1 /*
2 * Copyright (c) 1997, 2026, 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 #ifndef SHARE_CODE_VTABLESTUBS_HPP
26 #define SHARE_CODE_VTABLESTUBS_HPP
27
28 #include "asm/macroAssembler.hpp"
29 #include "code/vmreg.hpp"
30 #include "memory/allStatic.hpp"
31 #include "runtime/atomicAccess.hpp"
32 #include "utilities/checkedCast.hpp"
33
34 // A VtableStub holds an individual code stub for a pair (vtable index, #args) for either itables or vtables
35 // There's a one-to-one relationship between a VtableStub and such a pair.
36
37 // A word on VtableStub sizing:
38 // Such a vtable/itable stub consists of the instance data
39 // and an immediately following CodeBuffer.
40 // Unfortunately, the required space for the code buffer varies, depending on
41 // the setting of compile time macros (PRODUCT, ASSERT, ...) and of command line
42 // parameters. Actual data may have an influence on the size as well.
43 //
44 // A simple approximation for the VtableStub size would be to just take a value
45 // "large enough" for all circumstances - a worst case estimate.
46 // As there can exist many stubs - and they never go away - we certainly don't
47 // want to waste more code cache space than absolutely necessary.
48 //
49 // We need a different approach which, as far as possible, should be independent
50 // from or adaptive to code size variations. These variations may be caused by
51 // changed compile time or run time switches as well as by changed emitter code.
52 //
53 // Here is the idea:
54 // For the first stub we generate, we allocate a "large enough" code buffer.
55 // Once all instructions are emitted, we know the actual size of the stub.
56 // Remembering that size allows us to allocate a tightly matching code buffer
57 // for all subsequent stubs. That covers all "static variance", i.e. all variance
58 // that is due to compile time macros, command line parameters, machine capabilities,
59 // and other influences which are immutable for the life span of the vm.
60 //
61 // Life isn't always that easy. Code size may depend on actual data, "load constant"
62 // being an example for that. All code segments with such "dynamic variance" require
63 // additional care. We need to know or estimate the worst case code size for each
64 // such segment. With that knowledge, we can maintain a "slop counter" in the
65 // platform-specific stub emitters. It accumulates the difference between worst-case
66 // and actual code size. When the stub is fully generated, the actual stub size is
67 // adjusted (increased) by the slop counter value.
68 //
69 // As a result, we allocate all but the first code buffers with the same, tightly matching size.
70 //
71
72 // VtableStubs creates the code stubs for compiled calls through vtables.
73 // There is one stub per (vtable index, args_size) pair, and the stubs are
74 // never deallocated. They don't need to be GCed because they contain no oops.
75 class VtableStub;
76
77 class VtableStubs : AllStatic {
78 public: // N must be public (some compilers need this for _table)
79 enum {
80 N = 256, // size of stub table; must be power of two
81 mask = N - 1
82 };
83
84 static_assert(is_power_of_2((int)N), "N must be a power of 2");
85
86 private:
87 friend class VtableStub;
88 static VtableStub* volatile _table[N]; // table of existing stubs
89 static int _vtab_stub_size; // current size estimate for vtable stub (quasi-constant)
90 static int _itab_stub_size; // current size estimate for itable stub (quasi-constant)
91
92 static VtableStub* create_vtable_stub(int vtable_index);
93 static VtableStub* create_itable_stub(int vtable_index);
94 static VtableStub* lookup (bool is_vtable_stub, int vtable_index);
95 static void enter (bool is_vtable_stub, int vtable_index, VtableStub* s);
96 static inline uint hash (bool is_vtable_stub, int vtable_index);
97 static inline uint unsafe_hash (address entry_point);
98 static address find_stub (bool is_vtable_stub, int vtable_index);
99 static void bookkeeping(MacroAssembler* masm, outputStream* out, VtableStub* s,
100 address npe_addr, address ame_addr, bool is_vtable_stub,
101 int index, int slop_bytes, int index_dependent_slop);
102 static int code_size_limit(bool is_vtable_stub);
103 static void check_and_set_size_limit(bool is_vtable_stub,
104 int code_size,
105 int padding);
106
107 public:
108 static address find_vtable_stub(int vtable_index) { return find_stub(true, vtable_index); }
109 static address find_itable_stub(int itable_index) { return find_stub(false, itable_index); }
110
111 static VtableStub* entry_point(address pc); // vtable stub entry point for a pc
112 static bool contains(address pc); // is pc within any stub?
113 static VtableStub* stub_containing(address pc); // stub containing pc or nullptr
114 static void initialize();
115
116 template <typename F>
117 static void vtable_stub_do(F f);
118 };
119
120
121 class VtableStub {
122 private:
123 friend class VtableStubs;
124
125 enum class Type : uint8_t {
126 itable_stub,
127 vtable_stub,
128 };
129
130
131 static address _chunk; // For allocation
132 static address _chunk_end; // For allocation
133 static VMReg _receiver_location; // Where to find receiver
134
135 VtableStub* _next; // Pointer to next entry in hash table
136 const short _index; // vtable index
137 short _ame_offset; // Where an AbstractMethodError might occur
138 short _npe_offset; // Where a NullPointerException might occur
139 Type _type; // Type, either vtable stub or itable stub
140 /* code follows here */ // The vtableStub code
141
142 void* operator new(size_t size, int code_size) throw();
143
144 VtableStub(bool is_vtable_stub, short index)
145 : _next(nullptr), _index(index), _ame_offset(-1), _npe_offset(-1),
146 _type(is_vtable_stub ? Type::vtable_stub : Type::itable_stub) {}
147 VtableStub* next() const { return _next; }
148 static VMReg receiver_location() { return _receiver_location; }
149 void set_next(VtableStub* n) { _next = n; }
150
151 public:
152 int index() const { return _index; }
153 int code_size() const { return VtableStubs::code_size_limit(is_vtable_stub()); }
154 address code_begin() const { return (address)(this + 1); }
155 address code_end() const { return code_begin() + code_size(); }
156 address entry_point() const { return code_begin(); }
157 static int entry_offset() { return sizeof(class VtableStub); }
158
159 bool matches(bool is_vtable_stub, int index) const {
160 return _index == index && this->is_vtable_stub() == is_vtable_stub;
161 }
162 bool contains(address pc) const { return code_begin() <= pc && pc < code_end(); }
163
164 private:
165 void set_exception_points(address npe_addr, address ame_addr) {
166 _npe_offset = checked_cast<short>(npe_addr - code_begin());
167 _ame_offset = checked_cast<short>(ame_addr - code_begin());
168 assert(is_abstract_method_error(ame_addr), "offset must be correct");
169 assert(is_null_pointer_exception(npe_addr), "offset must be correct");
170 assert(!is_abstract_method_error(npe_addr), "offset must be correct");
171 assert(!is_null_pointer_exception(ame_addr), "offset must be correct");
172 }
173
174 // platform-dependent routines
175 static int pd_code_alignment();
176 // CNC: Removed because vtable stubs are now made with an ideal graph
177 // static bool pd_disregard_arg_size();
178
179 static void align_chunk() {
180 uintptr_t off = (uintptr_t)( _chunk + sizeof(VtableStub) ) % pd_code_alignment();
181 if (off != 0) _chunk += pd_code_alignment() - off;
182 }
183
184 public:
185 // Query
186 bool is_itable_stub() const { return _type == Type::itable_stub; }
187 bool is_vtable_stub() const { return _type == Type::vtable_stub; }
188 bool is_abstract_method_error(address epc) { return epc == code_begin()+_ame_offset; }
189 bool is_null_pointer_exception(address epc) { return epc == code_begin()+_npe_offset; }
190
191 void print_on(outputStream* st) const;
192 void print() const;
193
194 };
195
196 template <typename F>
197 void VtableStubs::vtable_stub_do(F f) {
198 for (int i = 0; i < N; i++) {
199 for (VtableStub* s = AtomicAccess::load_acquire(&_table[i]); s != nullptr; s = s->next()) {
200 f(s);
201 }
202 }
203 }
204
205 #endif // SHARE_CODE_VTABLESTUBS_HPP