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