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 // Subtract a page because something can get allocated at heap base.
52 // This also makes implicit null checking work, because the
53 // memory+1 page below heap_base needs to cause a signal.
54 // See needs_explicit_null_check.
55 // Only set the heap base for compressed oops because it indicates
56 // compressed oops for pstack code.
57 if ((uint64_t)heap_space.end() > UnscaledOopHeapMax) {
58 // Didn't reserve heap below 4Gb. Must shift.
59 set_shift(LogMinObjAlignmentInBytes);
60 }
61 if ((uint64_t)heap_space.end() <= OopEncodingHeapMax) {
62 // Did reserve heap below 32Gb. Can use base == 0;
63 set_base(nullptr);
64 } else {
65 set_base((address)heap_space.compressed_oop_base());
66 }
67
68 _heap_address_range = MemRegion((HeapWord*)heap_space.base(), (HeapWord*)heap_space.end());
69
70 LogTarget(Debug, gc, heap, coops) lt;
71 if (lt.is_enabled()) {
72 ResourceMark rm;
73 LogStream ls(lt);
74 print_mode(&ls);
75 }
76
77 // Tell tests in which mode we run.
78 Arguments::PropertyList_add(new SystemProperty("java.vm.compressedOopsMode",
79 mode_to_string(mode()),
80 false));
81
82 // base() is one page below the heap.
83 assert((intptr_t)base() <= ((intptr_t)_heap_address_range.start() - (intptr_t)os::vm_page_size()) ||
84 base() == nullptr, "invalid value");
85 assert(shift() == LogMinObjAlignmentInBytes ||
86 shift() == 0, "invalid value");
87 #endif
88 }
89
90 void CompressedOops::set_base(address base) {
91 assert(UseCompressedOops, "no compressed oops?");
92 _base = base;
93 }
94
95 void CompressedOops::set_shift(int shift) {
96 _shift = shift;
97 }
98
99 void CompressedOops::set_use_implicit_null_checks(bool use) {
100 assert(UseCompressedOops, "no compressed ptrs?");
101 _use_implicit_null_checks = use;
102 }
103
104 bool CompressedOops::is_in(void* addr) {
105 return _heap_address_range.contains(addr);
106 }
107
108 bool CompressedOops::is_in(MemRegion mr) {
109 return _heap_address_range.contains(mr);
110 }
111
112 CompressedOops::Mode CompressedOops::mode() {
113 if (base_disjoint()) {
114 return DisjointBaseNarrowOop;
115 }
116
117 if (base() != nullptr) {
118 return HeapBasedNarrowOop;
119 }
120
121 if (shift() != 0) {
122 return ZeroBasedNarrowOop;
123 }
124
125 return UnscaledNarrowOop;
126 }
127
128 const char* CompressedOops::mode_to_string(Mode mode) {
129 switch (mode) {
130 case UnscaledNarrowOop:
131 return "32-bit";
132 case ZeroBasedNarrowOop:
133 return "Zero based";
134 case DisjointBaseNarrowOop:
135 return "Non-zero disjoint base";
136 case HeapBasedNarrowOop:
137 return "Non-zero based";
138 default:
139 ShouldNotReachHere();
140 return "";
141 }
142 }
143
144 // Test whether bits of addr and possible offsets into the heap overlap.
145 bool CompressedOops::is_disjoint_heap_base_address(address addr) {
146 return (((uint64_t)(intptr_t)addr) &
147 (((uint64_t)UCONST64(0xFFFFffffFFFFffff)) >> (32-LogMinObjAlignmentInBytes))) == 0;
148 }
149
150 // Check for disjoint base compressed oops.
151 bool CompressedOops::base_disjoint() {
152 return _base != nullptr && is_disjoint_heap_base_address(_base);
153 }
154
155 // Check for real heapbased compressed oops.
156 // We must subtract the base as the bits overlap.
157 // If we negate above function, we also get unscaled and zerobased.
158 bool CompressedOops::base_overlaps() {
159 return _base != nullptr && !is_disjoint_heap_base_address(_base);
160 }
161
162 void CompressedOops::print_mode(outputStream* st) {
163 st->print("Heap address: " PTR_FORMAT ", size: %zu MB",
164 p2i(_heap_address_range.start()), _heap_address_range.byte_size()/M);
165
166 st->print(", Compressed Oops mode: %s", mode_to_string(mode()));
167
168 if (base() != nullptr) {
169 st->print(": " PTR_FORMAT, p2i(base()));
170 }
171
172 if (shift() != 0) {
173 st->print(", Oop shift amount: %d", shift());
174 }
175
176 if (!use_implicit_null_checks()) {
177 st->print(", no protected page in front of the heap");
178 }
179 st->cr();
180 }