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 "WebAssembly.h" 20 #include "llvm/MC/MCContext.h" 21 #include "llvm/MC/MCDisassembler/MCDisassembler.h" 22 #include "llvm/MC/MCFixedLenDisassembler.h" 23 #include "llvm/MC/MCInst.h" 24 #include "llvm/MC/MCInstrInfo.h" 25 #include "llvm/MC/MCSubtargetInfo.h" 26 #include "llvm/MC/MCSymbol.h" 27 #include "llvm/Support/Endian.h" 28 #include "llvm/Support/LEB128.h" 29 #include "llvm/Support/TargetRegistry.h" 30 31 using namespace llvm; 32 33 #define DEBUG_TYPE "wasm-disassembler" 34 35 using DecodeStatus = MCDisassembler::DecodeStatus; 36 37 #include "WebAssemblyGenDisassemblerTables.inc" 38 39 namespace { 40 class WebAssemblyDisassembler final : public MCDisassembler { 41 std::unique_ptr<const MCInstrInfo> MCII; 42 43 DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size, 44 ArrayRef<uint8_t> Bytes, uint64_t Address, 45 raw_ostream &VStream, 46 raw_ostream &CStream) const override; 47 48 public: 49 WebAssemblyDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx, 50 std::unique_ptr<const MCInstrInfo> MCII) 51 : MCDisassembler(STI, Ctx), MCII(std::move(MCII)) {} 52 }; 53 } // end anonymous namespace 54 55 static MCDisassembler *createWebAssemblyDisassembler(const Target &T, 56 const MCSubtargetInfo &STI, 57 MCContext &Ctx) { 58 std::unique_ptr<const MCInstrInfo> MCII(T.createMCInstrInfo()); 59 return new WebAssemblyDisassembler(STI, Ctx, std::move(MCII)); 60 } 61 62 extern "C" void LLVMInitializeWebAssemblyDisassembler() { 63 // Register the disassembler for each target. 64 TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(), 65 createWebAssemblyDisassembler); 66 TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget64(), 67 createWebAssemblyDisassembler); 68 } 69 70 static int nextByte(ArrayRef<uint8_t> Bytes, uint64_t &Size) { 71 if (Size >= Bytes.size()) 72 return -1; 73 auto V = Bytes[Size]; 74 Size++; 75 return V; 76 } 77 78 static bool parseLEBImmediate(MCInst &MI, uint64_t &Size, 79 ArrayRef<uint8_t> Bytes, bool Signed) { 80 unsigned N = 0; 81 const char *Error = nullptr; 82 auto Val = Signed ? decodeSLEB128(Bytes.data() + Size, &N, 83 Bytes.data() + Bytes.size(), &Error) 84 : static_cast<int64_t>( 85 decodeULEB128(Bytes.data() + Size, &N, 86 Bytes.data() + Bytes.size(), &Error)); 87 if (Error) 88 return false; 89 Size += N; 90 MI.addOperand(MCOperand::createImm(Val)); 91 return true; 92 } 93 94 template <typename T> 95 bool parseFPImmediate(MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes) { 96 if (Size + sizeof(T) > Bytes.size()) 97 return false; 98 T Val; 99 memcpy(&Val, Bytes.data() + Size, sizeof(T)); 100 support::endian::byte_swap<T, support::endianness::little>(Val); 101 Size += sizeof(T); 102 MI.addOperand(MCOperand::createFPImm(static_cast<double>(Val))); 103 return true; 104 } 105 106 MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction( 107 MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t /*Address*/, 108 raw_ostream & /*OS*/, raw_ostream &CS) const { 109 CommentStream = &CS; 110 Size = 0; 111 auto Opc = nextByte(Bytes, Size); 112 if (Opc < 0) 113 return MCDisassembler::Fail; 114 const auto *WasmInst = &InstructionTable0[Opc]; 115 // If this is a prefix byte, indirect to another table. 116 if (WasmInst->ET == ET_Prefix) { 117 WasmInst = nullptr; 118 // Linear search, so far only 2 entries. 119 for (auto PT = PrefixTable; PT->Table; PT++) { 120 if (PT->Prefix == Opc) { 121 WasmInst = PT->Table; 122 break; 123 } 124 } 125 if (!WasmInst) 126 return MCDisassembler::Fail; 127 Opc = nextByte(Bytes, Size); 128 if (Opc < 0) 129 return MCDisassembler::Fail; 130 WasmInst += Opc; 131 } 132 if (WasmInst->ET == ET_Unused) 133 return MCDisassembler::Fail; 134 // At this point we must have a valid instruction to decode. 135 assert(WasmInst->ET == ET_Instruction); 136 MI.setOpcode(WasmInst->Opcode); 137 // Parse any operands. 138 for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) { 139 switch (WasmInst->Operands[OPI]) { 140 // ULEB operands: 141 case WebAssembly::OPERAND_BASIC_BLOCK: 142 case WebAssembly::OPERAND_LOCAL: 143 case WebAssembly::OPERAND_GLOBAL: 144 case WebAssembly::OPERAND_FUNCTION32: 145 case WebAssembly::OPERAND_OFFSET32: 146 case WebAssembly::OPERAND_P2ALIGN: 147 case WebAssembly::OPERAND_TYPEINDEX: 148 case MCOI::OPERAND_IMMEDIATE: { 149 if (!parseLEBImmediate(MI, Size, Bytes, false)) 150 return MCDisassembler::Fail; 151 break; 152 } 153 // SLEB operands: 154 case WebAssembly::OPERAND_I32IMM: 155 case WebAssembly::OPERAND_I64IMM: 156 case WebAssembly::OPERAND_SIGNATURE: { 157 if (!parseLEBImmediate(MI, Size, Bytes, true)) 158 return MCDisassembler::Fail; 159 break; 160 } 161 // FP operands. 162 case WebAssembly::OPERAND_F32IMM: { 163 if (!parseFPImmediate<float>(MI, Size, Bytes)) 164 return MCDisassembler::Fail; 165 break; 166 } 167 case WebAssembly::OPERAND_F64IMM: { 168 if (!parseFPImmediate<double>(MI, Size, Bytes)) 169 return MCDisassembler::Fail; 170 break; 171 } 172 case MCOI::OPERAND_REGISTER: { 173 // These are NOT actually in the instruction stream, but MC is going to 174 // expect operands to be present for them! 175 // FIXME: can MC re-generate register assignments or do we have to 176 // do this? Since this function decodes a single instruction, we don't 177 // have the proper context for tracking an operand stack here. 178 MI.addOperand(MCOperand::createReg(0)); 179 break; 180 } 181 default: 182 llvm_unreachable("Unknown operand type in WebAssemblyDisassembler"); 183 } 184 } 185 return MCDisassembler::Success; 186 } 187