// 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