1 /*
2 * Copyright (c) 2022, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
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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).
14 *
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23 */
24
25 #include "cds/aotClassInitializer.hpp"
26 #include "cds/archiveBuilder.hpp"
27 #include "cds/cdsHeapVerifier.hpp"
28 #include "classfile/classLoaderDataGraph.hpp"
29 #include "classfile/javaClasses.inline.hpp"
30 #include "classfile/moduleEntry.hpp"
31 #include "classfile/stringTable.hpp"
32 #include "classfile/symbolTable.hpp"
33 #include "classfile/systemDictionary.hpp"
34 #include "classfile/systemDictionaryShared.hpp"
35 #include "classfile/vmSymbols.hpp"
36 #include "logging/log.hpp"
37 #include "logging/logStream.hpp"
38 #include "memory/resourceArea.hpp"
39 #include "oops/fieldStreams.inline.hpp"
40 #include "oops/klass.inline.hpp"
41 #include "oops/oop.inline.hpp"
42 #include "oops/oopHandle.inline.hpp"
43 #include "runtime/fieldDescriptor.inline.hpp"
44
45 #if INCLUDE_CDS_JAVA_HEAP
46
47 // CDSHeapVerifier is used to check for problems where an archived object references a
48 // static field that may be get a different value at runtime.
49 //
50 // *Please see comments in aotClassInitializer.cpp for how to avoid such problems*,
51 //
52 // In the following example,
53 // Foo.get.test()
54 // correctly returns true when CDS disabled, but incorrectly returns false when CDS is enabled,
55 // because the archived archivedFoo.bar value is different than Bar.bar.
56 //
57 // class Foo {
58 // static final Foo archivedFoo; // this field is archived by CDS
59 // Bar bar;
60 // static {
61 // CDS.initializeFromArchive(Foo.class);
62 // if (archivedFoo == null) {
63 // archivedFoo = new Foo();
64 // archivedFoo.bar = Bar.bar;
65 // }
66 // }
67 // static Foo get() { return archivedFoo; }
68 // boolean test() {
69 // return bar == Bar.bar;
70 // }
71 // }
72 //
73 // class Bar {
74 // // this field is initialized in both CDS dump time and runtime.
75 // static final Bar bar = new Bar();
76 // }
77 //
78 // The check itself is simple:
79 // [1] CDSHeapVerifier::do_klass() collects all static fields
80 // [2] CDSHeapVerifier::do_entry() checks all the archived objects. None of them
81 // should be in [1]
82 //
83 // However, it's legal for *some* static fields to be referenced. The reasons are explained
84 // in the table of ADD_EXCL below.
85 //
86 // [A] In most of the cases, the module bootstrap code will update the static field
87 // to point to part of the archived module graph. E.g.,
88 // - java/lang/System::bootLayer
89 // - jdk/internal/loader/ClassLoaders::BOOT_LOADER
90 // [B] A final static String that's explicitly initialized inside <clinit>, but
91 // its value is deterministic and is always the same string literal.
92 // [C] A non-final static string that is assigned a string literal during class
93 // initialization; this string is never changed during -Xshare:dump.
94 // [D] Simple caches whose value doesn't matter.
95 // [E] Other cases (see comments in-line below).
96 //
97 // LIMITATION:
98 //
99 // CDSHeapVerifier can only check for problems with object identity. In the example above,
100 // if the Bar type has identity, the program's correctness requires that the identity
101 // of Foo.bar and Bar.bar to be equal. This requirement can be checked by CDSHeapVerifier.
102 //
103 // However, if Bar does not have identity (e.g., it's a value class, or is a primitive type),
104 // the program's correctness no longer requires that the identity of Foo.bar and Bar.bar
105 // to be equal (since they don't have an identity anymore). While the program's
106 // correctness may still have certain assumptions about Foo.bar and Bar.bar (such as the
107 // internal fields of these two values), such assumptions cannot be checked by CDSHeapVerifier.
108
109 CDSHeapVerifier::CDSHeapVerifier() : _archived_objs(0), _problems(0)
110 {
111 # define ADD_EXCL(...) { static const char* e[] = {__VA_ARGS__, nullptr}; add_exclusion(e); }
112
113 // Unfortunately this needs to be manually maintained. If
114 // test/hotspot/jtreg/runtime/cds/appcds/cacheObject/ArchivedEnumTest.java fails,
115 // you might need to fix the core library code, or fix the ADD_EXCL entries below.
116 //
117 // class field type
118 ADD_EXCL("java/lang/ClassLoader$Holder", "scl"); // A
119 ADD_EXCL("java/lang/Module", "ALL_UNNAMED_MODULE", // A
120 "ALL_UNNAMED_MODULE_SET", // A
121 "EVERYONE_MODULE", // A
122 "EVERYONE_SET"); // A
123
124 // This is the same as java/util/ImmutableCollections::EMPTY_SET, which is archived
125 ADD_EXCL("java/lang/reflect/AccessFlag$Location", "EMPTY_SET"); // E
126
127 ADD_EXCL("java/lang/System", "bootLayer"); // A
128
129 ADD_EXCL("java/util/Collections", "EMPTY_LIST"); // E
130
131 // A dummy object used by HashSet. The value doesn't matter and it's never
132 // tested for equality.
133 ADD_EXCL("java/util/HashSet", "PRESENT"); // E
134
135 ADD_EXCL("jdk/internal/loader/BootLoader", "UNNAMED_MODULE"); // A
136 ADD_EXCL("jdk/internal/loader/BuiltinClassLoader", "packageToModule"); // A
137 ADD_EXCL("jdk/internal/loader/ClassLoaders", "BOOT_LOADER", // A
138 "APP_LOADER", // A
139 "PLATFORM_LOADER"); // A
140 ADD_EXCL("jdk/internal/module/Builder", "cachedVersion"); // D
141 ADD_EXCL("jdk/internal/module/ModuleLoaderMap$Mapper", "APP_CLASSLOADER", // A
142 "APP_LOADER_INDEX", // A
143 "PLATFORM_CLASSLOADER", // A
144 "PLATFORM_LOADER_INDEX"); // A
145 ADD_EXCL("jdk/internal/module/ServicesCatalog", "CLV"); // A
146
147 // This just points to an empty Map
148 ADD_EXCL("jdk/internal/reflect/Reflection", "methodFilterMap"); // E
149
150 // Integer for 0 and 1 are in java/lang/Integer$IntegerCache and are archived
151 ADD_EXCL("sun/invoke/util/ValueConversions", "ONE_INT", // E
152 "ZERO_INT"); // E
153
154 if (CDSConfig::is_dumping_method_handles()) {
155 ADD_EXCL("java/lang/invoke/InvokerBytecodeGenerator", "MEMBERNAME_FACTORY", // D
156 "CD_Object_array", // E same as <...>ConstantUtils.CD_Object_array::CD_Object
157 "INVOKER_SUPER_DESC"); // E same as java.lang.constant.ConstantDescs::CD_Object
158
159 ADD_EXCL("java/lang/runtime/ObjectMethods", "CLASS_IS_INSTANCE", // D
160 "FALSE", // D
161 "TRUE", // D
162 "ZERO"); // D
163 }
164
165 if (CDSConfig::is_dumping_aot_linked_classes()) {
166 ADD_EXCL("java/lang/Package$VersionInfo", "NULL_VERSION_INFO"); // D
167 }
168
169 # undef ADD_EXCL
170
171 if (CDSConfig::is_dumping_aot_linked_classes()) {
172 add_shared_secret_accessors();
173 }
174 ClassLoaderDataGraph::classes_do(this);
175 }
176
177 // We allow only "stateless" accessors in the SharedSecrets class to be AOT-initialized, for example,
178 // in the following pattern:
179 //
180 // class URL {
181 // static {
182 // SharedSecrets.setJavaNetURLAccess(
183 // new JavaNetURLAccess() { ... });
184 // }
185 //
186 // This initializes the field SharedSecrets::javaNetUriAccess, whose type (the inner case in the
187 // above example) has no fields (static or otherwise) and is not a hidden class, so it cannot possibly
188 // capture any transient state from the assembly phase that might become invalid in the production run.
189 //
190 class CDSHeapVerifier::SharedSecretsAccessorFinder : public FieldClosure {
191 CDSHeapVerifier* _verifier;
192 InstanceKlass* _ik;
193 public:
194 SharedSecretsAccessorFinder(CDSHeapVerifier* verifier, InstanceKlass* ik)
195 : _verifier(verifier), _ik(ik) {}
196
197 void do_field(fieldDescriptor* fd) {
198 if (fd->field_type() == T_OBJECT) {
199 oop static_obj_field = _ik->java_mirror()->obj_field(fd->offset());
200 if (static_obj_field != nullptr) {
201 Klass* field_type = static_obj_field->klass();
202
203 if (!field_type->is_instance_klass()) {
204 ResourceMark rm;
205 log_error(aot, heap)("jdk.internal.access.SharedSecrets::%s must not be an array",
206 fd->name()->as_C_string());
207 AOTMetaspace::unrecoverable_writing_error();
208 }
209
210 InstanceKlass* field_type_ik = InstanceKlass::cast(field_type);
211 if (has_any_fields(field_type_ik) || field_type_ik->is_hidden()) {
212 // If field_type_ik is a hidden class, the accessor is probably initialized using a
213 // Lambda, which may contain transient states.
214 ResourceMark rm;
215 log_error(aot, heap)("jdk.internal.access.SharedSecrets::%s (%s) must be stateless",
216 fd->name()->as_C_string(), field_type_ik->external_name());
217 AOTMetaspace::unrecoverable_writing_error();
218 }
219
220 _verifier->add_shared_secret_accessor(static_obj_field);
221 }
222 }
223 }
224
225 // Does k (or any of its supertypes) have at least one (static or non-static) field?
226 static bool has_any_fields(InstanceKlass* k) {
227 if (k->static_field_size() != 0 || k->nonstatic_field_size() != 0) {
228 return true;
229 }
230
231 if (k->super() != nullptr && has_any_fields(k->super())) {
232 return true;
233 }
234
235 Array<InstanceKlass*>* interfaces = k->local_interfaces();
236 int num_interfaces = interfaces->length();
237 for (int index = 0; index < num_interfaces; index++) {
238 if (has_any_fields(interfaces->at(index))) {
239 return true;
240 }
241 }
242
243 return false;
244 }
245 };
246
247 // This function is for allowing the following pattern in the core libraries:
248 //
249 // public class URLClassPath {
250 // private static final JavaNetURLAccess JNUA = SharedSecrets.getJavaNetURLAccess();
251 //
252 // SharedSecrets::javaNetUriAccess has no states so it can be safely AOT-initialized. During
253 // the production run, even if URLClassPath.<clinit> is re-executed, it will get back the same
254 // instance of javaNetUriAccess as it did during the assembly phase.
255 //
256 // Note: this will forbid complex accessors such as SharedSecrets::javaObjectInputFilterAccess
257 // to be initialized during the AOT assembly phase.
258 void CDSHeapVerifier::add_shared_secret_accessors() {
259 TempNewSymbol klass_name = SymbolTable::new_symbol("jdk/internal/access/SharedSecrets");
260 InstanceKlass* ik = SystemDictionary::find_instance_klass(Thread::current(), klass_name,
261 Handle());
262 assert(ik != nullptr, "must have been loaded");
263
264 SharedSecretsAccessorFinder finder(this, ik);
265 ik->do_local_static_fields(&finder);
266 }
267
268 CDSHeapVerifier::~CDSHeapVerifier() {
269 if (_problems > 0) {
270 log_error(aot, heap)("Scanned %zu objects. Found %d case(s) where "
271 "an object points to a static field that "
272 "may hold a different value at runtime.", _archived_objs, _problems);
273 log_error(aot, heap)("Please see cdsHeapVerifier.cpp and aotClassInitializer.cpp for details");
274 AOTMetaspace::unrecoverable_writing_error();
275 }
276 }
277
278 class CDSHeapVerifier::CheckStaticFields : public FieldClosure {
279 CDSHeapVerifier* _verifier;
280 InstanceKlass* _ik; // The class whose static fields are being checked.
281 const char** _exclusions;
282 public:
283 CheckStaticFields(CDSHeapVerifier* verifier, InstanceKlass* ik)
284 : _verifier(verifier), _ik(ik) {
285 _exclusions = _verifier->find_exclusion(_ik);
286 }
287
288 void do_field(fieldDescriptor* fd) {
289 if (fd->field_type() != T_OBJECT) {
290 return;
291 }
292
293 oop static_obj_field = _ik->java_mirror()->obj_field(fd->offset());
294 if (static_obj_field != nullptr) {
295 if (_verifier->is_shared_secret_accessor(static_obj_field)) {
296 return;
297 }
298
299 Klass* field_type = static_obj_field->klass();
300 if (_exclusions != nullptr) {
301 for (const char** p = _exclusions; *p != nullptr; p++) {
302 if (fd->name()->equals(*p)) {
303 return;
304 }
305 }
306 }
307
308 if (!field_type->is_identity_class()) {
309 // See comment of LIMITATION above
310 // Any concrete value class will have a field ".null_reset" which holds an
311 // all-zero instance of the value class so it will not change between
312 // dump time and runtime.
313 return;
314 }
315
316 if (fd->is_final() && java_lang_String::is_instance(static_obj_field) && fd->has_initial_value()) {
317 // This field looks like like this in the Java source:
318 // static final SOME_STRING = "a string literal";
319 // This string literal has been stored in the shared string table, so it's OK
320 // for the archived objects to refer to it.
321 return;
322 }
323 if (fd->is_final() && java_lang_Class::is_instance(static_obj_field)) {
324 // This field points to an archived mirror.
325 return;
326 }
327
328 if (field_type->is_instance_klass()) {
329 InstanceKlass* field_ik = InstanceKlass::cast(field_type);
330 if (field_ik->is_enum_subclass()) {
331 if (field_ik->has_archived_enum_objs() || ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
332 // This field is an Enum. If any instance of this Enum has been archived, we will archive
333 // all static fields of this Enum as well.
334 return;
335 }
336 }
337
338 if (field_ik->is_hidden() && ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
339 // We have a static field in a core-library class that points to a method reference, which
340 // are safe to archive.
341 guarantee(_ik->module()->name() == vmSymbols::java_base(), "sanity");
342 return;
343 }
344
345 if (field_ik == vmClasses::MethodType_klass()) {
346 // The identity of MethodTypes are preserved between assembly phase and production runs
347 // (by MethodType::AOTHolder::archivedMethodTypes). No need to check.
348 return;
349 }
350
351 if (ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
352 if (field_ik == vmClasses::internal_Unsafe_klass()) {
353 // There's only a single instance of jdk/internal/misc/Unsafe, so all references will
354 // be pointing to this singleton, which has been archived.
355 return;
356 }
357 if (field_ik == vmClasses::Boolean_klass()) {
358 // TODO: check if is TRUE or FALSE
359 return;
360 }
361 }
362 }
363
364 // This field *may* be initialized to a different value at runtime. Remember it
365 // and check later if it appears in the archived object graph.
366 _verifier->add_static_obj_field(_ik, static_obj_field, fd->name());
367 }
368 }
369 };
370
371 // Remember all the static object fields of every class that are currently
372 // loaded. Later, we will check if any archived objects reference one of
373 // these fields.
374 void CDSHeapVerifier::do_klass(Klass* k) {
375 if (k->is_instance_klass()) {
376 InstanceKlass* ik = InstanceKlass::cast(k);
377
378 if (HeapShared::is_subgraph_root_class(ik)) {
379 // ik is inside one of the ArchivableStaticFieldInfo tables
380 // in heapShared.cpp. We assume such classes are programmed to
381 // update their static fields correctly at runtime.
382 return;
383 }
384
385 if (ArchiveUtils::has_aot_initialized_mirror(ik)) {
386 // ik's <clinit> won't be executed at runtime, the static fields in
387 // ik will carry their values to runtime.
388 return;
389 }
390
391 CheckStaticFields csf(this, ik);
392 ik->do_local_static_fields(&csf);
393 }
394 }
395
396 void CDSHeapVerifier::add_static_obj_field(InstanceKlass* ik, oop field, Symbol* name) {
397 StaticFieldInfo info = {ik, name};
398 _table.put(field, info);
399 }
400
401 // This function is called once for every archived heap object. Warn if this object is referenced by
402 // a static field of a class that's not aot-initialized.
403 inline bool CDSHeapVerifier::do_entry(OopHandle& orig_obj_handle, HeapShared::CachedOopInfo& value) {
404 oop orig_obj = orig_obj_handle.resolve();
405 _archived_objs++;
406
407 if (java_lang_String::is_instance(orig_obj) && HeapShared::is_dumped_interned_string(orig_obj)) {
408 // It's quite often for static fields to have interned strings. These are most likely not
409 // problematic (and are hard to filter). So we will ignore them.
410 return true;
411 }
412
413 StaticFieldInfo* info = _table.get(orig_obj);
414 if (info != nullptr) {
415 ResourceMark rm;
416 char* class_name = info->_holder->name()->as_C_string();
417 char* field_name = info->_name->as_C_string();
418 LogStream ls(Log(aot, heap)::warning());
419 ls.print_cr("Archive heap points to a static field that may hold a different value at runtime:");
420 ls.print_cr("Field: %s::%s", class_name, field_name);
421 ls.print("Value: ");
422 orig_obj->print_on(&ls);
423 ls.print_cr("--- trace begin ---");
424 trace_to_root(&ls, orig_obj, nullptr, &value);
425 ls.print_cr("--- trace end ---");
426 ls.cr();
427 _problems ++;
428 }
429
430 return true; /* keep on iterating */
431 }
432
433 class CDSHeapVerifier::TraceFields : public FieldClosure {
434 oop _orig_obj;
435 oop _orig_field;
436 outputStream* _st;
437
438 public:
439 TraceFields(oop orig_obj, oop orig_field, outputStream* st)
440 : _orig_obj(orig_obj), _orig_field(orig_field), _st(st) {}
441
442 void do_field(fieldDescriptor* fd) {
443 if (fd->field_type() == T_OBJECT || fd->field_type() == T_ARRAY) {
444 oop obj_field = _orig_obj->obj_field(fd->offset());
445 if (obj_field == _orig_field) {
446 _st->print("::%s (offset = %d)", fd->name()->as_C_string(), fd->offset());
447 }
448 }
449 }
450 };
451
452 // Call this function (from gdb, etc) if you want to know why an object is archived.
453 void CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj) {
454 HeapShared::CachedOopInfo* info = HeapShared::get_cached_oop_info(orig_obj);
455 if (info != nullptr) {
456 trace_to_root(st, orig_obj, nullptr, info);
457 } else {
458 st->print_cr("Not an archived object??");
459 }
460 }
461
462 const char* static_field_name(oop mirror, oop field) {
463 Klass* k = java_lang_Class::as_Klass(mirror);
464 if (k->is_instance_klass()) {
465 for (JavaFieldStream fs(InstanceKlass::cast(k)); !fs.done(); fs.next()) {
466 if (fs.access_flags().is_static()) {
467 fieldDescriptor& fd = fs.field_descriptor();
468 switch (fd.field_type()) {
469 case T_OBJECT:
470 case T_ARRAY:
471 if (mirror->obj_field(fd.offset()) == field) {
472 return fs.name()->as_C_string();
473 }
474 break;
475 default:
476 break;
477 }
478 }
479 }
480 }
481
482 return "<unknown>";
483 }
484
485 int CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj, oop orig_field, HeapShared::CachedOopInfo* info) {
486 int level = 0;
487 if (info->orig_referrer() != nullptr) {
488 HeapShared::CachedOopInfo* ref = HeapShared::get_cached_oop_info(info->orig_referrer());
489 assert(ref != nullptr, "sanity");
490 level = trace_to_root(st, info->orig_referrer(), orig_obj, ref) + 1;
491 } else if (java_lang_String::is_instance(orig_obj)) {
492 st->print_cr("[%2d] (shared string table)", level++);
493 }
494 Klass* k = orig_obj->klass();
495 ResourceMark rm;
496 st->print("[%2d] ", level);
497 orig_obj->print_address_on(st);
498 st->print(" %s", k->internal_name());
499 if (java_lang_Class::is_instance(orig_obj)) {
500 st->print(" (%s::%s)", java_lang_Class::as_Klass(orig_obj)->external_name(), static_field_name(orig_obj, orig_field));
501 }
502 if (orig_field != nullptr) {
503 if (k->is_instance_klass()) {
504 TraceFields clo(orig_obj, orig_field, st);
505 InstanceKlass::cast(k)->do_nonstatic_fields(&clo);
506 } else {
507 assert(orig_obj->is_objArray(), "must be");
508 objArrayOop array = (objArrayOop)orig_obj;
509 for (int i = 0; i < array->length(); i++) {
510 if (array->obj_at(i) == orig_field) {
511 st->print(" @[%d]", i);
512 break;
513 }
514 }
515 }
516 }
517 st->cr();
518
519 return level;
520 }
521
522 void CDSHeapVerifier::verify() {
523 CDSHeapVerifier verf;
524 HeapShared::archived_object_cache()->iterate(&verf);
525 }
526
527 #endif // INCLUDE_CDS_JAVA_HEAP