1 /*
2 * Copyright (c) 2019, 2024, 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 "precompiled.hpp"
26 #include "logging/log.hpp"
27 #include "logging/logStream.hpp"
28 #include "memory/memRegion.hpp"
29 #include "memory/resourceArea.hpp"
30 #include "memory/universe.hpp"
31 #include "memory/virtualspace.hpp"
32 #include "oops/compressedOops.hpp"
33 #include "gc/shared/collectedHeap.hpp"
34 #include "runtime/arguments.hpp"
35 #include "runtime/globals.hpp"
36
37 // For UseCompressedOops.
38 address CompressedOops::_base = nullptr;
39 int CompressedOops::_shift = 0;
40 bool CompressedOops::_use_implicit_null_checks = true;
41 MemRegion CompressedOops::_heap_address_range;
42
43 // Choose the heap base address and oop encoding mode
44 // when compressed oops are used:
45 // Unscaled - Use 32-bits oops without encoding when
46 // NarrowOopHeapBaseMin + heap_size < 4Gb
47 // ZeroBased - Use zero based compressed oops with encoding when
48 // NarrowOopHeapBaseMin + heap_size < 32Gb
49 // HeapBased - Use compressed oops with heap base + encoding.
50 void CompressedOops::initialize(const ReservedHeapSpace& heap_space) {
51 #ifdef _LP64
52 // Subtract a page because something can get allocated at heap base.
53 // This also makes implicit null checking work, because the
54 // memory+1 page below heap_base needs to cause a signal.
55 // See needs_explicit_null_check.
56 // Only set the heap base for compressed oops because it indicates
57 // compressed oops for pstack code.
58 if ((uint64_t)heap_space.end() > UnscaledOopHeapMax) {
59 // Didn't reserve heap below 4Gb. Must shift.
60 set_shift(LogMinObjAlignmentInBytes);
61 }
62 if ((uint64_t)heap_space.end() <= OopEncodingHeapMax) {
63 // Did reserve heap below 32Gb. Can use base == 0;
64 set_base(nullptr);
65 } else {
66 set_base((address)heap_space.compressed_oop_base());
67 }
68
69 _heap_address_range = heap_space.region();
70
71 LogTarget(Debug, gc, heap, coops) lt;
72 if (lt.is_enabled()) {
73 ResourceMark rm;
74 LogStream ls(lt);
75 print_mode(&ls);
76 }
77
78 // Tell tests in which mode we run.
79 Arguments::PropertyList_add(new SystemProperty("java.vm.compressedOopsMode",
80 mode_to_string(mode()),
81 false));
82
83 // base() is one page below the heap.
84 assert((intptr_t)base() <= ((intptr_t)_heap_address_range.start() - (intptr_t)os::vm_page_size()) ||
85 base() == nullptr, "invalid value");
86 assert(shift() == LogMinObjAlignmentInBytes ||
87 shift() == 0, "invalid value");
88 #endif
89 }
90
91 void CompressedOops::set_base(address base) {
92 assert(UseCompressedOops, "no compressed oops?");
93 _base = base;
94 }
95
96 void CompressedOops::set_shift(int shift) {
97 _shift = shift;
98 }
99
100 void CompressedOops::set_use_implicit_null_checks(bool use) {
101 assert(UseCompressedOops, "no compressed ptrs?");
102 _use_implicit_null_checks = use;
103 }
104
105 bool CompressedOops::is_in(void* addr) {
106 return _heap_address_range.contains(addr);
107 }
108
109 bool CompressedOops::is_in(MemRegion mr) {
110 return _heap_address_range.contains(mr);
111 }
112
113 CompressedOops::Mode CompressedOops::mode() {
114 if (base_disjoint()) {
115 return DisjointBaseNarrowOop;
116 }
117
118 if (base() != nullptr) {
119 return HeapBasedNarrowOop;
120 }
121
122 if (shift() != 0) {
123 return ZeroBasedNarrowOop;
124 }
125
126 return UnscaledNarrowOop;
127 }
128
129 const char* CompressedOops::mode_to_string(Mode mode) {
130 switch (mode) {
131 case UnscaledNarrowOop:
132 return "32-bit";
133 case ZeroBasedNarrowOop:
134 return "Zero based";
135 case DisjointBaseNarrowOop:
136 return "Non-zero disjoint base";
137 case HeapBasedNarrowOop:
138 return "Non-zero based";
139 default:
140 ShouldNotReachHere();
141 return "";
142 }
143 }
144
145 // Test whether bits of addr and possible offsets into the heap overlap.
146 bool CompressedOops::is_disjoint_heap_base_address(address addr) {
147 return (((uint64_t)(intptr_t)addr) &
148 (((uint64_t)UCONST64(0xFFFFffffFFFFffff)) >> (32-LogMinObjAlignmentInBytes))) == 0;
149 }
150
151 // Check for disjoint base compressed oops.
152 bool CompressedOops::base_disjoint() {
153 return _base != nullptr && is_disjoint_heap_base_address(_base);
154 }
155
156 // Check for real heapbased compressed oops.
157 // We must subtract the base as the bits overlap.
158 // If we negate above function, we also get unscaled and zerobased.
159 bool CompressedOops::base_overlaps() {
160 return _base != nullptr && !is_disjoint_heap_base_address(_base);
161 }
162
163 void CompressedOops::print_mode(outputStream* st) {
164 st->print("Heap address: " PTR_FORMAT ", size: " SIZE_FORMAT " MB",
165 p2i(_heap_address_range.start()), _heap_address_range.byte_size()/M);
166
167 st->print(", Compressed Oops mode: %s", mode_to_string(mode()));
168
169 if (base() != nullptr) {
170 st->print(": " PTR_FORMAT, p2i(base()));
171 }
172
173 if (shift() != 0) {
174 st->print(", Oop shift amount: %d", shift());
175 }
176
177 if (!use_implicit_null_checks()) {
178 st->print(", no protected page in front of the heap");
179 }
180 st->cr();
181 }