1 /*
2 * Copyright (c) 2019, 2023, 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
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
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 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
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 const int LogKlassAlignmentInBytes = 3;
38 const int KlassAlignmentInBytes = 1 << LogKlassAlignmentInBytes;
39
40 // Maximal size of compressed class space. Above this limit compression is not possible.
41 // Also upper bound for placement of zero based class space. (Class space is further limited
42 // to be < 3G, see arguments.cpp.)
43 const uint64_t KlassEncodingMetaspaceMax = (uint64_t(max_juint) + 1) << LogKlassAlignmentInBytes;
44
45 // For UseCompressedClassPointers.
46 class CompressedKlassPointers : public AllStatic {
47 friend class VMStructs;
48 friend class ArchiveBuilder;
49
50 static address _base;
51 static int _shift;
52
53 // Together with base, this defines the address range within which Klass
54 // structures will be located: [base, base+range). While the maximal
55 // possible encoding range is 4|32G for shift 0|3, if we know beforehand
56 // the expected range of Klass* pointers will be smaller, a platform
57 // could use this info to optimize encoding.
58 static size_t _range;
59
60 // Helper function for common cases.
61 static char* reserve_address_space_X(uintptr_t from, uintptr_t to, size_t size, size_t alignment, bool aslr);
62 static char* reserve_address_space_for_unscaled_encoding(size_t size, bool aslr);
63 static char* reserve_address_space_for_zerobased_encoding(size_t size, bool aslr);
64 static char* reserve_address_space_for_16bit_move(size_t size, bool aslr);
65
66 DEBUG_ONLY(static void assert_is_valid_encoding(address addr, size_t len, address base, int shift);)
67
68 static inline Klass* decode_not_null_without_asserts(narrowKlass v, address base, int shift);
69 static inline Klass* decode_not_null(narrowKlass v, address base, int shift);
70
71 static inline narrowKlass encode_not_null(Klass* v, address base, int shift);
72
73 public:
74
75 // Reserve a range of memory that is to contain Klass strucutures which are referenced by narrow Klass IDs.
76 // If optimize_for_zero_base is true, the implementation will attempt to reserve optimized for zero-based encoding.
77 static char* reserve_address_space_for_compressed_classes(size_t size, bool aslr, bool optimize_for_zero_base);
78
79 // Given a klass range [addr, addr+len) and a given encoding scheme, assert that this scheme covers the range, then
80 // set this encoding scheme. Used by CDS at runtime to re-instate the scheme used to pre-compute klass ids for
81 // archived heap objects. In this case, we don't have the freedom to choose base and shift; they are handed to
82 // us from CDS.
83 static void initialize_for_given_encoding(address addr, size_t len, address requested_base, int requested_shift);
84
85 // Given an address range [addr, addr+len) which the encoding is supposed to
86 // cover, choose base, shift and range.
87 // The address range is the expected range of uncompressed Klass pointers we
88 // will encounter (and the implicit promise that there will be no Klass
89 // structures outside this range).
90 static void initialize(address addr, size_t len);
91
92 static void print_mode(outputStream* st);
93
94 static address base() { return _base; }
95 static size_t range() { return _range; }
96 static int shift() { return _shift; }
97
98 static bool is_null(Klass* v) { return v == nullptr; }
99 static bool is_null(narrowKlass v) { return v == 0; }
100
101 // Versions without asserts
102 static inline Klass* decode_not_null_without_asserts(narrowKlass v);
103 static inline Klass* decode_without_asserts(narrowKlass v);
104
105 static inline Klass* decode_not_null(narrowKlass v);
106 static inline Klass* decode(narrowKlass v);
107
108 static inline narrowKlass encode_not_null(Klass* v);
109 static inline narrowKlass encode(Klass* v);
110 };
111
112 #endif // SHARE_OOPS_COMPRESSEDKLASS_HPP