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.
8 *
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).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
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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 CDSHeapVerifier::CDSHeapVerifier() : _archived_objs(0), _problems(0)
98 {
99 # define ADD_EXCL(...) { static const char* e[] = {__VA_ARGS__, nullptr}; add_exclusion(e); }
100
101 // Unfortunately this needs to be manually maintained. If
102 // test/hotspot/jtreg/runtime/cds/appcds/cacheObject/ArchivedEnumTest.java fails,
103 // you might need to fix the core library code, or fix the ADD_EXCL entries below.
104 //
105 // class field type
106 ADD_EXCL("java/lang/ClassLoader$Holder", "scl"); // A
107 ADD_EXCL("java/lang/Module", "ALL_UNNAMED_MODULE", // A
108 "ALL_UNNAMED_MODULE_SET", // A
109 "EVERYONE_MODULE", // A
110 "EVERYONE_SET"); // A
111
112 // This is the same as java/util/ImmutableCollections::EMPTY_SET, which is archived
113 ADD_EXCL("java/lang/reflect/AccessFlag$Location", "EMPTY_SET"); // E
114
115 ADD_EXCL("java/lang/System", "bootLayer"); // A
116
117 ADD_EXCL("java/util/Collections", "EMPTY_LIST"); // E
118
119 // A dummy object used by HashSet. The value doesn't matter and it's never
120 // tested for equality.
121 ADD_EXCL("java/util/HashSet", "PRESENT"); // E
122
123 ADD_EXCL("jdk/internal/loader/BootLoader", "UNNAMED_MODULE"); // A
124 ADD_EXCL("jdk/internal/loader/BuiltinClassLoader", "packageToModule"); // A
125 ADD_EXCL("jdk/internal/loader/ClassLoaders", "BOOT_LOADER", // A
126 "APP_LOADER", // A
127 "PLATFORM_LOADER"); // A
128 ADD_EXCL("jdk/internal/module/Builder", "cachedVersion"); // D
129 ADD_EXCL("jdk/internal/module/ModuleLoaderMap$Mapper", "APP_CLASSLOADER", // A
130 "APP_LOADER_INDEX", // A
131 "PLATFORM_CLASSLOADER", // A
132 "PLATFORM_LOADER_INDEX"); // A
133 ADD_EXCL("jdk/internal/module/ServicesCatalog", "CLV"); // A
134
135 // This just points to an empty Map
136 ADD_EXCL("jdk/internal/reflect/Reflection", "methodFilterMap"); // E
137
138 // Integer for 0 and 1 are in java/lang/Integer$IntegerCache and are archived
139 ADD_EXCL("sun/invoke/util/ValueConversions", "ONE_INT", // E
140 "ZERO_INT"); // E
141
142 if (CDSConfig::is_dumping_method_handles()) {
143 ADD_EXCL("java/lang/invoke/InvokerBytecodeGenerator", "MEMBERNAME_FACTORY", // D
144 "CD_Object_array", // E same as <...>ConstantUtils.CD_Object_array::CD_Object
145 "INVOKER_SUPER_DESC"); // E same as java.lang.constant.ConstantDescs::CD_Object
146
147 ADD_EXCL("java/lang/runtime/ObjectMethods", "CLASS_IS_INSTANCE", // D
148 "FALSE", // D
149 "TRUE", // D
150 "ZERO"); // D
151 }
152
153 if (CDSConfig::is_dumping_aot_linked_classes()) {
154 ADD_EXCL("java/lang/Package$VersionInfo", "NULL_VERSION_INFO"); // D
155 }
156
157 if (CDSConfig::is_dumping_dynamic_proxies()) {
158 ADD_EXCL("java/lang/reflect/ProxyGenerator", "CD_Object_array"); // D
159 }
160
161 // These are used by BuiltinClassLoader::negativeLookupCache, etc but seem to be
162 // OK. TODO - we should completely disable the caching unless ArchiveLoaderLookupCache
163 // is enabled
164 ADD_EXCL("java/lang/Boolean", "TRUE", // E
165 "FALSE"); // E
166
167 # undef ADD_EXCL
168
169 if (CDSConfig::is_initing_classes_at_dump_time()) {
170 add_shared_secret_accessors();
171 }
172 ClassLoaderDataGraph::classes_do(this);
173 }
174
175 // We allow only "stateless" accessors in the SharedSecrets class to be AOT-initialized, for example,
176 // in the following pattern:
177 //
178 // class URL {
179 // static {
180 // SharedSecrets.setJavaNetURLAccess(
181 // new JavaNetURLAccess() { ... });
182 // }
183 //
184 // This initializes the field SharedSecrets::javaNetUriAccess, whose type (the inner case in the
185 // above example) has no fields (static or otherwise) and is not a hidden class, so it cannot possibly
186 // capture any transient state from the assembly phase that might become invalid in the production run.
187 //
188 class CDSHeapVerifier::SharedSecretsAccessorFinder : public FieldClosure {
189 CDSHeapVerifier* _verifier;
190 InstanceKlass* _ik;
191 public:
192 SharedSecretsAccessorFinder(CDSHeapVerifier* verifier, InstanceKlass* ik)
193 : _verifier(verifier), _ik(ik) {}
194
195 void do_field(fieldDescriptor* fd) {
196 if (fd->field_type() == T_OBJECT) {
197 oop static_obj_field = _ik->java_mirror()->obj_field(fd->offset());
198 if (static_obj_field != nullptr) {
199 Klass* field_type = static_obj_field->klass();
200
201 if (!field_type->is_instance_klass()) {
202 ResourceMark rm;
203 log_error(aot, heap)("jdk.internal.access.SharedSecrets::%s must not be an array",
204 fd->name()->as_C_string());
205 AOTMetaspace::unrecoverable_writing_error();
206 }
207
208 InstanceKlass* field_type_ik = InstanceKlass::cast(field_type);
209 if (has_any_fields(field_type_ik) || field_type_ik->is_hidden()) {
210 // If field_type_ik is a hidden class, the accessor is probably initialized using a
211 // Lambda, which may contain transient states.
212 ResourceMark rm;
213 log_error(aot, heap)("jdk.internal.access.SharedSecrets::%s (%s) must be stateless",
214 fd->name()->as_C_string(), field_type_ik->external_name());
215 AOTMetaspace::unrecoverable_writing_error();
216 }
217
218 _verifier->add_shared_secret_accessor(static_obj_field);
219 }
220 }
221 }
222
223 // Does k (or any of its supertypes) have at least one (static or non-static) field?
224 static bool has_any_fields(InstanceKlass* k) {
225 if (k->static_field_size() != 0 || k->nonstatic_field_size() != 0) {
226 return true;
227 }
228
229 if (k->super() != nullptr && has_any_fields(k->super())) {
230 return true;
231 }
232
233 Array<InstanceKlass*>* interfaces = k->local_interfaces();
234 int num_interfaces = interfaces->length();
235 for (int index = 0; index < num_interfaces; index++) {
236 if (has_any_fields(interfaces->at(index))) {
237 return true;
238 }
239 }
240
241 return false;
242 }
243 };
244
245 // This function is for allowing the following pattern in the core libraries:
246 //
247 // public class URLClassPath {
248 // private static final JavaNetURLAccess JNUA = SharedSecrets.getJavaNetURLAccess();
249 //
250 // SharedSecrets::javaNetUriAccess has no states so it can be safely AOT-initialized. During
251 // the production run, even if URLClassPath.<clinit> is re-executed, it will get back the same
252 // instance of javaNetUriAccess as it did during the assembly phase.
253 //
254 // Note: this will forbid complex accessors such as SharedSecrets::javaObjectInputFilterAccess
255 // to be initialized during the AOT assembly phase.
256 void CDSHeapVerifier::add_shared_secret_accessors() {
257 TempNewSymbol klass_name = SymbolTable::new_symbol("jdk/internal/access/SharedSecrets");
258 InstanceKlass* ik = SystemDictionary::find_instance_klass(Thread::current(), klass_name,
259 Handle());
260 assert(ik != nullptr, "must have been loaded");
261
262 SharedSecretsAccessorFinder finder(this, ik);
263 ik->do_local_static_fields(&finder);
264 }
265
266 CDSHeapVerifier::~CDSHeapVerifier() {
267 if (_problems > 0) {
268 log_error(aot, heap)("Scanned %zu objects. Found %d case(s) where "
269 "an object points to a static field that "
270 "may hold a different value at runtime.", _archived_objs, _problems);
271 log_error(aot, heap)("Please see cdsHeapVerifier.cpp and aotClassInitializer.cpp for details");
272 AOTMetaspace::unrecoverable_writing_error();
273 }
274 }
275
276 class CDSHeapVerifier::CheckStaticFields : public FieldClosure {
277 CDSHeapVerifier* _verifier;
278 InstanceKlass* _ik; // The class whose static fields are being checked.
279 const char** _exclusions;
280 public:
281 CheckStaticFields(CDSHeapVerifier* verifier, InstanceKlass* ik)
282 : _verifier(verifier), _ik(ik) {
283 _exclusions = _verifier->find_exclusion(_ik);
284 }
285
286 void do_field(fieldDescriptor* fd) {
287 if (fd->field_type() != T_OBJECT) {
288 return;
289 }
290
291 if (fd->signature()->equals("Ljdk/internal/reflect/ReflectionFactory;")) {
292 return;
293 }
294 oop static_obj_field = _ik->java_mirror()->obj_field(fd->offset());
295 if (static_obj_field != nullptr) {
296 if (_verifier->is_shared_secret_accessor(static_obj_field)) {
297 return;
298 }
299
300 Klass* field_type = static_obj_field->klass();
301 if (_exclusions != nullptr) {
302 for (const char** p = _exclusions; *p != nullptr; p++) {
303 if (fd->name()->equals(*p)) {
304 return;
305 }
306 }
307 }
308
309 if (fd->is_final() && java_lang_String::is_instance(static_obj_field) && fd->has_initial_value()) {
310 // This field looks like like this in the Java source:
311 // static final SOME_STRING = "a string literal";
312 // This string literal has been stored in the shared string table, so it's OK
313 // for the archived objects to refer to it.
314 return;
315 }
316 if (fd->is_final() && java_lang_Class::is_instance(static_obj_field)) {
317 // This field points to an archived mirror.
318 return;
319 }
320
321 if (field_type->is_instance_klass()) {
322 InstanceKlass* field_ik = InstanceKlass::cast(field_type);
323 if (field_ik->is_enum_subclass()) {
324 if (field_ik->has_archived_enum_objs() || ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
325 // This field is an Enum. If any instance of this Enum has been archived, we will archive
326 // all static fields of this Enum as well.
327 return;
328 }
329 }
330
331 if (field_ik->is_hidden() && ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
332 // We have a static field in a core-library class that points to a method reference, which
333 // are safe to archive.
334 guarantee(_ik->module()->name() == vmSymbols::java_base(), "sanity");
335 return;
336 }
337
338 if (field_ik == vmClasses::MethodType_klass()) {
339 // The identity of MethodTypes are preserved between assembly phase and production runs
340 // (by MethodType::AOTHolder::archivedMethodTypes). No need to check.
341 return;
342 }
343
344 if (ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
345 if (field_ik == vmClasses::internal_Unsafe_klass()) {
346 // There's only a single instance of jdk/internal/misc/Unsafe, so all references will
347 // be pointing to this singleton, which has been archived.
348 return;
349 }
350 if (field_ik == vmClasses::Boolean_klass()) {
351 // TODO: check if is TRUE or FALSE
352 return;
353 }
354 }
355 }
356
357 // This field *may* be initialized to a different value at runtime. Remember it
358 // and check later if it appears in the archived object graph.
359 _verifier->add_static_obj_field(_ik, static_obj_field, fd->name());
360 }
361 }
362 };
363
364 // Remember all the static object fields of every class that are currently
365 // loaded. Later, we will check if any archived objects reference one of
366 // these fields.
367 void CDSHeapVerifier::do_klass(Klass* k) {
368 if (k->is_instance_klass()) {
369 InstanceKlass* ik = InstanceKlass::cast(k);
370
371 if (HeapShared::is_subgraph_root_class(ik)) {
372 // ik is inside one of the ArchivableStaticFieldInfo tables
373 // in heapShared.cpp. We assume such classes are programmed to
374 // update their static fields correctly at runtime.
375 return;
376 }
377
378 if (ArchiveUtils::has_aot_initialized_mirror(ik)) {
379 // ik's <clinit> won't be executed at runtime, the static fields in
380 // ik will carry their values to runtime.
381 return;
382 }
383
384 CheckStaticFields csf(this, ik);
385 ik->do_local_static_fields(&csf);
386 }
387 }
388
389 void CDSHeapVerifier::add_static_obj_field(InstanceKlass* ik, oop field, Symbol* name) {
390 StaticFieldInfo info = {ik, name};
391 _table.put(field, info);
392 }
393
394 // This function is called once for every archived heap object. Warn if this object is referenced by
395 // a static field of a class that's not aot-initialized.
396 inline bool CDSHeapVerifier::do_entry(OopHandle& orig_obj_handle, HeapShared::CachedOopInfo& value) {
397 oop orig_obj = orig_obj_handle.resolve();
398 _archived_objs++;
399
400 if (java_lang_String::is_instance(orig_obj) && HeapShared::is_dumped_interned_string(orig_obj)) {
401 // It's quite often for static fields to have interned strings. These are most likely not
402 // problematic (and are hard to filter). So we will ignore them.
403 return true;
404 }
405
406 StaticFieldInfo* info = _table.get(orig_obj);
407 if (info != nullptr) {
408 ResourceMark rm;
409 char* class_name = info->_holder->name()->as_C_string();
410 char* field_name = info->_name->as_C_string();
411 LogStream ls(Log(aot, heap)::warning());
412 ls.print_cr("Archive heap points to a static field that may hold a different value at runtime:");
413 ls.print_cr("Field: %s::%s", class_name, field_name);
414 ls.print("Value: ");
415 orig_obj->print_on(&ls);
416 ls.print_cr("--- trace begin ---");
417 trace_to_root(&ls, orig_obj, nullptr, &value);
418 ls.print_cr("--- trace end ---");
419 ls.cr();
420 _problems ++;
421 }
422
423 return true; /* keep on iterating */
424 }
425
426 class CDSHeapVerifier::TraceFields : public FieldClosure {
427 oop _orig_obj;
428 oop _orig_field;
429 outputStream* _st;
430
431 public:
432 TraceFields(oop orig_obj, oop orig_field, outputStream* st)
433 : _orig_obj(orig_obj), _orig_field(orig_field), _st(st) {}
434
435 void do_field(fieldDescriptor* fd) {
436 if (fd->field_type() == T_OBJECT || fd->field_type() == T_ARRAY) {
437 oop obj_field = _orig_obj->obj_field(fd->offset());
438 if (obj_field == _orig_field) {
439 _st->print("::%s (offset = %d)", fd->name()->as_C_string(), fd->offset());
440 }
441 }
442 }
443 };
444
445 // Call this function (from gdb, etc) if you want to know why an object is archived.
446 void CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj) {
447 HeapShared::CachedOopInfo* info = HeapShared::get_cached_oop_info(orig_obj);
448 if (info != nullptr) {
449 trace_to_root(st, orig_obj, nullptr, info);
450 } else {
451 st->print_cr("Not an archived object??");
452 }
453 }
454
455 const char* static_field_name(oop mirror, oop field) {
456 Klass* k = java_lang_Class::as_Klass(mirror);
457 if (k->is_instance_klass()) {
458 for (JavaFieldStream fs(InstanceKlass::cast(k)); !fs.done(); fs.next()) {
459 if (fs.access_flags().is_static()) {
460 fieldDescriptor& fd = fs.field_descriptor();
461 switch (fd.field_type()) {
462 case T_OBJECT:
463 case T_ARRAY:
464 if (mirror->obj_field(fd.offset()) == field) {
465 return fs.name()->as_C_string();
466 }
467 break;
468 default:
469 break;
470 }
471 }
472 }
473 }
474
475 return "<unknown>";
476 }
477
478 int CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj, oop orig_field, HeapShared::CachedOopInfo* info) {
479 int level = 0;
480 if (info->orig_referrer() != nullptr) {
481 HeapShared::CachedOopInfo* ref = HeapShared::get_cached_oop_info(info->orig_referrer());
482 assert(ref != nullptr, "sanity");
483 level = trace_to_root(st, info->orig_referrer(), orig_obj, ref) + 1;
484 } else if (java_lang_String::is_instance(orig_obj)) {
485 st->print_cr("[%2d] (shared string table)", level++);
486 }
487 Klass* k = orig_obj->klass();
488 ResourceMark rm;
489 st->print("[%2d] ", level);
490 orig_obj->print_address_on(st);
491 st->print(" %s", k->internal_name());
492 if (java_lang_Class::is_instance(orig_obj)) {
493 st->print(" (%s::%s)", java_lang_Class::as_Klass(orig_obj)->external_name(), static_field_name(orig_obj, orig_field));
494 }
495 if (orig_field != nullptr) {
496 if (k->is_instance_klass()) {
497 TraceFields clo(orig_obj, orig_field, st);
498 InstanceKlass::cast(k)->do_nonstatic_fields(&clo);
499 } else {
500 assert(orig_obj->is_objArray(), "must be");
501 objArrayOop array = (objArrayOop)orig_obj;
502 for (int i = 0; i < array->length(); i++) {
503 if (array->obj_at(i) == orig_field) {
504 st->print(" @[%d]", i);
505 break;
506 }
507 }
508 }
509 }
510 st->cr();
511
512 return level;
513 }
514
515 void CDSHeapVerifier::verify() {
516 CDSHeapVerifier verf;
517 HeapShared::archived_object_cache()->iterate(&verf);
518 }
519
520 #endif // INCLUDE_CDS_JAVA_HEAP