1 /*
2 * Copyright (c) 2019, 2025, 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 #include "logging/log.hpp"
26 #include "logging/logStream.hpp"
27 #include "memory/memRegion.hpp"
28 #include "memory/reservedSpace.hpp"
29 #include "memory/resourceArea.hpp"
30 #include "memory/universe.hpp"
31 #include "oops/compressedOops.hpp"
32 #include "gc/shared/collectedHeap.hpp"
33 #include "runtime/arguments.hpp"
34 #include "runtime/globals.hpp"
35
36 // For UseCompressedOops.
37 address CompressedOops::_base = nullptr;
38 int CompressedOops::_shift = 0;
39 bool CompressedOops::_use_implicit_null_checks = true;
40 MemRegion CompressedOops::_heap_address_range;
41
42 // Choose the heap base address and oop encoding mode
43 // when compressed oops are used:
44 // Unscaled - Use 32-bits oops without encoding when
45 // NarrowOopHeapBaseMin + heap_size < 4Gb
46 // ZeroBased - Use zero based compressed oops with encoding when
47 // NarrowOopHeapBaseMin + heap_size < 32Gb
48 // HeapBased - Use compressed oops with heap base + encoding.
49 void CompressedOops::initialize(const ReservedHeapSpace& heap_space) {
50 #ifdef _LP64
51 if (UseCompatibleCompressedOops) {
52 set_shift(LogMinObjAlignmentInBytes);
53 set_base((address)heap_space.compressed_oop_base());
54 } else {
55 // Subtract a page because something can get allocated at heap base.
56 // This also makes implicit null checking work, because the
57 // memory+1 page below heap_base needs to cause a signal.
58 // See needs_explicit_null_check.
59 // Only set the heap base for compressed oops because it indicates
60 // compressed oops for pstack code.
61 if ((uint64_t)heap_space.end() > UnscaledOopHeapMax) {
62 // Didn't reserve heap below 4Gb. Must shift.
63 set_shift(LogMinObjAlignmentInBytes);
64 }
65 if ((uint64_t)heap_space.end() <= OopEncodingHeapMax) {
66 // Did reserve heap below 32Gb. Can use base == 0;
67 set_base(nullptr);
68 } else {
69 set_base((address)heap_space.compressed_oop_base());
70 }
71 }
72
73 _heap_address_range = MemRegion((HeapWord*)heap_space.base(), (HeapWord*)heap_space.end());
74
75 LogTarget(Debug, gc, heap, coops) lt;
76 if (lt.is_enabled()) {
77 ResourceMark rm;
78 LogStream ls(lt);
79 print_mode(&ls);
80 }
81
82 // Tell tests in which mode we run.
83 Arguments::PropertyList_add(new SystemProperty("java.vm.compressedOopsMode",
84 mode_to_string(mode()),
85 false));
86
87 // base() is one page below the heap.
88 assert((intptr_t)base() <= ((intptr_t)_heap_address_range.start() - (intptr_t)os::vm_page_size()) ||
89 base() == nullptr, "invalid value");
90 assert(shift() == LogMinObjAlignmentInBytes ||
91 shift() == 0, "invalid value");
92 #endif
93 }
94
95 void CompressedOops::set_base(address base) {
96 assert(UseCompressedOops, "no compressed oops?");
97 _base = base;
98 }
99
100 void CompressedOops::set_shift(int shift) {
101 _shift = shift;
102 }
103
104 void CompressedOops::set_use_implicit_null_checks(bool use) {
105 assert(UseCompressedOops, "no compressed ptrs?");
106 _use_implicit_null_checks = use;
107 }
108
109 bool CompressedOops::is_in(void* addr) {
110 return _heap_address_range.contains(addr);
111 }
112
113 bool CompressedOops::is_in(MemRegion mr) {
114 return _heap_address_range.contains(mr);
115 }
116
117 CompressedOops::Mode CompressedOops::mode() {
118 if (base_disjoint()) {
119 return DisjointBaseNarrowOop;
120 }
121
122 if (base() != nullptr) {
123 return HeapBasedNarrowOop;
124 }
125
126 if (shift() != 0) {
127 return ZeroBasedNarrowOop;
128 }
129
130 return UnscaledNarrowOop;
131 }
132
133 const char* CompressedOops::mode_to_string(Mode mode) {
134 switch (mode) {
135 case UnscaledNarrowOop:
136 return "32-bit";
137 case ZeroBasedNarrowOop:
138 return "Zero based";
139 case DisjointBaseNarrowOop:
140 return "Non-zero disjoint base";
141 case HeapBasedNarrowOop:
142 return "Non-zero based";
143 default:
144 ShouldNotReachHere();
145 return "";
146 }
147 }
148
149 // Test whether bits of addr and possible offsets into the heap overlap.
150 bool CompressedOops::is_disjoint_heap_base_address(address addr) {
151 return (((uint64_t)(intptr_t)addr) &
152 (((uint64_t)UCONST64(0xFFFFffffFFFFffff)) >> (32-LogMinObjAlignmentInBytes))) == 0;
153 }
154
155 // Check for disjoint base compressed oops.
156 bool CompressedOops::base_disjoint() {
157 return _base != nullptr && is_disjoint_heap_base_address(_base);
158 }
159
160 // Check for real heapbased compressed oops.
161 // We must subtract the base as the bits overlap.
162 // If we negate above function, we also get unscaled and zerobased.
163 bool CompressedOops::base_overlaps() {
164 return _base != nullptr && !is_disjoint_heap_base_address(_base);
165 }
166
167 void CompressedOops::print_mode(outputStream* st) {
168 st->print("Heap address: " PTR_FORMAT ", size: %zu MB",
169 p2i(_heap_address_range.start()), _heap_address_range.byte_size()/M);
170
171 st->print(", Compressed Oops mode: %s", mode_to_string(mode()));
172
173 if (base() != nullptr) {
174 st->print(": " PTR_FORMAT, p2i(base()));
175 }
176
177 if (shift() != 0) {
178 st->print(", Oop shift amount: %d", shift());
179 }
180
181 if (!use_implicit_null_checks()) {
182 st->print(", no protected page in front of the heap");
183 }
184 st->cr();
185 }