91 // |//////////|///////////////////////////| |
92 // |///CDS////|////1gb class space////////| ... ... |
93 // |//////////|///////////////////////////| |
94 // | | |
95 // 0x8_0000_0000 0x8_4800_0000 0x9_0000_0000
96 //
97
98 // If compressed klass pointers then use narrowKlass.
99 typedef juint narrowKlass;
100
101 // For UseCompressedClassPointers.
102 class CompressedKlassPointers : public AllStatic {
103 friend class VMStructs;
104 friend class ArchiveBuilder;
105
106 // We use a different narrow Klass pointer geometry depending on
107 // whether we run in standard mode or in compact-object-header-mode.
108
109 // Narrow klass pointer bits for an unshifted narrow Klass pointer.
110 static constexpr int narrow_klass_pointer_bits_noncoh = 32;
111 static constexpr int narrow_klass_pointer_bits_coh = 22;
112
113 // Bit size of a narrowKlass
114 static int _narrow_klass_pointer_bits;
115
116 // The maximum shift values we can use depending on UseCompactObjectHeaders
117 static constexpr int max_shift_noncoh = 3;
118 static constexpr int max_shift_coh = 10;
119
120 // Maximum shift usable
121 static int _max_shift;
122
123 // Encoding Base, Encoding Shift
124 static address _base;
125 static int _shift;
126
127 // Start and end of the Klass Range.
128 // Note: guaranteed to be aligned to 1<<shift (klass_alignment_in_bytes)
129 static address _klass_range_start;
130 static address _klass_range_end;
131
173 // 5) Initialize the narrow Klass encoding scheme by determining encoding base and shift:
174 // 5a) if CDS=on: Calls initialize_for_given_encoding() with the reservation base from step (4) and the
175 // CDS-intrinsic setting for shift; here, we don't have any freedom to deviate from the base.
176 // 5b) if CDS=off: Calls initialize() - here, we have more freedom and, if we want, can choose an encoding
177 // base that differs from the reservation base from step (4). That allows us, e.g., to later use
178 // zero-based encoding.
179 // 6) ... from now on, we can use base() and shift().
180
181 // Called right after argument parsing; defines narrow klass pointer geometry limits
182 static void pre_initialize();
183
184 // The number of bits a narrow Klass pointer has;
185 static int narrow_klass_pointer_bits() { check_init(_narrow_klass_pointer_bits); return _narrow_klass_pointer_bits; }
186
187 // The maximum possible shift; the actual shift employed later can be smaller (see initialize())
188 static int max_shift() { check_init(_max_shift); return _max_shift; }
189
190 // Returns the maximum encoding range, given the current geometry (narrow klass bit size and shift)
191 static size_t max_encoding_range_size() { return nth_bit(narrow_klass_pointer_bits() + max_shift()); }
192
193 // Returns the maximum allowed klass range size.
194 static size_t max_klass_range_size();
195
196 // Reserve a range of memory that is to contain Klass strucutures which are referenced by narrow Klass IDs.
197 // If optimize_for_zero_base is true, the implementation will attempt to reserve optimized for zero-based encoding.
198 static char* reserve_address_space_for_compressed_classes(size_t size, bool aslr, bool optimize_for_zero_base);
199
200 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
201 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
202 // archived heap objects. In this case, we don't have the freedom to choose base and shift; they are handed to
203 // us from CDS.
204 static void initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift);
205
206 // Given an address range [addr, addr+len) which the encoding is supposed to
207 // cover, choose base, shift and range.
208 // The address range is the expected range of uncompressed Klass pointers we
209 // will encounter (and the implicit promise that there will be no Klass
210 // structures outside this range).
211 static void initialize(address addr, size_t len);
212
|
91 // |//////////|///////////////////////////| |
92 // |///CDS////|////1gb class space////////| ... ... |
93 // |//////////|///////////////////////////| |
94 // | | |
95 // 0x8_0000_0000 0x8_4800_0000 0x9_0000_0000
96 //
97
98 // If compressed klass pointers then use narrowKlass.
99 typedef juint narrowKlass;
100
101 // For UseCompressedClassPointers.
102 class CompressedKlassPointers : public AllStatic {
103 friend class VMStructs;
104 friend class ArchiveBuilder;
105
106 // We use a different narrow Klass pointer geometry depending on
107 // whether we run in standard mode or in compact-object-header-mode.
108
109 // Narrow klass pointer bits for an unshifted narrow Klass pointer.
110 static constexpr int narrow_klass_pointer_bits_noncoh = 32;
111 static constexpr int narrow_klass_pointer_bits_coh = 19;
112
113 // Bit size of a narrowKlass
114 static int _narrow_klass_pointer_bits;
115
116 // The maximum shift values we can use depending on UseCompactObjectHeaders
117 static constexpr int max_shift_noncoh = 3;
118 static constexpr int max_shift_coh = 10;
119
120 // Maximum shift usable
121 static int _max_shift;
122
123 // Encoding Base, Encoding Shift
124 static address _base;
125 static int _shift;
126
127 // Start and end of the Klass Range.
128 // Note: guaranteed to be aligned to 1<<shift (klass_alignment_in_bytes)
129 static address _klass_range_start;
130 static address _klass_range_end;
131
173 // 5) Initialize the narrow Klass encoding scheme by determining encoding base and shift:
174 // 5a) if CDS=on: Calls initialize_for_given_encoding() with the reservation base from step (4) and the
175 // CDS-intrinsic setting for shift; here, we don't have any freedom to deviate from the base.
176 // 5b) if CDS=off: Calls initialize() - here, we have more freedom and, if we want, can choose an encoding
177 // base that differs from the reservation base from step (4). That allows us, e.g., to later use
178 // zero-based encoding.
179 // 6) ... from now on, we can use base() and shift().
180
181 // Called right after argument parsing; defines narrow klass pointer geometry limits
182 static void pre_initialize();
183
184 // The number of bits a narrow Klass pointer has;
185 static int narrow_klass_pointer_bits() { check_init(_narrow_klass_pointer_bits); return _narrow_klass_pointer_bits; }
186
187 // The maximum possible shift; the actual shift employed later can be smaller (see initialize())
188 static int max_shift() { check_init(_max_shift); return _max_shift; }
189
190 // Returns the maximum encoding range, given the current geometry (narrow klass bit size and shift)
191 static size_t max_encoding_range_size() { return nth_bit(narrow_klass_pointer_bits() + max_shift()); }
192
193 // For use before pre-initialization
194 static constexpr size_t max_klass_range_size_coh = nth_bit(narrow_klass_pointer_bits_coh + max_shift_coh);
195
196 // Returns the maximum allowed klass range size.
197 static size_t max_klass_range_size();
198
199 // Reserve a range of memory that is to contain Klass strucutures which are referenced by narrow Klass IDs.
200 // If optimize_for_zero_base is true, the implementation will attempt to reserve optimized for zero-based encoding.
201 static char* reserve_address_space_for_compressed_classes(size_t size, bool aslr, bool optimize_for_zero_base);
202
203 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
204 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
205 // archived heap objects. In this case, we don't have the freedom to choose base and shift; they are handed to
206 // us from CDS.
207 static void initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift);
208
209 // Given an address range [addr, addr+len) which the encoding is supposed to
210 // cover, choose base, shift and range.
211 // The address range is the expected range of uncompressed Klass pointers we
212 // will encounter (and the implicit promise that there will be no Klass
213 // structures outside this range).
214 static void initialize(address addr, size_t len);
215
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