1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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24
25 #include "cds/aotClassInitializer.hpp"
26 #include "cds/archiveBuilder.hpp"
27 #include "cds/cdsConfig.hpp"
28 #include "cds/heapShared.hpp"
29 #include "cds/regeneratedClasses.hpp"
30 #include "classfile/symbolTable.hpp"
31 #include "classfile/systemDictionaryShared.hpp"
32 #include "classfile/vmSymbols.hpp"
33 #include "dumpTimeClassInfo.inline.hpp"
34 #include "memory/resourceArea.hpp"
35 #include "oops/fieldStreams.inline.hpp"
36 #include "oops/instanceKlass.inline.hpp"
37 #include "oops/symbol.hpp"
38 #include "runtime/fieldDescriptor.inline.hpp"
39 #include "runtime/java.hpp"
40 #include "runtime/javaCalls.hpp"
41 #include "runtime/mutexLocker.hpp"
42
43 DEBUG_ONLY(InstanceKlass* _aot_init_class = nullptr;)
44
45 bool AOTClassInitializer::can_archive_initialized_mirror(InstanceKlass* ik) {
46 assert(!ArchiveBuilder::is_active() || !ArchiveBuilder::current()->is_in_buffer_space(ik), "must be source klass");
47 if (!CDSConfig::is_initing_classes_at_dump_time()) {
48 return false;
49 }
50
51 if (RegeneratedClasses::is_regenerated_object(ik)) {
52 ik = RegeneratedClasses::get_original_object(ik);
53 }
54
55 if (!ik->is_initialized() && !ik->is_being_initialized()) {
56 return false;
57 }
58
59 // About "static field that may hold a different value" errors:
60 //
61 // Automatic selection for aot-inited classes
62 // ==========================================
63 //
64 // When CDSConfig::is_initing_classes_at_dump_time is enabled,
65 // AOTArtifactFinder::find_artifacts() finds the classes of all
66 // heap objects that are reachable from HeapShared::_run_time_special_subgraph,
67 // and mark these classes as aot-inited. This preserves the initialized
68 // mirrors of these classes, and their <clinit> methods are NOT executed
69 // at runtime. See aotArtifactFinder.hpp for more info.
70 //
71 // For example, with -XX:+AOTInvokeDynamicLinking, _run_time_special_subgraph
72 // will contain some DirectMethodHandle objects. As a result, the DirectMethodHandle
73 // class is automatically marked as aot-inited.
74 //
75 // When a class is aot-inited, its static fields are already set up
76 // by executing the <clinit> method at AOT assembly time. Later on
77 // in the production run, when the class would normally be
78 // initialized, the VM performs guarding and synchronization as if
79 // it were going to run the <clinit> again, but instead it simply
80 // observes that that class was aot-inited. The VM assumes that, if
81 // it were to run <clinit> again, it would get a semantically
82 // equivalent set of final field values, so it just adopts the
83 // existing field values (from AOT assembly) and skips the call to
84 // <clinit>. There may at that point be fixups performed by ad hoc
85 // code, if the VM recognizes a request in the library.
86 //
87 // It is true that this is not generally correct for all possible
88 // Java code. A <clinit> method might have a side effect beyond
89 // initializing the static fields. It might send an email somewhere
90 // noting the current time of day. In that case, such an email
91 // would have been sent during the AOT assembly phase, and the email
92 // would NOT be sent again during production. This is clearly NOT
93 // what a user would want, if this were a general purpose facility.
94 // But in fact it is only for certain well-behaved classes, which
95 // are known NOT to have such side effects. We know this because
96 // the optimization (of skipping <clinit> for aot-init classes) is
97 // only applied to classes fully defined by the JDK.
98 //
99 // (A day may come when we figure out how to gracefully extend this
100 // optimization to untrusted third parties, but it is not this day.)
101 //
102 // Manual selection
103 // ================
104 //
105 // There are important cases where one aot-init class has a side
106 // effect on another aot-class, a side effect which is not captured
107 // in any static field value in either class. The simplest example
108 // is class A forces the initialization of class B. In that case,
109 // we need to aot-init either both classes or neither. From looking
110 // at the JDK state after AOT assembly is done, it is hard to tell
111 // that A "touched" B and B might escape our notice. Another common
112 // example is A copying a field value from B. We don't know where A
113 // got the value, but it would be wrong to re-initialize B at
114 // startup, while keeping the snapshot of the old B value in A. In
115 // general, if we aot-init A, we need to aot-init every class B that
116 // somehow contributed to A's initial state, and every class C that
117 // was somehow side-effected by A's initialization. We say that the
118 // aot-init of A is "init-coupled" to those of B and C.
119 //
120 // So there are init-coupled classes that cannot be automatically discovered. For
121 // example, DirectMethodHandle::IMPL_NAMES points to MethodHandles::IMPL_NAMES,
122 // but the MethodHandles class is not automatically marked because there are
123 // no archived instances of the MethodHandles type.
124 //
125 // If we aot-initialize DirectMethodHandle, but allow MethodHandles to be
126 // initialized at runtime, MethodHandles::IMPL_NAMES will get a different
127 // value than DirectMethodHandle::IMPL_NAMES. This *may or may not* be a problem,
128 // but to ensure compatibility, we should try to preserve the identity equality
129 // of these two fields.
130 //
131 // To do that, we add MethodHandles to the indy_specs[] table below.
132 //
133 // Luckily we do not need to be all-knowing in order to choose which
134 // items to add to that table. We have tools to help detect couplings.
135 //
136 // Automatic validation
137 // ====================
138 //
139 // CDSHeapVerifier is used to detect potential problems with identity equality.
140 //
141 // A class B is assumed to be init-coupled to some aot-init class if
142 // B has a field which points to a live object X in the AOT heap.
143 // The live object X was created by some other class A which somehow
144 // used B's reference to X, perhaps with the help of an intermediate
145 // class Z. Or, B pulled the reference to X from some other class
146 // Y, and B obtained that reference from Y (or an intermediate Z).
147 // It is not certain how X got into the heap, nor whether B
148 // contributed it, but it is a good heuristic that B is init-coupled
149 // to X's class or some other aot-init class. In any case, B should
150 // be made an aot-init class as well, unless a manual inspection
151 // shows that would be a problem. If there is a problem, then the
152 // JDK code for B and/or X probably needs refactoring. If there is
153 // no problem, we add B to the list. Typically the same scan will
154 // find any other accomplices Y, Z, etc. One failure would be a
155 // class Q whose only initialization action is to scribble a special
156 // value into B, from which the value X is derived and then makes
157 // its way into the heap. In that case, the heuristic does not
158 // identify Q. It is (currently) a human responsibility, of JDK
159 // engineers, not to write such dirty JDK code, or to repair it if
160 // it crops up. Eventually we may have tools, or even a user mode
161 // with design rules and checks, that will vet our code base more
162 // automatically.
163 //
164 // To see how the tool detects the problem with MethodHandles::IMPL_NAMES:
165 //
166 // - Comment out all the lines in indy_specs[] except the {nullptr} line.
167 // - Rebuild the JDK
168 //
169 // Then run the following:
170 // java -XX:AOTMode=record -XX:AOTConfiguration=jc.aotconfig com.sun.tools.javac.Main
171 // java -XX:AOTMode=create -Xlog:aot -XX:AOTCache=jc.aot -XX:AOTConfiguration=jc.aotconfig
172 //
173 // You will see an error like this:
174 //
175 // Archive heap points to a static field that may hold a different value at runtime:
176 // Field: java/lang/invoke/MethodHandles::IMPL_NAMES
177 // Value: java.lang.invoke.MemberName$Factory
178 // {0x000000060e906ae8} - klass: 'java/lang/invoke/MemberName$Factory' - flags:
179 //
180 // - ---- fields (total size 2 words):
181 // --- trace begin ---
182 // [ 0] {0x000000060e8deeb0} java.lang.Class (java.lang.invoke.DirectMethodHandle::IMPL_NAMES)
183 // [ 1] {0x000000060e906ae8} java.lang.invoke.MemberName$Factory
184 // --- trace end ---
185 //
186 // Trouble-shooting
187 // ================
188 //
189 // If you see a "static field that may hold a different value" error, it's probably
190 // because you've made some changes in the JDK core libraries (most likely
191 // java.lang.invoke).
192 //
193 // - Did you add a new static field to a class that could be referenced by
194 // cached object instances of MethodType, MethodHandle, etc? You may need
195 // to add that class to indy_specs[].
196 // - Did you modify the <clinit> of the classes in java.lang.invoke such that
197 // a static field now points to an object that should not be cached (e.g.,
198 // a native resource such as a file descriptior, or a Thread)?
199 //
200 // Note that these potential problems only occur when one class gets
201 // the aot-init treatment, AND another class is init-coupled to it,
202 // AND the coupling is not detected. Currently there are a number
203 // classes that get the aot-init treatment, in java.lang.invoke
204 // because of invokedynamic. They are few enough for now to be
205 // manually tracked. There may be more in the future.
206
207 {
208 if (ik == vmClasses::Object_klass()) {
209 // everybody's favorite super
210 return true;
211 }
212 }
213
214 if (CDSConfig::is_dumping_method_handles()) {
215 // The minimal list of @AOTSafeClassInitializer was created with the help of CDSHeapVerifier.
216 // Also, some $Holder classes are needed. E.g., Invokers.<clinit> explicitly
217 // initializes Invokers$Holder. Since Invokers.<clinit> won't be executed
218 // at runtime, we need to make sure Invokers$Holder is also aot-inited.
219 if (ik->has_aot_safe_initializer()) {
220 return true;
221 }
222 }
223
224 #ifdef ASSERT
225 if (ik == _aot_init_class) {
226 return true;
227 }
228 #endif
229
230 return false;
231 }
232
233 void AOTClassInitializer::call_runtime_setup(JavaThread* current, InstanceKlass* ik) {
234 assert(ik->has_aot_initialized_mirror(), "sanity");
235 if (ik->is_runtime_setup_required()) {
236 if (log_is_enabled(Info, aot, init)) {
237 ResourceMark rm;
238 log_info(aot, init)("Calling %s::runtimeSetup()", ik->external_name());
239 }
240 JavaValue result(T_VOID);
241 JavaCalls::call_static(&result, ik,
242 vmSymbols::runtimeSetup(),
243 vmSymbols::void_method_signature(), current);
244 if (current->has_pending_exception()) {
245 // We cannot continue, as we might have cached instances of ik in the heap, but propagating the
246 // exception would cause ik to be in an error state.
247 AOTLinkedClassBulkLoader::exit_on_exception(current);
248 }
249 }
250 }
251
252 // check_can_be_preinited() is quite costly, so we cache the results inside
253 // DumpTimeClassInfo::_can_be_preinited. See also AOTClassInitializer::reset_preinit_check().
254 bool AOTClassInitializer::check_can_be_preinited(InstanceKlass* ik) {
255 ResourceMark rm;
256
257 if (!SystemDictionaryShared::is_builtin(ik)) {
258 log_info(cds, init)("cannot initialize %s (not built-in loader)", ik->external_name());
259 return false;
260 }
261
262 InstanceKlass* super = ik->java_super();
263 if (super != nullptr && !can_be_preinited_locked(super)) {
264 log_info(cds, init)("cannot initialize %s (super %s not initable)", ik->external_name(), super->external_name());
265 return false;
266 }
267
268 Array<InstanceKlass*>* interfaces = ik->local_interfaces();
269 for (int i = 0; i < interfaces->length(); i++) {
270 if (!can_be_preinited_locked(interfaces->at(i))) {
271 log_info(cds, init)("cannot initialize %s (interface %s not initable)",
272 ik->external_name(), interfaces->at(i)->external_name());
273 return false;
274 }
275 }
276
277 if (HeapShared::is_lambda_form_klass(ik)) {
278 // We allow only these to have <clinit> or non-default static fields
279 return true;
280 }
281
282 if (ik->class_initializer() != nullptr) {
283 log_info(cds, init)("cannot initialize %s (has <clinit>)", ik->external_name());
284 return false;
285 }
286 if (ik->is_initialized() && !has_default_static_fields(ik)) {
287 return false;
288 }
289
290 return true;
291 }
292
293 bool AOTClassInitializer::has_default_static_fields(InstanceKlass* ik) {
294 oop mirror = ik->java_mirror();
295
296 for (JavaFieldStream fs(ik); !fs.done(); fs.next()) {
297 if (fs.access_flags().is_static()) {
298 fieldDescriptor& fd = fs.field_descriptor();
299 int offset = fd.offset();
300 bool is_default = true;
301 bool has_initval = fd.has_initial_value();
302 switch (fd.field_type()) {
303 case T_OBJECT:
304 case T_ARRAY:
305 is_default = mirror->obj_field(offset) == nullptr;
306 break;
307 case T_BOOLEAN:
308 is_default = mirror->bool_field(offset) == (has_initval ? fd.int_initial_value() : 0);
309 break;
310 case T_BYTE:
311 is_default = mirror->byte_field(offset) == (has_initval ? fd.int_initial_value() : 0);
312 break;
313 case T_SHORT:
314 is_default = mirror->short_field(offset) == (has_initval ? fd.int_initial_value() : 0);
315 break;
316 case T_CHAR:
317 is_default = mirror->char_field(offset) == (has_initval ? fd.int_initial_value() : 0);
318 break;
319 case T_INT:
320 is_default = mirror->int_field(offset) == (has_initval ? fd.int_initial_value() : 0);
321 break;
322 case T_LONG:
323 is_default = mirror->long_field(offset) == (has_initval ? fd.long_initial_value() : 0);
324 break;
325 case T_FLOAT:
326 is_default = mirror->float_field(offset) == (has_initval ? fd.float_initial_value() : 0);
327 break;
328 case T_DOUBLE:
329 is_default = mirror->double_field(offset) == (has_initval ? fd.double_initial_value() : 0);
330 break;
331 default:
332 ShouldNotReachHere();
333 }
334
335 if (!is_default) {
336 log_info(cds, init)("cannot initialize %s (static field %s has non-default value)",
337 ik->external_name(), fd.name()->as_C_string());
338 return false;
339 }
340 }
341 }
342
343 return true;
344 }
345
346 bool AOTClassInitializer::can_be_preinited(InstanceKlass* ik) {
347 MutexLocker ml(DumpTimeTable_lock, Mutex::_no_safepoint_check_flag);
348 return can_be_preinited_locked(ik);
349 }
350
351 bool AOTClassInitializer::can_be_preinited_locked(InstanceKlass* ik) {
352 if (!CDSConfig::is_initing_classes_at_dump_time()) {
353 return false;
354 }
355
356 assert_lock_strong(DumpTimeTable_lock);
357 DumpTimeClassInfo* info = SystemDictionaryShared::get_info_locked(ik);
358 if (!info->has_done_preinit_check()) {
359 info->set_can_be_preinited(AOTClassInitializer::check_can_be_preinited(ik));
360 }
361 return info->can_be_preinited();
362 }
363
364 // Initialize a class at dump time, if possible.
365 void AOTClassInitializer::maybe_preinit_class(InstanceKlass* ik, TRAPS) {
366 #if 0 // FIXME -- leyden+JEP483 merge
367 if (!ik->is_initialized() && AOTClassInitializer::can_be_preinited(ik)) {
368 if (log_is_enabled(Info, cds, init)) {
369 ResourceMark rm;
370 log_info(cds, init)("preinitializing %s", ik->external_name());
371 }
372 ik->initialize(CHECK);
373 }
374 #endif
375 }
376
377 #ifdef ASSERT
378 void AOTClassInitializer::init_test_class(TRAPS) {
379 // -XX:AOTInitTestClass is used in regression tests for adding additional AOT-initialized classes
380 // and heap objects into the AOT cache. The tests must be carefully written to avoid including
381 // any classes that cannot be AOT-initialized.
382 //
383 // -XX:AOTInitTestClass is NOT a general mechanism for including user-defined objects into
384 // the AOT cache. Therefore, this option is NOT available in product JVM.
385 if (AOTInitTestClass != nullptr && CDSConfig::is_initing_classes_at_dump_time()) {
386 log_info(aot)("Debug build only: force initialization of AOTInitTestClass %s", AOTInitTestClass);
387 TempNewSymbol class_name = SymbolTable::new_symbol(AOTInitTestClass);
388 Handle app_loader(THREAD, SystemDictionary::java_system_loader());
389 Klass* k = SystemDictionary::resolve_or_null(class_name, app_loader, CHECK);
390 if (k == nullptr) {
391 vm_exit_during_initialization("AOTInitTestClass not found", AOTInitTestClass);
392 }
393 if (!k->is_instance_klass()) {
394 vm_exit_during_initialization("Invalid name for AOTInitTestClass", AOTInitTestClass);
395 }
396
397 _aot_init_class = InstanceKlass::cast(k);
398 _aot_init_class->initialize(CHECK);
399 }
400 }
401
402 bool AOTClassInitializer::has_test_class() {
403 return _aot_init_class != nullptr;
404 }
405 #endif