1 /*
2 * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.
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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 *
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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 "utilities/checkedCast.hpp"
32
33 // A VtableStub holds an individual code stub for a pair (vtable index, #args) for either itables or vtables
34 // There's a one-to-one relationship between a VtableStub and such a pair.
35
36 // A word on VtableStub sizing:
37 // Such a vtable/itable stub consists of the instance data
38 // and an immediately following CodeBuffer.
39 // Unfortunately, the required space for the code buffer varies, depending on
40 // the setting of compile time macros (PRODUCT, ASSERT, ...) and of command line
41 // parameters. Actual data may have an influence on the size as well.
42 //
43 // A simple approximation for the VtableStub size would be to just take a value
44 // "large enough" for all circumstances - a worst case estimate.
45 // As there can exist many stubs - and they never go away - we certainly don't
46 // want to waste more code cache space than absolutely necessary.
47 //
48 // We need a different approach which, as far as possible, should be independent
49 // from or adaptive to code size variations. These variations may be caused by
50 // changed compile time or run time switches as well as by changed emitter code.
51 //
52 // Here is the idea:
53 // For the first stub we generate, we allocate a "large enough" code buffer.
54 // Once all instructions are emitted, we know the actual size of the stub.
55 // Remembering that size allows us to allocate a tightly matching code buffer
56 // for all subsequent stubs. That covers all "static variance", i.e. all variance
57 // that is due to compile time macros, command line parameters, machine capabilities,
58 // and other influences which are immutable for the life span of the vm.
59 //
60 // Life isn't always that easy. Code size may depend on actual data, "load constant"
61 // being an example for that. All code segments with such "dynamic variance" require
62 // additional care. We need to know or estimate the worst case code size for each
63 // such segment. With that knowledge, we can maintain a "slop counter" in the
64 // platform-specific stub emitters. It accumulates the difference between worst-case
65 // and actual code size. When the stub is fully generated, the actual stub size is
66 // adjusted (increased) by the slop counter value.
67 //
68 // As a result, we allocate all but the first code buffers with the same, tightly matching size.
69 //
70
71 // VtableStubs creates the code stubs for compiled calls through vtables.
72 // There is one stub per (vtable index, args_size) pair, and the stubs are
73 // never deallocated. They don't need to be GCed because they contain no oops.
74 class VtableStub;
75
76 class VtableStubs : AllStatic {
77 public: // N must be public (some compilers need this for _table)
78 enum {
79 N = 256, // size of stub table; must be power of two
80 mask = N - 1
81 };
82
83 static_assert(is_power_of_2((int)N), "N must be a power of 2");
84
85 private:
86 friend class VtableStub;
87 static VtableStub* volatile _table[N]; // table of existing stubs
88 static int _vtab_stub_size; // current size estimate for vtable stub (quasi-constant)
89 static int _itab_stub_size; // current size estimate for itable stub (quasi-constant)
90
91 static VtableStub* create_vtable_stub(int vtable_index);
92 static VtableStub* create_itable_stub(int vtable_index);
93 static VtableStub* lookup (bool is_vtable_stub, int vtable_index);
94 static void enter (bool is_vtable_stub, int vtable_index, VtableStub* s);
95 static inline uint hash (bool is_vtable_stub, int vtable_index);
96 static address find_stub (bool is_vtable_stub, int vtable_index);
97 static void bookkeeping(MacroAssembler* masm, outputStream* out, VtableStub* s,
98 address npe_addr, address ame_addr, bool is_vtable_stub,
99 int index, int slop_bytes, int index_dependent_slop);
100 static int code_size_limit(bool is_vtable_stub);
101 static void check_and_set_size_limit(bool is_vtable_stub,
102 int code_size,
103 int padding);
104
105 public:
106 static address find_vtable_stub(int vtable_index) { return find_stub(true, vtable_index); }
107 static address find_itable_stub(int itable_index) { return find_stub(false, itable_index); }
108
109 static VtableStub* entry_point(address pc); // vtable stub entry point for a pc
110 static bool is_icholder_entry(address pc); // is the blob containing pc (which must be a vtable blob) an icholder?
111 static bool contains(address pc); // is pc within any stub?
112 static VtableStub* stub_containing(address pc); // stub containing pc or nullptr
113 static void initialize();
114 static void vtable_stub_do(void f(VtableStub*)); // iterates over all vtable stubs
115 };
116
117
118 class VtableStub {
119 private:
120 friend class VtableStubs;
121
122 static address _chunk; // For allocation
123 static address _chunk_end; // For allocation
124 static VMReg _receiver_location; // Where to find receiver
125
126 VtableStub* _next; // Pointer to next entry in hash table
127 const short _index; // vtable index
128 short _ame_offset; // Where an AbstractMethodError might occur
129 short _npe_offset; // Where a NullPointerException might occur
130 bool _is_vtable_stub; // True if vtable stub, false, is itable stub
131 /* code follows here */ // The vtableStub code
132
133 void* operator new(size_t size, int code_size) throw();
134
135 VtableStub(bool is_vtable_stub, short index)
136 : _next(nullptr), _index(index), _ame_offset(-1), _npe_offset(-1),
137 _is_vtable_stub(is_vtable_stub) {}
138 VtableStub* next() const { return _next; }
139 int index() const { return _index; }
140 static VMReg receiver_location() { return _receiver_location; }
141 void set_next(VtableStub* n) { _next = n; }
142
143 public:
144 address code_begin() const { return (address)(this + 1); }
145 address code_end() const { return code_begin() + VtableStubs::code_size_limit(_is_vtable_stub); }
146 address entry_point() const { return code_begin(); }
147 static int entry_offset() { return sizeof(class VtableStub); }
148
149 bool matches(bool is_vtable_stub, int index) const {
150 return _index == index && _is_vtable_stub == is_vtable_stub;
151 }
152 bool contains(address pc) const { return code_begin() <= pc && pc < code_end(); }
153
154 private:
155 void set_exception_points(address npe_addr, address ame_addr) {
156 _npe_offset = checked_cast<short>(npe_addr - code_begin());
157 _ame_offset = checked_cast<short>(ame_addr - code_begin());
158 assert(is_abstract_method_error(ame_addr), "offset must be correct");
159 assert(is_null_pointer_exception(npe_addr), "offset must be correct");
160 assert(!is_abstract_method_error(npe_addr), "offset must be correct");
161 assert(!is_null_pointer_exception(ame_addr), "offset must be correct");
162 }
163
164 // platform-dependent routines
165 static int pd_code_alignment();
166 // CNC: Removed because vtable stubs are now made with an ideal graph
167 // static bool pd_disregard_arg_size();
168
169 static void align_chunk() {
170 uintptr_t off = (uintptr_t)( _chunk + sizeof(VtableStub) ) % pd_code_alignment();
171 if (off != 0) _chunk += pd_code_alignment() - off;
172 }
173
174 public:
175 // Query
176 bool is_itable_stub() { return !_is_vtable_stub; }
177 bool is_vtable_stub() { return _is_vtable_stub; }
178 bool is_abstract_method_error(address epc) { return epc == code_begin()+_ame_offset; }
179 bool is_null_pointer_exception(address epc) { return epc == code_begin()+_npe_offset; }
180
181 void print_on(outputStream* st) const;
182 void print() const;
183
184 };
185
186 #endif // SHARE_CODE_VTABLESTUBS_HPP