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// Copyright 2018 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/reloc-info.h"
#include "src/codegen/assembler-inl.h"
#include "src/codegen/code-reference.h"
#include "src/deoptimizer/deoptimize-reason.h"
#include "src/deoptimizer/deoptimizer.h"
#include "src/heap/heap-write-barrier-inl.h"
#include "src/objects/code-inl.h"
#include "src/snapshot/snapshot.h"
namespace v8 {
namespace internal {
const char* const RelocInfo::kFillerCommentString = "DEOPTIMIZATION PADDING";
// -----------------------------------------------------------------------------
// Implementation of RelocInfoWriter and RelocIterator
//
// Relocation information is written backwards in memory, from high addresses
// towards low addresses, byte by byte. Therefore, in the encodings listed
// below, the first byte listed it at the highest address, and successive
// bytes in the record are at progressively lower addresses.
//
// Encoding
//
// The most common modes are given single-byte encodings. Also, it is
// easy to identify the type of reloc info and skip unwanted modes in
// an iteration.
//
// The encoding relies on the fact that there are fewer than 14
// different relocation modes using standard non-compact encoding.
//
// The first byte of a relocation record has a tag in its low 2 bits:
// Here are the record schemes, depending on the low tag and optional higher
// tags.
//
// Low tag:
// 00: embedded_object: [6-bit pc delta] 00
//
// 01: code_target: [6-bit pc delta] 01
//
// 10: wasm_stub_call: [6-bit pc delta] 10
//
// 11: long_record [6 bit reloc mode] 11
// followed by pc delta
// followed by optional data depending on type.
//
// If a pc delta exceeds 6 bits, it is split into a remainder that fits into
// 6 bits and a part that does not. The latter is encoded as a long record
// with PC_JUMP as pseudo reloc info mode. The former is encoded as part of
// the following record in the usual way. The long pc jump record has variable
// length:
// pc-jump: [PC_JUMP] 11
// [7 bits data] 0
// ...
// [7 bits data] 1
// (Bits 6..31 of pc delta, with leading zeroes
// dropped, and last non-zero chunk tagged with 1.)
const int kTagBits = 2;
const int kTagMask = (1 << kTagBits) - 1;
const int kLongTagBits = 6;
const int kEmbeddedObjectTag = 0;
const int kCodeTargetTag = 1;
const int kWasmStubCallTag = 2;
const int kDefaultTag = 3;
const int kSmallPCDeltaBits = kBitsPerByte - kTagBits;
const int kSmallPCDeltaMask = (1 << kSmallPCDeltaBits) - 1;
const int RelocInfo::kMaxSmallPCDelta = kSmallPCDeltaMask;
const int kChunkBits = 7;
const int kChunkMask = (1 << kChunkBits) - 1;
const int kLastChunkTagBits = 1;
const int kLastChunkTagMask = 1;
const int kLastChunkTag = 1;
uint32_t RelocInfoWriter::WriteLongPCJump(uint32_t pc_delta) {
// Return if the pc_delta can fit in kSmallPCDeltaBits bits.
// Otherwise write a variable length PC jump for the bits that do
// not fit in the kSmallPCDeltaBits bits.
if (is_uintn(pc_delta, kSmallPCDeltaBits)) return pc_delta;
WriteMode(RelocInfo::PC_JUMP);
uint32_t pc_jump = pc_delta >> kSmallPCDeltaBits;
DCHECK_GT(pc_jump, 0);
// Write kChunkBits size chunks of the pc_jump.
for (; pc_jump > 0; pc_jump = pc_jump >> kChunkBits) {
byte b = pc_jump & kChunkMask;
*--pos_ = b << kLastChunkTagBits;
}
// Tag the last chunk so it can be identified.
*pos_ = *pos_ | kLastChunkTag;
// Return the remaining kSmallPCDeltaBits of the pc_delta.
return pc_delta & kSmallPCDeltaMask;
}
void RelocInfoWriter::WriteShortTaggedPC(uint32_t pc_delta, int tag) {
// Write a byte of tagged pc-delta, possibly preceded by an explicit pc-jump.
pc_delta = WriteLongPCJump(pc_delta);
*--pos_ = pc_delta << kTagBits | tag;
}
void RelocInfoWriter::WriteShortData(intptr_t data_delta) {
*--pos_ = static_cast<byte>(data_delta);
}
void RelocInfoWriter::WriteMode(RelocInfo::Mode rmode) {
STATIC_ASSERT(RelocInfo::NUMBER_OF_MODES <= (1 << kLongTagBits));
*--pos_ = static_cast<int>((rmode << kTagBits) | kDefaultTag);
}
void RelocInfoWriter::WriteModeAndPC(uint32_t pc_delta, RelocInfo::Mode rmode) {
// Write two-byte tagged pc-delta, possibly preceded by var. length pc-jump.
pc_delta = WriteLongPCJump(pc_delta);
WriteMode(rmode);
*--pos_ = pc_delta;
}
void RelocInfoWriter::WriteIntData(int number) {
for (int i = 0; i < kIntSize; i++) {
*--pos_ = static_cast<byte>(number);
// Signed right shift is arithmetic shift. Tested in test-utils.cc.
number = number >> kBitsPerByte;
}
}
void RelocInfoWriter::WriteData(intptr_t data_delta) {
for (int i = 0; i < kIntptrSize; i++) {
*--pos_ = static_cast<byte>(data_delta);
// Signed right shift is arithmetic shift. Tested in test-utils.cc.
data_delta = data_delta >> kBitsPerByte;
}
}
void RelocInfoWriter::Write(const RelocInfo* rinfo) {
RelocInfo::Mode rmode = rinfo->rmode();
#ifdef DEBUG
byte* begin_pos = pos_;
#endif
DCHECK(rinfo->rmode() < RelocInfo::NUMBER_OF_MODES);
DCHECK_GE(rinfo->pc() - reinterpret_cast<Address>(last_pc_), 0);
// Use unsigned delta-encoding for pc.
uint32_t pc_delta =
static_cast<uint32_t>(rinfo->pc() - reinterpret_cast<Address>(last_pc_));
// The two most common modes are given small tags, and usually fit in a byte.
if (rmode == RelocInfo::FULL_EMBEDDED_OBJECT) {
WriteShortTaggedPC(pc_delta, kEmbeddedObjectTag);
} else if (rmode == RelocInfo::CODE_TARGET) {
WriteShortTaggedPC(pc_delta, kCodeTargetTag);
DCHECK_LE(begin_pos - pos_, RelocInfo::kMaxCallSize);
} else if (rmode == RelocInfo::WASM_STUB_CALL) {
WriteShortTaggedPC(pc_delta, kWasmStubCallTag);
} else {
WriteModeAndPC(pc_delta, rmode);
if (RelocInfo::IsDeoptReason(rmode)) {
DCHECK_LT(rinfo->data(), 1 << kBitsPerByte);
WriteShortData(rinfo->data());
} else if (RelocInfo::IsConstPool(rmode) ||
RelocInfo::IsVeneerPool(rmode) || RelocInfo::IsDeoptId(rmode) ||
RelocInfo::IsDeoptPosition(rmode)) {
WriteIntData(static_cast<int>(rinfo->data()));
}
}
last_pc_ = reinterpret_cast<byte*>(rinfo->pc());
#ifdef DEBUG
DCHECK_LE(begin_pos - pos_, kMaxSize);
#endif
}
inline int RelocIterator::AdvanceGetTag() { return *--pos_ & kTagMask; }
inline RelocInfo::Mode RelocIterator::GetMode() {
return static_cast<RelocInfo::Mode>((*pos_ >> kTagBits) &
((1 << kLongTagBits) - 1));
}
inline void RelocIterator::ReadShortTaggedPC() {
rinfo_.pc_ += *pos_ >> kTagBits;
}
inline void RelocIterator::AdvanceReadPC() { rinfo_.pc_ += *--pos_; }
void RelocIterator::AdvanceReadInt() {
int x = 0;
for (int i = 0; i < kIntSize; i++) {
x |= static_cast<int>(*--pos_) << i * kBitsPerByte;
}
rinfo_.data_ = x;
}
void RelocIterator::AdvanceReadData() {
intptr_t x = 0;
for (int i = 0; i < kIntptrSize; i++) {
x |= static_cast<intptr_t>(*--pos_) << i * kBitsPerByte;
}
rinfo_.data_ = x;
}
void RelocIterator::AdvanceReadLongPCJump() {
// Read the 32-kSmallPCDeltaBits most significant bits of the
// pc jump in kChunkBits bit chunks and shift them into place.
// Stop when the last chunk is encountered.
uint32_t pc_jump = 0;
for (int i = 0; i < kIntSize; i++) {
byte pc_jump_part = *--pos_;
pc_jump |= (pc_jump_part >> kLastChunkTagBits) << i * kChunkBits;
if ((pc_jump_part & kLastChunkTagMask) == 1) break;
}
// The least significant kSmallPCDeltaBits bits will be added
// later.
rinfo_.pc_ += pc_jump << kSmallPCDeltaBits;
}
inline void RelocIterator::ReadShortData() {
uint8_t unsigned_b = *pos_;
rinfo_.data_ = unsigned_b;
}
void RelocIterator::next() {
DCHECK(!done());
// Basically, do the opposite of RelocInfoWriter::Write.
// Reading of data is as far as possible avoided for unwanted modes,
// but we must always update the pc.
//
// We exit this loop by returning when we find a mode we want.
while (pos_ > end_) {
int tag = AdvanceGetTag();
if (tag == kEmbeddedObjectTag) {
ReadShortTaggedPC();
if (SetMode(RelocInfo::FULL_EMBEDDED_OBJECT)) return;
} else if (tag == kCodeTargetTag) {
ReadShortTaggedPC();
if (SetMode(RelocInfo::CODE_TARGET)) return;
} else if (tag == kWasmStubCallTag) {
ReadShortTaggedPC();
if (SetMode(RelocInfo::WASM_STUB_CALL)) return;
} else {
DCHECK_EQ(tag, kDefaultTag);
RelocInfo::Mode rmode = GetMode();
if (rmode == RelocInfo::PC_JUMP) {
AdvanceReadLongPCJump();
} else {
AdvanceReadPC();
if (RelocInfo::IsDeoptReason(rmode)) {
Advance();
if (SetMode(rmode)) {
ReadShortData();
return;
}
} else if (RelocInfo::IsConstPool(rmode) ||
RelocInfo::IsVeneerPool(rmode) ||
RelocInfo::IsDeoptId(rmode) ||
RelocInfo::IsDeoptPosition(rmode)) {
if (SetMode(rmode)) {
AdvanceReadInt();
return;
}
Advance(kIntSize);
} else if (SetMode(static_cast<RelocInfo::Mode>(rmode))) {
return;
}
}
}
}
done_ = true;
}
RelocIterator::RelocIterator(Code code, int mode_mask)
: RelocIterator(code, code.unchecked_relocation_info(), mode_mask) {}
RelocIterator::RelocIterator(Code code, ByteArray relocation_info,
int mode_mask)
: RelocIterator(code, code.raw_instruction_start(), code.constant_pool(),
relocation_info.GetDataEndAddress(),
relocation_info.GetDataStartAddress(), mode_mask) {}
RelocIterator::RelocIterator(const CodeReference code_reference, int mode_mask)
: RelocIterator(Code(), code_reference.instruction_start(),
code_reference.constant_pool(),
code_reference.relocation_end(),
code_reference.relocation_start(), mode_mask) {}
RelocIterator::RelocIterator(EmbeddedData* embedded_data, Code code,
int mode_mask)
: RelocIterator(
code, embedded_data->InstructionStartOfBuiltin(code.builtin_index()),
code.constant_pool(),
code.relocation_start() + code.relocation_size(),
code.relocation_start(), mode_mask) {}
RelocIterator::RelocIterator(const CodeDesc& desc, int mode_mask)
: RelocIterator(Code(), reinterpret_cast<Address>(desc.buffer), 0,
desc.buffer + desc.buffer_size,
desc.buffer + desc.buffer_size - desc.reloc_size,
mode_mask) {}
RelocIterator::RelocIterator(Vector<byte> instructions,
Vector<const byte> reloc_info, Address const_pool,
int mode_mask)
: RelocIterator(Code(), reinterpret_cast<Address>(instructions.begin()),
const_pool, reloc_info.begin() + reloc_info.size(),
reloc_info.begin(), mode_mask) {}
RelocIterator::RelocIterator(Code host, Address pc, Address constant_pool,
const byte* pos, const byte* end, int mode_mask)
: pos_(pos), end_(end), mode_mask_(mode_mask) {
// Relocation info is read backwards.
DCHECK_GE(pos_, end_);
rinfo_.host_ = host;
rinfo_.pc_ = pc;
rinfo_.constant_pool_ = constant_pool;
if (mode_mask_ == 0) pos_ = end_;
next();
}
// -----------------------------------------------------------------------------
// Implementation of RelocInfo
// static
bool RelocInfo::OffHeapTargetIsCodedSpecially() {
#if defined(V8_TARGET_ARCH_ARM) || defined(V8_TARGET_ARCH_ARM64) || \
defined(V8_TARGET_ARCH_X64)
return false;
#elif defined(V8_TARGET_ARCH_IA32) || defined(V8_TARGET_ARCH_MIPS) || \
defined(V8_TARGET_ARCH_MIPS64) || defined(V8_TARGET_ARCH_PPC) || \
defined(V8_TARGET_ARCH_S390)
return true;
#endif
}
Address RelocInfo::wasm_call_address() const {
DCHECK_EQ(rmode_, WASM_CALL);
return Assembler::target_address_at(pc_, constant_pool_);
}
void RelocInfo::set_wasm_call_address(Address address,
ICacheFlushMode icache_flush_mode) {
DCHECK_EQ(rmode_, WASM_CALL);
Assembler::set_target_address_at(pc_, constant_pool_, address,
icache_flush_mode);
}
Address RelocInfo::wasm_stub_call_address() const {
DCHECK_EQ(rmode_, WASM_STUB_CALL);
return Assembler::target_address_at(pc_, constant_pool_);
}
void RelocInfo::set_wasm_stub_call_address(Address address,
ICacheFlushMode icache_flush_mode) {
DCHECK_EQ(rmode_, WASM_STUB_CALL);
Assembler::set_target_address_at(pc_, constant_pool_, address,
icache_flush_mode);
}
void RelocInfo::set_target_address(Address target,
WriteBarrierMode write_barrier_mode,
ICacheFlushMode icache_flush_mode) {
DCHECK(IsCodeTargetMode(rmode_) || IsRuntimeEntry(rmode_) ||
IsWasmCall(rmode_));
Assembler::set_target_address_at(pc_, constant_pool_, target,
icache_flush_mode);
if (write_barrier_mode == UPDATE_WRITE_BARRIER && !host().is_null() &&
IsCodeTargetMode(rmode_)) {
Code target_code = Code::GetCodeFromTargetAddress(target);
MarkingBarrierForCode(host(), this, target_code);
}
}
bool RelocInfo::HasTargetAddressAddress() const {
// TODO(jgruber): Investigate whether WASM_CALL is still appropriate on
// non-intel platforms now that wasm code is no longer on the heap.
#if defined(V8_TARGET_ARCH_IA32) || defined(V8_TARGET_ARCH_X64)
static constexpr int kTargetAddressAddressModeMask =
ModeMask(CODE_TARGET) | ModeMask(FULL_EMBEDDED_OBJECT) |
ModeMask(COMPRESSED_EMBEDDED_OBJECT) | ModeMask(EXTERNAL_REFERENCE) |
ModeMask(OFF_HEAP_TARGET) | ModeMask(RUNTIME_ENTRY) |
ModeMask(WASM_CALL) | ModeMask(WASM_STUB_CALL);
#else
static constexpr int kTargetAddressAddressModeMask =
ModeMask(CODE_TARGET) | ModeMask(RELATIVE_CODE_TARGET) |
ModeMask(FULL_EMBEDDED_OBJECT) | ModeMask(EXTERNAL_REFERENCE) |
ModeMask(OFF_HEAP_TARGET) | ModeMask(RUNTIME_ENTRY) | ModeMask(WASM_CALL);
#endif
return (ModeMask(rmode_) & kTargetAddressAddressModeMask) != 0;
}
bool RelocInfo::RequiresRelocationAfterCodegen(const CodeDesc& desc) {
RelocIterator it(desc, RelocInfo::PostCodegenRelocationMask());
return !it.done();
}
bool RelocInfo::RequiresRelocation(Code code) {
RelocIterator it(code, RelocInfo::kApplyMask);
return !it.done();
}
#ifdef ENABLE_DISASSEMBLER
const char* RelocInfo::RelocModeName(RelocInfo::Mode rmode) {
switch (rmode) {
case NONE:
return "no reloc";
case COMPRESSED_EMBEDDED_OBJECT:
return "compressed embedded object";
case FULL_EMBEDDED_OBJECT:
return "full embedded object";
case CODE_TARGET:
return "code target";
case RELATIVE_CODE_TARGET:
return "relative code target";
case RUNTIME_ENTRY:
return "runtime entry";
case EXTERNAL_REFERENCE:
return "external reference";
case INTERNAL_REFERENCE:
return "internal reference";
case INTERNAL_REFERENCE_ENCODED:
return "encoded internal reference";
case OFF_HEAP_TARGET:
return "off heap target";
case DEOPT_SCRIPT_OFFSET:
return "deopt script offset";
case DEOPT_INLINING_ID:
return "deopt inlining id";
case DEOPT_REASON:
return "deopt reason";
case DEOPT_ID:
return "deopt index";
case CONST_POOL:
return "constant pool";
case VENEER_POOL:
return "veneer pool";
case WASM_CALL:
return "internal wasm call";
case WASM_STUB_CALL:
return "wasm stub call";
case NUMBER_OF_MODES:
case PC_JUMP:
UNREACHABLE();
}
return "unknown relocation type";
}
void RelocInfo::Print(Isolate* isolate, std::ostream& os) { // NOLINT
os << reinterpret_cast<const void*>(pc_) << " " << RelocModeName(rmode_);
if (rmode_ == DEOPT_SCRIPT_OFFSET || rmode_ == DEOPT_INLINING_ID) {
os << " (" << data() << ")";
} else if (rmode_ == DEOPT_REASON) {
os << " ("
<< DeoptimizeReasonToString(static_cast<DeoptimizeReason>(data_)) << ")";
} else if (rmode_ == FULL_EMBEDDED_OBJECT) {
os << " (" << Brief(target_object()) << ")";
} else if (rmode_ == COMPRESSED_EMBEDDED_OBJECT) {
os << " (" << Brief(target_object()) << " compressed)";
} else if (rmode_ == EXTERNAL_REFERENCE) {
if (isolate) {
ExternalReferenceEncoder ref_encoder(isolate);
os << " ("
<< ref_encoder.NameOfAddress(isolate, target_external_reference())
<< ") ";
}
os << " (" << reinterpret_cast<const void*>(target_external_reference())
<< ")";
} else if (IsCodeTargetMode(rmode_)) {
const Address code_target = target_address();
Code code = Code::GetCodeFromTargetAddress(code_target);
DCHECK(code.IsCode());
os << " (" << Code::Kind2String(code.kind());
if (Builtins::IsBuiltin(code)) {
os << " " << Builtins::name(code.builtin_index());
}
os << ") (" << reinterpret_cast<const void*>(target_address()) << ")";
} else if (IsRuntimeEntry(rmode_) && isolate->deoptimizer_data() != nullptr) {
// Deoptimization bailouts are stored as runtime entries.
DeoptimizeKind type;
if (Deoptimizer::IsDeoptimizationEntry(isolate, target_address(), &type)) {
os << " (" << Deoptimizer::MessageFor(type)
<< " deoptimization bailout)";
}
} else if (IsConstPool(rmode_)) {
os << " (size " << static_cast<int>(data_) << ")";
}
os << "\n";
}
#endif // ENABLE_DISASSEMBLER
#ifdef VERIFY_HEAP
void RelocInfo::Verify(Isolate* isolate) {
switch (rmode_) {
case COMPRESSED_EMBEDDED_OBJECT:
case FULL_EMBEDDED_OBJECT:
Object::VerifyPointer(isolate, target_object());
break;
case CODE_TARGET:
case RELATIVE_CODE_TARGET: {
// convert inline target address to code object
Address addr = target_address();
CHECK_NE(addr, kNullAddress);
// Check that we can find the right code object.
Code code = Code::GetCodeFromTargetAddress(addr);
Object found = isolate->FindCodeObject(addr);
CHECK(found.IsCode());
CHECK(code.address() == HeapObject::cast(found).address());
break;
}
case INTERNAL_REFERENCE:
case INTERNAL_REFERENCE_ENCODED: {
Address target = target_internal_reference();
Address pc = target_internal_reference_address();
Code code = Code::cast(isolate->FindCodeObject(pc));
CHECK(target >= code.InstructionStart());
CHECK(target <= code.InstructionEnd());
break;
}
case OFF_HEAP_TARGET: {
Address addr = target_off_heap_target();
CHECK_NE(addr, kNullAddress);
CHECK(!InstructionStream::TryLookupCode(isolate, addr).is_null());
break;
}
case RUNTIME_ENTRY:
case EXTERNAL_REFERENCE:
case DEOPT_SCRIPT_OFFSET:
case DEOPT_INLINING_ID:
case DEOPT_REASON:
case DEOPT_ID:
case CONST_POOL:
case VENEER_POOL:
case WASM_CALL:
case WASM_STUB_CALL:
case NONE:
break;
case NUMBER_OF_MODES:
case PC_JUMP:
UNREACHABLE();
}
}
#endif // VERIFY_HEAP
} // namespace internal
} // namespace v8