1 /*
2 * Copyright (c) 1997, 2019, 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
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7 * published by the Free Software Foundation.
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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 *
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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/allocation.hpp"
31
32 // A VtableStub holds an individual code stub for a pair (vtable index, #args) for either itables or vtables
33 // There's a one-to-one relationship between a VtableStub and such a pair.
34
35 // A word on VtableStub sizing:
36 // Such a vtable/itable stub consists of the instance data
37 // and an immediately following CodeBuffer.
38 // Unfortunately, the required space for the code buffer varies, depending on
39 // the setting of compile time macros (PRODUCT, ASSERT, ...) and of command line
40 // parameters. Actual data may have an influence on the size as well.
41 //
42 // A simple approximation for the VtableStub size would be to just take a value
43 // "large enough" for all circumstances - a worst case estimate.
44 // As there can exist many stubs - and they never go away - we certainly don't
45 // want to waste more code cache space than absolutely necessary.
46 //
47 // We need a different approach which, as far as possible, should be independent
48 // from or adaptive to code size variations. These variations may be caused by
49 // changed compile time or run time switches as well as by changed emitter code.
50 //
51 // Here is the idea:
52 // For the first stub we generate, we allocate a "large enough" code buffer.
53 // Once all instructions are emitted, we know the actual size of the stub.
54 // Remembering that size allows us to allocate a tightly matching code buffer
55 // for all subsequent stubs. That covers all "static variance", i.e. all variance
56 // that is due to compile time macros, command line parameters, machine capabilities,
57 // and other influences which are immutable for the life span of the vm.
58 //
59 // Life isn't always that easy. Code size may depend on actual data, "load constant"
60 // being an example for that. All code segments with such "dynamic variance" require
61 // additional care. We need to know or estimate the worst case code size for each
62 // such segment. With that knowledge, we can maintain a "slop counter" in the
63 // platform-specific stub emitters. It accumulates the difference between worst-case
64 // and actual code size. When the stub is fully generated, the actual stub size is
65 // adjusted (increased) by the slop counter value.
66 //
67 // As a result, we allocate all but the first code buffers with the same, tightly matching size.
68 //
69
70 // VtableStubs creates the code stubs for compiled calls through vtables.
71 // There is one stub per (vtable index, args_size) pair, and the stubs are
72 // never deallocated. They don't need to be GCed because they contain no oops.
73 class VtableStub;
74
75 class VtableStubs : AllStatic {
76 public: // N must be public (some compilers need this for _table)
77 enum {
78 N = 256, // size of stub table; must be power of two
79 mask = N - 1
80 };
81
82 private:
83 friend class VtableStub;
84 static VtableStub* _table[N]; // table of existing stubs
85 static int _number_of_vtable_stubs; // number of stubs created so far (for statistics)
86 static int _vtab_stub_size; // current size estimate for vtable stub (quasi-constant)
87 static int _itab_stub_size; // current size estimate for itable stub (quasi-constant)
88
89 static VtableStub* create_vtable_stub(int vtable_index);
90 static VtableStub* create_itable_stub(int vtable_index);
91 static VtableStub* lookup (bool is_vtable_stub, int vtable_index);
92 static void enter (bool is_vtable_stub, int vtable_index, VtableStub* s);
93 static inline uint hash (bool is_vtable_stub, int vtable_index);
94 static address find_stub (bool is_vtable_stub, int vtable_index);
95 static void bookkeeping(MacroAssembler* masm, outputStream* out, VtableStub* s,
96 address npe_addr, address ame_addr, bool is_vtable_stub,
97 int index, int slop_bytes, int index_dependent_slop);
98 static int code_size_limit(bool is_vtable_stub);
99 static void check_and_set_size_limit(bool is_vtable_stub,
100 int code_size,
101 int padding);
102
103 public:
104 static address find_vtable_stub(int vtable_index) { return find_stub(true, vtable_index); }
105 static address find_itable_stub(int itable_index) { return find_stub(false, itable_index); }
106
107 static VtableStub* entry_point(address pc); // vtable stub entry point for a pc
108 static bool contains(address pc); // is pc within any stub?
109 static VtableStub* stub_containing(address pc); // stub containing pc or NULL
110 static int number_of_vtable_stubs() { return _number_of_vtable_stubs; }
111 static void initialize();
112 static void vtable_stub_do(void f(VtableStub*)); // iterates over all vtable stubs
113 };
114
115
116 class VtableStub {
117 private:
118 friend class VtableStubs;
119
120 static address _chunk; // For allocation
121 static address _chunk_end; // For allocation
122 static VMReg _receiver_location; // Where to find receiver
123
124 VtableStub* _next; // Pointer to next entry in hash table
125 const short _index; // vtable index
126 short _ame_offset; // Where an AbstractMethodError might occur
127 short _npe_offset; // Where a NullPointerException might occur
128 bool _is_vtable_stub; // True if vtable stub, false, is itable stub
129 /* code follows here */ // The vtableStub code
130
131 void* operator new(size_t size, int code_size) throw();
132
133 VtableStub(bool is_vtable_stub, int index)
134 : _next(NULL), _index(index), _ame_offset(-1), _npe_offset(-1),
135 _is_vtable_stub(is_vtable_stub) {}
136 VtableStub* next() const { return _next; }
137 int index() const { return _index; }
138 static VMReg receiver_location() { return _receiver_location; }
139 void set_next(VtableStub* n) { _next = n; }
140
141 public:
142 address code_begin() const { return (address)(this + 1); }
143 address code_end() const { return code_begin() + VtableStubs::code_size_limit(_is_vtable_stub); }
144 address entry_point() const { return code_begin(); }
145 static int entry_offset() { return sizeof(class VtableStub); }
146
147 bool matches(bool is_vtable_stub, int index) const {
148 return _index == index && _is_vtable_stub == is_vtable_stub;
149 }
150 bool contains(address pc) const { return code_begin() <= pc && pc < code_end(); }
151
152 private:
153 void set_exception_points(address npe_addr, address ame_addr) {
154 _npe_offset = npe_addr - code_begin();
155 _ame_offset = ame_addr - code_begin();
156 assert(is_abstract_method_error(ame_addr), "offset must be correct");
157 assert(is_null_pointer_exception(npe_addr), "offset must be correct");
158 assert(!is_abstract_method_error(npe_addr), "offset must be correct");
159 assert(!is_null_pointer_exception(ame_addr), "offset must be correct");
160 }
161
162 // platform-dependent routines
163 static int pd_code_alignment();
164 // CNC: Removed because vtable stubs are now made with an ideal graph
165 // static bool pd_disregard_arg_size();
166
167 static void align_chunk() {
168 uintptr_t off = (uintptr_t)( _chunk + sizeof(VtableStub) ) % pd_code_alignment();
169 if (off != 0) _chunk += pd_code_alignment() - off;
170 }
171
172 public:
173 // Query
174 bool is_itable_stub() { return !_is_vtable_stub; }
175 bool is_vtable_stub() { return _is_vtable_stub; }
176 bool is_abstract_method_error(address epc) { return epc == code_begin()+_ame_offset; }
177 bool is_null_pointer_exception(address epc) { return epc == code_begin()+_npe_offset; }
178
179 void print_on(outputStream* st) const;
180 void print() const { print_on(tty); }
181
182 };
183
184 #endif // SHARE_CODE_VTABLESTUBS_HPP