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,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
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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/systemDictionaryShared.hpp"
32 #include "classfile/vmSymbols.hpp"
33 #include "logging/log.hpp"
34 #include "logging/logStream.hpp"
35 #include "memory/resourceArea.hpp"
36 #include "oops/fieldStreams.inline.hpp"
37 #include "oops/klass.inline.hpp"
38 #include "oops/oop.inline.hpp"
39 #include "runtime/fieldDescriptor.inline.hpp"
40
41 #if INCLUDE_CDS_JAVA_HEAP
42
43 // CDSHeapVerifier is used to check for problems where an archived object references a
44 // static field that may be get a different value at runtime.
45 //
46 // *Please see comments in aotClassInitializer.cpp for how to avoid such problems*,
47 //
48 // In the following example,
49 // Foo.get.test()
50 // correctly returns true when CDS disabled, but incorrectly returns false when CDS is enabled,
51 // because the archived archivedFoo.bar value is different than Bar.bar.
52 //
53 // class Foo {
54 // static final Foo archivedFoo; // this field is archived by CDS
55 // Bar bar;
56 // static {
57 // CDS.initializeFromArchive(Foo.class);
58 // if (archivedFoo == null) {
59 // archivedFoo = new Foo();
60 // archivedFoo.bar = Bar.bar;
61 // }
62 // }
63 // static Foo get() { return archivedFoo; }
64 // boolean test() {
65 // return bar == Bar.bar;
66 // }
67 // }
68 //
69 // class Bar {
70 // // this field is initialized in both CDS dump time and runtime.
71 // static final Bar bar = new Bar();
72 // }
73 //
74 // The check itself is simple:
75 // [1] CDSHeapVerifier::do_klass() collects all static fields
76 // [2] CDSHeapVerifier::do_entry() checks all the archived objects. None of them
77 // should be in [1]
78 //
79 // However, it's legal for *some* static fields to be referenced. The reasons are explained
80 // in the table of ADD_EXCL below.
81 //
82 // [A] In most of the cases, the module bootstrap code will update the static field
83 // to point to part of the archived module graph. E.g.,
84 // - java/lang/System::bootLayer
85 // - jdk/internal/loader/ClassLoaders::BOOT_LOADER
86 // [B] A final static String that's explicitly initialized inside <clinit>, but
87 // its value is deterministic and is always the same string literal.
88 // [C] A non-final static string that is assigned a string literal during class
89 // initialization; this string is never changed during -Xshare:dump.
90 // [D] Simple caches whose value doesn't matter.
91 // [E] Other cases (see comments in-line below).
92
93 CDSHeapVerifier::CDSHeapVerifier() : _archived_objs(0), _problems(0)
94 {
95 # define ADD_EXCL(...) { static const char* e[] = {__VA_ARGS__, nullptr}; add_exclusion(e); }
96
97 // Unfortunately this needs to be manually maintained. If
98 // test/hotspot/jtreg/runtime/cds/appcds/cacheObject/ArchivedEnumTest.java fails,
99 // you might need to fix the core library code, or fix the ADD_EXCL entries below.
100 //
101 // class field type
102 ADD_EXCL("java/lang/ClassLoader", "scl"); // A
103 ADD_EXCL("java/lang/Module", "ALL_UNNAMED_MODULE", // A
104 "ALL_UNNAMED_MODULE_SET", // A
105 "EVERYONE_MODULE", // A
106 "EVERYONE_SET"); // A
107
108 // This is the same as java/util/ImmutableCollections::EMPTY_SET, which is archived
109 ADD_EXCL("java/lang/reflect/AccessFlag$Location", "EMPTY_SET"); // E
110
111 ADD_EXCL("java/lang/System", "bootLayer"); // A
112
113 ADD_EXCL("java/util/Collections", "EMPTY_LIST"); // E
114
115 // A dummy object used by HashSet. The value doesn't matter and it's never
116 // tested for equality.
117 ADD_EXCL("java/util/HashSet", "PRESENT"); // E
118 ADD_EXCL("jdk/internal/loader/BuiltinClassLoader", "packageToModule"); // A
119 ADD_EXCL("jdk/internal/loader/ClassLoaders", "BOOT_LOADER", // A
120 "APP_LOADER", // A
121 "PLATFORM_LOADER"); // A
122 ADD_EXCL("jdk/internal/module/Builder", "cachedVersion"); // D
123 ADD_EXCL("jdk/internal/module/ModuleLoaderMap$Mapper", "APP_CLASSLOADER", // A
124 "APP_LOADER_INDEX", // A
125 "PLATFORM_CLASSLOADER", // A
126 "PLATFORM_LOADER_INDEX"); // A
127 ADD_EXCL("jdk/internal/module/ServicesCatalog", "CLV"); // A
128
129 // This just points to an empty Map
130 ADD_EXCL("jdk/internal/reflect/Reflection", "methodFilterMap"); // E
131
132 // Integer for 0 and 1 are in java/lang/Integer$IntegerCache and are archived
133 ADD_EXCL("sun/invoke/util/ValueConversions", "ONE_INT", // E
134 "ZERO_INT"); // E
135
136 if (CDSConfig::is_dumping_method_handles()) {
137 ADD_EXCL("java/lang/invoke/InvokerBytecodeGenerator", "MEMBERNAME_FACTORY", // D
138 "CD_Object_array", // E same as <...>ConstantUtils.CD_Object_array::CD_Object
139 "INVOKER_SUPER_DESC"); // E same as java.lang.constant.ConstantDescs::CD_Object
140
141 ADD_EXCL("java/lang/runtime/ObjectMethods", "CLASS_IS_INSTANCE", // D
142 "FALSE", // D
143 "TRUE", // D
144 "ZERO"); // D
145 }
146
147 # undef ADD_EXCL
148
149 ClassLoaderDataGraph::classes_do(this);
150 }
151
152 CDSHeapVerifier::~CDSHeapVerifier() {
153 if (_problems > 0) {
154 log_error(aot, heap)("Scanned %d objects. Found %d case(s) where "
155 "an object points to a static field that "
156 "may hold a different value at runtime.", _archived_objs, _problems);
157 log_error(aot, heap)("Please see cdsHeapVerifier.cpp and aotClassInitializer.cpp for details");
158 MetaspaceShared::unrecoverable_writing_error();
159 }
160 }
161
162 class CDSHeapVerifier::CheckStaticFields : public FieldClosure {
163 CDSHeapVerifier* _verifier;
164 InstanceKlass* _ik; // The class whose static fields are being checked.
165 const char** _exclusions;
166 public:
167 CheckStaticFields(CDSHeapVerifier* verifier, InstanceKlass* ik)
168 : _verifier(verifier), _ik(ik) {
169 _exclusions = _verifier->find_exclusion(_ik);
170 }
171
172 void do_field(fieldDescriptor* fd) {
173 if (fd->field_type() != T_OBJECT) {
174 return;
175 }
176
177 if (fd->signature()->equals("Ljdk/internal/access/JavaLangAccess;")) {
178 // A few classes have static fields that point to SharedSecrets.getJavaLangAccess().
179 // This object carries no state and we can create a new one in the production run.
180 return;
181 }
182 oop static_obj_field = _ik->java_mirror()->obj_field(fd->offset());
183 if (static_obj_field != nullptr) {
184 Klass* field_type = static_obj_field->klass();
185 if (_exclusions != nullptr) {
186 for (const char** p = _exclusions; *p != nullptr; p++) {
187 if (fd->name()->equals(*p)) {
188 return;
189 }
190 }
191 }
192
193 if (fd->is_final() && java_lang_String::is_instance(static_obj_field) && fd->has_initial_value()) {
194 // This field looks like like this in the Java source:
195 // static final SOME_STRING = "a string literal";
196 // This string literal has been stored in the shared string table, so it's OK
197 // for the archived objects to refer to it.
198 return;
199 }
200 if (fd->is_final() && java_lang_Class::is_instance(static_obj_field)) {
201 // This field points to an archived mirror.
202 return;
203 }
204
205 if (field_type->is_instance_klass()) {
206 InstanceKlass* field_ik = InstanceKlass::cast(field_type);
207 if (field_ik->is_enum_subclass()) {
208 if (field_ik->has_archived_enum_objs() || ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
209 // This field is an Enum. If any instance of this Enum has been archived, we will archive
210 // all static fields of this Enum as well.
211 return;
212 }
213 }
214
215 if (field_ik->is_hidden() && ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
216 // We have a static field in a core-library class that points to a method reference, which
217 // are safe to archive.
218 guarantee(_ik->module()->name() == vmSymbols::java_base(), "sanity");
219 return;
220 }
221
222 if (field_ik == vmClasses::MethodType_klass()) {
223 // The identity of MethodTypes are preserved between assembly phase and production runs
224 // (by MethodType::AOTHolder::archivedMethodTypes). No need to check.
225 return;
226 }
227
228 if (field_ik == vmClasses::internal_Unsafe_klass() && ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
229 // There's only a single instance of jdk/internal/misc/Unsafe, so all references will
230 // be pointing to this singleton, which has been archived.
231 return;
232 }
233 }
234
235 // This field *may* be initialized to a different value at runtime. Remember it
236 // and check later if it appears in the archived object graph.
237 _verifier->add_static_obj_field(_ik, static_obj_field, fd->name());
238 }
239 }
240 };
241
242 // Remember all the static object fields of every class that are currently
243 // loaded. Later, we will check if any archived objects reference one of
244 // these fields.
245 void CDSHeapVerifier::do_klass(Klass* k) {
246 if (k->is_instance_klass()) {
247 InstanceKlass* ik = InstanceKlass::cast(k);
248
249 if (HeapShared::is_subgraph_root_class(ik)) {
250 // ik is inside one of the ArchivableStaticFieldInfo tables
251 // in heapShared.cpp. We assume such classes are programmed to
252 // update their static fields correctly at runtime.
253 return;
254 }
255
256 if (ArchiveUtils::has_aot_initialized_mirror(ik)) {
257 // ik's <clinit> won't be executed at runtime, the static fields in
258 // ik will carry their values to runtime.
259 return;
260 }
261
262 CheckStaticFields csf(this, ik);
263 ik->do_local_static_fields(&csf);
264 }
265 }
266
267 void CDSHeapVerifier::add_static_obj_field(InstanceKlass* ik, oop field, Symbol* name) {
268 StaticFieldInfo info = {ik, name};
269 _table.put(field, info);
270 }
271
272 // This function is called once for every archived heap object. Warn if this object is referenced by
273 // a static field of a class that's not aot-initialized.
274 inline bool CDSHeapVerifier::do_entry(oop& orig_obj, HeapShared::CachedOopInfo& value) {
275 _archived_objs++;
276
277 if (java_lang_String::is_instance(orig_obj) && HeapShared::is_dumped_interned_string(orig_obj)) {
278 // It's quite often for static fields to have interned strings. These are most likely not
279 // problematic (and are hard to filter). So we will ignore them.
280 return true; /* keep on iterating */
281 }
282
283 StaticFieldInfo* info = _table.get(orig_obj);
284 if (info != nullptr) {
285 ResourceMark rm;
286 char* class_name = info->_holder->name()->as_C_string();
287 char* field_name = info->_name->as_C_string();
288 LogStream ls(Log(aot, heap)::warning());
289 ls.print_cr("Archive heap points to a static field that may hold a different value at runtime:");
290 ls.print_cr("Field: %s::%s", class_name, field_name);
291 ls.print("Value: ");
292 orig_obj->print_on(&ls);
293 ls.print_cr("--- trace begin ---");
294 trace_to_root(&ls, orig_obj, nullptr, &value);
295 ls.print_cr("--- trace end ---");
296 ls.cr();
297 _problems ++;
298 }
299
300 return true; /* keep on iterating */
301 }
302
303 class CDSHeapVerifier::TraceFields : public FieldClosure {
304 oop _orig_obj;
305 oop _orig_field;
306 outputStream* _st;
307
308 public:
309 TraceFields(oop orig_obj, oop orig_field, outputStream* st)
310 : _orig_obj(orig_obj), _orig_field(orig_field), _st(st) {}
311
312 void do_field(fieldDescriptor* fd) {
313 if (fd->field_type() == T_OBJECT || fd->field_type() == T_ARRAY) {
314 oop obj_field = _orig_obj->obj_field(fd->offset());
315 if (obj_field == _orig_field) {
316 _st->print("::%s (offset = %d)", fd->name()->as_C_string(), fd->offset());
317 }
318 }
319 }
320 };
321
322 // Call this function (from gdb, etc) if you want to know why an object is archived.
323 void CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj) {
324 HeapShared::CachedOopInfo* info = HeapShared::archived_object_cache()->get(orig_obj);
325 if (info != nullptr) {
326 trace_to_root(st, orig_obj, nullptr, info);
327 } else {
328 st->print_cr("Not an archived object??");
329 }
330 }
331
332 const char* static_field_name(oop mirror, oop field) {
333 Klass* k = java_lang_Class::as_Klass(mirror);
334 if (k->is_instance_klass()) {
335 for (JavaFieldStream fs(InstanceKlass::cast(k)); !fs.done(); fs.next()) {
336 if (fs.access_flags().is_static()) {
337 fieldDescriptor& fd = fs.field_descriptor();
338 switch (fd.field_type()) {
339 case T_OBJECT:
340 case T_ARRAY:
341 if (mirror->obj_field(fd.offset()) == field) {
342 return fs.name()->as_C_string();
343 }
344 break;
345 default:
346 break;
347 }
348 }
349 }
350 }
351
352 return "<unknown>";
353 }
354
355 int CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj, oop orig_field, HeapShared::CachedOopInfo* info) {
356 int level = 0;
357 if (info->orig_referrer() != nullptr) {
358 HeapShared::CachedOopInfo* ref = HeapShared::archived_object_cache()->get(info->orig_referrer());
359 assert(ref != nullptr, "sanity");
360 level = trace_to_root(st, info->orig_referrer(), orig_obj, ref) + 1;
361 } else if (java_lang_String::is_instance(orig_obj)) {
362 st->print_cr("[%2d] (shared string table)", level++);
363 }
364 Klass* k = orig_obj->klass();
365 ResourceMark rm;
366 st->print("[%2d] ", level);
367 orig_obj->print_address_on(st);
368 st->print(" %s", k->internal_name());
369 if (java_lang_Class::is_instance(orig_obj)) {
370 st->print(" (%s::%s)", java_lang_Class::as_Klass(orig_obj)->external_name(), static_field_name(orig_obj, orig_field));
371 }
372 if (orig_field != nullptr) {
373 if (k->is_instance_klass()) {
374 TraceFields clo(orig_obj, orig_field, st);
375 InstanceKlass::cast(k)->do_nonstatic_fields(&clo);
376 } else {
377 assert(orig_obj->is_objArray(), "must be");
378 objArrayOop array = (objArrayOop)orig_obj;
379 for (int i = 0; i < array->length(); i++) {
380 if (array->obj_at(i) == orig_field) {
381 st->print(" @[%d]", i);
382 break;
383 }
384 }
385 }
386 }
387 st->cr();
388
389 return level;
390 }
391
392 void CDSHeapVerifier::verify() {
393 CDSHeapVerifier verf;
394 HeapShared::archived_object_cache()->iterate(&verf);
395 }
396
397 #endif // INCLUDE_CDS_JAVA_HEAP