1 /*
2 * Copyright (c) 1999, 2024, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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23 */
24
25 #include "precompiled.hpp"
26 #include "ci/ciField.hpp"
27 #include "ci/ciInstanceKlass.hpp"
28 #include "ci/ciSymbols.hpp"
29 #include "ci/ciUtilities.inline.hpp"
30 #include "classfile/javaClasses.hpp"
31 #include "classfile/vmClasses.hpp"
32 #include "gc/shared/collectedHeap.inline.hpp"
33 #include "interpreter/linkResolver.hpp"
34 #include "oops/klass.inline.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/fieldDescriptor.inline.hpp"
37 #include "runtime/handles.inline.hpp"
38 #include "runtime/reflection.hpp"
39
40 // ciField
41 //
42 // This class represents the result of a field lookup in the VM.
43 // The lookup may not succeed, in which case the information in
44 // the ciField will be incomplete.
45
46 // The ciObjectFactory cannot create circular data structures in one query.
47 // To avoid vicious circularities, we initialize ciField::_type to null
48 // for reference types and derive it lazily from the ciField::_signature.
49 // Primitive types are eagerly initialized, and basic layout queries
50 // can succeed without initialization, using only the BasicType of the field.
51
52 // Notes on bootstrapping and shared CI objects: A field is shared if and
53 // only if it is (a) non-static and (b) declared by a shared instance klass.
54 // This allows non-static field lists to be cached on shared types.
55 // Because the _type field is lazily initialized, however, there is a
56 // special restriction that a shared field cannot cache an unshared type.
57 // This puts a small performance penalty on shared fields with unshared
58 // types, such as StackTraceElement[] Throwable.stackTrace.
59 // (Throwable is shared because ClassCastException is shared, but
60 // StackTraceElement is not presently shared.)
61
62 // It is not a vicious circularity for a ciField to recursively create
63 // the ciSymbols necessary to represent its name and signature.
64 // Therefore, these items are created eagerly, and the name and signature
65 // of a shared field are themselves shared symbols. This somewhat
66 // pollutes the set of shared CI objects: It grows from 50 to 93 items,
67 // with all of the additional 43 being uninteresting shared ciSymbols.
68 // This adds at most one step to the binary search, an amount which
69 // decreases for complex compilation tasks.
70
71 // ------------------------------------------------------------------
72 // ciField::ciField
73 ciField::ciField(ciInstanceKlass* klass, int index, Bytecodes::Code bc) :
74 _original_holder(nullptr), _is_flat(false), _known_to_link_with_put(nullptr), _known_to_link_with_get(nullptr) {
75 ASSERT_IN_VM;
76 CompilerThread *THREAD = CompilerThread::current();
77
78 assert(ciObjectFactory::is_initialized(), "not a shared field");
79
80 assert(klass->get_instanceKlass()->is_linked(), "must be linked before using its constant-pool");
81
82 constantPoolHandle cpool(THREAD, klass->get_instanceKlass()->constants());
83
84 // Get the field's name, signature, and type.
85 Symbol* name = cpool->name_ref_at(index, bc);
86 _name = ciEnv::current(THREAD)->get_symbol(name);
87
88 int nt_index = cpool->name_and_type_ref_index_at(index, bc);
89 int sig_index = cpool->signature_ref_index_at(nt_index);
90 Symbol* signature = cpool->symbol_at(sig_index);
91 _signature = ciEnv::current(THREAD)->get_symbol(signature);
92
93 BasicType field_type = Signature::basic_type(signature);
94
95 // If the field is a pointer type, get the klass of the
96 // field.
97 if (is_reference_type(field_type)) {
98 bool ignore;
99 // This is not really a class reference; the index always refers to the
100 // field's type signature, as a symbol. Linkage checks do not apply.
101 _type = ciEnv::current(THREAD)->get_klass_by_index(cpool, sig_index, ignore, klass);
102 } else {
103 _type = ciType::make(field_type);
104 }
105
106 _name = (ciSymbol*)ciEnv::current(THREAD)->get_symbol(name);
107
108 _is_null_free = false;
109
110 // Get the field's declared holder.
111 //
112 // Note: we actually create a ciInstanceKlass for this klass,
113 // even though we may not need to.
114 int holder_index = cpool->klass_ref_index_at(index, bc);
115 bool holder_is_accessible;
116
117 ciKlass* generic_declared_holder = ciEnv::current(THREAD)->get_klass_by_index(cpool, holder_index,
118 holder_is_accessible,
119 klass);
120
121 if (generic_declared_holder->is_array_klass()) {
122 // If the declared holder of the field is an array class, assume that
123 // the canonical holder of that field is java.lang.Object. Arrays
124 // do not have fields; java.lang.Object is the only supertype of an
125 // array type that can declare fields and is therefore the canonical
126 // holder of the array type.
127 //
128 // Furthermore, the compilers assume that java.lang.Object does not
129 // have any fields. Therefore, the field is not looked up. Instead,
130 // the method returns partial information that will trigger special
131 // handling in ciField::will_link and will result in a
132 // java.lang.NoSuchFieldError exception being thrown by the compiled
133 // code (the expected behavior in this case).
134 _holder = ciEnv::current(THREAD)->Object_klass();
135 _offset = -1;
136 _is_constant = false;
137 return;
138 }
139
140 ciInstanceKlass* declared_holder = generic_declared_holder->as_instance_klass();
141
142 // The declared holder of this field may not have been loaded.
143 // Bail out with partial field information.
144 if (!holder_is_accessible) {
145 // _type has already been set.
146 // The default values for _flags and _constant_value will suffice.
147 // We need values for _holder, _offset, and _is_constant,
148 _holder = declared_holder;
149 _offset = -1;
150 _is_constant = false;
151 return;
152 }
153
154 InstanceKlass* loaded_decl_holder = declared_holder->get_instanceKlass();
155
156 // Perform the field lookup.
157 fieldDescriptor field_desc;
158 Klass* canonical_holder =
159 loaded_decl_holder->find_field(name, signature, &field_desc);
160 if (canonical_holder == nullptr) {
161 // Field lookup failed. Will be detected by will_link.
162 _holder = declared_holder;
163 _offset = -1;
164 _is_constant = false;
165 return;
166 }
167
168 // Access check based on declared_holder. canonical_holder should not be used
169 // to check access because it can erroneously succeed. If this check fails,
170 // propagate the declared holder to will_link() which in turn will bail out
171 // compilation for this field access.
172 bool can_access = Reflection::verify_member_access(klass->get_Klass(),
173 declared_holder->get_Klass(),
174 canonical_holder,
175 field_desc.access_flags(),
176 true, false, THREAD);
177 if (!can_access) {
178 _holder = declared_holder;
179 _offset = -1;
180 _is_constant = false;
181 // It's possible the access check failed due to a nestmate access check
182 // encountering an exception. We can't propagate the exception from here
183 // so we have to clear it. If the access check happens again in a different
184 // context then the exception will be thrown there.
185 if (HAS_PENDING_EXCEPTION) {
186 CLEAR_PENDING_EXCEPTION;
187 }
188 return;
189 }
190
191 assert(canonical_holder == field_desc.field_holder(), "just checking");
192 initialize_from(&field_desc);
193 }
194
195 ciField::ciField(fieldDescriptor *fd) :
196 _known_to_link_with_put(nullptr), _known_to_link_with_get(nullptr) {
197 ASSERT_IN_VM;
198
199 // Get the field's name, signature, and type.
200 ciEnv* env = CURRENT_ENV;
201 _name = env->get_symbol(fd->name());
202 _signature = env->get_symbol(fd->signature());
203
204 BasicType field_type = fd->field_type();
205
206 // If the field is a pointer type, get the klass of the
207 // field.
208 if (is_reference_type(field_type)) {
209 _type = nullptr; // must call compute_type on first access
210 } else {
211 _type = ciType::make(field_type);
212 }
213
214 initialize_from(fd);
215
216 // Either (a) it is marked shared, or else (b) we are done bootstrapping.
217 assert(is_shared() || ciObjectFactory::is_initialized(),
218 "bootstrap classes must not create & cache unshared fields");
219 }
220
221 // Special copy constructor used to flatten inline type fields by
222 // copying the fields of the inline type to a new holder klass.
223 ciField::ciField(ciField* field, ciInstanceKlass* holder, int offset, bool is_final) {
224 assert(field->holder()->is_inlinetype(), "should only be used for inline type field flattening");
225 // Set the is_final flag
226 jint final = is_final ? JVM_ACC_FINAL : ~JVM_ACC_FINAL;
227 AccessFlags flags(field->flags().as_int() & final);
228 _flags = ciFlags(flags);
229 _holder = holder;
230 _offset = offset;
231 // Copy remaining fields
232 _name = field->_name;
233 _signature = field->_signature;
234 _type = field->_type;
235 // Trust final flat fields
236 _is_constant = is_final;
237 _known_to_link_with_put = field->_known_to_link_with_put;
238 _known_to_link_with_get = field->_known_to_link_with_get;
239 _constant_value = field->_constant_value;
240 assert(!field->is_flat(), "field must not be flat");
241 _is_flat = false;
242 _is_null_free = field->_is_null_free;
243 _original_holder = (field->_original_holder != nullptr) ? field->_original_holder : field->_holder;
244 }
245
246 static bool trust_final_non_static_fields(ciInstanceKlass* holder) {
247 if (holder == nullptr)
248 return false;
249 if (holder->name() == ciSymbols::java_lang_System())
250 // Never trust strangely unstable finals: System.out, etc.
251 return false;
252 // Even if general trusting is disabled, trust system-built closures in these packages.
253 if (holder->is_in_package("java/lang/invoke") || holder->is_in_package("sun/invoke") ||
254 holder->is_in_package("java/lang/reflect") || holder->is_in_package("jdk/internal/reflect") ||
255 holder->is_in_package("jdk/internal/foreign/layout") || holder->is_in_package("jdk/internal/foreign") ||
256 holder->is_in_package("jdk/internal/vm/vector") || holder->is_in_package("jdk/incubator/vector") ||
257 holder->is_in_package("java/lang"))
258 return true;
259 // Trust hidden classes. They are created via Lookup.defineHiddenClass and
260 // can't be serialized, so there is no hacking of finals going on with them.
261 if (holder->is_hidden())
262 return true;
263 // Trust final fields in inline type buffers
264 if (holder->is_inlinetype())
265 return true;
266 // Trust final fields in all boxed classes
267 if (holder->is_box_klass())
268 return true;
269 // Trust final fields in records
270 if (holder->is_record())
271 return true;
272 // Trust final fields in String
273 if (holder->name() == ciSymbols::java_lang_String())
274 return true;
275 // Trust Atomic*FieldUpdaters: they are very important for performance, and make up one
276 // more reason not to use Unsafe, if their final fields are trusted. See more in JDK-8140483.
277 if (holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicIntegerFieldUpdater_Impl() ||
278 holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicLongFieldUpdater_CASUpdater() ||
279 holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicLongFieldUpdater_LockedUpdater() ||
280 holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicReferenceFieldUpdater_Impl()) {
281 return true;
282 }
283 return TrustFinalNonStaticFields;
284 }
285
286 void ciField::initialize_from(fieldDescriptor* fd) {
287 // Get the flags, offset, and canonical holder of the field.
288 _flags = ciFlags(fd->access_flags(), fd->field_flags().is_stable(), fd->field_status().is_initialized_final_update());
289 _offset = fd->offset();
290 Klass* field_holder = fd->field_holder();
291 assert(field_holder != nullptr, "null field_holder");
292 _holder = CURRENT_ENV->get_instance_klass(field_holder);
293 _is_flat = fd->is_flat();
294 _is_null_free = fd->is_null_free_inline_type();
295 _original_holder = nullptr;
296
297 // Check to see if the field is constant.
298 Klass* k = _holder->get_Klass();
299 bool is_stable_field = FoldStableValues && is_stable();
300 if ((is_final() && !has_initialized_final_update()) || is_stable_field) {
301 if (is_static()) {
302 // This field just may be constant. The only case where it will
303 // not be constant is when the field is a *special* static & final field
304 // whose value may change. The three examples are java.lang.System.in,
305 // java.lang.System.out, and java.lang.System.err.
306 assert(vmClasses::System_klass() != nullptr, "Check once per vm");
307 if (k == vmClasses::System_klass()) {
308 // Check offsets for case 2: System.in, System.out, or System.err
309 if (_offset == java_lang_System::in_offset() ||
310 _offset == java_lang_System::out_offset() ||
311 _offset == java_lang_System::err_offset()) {
312 _is_constant = false;
313 return;
314 }
315 }
316 _is_constant = true;
317 } else {
318 // An instance field can be constant if it's a final static field or if
319 // it's a final non-static field of a trusted class (classes in
320 // java.lang.invoke and sun.invoke packages and subpackages).
321 _is_constant = is_stable_field || trust_final_non_static_fields(_holder);
322 }
323 } else {
324 // For CallSite objects treat the target field as a compile time constant.
325 assert(vmClasses::CallSite_klass() != nullptr, "should be already initialized");
326 if (k == vmClasses::CallSite_klass() &&
327 _offset == java_lang_invoke_CallSite::target_offset()) {
328 assert(!has_initialized_final_update(), "CallSite is not supposed to have writes to final fields outside initializers");
329 _is_constant = true;
330 } else {
331 // Non-final & non-stable fields are not constants.
332 _is_constant = false;
333 }
334 }
335 }
336
337 // ------------------------------------------------------------------
338 // ciField::constant_value
339 // Get the constant value of a this static field.
340 ciConstant ciField::constant_value() {
341 assert(is_static() && is_constant(), "illegal call to constant_value()");
342 if (!_holder->is_initialized()) {
343 return ciConstant(); // Not initialized yet
344 }
345 if (_constant_value.basic_type() == T_ILLEGAL) {
346 // Static fields are placed in mirror objects.
347 ciInstance* mirror = _holder->java_mirror();
348 _constant_value = mirror->field_value_impl(type()->basic_type(), offset_in_bytes());
349 }
350 if (FoldStableValues && is_stable() && _constant_value.is_null_or_zero()) {
351 return ciConstant();
352 }
353 return _constant_value;
354 }
355
356 // ------------------------------------------------------------------
357 // ciField::constant_value_of
358 // Get the constant value of non-static final field in the given object.
359 ciConstant ciField::constant_value_of(ciObject* object) {
360 assert(!is_static() && is_constant(), "only if field is non-static constant");
361 assert(object->is_instance(), "must be instance");
362 ciConstant field_value = object->as_instance()->field_value(this);
363 if (FoldStableValues && is_stable() && field_value.is_null_or_zero()) {
364 return ciConstant();
365 }
366 return field_value;
367 }
368
369 // ------------------------------------------------------------------
370 // ciField::compute_type
371 //
372 // Lazily compute the type, if it is an instance klass.
373 ciType* ciField::compute_type() {
374 GUARDED_VM_ENTRY(return compute_type_impl();)
375 }
376
377 ciType* ciField::compute_type_impl() {
378 // Use original holder for fields that came in through flattening
379 ciKlass* accessing_klass = (_original_holder != nullptr) ? _original_holder : _holder;
380 ciKlass* type = CURRENT_ENV->get_klass_by_name_impl(accessing_klass, constantPoolHandle(), _signature, false);
381 if (!type->is_primitive_type() && is_shared()) {
382 // We must not cache a pointer to an unshared type, in a shared field.
383 bool type_is_also_shared = false;
384 if (type->is_type_array_klass()) {
385 type_is_also_shared = true; // int[] etc. are explicitly bootstrapped
386 } else if (type->is_instance_klass()) {
387 type_is_also_shared = type->as_instance_klass()->is_shared();
388 } else {
389 // Currently there is no 'shared' query for array types.
390 type_is_also_shared = !ciObjectFactory::is_initialized();
391 }
392 if (!type_is_also_shared)
393 return type; // Bummer.
394 }
395 _type = type;
396 return type;
397 }
398
399
400 // ------------------------------------------------------------------
401 // ciField::will_link
402 //
403 // Can a specific access to this field be made without causing
404 // link errors?
405 bool ciField::will_link(ciMethod* accessing_method,
406 Bytecodes::Code bc) {
407 VM_ENTRY_MARK;
408 assert(bc == Bytecodes::_getstatic || bc == Bytecodes::_putstatic ||
409 bc == Bytecodes::_getfield || bc == Bytecodes::_putfield,
410 "unexpected bytecode");
411
412 if (_offset == -1) {
413 // at creation we couldn't link to our holder so we need to
414 // maintain that stance, otherwise there's no safe way to use this
415 // ciField.
416 return false;
417 }
418
419 // Check for static/nonstatic mismatch
420 bool is_static = (bc == Bytecodes::_getstatic || bc == Bytecodes::_putstatic);
421 if (is_static != this->is_static()) {
422 return false;
423 }
424
425 // Get and put can have different accessibility rules
426 bool is_put = (bc == Bytecodes::_putfield || bc == Bytecodes::_putstatic);
427 if (is_put) {
428 if (_known_to_link_with_put == accessing_method) {
429 return true;
430 }
431 } else {
432 if (_known_to_link_with_get == accessing_method->holder()) {
433 return true;
434 }
435 }
436
437 LinkInfo link_info(_holder->get_instanceKlass(),
438 _name->get_symbol(), _signature->get_symbol(),
439 methodHandle(THREAD, accessing_method->get_Method()));
440 fieldDescriptor result;
441 LinkResolver::resolve_field(result, link_info, bc, false, CHECK_AND_CLEAR_(false));
442
443 // update the hit-cache, unless there is a problem with memory scoping:
444 if (accessing_method->holder()->is_shared() || !is_shared()) {
445 if (is_put) {
446 _known_to_link_with_put = accessing_method;
447 } else {
448 _known_to_link_with_get = accessing_method->holder();
449 }
450 }
451
452 return true;
453 }
454
455 bool ciField::is_call_site_target() {
456 ciInstanceKlass* callsite_klass = CURRENT_ENV->CallSite_klass();
457 if (callsite_klass == nullptr)
458 return false;
459 return (holder()->is_subclass_of(callsite_klass) && (name() == ciSymbols::target_name()));
460 }
461
462 bool ciField::is_autobox_cache() {
463 ciSymbol* klass_name = holder()->name();
464 return (name() == ciSymbols::cache_field_name() &&
465 holder()->uses_default_loader() &&
466 (klass_name == ciSymbols::java_lang_Character_CharacterCache() ||
467 klass_name == ciSymbols::java_lang_Byte_ByteCache() ||
468 klass_name == ciSymbols::java_lang_Short_ShortCache() ||
469 klass_name == ciSymbols::java_lang_Integer_IntegerCache() ||
470 klass_name == ciSymbols::java_lang_Long_LongCache()));
471 }
472
473 // ------------------------------------------------------------------
474 // ciField::print
475 void ciField::print() {
476 tty->print("<ciField name=");
477 _holder->print_name();
478 tty->print(".");
479 _name->print_symbol();
480 tty->print(" signature=");
481 _signature->print_symbol();
482 tty->print(" offset=%d type=", _offset);
483 if (_type != nullptr)
484 _type->print_name();
485 else
486 tty->print("(reference)");
487 tty->print(" flags=%04x", flags().as_int());
488 tty->print(" is_constant=%s", bool_to_str(_is_constant));
489 if (_is_constant && is_static()) {
490 tty->print(" constant_value=");
491 _constant_value.print();
492 }
493 tty->print(" is_flat=%s", bool_to_str(_is_flat));
494 tty->print(" is_null_free=%s", bool_to_str(_is_null_free));
495 tty->print(">");
496 }
497
498 // ------------------------------------------------------------------
499 // ciField::print_name_on
500 //
501 // Print the name of this field
502 void ciField::print_name_on(outputStream* st) {
503 name()->print_symbol_on(st);
504 }