1 /*
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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 // - UseCompressedClassPointers108 // - UseCompactObjectHeaders109 // - Xshare on off dump110 // - CompressedClassSpaceSize111 // 2) call pre_initialize(): depending on UseCompactObjectHeaders, defines the limits of narrow Klass pointer112 // geometry (how many bits, the max. possible shift)113 // 3) .. from here on, narrow_klass_pointer_bits() and max_shift() can be used114 // 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 that116 // 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 the119 // 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 encoding121 // base that differs from the reservation base from step (4). That allows us, e.g., to later use122 // 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 limits126 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 // Returns the maximum encoding range that can be covered with the currently137 // choosen nKlassID geometry (nKlass bit size, max shift)138 static size_t max_encoding_range_size();139
140 // Reserve a range of memory that is to contain Klass strucutures which are referenced by narrow Klass IDs.
141 // If optimize_for_zero_base is true, the implementation will attempt to reserve optimized for zero-based encoding.
142 static char* reserve_address_space_for_compressed_classes(size_t size, bool aslr, bool optimize_for_zero_base);
143
144 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
145 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
146 // archived heap objects. In this case, we don't have the freedom to choose base and shift; they are handed to
147 // us from CDS.
148 static void initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift);
149
150 // Given an address range [addr, addr+len) which the encoding is supposed to
151 // cover, choose base, shift and range.
152 // The address range is the expected range of uncompressed Klass pointers we
153 // will encounter (and the implicit promise that there will be no Klass
154 // structures outside this range).
155 static void initialize(address addr, size_t len);
156
157 static void print_mode(outputStream* st);
158
159 // Can only be used after initialization160 static address base() { check_init(_base); return _base; }161 static size_t range() { check_init(_range); return _range; }162 static int shift() { check_init(_shift); return _shift; }163 164 // Returns the alignment a Klass* is guaranteed to have.165 // Note: *Not* the same as 1 << shift ! Klass are always guaranteed to be at least 64-bit aligned,166 // so this will return 8 even if shift is 0.167 static int klass_alignment_in_bytes() { return nth_bit(MAX2(3, _shift)); }168 static int klass_alignment_in_words() { return klass_alignment_in_bytes() / BytesPerWord; }
169
170 static bool is_null(Klass* v) { return v == nullptr; }
171 static bool is_null(narrowKlass v) { return v == 0; }
172
173 // Versions without asserts
174 static inline Klass* decode_not_null_without_asserts(narrowKlass v);
175 static inline Klass* decode_without_asserts(narrowKlass v);
176
177 static inline Klass* decode_not_null(narrowKlass v);
178 static inline Klass* decode(narrowKlass v);
179
180 static inline narrowKlass encode_not_null_without_asserts(Klass* k, address narrow_base, int shift);
181 static inline narrowKlass encode_not_null(Klass* v);
182 static inline narrowKlass encode(Klass* v);
183 184 #ifdef ASSERT185 // Given a Klass* k and an encoding (base, shift), check that k can be encoded186 inline static void check_valid_klass(const Klass* k, address base, int shift);187 // Given a Klass* k, check that k can be encoded with the current encoding188 inline static void check_valid_klass(const Klass* k);189 // Given a narrow Klass ID, check that it is valid according to current encoding190 inline static void check_valid_narrow_klass_id(narrowKlass nk);191 #endif192
193 };
194
195 #endif // SHARE_OOPS_COMPRESSEDKLASS_HPP
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