1 /*
2 * Copyright (c) 2020, 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.
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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/archiveUtils.hpp"
26 #include "cds/archiveBuilder.hpp"
27 #include "cds/cdsConfig.hpp"
28 #include "cds/cppVtables.hpp"
29 #include "cds/metaspaceShared.hpp"
30 #include "logging/log.hpp"
31 #include "oops/instanceClassLoaderKlass.hpp"
32 #include "oops/instanceMirrorKlass.hpp"
33 #include "oops/instanceRefKlass.hpp"
34 #include "oops/instanceStackChunkKlass.hpp"
35 #include "oops/methodData.hpp"
36 #include "oops/objArrayKlass.hpp"
37 #include "oops/typeArrayKlass.hpp"
38 #include "runtime/arguments.hpp"
39 #include "utilities/globalDefinitions.hpp"
40
41 // Objects of the Metadata types (such as Klass and ConstantPool) have C++ vtables.
42 // (In GCC this is the field <Type>::_vptr, i.e., first word in the object.)
43 //
44 // Addresses of the vtables and the methods may be different across JVM runs,
45 // if libjvm.so is dynamically loaded at a different base address.
46 //
47 // To ensure that the Metadata objects in the CDS archive always have the correct vtable:
48 //
49 // + at dump time: we redirect the _vptr to point to our own vtables inside
50 // the CDS image
51 // + at run time: we clone the actual contents of the vtables from libjvm.so
52 // into our own tables.
53
54 // Currently, the archive contains ONLY the following types of objects that have C++ vtables.
55 #define CPP_VTABLE_TYPES_DO(f) \
56 f(ConstantPool) \
57 f(InstanceKlass) \
58 f(InstanceClassLoaderKlass) \
59 f(InstanceMirrorKlass) \
60 f(InstanceRefKlass) \
61 f(InstanceStackChunkKlass) \
62 f(Method) \
63 f(ObjArrayKlass) \
64 f(TypeArrayKlass)
65
66 class CppVtableInfo {
67 intptr_t _vtable_size;
68 intptr_t _cloned_vtable[1]; // Pseudo flexible array member.
69 static size_t cloned_vtable_offset() { return offset_of(CppVtableInfo, _cloned_vtable); }
70 public:
71 int vtable_size() { return int(uintx(_vtable_size)); }
72 void set_vtable_size(int n) { _vtable_size = intptr_t(n); }
73 // Using _cloned_vtable[i] for i > 0 causes undefined behavior. We use address calculation instead.
74 intptr_t* cloned_vtable() { return (intptr_t*)((char*)this + cloned_vtable_offset()); }
75 void zero() { memset(cloned_vtable(), 0, sizeof(intptr_t) * vtable_size()); }
76 // Returns the address of the next CppVtableInfo that can be placed immediately after this CppVtableInfo
77 static size_t byte_size(int vtable_size) {
78 return cloned_vtable_offset() + (sizeof(intptr_t) * vtable_size);
79 }
80 };
81
82 static inline intptr_t* vtable_of(const Metadata* m) {
83 return *((intptr_t**)m);
84 }
85
86 template <class T> class CppVtableCloner {
87 static int get_vtable_length(const char* name);
88
89 public:
90 // Allocate a clone of the vtable of T from the shared metaspace;
91 // Initialize the contents of this clone.
92 static CppVtableInfo* allocate_and_initialize(const char* name);
93
94 // Copy the contents of the vtable of T into info->_cloned_vtable;
95 static void initialize(const char* name, CppVtableInfo* info);
96
97 static void init_orig_cpp_vtptr(int kind);
98 };
99
100 template <class T>
101 CppVtableInfo* CppVtableCloner<T>::allocate_and_initialize(const char* name) {
102 int n = get_vtable_length(name);
103 CppVtableInfo* info =
104 (CppVtableInfo*)ArchiveBuilder::current()->rw_region()->allocate(CppVtableInfo::byte_size(n));
105 info->set_vtable_size(n);
106 initialize(name, info);
107 return info;
108 }
109
110 template <class T>
111 void CppVtableCloner<T>::initialize(const char* name, CppVtableInfo* info) {
112 T tmp; // Allocate temporary dummy metadata object to get to the original vtable.
113 int n = info->vtable_size();
114 intptr_t* srcvtable = vtable_of(&tmp);
115 intptr_t* dstvtable = info->cloned_vtable();
116
117 // We already checked (and, if necessary, adjusted n) when the vtables were allocated, so we are
118 // safe to do memcpy.
119 log_debug(cds, vtables)("Copying %3d vtable entries for %s", n, name);
120 memcpy(dstvtable, srcvtable, sizeof(intptr_t) * n);
121 }
122
123 // To determine the size of the vtable for each type, we use the following
124 // trick by declaring 2 subclasses:
125 //
126 // class CppVtableTesterA: public InstanceKlass {virtual int last_virtual_method() {return 1;} };
127 // class CppVtableTesterB: public InstanceKlass {virtual void* last_virtual_method() {return nullptr}; };
128 //
129 // CppVtableTesterA and CppVtableTesterB's vtables have the following properties:
130 // - Their size (N+1) is exactly one more than the size of InstanceKlass's vtable (N)
131 // - The first N entries have are exactly the same as in InstanceKlass's vtable.
132 // - Their last entry is different.
133 //
134 // So to determine the value of N, we just walk CppVtableTesterA and CppVtableTesterB's tables
135 // and find the first entry that's different.
136 //
137 // This works on all C++ compilers supported by Oracle, but you may need to tweak it for more
138 // esoteric compilers.
139
140 template <class T> class CppVtableTesterB: public T {
141 public:
142 virtual int last_virtual_method() {return 1;}
143 };
144
145 template <class T> class CppVtableTesterA : public T {
146 public:
147 virtual void* last_virtual_method() {
148 // Make this different than CppVtableTesterB::last_virtual_method so the C++
149 // compiler/linker won't alias the two functions.
150 return nullptr;
151 }
152 };
153
154 template <class T>
155 int CppVtableCloner<T>::get_vtable_length(const char* name) {
156 CppVtableTesterA<T> a;
157 CppVtableTesterB<T> b;
158
159 intptr_t* avtable = vtable_of(&a);
160 intptr_t* bvtable = vtable_of(&b);
161
162 // Start at slot 1, because slot 0 may be RTTI (on Solaris/Sparc)
163 int vtable_len = 1;
164 for (; ; vtable_len++) {
165 if (avtable[vtable_len] != bvtable[vtable_len]) {
166 break;
167 }
168 }
169 log_debug(cds, vtables)("Found %3d vtable entries for %s", vtable_len, name);
170
171 return vtable_len;
172 }
173
174 #define ALLOCATE_AND_INITIALIZE_VTABLE(c) \
175 _index[c##_Kind] = CppVtableCloner<c>::allocate_and_initialize(#c); \
176 ArchivePtrMarker::mark_pointer(&_index[c##_Kind]);
177
178 #define INITIALIZE_VTABLE(c) \
179 CppVtableCloner<c>::initialize(#c, _index[c##_Kind]);
180
181 #define INIT_ORIG_CPP_VTPTRS(c) \
182 CppVtableCloner<c>::init_orig_cpp_vtptr(c##_Kind);
183
184 #define DECLARE_CLONED_VTABLE_KIND(c) c ## _Kind,
185
186 enum ClonedVtableKind {
187 // E.g., ConstantPool_Kind == 0, InstanceKlass_Kind == 1, etc.
188 CPP_VTABLE_TYPES_DO(DECLARE_CLONED_VTABLE_KIND)
189 _num_cloned_vtable_kinds
190 };
191
192 // _orig_cpp_vtptrs and _archived_cpp_vtptrs are used for type checking in
193 // CppVtables::get_archived_vtable().
194 //
195 // _orig_cpp_vtptrs is a map of all the original vtptrs. E.g., for
196 // ConstantPool *cp = new (...) ConstantPool(...) ; // a dynamically allocated constant pool
197 // the following holds true:
198 // _orig_cpp_vtptrs[ConstantPool_Kind] == ((intptr_t**)cp)[0]
199 //
200 // _archived_cpp_vtptrs is a map of all the vptprs used by classes in a preimage. E.g., for
201 // InstanceKlass* k = a class loaded from the preimage;
202 // ConstantPool* cp = k->constants();
203 // the following holds true:
204 // _archived_cpp_vtptrs[ConstantPool_Kind] == ((intptr_t**)cp)[0]
205 static bool _orig_cpp_vtptrs_inited = false;
206 static intptr_t* _orig_cpp_vtptrs[_num_cloned_vtable_kinds];
207 static intptr_t* _archived_cpp_vtptrs[_num_cloned_vtable_kinds];
208
209 template <class T>
210 void CppVtableCloner<T>::init_orig_cpp_vtptr(int kind) {
211 assert(kind < _num_cloned_vtable_kinds, "sanity");
212 T tmp; // Allocate temporary dummy metadata object to get to the original vtable.
213 intptr_t* srcvtable = vtable_of(&tmp);
214 _orig_cpp_vtptrs[kind] = srcvtable;
215 }
216
217 // This is the index of all the cloned vtables. E.g., for
218 // ConstantPool* cp = ....; // an archived constant pool
219 // InstanceKlass* ik = ....;// an archived class
220 // the following holds true:
221 // _index[ConstantPool_Kind]->cloned_vtable() == ((intptr_t**)cp)[0]
222 // _index[InstanceKlass_Kind]->cloned_vtable() == ((intptr_t**)ik)[0]
223 static CppVtableInfo* _index[_num_cloned_vtable_kinds];
224
225 // This marks the location in the archive where _index[0] is stored. This location
226 // will be stored as FileMapHeader::_cloned_vtables_offset into the archive header.
227 // Serviceability Agent uses this information to determine the vtables of
228 // archived Metadata objects.
229 char* CppVtables::_vtables_serialized_base = nullptr;
230
231 void CppVtables::dumptime_init(ArchiveBuilder* builder) {
232 assert(CDSConfig::is_dumping_static_archive(), "cpp tables are only dumped into static archive");
233
234 if (CDSConfig::is_dumping_final_static_archive()) {
235 // When dumping final archive, _index[kind] at this point is in the preimage.
236 // Remember these vtable pointers in _archived_cpp_vtptrs, as _index[kind] will now be rewritten
237 // to point to the runtime vtable data.
238 for (int i = 0; i < _num_cloned_vtable_kinds; i++) {
239 assert(_index[i] != nullptr, "must have been restored by CppVtables::serialize()");
240 _archived_cpp_vtptrs[i] = _index[i]->cloned_vtable();
241 }
242 } else {
243 memset(_archived_cpp_vtptrs, 0, sizeof(_archived_cpp_vtptrs));
244 }
245
246 CPP_VTABLE_TYPES_DO(ALLOCATE_AND_INITIALIZE_VTABLE);
247
248 size_t cpp_tables_size = builder->rw_region()->top() - builder->rw_region()->base();
249 builder->alloc_stats()->record_cpp_vtables((int)cpp_tables_size);
250 }
251
252 void CppVtables::serialize(SerializeClosure* soc) {
253 if (!soc->reading()) {
254 _vtables_serialized_base = (char*)ArchiveBuilder::current()->buffer_top();
255 }
256 for (int i = 0; i < _num_cloned_vtable_kinds; i++) {
257 soc->do_ptr(&_index[i]);
258 }
259 if (soc->reading()) {
260 CPP_VTABLE_TYPES_DO(INITIALIZE_VTABLE);
261 }
262 }
263
264 intptr_t* CppVtables::get_archived_vtable(MetaspaceObj::Type msotype, address obj) {
265 if (!_orig_cpp_vtptrs_inited) {
266 CPP_VTABLE_TYPES_DO(INIT_ORIG_CPP_VTPTRS);
267 _orig_cpp_vtptrs_inited = true;
268 }
269
270 assert(CDSConfig::is_dumping_archive(), "sanity");
271 int kind = -1;
272 switch (msotype) {
273 case MetaspaceObj::SymbolType:
274 case MetaspaceObj::TypeArrayU1Type:
275 case MetaspaceObj::TypeArrayU2Type:
276 case MetaspaceObj::TypeArrayU4Type:
277 case MetaspaceObj::TypeArrayU8Type:
278 case MetaspaceObj::TypeArrayOtherType:
279 case MetaspaceObj::ConstMethodType:
280 case MetaspaceObj::ConstantPoolCacheType:
281 case MetaspaceObj::AnnotationsType:
282 case MetaspaceObj::MethodCountersType:
283 case MetaspaceObj::RecordComponentType:
284 // These have no vtables.
285 break;
286 case MetaspaceObj::MethodDataType:
287 // We don't archive MethodData <-- should have been removed in removed_unsharable_info
288 ShouldNotReachHere();
289 break;
290 default:
291 for (kind = 0; kind < _num_cloned_vtable_kinds; kind ++) {
292 if (vtable_of((Metadata*)obj) == _orig_cpp_vtptrs[kind] ||
293 vtable_of((Metadata*)obj) == _archived_cpp_vtptrs[kind]) {
294 break;
295 }
296 }
297 if (kind >= _num_cloned_vtable_kinds) {
298 fatal("Cannot find C++ vtable for " INTPTR_FORMAT " -- you probably added"
299 " a new subtype of Klass or MetaData without updating CPP_VTABLE_TYPES_DO or the cases in this 'switch' statement",
300 p2i(obj));
301 }
302 }
303
304 if (kind >= 0) {
305 assert(kind < _num_cloned_vtable_kinds, "must be");
306 return _index[kind]->cloned_vtable();
307 } else {
308 return nullptr;
309 }
310 }
311
312 void CppVtables::zero_archived_vtables() {
313 assert(CDSConfig::is_dumping_static_archive(), "cpp tables are only dumped into static archive");
314 for (int kind = 0; kind < _num_cloned_vtable_kinds; kind ++) {
315 _index[kind]->zero();
316 }
317 }
318
319 bool CppVtables::is_valid_shared_method(const Method* m) {
320 assert(MetaspaceShared::is_in_shared_metaspace(m), "must be");
321 return vtable_of(m) == _index[Method_Kind]->cloned_vtable() ||
322 vtable_of(m) == _archived_cpp_vtptrs[Method_Kind];
323 }