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