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 LogStream ls(lt); 73 print_mode(&ls); 74 } 75 76 // Tell tests in which mode we run. 77 Arguments::PropertyList_add(new SystemProperty("java.vm.compressedOopsMode", 78 mode_to_string(mode()), 79 false)); 80 81 // base() is one page below the heap. 82 assert((intptr_t)base() <= ((intptr_t)_heap_address_range.start() - (intptr_t)os::vm_page_size()) || 83 base() == nullptr, "invalid value"); 84 assert(shift() == LogMinObjAlignmentInBytes || 85 shift() == 0, "invalid value"); 86 #endif 87 } 88 89 void CompressedOops::set_base(address base) { 90 assert(UseCompressedOops, "no compressed oops?"); 91 _base = base; 92 } 93 94 void CompressedOops::set_shift(int shift) { 95 _shift = shift; 96 } 97 98 void CompressedOops::set_use_implicit_null_checks(bool use) { 99 assert(UseCompressedOops, "no compressed ptrs?"); 100 _use_implicit_null_checks = use; 101 } 102 103 bool CompressedOops::is_in(void* addr) { 104 return _heap_address_range.contains(addr); 105 } 106 107 bool CompressedOops::is_in(MemRegion mr) { 108 return _heap_address_range.contains(mr); 109 } 110 111 CompressedOops::Mode CompressedOops::mode() { 112 if (base_disjoint()) { 113 return DisjointBaseNarrowOop; 114 } 115 116 if (base() != nullptr) { 117 return HeapBasedNarrowOop; 118 } 119 120 if (shift() != 0) { 121 return ZeroBasedNarrowOop; 122 } 123 124 return UnscaledNarrowOop; 125 } 126 127 const char* CompressedOops::mode_to_string(Mode mode) { 128 switch (mode) { 129 case UnscaledNarrowOop: 130 return "32-bit"; 131 case ZeroBasedNarrowOop: 132 return "Zero based"; 133 case DisjointBaseNarrowOop: 134 return "Non-zero disjoint base"; 135 case HeapBasedNarrowOop: 136 return "Non-zero based"; 137 default: 138 ShouldNotReachHere(); 139 return ""; 140 } 141 } 142 143 // Test whether bits of addr and possible offsets into the heap overlap. 144 bool CompressedOops::is_disjoint_heap_base_address(address addr) { 145 return (((uint64_t)(intptr_t)addr) & 146 (((uint64_t)UCONST64(0xFFFFffffFFFFffff)) >> (32-LogMinObjAlignmentInBytes))) == 0; 147 } 148 149 // Check for disjoint base compressed oops. 150 bool CompressedOops::base_disjoint() { 151 return _base != nullptr && is_disjoint_heap_base_address(_base); 152 } 153 154 // Check for real heapbased compressed oops. 155 // We must subtract the base as the bits overlap. 156 // If we negate above function, we also get unscaled and zerobased. 157 bool CompressedOops::base_overlaps() { 158 return _base != nullptr && !is_disjoint_heap_base_address(_base); 159 } 160 161 void CompressedOops::print_mode(outputStream* st) { 162 st->print("Heap address: " PTR_FORMAT ", size: %zu MB", 163 p2i(_heap_address_range.start()), _heap_address_range.byte_size()/M); 164 165 st->print(", Compressed Oops mode: %s", mode_to_string(mode())); 166 167 if (base() != nullptr) { 168 st->print(": " PTR_FORMAT, p2i(base())); 169 } 170 171 if (shift() != 0) { 172 st->print(", Oop shift amount: %d", shift()); 173 } 174 175 if (!use_implicit_null_checks()) { 176 st->print(", no protected page in front of the heap"); 177 } 178 st->cr(); 179 }