element_klass, name, null_free, CHECK_NULL);
126 
127   ModuleEntry* module = oak->module();
128   assert(module != NULL, "No module entry for array");
129 
130   // Call complete_create_array_klass after all instance variables has been initialized.
131   ArrayKlass::complete_create_array_klass(oak, super_klass, module, CHECK_NULL);
132 
133   // Add all classes to our internal class loader list here,
134   // including classes in the bootstrap (NULL) class loader.
135   // Do this step after creating the mirror so that if the
136   // mirror creation fails, loaded_classes_do() doesn't find
137   // an array class without a mirror.
138   loader_data->add_class(oak);
139 
140   return oak;
141 }
142 
143 ObjArrayKlass::ObjArrayKlass(int n, Klass* element_klass, Symbol* name, bool null_free) : ArrayKlass(name, ID) {
144   set_dimension(n);
145   set_element_klass(element_klass);
146 
147   assert(!null_free || name->is_Q_array_signature(), "sanity check");
148 
149   Klass* bk;
150   if (element_klass->is_objArray_klass()) {
151     bk = ObjArrayKlass::cast(element_klass)->bottom_klass();
152   } else if (element_klass->is_flatArray_klass()) {
153     bk = FlatArrayKlass::cast(element_klass)->element_klass();
154   } else {
155     bk = element_klass;
156   }
157   assert(bk != NULL && (bk->is_instance_klass() || bk->is_typeArray_klass()), "invalid bottom klass");
158   set_bottom_klass(bk);
159   set_class_loader_data(bk->class_loader_data());
160 
161   int lh = array_layout_helper(T_OBJECT);
162   if (null_free) {
163     assert(n == 1, "Bytecode does not support null-free multi-dim");
164     lh = layout_helper_set_null_free(lh);
165 #ifdef _LP64
166     set_prototype_header(markWord::null_free_array_prototype());
167     assert(prototype_header().is_null_free_array(), "sanity");
168 #else
169     set_prototype_header(markWord::inline_type_prototype());
170 #endif
171   }
172   set_layout_helper(lh);
173   assert(is_array_klass(), "sanity");
174   assert(is_objArray_klass(), "sanity");
175 }
176 
177 int ObjArrayKlass::oop_size(oop obj) const {
178   assert(obj->is_objArray(), "must be object array");
179   return objArrayOop(obj)->object_size();
180 }
181 
182 objArrayOop ObjArrayKlass::allocate(int length, TRAPS) {
183   check_array_allocation_length(length, arrayOopDesc::max_array_length(T_OBJECT), CHECK_NULL);
184   int size = objArrayOopDesc::object_size(length);
185   bool populate_null_free = is_null_free_array_klass();
186   objArrayOop array =  (objArrayOop)Universe::heap()->array_allocate(this, size, length,
187                                                        /* do_zero */ true, THREAD);
188   if (populate_null_free) {
189     assert(dimension() == 1, "Can only populate the final dimension");
190     assert(element_klass()->is_inline_klass(), "Unexpected");
191     assert(!element_klass()->is_array_klass(), "ArrayKlass unexpected here");
192     assert(!InlineKlass::cast(element_klass())->flatten_array(), "Expected flatArrayOop allocation");
193     element_klass()->initialize(CHECK_NULL);
194     // Populate default values...
195     objArrayHandle array_h(THREAD, array);
196     instanceOop value = (instanceOop) InlineKlass::cast(element_klass())->default_value();
197     for (int i = 0; i < length; i++) {
198       array_h->obj_at_put(i, value);
199     }
200   }
201   return array;
202 }
203 
204 oop ObjArrayKlass::multi_allocate(int rank, jint* sizes, TRAPS) {
205   int length = *sizes;
206   if (rank == 1) { // last dim may be flatArray, check if we have any special storage requirements
207     if (name()->char_at(1) != JVM_SIGNATURE_ARRAY &&  name()->is_Q_array_signature()) {
208       return oopFactory::new_flatArray(element_klass(), length, CHECK_NULL);
209     } else {
210       return oopFactory::new_objArray(element_klass(), length, CHECK_NULL);
211     }
212   }
213   guarantee(rank > 1, "Rank below 1");
214   // Call to lower_dimension uses this pointer, so most be called before a
215   // possible GC
216   Klass* ld_klass = lower_dimension();
217   // If length < 0 allocate will throw an exception.
218   objArrayOop array = allocate(length, CHECK_NULL);
219   objArrayHandle h_array (THREAD, array);
220   if (length != 0) {
221     for (int index = 0; index < length; index++) {
222       ArrayKlass* ak = ArrayKlass::cast(ld_klass);
223       oop sub_array = ak->multi_allocate(rank-1, &sizes[1], CHECK_NULL);
224       h_array->obj_at_put(index, sub_array);
225     }
226   } else {
227     // Since this array dimension has zero length, nothing will be
228     // allocated, however the lower dimension values must be checked
229     // for illegal values.
230     for (int i = 0; i < rank - 1; ++i) {
231       sizes += 1;
232       if (*sizes < 0) {
233         THROW_MSG_0(vmSymbols::java_lang_NegativeArraySizeException(), err_msg("%d", *sizes));
234       }
235     }
236   }
237   return h_array();
238 }
239 
240 // Either oop or narrowOop depending on UseCompressedOops.
241 void ObjArrayKlass::do_copy(arrayOop s, size_t src_offset,
242                             arrayOop d, size_t dst_offset, int length, TRAPS) {
243   if (s == d) {
244     // since source and destination are equal we do not need conversion checks.
245     assert(length > 0, "sanity check");
246     ArrayAccess<>::oop_arraycopy(s, src_offset, d, dst_offset, length);
247   } else {
248     // We have to make sure all elements conform to the destination array
249     Klass* bound = ObjArrayKlass::cast(d->klass())->element_klass();
250     Klass* stype = ObjArrayKlass::cast(s->klass())->element_klass();
251     // Perform null check if dst is null-free but src has no such guarantee
252     bool null_check = ((!s->klass()->is_null_free_array_klass()) &&
253         d->klass()->is_null_free_array_klass());
254     if (stype == bound || stype->is_subtype_of(bound)) {
255       if (null_check) {
256         ArrayAccess<ARRAYCOPY_DISJOINT | ARRAYCOPY_NOTNULL>::oop_arraycopy(s, src_offset, d, dst_offset, length);
257       } else {
258         ArrayAccess<ARRAYCOPY_DISJOINT>::oop_arraycopy(s, src_offset, d, dst_offset, length);
259       }
260     } else {
261       if (null_check) {
262         ArrayAccess<ARRAYCOPY_DISJOINT | ARRAYCOPY_CHECKCAST | ARRAYCOPY_NOTNULL>::oop_arraycopy(s, src_offset, d, dst_offset, length);
263       } else {
264         ArrayAccess<ARRAYCOPY_DISJOINT | ARRAYCOPY_CHECKCAST>::oop_arraycopy(s, src_offset, d, dst_offset, length);
265       }
266     }
267   }
268 }
269 
270 void ObjArrayKlass::copy_array(arrayOop s, int src_pos, arrayOop d,
271                                int dst_pos, int length, TRAPS) {
272   assert(s->is_objArray(), "must be obj array");
273 
274   if (EnableValhalla) {
275     if (d->is_flatArray()) {
276       FlatArrayKlass::cast(d->klass())->copy_array(s, src_pos, d, dst_pos, length, THREAD);
277       return;
278     }
279   }
280 
281   if (!d->is_objArray()) {
282     ResourceMark rm(THREAD);
283     stringStream ss;
284     if (d->is_typeArray()) {
285       ss.print("arraycopy: type mismatch: can not copy object array[] into %s[]",
286                type2name_tab[ArrayKlass::cast(d->klass())->element_type()]);
287     } else {
288       ss.print("arraycopy: destination type %s is not an array", d->klass()->external_name());
289     }
290     THROW_MSG(vmSymbols::java_lang_ArrayStoreException(), ss.as_string());
291   }
292 
293   // Check is all offsets and lengths are non negative
294   if (src_pos < 0 || dst_pos < 0 || length < 0) {
295     // Pass specific exception reason.
296     ResourceMark rm(THREAD);
297     stringStream ss;
298     if (src_pos < 0) {
299       ss.print("arraycopy: source index %d out of bounds for object array[%d]",
300                src_pos, s->length());
301     } else if (dst_pos < 0) {
302       ss.print("arraycopy: destination index %d out of bounds for object array[%d]",
303                dst_pos, d->length());
304     } else {
305       ss.print("arraycopy: length %d is negative", length);
306     }
307     THROW_MSG(vmSymbols::java_lang_ArrayIndexOutOfBoundsException(), ss.as_string());
308   }
309   // Check if the ranges are valid
310   if ((((unsigned int) length + (unsigned int) src_pos) > (unsigned int) s->length()) ||
311       (((unsigned int) length + (unsigned int) dst_pos) > (unsigned int) d->length())) {
312     // Pass specific exception reason.
313     ResourceMark rm(THREAD);
314     stringStream ss;
315     if (((unsigned int) length + (unsigned int) src_pos) > (unsigned int) s->length()) {
316       ss.print("arraycopy: last source index %u out of bounds for object array[%d]",
317                (unsigned int) length + (unsigned int) src_pos, s->length());
318     } else {
319       ss.print("arraycopy: last destination index %u out of bounds for object array[%d]",
320                (unsigned int) length + (unsigned int) dst_pos, d->length());
321     }
322     THROW_MSG(vmSymbols::java_lang_ArrayIndexOutOfBoundsException(), ss.as_string());
323   }
324 
325   // Special case. Boundary cases must be checked first
326   // This allows the following call: copy_array(s, s.length(), d.length(), 0).
327   // This is correct, since the position is supposed to be an 'in between point', i.e., s.length(),
328   // points to the right of the last element.
329   if (length==0) {
330     return;
331   }
332   if (UseCompressedOops) {
333     size_t src_offset = (size_t) objArrayOopDesc::obj_at_offset<narrowOop>(src_pos);
334     size_t dst_offset = (size_t) objArrayOopDesc::obj_at_offset<narrowOop>(dst_pos);
335     assert(arrayOopDesc::obj_offset_to_raw<narrowOop>(s, src_offset, NULL) ==
336            objArrayOop(s)->obj_at_addr<narrowOop>(src_pos), "sanity");
337     assert(arrayOopDesc::obj_offset_to_raw<narrowOop>(d, dst_offset, NULL) ==
338            objArrayOop(d)->obj_at_addr<narrowOop>(dst_pos), "sanity");
339     do_copy(s, src_offset, d, dst_offset, length, CHECK);
340   } else {
341     size_t src_offset = (size_t) objArrayOopDesc::obj_at_offset<oop>(src_pos);
342     size_t dst_offset = (size_t) objArrayOopDesc::obj_at_offset<oop>(dst_pos);
343     assert(arrayOopDesc::obj_offset_to_raw<oop>(s, src_offset, NULL) ==
344            objArrayOop(s)->obj_at_addr<oop>(src_pos), "sanity");
345     assert(arrayOopDesc::obj_offset_to_raw<oop>(d, dst_offset, NULL) ==
346            objArrayOop(d)->obj_at_addr<oop>(dst_pos), "sanity");
347     do_copy(s, src_offset, d, dst_offset, length, CHECK);
348   }
349 }
350 
351 
352 Klass* ObjArrayKlass::array_klass(int n, TRAPS) {
353   assert(dimension() <= n, "check order of chain");
354   int dim = dimension();
355   if (dim == n) return this;
356 
357   // lock-free read needs acquire semantics
358   if (higher_dimension_acquire() == NULL) {
359 
360     ResourceMark rm(THREAD);
361     {
362       // Ensure atomic creation of higher dimensions
363       MutexLocker mu(THREAD, MultiArray_lock);
364 
365       // Check if another thread beat us
366       if (higher_dimension() == NULL) {
367 
368         // Create multi-dim klass object and link them together
369         Klass* k = ObjArrayKlass::allocate_objArray_klass(class_loader_data(), dim + 1, this,
370                                                           false, this->name()->is_Q_array_signature(), CHECK_NULL);
371         ObjArrayKlass* ak = ObjArrayKlass::cast(k);
372         ak->set_lower_dimension(this);
373         // use 'release' to pair with lock-free load
374         release_set_higher_dimension(ak);
375         assert(ak->is_objArray_klass(), "incorrect initialization of ObjArrayKlass");
376       }
377     }
378   }
379 
380   ObjArrayKlass *ak = ObjArrayKlass::cast(higher_dimension());
381   THREAD->check_possible_safepoint();
382   return ak->array_klass(n, THREAD);
383 }
384 
385 Klass* ObjArrayKlass::array_klass_or_null(int n) {
386 
387   assert(dimension() <= n, "check order of chain");
388   int dim = dimension();
389   if (dim == n) return this;
390 
391   // lock-free read needs acquire semantics
392   if (higher_dimension_acquire() == NULL) {
393     return NULL;
394   }
395 
396   ObjArrayKlass *ak = ObjArrayKlass::cast(higher_dimension());
397   return ak->array_klass_or_null(n);
398 }
399 
400 Klass* ObjArrayKlass::array_klass(TRAPS) {
401   return array_klass(dimension() +  1, THREAD);
402 }
403 
404 Klass* ObjArrayKlass::array_klass_or_null() {
405   return array_klass_or_null(dimension() +  1);
406 }
407 
408 bool ObjArrayKlass::can_be_primary_super_slow() const {
409   if (!bottom_klass()->can_be_primary_super())
410     // array of interfaces
411     return false;
412   else
413     return Klass::can_be_primary_super_slow();
414 }
415 
416 GrowableArray<Klass*>* ObjArrayKlass::compute_secondary_supers(int num_extra_slots,
417                                                                Array<InstanceKlass*>* transitive_interfaces) {
418   assert(transitive_interfaces == NULL, "sanity");
419   // interfaces = { cloneable_klass, serializable_klass, elemSuper[], ... };
420   const Array<Klass*>* elem_supers = element_klass()->secondary_supers();
421   int num_elem_supers = elem_supers == NULL ? 0 : elem_supers->length();
422   int num_secondaries = num_extra_slots + 2 + num_elem_supers;
423   if (num_secondaries == 2) {
424     // Must share this for correct bootstrapping!
425     set_secondary_supers(Universe::the_array_interfaces_array());
426     return NULL;
427   } else {
428     GrowableArray<Klass*>* secondaries = new GrowableArray<Klass*>(num_elem_supers+3);
429     secondaries->push(vmClasses::Cloneable_klass());
430     secondaries->push(vmClasses::Serializable_klass());
431     secondaries->push(vmClasses::IdentityObject_klass());
432     for (int i = 0; i < num_elem_supers; i++) {
433       Klass* elem_super = elem_supers->at(i);
434       Klass* array_super = elem_super->array_klass_or_null();
435       assert(array_super != NULL, "must already have been created");
436       secondaries->push(array_super);
437     }
438     return secondaries;
439   }
440 }
441 
442 void ObjArrayKlass::initialize(TRAPS) {
443   bottom_klass()->initialize(THREAD);  // dispatches to either InstanceKlass or TypeArrayKlass
444 }
445 
446 void ObjArrayKlass::metaspace_pointers_do(MetaspaceClosure* it) {
447   ArrayKlass::metaspace_pointers_do(it);
448   it->push(&_element_klass);
449   it->push(&_bottom_klass);
450 }
451 
452 jint ObjArrayKlass::compute_modifier_flags() const {
453   // The modifier for an objectArray is the same as its element
454   if (element_klass() == NULL) {
455     assert(Universe::is_bootstrapping(), "partial objArray only at startup");
456     return JVM_ACC_ABSTRACT | JVM_ACC_FINAL | JVM_ACC_PUBLIC;
457   }
458   // Return the flags of the bottom element type.
459   jint element_flags = bottom_klass()->compute_modifier_flags();
460 
461   return (element_flags & (JVM_ACC_PUBLIC | JVM_ACC_PRIVATE | JVM_ACC_PROTECTED))
462                         | (JVM_ACC_ABSTRACT | JVM_ACC_FINAL);
463 }
464 
465 ModuleEntry* ObjArrayKlass::module() const {
466   assert(bottom_klass() != NULL, "ObjArrayKlass returned unexpected NULL bottom_klass");
467   // The array is defined in the module of its bottom class
468   return bottom_klass()->module();
469 }
470 
471 PackageEntry* ObjArrayKlass::package() const {
472   assert(bottom_klass() != NULL, "ObjArrayKlass returned unexpected NULL bottom_klass");
473   return bottom_klass()->package();
474 }
475 
476 // Printing
477 
478 void ObjArrayKlass::print_on(outputStream* st) const {
479 #ifndef PRODUCT
480   Klass::print_on(st);
481   st->print(" - element klass: ");
482   element_klass()->print_value_on(st);
483   st->cr();
484 #endif //PRODUCT
485 }
486 
487 void ObjArrayKlass::print_value_on(outputStream* st) const {
488   assert(is_klass(), "must be klass");
489 
490   element_klass()->print_value_on(st);
491   st->print("[]");
492 }
493 
494 #ifndef PRODUCT
495 
496 void ObjArrayKlass::oop_print_on(oop obj, outputStream* st) {
497   ArrayKlass::oop_print_on(obj, st);
498   assert(obj->is_objArray(), "must be objArray");
499   objArrayOop oa = objArrayOop(obj);
500   int print_len = MIN2((intx) oa->length(), MaxElementPrintSize);
501   for(int index = 0; index < print_len; index++) {
502     st->print(" - %3d : ", index);
503     if (oa->obj_at(index) != NULL) {
504       oa->obj_at(index)->print_value_on(st);
505       st->cr();
506     } else {
507       st->print_cr("NULL");
508     }
509   }
510   int remaining = oa->length() - print_len;
511   if (remaining > 0) {
512     st->print_cr(" - <%d more elements, increase MaxElementPrintSize to print>", remaining);
513   }
514 }
515 
516 #endif //PRODUCT
517 
518 void ObjArrayKlass::oop_print_value_on(oop obj, outputStream* st) {
519   assert(obj->is_objArray(), "must be objArray");
520   st->print("a ");
521   element_klass()->print_value_on(st);
522   int len = objArrayOop(obj)->length();
523   st->print("[%d] ", len);
524   if (obj != NULL) {
525     obj->print_address_on(st);
526   } else {
527     st->print_cr("NULL");
528   }
529 }
530 
531 const char* ObjArrayKlass::internal_name() const {
532   return external_name();
533 }
534 
535 
536 // Verification
537 
538 void ObjArrayKlass::verify_on(outputStream* st) {
539   ArrayKlass::verify_on(st);
540   guarantee(element_klass()->is_klass(), "should be klass");
541   guarantee(bottom_klass()->is_klass(), "should be klass");
542   Klass* bk = bottom_klass();
543   guarantee(bk->is_instance_klass() || bk->is_typeArray_klass() || bk->is_flatArray_klass(),
544             "invalid bottom klass");
545 }
546 
547 void ObjArrayKlass::oop_verify_on(oop obj, outputStream* st) {
548   ArrayKlass::oop_verify_on(obj, st);
549   guarantee(obj->is_objArray(), "must be objArray");
550   guarantee(obj->is_null_free_array() || (!is_null_free_array_klass()), "null-free klass but not object");
551   objArrayOop oa = objArrayOop(obj);
552   for(int index = 0; index < oa->length(); index++) {
553     guarantee(oopDesc::is_oop_or_null(oa->obj_at(index)), "should be oop");
554   }
555 }