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// Copyright 2011 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "src/codegen/safepoint-table.h"
#include <iomanip>
#include "src/codegen/assembler-inl.h"
#include "src/codegen/macro-assembler.h"
#include "src/deoptimizer/deoptimizer.h"
#include "src/diagnostics/disasm.h"
#include "src/execution/frames-inl.h"
#include "src/utils/ostreams.h"
#if V8_ENABLE_WEBASSEMBLY
#include "src/wasm/wasm-code-manager.h"
#endif // V8_ENABLE_WEBASSEMBLY
namespace v8 {
namespace internal {
SafepointTable::SafepointTable(Isolate* isolate, Address pc, Tagged<Code> code)
: SafepointTable(code->InstructionStart(isolate, pc),
code->safepoint_table_address()) {}
SafepointTable::SafepointTable(Isolate* isolate, Address pc,
Tagged<GcSafeCode> code)
: SafepointTable(code->InstructionStart(isolate, pc),
code->safepoint_table_address()) {}
#if V8_ENABLE_WEBASSEMBLY
SafepointTable::SafepointTable(const wasm::WasmCode* code)
: SafepointTable(
code->instruction_start(),
code->instruction_start() + code->safepoint_table_offset()) {}
#endif // V8_ENABLE_WEBASSEMBLY
SafepointTable::SafepointTable(Address instruction_start,
Address safepoint_table_address)
: instruction_start_(instruction_start),
safepoint_table_address_(safepoint_table_address),
length_(base::Memory<int>(safepoint_table_address + kLengthOffset)),
entry_configuration_(base::Memory<uint32_t>(safepoint_table_address +
kEntryConfigurationOffset)) {}
int SafepointTable::find_return_pc(int pc_offset) {
for (int i = 0; i < length(); i++) {
SafepointEntry entry = GetEntry(i);
if (entry.trampoline_pc() == pc_offset || entry.pc() == pc_offset) {
return entry.pc();
}
}
UNREACHABLE();
}
SafepointEntry SafepointTable::FindEntry(Address pc) const {
int pc_offset = static_cast<int>(pc - instruction_start_);
// Check if the PC is pointing at a trampoline.
if (has_deopt_data()) {
int candidate = -1;
for (int i = 0; i < length_; ++i) {
int trampoline_pc = GetEntry(i).trampoline_pc();
if (trampoline_pc != -1 && trampoline_pc <= pc_offset) candidate = i;
if (trampoline_pc > pc_offset) break;
}
if (candidate != -1) return GetEntry(candidate);
}
for (int i = 0; i < length_; ++i) {
SafepointEntry entry = GetEntry(i);
if (i == length_ - 1 || GetEntry(i + 1).pc() > pc_offset) {
DCHECK_LE(entry.pc(), pc_offset);
return entry;
}
}
UNREACHABLE();
}
// static
SafepointEntry SafepointTable::FindEntry(Isolate* isolate,
Tagged<GcSafeCode> code, Address pc) {
SafepointTable table(isolate, pc, code);
return table.FindEntry(pc);
}
void SafepointTable::Print(std::ostream& os) const {
os << "Safepoints (entries = " << length_ << ", byte size = " << byte_size()
<< ")\n";
for (int index = 0; index < length_; index++) {
SafepointEntry entry = GetEntry(index);
os << reinterpret_cast<const void*>(instruction_start_ + entry.pc()) << " "
<< std::setw(6) << std::hex << entry.pc() << std::dec;
if (!entry.tagged_slots().empty()) {
os << " slots (sp->fp): ";
for (uint8_t bits : entry.tagged_slots()) {
for (int bit = 0; bit < kBitsPerByte; ++bit) {
os << ((bits >> bit) & 1);
}
}
}
if (entry.tagged_register_indexes() != 0) {
os << " registers: ";
uint32_t register_bits = entry.tagged_register_indexes();
int bits = 32 - base::bits::CountLeadingZeros32(register_bits);
for (int j = bits - 1; j >= 0; --j) {
os << ((register_bits >> j) & 1);
}
}
if (entry.has_deoptimization_index()) {
os << " deopt " << std::setw(6) << entry.deoptimization_index()
<< " trampoline: " << std::setw(6) << std::hex
<< entry.trampoline_pc();
}
os << "\n";
}
}
SafepointTableBuilder::Safepoint SafepointTableBuilder::DefineSafepoint(
Assembler* assembler) {
entries_.emplace_back(zone_, assembler->pc_offset_for_safepoint());
return SafepointTableBuilder::Safepoint(&entries_.back(), this);
}
int SafepointTableBuilder::UpdateDeoptimizationInfo(int pc, int trampoline,
int start,
int deopt_index) {
DCHECK_NE(SafepointEntry::kNoTrampolinePC, trampoline);
DCHECK_NE(SafepointEntry::kNoDeoptIndex, deopt_index);
auto it = entries_.begin() + start;
DCHECK(std::any_of(it, entries_.end(),
[pc](auto& entry) { return entry.pc == pc; }));
int index = start;
while (it->pc != pc) ++it, ++index;
it->trampoline = trampoline;
it->deopt_index = deopt_index;
return index;
}
void SafepointTableBuilder::Emit(Assembler* assembler, int tagged_slots_size) {
DCHECK_LT(max_stack_index_, tagged_slots_size);
#ifdef DEBUG
int last_pc = -1;
int last_trampoline = -1;
for (const EntryBuilder& entry : entries_) {
// Entries are ordered by PC.
DCHECK_LT(last_pc, entry.pc);
last_pc = entry.pc;
// Trampoline PCs are increasing, and larger than regular PCs.
if (entry.trampoline != SafepointEntry::kNoTrampolinePC) {
DCHECK_LT(last_trampoline, entry.trampoline);
DCHECK_LT(entries_.back().pc, entry.trampoline);
last_trampoline = entry.trampoline;
}
// An entry either has trampoline and deopt index, or none of the two.
DCHECK_EQ(entry.trampoline == SafepointEntry::kNoTrampolinePC,
entry.deopt_index == SafepointEntry::kNoDeoptIndex);
}
#endif // DEBUG
RemoveDuplicates();
// The encoding is compacted by translating stack slot indices s.t. they
// start at 0. See also below.
tagged_slots_size -= min_stack_index();
#if V8_TARGET_ARCH_ARM || V8_TARGET_ARCH_ARM64
// We cannot emit a const pool within the safepoint table.
Assembler::BlockConstPoolScope block_const_pool(assembler);
#endif
// Make sure the safepoint table is properly aligned. Pad with nops.
assembler->Align(InstructionStream::kMetadataAlignment);
assembler->RecordComment(";;; Safepoint table.");
set_safepoint_table_offset(assembler->pc_offset());
// Compute the required sizes of the fields.
int used_register_indexes = 0;
static_assert(SafepointEntry::kNoTrampolinePC == -1);
int max_pc = SafepointEntry::kNoTrampolinePC;
static_assert(SafepointEntry::kNoDeoptIndex == -1);
int max_deopt_index = SafepointEntry::kNoDeoptIndex;
for (const EntryBuilder& entry : entries_) {
used_register_indexes |= entry.register_indexes;
max_pc = std::max(max_pc, std::max(entry.pc, entry.trampoline));
max_deopt_index = std::max(max_deopt_index, entry.deopt_index);
}
// Derive the bytes and bools for the entry configuration from the values.
auto value_to_bytes = [](int value) {
DCHECK_LE(0, value);
if (value == 0) return 0;
if (value <= 0xff) return 1;
if (value <= 0xffff) return 2;
if (value <= 0xffffff) return 3;
return 4;
};
bool has_deopt_data = max_deopt_index != -1;
int register_indexes_size = value_to_bytes(used_register_indexes);
// Add 1 so all values (including kNoDeoptIndex and kNoTrampolinePC) are
// non-negative.
static_assert(SafepointEntry::kNoDeoptIndex == -1);
static_assert(SafepointEntry::kNoTrampolinePC == -1);
int pc_size = value_to_bytes(max_pc + 1);
int deopt_index_size = value_to_bytes(max_deopt_index + 1);
int tagged_slots_bytes =
(tagged_slots_size + kBitsPerByte - 1) / kBitsPerByte;
// Add a CHECK to ensure we never overflow the space in the bitfield, even for
// huge functions which might not be covered by tests.
CHECK(SafepointTable::RegisterIndexesSizeField::is_valid(
register_indexes_size));
CHECK(SafepointTable::PcSizeField::is_valid(pc_size));
CHECK(SafepointTable::DeoptIndexSizeField::is_valid(deopt_index_size));
CHECK(SafepointTable::TaggedSlotsBytesField::is_valid(tagged_slots_bytes));
uint32_t entry_configuration =
SafepointTable::HasDeoptDataField::encode(has_deopt_data) |
SafepointTable::RegisterIndexesSizeField::encode(register_indexes_size) |
SafepointTable::PcSizeField::encode(pc_size) |
SafepointTable::DeoptIndexSizeField::encode(deopt_index_size) |
SafepointTable::TaggedSlotsBytesField::encode(tagged_slots_bytes);
// Emit the table header.
static_assert(SafepointTable::kLengthOffset == 0 * kIntSize);
static_assert(SafepointTable::kEntryConfigurationOffset == 1 * kIntSize);
static_assert(SafepointTable::kHeaderSize == 2 * kIntSize);
int length = static_cast<int>(entries_.size());
assembler->dd(length);
assembler->dd(entry_configuration);
auto emit_bytes = [assembler](int value, int bytes) {
DCHECK_LE(0, value);
for (; bytes > 0; --bytes, value >>= 8) assembler->db(value);
DCHECK_EQ(0, value);
};
// Emit entries, sorted by pc offsets.
for (const EntryBuilder& entry : entries_) {
emit_bytes(entry.pc, pc_size);
if (has_deopt_data) {
// Add 1 so all values (including kNoDeoptIndex and kNoTrampolinePC) are
// non-negative.
static_assert(SafepointEntry::kNoDeoptIndex == -1);
static_assert(SafepointEntry::kNoTrampolinePC == -1);
emit_bytes(entry.deopt_index + 1, deopt_index_size);
emit_bytes(entry.trampoline + 1, pc_size);
}
emit_bytes(entry.register_indexes, register_indexes_size);
}
// Emit bitmaps of tagged stack slots. Note the slot list is reversed in the
// encoding.
// TODO(jgruber): Avoid building a reversed copy of the bit vector.
ZoneVector<uint8_t> bits(tagged_slots_bytes, 0, zone_);
for (const EntryBuilder& entry : entries_) {
std::fill(bits.begin(), bits.end(), 0);
// Run through the indexes and build a bitmap.
for (int idx : *entry.stack_indexes) {
// The encoding is compacted by translating stack slot indices s.t. they
// start at 0. See also above.
const int adjusted_idx = idx - min_stack_index();
DCHECK_GT(tagged_slots_size, adjusted_idx);
int index = tagged_slots_size - 1 - adjusted_idx;
int byte_index = index >> kBitsPerByteLog2;
int bit_index = index & (kBitsPerByte - 1);
bits[byte_index] |= (1u << bit_index);
}
// Emit the bitmap for the current entry.
for (uint8_t byte : bits) assembler->db(byte);
}
}
void SafepointTableBuilder::RemoveDuplicates() {
// Remove any duplicate entries, i.e. succeeding entries that are identical
// except for the PC. During lookup, we will find the first entry whose PC is
// not larger than the PC at hand, and find the first non-duplicate.
if (entries_.size() < 2) return;
auto is_identical_except_for_pc = [](const EntryBuilder& entry1,
const EntryBuilder& entry2) {
if (entry1.deopt_index != entry2.deopt_index) return false;
DCHECK_EQ(entry1.trampoline, entry2.trampoline);
return entry1.register_indexes == entry2.register_indexes &&
entry1.stack_indexes->Equals(*entry2.stack_indexes);
};
auto remaining_it = entries_.begin();
auto end = entries_.end();
for (auto it = entries_.begin(); it != end; ++remaining_it) {
if (remaining_it != it) *remaining_it = *it;
// Merge identical entries.
do {
++it;
} while (it != end && is_identical_except_for_pc(*it, *remaining_it));
}
entries_.erase(remaining_it, end);
}
} // namespace internal
} // namespace v8
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