1 //==- WebAssemblyDisassembler.cpp - Disassembler for WebAssembly -*- C++ -*-==// 2 // 3 // The LLVM Compiler Infrastructure 4 // 5 // This file is distributed under the University of Illinois Open Source 6 // License. See LICENSE.TXT for details. 7 // 8 //===----------------------------------------------------------------------===// 9 /// 10 /// \file 11 /// This file is part of the WebAssembly Disassembler. 12 /// 13 /// It contains code to translate the data produced by the decoder into 14 /// MCInsts. 15 /// 16 //===----------------------------------------------------------------------===// 17 18 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h" 19 #include "llvm/MC/MCContext.h" 20 #include "llvm/MC/MCDisassembler/MCDisassembler.h" 21 #include "llvm/MC/MCFixedLenDisassembler.h" 22 #include "llvm/MC/MCInst.h" 23 #include "llvm/MC/MCInstrInfo.h" 24 #include "llvm/MC/MCSubtargetInfo.h" 25 #include "llvm/MC/MCSymbol.h" 26 #include "llvm/Support/Endian.h" 27 #include "llvm/Support/LEB128.h" 28 #include "llvm/Support/TargetRegistry.h" 29 30 using namespace llvm; 31 32 #define DEBUG_TYPE "wasm-disassembler" 33 34 using DecodeStatus = MCDisassembler::DecodeStatus; 35 36 #include "WebAssemblyGenDisassemblerTables.inc" 37 38 namespace { 39 class WebAssemblyDisassembler final : public MCDisassembler { 40 std::unique_ptr<const MCInstrInfo> MCII; 41 42 DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size, 43 ArrayRef<uint8_t> Bytes, uint64_t Address, 44 raw_ostream &VStream, 45 raw_ostream &CStream) const override; 46 47 public: 48 WebAssemblyDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx, 49 std::unique_ptr<const MCInstrInfo> MCII) 50 : MCDisassembler(STI, Ctx), MCII(std::move(MCII)) {} 51 }; 52 } // end anonymous namespace 53 54 static MCDisassembler *createWebAssemblyDisassembler(const Target &T, 55 const MCSubtargetInfo &STI, 56 MCContext &Ctx) { 57 std::unique_ptr<const MCInstrInfo> MCII(T.createMCInstrInfo()); 58 return new WebAssemblyDisassembler(STI, Ctx, std::move(MCII)); 59 } 60 61 extern "C" void LLVMInitializeWebAssemblyDisassembler() { 62 // Register the disassembler for each target. 63 TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(), 64 createWebAssemblyDisassembler); 65 TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget64(), 66 createWebAssemblyDisassembler); 67 } 68 69 static int nextByte(ArrayRef<uint8_t> Bytes, uint64_t &Size) { 70 if (Size >= Bytes.size()) 71 return -1; 72 auto V = Bytes[Size]; 73 Size++; 74 return V; 75 } 76 77 static bool parseLEBImmediate(MCInst &MI, uint64_t &Size, 78 ArrayRef<uint8_t> Bytes, bool Signed) { 79 unsigned N = 0; 80 const char *Error = nullptr; 81 auto Val = Signed ? decodeSLEB128(Bytes.data() + Size, &N, 82 Bytes.data() + Bytes.size(), &Error) 83 : static_cast<int64_t>( 84 decodeULEB128(Bytes.data() + Size, &N, 85 Bytes.data() + Bytes.size(), &Error)); 86 if (Error) 87 return false; 88 Size += N; 89 MI.addOperand(MCOperand::createImm(Val)); 90 return true; 91 } 92 93 template <typename T> 94 bool parseImmediate(MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes) { 95 if (Size + sizeof(T) > Bytes.size()) 96 return false; 97 T Val; 98 memcpy(&Val, Bytes.data() + Size, sizeof(T)); 99 support::endian::byte_swap<T, support::endianness::little>(Val); 100 Size += sizeof(T); 101 if (std::is_floating_point<T>::value) { 102 MI.addOperand(MCOperand::createFPImm(static_cast<double>(Val))); 103 } else { 104 MI.addOperand(MCOperand::createImm(static_cast<int64_t>(Val))); 105 } 106 return true; 107 } 108 109 MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction( 110 MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t /*Address*/, 111 raw_ostream & /*OS*/, raw_ostream &CS) const { 112 CommentStream = &CS; 113 Size = 0; 114 auto Opc = nextByte(Bytes, Size); 115 if (Opc < 0) 116 return MCDisassembler::Fail; 117 const auto *WasmInst = &InstructionTable0[Opc]; 118 // If this is a prefix byte, indirect to another table. 119 if (WasmInst->ET == ET_Prefix) { 120 WasmInst = nullptr; 121 // Linear search, so far only 2 entries. 122 for (auto PT = PrefixTable; PT->Table; PT++) { 123 if (PT->Prefix == Opc) { 124 WasmInst = PT->Table; 125 break; 126 } 127 } 128 if (!WasmInst) 129 return MCDisassembler::Fail; 130 Opc = nextByte(Bytes, Size); 131 if (Opc < 0) 132 return MCDisassembler::Fail; 133 WasmInst += Opc; 134 } 135 if (WasmInst->ET == ET_Unused) 136 return MCDisassembler::Fail; 137 // At this point we must have a valid instruction to decode. 138 assert(WasmInst->ET == ET_Instruction); 139 MI.setOpcode(WasmInst->Opcode); 140 // Parse any operands. 141 for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) { 142 switch (OperandTable[WasmInst->OperandStart + OPI]) { 143 // ULEB operands: 144 case WebAssembly::OPERAND_BASIC_BLOCK: 145 case WebAssembly::OPERAND_LOCAL: 146 case WebAssembly::OPERAND_GLOBAL: 147 case WebAssembly::OPERAND_FUNCTION32: 148 case WebAssembly::OPERAND_OFFSET32: 149 case WebAssembly::OPERAND_P2ALIGN: 150 case WebAssembly::OPERAND_TYPEINDEX: 151 case MCOI::OPERAND_IMMEDIATE: { 152 if (!parseLEBImmediate(MI, Size, Bytes, false)) 153 return MCDisassembler::Fail; 154 break; 155 } 156 // SLEB operands: 157 case WebAssembly::OPERAND_I32IMM: 158 case WebAssembly::OPERAND_I64IMM: 159 case WebAssembly::OPERAND_SIGNATURE: { 160 if (!parseLEBImmediate(MI, Size, Bytes, true)) 161 return MCDisassembler::Fail; 162 break; 163 } 164 // FP operands. 165 case WebAssembly::OPERAND_F32IMM: { 166 if (!parseImmediate<float>(MI, Size, Bytes)) 167 return MCDisassembler::Fail; 168 break; 169 } 170 case WebAssembly::OPERAND_F64IMM: { 171 if (!parseImmediate<double>(MI, Size, Bytes)) 172 return MCDisassembler::Fail; 173 break; 174 } 175 // Vector lane operands (not LEB encoded). 176 case WebAssembly::OPERAND_VEC_I8IMM: { 177 if (!parseImmediate<uint8_t>(MI, Size, Bytes)) 178 return MCDisassembler::Fail; 179 break; 180 } 181 case WebAssembly::OPERAND_VEC_I16IMM: { 182 if (!parseImmediate<uint16_t>(MI, Size, Bytes)) 183 return MCDisassembler::Fail; 184 break; 185 } 186 case WebAssembly::OPERAND_VEC_I32IMM: { 187 if (!parseImmediate<uint32_t>(MI, Size, Bytes)) 188 return MCDisassembler::Fail; 189 break; 190 } 191 case WebAssembly::OPERAND_VEC_I64IMM: { 192 if (!parseImmediate<uint64_t>(MI, Size, Bytes)) 193 return MCDisassembler::Fail; 194 break; 195 } 196 case MCOI::OPERAND_REGISTER: 197 // The tablegen header currently does not have any register operands since 198 // we use only the stack (_S) instructions. 199 // If you hit this that probably means a bad instruction definition in 200 // tablegen. 201 llvm_unreachable("Register operand in WebAssemblyDisassembler"); 202 default: 203 llvm_unreachable("Unknown operand type in WebAssemblyDisassembler"); 204 } 205 } 206 return MCDisassembler::Success; 207 } 208