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