lib/Target/WebAssembly/Disassembler/WebAssemblyDisassembler.cpp

   1 //==- WebAssemblyDisassembler.cpp - Disassembler for WebAssembly -*- C++ -*-==//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 ///
   9 /// \file
  10 /// This file is part of the WebAssembly Disassembler.
  11 ///
  12 /// It contains code to translate the data produced by the decoder into
  13 /// MCInsts.
  14 ///
  15 //===----------------------------------------------------------------------===//
  16
  17 #include "MCTargetDesc/WebAssemblyInstPrinter.h"
  18 #include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
  19 #include "TargetInfo/WebAssemblyTargetInfo.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/MC/MCSymbolWasm.h"
  28 #include "llvm/Support/Endian.h"
  29 #include "llvm/Support/LEB128.h"
  30 #include "llvm/Support/TargetRegistry.h"
  31
  32 using namespace llvm;
  33
  34 #define DEBUG_TYPE "wasm-disassembler"
  35
  36 using DecodeStatus = MCDisassembler::DecodeStatus;
  37
  38 #include "WebAssemblyGenDisassemblerTables.inc"
  39
  40 namespace {
  41 static constexpr int WebAssemblyInstructionTableSize = 256;
  42
  43 class WebAssemblyDisassembler final : public MCDisassembler {
  44   std::unique_ptr<const MCInstrInfo> MCII;
  45
  46   DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
  47                               ArrayRef<uint8_t> Bytes, uint64_t Address,
  48                               raw_ostream &VStream,
  49                               raw_ostream &CStream) const override;
  50   DecodeStatus onSymbolStart(StringRef Name, uint64_t &Size,
  51                              ArrayRef<uint8_t> Bytes, uint64_t Address,
  52                              raw_ostream &VStream,
  53                              raw_ostream &CStream) const override;
  54
  55 public:
  56   WebAssemblyDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
  57                           std::unique_ptr<const MCInstrInfo> MCII)
  58       : MCDisassembler(STI, Ctx), MCII(std::move(MCII)) {}
  59 };
  60 } // end anonymous namespace
  61
  62 static MCDisassembler *createWebAssemblyDisassembler(const Target &T,
  63                                                      const MCSubtargetInfo &STI,
  64                                                      MCContext &Ctx) {
  65   std::unique_ptr<const MCInstrInfo> MCII(T.createMCInstrInfo());
  66   return new WebAssemblyDisassembler(STI, Ctx, std::move(MCII));
  67 }
  68
  69 extern "C" void LLVMInitializeWebAssemblyDisassembler() {
  70   // Register the disassembler for each target.
  71   TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(),
  72                                          createWebAssemblyDisassembler);
  73   TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget64(),
  74                                          createWebAssemblyDisassembler);
  75 }
  76
  77 static int nextByte(ArrayRef<uint8_t> Bytes, uint64_t &Size) {
  78   if (Size >= Bytes.size())
  79     return -1;
  80   auto V = Bytes[Size];
  81   Size++;
  82   return V;
  83 }
  84
  85 static bool nextLEB(int64_t &Val, ArrayRef<uint8_t> Bytes, uint64_t &Size,
  86                     bool Signed) {
  87   unsigned N = 0;
  88   const char *Error = nullptr;
  89   Val = Signed ? decodeSLEB128(Bytes.data() + Size, &N,
  90                                Bytes.data() + Bytes.size(), &Error)
  91                : static_cast<int64_t>(decodeULEB128(Bytes.data() + Size, &N,
  92                                                     Bytes.data() + Bytes.size(),
  93                                                     &Error));
  94   if (Error)
  95     return false;
  96   Size += N;
  97   return true;
  98 }
  99
 100 static bool parseLEBImmediate(MCInst &MI, uint64_t &Size,
 101                               ArrayRef<uint8_t> Bytes, bool Signed) {
 102   int64_t Val;
 103   if (!nextLEB(Val, Bytes, Size, Signed))
 104     return false;
 105   MI.addOperand(MCOperand::createImm(Val));
 106   return true;
 107 }
 108
 109 template <typename T>
 110 bool parseImmediate(MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes) {
 111   if (Size + sizeof(T) > Bytes.size())
 112     return false;
 113   T Val = support::endian::read<T, support::endianness::little, 1>(
 114       Bytes.data() + Size);
 115   Size += sizeof(T);
 116   if (std::is_floating_point<T>::value) {
 117     MI.addOperand(MCOperand::createFPImm(static_cast<double>(Val)));
 118   } else {
 119     MI.addOperand(MCOperand::createImm(static_cast<int64_t>(Val)));
 120   }
 121   return true;
 122 }
 123
 124 MCDisassembler::DecodeStatus WebAssemblyDisassembler::onSymbolStart(
 125     StringRef Name, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t Address,
 126     raw_ostream &VStream, raw_ostream &CStream) const {
 127   Size = 0;
 128   if (Address == 0) {
 129     // Start of a code section: we're parsing only the function count.
 130     int64_t FunctionCount;
 131     if (!nextLEB(FunctionCount, Bytes, Size, false))
 132       return MCDisassembler::Fail;
 133     outs() << "        # " << FunctionCount << " functions in section.";
 134   } else {
 135     // Parse the start of a single function.
 136     int64_t BodySize, LocalEntryCount;
 137     if (!nextLEB(BodySize, Bytes, Size, false) ||
 138         !nextLEB(LocalEntryCount, Bytes, Size, false))
 139       return MCDisassembler::Fail;
 140     if (LocalEntryCount) {
 141       outs() << "        .local ";
 142       for (int64_t I = 0; I < LocalEntryCount; I++) {
 143         int64_t Count, Type;
 144         if (!nextLEB(Count, Bytes, Size, false) ||
 145             !nextLEB(Type, Bytes, Size, false))
 146           return MCDisassembler::Fail;
 147         for (int64_t J = 0; J < Count; J++) {
 148           if (I || J)
 149             outs() << ", ";
 150           outs() << WebAssembly::anyTypeToString(Type);
 151         }
 152       }
 153     }
 154   }
 155   outs() << "\n";
 156   return MCDisassembler::Success;
 157 }
 158
 159 MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction(
 160     MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t /*Address*/,
 161     raw_ostream & /*OS*/, raw_ostream &CS) const {
 162   CommentStream = &CS;
 163   Size = 0;
 164   int Opc = nextByte(Bytes, Size);
 165   if (Opc < 0)
 166     return MCDisassembler::Fail;
 167   const auto *WasmInst = &InstructionTable0[Opc];
 168   // If this is a prefix byte, indirect to another table.
 169   if (WasmInst->ET == ET_Prefix) {
 170     WasmInst = nullptr;
 171     // Linear search, so far only 2 entries.
 172     for (auto PT = PrefixTable; PT->Table; PT++) {
 173       if (PT->Prefix == Opc) {
 174         WasmInst = PT->Table;
 175         break;
 176       }
 177     }
 178     if (!WasmInst)
 179       return MCDisassembler::Fail;
 180     int64_t PrefixedOpc;
 181     if (!nextLEB(PrefixedOpc, Bytes, Size, false))
 182       return MCDisassembler::Fail;
 183     if (PrefixedOpc < 0 || PrefixedOpc >= WebAssemblyInstructionTableSize)
 184       return MCDisassembler::Fail;
 185     WasmInst += PrefixedOpc;
 186   }
 187   if (WasmInst->ET == ET_Unused)
 188     return MCDisassembler::Fail;
 189   // At this point we must have a valid instruction to decode.
 190   assert(WasmInst->ET == ET_Instruction);
 191   MI.setOpcode(WasmInst->Opcode);
 192   // Parse any operands.
 193   for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) {
 194     auto OT = OperandTable[WasmInst->OperandStart + OPI];
 195     switch (OT) {
 196     // ULEB operands:
 197     case WebAssembly::OPERAND_BASIC_BLOCK:
 198     case WebAssembly::OPERAND_LOCAL:
 199     case WebAssembly::OPERAND_GLOBAL:
 200     case WebAssembly::OPERAND_FUNCTION32:
 201     case WebAssembly::OPERAND_OFFSET32:
 202     case WebAssembly::OPERAND_P2ALIGN:
 203     case WebAssembly::OPERAND_TYPEINDEX:
 204     case WebAssembly::OPERAND_EVENT:
 205     case MCOI::OPERAND_IMMEDIATE: {
 206       if (!parseLEBImmediate(MI, Size, Bytes, false))
 207         return MCDisassembler::Fail;
 208       break;
 209     }
 210     // SLEB operands:
 211     case WebAssembly::OPERAND_I32IMM:
 212     case WebAssembly::OPERAND_I64IMM: {
 213       if (!parseLEBImmediate(MI, Size, Bytes, true))
 214         return MCDisassembler::Fail;
 215       break;
 216     }
 217     // block_type operands:
 218     case WebAssembly::OPERAND_SIGNATURE: {
 219       int64_t Val;
 220       uint64_t PrevSize = Size;
 221       if (!nextLEB(Val, Bytes, Size, true))
 222         return MCDisassembler::Fail;
 223       if (Val < 0) {
 224         // Negative values are single septet value types or empty types
 225         if (Size != PrevSize + 1) {
 226           MI.addOperand(
 227               MCOperand::createImm(int64_t(WebAssembly::BlockType::Invalid)));
 228         } else {
 229           MI.addOperand(MCOperand::createImm(Val & 0x7f));
 230         }
 231       } else {
 232         // We don't have access to the signature, so create a symbol without one
 233         MCSymbol *Sym = getContext().createTempSymbol("typeindex", true);
 234         auto *WasmSym = cast<MCSymbolWasm>(Sym);
 235         WasmSym->setType(wasm::WASM_SYMBOL_TYPE_FUNCTION);
 236         const MCExpr *Expr = MCSymbolRefExpr::create(
 237             WasmSym, MCSymbolRefExpr::VK_WASM_TYPEINDEX, getContext());
 238         MI.addOperand(MCOperand::createExpr(Expr));
 239       }
 240       break;
 241     }
 242     // FP operands.
 243     case WebAssembly::OPERAND_F32IMM: {
 244       if (!parseImmediate<float>(MI, Size, Bytes))
 245         return MCDisassembler::Fail;
 246       break;
 247     }
 248     case WebAssembly::OPERAND_F64IMM: {
 249       if (!parseImmediate<double>(MI, Size, Bytes))
 250         return MCDisassembler::Fail;
 251       break;
 252     }
 253     // Vector lane operands (not LEB encoded).
 254     case WebAssembly::OPERAND_VEC_I8IMM: {
 255       if (!parseImmediate<uint8_t>(MI, Size, Bytes))
 256         return MCDisassembler::Fail;
 257       break;
 258     }
 259     case WebAssembly::OPERAND_VEC_I16IMM: {
 260       if (!parseImmediate<uint16_t>(MI, Size, Bytes))
 261         return MCDisassembler::Fail;
 262       break;
 263     }
 264     case WebAssembly::OPERAND_VEC_I32IMM: {
 265       if (!parseImmediate<uint32_t>(MI, Size, Bytes))
 266         return MCDisassembler::Fail;
 267       break;
 268     }
 269     case WebAssembly::OPERAND_VEC_I64IMM: {
 270       if (!parseImmediate<uint64_t>(MI, Size, Bytes))
 271         return MCDisassembler::Fail;
 272       break;
 273     }
 274     case WebAssembly::OPERAND_BRLIST: {
 275       int64_t TargetTableLen;
 276       if (!nextLEB(TargetTableLen, Bytes, Size, false))
 277         return MCDisassembler::Fail;
 278       for (int64_t I = 0; I < TargetTableLen; I++) {
 279         if (!parseLEBImmediate(MI, Size, Bytes, false))
 280           return MCDisassembler::Fail;
 281       }
 282       // Default case.
 283       if (!parseLEBImmediate(MI, Size, Bytes, false))
 284         return MCDisassembler::Fail;
 285       break;
 286     }
 287     case MCOI::OPERAND_REGISTER:
 288       // The tablegen header currently does not have any register operands since
 289       // we use only the stack (_S) instructions.
 290       // If you hit this that probably means a bad instruction definition in
 291       // tablegen.
 292       llvm_unreachable("Register operand in WebAssemblyDisassembler");
 293     default:
 294       llvm_unreachable("Unknown operand type in WebAssemblyDisassembler");
 295     }
 296   }
 297   return MCDisassembler::Success;
 298 }