1 /*
2 * Copyright (c) 1997, 2024, 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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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, bool caller_is_c1);
92 static VtableStub* create_itable_stub(int vtable_index, bool caller_is_c1);
93 static VtableStub* lookup (bool is_vtable_stub, int vtable_index, bool caller_is_c1);
94 static void enter (bool is_vtable_stub, int vtable_index, bool caller_is_c1, VtableStub* s);
95 static inline uint hash (bool is_vtable_stub, int vtable_index, bool caller_is_c1);
96 static inline uint unsafe_hash (address entry_point, bool caller_is_c1);
97 static address find_stub (bool is_vtable_stub, int vtable_index, bool caller_is_c1);
98 static void bookkeeping(MacroAssembler* masm, outputStream* out, VtableStub* s,
99 address npe_addr, address ame_addr, bool is_vtable_stub,
100 int index, int slop_bytes, int index_dependent_slop);
101 static int code_size_limit(bool is_vtable_stub);
102 static void check_and_set_size_limit(bool is_vtable_stub,
103 int code_size,
104 int padding);
105
106 public:
107 static address find_vtable_stub(int vtable_index, bool caller_is_c1) { return find_stub(true, vtable_index, caller_is_c1); }
108 static address find_itable_stub(int itable_index, bool caller_is_c1) { return find_stub(false, itable_index, caller_is_c1); }
109
110 static VtableStub* entry_point(address pc); // vtable stub entry point for a pc
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 enum class Type : uint8_t {
123 itable_stub,
124 vtable_stub,
125 };
126
127
128 static address _chunk; // For allocation
129 static address _chunk_end; // For allocation
130 static VMReg _receiver_location; // Where to find receiver
131
132 VtableStub* _next; // Pointer to next entry in hash table
133 const short _index; // vtable index
134 short _ame_offset; // Where an AbstractMethodError might occur
135 short _npe_offset; // Where a NullPointerException might occur
136 Type _type; // Type, either vtable stub or itable stub
137 bool _caller_is_c1; // True if this is for a caller compiled by C1,
138 // which doesn't scalarize parameters.
139 /* code follows here */ // The vtableStub code
140
141 void* operator new(size_t size, int code_size) throw();
142
143 VtableStub(bool is_vtable_stub, short index, bool caller_is_c1)
144 : _next(nullptr), _index(index), _ame_offset(-1), _npe_offset(-1),
145 _type(is_vtable_stub ? Type::vtable_stub : Type::itable_stub), _caller_is_c1(caller_is_c1) {}
146 VtableStub* next() const { return _next; }
147 int index() const { return _index; }
148 static VMReg receiver_location() { return _receiver_location; }
149 void set_next(VtableStub* n) { _next = n; }
150
151 public:
152 address code_begin() const { return (address)(this + 1); }
153 address code_end() const { return code_begin() + VtableStubs::code_size_limit(is_vtable_stub()); }
154 address entry_point() const { return code_begin(); }
155 static int entry_offset() { return sizeof(class VtableStub); }
156
157 bool matches(bool is_vtable_stub, int index, bool caller_is_c1) const {
158 return _index == index && this->is_vtable_stub() == is_vtable_stub && _caller_is_c1 == caller_is_c1;
159 }
160 bool contains(address pc) const { return code_begin() <= pc && pc < code_end(); }
161
162 private:
163 void set_exception_points(address npe_addr, address ame_addr) {
164 _npe_offset = checked_cast<short>(npe_addr - code_begin());
165 _ame_offset = checked_cast<short>(ame_addr - code_begin());
166 assert(is_abstract_method_error(ame_addr), "offset must be correct");
167 assert(is_null_pointer_exception(npe_addr), "offset must be correct");
168 assert(!is_abstract_method_error(npe_addr), "offset must be correct");
169 assert(!is_null_pointer_exception(ame_addr), "offset must be correct");
170 }
171
172 // platform-dependent routines
173 static int pd_code_alignment();
174 // CNC: Removed because vtable stubs are now made with an ideal graph
175 // static bool pd_disregard_arg_size();
176
177 static void align_chunk() {
178 uintptr_t off = (uintptr_t)( _chunk + sizeof(VtableStub) ) % pd_code_alignment();
179 if (off != 0) _chunk += pd_code_alignment() - off;
180 }
181
182 public:
183 // Query
184 bool is_itable_stub() const { return _type == Type::itable_stub; }
185 bool is_vtable_stub() const { return _type == Type::vtable_stub; }
186 bool caller_is_c1() { return _caller_is_c1; }
187 bool is_abstract_method_error(address epc) { return epc == code_begin()+_ame_offset; }
188 bool is_null_pointer_exception(address epc) { return epc == code_begin()+_npe_offset; }
189
190 void print_on(outputStream* st) const;
191 void print() const;
192
193 };
194
195 #endif // SHARE_CODE_VTABLESTUBS_HPP