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 "base/logging.h" 20 #include "base/systrace.h" 21 #include "card_table-inl.h" 22 #include "gc/heap.h" 23 #include "gc/space/space.h" 24 #include "heap_bitmap.h" 25 #include "mem_map.h" 26 #include "runtime.h" 27 #include "utils.h" 28 29 namespace art { 30 namespace gc { 31 namespace accounting { 32 33 constexpr size_t CardTable::kCardShift; 34 constexpr size_t CardTable::kCardSize; 35 constexpr uint8_t CardTable::kCardClean; 36 constexpr uint8_t CardTable::kCardDirty; 37 38 /* 39 * Maintain a card table from the write barrier. All writes of 40 * non-null values to heap addresses should go through an entry in 41 * WriteBarrier, and from there to here. 42 * 43 * The heap is divided into "cards" of GC_CARD_SIZE bytes, as 44 * determined by GC_CARD_SHIFT. The card table contains one byte of 45 * data per card, to be used by the GC. The value of the byte will be 46 * one of GC_CARD_CLEAN or GC_CARD_DIRTY. 47 * 48 * After any store of a non-null object pointer into a heap object, 49 * code is obliged to mark the card dirty. The setters in 50 * object.h [such as SetFieldObject] do this for you. The 51 * compiler also contains code to mark cards as dirty. 52 * 53 * The card table's base [the "biased card table"] gets set to a 54 * rather strange value. In order to keep the JIT from having to 55 * fabricate or load GC_DIRTY_CARD to store into the card table, 56 * biased base is within the mmap allocation at a point where its low 57 * byte is equal to GC_DIRTY_CARD. See CardTable::Create for details. 58 */ 59 60 CardTable* CardTable::Create(const uint8_t* heap_begin, size_t heap_capacity) { 61 ScopedTrace trace(__PRETTY_FUNCTION__); 62 /* Set up the card table */ 63 size_t capacity = heap_capacity / kCardSize; 64 /* Allocate an extra 256 bytes to allow fixed low-byte of base */ 65 std::string error_msg; 66 std::unique_ptr<MemMap> mem_map( 67 MemMap::MapAnonymous("card table", nullptr, capacity + 256, PROT_READ | PROT_WRITE, 68 false, false, &error_msg)); 69 CHECK(mem_map.get() != nullptr) << "couldn't allocate card table: " << error_msg; 70 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we 71 // don't clear the card table to avoid unnecessary pages being allocated 72 static_assert(kCardClean == 0, "kCardClean must be 0"); 73 74 uint8_t* cardtable_begin = mem_map->Begin(); 75 CHECK(cardtable_begin != nullptr); 76 77 // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal 78 // kCardDirty, compute a offset value to make this the case 79 size_t offset = 0; 80 uint8_t* biased_begin = reinterpret_cast<uint8_t*>(reinterpret_cast<uintptr_t>(cardtable_begin) - 81 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift)); 82 uintptr_t biased_byte = reinterpret_cast<uintptr_t>(biased_begin) & 0xff; 83 if (biased_byte != kCardDirty) { 84 int delta = kCardDirty - biased_byte; 85 offset = delta + (delta < 0 ? 0x100 : 0); 86 biased_begin += offset; 87 } 88 CHECK_EQ(reinterpret_cast<uintptr_t>(biased_begin) & 0xff, kCardDirty); 89 return new CardTable(mem_map.release(), biased_begin, offset); 90 } 91 92 CardTable::CardTable(MemMap* mem_map, uint8_t* biased_begin, size_t offset) 93 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) { 94 } 95 96 CardTable::~CardTable() { 97 // Destroys MemMap via std::unique_ptr<>. 98 } 99 100 void CardTable::ClearSpaceCards(space::ContinuousSpace* space) { 101 // TODO: clear just the range of the table that has been modified 102 uint8_t* card_start = CardFromAddr(space->Begin()); 103 uint8_t* card_end = CardFromAddr(space->End()); // Make sure to round up. 104 memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start); 105 } 106 107 void CardTable::ClearCardTable() { 108 static_assert(kCardClean == 0, "kCardClean must be 0"); 109 mem_map_->MadviseDontNeedAndZero(); 110 } 111 112 void CardTable::ClearCardRange(uint8_t* start, uint8_t* end) { 113 if (!kMadviseZeroes) { 114 memset(start, 0, end - start); 115 return; 116 } 117 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(start), kCardSize); 118 CHECK_ALIGNED(reinterpret_cast<uintptr_t>(end), kCardSize); 119 static_assert(kCardClean == 0, "kCardClean must be 0"); 120 uint8_t* start_card = CardFromAddr(start); 121 uint8_t* end_card = CardFromAddr(end); 122 uint8_t* round_start = AlignUp(start_card, kPageSize); 123 uint8_t* round_end = AlignDown(end_card, kPageSize); 124 if (round_start < round_end) { 125 madvise(round_start, round_end - round_start, MADV_DONTNEED); 126 } 127 // Handle unaligned regions at start / end. 128 memset(start_card, 0, std::min(round_start, end_card) - start_card); 129 memset(std::max(round_end, start_card), 0, end_card - std::max(round_end, start_card)); 130 } 131 132 bool CardTable::AddrIsInCardTable(const void* addr) const { 133 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift)); 134 } 135 136 void CardTable::CheckAddrIsInCardTable(const uint8_t* addr) const { 137 uint8_t* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift); 138 uint8_t* begin = mem_map_->Begin() + offset_; 139 uint8_t* end = mem_map_->End(); 140 CHECK(AddrIsInCardTable(addr)) 141 << "Card table " << this 142 << " begin: " << reinterpret_cast<void*>(begin) 143 << " end: " << reinterpret_cast<void*>(end) 144 << " card_addr: " << reinterpret_cast<void*>(card_addr) 145 << " heap begin: " << AddrFromCard(begin) 146 << " heap end: " << AddrFromCard(end) 147 << " addr: " << reinterpret_cast<const void*>(addr); 148 } 149 150 void CardTable::VerifyCardTable() { 151 UNIMPLEMENTED(WARNING) << "Card table verification"; 152 } 153 154 } // namespace accounting 155 } // namespace gc 156 } // namespace art 157
