1 /* 2 * Copyright (C) 2010 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 #include "card_table.h" 18 19 #include <sys/mman.h> 20 21 #include "base/mem_map.h" 22 #include "base/systrace.h" 23 #include "base/utils.h" 24 #include "card_table-inl.h" 25 #include "gc/heap.h" 26 #include "gc/space/space.h" 27 #include "heap_bitmap.h" 28 #include "runtime.h" 29 30 namespace art { 31 namespace gc { 32 namespace accounting { 33 34 constexpr size_t CardTable::kCardShift; 35 constexpr size_t CardTable::kCardSize; 36 constexpr uint8_t CardTable::kCardClean; 37 constexpr uint8_t CardTable::kCardDirty; 38 39 /* 40 * Maintain a card table from the write barrier. All writes of 41 * non-null values to heap addresses should go through an entry in 42 * WriteBarrier, and from there to here. 43 * 44 * The heap is divided into "cards" of `kCardSize` bytes, as 45 * determined by `kCardShift`. The card table contains one byte of 46 * data per card, to be used by the GC. The value of the byte will be 47 * one of `kCardClean` or `kCardDirty`. 48 * 49 * After any store of a non-null object pointer into a heap object, 50 * code is obliged to mark the card dirty. The setters in 51 * object.h [such as SetFieldObject] do this for you. The 52 * compiler also contains code to mark cards as dirty. 53 * 54 * The card table's base [the "biased card table"] gets set to a 55 * rather strange value. In order to keep the JIT from having to 56 * fabricate or load `kCardDirty` to store into the card table, 57 * biased base is within the mmap allocation at a point where its low 58 * byte is equal to `kCardDirty`. See CardTable::Create for details. 59 */ 60 61 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) { 62 ScopedTrace trace(__PRETTY_FUNCTION__); 63 /* Set up the card table */ 64 size_t capacity = heap_capacity / kCardSize; 65 /* Allocate an extra 256 bytes to allow fixed low-byte of base */ 66 std::string error_msg; 67 MemMap mem_map = MemMap::MapAnonymous("card table", 68 capacity + 256, 69 PROT_READ | PROT_WRITE, 70 /*low_4gb=*/ false, 71 &error_msg); 72 CHECK(mem_map.IsValid()) << "couldn't allocate card table: " << error_msg; 73 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we 74 // don't clear the card table to avoid unnecessary pages being allocated 75 static_assert(kCardClean == 0, "kCardClean must be 0"); 76 77 uint8_t* cardtable_begin = mem_map.Begin(); 78 CHECK(cardtable_begin != nullptr); 79 80 // We allocated up to a bytes worth of extra space to allow `biased_begin`'s byte value to equal 81 // `kCardDirty`, compute a offset value to make this the case 82 size_t offset = 0; 83 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) - 84 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift)); 85 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff; 86 if (biased_byte != kCardDirty) { 87 int delta = kCardDirty - biased_byte; 88 offset = delta + (delta < 0 ? 0x100 : 0); 89 biased_begin += offset; 90 } 91 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty); 92 return new CardTable(std::move(mem_map), biased_begin, offset); 93 } 94 95 CardTable::CardTable(MemMap&& mem_map, uint8_t* biased_begin, size_t offset) 96 : mem_map_(std::move(mem_map)), biased_begin_(biased_begin), offset_(offset) { 97 } 98 99 CardTable::~CardTable() { 100 // Destroys MemMap via std::unique_ptr<>. 101 } 102 103 void CardTable::ClearCardTable() { 104 static_assert(kCardClean == 0, "kCardClean must be 0"); 105 mem_map_.MadviseDontNeedAndZero(); 106 } 107 108 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) { 109 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize); 110 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize); 111 static_assert(kCardClean == 0, "kCardClean must be 0"); 112 uint8_t* start_card = CardFromAddr(start); 113 uint8_t* end_card = CardFromAddr(end); 114 ZeroAndReleasePages(start_card, end_card - start_card); 115 } 116 117 bool CardTable::AddrIsInCardTable(const void* addr) const { 118 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift)); 119 } 120 121 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const { 122 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift); 123 uint8_t* begin = mem_map_.Begin() + offset_; 124 uint8_t* end = mem_map_.End(); 125 CHECK(AddrIsInCardTable(addr)) 126 << "Card table " << this 127 << " begin: " << reinterpret_cast<void*>(begin) 128 << " end: " << reinterpret_cast<void*>(end) 129 << " card_addr: " << reinterpret_cast<void*>(card_addr) 130 << " heap begin: " << AddrFromCard(begin) 131 << " heap end: " << AddrFromCard(end) 132 << " addr: " << reinterpret_cast<const void*>(addr); 133 } 134 135 void CardTable::VerifyCardTable() { 136 UNIMPLEMENTED(WARNING) << "Card table verification"; 137 } 138 139 } // namespace accounting 140 } // namespace gc 141 } // namespace art 142
