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