1 /*
2 * Copyright (c) 1999, 2025, 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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13 * accompanied this code).
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23 */
24
25 #include "ci/ciField.hpp"
26 #include "ci/ciInstanceKlass.hpp"
27 #include "ci/ciSymbols.hpp"
28 #include "ci/ciUtilities.inline.hpp"
29 #include "classfile/javaClasses.hpp"
30 #include "classfile/vmClasses.hpp"
31 #include "code/SCCache.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 _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 // Get the field's declared holder.
107 //
108 // Note: we actually create a ciInstanceKlass for this klass,
109 // even though we may not need to.
110 int holder_index = cpool->klass_ref_index_at(index, bc);
111 bool holder_is_accessible;
112
113 ciKlass* generic_declared_holder = ciEnv::current(THREAD)->get_klass_by_index(cpool, holder_index,
114 holder_is_accessible,
115 klass);
116
117 if (generic_declared_holder->is_array_klass()) {
118 // If the declared holder of the field is an array class, assume that
119 // the canonical holder of that field is java.lang.Object. Arrays
120 // do not have fields; java.lang.Object is the only supertype of an
121 // array type that can declare fields and is therefore the canonical
122 // holder of the array type.
123 //
124 // Furthermore, the compilers assume that java.lang.Object does not
125 // have any fields. Therefore, the field is not looked up. Instead,
126 // the method returns partial information that will trigger special
127 // handling in ciField::will_link and will result in a
128 // java.lang.NoSuchFieldError exception being thrown by the compiled
129 // code (the expected behavior in this case).
130 _holder = ciEnv::current(THREAD)->Object_klass();
131 _offset = -1;
132 _is_constant = false;
133 return;
134 }
135
136 ciInstanceKlass* declared_holder = generic_declared_holder->as_instance_klass();
137
138 // The declared holder of this field may not have been loaded.
139 // Bail out with partial field information.
140 if (!holder_is_accessible) {
141 // _type has already been set.
142 // The default values for _flags and _constant_value will suffice.
143 // We need values for _holder, _offset, and _is_constant,
144 _holder = declared_holder;
145 _offset = -1;
146 _is_constant = false;
147 return;
148 }
149
150 InstanceKlass* loaded_decl_holder = declared_holder->get_instanceKlass();
151
152 // Perform the field lookup.
153 fieldDescriptor field_desc;
154 Klass* canonical_holder =
155 loaded_decl_holder->find_field(name, signature, &field_desc);
156 if (canonical_holder == nullptr) {
157 // Field lookup failed. Will be detected by will_link.
158 _holder = declared_holder;
159 _offset = -1;
160 _is_constant = false;
161 return;
162 }
163
164 // Access check based on declared_holder. canonical_holder should not be used
165 // to check access because it can erroneously succeed. If this check fails,
166 // propagate the declared holder to will_link() which in turn will bail out
167 // compilation for this field access.
168 bool can_access = Reflection::verify_member_access(klass->get_Klass(),
169 declared_holder->get_Klass(),
170 canonical_holder,
171 field_desc.access_flags(),
172 true, false, THREAD);
173 if (!can_access) {
174 _holder = declared_holder;
175 _offset = -1;
176 _is_constant = false;
177 // It's possible the access check failed due to a nestmate access check
178 // encountering an exception. We can't propagate the exception from here
179 // so we have to clear it. If the access check happens again in a different
180 // context then the exception will be thrown there.
181 if (HAS_PENDING_EXCEPTION) {
182 CLEAR_PENDING_EXCEPTION;
183 }
184 return;
185 }
186
187 assert(canonical_holder == field_desc.field_holder(), "just checking");
188 initialize_from(&field_desc);
189 }
190
191 ciField::ciField(fieldDescriptor *fd) :
192 _known_to_link_with_put(nullptr), _known_to_link_with_get(nullptr) {
193 ASSERT_IN_VM;
194
195 // Get the field's name, signature, and type.
196 ciEnv* env = CURRENT_ENV;
197 _name = env->get_symbol(fd->name());
198 _signature = env->get_symbol(fd->signature());
199
200 BasicType field_type = fd->field_type();
201
202 // If the field is a pointer type, get the klass of the
203 // field.
204 if (is_reference_type(field_type)) {
205 _type = nullptr; // must call compute_type on first access
206 } else {
207 _type = ciType::make(field_type);
208 }
209
210 initialize_from(fd);
211
212 // Either (a) it is marked shared, or else (b) we are done bootstrapping.
213 assert(is_shared() || ciObjectFactory::is_initialized(),
214 "bootstrap classes must not create & cache unshared fields");
215 }
216
217 static bool trust_final_non_static_fields(ciInstanceKlass* holder) {
218 if (holder == nullptr)
219 return false;
220 if (holder->name() == ciSymbols::java_lang_System())
221 // Never trust strangely unstable finals: System.out, etc.
222 return false;
223 // Even if general trusting is disabled, trust system-built closures in these packages.
224 if (holder->is_in_package("java/lang/invoke") || holder->is_in_package("sun/invoke") ||
225 holder->is_in_package("java/lang/reflect") || holder->is_in_package("jdk/internal/reflect") ||
226 holder->is_in_package("jdk/internal/foreign/layout") || holder->is_in_package("jdk/internal/foreign") ||
227 holder->is_in_package("jdk/internal/vm/vector") || holder->is_in_package("jdk/incubator/vector") ||
228 holder->is_in_package("java/lang"))
229 return true;
230 // Trust hidden classes. They are created via Lookup.defineHiddenClass and
231 // can't be serialized, so there is no hacking of finals going on with them.
232 if (holder->is_hidden())
233 return true;
234 // Trust final fields in all boxed classes
235 if (holder->is_box_klass())
236 return true;
237 // Trust final fields in records
238 if (holder->is_record())
239 return true;
240 // Trust final fields in String
241 if (holder->name() == ciSymbols::java_lang_String())
242 return true;
243 // Trust Atomic*FieldUpdaters: they are very important for performance, and make up one
244 // more reason not to use Unsafe, if their final fields are trusted. See more in JDK-8140483.
245 if (holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicIntegerFieldUpdater_Impl() ||
246 holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicLongFieldUpdater_CASUpdater() ||
247 holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicLongFieldUpdater_LockedUpdater() ||
248 holder->name() == ciSymbols::java_util_concurrent_atomic_AtomicReferenceFieldUpdater_Impl()) {
249 return true;
250 }
251 return TrustFinalNonStaticFields;
252 }
253
254 void ciField::initialize_from(fieldDescriptor* fd) {
255 // Get the flags, offset, and canonical holder of the field.
256 _flags = ciFlags(fd->access_flags(), fd->field_flags().is_stable(), fd->field_status().is_initialized_final_update());
257 _offset = fd->offset();
258 Klass* field_holder = fd->field_holder();
259 assert(field_holder != nullptr, "null field_holder");
260 _holder = CURRENT_ENV->get_instance_klass(field_holder);
261
262 // Check to see if the field is constant.
263 Klass* k = _holder->get_Klass();
264 bool is_stable_field = FoldStableValues && is_stable();
265 if ((is_final() && !has_initialized_final_update()) || is_stable_field) {
266 if (is_static()) {
267 // This field just may be constant. The only case where it will
268 // not be constant is when the field is a *special* static & final field
269 // whose value may change. The three examples are java.lang.System.in,
270 // java.lang.System.out, and java.lang.System.err.
271 assert(vmClasses::System_klass() != nullptr, "Check once per vm");
272 if (k == vmClasses::System_klass()) {
273 // Check offsets for case 2: System.in, System.out, or System.err
274 if (_offset == java_lang_System::in_offset() ||
275 _offset == java_lang_System::out_offset() ||
276 _offset == java_lang_System::err_offset()) {
277 _is_constant = false;
278 return;
279 }
280 }
281 _is_constant = true;
282 } else {
283 // An instance field can be constant if it's a final static field or if
284 // it's a final non-static field of a trusted class (classes in
285 // java.lang.invoke and sun.invoke packages and subpackages).
286 _is_constant = is_stable_field || trust_final_non_static_fields(_holder);
287 }
288 } else {
289 // For CallSite objects treat the target field as a compile time constant.
290 assert(vmClasses::CallSite_klass() != nullptr, "should be already initialized");
291 if (k == vmClasses::CallSite_klass() &&
292 _offset == java_lang_invoke_CallSite::target_offset()) {
293 assert(!has_initialized_final_update(), "CallSite is not supposed to have writes to final fields outside initializers");
294 _is_constant = true;
295 } else {
296 // Non-final & non-stable fields are not constants.
297 _is_constant = false;
298 }
299 }
300 }
301
302 // ------------------------------------------------------------------
303 // ciField::constant_value
304 // Get the constant value of a this static field.
305 ciConstant ciField::constant_value() {
306 assert(is_static() && is_constant(), "illegal call to constant_value()");
307 if (!_holder->is_initialized()) {
308 return ciConstant(); // Not initialized yet
309 }
310 if (_constant_value.basic_type() == T_ILLEGAL) {
311 // Static fields are placed in mirror objects.
312 ciInstance* mirror = _holder->java_mirror();
313 _constant_value = mirror->field_value_impl(type()->basic_type(), offset_in_bytes());
314 }
315 if (FoldStableValues && is_stable() && _constant_value.is_null_or_zero()) {
316 return ciConstant();
317 }
318 if (!SCCache::allow_const_field(_constant_value)) {
319 return ciConstant();
320 }
321 return _constant_value;
322 }
323
324 // ------------------------------------------------------------------
325 // ciField::constant_value_of
326 // Get the constant value of non-static final field in the given object.
327 ciConstant ciField::constant_value_of(ciObject* object) {
328 assert(!is_static() && is_constant(), "only if field is non-static constant");
329 assert(object->is_instance(), "must be instance");
330 ciConstant field_value = object->as_instance()->field_value(this);
331 if (FoldStableValues && is_stable() && field_value.is_null_or_zero()) {
332 return ciConstant();
333 }
334 if (!SCCache::allow_const_field(field_value)) {
335 return ciConstant();
336 }
337 return field_value;
338 }
339
340 // ------------------------------------------------------------------
341 // ciField::compute_type
342 //
343 // Lazily compute the type, if it is an instance klass.
344 ciType* ciField::compute_type() {
345 GUARDED_VM_ENTRY(return compute_type_impl();)
346 }
347
348 ciType* ciField::compute_type_impl() {
349 ciKlass* type = CURRENT_ENV->get_klass_by_name_impl(_holder, constantPoolHandle(), _signature, false);
350 if (!type->is_primitive_type() && is_shared()) {
351 // We must not cache a pointer to an unshared type, in a shared field.
352 bool type_is_also_shared = false;
353 if (type->is_type_array_klass()) {
354 type_is_also_shared = true; // int[] etc. are explicitly bootstrapped
355 } else if (type->is_instance_klass()) {
356 type_is_also_shared = type->as_instance_klass()->is_shared();
357 } else {
358 // Currently there is no 'shared' query for array types.
359 type_is_also_shared = !ciObjectFactory::is_initialized();
360 }
361 if (!type_is_also_shared)
362 return type; // Bummer.
363 }
364 _type = type;
365 return type;
366 }
367
368
369 // ------------------------------------------------------------------
370 // ciField::will_link
371 //
372 // Can a specific access to this field be made without causing
373 // link errors?
374 bool ciField::will_link(ciMethod* accessing_method,
375 Bytecodes::Code bc) {
376 VM_ENTRY_MARK;
377 assert(bc == Bytecodes::_getstatic || bc == Bytecodes::_putstatic ||
378 bc == Bytecodes::_getfield || bc == Bytecodes::_putfield,
379 "unexpected bytecode");
380
381 if (_offset == -1) {
382 // at creation we couldn't link to our holder so we need to
383 // maintain that stance, otherwise there's no safe way to use this
384 // ciField.
385 return false;
386 }
387
388 // Check for static/nonstatic mismatch
389 bool is_static = (bc == Bytecodes::_getstatic || bc == Bytecodes::_putstatic);
390 if (is_static != this->is_static()) {
391 return false;
392 }
393
394 // Get and put can have different accessibility rules
395 bool is_put = (bc == Bytecodes::_putfield || bc == Bytecodes::_putstatic);
396 if (is_put) {
397 if (_known_to_link_with_put == accessing_method) {
398 return true;
399 }
400 } else {
401 if (_known_to_link_with_get == accessing_method->holder()) {
402 return true;
403 }
404 }
405
406 LinkInfo link_info(_holder->get_instanceKlass(),
407 _name->get_symbol(), _signature->get_symbol(),
408 methodHandle(THREAD, accessing_method->get_Method()));
409 fieldDescriptor result;
410 LinkResolver::resolve_field(result, link_info, bc, false, CHECK_AND_CLEAR_(false));
411
412 // update the hit-cache, unless there is a problem with memory scoping:
413 if (accessing_method->holder()->is_shared() || !is_shared()) {
414 if (is_put) {
415 _known_to_link_with_put = accessing_method;
416 } else {
417 _known_to_link_with_get = accessing_method->holder();
418 }
419 }
420
421 return true;
422 }
423
424 bool ciField::is_call_site_target() {
425 ciInstanceKlass* callsite_klass = CURRENT_ENV->CallSite_klass();
426 if (callsite_klass == nullptr)
427 return false;
428 return (holder()->is_subclass_of(callsite_klass) && (name() == ciSymbols::target_name()));
429 }
430
431 bool ciField::is_autobox_cache() {
432 ciSymbol* klass_name = holder()->name();
433 return (name() == ciSymbols::cache_field_name() &&
434 holder()->uses_default_loader() &&
435 (klass_name == ciSymbols::java_lang_Character_CharacterCache() ||
436 klass_name == ciSymbols::java_lang_Byte_ByteCache() ||
437 klass_name == ciSymbols::java_lang_Short_ShortCache() ||
438 klass_name == ciSymbols::java_lang_Integer_IntegerCache() ||
439 klass_name == ciSymbols::java_lang_Long_LongCache()));
440 }
441
442 // ------------------------------------------------------------------
443 // ciField::print
444 void ciField::print() {
445 tty->print("<ciField name=");
446 _holder->print_name();
447 tty->print(".");
448 _name->print_symbol();
449 tty->print(" signature=");
450 _signature->print_symbol();
451 tty->print(" offset=%d type=", _offset);
452 if (_type != nullptr)
453 _type->print_name();
454 else
455 tty->print("(reference)");
456 tty->print(" flags=%04x", flags().as_int());
457 tty->print(" is_constant=%s", bool_to_str(_is_constant));
458 if (_is_constant && is_static()) {
459 tty->print(" constant_value=");
460 _constant_value.print();
461 }
462 tty->print(">");
463 }
464
465 // ------------------------------------------------------------------
466 // ciField::print_name_on
467 //
468 // Print the name of this field
469 void ciField::print_name_on(outputStream* st) {
470 name()->print_symbol_on(st);
471 }