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/*
* Copyright (C) 2010 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "card_table.h"
#include <sys/mman.h> /* for PROT_* */
#include "heap.h"
#include "heap_bitmap.h"
#include "logging.h"
#include "utils.h"
namespace art {
/*
* Maintain a card table from the write barrier. All writes of
* non-NULL values to heap addresses should go through an entry in
* WriteBarrier, and from there to here.
*
* The heap is divided into "cards" of GC_CARD_SIZE bytes, as
* determined by GC_CARD_SHIFT. The card table contains one byte of
* data per card, to be used by the GC. The value of the byte will be
* one of GC_CARD_CLEAN or GC_CARD_DIRTY.
*
* After any store of a non-NULL object pointer into a heap object,
* code is obliged to mark the card dirty. The setters in
* object.h [such as SetFieldObject] do this for you. The
* compiler also contains code to mark cards as dirty.
*
* The card table's base [the "biased card table"] gets set to a
* rather strange value. In order to keep the JIT from having to
* fabricate or load GC_DIRTY_CARD to store into the card table,
* biased base is within the mmap allocation at a point where its low
* byte is equal to GC_DIRTY_CARD. See CardTable::Create for details.
*/
CardTable* CardTable::Create(const byte* heap_begin, size_t heap_capacity) {
/* Set up the card table */
size_t capacity = heap_capacity / GC_CARD_SIZE;
/* Allocate an extra 256 bytes to allow fixed low-byte of base */
UniquePtr<MemMap> mem_map(MemMap::MapAnonymous("dalvik-card-table", NULL,
capacity + 256, PROT_READ | PROT_WRITE));
if (mem_map.get() == NULL) {
std::string maps;
ReadFileToString("/proc/self/maps", &maps);
LOG(FATAL) << "couldn't allocate card table\n" << maps;
}
// All zeros is the correct initial value; all clean. Anonymous mmaps are initialized to zero, we
// don't clear the card table to avoid unnecessary pages being allocated
CHECK_EQ(GC_CARD_CLEAN, 0);
byte* cardtable_begin = mem_map->Begin();
CHECK(cardtable_begin != NULL);
// We allocated up to a bytes worth of extra space to allow biased_begin's byte value to equal
// GC_CARD_DIRTY, compute a offset value to make this the case
size_t offset = 0;
byte* biased_begin = (byte *)((uintptr_t)cardtable_begin -((uintptr_t)heap_begin >> GC_CARD_SHIFT));
if (((uintptr_t)biased_begin & 0xff) != GC_CARD_DIRTY) {
int delta = GC_CARD_DIRTY - (reinterpret_cast<int>(biased_begin) & 0xff);
offset = delta + (delta < 0 ? 0x100 : 0);
biased_begin += offset;
}
CHECK_EQ(reinterpret_cast<int>(biased_begin) & 0xff, GC_CARD_DIRTY);
return new CardTable(mem_map.release(), biased_begin, offset);
}
void CardTable::ClearCardTable() {
// TODO: clear just the range of the table that has been modified
memset(mem_map_->Begin(), GC_CARD_CLEAN, mem_map_->Size());
}
void CardTable::CheckAddrIsInCardTable(const byte* addr) const {
byte* cardAddr = biased_begin_ + ((uintptr_t)addr >> GC_CARD_SHIFT);
if (!IsValidCard(cardAddr)) {
byte* begin = mem_map_->Begin() + offset_;
byte* end = mem_map_->End();
LOG(FATAL) << "Cardtable - begin: " << reinterpret_cast<void*>(begin)
<< " end: " << reinterpret_cast<void*>(end)
<< " addr: " << reinterpret_cast<const void*>(addr)
<< " cardAddr: " << reinterpret_cast<void*>(cardAddr);
}
}
void CardTable::Scan(byte* heap_begin, byte* heap_end, Callback* visitor, void* arg) const {
byte* card_cur = CardFromAddr(heap_begin);
byte* card_end = CardFromAddr(heap_end);
while (card_cur < card_end) {
while (card_cur < card_end && *card_cur == GC_CARD_CLEAN) {
card_cur++;
}
byte* run_start = card_cur;
size_t run = 0;
while (card_cur < card_end && *card_cur == GC_CARD_DIRTY) {
run++;
card_cur++;
}
if (run > 0) {
byte* run_end = &card_cur[run];
Heap::GetLiveBits()->VisitRange(reinterpret_cast<uintptr_t>(AddrFromCard(run_start)),
reinterpret_cast<uintptr_t>(AddrFromCard(run_end)),
visitor, arg);
}
}
}
void CardTable::VerifyCardTable() {
UNIMPLEMENTED(WARNING) << "Card table verification";
}
} // namespace art
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