1 /*
2 * Copyright (c) 2024, 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.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "cds/aotClassInitializer.hpp"
27 #include "cds/archiveBuilder.hpp"
28 #include "cds/cdsConfig.hpp"
29 #include "dumpTimeClassInfo.inline.hpp"
30 #include "cds/heapShared.hpp"
31 #include "classfile/systemDictionaryShared.hpp"
32 #include "classfile/vmSymbols.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "oops/fieldStreams.inline.hpp"
35 #include "oops/instanceKlass.inline.hpp"
36 #include "oops/symbol.hpp"
37 #include "runtime/fieldDescriptor.inline.hpp"
38 #include "runtime/javaCalls.hpp"
39 #include "runtime/mutexLocker.hpp"
40
41 // Detector for class names we wish to handle specially.
42 // It is either an exact string match or a string prefix match.
43 class AOTClassInitializer::AllowedSpec {
44 const char* _class_name;
45 bool _is_prefix;
46 int _len;
47 public:
48 AllowedSpec(const char* class_name, bool is_prefix = false)
49 : _class_name(class_name), _is_prefix(is_prefix)
50 {
51 _len = (class_name == nullptr) ? 0 : (int)strlen(class_name);
52 }
53 const char* class_name() { return _class_name; }
54
55 bool matches(Symbol* name, int len) {
56 assert(_class_name != nullptr, "caller resp.");
57 if (_is_prefix) {
58 return len >= _len && name->starts_with(_class_name);
59 } else {
60 return len == _len && name->equals(_class_name);
61 }
62 }
63 };
64
65
66 // Tell if ik has a name that matches one of the given specs.
67 bool AOTClassInitializer::is_allowed(AllowedSpec* specs, InstanceKlass* ik) {
68 Symbol* name = ik->name();
69 int len = name->utf8_length();
70 for (AllowedSpec* s = specs; s->class_name() != nullptr; s++) {
71 if (s->matches(name, len)) {
72 // If a type is included in the tables inside can_archive_initialized_mirror(), we require that
73 // - all super classes must be included
74 // - all super interfaces that have <clinit> must be included.
75 // This ensures that in the production run, we don't run the <clinit> of a supertype but skips
76 // ik's <clinit>.
77 if (ik->java_super() != nullptr) {
78 DEBUG_ONLY(ResourceMark rm);
79 assert(AOTClassInitializer::can_archive_initialized_mirror(ik->java_super()),
80 "super class %s of %s must be aot-initialized", ik->java_super()->external_name(),
81 ik->external_name());
82 }
83
84 Array<InstanceKlass*>* interfaces = ik->local_interfaces();
85 int len = interfaces->length();
86 for (int i = 0; i < len; i++) {
87 InstanceKlass* intf = interfaces->at(i);
88 if (intf->class_initializer() != nullptr) {
89 assert(AOTClassInitializer::can_archive_initialized_mirror(intf),
90 "super interface %s (which has <clinit>) of %s must be aot-initialized", intf->external_name(),
91 ik->external_name());
92 }
93 }
94
95 return true;
96 }
97 }
98 return false;
99 }
100
101
102 bool AOTClassInitializer::can_archive_initialized_mirror(InstanceKlass* ik) {
103 assert(!ArchiveBuilder::current()->is_in_buffer_space(ik), "must be source klass");
104 if (!CDSConfig::is_initing_classes_at_dump_time()) {
105 return false;
106 }
107
108 if (!ik->is_initialized()) {
109 return false;
110 }
111
112 if (ik->is_hidden()) {
113 return HeapShared::is_archivable_hidden_klass(ik);
114 }
115
116 if (ik->is_enum_subclass()) {
117 return true;
118 }
119
120 // About "static field that may hold a different value" errors:
121 //
122 // Automatic selection for aot-inited classes
123 // ==========================================
124 //
125 // When CDSConfig::is_initing_classes_at_dump_time() is enabled,
126 // HeapShared::find_all_aot_initialized_classes() finds the classes of all
127 // heap objects that are reachable from HeapShared::_run_time_special_subgraph,
128 // and mark these classes as aot-inited. This preserves the initialized
129 // mirrors of these classes, and their <clinit> methods are NOT executed
130 // at runtime.
131 //
132 // For example, with -XX:+AOTInvokeDynamicLinking, _run_time_special_subgraph
133 // will contain some DirectMethodHandle objects. As a result, the DirectMethodHandle
134 // class is automatically marked as aot-inited.
135 //
136 // When a class is aot-inited, its static fields are already set up
137 // by executing the <clinit> method at AOT assembly time. Later on
138 // in the production run, when the class would normally be
139 // initialized, the VM performs guarding and synchronization as if
140 // it were going to run the <clinit> again, but instead it simply
141 // observes that that class was aot-inited. The VM assumes that, if
142 // it were to run <clinit> again, it would get a semantically
143 // equivalent set of final field values, so it just adopts the
144 // existing field values (from AOT assembly) and skips the call to
145 // <clinit>. There may at that point be fixups performed by ad hoc
146 // code, if the VM recognizes a request in the library.
147 //
148 // It is true that this is not generally correct for all possible
149 // Java code. A <clinit> method might have a side effect beyond
150 // initializing the static fields. It might send an email somewhere
151 // noting the current time of day. In that case, such an email
152 // would have been sent during the AOT assembly phase, and the email
153 // would NOT be sent again during production. This is clearly NOT
154 // what a user would want, if this were a general purpose facility.
155 // But in fact it is only for certain well-behaved classes, which
156 // are known NOT to have such side effects. We know this because
157 // the optimization (of skipping <clinit> for aot-init classes) is
158 // only applied to classes fully defined by the JDK.
159 //
160 // (A day may come when we figure out how to gracefully extend this
161 // optimization to untrusted third parties, but it is not this day.)
162 //
163 // Manual selection
164 // ================
165 //
166 // There are important cases where one aot-init class has a side
167 // effect on another aot-class, a side effect which is not captured
168 // in any static field value in either class. The simplest example
169 // is class A forces the initialization of class B. In that case,
170 // we need to aot-init either both classes or neither. From looking
171 // at the JDK state after AOT assembly is done, it is hard to tell
172 // that A "touched" B and B might escape our notice. Another common
173 // example is A copying a field value from B. We don't know where A
174 // got the value, but it would be wrong to re-initialize B at
175 // startup, while keeping the snapshot of the old B value in A. In
176 // general, if we aot-init A, we need to aot-init every class B that
177 // somehow contributed to A's initial state, and every class C that
178 // was somehow side-effected by A's initialization. We say that the
179 // aot-init of A is "init-coupled" to those of B and C.
180 //
181 // So there are init-coupled classes that cannot be automatically discovered. For
182 // example, DirectMethodHandle::IMPL_NAMES points to MethodHandles::IMPL_NAMES,
183 // but the MethodHandles class is not automatically marked because there are
184 // no archived instances of the MethodHandles type.
185 //
186 // If we aot-initialize DirectMethodHandle, but allow MethodHandles to be
187 // initialized at runtime, MethodHandles::IMPL_NAMES will get a different
188 // value than DirectMethodHandle::IMPL_NAMES. This *may or may not* be a problem,
189 // but to ensure compatibility, we should try to preserve the identity equality
190 // of these two fields.
191 //
192 // To do that, we add MethodHandles to the indy_specs[] table below.
193 //
194 // Luckily we do not need to be all-knowing in order to choose which
195 // items to add to that table. We have tools to help detect couplings.
196 //
197 // Automatic validation
198 // ====================
199 //
200 // CDSHeapVerifier is used to detect potential problems with identity equality.
201 //
202 // A class B is assumed to be init-coupled to some aot-init class if
203 // B has a field which points to a live object X in the AOT heap.
204 // The live object X was created by some other class A which somehow
205 // used B's reference to X, perhaps with the help of an intermediate
206 // class Z. Or, B pulled the reference to X from some other class
207 // Y, and B obtained that reference from Y (or an intermediate Z).
208 // It is not certain how X got into the heap, nor whether B
209 // contributed it, but it is a good heuristic that B is init-coupled
210 // to X's class or some other aot-init class. In any case, B should
211 // be made an aot-init class as well, unless a manual inspection
212 // shows that would be a problem. If there is a problem, then the
213 // JDK code for B and/or X probably needs refactoring. If there is
214 // no problem, we add B to the list. Typically the same scan will
215 // find any other accomplices Y, Z, etc. One failure would be a
216 // class Q whose only initialization action is to scribble a special
217 // value into B, from which the value X is derived and then makes
218 // its way into the heap. In that case, the heuristic does not
219 // identify Q. It is (currently) a human responsibility, of JDK
220 // engineers, not to write such dirty JDK code, or to repair it if
221 // it crops up. Eventually we may have tools, or even a user mode
222 // with design rules and checks, that will vet our code base more
223 // automatically.
224 //
225 // To see how the tool detects the problem with MethodHandles::IMPL_NAMES:
226 //
227 // - Comment out all the lines in indy_specs[] except the {nullptr} line.
228 // - Rebuild the JDK
229 //
230 // Then run the following:
231 // java -XX:AOTMode=record -XX:AOTConfiguration=jc.aotconfig com.sun.tools.javac.Main
232 // java -XX:AOTMode=create -Xlog:cds -XX:AOTCache=jc.aot -XX:AOTConfiguration=jc.aotconfig
233 //
234 // You will see an error like this:
235 //
236 // Archive heap points to a static field that may hold a different value at runtime:
237 // Field: java/lang/invoke/MethodHandles::IMPL_NAMES
238 // Value: java.lang.invoke.MemberName$Factory
239 // {0x000000060e906ae8} - klass: 'java/lang/invoke/MemberName$Factory' - flags:
240 //
241 // - ---- fields (total size 2 words):
242 // --- trace begin ---
243 // [ 0] {0x000000060e8deeb0} java.lang.Class (java.lang.invoke.DirectMethodHandle::IMPL_NAMES)
244 // [ 1] {0x000000060e906ae8} java.lang.invoke.MemberName$Factory
245 // --- trace end ---
246 //
247 // Trouble-shooting
248 // ================
249 //
250 // If you see a "static field that may hold a different value" error, it's probably
251 // because you've made some changes in the JDK core libraries (most likely
252 // java.lang.invoke).
253 //
254 // - Did you add a new static field to a class that could be referenced by
255 // cached object instances of MethodType, MethodHandle, etc? You may need
256 // to add that class to indy_specs[].
257 // - Did you modify the <clinit> of the classes in java.lang.invoke such that
258 // a static field now points to an object that should not be cached (e.g.,
259 // a native resource such as a file descriptior, or a Thread)?
260 //
261 // Note that these potential problems only occur when one class gets
262 // the aot-init treatment, AND another class is init-coupled to it,
263 // AND the coupling is not detected. Currently there are a number
264 // classes that get the aot-init treatment, in java.lang.invoke
265 // because of invokedynamic. They are few enough for now to be
266 // manually tracked. There may be more in the future.
267
268 // IS_PREFIX means that we match all class names that start with a
269 // prefix. Otherwise, it is an exact match, of just one class name.
270 const bool IS_PREFIX = true;
271
272 {
273 static AllowedSpec specs[] = {
274 // everybody's favorite super
275 {"java/lang/Object"},
276
277 // above we selected all enums; we must include their super as well
278 {"java/lang/Enum"},
279 {nullptr}
280 };
281 if (is_allowed(specs, ik)) {
282 return true;
283 }
284 }
285
286 if (CDSConfig::is_dumping_invokedynamic()) {
287 // This table was created with the help of CDSHeapVerifier.
288 // Also, some $Holder classes are needed. E.g., Invokers.<clinit> explicitly
289 // initializes Invokers$Holder. Since Invokers.<clinit> won't be executed
290 // at runtime, we need to make sure Invokers$Holder is also aot-inited.
291 //
292 // We hope we can reduce the size of this list over time, and move
293 // the responsibility for identifying such classes into the JDK
294 // code itself. See tracking RFE JDK-8342481.
295 static AllowedSpec indy_specs[] = {
296 {"java/lang/constant/ConstantDescs"},
297 {"java/lang/constant/DynamicConstantDesc"},
298 {"java/lang/invoke/BoundMethodHandle"},
299 {"java/lang/invoke/BoundMethodHandle$Specializer"},
300 {"java/lang/invoke/BoundMethodHandle$Species_", IS_PREFIX},
301 {"java/lang/invoke/ClassSpecializer"},
302 {"java/lang/invoke/ClassSpecializer$", IS_PREFIX},
303 {"java/lang/invoke/DelegatingMethodHandle"},
304 {"java/lang/invoke/DelegatingMethodHandle$Holder"}, // UNSAFE.ensureClassInitialized()
305 {"java/lang/invoke/DirectMethodHandle"},
306 {"java/lang/invoke/DirectMethodHandle$Constructor"},
307 {"java/lang/invoke/DirectMethodHandle$Holder"}, // UNSAFE.ensureClassInitialized()
308 {"java/lang/invoke/Invokers"},
309 {"java/lang/invoke/Invokers$Holder"}, // UNSAFE.ensureClassInitialized()
310 {"java/lang/invoke/LambdaForm"},
311 {"java/lang/invoke/LambdaForm$Holder"}, // UNSAFE.ensureClassInitialized()
312 {"java/lang/invoke/LambdaForm$NamedFunction"},
313 {"java/lang/invoke/MethodHandle"},
314 {"java/lang/invoke/MethodHandles"},
315 {"java/lang/invoke/SimpleMethodHandle"},
316 {"java/util/Collections"},
317 {"java/util/stream/Collectors"},
318 {"jdk/internal/constant/ConstantUtils"},
319 {"jdk/internal/constant/PrimitiveClassDescImpl"},
320 {"jdk/internal/constant/ReferenceClassDescImpl"},
321
322 // Can't include this, as it will pull in MethodHandleStatics which has many environment
323 // dependencies (on system properties, etc).
324 // MethodHandleStatics is an example of a class that must NOT get the aot-init treatment,
325 // because of its strong reliance on (a) final fields which are (b) environmentally determined.
326 //{"java/lang/invoke/InvokerBytecodeGenerator"},
327
328 {nullptr}
329 };
330 if (is_allowed(indy_specs, ik)) {
331 return true;
332 }
333 }
334
335 return false;
336 }
337
338 // TODO: currently we have a hard-coded list. We should turn this into
339 // an annotation: @jdk.internal.vm.annotation.RuntimeSetupRequired
340 // See JDK-8342481.
341 bool AOTClassInitializer::is_runtime_setup_required(InstanceKlass* ik) {
342 return ik == vmClasses::Class_klass() ||
343 ik == vmClasses::internal_Unsafe_klass() ||
344 ik == vmClasses::ConcurrentHashMap_klass() ||
345 ik->name()->equals("java/net/URI") ||
346 ik->name()->equals("java/lang/module/ModuleDescriptor");
347 }
348
349 void AOTClassInitializer::call_runtime_setup(JavaThread* current, InstanceKlass* ik) {
350 assert(ik->has_aot_initialized_mirror(), "sanity");
351 if (ik->is_runtime_setup_required()) {
352 if (log_is_enabled(Info, cds, init)) {
353 ResourceMark rm;
354 log_info(cds, init)("Calling %s::runtimeSetup()", ik->external_name());
355 }
356 JavaValue result(T_VOID);
357 JavaCalls::call_static(&result, ik,
358 vmSymbols::runtimeSetup(),
359 vmSymbols::void_method_signature(), current);
360 if (current->has_pending_exception()) {
361 // We cannot continue, as we might have cached instances of ik in the heap, but propagating the
362 // exception would cause ik to be in an error state.
363 AOTLinkedClassBulkLoader::exit_on_exception(current);
364 }
365 }
366 }
367
368 // check_can_be_preinited() is quite costly, so we cache the results inside
369 // DumpTimeClassInfo::_can_be_preinited. See also AOTClassInitializer::reset_preinit_check().
370 bool AOTClassInitializer::check_can_be_preinited(InstanceKlass* ik) {
371 ResourceMark rm;
372
373 if (!SystemDictionaryShared::is_builtin(ik)) {
374 log_info(cds, init)("cannot initialize %s (not built-in loader)", ik->external_name());
375 return false;
376 }
377
378 InstanceKlass* super = ik->java_super();
379 if (super != nullptr && !can_be_preinited_locked(super)) {
380 log_info(cds, init)("cannot initialize %s (super %s not initable)", ik->external_name(), super->external_name());
381 return false;
382 }
383
384 Array<InstanceKlass*>* interfaces = ik->local_interfaces();
385 for (int i = 0; i < interfaces->length(); i++) {
386 if (!can_be_preinited_locked(interfaces->at(i))) {
387 log_info(cds, init)("cannot initialize %s (interface %s not initable)",
388 ik->external_name(), interfaces->at(i)->external_name());
389 return false;
390 }
391 }
392
393 if (HeapShared::is_lambda_form_klass(ik)) {
394 // We allow only these to have <clinit> or non-default static fields
395 return true;
396 }
397
398 if (ik->class_initializer() != nullptr) {
399 log_info(cds, init)("cannot initialize %s (has <clinit>)", ik->external_name());
400 return false;
401 }
402 if (ik->is_initialized() && !has_default_static_fields(ik)) {
403 return false;
404 }
405
406 return true;
407 }
408
409 bool AOTClassInitializer::has_default_static_fields(InstanceKlass* ik) {
410 oop mirror = ik->java_mirror();
411
412 for (JavaFieldStream fs(ik); !fs.done(); fs.next()) {
413 if (fs.access_flags().is_static()) {
414 fieldDescriptor& fd = fs.field_descriptor();
415 int offset = fd.offset();
416 bool is_default = true;
417 bool has_initval = fd.has_initial_value();
418 switch (fd.field_type()) {
419 case T_OBJECT:
420 case T_ARRAY:
421 is_default = mirror->obj_field(offset) == nullptr;
422 break;
423 case T_BOOLEAN:
424 is_default = mirror->bool_field(offset) == (has_initval ? fd.int_initial_value() : 0);
425 break;
426 case T_BYTE:
427 is_default = mirror->byte_field(offset) == (has_initval ? fd.int_initial_value() : 0);
428 break;
429 case T_SHORT:
430 is_default = mirror->short_field(offset) == (has_initval ? fd.int_initial_value() : 0);
431 break;
432 case T_CHAR:
433 is_default = mirror->char_field(offset) == (has_initval ? fd.int_initial_value() : 0);
434 break;
435 case T_INT:
436 is_default = mirror->int_field(offset) == (has_initval ? fd.int_initial_value() : 0);
437 break;
438 case T_LONG:
439 is_default = mirror->long_field(offset) == (has_initval ? fd.long_initial_value() : 0);
440 break;
441 case T_FLOAT:
442 is_default = mirror->float_field(offset) == (has_initval ? fd.float_initial_value() : 0);
443 break;
444 case T_DOUBLE:
445 is_default = mirror->double_field(offset) == (has_initval ? fd.double_initial_value() : 0);
446 break;
447 default:
448 ShouldNotReachHere();
449 }
450
451 if (!is_default) {
452 log_info(cds, init)("cannot initialize %s (static field %s has non-default value)",
453 ik->external_name(), fd.name()->as_C_string());
454 return false;
455 }
456 }
457 }
458
459 return true;
460 }
461
462 bool AOTClassInitializer::can_be_preinited(InstanceKlass* ik) {
463 MutexLocker ml(DumpTimeTable_lock, Mutex::_no_safepoint_check_flag);
464 return can_be_preinited_locked(ik);
465 }
466
467 bool AOTClassInitializer::can_be_preinited_locked(InstanceKlass* ik) {
468 if (!CDSConfig::is_initing_classes_at_dump_time()) {
469 return false;
470 }
471
472 assert_lock_strong(DumpTimeTable_lock);
473 DumpTimeClassInfo* info = SystemDictionaryShared::get_info_locked(ik);
474 if (!info->has_done_preinit_check()) {
475 info->set_can_be_preinited(AOTClassInitializer::check_can_be_preinited(ik));
476 }
477 return info->can_be_preinited();
478 }
479
480 // Initialize a class at dump time, if possible.
481 void AOTClassInitializer::maybe_preinit_class(InstanceKlass* ik, TRAPS) {
482 #if 0 // FIXME -- leyden+JEP483 merge
483 if (!ik->is_initialized() && AOTClassInitializer::can_be_preinited(ik)) {
484 if (log_is_enabled(Info, cds, init)) {
485 ResourceMark rm;
486 log_info(cds, init)("preinitializing %s", ik->external_name());
487 }
488 ik->initialize(CHECK);
489 }
490 #endif
491 }