1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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24
25 #ifndef SHARE_OOPS_COMPRESSEDKLASS_HPP
26 #define SHARE_OOPS_COMPRESSEDKLASS_HPP
27
28 #include "memory/allStatic.hpp"
29 #include "utilities/globalDefinitions.hpp"
30
31 class outputStream;
32 class Klass;
33
34 // If compressed klass pointers then use narrowKlass.
35 typedef juint narrowKlass;
36
37 // For UseCompressedClassPointers.
38 class CompressedKlassPointers : public AllStatic {
39 friend class VMStructs;
40 friend class ArchiveBuilder;
41
42 // Tiny-class-pointer mode
43 static int _tiny_cp; // -1, 0=true, 1=false
44
45 // We use a different narrow Klass pointer geometry depending on
46 // whether we run in standard mode or in compact-object-header-mode (Lilliput):
47 // In Lilliput, we use smaller-than-32-bit class pointers ("tiny classpointer mode")
48
49 // Narrow klass pointer bits for an unshifted narrow Klass pointer.
50 static constexpr int narrow_klass_pointer_bits_legacy = 32;
51 static constexpr int narrow_klass_pointer_bits_tinycp = 22;
52
53 static int _narrow_klass_pointer_bits;
54
55 // The maximum shift we can use for standard mode and for TinyCP mode
56 static constexpr int max_shift_legacy = 3;
57 static constexpr int max_shift_tinycp = 10;
58
59 static int _max_shift;
60
61 static address _base;
62 static int _shift;
63
64 // Together with base, this defines the address range within which Klass
65 // structures will be located: [base, base+range). While the maximal
66 // possible encoding range is 4|32G for shift 0|3, if we know beforehand
67 // the expected range of Klass* pointers will be smaller, a platform
68 // could use this info to optimize encoding.
69 static size_t _range;
70
71 // Helper function for common cases.
72 static char* reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr);
73 static char* reserve_address_space_for_unscaled_encoding(size_t size, bool aslr);
74 static char* reserve_address_space_for_zerobased_encoding(size_t size, bool aslr);
75 static char* reserve_address_space_for_16bit_move(size_t size, bool aslr);
76
77 // Returns the highest address expressable with an unshifted narrow Klass pointer
78 inline static uintptr_t highest_unscaled_address();
79
80 static bool pd_initialize(address addr, size_t len);
81
82 #ifdef ASSERT
83 // For sanity checks: Klass range
84 static address _klass_range_start;
85 static address _klass_range_end;
86 // For sanity checks: lowest, highest valid narrow klass ids != null
87 static narrowKlass _lowest_valid_narrow_klass_id;
88 static narrowKlass _highest_valid_narrow_klass_id;
89 static void calc_lowest_highest_narrow_klass_id();
90 static void sanity_check_after_initialization();
91 #endif // ASSERT
92
93 template <typename T>
94 static inline void check_init(T var) {
95 assert(var != (T)-1, "Not yet initialized");
96 }
97
98 static inline Klass* decode_not_null_without_asserts(narrowKlass v, address base, int shift);
99 static inline Klass* decode_not_null(narrowKlass v, address base, int shift);
100
101 static inline narrowKlass encode_not_null(Klass* v, address base, int shift);
102
103 public:
104
105 // Initialization sequence:
106 // 1) Parse arguments. The following arguments take a role:
107 // - UseCompressedClassPointers
108 // - UseCompactObjectHeaders
109 // - Xshare on off dump
110 // - CompressedClassSpaceSize
111 // 2) call pre_initialize(): depending on UseCompactObjectHeaders, defines the limits of narrow Klass pointer
112 // geometry (how many bits, the max. possible shift)
113 // 3) .. from here on, narrow_klass_pointer_bits() and max_shift() can be used
114 // 4) call reserve_address_space_for_compressed_classes() either from CDS initialization or, if CDS is off,
115 // from metaspace initialization. Reserves space for class space + CDS, attempts to reserve such that
116 // we later can use a "good" encoding scheme. Reservation is highly CPU-specific.
117 // 5) Initialize the narrow Klass encoding scheme by determining encoding base and shift:
118 // 5a) if CDS=on: Calls initialize_for_given_encoding() with the reservation base from step (4) and the
119 // CDS-intrinsic setting for shift; here, we don't have any freedom to deviate from the base.
120 // 5b) if CDS=off: Calls initialize() - here, we have more freedom and, if we want, can choose an encoding
121 // base that differs from the reservation base from step (4). That allows us, e.g., to later use
122 // zero-based encoding.
123 // 6) ... from now on, we can use base() and shift().
124
125 // Called right after argument parsing; defines narrow klass pointer geometry limits
126 static void pre_initialize();
127
128 static bool tiny_classpointer_mode() { check_init(_tiny_cp); return (_tiny_cp == 1); }
129
130 // The number of bits a narrow Klass pointer has;
131 static int narrow_klass_pointer_bits() { check_init(_narrow_klass_pointer_bits); return _narrow_klass_pointer_bits; }
132
133 // The maximum possible shift; the actual shift employed later can be smaller (see initialize())
134 static int max_shift() { check_init(_max_shift); return _max_shift; }
135
136 // Reserve a range of memory that is to contain Klass strucutures which are referenced by narrow Klass IDs.
137 // If optimize_for_zero_base is true, the implementation will attempt to reserve optimized for zero-based encoding.
138 static char* reserve_address_space_for_compressed_classes(size_t size, bool aslr, bool optimize_for_zero_base);
139
140 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
141 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
142 // archived heap objects. In this case, we don't have the freedom to choose base and shift; they are handed to
143 // us from CDS.
144 static void initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift);
145
146 // Given an address range [addr, addr+len) which the encoding is supposed to
147 // cover, choose base, shift and range.
148 // The address range is the expected range of uncompressed Klass pointers we
149 // will encounter (and the implicit promise that there will be no Klass
150 // structures outside this range).
151 static void initialize(address addr, size_t len);
152
153 static void print_mode(outputStream* st);
154
155 // Can only be used after initialization
156 static address base() { check_init(_base); return _base; }
157 static size_t range() { check_init(_range); return _range; }
158 static int shift() { check_init(_shift); return _shift; }
159
160 // Returns the alignment a Klass* is guaranteed to have.
161 // Note: *Not* the same as 1 << shift ! Klass are always guaranteed to be at least 64-bit aligned,
162 // so this will return 8 even if shift is 0.
163 static int klass_alignment_in_bytes() { return nth_bit(MAX2(3, _shift)); }
164 static int klass_alignment_in_words() { return klass_alignment_in_bytes() / BytesPerWord; }
165
166 static bool is_null(Klass* v) { return v == nullptr; }
167 static bool is_null(narrowKlass v) { return v == 0; }
168
169 // Versions without asserts
170 static inline Klass* decode_not_null_without_asserts(narrowKlass v);
171 static inline Klass* decode_without_asserts(narrowKlass v);
172
173 static inline Klass* decode_not_null(narrowKlass v);
174 static inline Klass* decode(narrowKlass v);
175
176 static inline narrowKlass encode_not_null_without_asserts(Klass* k, address narrow_base, int shift);
177 static inline narrowKlass encode_not_null(Klass* v);
178 static inline narrowKlass encode(Klass* v);
179
180 #ifdef ASSERT
181 // Given a Klass* k and an encoding (base, shift), check that k can be encoded
182 inline static void check_valid_klass(const Klass* k, address base, int shift);
183 // Given a Klass* k, check that k can be encoded with the current encoding
184 inline static void check_valid_klass(const Klass* k);
185 // Given a narrow Klass ID, check that it is valid according to current encoding
186 inline static void check_valid_narrow_klass_id(narrowKlass nk);
187 #endif
188
189 };
190
191 #endif // SHARE_OOPS_COMPRESSEDKLASS_HPP