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$Location", "EMPTY_SET"); // E
110
111 ADD_EXCL("java/lang/System", "bootLayer"); // A
112
113 ADD_EXCL("java/util/Collections", "EMPTY_LIST"); // E
114
115 // A dummy object used by HashSet. The value doesn't matter and it's never
116 // tested for equality.
117 ADD_EXCL("java/util/HashSet", "PRESENT"); // E
118
119 ADD_EXCL("jdk/internal/loader/BootLoader", "UNNAMED_MODULE"); // A
120 ADD_EXCL("jdk/internal/loader/BuiltinClassLoader", "packageToModule"); // A
121 ADD_EXCL("jdk/internal/loader/ClassLoaders", "BOOT_LOADER", // A
122 "APP_LOADER", // A
123 "PLATFORM_LOADER"); // A
124 ADD_EXCL("jdk/internal/module/Builder", "cachedVersion"); // D
125 ADD_EXCL("jdk/internal/module/ModuleLoaderMap$Mapper", "APP_CLASSLOADER", // A
126 "APP_LOADER_INDEX", // A
127 "PLATFORM_CLASSLOADER", // A
128 "PLATFORM_LOADER_INDEX"); // A
129 ADD_EXCL("jdk/internal/module/ServicesCatalog", "CLV"); // A
130
131 // This just points to an empty Map
132 ADD_EXCL("jdk/internal/reflect/Reflection", "methodFilterMap"); // E
133
134 // Integer for 0 and 1 are in java/lang/Integer$IntegerCache and are archived
135 ADD_EXCL("sun/invoke/util/ValueConversions", "ONE_INT", // E
136 "ZERO_INT"); // E
137
138 if (CDSConfig::is_dumping_method_handles()) {
139 ADD_EXCL("java/lang/invoke/InvokerBytecodeGenerator", "MEMBERNAME_FACTORY", // D
140 "CD_Object_array", // E same as <...>ConstantUtils.CD_Object_array::CD_Object
141 "INVOKER_SUPER_DESC"); // E same as java.lang.constant.ConstantDescs::CD_Object
142
143 ADD_EXCL("java/lang/runtime/ObjectMethods", "CLASS_IS_INSTANCE", // D
144 "FALSE", // D
145 "TRUE", // D
146 "ZERO"); // D
147 }
148
149 # undef ADD_EXCL
150
151 ClassLoaderDataGraph::classes_do(this);
152 }
153
154 CDSHeapVerifier::~CDSHeapVerifier() {
155 if (_problems > 0) {
156 log_error(aot, heap)("Scanned %d objects. Found %d case(s) where "
157 "an object points to a static field that "
158 "may hold a different value at runtime.", _archived_objs, _problems);
159 log_error(aot, heap)("Please see cdsHeapVerifier.cpp and aotClassInitializer.cpp for details");
160 AOTMetaspace::unrecoverable_writing_error();
161 }
162 }
163
164 class CDSHeapVerifier::CheckStaticFields : public FieldClosure {
165 CDSHeapVerifier* _verifier;
166 InstanceKlass* _ik; // The class whose static fields are being checked.
167 const char** _exclusions;
168 public:
169 CheckStaticFields(CDSHeapVerifier* verifier, InstanceKlass* ik)
170 : _verifier(verifier), _ik(ik) {
171 _exclusions = _verifier->find_exclusion(_ik);
172 }
173
174 void do_field(fieldDescriptor* fd) {
175 if (fd->field_type() != T_OBJECT) {
176 return;
177 }
178
179 if (fd->signature()->equals("Ljdk/internal/access/JavaLangAccess;")) {
180 // A few classes have static fields that point to SharedSecrets.getJavaLangAccess().
181 // This object carries no state and we can create a new one in the production run.
182 return;
183 }
184 oop static_obj_field = _ik->java_mirror()->obj_field(fd->offset());
185 if (static_obj_field != nullptr) {
186 Klass* field_type = static_obj_field->klass();
187 if (_exclusions != nullptr) {
188 for (const char** p = _exclusions; *p != nullptr; p++) {
189 if (fd->name()->equals(*p)) {
190 return;
191 }
192 }
193 }
194
195 if (fd->is_final() && java_lang_String::is_instance(static_obj_field) && fd->has_initial_value()) {
196 // This field looks like like this in the Java source:
197 // static final SOME_STRING = "a string literal";
198 // This string literal has been stored in the shared string table, so it's OK
199 // for the archived objects to refer to it.
200 return;
201 }
202 if (fd->is_final() && java_lang_Class::is_instance(static_obj_field)) {
203 // This field points to an archived mirror.
204 return;
205 }
206
207 if (field_type->is_instance_klass()) {
208 InstanceKlass* field_ik = InstanceKlass::cast(field_type);
209 if (field_ik->is_enum_subclass()) {
210 if (field_ik->has_archived_enum_objs() || ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
211 // This field is an Enum. If any instance of this Enum has been archived, we will archive
212 // all static fields of this Enum as well.
213 return;
214 }
215 }
216
217 if (field_ik->is_hidden() && ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
218 // We have a static field in a core-library class that points to a method reference, which
219 // are safe to archive.
220 guarantee(_ik->module()->name() == vmSymbols::java_base(), "sanity");
221 return;
222 }
223
224 if (field_ik == vmClasses::MethodType_klass()) {
225 // The identity of MethodTypes are preserved between assembly phase and production runs
226 // (by MethodType::AOTHolder::archivedMethodTypes). No need to check.
227 return;
228 }
229
230 if (field_ik == vmClasses::internal_Unsafe_klass() && ArchiveUtils::has_aot_initialized_mirror(field_ik)) {
231 // There's only a single instance of jdk/internal/misc/Unsafe, so all references will
232 // be pointing to this singleton, which has been archived.
233 return;
234 }
235 }
236
237 // This field *may* be initialized to a different value at runtime. Remember it
238 // and check later if it appears in the archived object graph.
239 _verifier->add_static_obj_field(_ik, static_obj_field, fd->name());
240 }
241 }
242 };
243
244 // Remember all the static object fields of every class that are currently
245 // loaded. Later, we will check if any archived objects reference one of
246 // these fields.
247 void CDSHeapVerifier::do_klass(Klass* k) {
248 if (k->is_instance_klass()) {
249 InstanceKlass* ik = InstanceKlass::cast(k);
250
251 if (HeapShared::is_subgraph_root_class(ik)) {
252 // ik is inside one of the ArchivableStaticFieldInfo tables
253 // in heapShared.cpp. We assume such classes are programmed to
254 // update their static fields correctly at runtime.
255 return;
256 }
257
258 if (ArchiveUtils::has_aot_initialized_mirror(ik)) {
259 // ik's <clinit> won't be executed at runtime, the static fields in
260 // ik will carry their values to runtime.
261 return;
262 }
263
264 CheckStaticFields csf(this, ik);
265 ik->do_local_static_fields(&csf);
266 }
267 }
268
269 void CDSHeapVerifier::add_static_obj_field(InstanceKlass* ik, oop field, Symbol* name) {
270 StaticFieldInfo info = {ik, name};
271 _table.put(field, info);
272 }
273
274 // This function is called once for every archived heap object. Warn if this object is referenced by
275 // a static field of a class that's not aot-initialized.
276 inline bool CDSHeapVerifier::do_entry(oop& orig_obj, HeapShared::CachedOopInfo& value) {
277 _archived_objs++;
278
279 if (java_lang_String::is_instance(orig_obj) && HeapShared::is_dumped_interned_string(orig_obj)) {
280 // It's quite often for static fields to have interned strings. These are most likely not
281 // problematic (and are hard to filter). So we will ignore them.
282 return true; /* keep on iterating */
283 }
284
285 StaticFieldInfo* info = _table.get(orig_obj);
286 if (info != nullptr) {
287 ResourceMark rm;
288 char* class_name = info->_holder->name()->as_C_string();
289 char* field_name = info->_name->as_C_string();
290 LogStream ls(Log(aot, heap)::warning());
291 ls.print_cr("Archive heap points to a static field that may hold a different value at runtime:");
292 ls.print_cr("Field: %s::%s", class_name, field_name);
293 ls.print("Value: ");
294 orig_obj->print_on(&ls);
295 ls.print_cr("--- trace begin ---");
296 trace_to_root(&ls, orig_obj, nullptr, &value);
297 ls.print_cr("--- trace end ---");
298 ls.cr();
299 _problems ++;
300 }
301
302 return true; /* keep on iterating */
303 }
304
305 class CDSHeapVerifier::TraceFields : public FieldClosure {
306 oop _orig_obj;
307 oop _orig_field;
308 outputStream* _st;
309
310 public:
311 TraceFields(oop orig_obj, oop orig_field, outputStream* st)
312 : _orig_obj(orig_obj), _orig_field(orig_field), _st(st) {}
313
314 void do_field(fieldDescriptor* fd) {
315 if (fd->field_type() == T_OBJECT || fd->field_type() == T_ARRAY) {
316 oop obj_field = _orig_obj->obj_field(fd->offset());
317 if (obj_field == _orig_field) {
318 _st->print("::%s (offset = %d)", fd->name()->as_C_string(), fd->offset());
319 }
320 }
321 }
322 };
323
324 // Call this function (from gdb, etc) if you want to know why an object is archived.
325 void CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj) {
326 HeapShared::CachedOopInfo* info = HeapShared::archived_object_cache()->get(orig_obj);
327 if (info != nullptr) {
328 trace_to_root(st, orig_obj, nullptr, info);
329 } else {
330 st->print_cr("Not an archived object??");
331 }
332 }
333
334 const char* static_field_name(oop mirror, oop field) {
335 Klass* k = java_lang_Class::as_Klass(mirror);
336 if (k->is_instance_klass()) {
337 for (JavaFieldStream fs(InstanceKlass::cast(k)); !fs.done(); fs.next()) {
338 if (fs.access_flags().is_static()) {
339 fieldDescriptor& fd = fs.field_descriptor();
340 switch (fd.field_type()) {
341 case T_OBJECT:
342 case T_ARRAY:
343 if (mirror->obj_field(fd.offset()) == field) {
344 return fs.name()->as_C_string();
345 }
346 break;
347 default:
348 break;
349 }
350 }
351 }
352 }
353
354 return "<unknown>";
355 }
356
357 int CDSHeapVerifier::trace_to_root(outputStream* st, oop orig_obj, oop orig_field, HeapShared::CachedOopInfo* info) {
358 int level = 0;
359 if (info->orig_referrer() != nullptr) {
360 HeapShared::CachedOopInfo* ref = HeapShared::archived_object_cache()->get(info->orig_referrer());
361 assert(ref != nullptr, "sanity");
362 level = trace_to_root(st, info->orig_referrer(), orig_obj, ref) + 1;
363 } else if (java_lang_String::is_instance(orig_obj)) {
364 st->print_cr("[%2d] (shared string table)", level++);
365 }
366 Klass* k = orig_obj->klass();
367 ResourceMark rm;
368 st->print("[%2d] ", level);
369 orig_obj->print_address_on(st);
370 st->print(" %s", k->internal_name());
371 if (java_lang_Class::is_instance(orig_obj)) {
372 st->print(" (%s::%s)", java_lang_Class::as_Klass(orig_obj)->external_name(), static_field_name(orig_obj, orig_field));
373 }
374 if (orig_field != nullptr) {
375 if (k->is_instance_klass()) {
376 TraceFields clo(orig_obj, orig_field, st);
377 InstanceKlass::cast(k)->do_nonstatic_fields(&clo);
378 } else {
379 assert(orig_obj->is_objArray(), "must be");
380 objArrayOop array = (objArrayOop)orig_obj;
381 for (int i = 0; i < array->length(); i++) {
382 if (array->obj_at(i) == orig_field) {
383 st->print(" @[%d]", i);
384 break;
385 }
386 }
387 }
388 }
389 st->cr();
390
391 return level;
392 }
393
394 void CDSHeapVerifier::verify() {
395 CDSHeapVerifier verf;
396 HeapShared::archived_object_cache()->iterate(&verf);
397 }
398
399 #endif // INCLUDE_CDS_JAVA_HEAP