//==- WebAssemblyDisassembler.cpp - Disassembler for WebAssembly -*- C++ -*-==//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file is part of the WebAssembly Disassembler.
///
/// It contains code to translate the data produced by the decoder into
/// MCInsts.
///
//===----------------------------------------------------------------------===//

#include "MCTargetDesc/WebAssemblyMCTargetDesc.h"
#include "WebAssembly.h"
#include "llvm/MC/MCContext.h"
#include "llvm/MC/MCDisassembler/MCDisassembler.h"
#include "llvm/MC/MCFixedLenDisassembler.h"
#include "llvm/MC/MCInst.h"
#include "llvm/MC/MCInstrInfo.h"
#include "llvm/MC/MCSubtargetInfo.h"
#include "llvm/MC/MCSymbol.h"
#include "llvm/Support/Endian.h"
#include "llvm/Support/LEB128.h"
#include "llvm/Support/TargetRegistry.h"

using namespace llvm;

#define DEBUG_TYPE "wasm-disassembler"

using DecodeStatus = MCDisassembler::DecodeStatus;

#include "WebAssemblyGenDisassemblerTables.inc"

namespace {
class WebAssemblyDisassembler final : public MCDisassembler {
  std::unique_ptr<const MCInstrInfo> MCII;

  DecodeStatus getInstruction(MCInst &Instr, uint64_t &Size,
                              ArrayRef<uint8_t> Bytes, uint64_t Address,
                              raw_ostream &VStream,
                              raw_ostream &CStream) const override;

public:
  WebAssemblyDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
                          std::unique_ptr<const MCInstrInfo> MCII)
      : MCDisassembler(STI, Ctx), MCII(std::move(MCII)) {}
};
} // end anonymous namespace

static MCDisassembler *createWebAssemblyDisassembler(const Target &T,
                                                     const MCSubtargetInfo &STI,
                                                     MCContext &Ctx) {
  std::unique_ptr<const MCInstrInfo> MCII(T.createMCInstrInfo());
  return new WebAssemblyDisassembler(STI, Ctx, std::move(MCII));
}

extern "C" void LLVMInitializeWebAssemblyDisassembler() {
  // Register the disassembler for each target.
  TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget32(),
                                         createWebAssemblyDisassembler);
  TargetRegistry::RegisterMCDisassembler(getTheWebAssemblyTarget64(),
                                         createWebAssemblyDisassembler);
}

static int nextByte(ArrayRef<uint8_t> Bytes, uint64_t &Size) {
  if (Size >= Bytes.size())
    return -1;
  auto V = Bytes[Size];
  Size++;
  return V;
}

static bool parseLEBImmediate(MCInst &MI, uint64_t &Size,
                              ArrayRef<uint8_t> Bytes, bool Signed) {
  unsigned N = 0;
  const char *Error = nullptr;
  auto Val = Signed ? decodeSLEB128(Bytes.data() + Size, &N,
                                    Bytes.data() + Bytes.size(), &Error)
                    : static_cast<int64_t>(
                          decodeULEB128(Bytes.data() + Size, &N,
                                        Bytes.data() + Bytes.size(), &Error));
  if (Error)
    return false;
  Size += N;
  MI.addOperand(MCOperand::createImm(Val));
  return true;
}

template <typename T>
bool parseFPImmediate(MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes) {
  if (Size + sizeof(T) > Bytes.size())
    return false;
  T Val;
  memcpy(&Val, Bytes.data() + Size, sizeof(T));
  support::endian::byte_swap<T, support::endianness::little>(Val);
  Size += sizeof(T);
  MI.addOperand(MCOperand::createFPImm(static_cast<double>(Val)));
  return true;
}

MCDisassembler::DecodeStatus WebAssemblyDisassembler::getInstruction(
    MCInst &MI, uint64_t &Size, ArrayRef<uint8_t> Bytes, uint64_t /*Address*/,
    raw_ostream & /*OS*/, raw_ostream &CS) const {
  CommentStream = &CS;
  Size = 0;
  auto Opc = nextByte(Bytes, Size);
  if (Opc < 0)
    return MCDisassembler::Fail;
  const auto *WasmInst = &InstructionTable0[Opc];
  // If this is a prefix byte, indirect to another table.
  if (WasmInst->ET == ET_Prefix) {
    WasmInst = nullptr;
    // Linear search, so far only 2 entries.
    for (auto PT = PrefixTable; PT->Table; PT++) {
      if (PT->Prefix == Opc) {
        WasmInst = PT->Table;
        break;
      }
    }
    if (!WasmInst)
      return MCDisassembler::Fail;
    Opc = nextByte(Bytes, Size);
    if (Opc < 0)
      return MCDisassembler::Fail;
    WasmInst += Opc;
  }
  if (WasmInst->ET == ET_Unused)
    return MCDisassembler::Fail;
  // At this point we must have a valid instruction to decode.
  assert(WasmInst->ET == ET_Instruction);
  MI.setOpcode(WasmInst->Opcode);
  // Parse any operands.
  for (uint8_t OPI = 0; OPI < WasmInst->NumOperands; OPI++) {
    switch (WasmInst->Operands[OPI]) {
    // ULEB operands:
    case WebAssembly::OPERAND_BASIC_BLOCK:
    case WebAssembly::OPERAND_LOCAL:
    case WebAssembly::OPERAND_GLOBAL:
    case WebAssembly::OPERAND_FUNCTION32:
    case WebAssembly::OPERAND_OFFSET32:
    case WebAssembly::OPERAND_P2ALIGN:
    case WebAssembly::OPERAND_TYPEINDEX:
    case MCOI::OPERAND_IMMEDIATE: {
      if (!parseLEBImmediate(MI, Size, Bytes, false))
        return MCDisassembler::Fail;
      break;
    }
    // SLEB operands:
    case WebAssembly::OPERAND_I32IMM:
    case WebAssembly::OPERAND_I64IMM:
    case WebAssembly::OPERAND_SIGNATURE: {
      if (!parseLEBImmediate(MI, Size, Bytes, true))
        return MCDisassembler::Fail;
      break;
    }
    // FP operands.
    case WebAssembly::OPERAND_F32IMM: {
      if (!parseFPImmediate<float>(MI, Size, Bytes))
        return MCDisassembler::Fail;
      break;
    }
    case WebAssembly::OPERAND_F64IMM: {
      if (!parseFPImmediate<double>(MI, Size, Bytes))
        return MCDisassembler::Fail;
      break;
    }
    case MCOI::OPERAND_REGISTER: {
      // These are NOT actually in the instruction stream, but MC is going to
      // expect operands to be present for them!
      // FIXME: can MC re-generate register assignments or do we have to
      // do this? Since this function decodes a single instruction, we don't
      // have the proper context for tracking an operand stack here.
      MI.addOperand(MCOperand::createReg(0));
      break;
    }
    default:
      llvm_unreachable("Unknown operand type in WebAssemblyDisassembler");
    }
  }
  return MCDisassembler::Success;
}