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 "card_table-inl.h" 21 #include "gc/heap.h" 22 #include "gc/space/space.h" 23 #include "heap_bitmap.h" 24 #include "runtime.h" 25 #include "utils.h" 26 27 namespace art { 28 namespace gc { 29 namespace accounting { 30 31 /* 32 * Maintain a card table from the write barrier. All writes of 33 * non-NULL values to heap addresses should go through an entry in 34 * WriteBarrier, and from there to here. 35 * 36 * The heap is divided into "cards" of GC_CARD_SIZE bytes, as 37 * determined by GC_CARD_SHIFT. The card table contains one byte of 38 * data per card, to be used by the GC. The value of the byte will be 39 * one of GC_CARD_CLEAN or GC_CARD_DIRTY. 40 * 41 * After any store of a non-NULL object pointer into a heap object, 42 * code is obliged to mark the card dirty. The setters in 43 * object.h [such as SetFieldObject] do this for you. The 44 * compiler also contains code to mark cards as dirty. 45 * 46 * The card table's base [the "biased card table"] gets set to a 47 * rather strange value. In order to keep the JIT from having to 48 * fabricate or load GC_DIRTY_CARD to store into the card table, 49 * biased base is within the mmap allocation at a point where its low 50 * byte is equal to GC_DIRTY_CARD. See CardTable::Create for details. 51 */ 52 53 CardTable* CardTable::Create(const byte* heap_begin, size_t heap_capacity) { 54 /* Set up the card table */ 55 size_t capacity = heap_capacity / kCardSize; 56 /* Allocate an extra 256 bytes to allow fixed low-byte of base */ 57 UniquePtr<MemMap> mem_map(MemMap::MapAnonymous("card table", NULL, 58 capacity + 256, PROT_READ | PROT_WRITE)); 59 CHECK(mem_map.get() != NULL) << "couldn't allocate card table"; 60 // All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we 61 // don't clear the card table to avoid unnecessary pages being allocated 62 COMPILE_ASSERT(kCardClean == 0, card_clean_must_be_0); 63 64 byte* cardtable_begin = mem_map->Begin(); 65 CHECK(cardtable_begin != NULL); 66 67 // We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal 68 // GC_CARD_DIRTY, compute a offset value to make this the case 69 size_t offset = 0; 70 byte* biased_begin = reinterpret_cast<byte*>(reinterpret_cast<uintptr_t>(cardtable_begin) - 71 (reinterpret_cast<uintptr_t>(heap_begin) >> kCardShift)); 72 if (((uintptr_t)biased_begin & 0xff) != kCardDirty) { 73 int delta = kCardDirty - (reinterpret_cast<int>(biased_begin) & 0xff); 74 offset = delta + (delta < 0 ? 0x100 : 0); 75 biased_begin += offset; 76 } 77 CHECK_EQ(reinterpret_cast<int>(biased_begin) & 0xff, kCardDirty); 78 79 return new CardTable(mem_map.release(), biased_begin, offset); 80 } 81 82 CardTable::CardTable(MemMap* mem_map, byte* biased_begin, size_t offset) 83 : mem_map_(mem_map), biased_begin_(biased_begin), offset_(offset) { 84 byte* __attribute__((unused)) begin = mem_map_->Begin() + offset_; 85 byte* __attribute__((unused)) end = mem_map_->End(); 86 } 87 88 void CardTable::ClearSpaceCards(space::ContinuousSpace* space) { 89 // TODO: clear just the range of the table that has been modified 90 byte* card_start = CardFromAddr(space->Begin()); 91 byte* card_end = CardFromAddr(space->End()); // Make sure to round up. 92 memset(reinterpret_cast<void*>(card_start), kCardClean, card_end - card_start); 93 } 94 95 void CardTable::ClearCardTable() { 96 // TODO: clear just the range of the table that has been modified 97 memset(mem_map_->Begin(), kCardClean, mem_map_->Size()); 98 } 99 100 bool CardTable::AddrIsInCardTable(const void* addr) const { 101 return IsValidCard(biased_begin_ + ((uintptr_t)addr >> kCardShift)); 102 } 103 104 void CardTable::CheckAddrIsInCardTable(const byte* addr) const { 105 byte* card_addr = biased_begin_ + ((uintptr_t)addr >> kCardShift); 106 byte* begin = mem_map_->Begin() + offset_; 107 byte* end = mem_map_->End(); 108 CHECK(AddrIsInCardTable(addr)) 109 << "Card table " << this 110 << " begin: " << reinterpret_cast<void*>(begin) 111 << " end: " << reinterpret_cast<void*>(end) 112 << " card_addr: " << reinterpret_cast<void*>(card_addr) 113 << " heap begin: " << AddrFromCard(begin) 114 << " heap end: " << AddrFromCard(end) 115 << " addr: " << reinterpret_cast<const void*>(addr); 116 } 117 118 void CardTable::VerifyCardTable() { 119 UNIMPLEMENTED(WARNING) << "Card table verification"; 120 } 121 122 } // namespace accounting 123 } // namespace gc 124 } // namespace art 125
