/src/capstonenext/arch/X86/X86DisassemblerDecoder.c

Source
/*===-- X86DisassemblerDecoder.c - Disassembler decoder ------------*- C -*-===*
 *
 *                     The LLVM Compiler Infrastructure
 *
 * This file is distributed under the University of Illinois Open Source
 * License. See LICENSE.TXT for details.
 *
 *===----------------------------------------------------------------------===*
 *
 * This file is part of the X86 Disassembler.
 * It contains the implementation of the instruction decoder.
 * Documentation for the disassembler can be found in X86Disassembler.h.
 *
 *===----------------------------------------------------------------------===*/

/* Capstone Disassembly Engine */
/* By Nguyen Anh Quynh <aquynh@gmail.com>, 2013-2019 */

#ifdef CAPSTONE_HAS_X86

#include <stdarg.h> /* for va_*()       */
#if defined(CAPSTONE_HAS_OSXKERNEL)
#include <libkern/libkern.h>
#else
#include <stdlib.h> /* for exit()       */
#endif

#include <string.h>

#include "../../cs_priv.h"
#include "../../utils.h"

#include "X86DisassemblerDecoder.h"
#include "X86Mapping.h"

/// Specifies whether a ModR/M byte is needed and (if so) which
/// instruction each possible value of the ModR/M byte corresponds to.  Once
/// this information is known, we have narrowed down to a single instruction.
struct ModRMDecision {
  uint8_t modrm_type;
  uint16_t instructionIDs;
};

/// Specifies which set of ModR/M->instruction tables to look at
/// given a particular opcode.
struct OpcodeDecision {
  struct ModRMDecision modRMDecisions[256];
};

/// Specifies which opcode->instruction tables to look at given
/// a particular context (set of attributes).  Since there are many possible
/// contexts, the decoder first uses CONTEXTS_SYM to determine which context
/// applies given a specific set of attributes.  Hence there are only IC_max
/// entries in this table, rather than 2^(ATTR_max).
struct ContextDecision {
  struct OpcodeDecision opcodeDecisions[IC_max];
};

#ifdef CAPSTONE_X86_REDUCE
#include "X86GenDisassemblerTables_reduce.inc"
#include "X86GenDisassemblerTables_reduce2.inc"
#include "X86Lookup16_reduce.inc"
#else
#include "X86GenDisassemblerTables.inc"
#include "X86GenDisassemblerTables2.inc"
#include "X86Lookup16.inc"
#endif

/*
 * contextForAttrs - Client for the instruction context table.  Takes a set of
 *   attributes and returns the appropriate decode context.
 *
 * @param attrMask  - Attributes, from the enumeration attributeBits.
 * @return          - The InstructionContext to use when looking up an
 *                    an instruction with these attributes.
 */
static InstructionContext contextForAttrs(uint16_t attrMask)
{
  return CONTEXTS_SYM[attrMask];
}

/*
 * modRMRequired - Reads the appropriate instruction table to determine whether
 *   the ModR/M byte is required to decode a particular instruction.
 *
 * @param type        - The opcode type (i.e., how many bytes it has).
 * @param insnContext - The context for the instruction, as returned by
 *                      contextForAttrs.
 * @param opcode      - The last byte of the instruction's opcode, not counting
 *                      ModR/M extensions and escapes.
 * @return            - true if the ModR/M byte is required, false otherwise.
 */
static int modRMRequired(OpcodeType type, InstructionContext insnContext,
       uint16_t opcode)
{
  const struct OpcodeDecision *decision = NULL;
  const uint8_t *indextable = NULL;
  unsigned int index;

  switch (type) {
  default:
    break;
  case ONEBYTE:
    decision = ONEBYTE_SYM;
    indextable = index_x86DisassemblerOneByteOpcodes;
    break;
  case TWOBYTE:
    decision = TWOBYTE_SYM;
    indextable = index_x86DisassemblerTwoByteOpcodes;
    break;
  case THREEBYTE_38:
    decision = THREEBYTE38_SYM;
    indextable = index_x86DisassemblerThreeByte38Opcodes;
    break;
  case THREEBYTE_3A:
    decision = THREEBYTE3A_SYM;
    indextable = index_x86DisassemblerThreeByte3AOpcodes;
    break;
#ifndef CAPSTONE_X86_REDUCE
  case XOP8_MAP:
    decision = XOP8_MAP_SYM;
    indextable = index_x86DisassemblerXOP8Opcodes;
    break;
  case XOP9_MAP:
    decision = XOP9_MAP_SYM;
    indextable = index_x86DisassemblerXOP9Opcodes;
    break;
  case XOPA_MAP:
    decision = XOPA_MAP_SYM;
    indextable = index_x86DisassemblerXOPAOpcodes;
    break;
  case THREEDNOW_MAP:
    // 3DNow instructions always have ModRM byte
    return true;
#endif
  }

  // return decision->opcodeDecisions[insnContext].modRMDecisions[opcode].modrm_type != MODRM_ONEENTRY;
  index = indextable[insnContext];
  if (index)
    return decision[index - 1].modRMDecisions[opcode].modrm_type !=
           MODRM_ONEENTRY;
  else
    return false;
}

/*
 * decode - Reads the appropriate instruction table to obtain the unique ID of
 *   an instruction.
 *
 * @param type        - See modRMRequired().
 * @param insnContext - See modRMRequired().
 * @param opcode      - See modRMRequired().
 * @param modRM       - The ModR/M byte if required, or any value if not.
 * @return            - The UID of the instruction, or 0 on failure.
 */
static InstrUID decode(OpcodeType type, InstructionContext insnContext,
           uint8_t opcode, uint8_t modRM)
{
  const struct ModRMDecision *dec = NULL;
  unsigned int index;
  static const struct OpcodeDecision emptyDecision = { 0 };

  switch (type) {
  default:
    break; // never reach
  case ONEBYTE:
    // dec = &ONEBYTE_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerOneByteOpcodes[insnContext];
    if (index)
      dec = &ONEBYTE_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
  case TWOBYTE:
    //dec = &TWOBYTE_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerTwoByteOpcodes[insnContext];
    if (index)
      dec = &TWOBYTE_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
  case THREEBYTE_38:
    // dec = &THREEBYTE38_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerThreeByte38Opcodes[insnContext];
    if (index)
      dec = &THREEBYTE38_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
  case THREEBYTE_3A:
    //dec = &THREEBYTE3A_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerThreeByte3AOpcodes[insnContext];
    if (index)
      dec = &THREEBYTE3A_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
#ifndef CAPSTONE_X86_REDUCE
  case XOP8_MAP:
    // dec = &XOP8_MAP_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerXOP8Opcodes[insnContext];
    if (index)
      dec = &XOP8_MAP_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
  case XOP9_MAP:
    // dec = &XOP9_MAP_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerXOP9Opcodes[insnContext];
    if (index)
      dec = &XOP9_MAP_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
  case XOPA_MAP:
    // dec = &XOPA_MAP_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86DisassemblerXOPAOpcodes[insnContext];
    if (index)
      dec = &XOPA_MAP_SYM[index - 1].modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
  case THREEDNOW_MAP:
    // dec = &THREEDNOW_MAP_SYM.opcodeDecisions[insnContext].modRMDecisions[opcode];
    index = index_x86Disassembler3DNowOpcodes[insnContext];
    if (index)
      dec = &THREEDNOW_MAP_SYM[index - 1]
               .modRMDecisions[opcode];
    else
      dec = &emptyDecision.modRMDecisions[opcode];
    break;
#endif
  }

  switch (dec->modrm_type) {
  default:
    // debug("Corrupt table!  Unknown modrm_type");
    return 0;
  case MODRM_ONEENTRY:
    return modRMTable[dec->instructionIDs];
  case MODRM_SPLITRM:
    if (modFromModRM(modRM) == 0x3)
      return modRMTable[dec->instructionIDs + 1];
    return modRMTable[dec->instructionIDs];
  case MODRM_SPLITREG:
    if (modFromModRM(modRM) == 0x3)
      return modRMTable[dec->instructionIDs +
            ((modRM & 0x38) >> 3) + 8];
    return modRMTable[dec->instructionIDs + ((modRM & 0x38) >> 3)];
  case MODRM_SPLITMISC:
    if (modFromModRM(modRM) == 0x3)
      return modRMTable[dec->instructionIDs + (modRM & 0x3f) +
            8];
    return modRMTable[dec->instructionIDs + ((modRM & 0x38) >> 3)];
  case MODRM_FULL:
    return modRMTable[dec->instructionIDs + modRM];
  }
}

/*
 * specifierForUID - Given a UID, returns the name and operand specification for
 *   that instruction.
 *
 * @param uid - The unique ID for the instruction.  This should be returned by
 *              decode(); specifierForUID will not check bounds.
 * @return    - A pointer to the specification for that instruction.
 */
static const struct InstructionSpecifier *specifierForUID(InstrUID uid)
{
  return &INSTRUCTIONS_SYM[uid];
}

/*
 * consumeByte - Uses the reader function provided by the user to consume one
 *   byte from the instruction's memory and advance the cursor.
 *
 * @param insn  - The instruction with the reader function to use.  The cursor
 *                for this instruction is advanced.
 * @param byte  - A pointer to a pre-allocated memory buffer to be populated
 *                with the data read.
 * @return      - 0 if the read was successful; nonzero otherwise.
 */
static int consumeByte(struct InternalInstruction *insn, uint8_t *byte)
{
  int ret = insn->reader(insn->readerArg, byte, insn->readerCursor);

  if (!ret)
    ++(insn->readerCursor);

  return ret;
}

/*
 * lookAtByte - Like consumeByte, but does not advance the cursor.
 *
 * @param insn  - See consumeByte().
 * @param byte  - See consumeByte().
 * @return      - See consumeByte().
 */
static int lookAtByte(struct InternalInstruction *insn, uint8_t *byte)
{
  return insn->reader(insn->readerArg, byte, insn->readerCursor);
}

static void unconsumeByte(struct InternalInstruction *insn)
{
  insn->readerCursor--;
}

#define CONSUME_FUNC(name, type) \
  static int name(struct InternalInstruction *insn, type *ptr) \
  { \
    type combined = 0; \
    unsigned offset; \
    for (offset = 0; offset < sizeof(type); ++offset) { \
      uint8_t byte; \
      int ret = insn->reader(insn->readerArg, &byte, \
                 insn->readerCursor + offset); \
      if (ret) \
        return ret; \
      combined = combined | \
           ((uint64_t)byte << (offset * 8)); \
    } \
    *ptr = combined; \
    insn->readerCursor += sizeof(type); \
    return 0; \
  }

/*
 * consume* - Use the reader function provided by the user to consume data
 *   values of various sizes from the instruction's memory and advance the
 *   cursor appropriately.  These readers perform endian conversion.
 *
 * @param insn    - See consumeByte().
 * @param ptr     - A pointer to a pre-allocated memory of appropriate size to
 *                  be populated with the data read.
 * @return        - See consumeByte().
 */
CONSUME_FUNC(consumeInt8, int8_t)
CONSUME_FUNC(consumeInt16, int16_t)
CONSUME_FUNC(consumeInt32, int32_t)
CONSUME_FUNC(consumeUInt16, uint16_t)
CONSUME_FUNC(consumeUInt32, uint32_t)
CONSUME_FUNC(consumeUInt64, uint64_t)

static bool isREX(struct InternalInstruction *insn, uint8_t prefix)
{
  if (insn->mode == MODE_64BIT)
    return prefix >= 0x40 && prefix <= 0x4f;

  return false;
}

/*
 * setGroup0Prefix - Updates the decoded instruction according to the group 0-prefix.
 *
 * @param insn      - The instruction to be updated.
 * @param prefix    - The group 0 prefix that is present.
 */
static void setGroup0Prefix(struct InternalInstruction *insn, uint8_t prefix)
{
  switch (prefix) {
  case 0xf0: // LOCK
    insn->hasLockPrefix = true;
    break;

  case 0xf2: // REPNE/REPNZ
  case 0xf3: // REP or REPE/REPZ
    insn->repeatPrefix = prefix;
    break;
  }
}

/*
 * setSegmentOverride - Overrides an instruction's prefix1 based on CPU mode.
 *
 * @param insn      - The instruction to be overridden.
 * @param prefix    - The segment override to use.
 * @param byte      - The current decoded prefix byte. Must be a segment override.
 */
static void setSegmentOverride(struct InternalInstruction *insn,
             SegmentOverride prefix, uint8_t byte)
{
  // In 32-bit or 16-bit mode all segment override prefixes are used.
  if (insn->mode != MODE_64BIT) {
    insn->segmentOverride = prefix;
    insn->prefix1 = byte;
    return;
  }

  // In 64-bit mode, the ES/CS/SS/DS segment overrides should be ignored.
  // In the case there are multiple segment overrides, do not override
  // an existing FS or GS segment prefix.
  switch (insn->prefix1) {
  case 0x64: // FS
  case 0x65: // GS
    return;
  }

  // If the proposed override is for FS or GS, mark it overridden.
  // All other segment prefixes are ignored.
  switch (byte) {
  case 0x64: // FS
  case 0x65: // GS
    insn->segmentOverride = prefix;
    break;
  }

  // `prefix1` may later be used to decode the `notrack` prefix.
  // The `notrack` prefix reuses the DS segment override, so we
  // need to store the prefix even if it is ignored for the segment overrides.
  insn->prefix1 = byte;
}

/*
 * readPrefixes - Consumes all of an instruction's prefix bytes, and marks the
 *   instruction as having them.  Also sets the instruction's default operand,
 *   address, and other relevant data sizes to report operands correctly.
 *
 * @param insn  - The instruction whose prefixes are to be read.
 * @return      - 0 if the instruction could be read until the end of the prefix
 *                bytes, and no prefixes conflicted; nonzero otherwise.
 */
static int readPrefixes(struct InternalInstruction *insn)
{
  bool isPrefix = true;
  uint8_t byte = 0;
  uint8_t nextByte;

  while (isPrefix) {
    /* If we fail reading prefixes, just stop here and let the opcode reader deal with it */
    if (consumeByte(insn, &byte))
      return -1;

    if (insn->readerCursor - 1 == insn->startLocation &&
        (byte == 0xf2 || byte == 0xf3)) {
      // prefix requires next byte
      if (lookAtByte(insn, &nextByte))
        return -1;

      if (isREX(insn, nextByte)) {
        uint8_t nnextByte;

        // Go to REX prefix after the current one
        if (consumeByte(insn, &nnextByte))
          return -1;

        // We should be able to read next byte after REX prefix
        if (lookAtByte(insn, &nnextByte))
          return -1;

        unconsumeByte(insn);
      }
    }

    switch (byte) {
    case 0xf0: /* LOCK */
    case 0xf2: /* REPNE/REPNZ */
    case 0xf3: /* REP or REPE/REPZ */
      // only accept the last prefix
      setGroup0Prefix(insn, byte);
      insn->prefix0 = byte;
      insn->rexPrefix = 0;
      break;

    case 0x2e: /* CS segment override -OR- Branch not taken */
    case 0x36: /* SS segment override -OR- Branch taken */
    case 0x3e: /* DS segment override */
    case 0x26: /* ES segment override */
    case 0x64: /* FS segment override */
    case 0x65: /* GS segment override */
      switch (byte) {
      case 0x2e:
        setSegmentOverride(insn, SEG_OVERRIDE_CS, byte);
        break;
      case 0x36:
        setSegmentOverride(insn, SEG_OVERRIDE_SS, byte);
        break;
      case 0x3e:
        setSegmentOverride(insn, SEG_OVERRIDE_DS, byte);
        break;
      case 0x26:
        setSegmentOverride(insn, SEG_OVERRIDE_ES, byte);
        break;
      case 0x64:
        setSegmentOverride(insn, SEG_OVERRIDE_FS, byte);
        break;
      case 0x65:
        setSegmentOverride(insn, SEG_OVERRIDE_GS, byte);
        break;
      default:
        // debug("Unhandled override");
        return -1;
      }
      insn->rexPrefix = 0;
      break;

    case 0x66: /* Operand-size override */
      insn->hasOpSize = true;
      insn->prefix2 = byte;
      insn->rexPrefix = 0;
      break;

    case 0x67: /* Address-size override */
      insn->hasAdSize = true;
      insn->prefix3 = byte;
      insn->rexPrefix = 0;
      break;
    default:
      if (isREX(insn, byte)) {
        /* REX prefix byte */
        insn->rexPrefix = byte;
      } else {
        /* Not a prefix byte */
        isPrefix = false;
      }
      break;
    }
  }

  insn->vectorExtensionType = TYPE_NO_VEX_XOP;

  if (byte == 0x62) {
    uint8_t byte1, byte2;

    if (consumeByte(insn, &byte1)) {
      // dbgprintf(insn, "Couldn't read second byte of EVEX prefix");
      return -1;
    }

    if (lookAtByte(insn, &byte2)) {
      // dbgprintf(insn, "Couldn't read third byte of EVEX prefix");
      unconsumeByte(insn); /* unconsume byte1 */
      unconsumeByte(insn); /* unconsume byte  */
    } else {
      if ((insn->mode == MODE_64BIT ||
           (byte1 & 0xc0) == 0xc0) &&
          ((~byte1 & 0xc) == 0xc) && ((byte2 & 0x4) == 0x4)) {
        insn->vectorExtensionType = TYPE_EVEX;
      } else {
        unconsumeByte(insn); /* unconsume byte1 */
        unconsumeByte(insn); /* unconsume byte  */
      }
    }

    if (insn->vectorExtensionType == TYPE_EVEX) {
      insn->vectorExtensionPrefix[0] = byte;
      insn->vectorExtensionPrefix[1] = byte1;
      if (consumeByte(insn,
          &insn->vectorExtensionPrefix[2])) {
        // dbgprintf(insn, "Couldn't read third byte of EVEX prefix");
        return -1;
      }

      if (consumeByte(insn,
          &insn->vectorExtensionPrefix[3])) {
        // dbgprintf(insn, "Couldn't read fourth byte of EVEX prefix");
        return -1;
      }

      /* We simulate the REX prefix for simplicity's sake */
      if (insn->mode == MODE_64BIT) {
        insn->rexPrefix =
          0x40 |
          (wFromEVEX3of4(
             insn->vectorExtensionPrefix[2])
           << 3) |
          (rFromEVEX2of4(
             insn->vectorExtensionPrefix[1])
           << 2) |
          (xFromEVEX2of4(
             insn->vectorExtensionPrefix[1])
           << 1) |
          (bFromEVEX2of4(
             insn->vectorExtensionPrefix[1])
           << 0);
      }

      // dbgprintf(insn, "Found EVEX prefix 0x%hhx 0x%hhx 0x%hhx 0x%hhx",
      //    insn->vectorExtensionPrefix[0], insn->vectorExtensionPrefix[1],
      //    insn->vectorExtensionPrefix[2], insn->vectorExtensionPrefix[3]);
    }
  } else if (byte == 0xc4) {
    uint8_t byte1;

    if (lookAtByte(insn, &byte1)) {
      // dbgprintf(insn, "Couldn't read second byte of VEX");
      return -1;
    }

    if (insn->mode == MODE_64BIT || (byte1 & 0xc0) == 0xc0)
      insn->vectorExtensionType = TYPE_VEX_3B;
    else
      unconsumeByte(insn);

    if (insn->vectorExtensionType == TYPE_VEX_3B) {
      insn->vectorExtensionPrefix[0] = byte;
      consumeByte(insn, &insn->vectorExtensionPrefix[1]);
      consumeByte(insn, &insn->vectorExtensionPrefix[2]);

      /* We simulate the REX prefix for simplicity's sake */
      if (insn->mode == MODE_64BIT)
        insn->rexPrefix =
          0x40 |
          (wFromVEX3of3(
             insn->vectorExtensionPrefix[2])
           << 3) |
          (rFromVEX2of3(
             insn->vectorExtensionPrefix[1])
           << 2) |
          (xFromVEX2of3(
             insn->vectorExtensionPrefix[1])
           << 1) |
          (bFromVEX2of3(
             insn->vectorExtensionPrefix[1])
           << 0);

      // dbgprintf(insn, "Found VEX prefix 0x%hhx 0x%hhx 0x%hhx",
      //    insn->vectorExtensionPrefix[0], insn->vectorExtensionPrefix[1],
      //    insn->vectorExtensionPrefix[2]);
    }
  } else if (byte == 0xc5) {
    uint8_t byte1;

    if (lookAtByte(insn, &byte1)) {
      // dbgprintf(insn, "Couldn't read second byte of VEX");
      return -1;
    }

    if (insn->mode == MODE_64BIT || (byte1 & 0xc0) == 0xc0)
      insn->vectorExtensionType = TYPE_VEX_2B;
    else
      unconsumeByte(insn);

    if (insn->vectorExtensionType == TYPE_VEX_2B) {
      insn->vectorExtensionPrefix[0] = byte;
      consumeByte(insn, &insn->vectorExtensionPrefix[1]);

      if (insn->mode == MODE_64BIT)
        insn->rexPrefix =
          0x40 |
          (rFromVEX2of2(
             insn->vectorExtensionPrefix[1])
           << 2);

      switch (ppFromVEX2of2(insn->vectorExtensionPrefix[1])) {
      default:
        break;
      case VEX_PREFIX_66:
        insn->hasOpSize = true;
        break;
      }

      // dbgprintf(insn, "Found VEX prefix 0x%hhx 0x%hhx",
      //    insn->vectorExtensionPrefix[0],
      //    insn->vectorExtensionPrefix[1]);
    }
  } else if (byte == 0x8f) {
    uint8_t byte1;

    if (lookAtByte(insn, &byte1)) {
      // dbgprintf(insn, "Couldn't read second byte of XOP");
      return -1;
    }

    if ((byte1 & 0x38) !=
        0x0) /* 0 in these 3 bits is a POP instruction. */
      insn->vectorExtensionType = TYPE_XOP;
    else
      unconsumeByte(insn);

    if (insn->vectorExtensionType == TYPE_XOP) {
      insn->vectorExtensionPrefix[0] = byte;
      consumeByte(insn, &insn->vectorExtensionPrefix[1]);
      consumeByte(insn, &insn->vectorExtensionPrefix[2]);

      /* We simulate the REX prefix for simplicity's sake */
      if (insn->mode == MODE_64BIT)
        insn->rexPrefix =
          0x40 |
          (wFromXOP3of3(
             insn->vectorExtensionPrefix[2])
           << 3) |
          (rFromXOP2of3(
             insn->vectorExtensionPrefix[1])
           << 2) |
          (xFromXOP2of3(
             insn->vectorExtensionPrefix[1])
           << 1) |
          (bFromXOP2of3(
             insn->vectorExtensionPrefix[1])
           << 0);

      switch (ppFromXOP3of3(insn->vectorExtensionPrefix[2])) {
      default:
        break;
      case VEX_PREFIX_66:
        insn->hasOpSize = true;
        break;
      }

      // dbgprintf(insn, "Found XOP prefix 0x%hhx 0x%hhx 0x%hhx",
      //    insn->vectorExtensionPrefix[0], insn->vectorExtensionPrefix[1],
      //    insn->vectorExtensionPrefix[2]);
    }
  } else
    unconsumeByte(insn);

  if (insn->repeatPrefix != 0) {
    if (lookAtByte(insn, &nextByte))
      return -1;

    /*
    * REP prefix is present, and any of the following conditions are
    * met:
    * - it is followed by a LOCK (0xf0) prefix
    * - it is followed by an xchg instruction (except for 0x90 - NOP/PAUSE)
    * then it should be disassembled as a xacquire/xrelease not repne/rep.
    */
    if ((insn->hasLockPrefix || ((nextByte & 0xfe) == 0x86 ||
               (nextByte & 0xf8) == 0x90)) &&
        nextByte != 0x90) {
      insn->xAcquireRelease = insn->repeatPrefix;
    }

    /*
    * Also if the REP prefix is 0xf3, and the following condition is met:
    * - it is followed by a "mov mem, reg" (opcode 0x88/0x89) or
    *                       "mov mem, imm" (opcode 0xc6/0xc7) instructions.
    * then it should be disassembled as an xrelease not rep.
    */
    if (insn->repeatPrefix == 0xf3 &&
        (nextByte == 0x88 || nextByte == 0x89 || nextByte == 0xc6 ||
         nextByte == 0xc7)) {
      insn->xAcquireRelease = insn->repeatPrefix;
    }
  }

  if (insn->mode == MODE_16BIT) {
    insn->registerSize = (insn->hasOpSize ? 4 : 2);
    insn->addressSize = (insn->hasAdSize ? 4 : 2);
    insn->displacementSize = (insn->hasAdSize ? 4 : 2);
    insn->immediateSize = (insn->hasOpSize ? 4 : 2);
    insn->immSize = (insn->hasOpSize ? 4 : 2);
  } else if (insn->mode == MODE_32BIT) {
    insn->registerSize = (insn->hasOpSize ? 2 : 4);
    insn->addressSize = (insn->hasAdSize ? 2 : 4);
    insn->displacementSize = (insn->hasAdSize ? 2 : 4);
    insn->immediateSize = (insn->hasOpSize ? 2 : 4);
    insn->immSize = (insn->hasOpSize ? 2 : 4);
  } else if (insn->mode == MODE_64BIT) {
    if (insn->rexPrefix && wFromREX(insn->rexPrefix)) {
      insn->registerSize = 8;
      insn->addressSize = (insn->hasAdSize ? 4 : 8);
      insn->displacementSize = 4;
      insn->immediateSize = 4;
      insn->immSize = 4;
    } else {
      insn->registerSize = (insn->hasOpSize ? 2 : 4);
      insn->addressSize = (insn->hasAdSize ? 4 : 8);
      insn->displacementSize = (insn->hasOpSize ? 2 : 4);
      insn->immediateSize = (insn->hasOpSize ? 2 : 4);
      insn->immSize = (insn->hasOpSize ? 4 : 8);
    }
  }

  return 0;
}

static int readModRM(struct InternalInstruction *insn);

/*
 * readOpcode - Reads the opcode (excepting the ModR/M byte in the case of
 *   extended or escape opcodes).
 *
 * @param insn  - The instruction whose opcode is to be read.
 * @return      - 0 if the opcode could be read successfully; nonzero otherwise.
 */
static int readOpcode(struct InternalInstruction *insn)
{
  uint8_t current;

  // dbgprintf(insn, "readOpcode()");

  insn->opcodeType = ONEBYTE;

  if (insn->vectorExtensionType == TYPE_EVEX) {
    switch (mmFromEVEX2of4(insn->vectorExtensionPrefix[1])) {
    default:
      // dbgprintf(insn, "Unhandled mm field for instruction (0x%hhx)",
      //    mmFromEVEX2of4(insn->vectorExtensionPrefix[1]));
      return -1;
    case VEX_LOB_0F:
      insn->opcodeType = TWOBYTE;
      return consumeByte(insn, &insn->opcode);
    case VEX_LOB_0F38:
      insn->opcodeType = THREEBYTE_38;
      return consumeByte(insn, &insn->opcode);
    case VEX_LOB_0F3A:
      insn->opcodeType = THREEBYTE_3A;
      return consumeByte(insn, &insn->opcode);
    }
  } else if (insn->vectorExtensionType == TYPE_VEX_3B) {
    switch (mmmmmFromVEX2of3(insn->vectorExtensionPrefix[1])) {
    default:
      // dbgprintf(insn, "Unhandled m-mmmm field for instruction (0x%hhx)",
      //    mmmmmFromVEX2of3(insn->vectorExtensionPrefix[1]));
      return -1;
    case VEX_LOB_0F:
      //insn->twoByteEscape = 0x0f;
      insn->opcodeType = TWOBYTE;
      return consumeByte(insn, &insn->opcode);
    case VEX_LOB_0F38:
      //insn->twoByteEscape = 0x0f;
      insn->opcodeType = THREEBYTE_38;
      return consumeByte(insn, &insn->opcode);
    case VEX_LOB_0F3A:
      //insn->twoByteEscape = 0x0f;
      insn->opcodeType = THREEBYTE_3A;
      return consumeByte(insn, &insn->opcode);
    }
  } else if (insn->vectorExtensionType == TYPE_VEX_2B) {
    //insn->twoByteEscape = 0x0f;
    insn->opcodeType = TWOBYTE;
    return consumeByte(insn, &insn->opcode);
  } else if (insn->vectorExtensionType == TYPE_XOP) {
    switch (mmmmmFromXOP2of3(insn->vectorExtensionPrefix[1])) {
    default:
      // dbgprintf(insn, "Unhandled m-mmmm field for instruction (0x%hhx)",
      //    mmmmmFromVEX2of3(insn->vectorExtensionPrefix[1]));
      return -1;
    case XOP_MAP_SELECT_8:
      insn->opcodeType = XOP8_MAP;
      return consumeByte(insn, &insn->opcode);
    case XOP_MAP_SELECT_9:
      insn->opcodeType = XOP9_MAP;
      return consumeByte(insn, &insn->opcode);
    case XOP_MAP_SELECT_A:
      insn->opcodeType = XOPA_MAP;
      return consumeByte(insn, &insn->opcode);
    }
  }

  if (consumeByte(insn, &current))
    return -1;

  // save this first byte for MOVcr, MOVdr, MOVrc, MOVrd
  insn->firstByte = current;

  if (current == 0x0f) {
    // dbgprintf(insn, "Found a two-byte escape prefix (0x%hhx)", current);
    insn->twoByteEscape = current;

    if (consumeByte(insn, &current))
      return -1;

    if (current == 0x38) {
      // dbgprintf(insn, "Found a three-byte escape prefix (0x%hhx)", current);
      if (consumeByte(insn, &current))
        return -1;

      insn->opcodeType = THREEBYTE_38;
    } else if (current == 0x3a) {
      // dbgprintf(insn, "Found a three-byte escape prefix (0x%hhx)", current);
      if (consumeByte(insn, &current))
        return -1;

      insn->opcodeType = THREEBYTE_3A;
    } else if (current == 0x0f) {
      // dbgprintf(insn, "Found a 3dnow escape prefix (0x%hhx)", current);
      // Consume operands before the opcode to comply with the 3DNow encoding
      if (readModRM(insn))
        return -1;

      if (consumeByte(insn, &current))
        return -1;

      insn->opcodeType = THREEDNOW_MAP;
    } else {
      // dbgprintf(insn, "Didn't find a three-byte escape prefix");
      insn->opcodeType = TWOBYTE;
    }
  }

  /*
   * At this point we have consumed the full opcode.
   * Anything we consume from here on must be unconsumed.
   */

  insn->opcode = current;

  return 0;
}

// Hacky for FEMMS
#define GET_INSTRINFO_ENUM
#ifndef CAPSTONE_X86_REDUCE
#include "X86GenInstrInfo.inc"
#else
#include "X86GenInstrInfo_reduce.inc"
#endif

/*
 * getIDWithAttrMask - Determines the ID of an instruction, consuming
 *   the ModR/M byte as appropriate for extended and escape opcodes,
 *   and using a supplied attribute mask.
 *
 * @param instructionID - A pointer whose target is filled in with the ID of the
 *                        instruction.
 * @param insn          - The instruction whose ID is to be determined.
 * @param attrMask      - The attribute mask to search.
 * @return              - 0 if the ModR/M could be read when needed or was not
 *                        needed; nonzero otherwise.
 */
static int getIDWithAttrMask(uint16_t *instructionID,
           struct InternalInstruction *insn,
           uint16_t attrMask)
{
  bool hasModRMExtension;

  InstructionContext instructionClass = contextForAttrs(attrMask);

  hasModRMExtension =
    modRMRequired(insn->opcodeType, instructionClass, insn->opcode);

  if (hasModRMExtension) {
    if (readModRM(insn))
      return -1;

    *instructionID = decode(insn->opcodeType, instructionClass,
          insn->opcode, insn->modRM);
  } else {
    *instructionID = decode(insn->opcodeType, instructionClass,
          insn->opcode, 0);
  }

  return 0;
}

/*
 * is16BitEquivalent - Determines whether two instruction names refer to
 * equivalent instructions but one is 16-bit whereas the other is not.
 *
 * @param orig  - The instruction ID that is not 16-bit
 * @param equiv - The instruction ID that is 16-bit
 */
static bool is16BitEquivalent(unsigned orig, unsigned equiv)
{
  size_t i;
  uint16_t idx;

  if ((idx = x86_16_bit_eq_lookup[orig]) != 0) {
    for (i = idx - 1; i < ARR_SIZE(x86_16_bit_eq_tbl) &&
          x86_16_bit_eq_tbl[i].first == orig;
         i++) {
      if (x86_16_bit_eq_tbl[i].second == equiv)
        return true;
    }
  }

  return false;
}

/*
 * is64Bit - Determines whether this instruction is a 64-bit instruction.
 *
 * @param name - The instruction that is not 16-bit
 */
static bool is64Bit(uint16_t id)
{
  unsigned int i = find_insn(id);
  if (i != -1) {
    return insns[i].is64bit;
  }

  // not found??
  return false;
}

typedef enum {
  DO_NOT_RESOLVE = 0,
  IGNORE_REP = 1,
  IGNORE_DATA_SIZE = 2,
} MandatoryPrefixResolution;

/*
 * shouldResolveMandatoryPrefixConflict - Resolves conflicts between the 
 * data size override prefix and the REP/REPNZ prefixes in the attribute 
 * mask when needed.
 *
 * We need to resolve these conflicts, because the TableGen lookups we 
 * perform distinguish between instructions with and without REP.
 * For example, there may be an entry for SHLD with a DATA16 data size 
 * override prefix, but no entry for REP + DATA16.
 * These entries are split, because in some cases the REP and DATA16
 * prefixes are used as mandatory prefixes.
 * When both are mandatory prefixes, the effect of prefixing both 
 * to an instruction at the same time is not specified by
 * reference manuals.
 *
 * Conflicts are resolved by one of these three resolutions:
 *   - If conflicts should not be resolved, take no action.
 *   - If conflicts should be resolved and the instruction has no 
 *     mandatory prefixes, resolves in favor of data size override.
 *   - If conflicts should be resolved and the instruction has mandatory 
 *     prefixes, resolves in favor of REP/REPNZ.
 * 
 * @param insn - The instruction
 * @param attrMask - The current attribute mask.
 */
static uint16_t resolveMandatoryPrefixConflict(struct InternalInstruction *insn,
                 uint16_t attrMask)
{
  MandatoryPrefixResolution resolution = DO_NOT_RESOLVE;

  // We inspect the opcode map and opcode to determine how we need to resolve
  // a mandatory prefix conflict.
  switch (insn->opcodeType) {
  // No one-byte opcodes have mandatory prefixes.
  case ONEBYTE:
    resolution = DO_NOT_RESOLVE;
    break;
  case TWOBYTE:
    // Exceptions for instructions that operate on data size-overridable
    // operands.
    if (
      // XADD
      (insn->opcode & 0xFE) == 0xC0

      // BSWAP
      || (insn->opcode & 0xF8) == 0xC8

      // CMPXCHG, LSS, BTR, LFS, LGS, MOVZX
      || (insn->opcode & 0xF8) == 0xB0

      // Group 16, various NOPs
      || (insn->opcode & 0xF8) == 0x18

      // UD0
      || insn->opcode == 0xFF) {
      resolution = IGNORE_REP;
      break;
    }

    // We inspect the instruction to determine if it operates on xmm
    // registers or general-purpose registers.
    //
    // If it operates on general purpose registers, the data size override
    // prefix is not a mandatory prefix and should not be ignored.
    // In most cases, this also means that the REP prefix is not a mandatory
    // prefix and should be ignored.
    //
    // If the instruction operates on xmm registers, the data size override
    // is used to select the operation type (SS, SD, PS, or PD).
    // In this case, the REP prefixes take priority over the data size [1]
    // override prefixes, and when both are present the data size override
    // prefix should be ignored.
    //
    // The exception is 0xB0, where the REP prefixes are mandatory prefixes
    // but the data size override prefix should still be respected.
    // For this case we return DO_NOT_RESOLVE, which returns attrMask as-is.
    //
    // [1]: https://stackoverflow.com/a/7197365
    switch (insn->opcode & 0xf0) {
    case 0x10:
    case 0x50:
    case 0x60:
    case 0x70:
    case 0xC0:
    case 0xD0:
    case 0xE0:
    case 0xF0:
      resolution = IGNORE_DATA_SIZE;
      break;
    case 0x00:
    case 0x20:
    case 0x30:
    case 0x40:
    case 0x80:
    case 0x90:
    case 0xA0:
      resolution = IGNORE_REP;
      break;
    default: // 0xB0
      resolution = DO_NOT_RESOLVE;
      break;
    }
    break;
  case THREEBYTE_38:
    // Exception: the ADOX and CRC32 instructions.
    // These ignore the data size override prefix even though they
    // operate on general-purpose registers.
    if ((insn->opcode & 0xF0) == 0xF0) {
      resolution = IGNORE_DATA_SIZE;
      break;
    }

    // Do not need to be resolved, all REP+DATA16 combinations are UD
    // or separately specified.
    resolution = DO_NOT_RESOLVE;
    break;
  case THREEBYTE_3A:
    // Do not need to be resolved, all REP+DATA16 combinations are UD
    // or separately specified.
    resolution = DO_NOT_RESOLVE;
    break;
  case XOP8_MAP:
  case XOP9_MAP:
  case XOPA_MAP:
    // These instructions do not appear to operate on XMM/SSE registers,
    // so the REP prefixes can be safely ignored.
    resolution = IGNORE_REP;
    break;
  case THREEDNOW_MAP:
    // AMD Reference Manual Volume 3, Section 1.2.1, states that all
    // 3DNow! instructions ignore the data size override prefix.
    resolution = IGNORE_DATA_SIZE;
    break;
  }

  switch (resolution) {
  case IGNORE_REP:
    return attrMask & ~(ATTR_XD | ATTR_XS);
  case IGNORE_DATA_SIZE:
    return attrMask & ~ATTR_OPSIZE;
  default:
  case DO_NOT_RESOLVE:
    return attrMask;
  }
}

/*
 * getID - Determines the ID of an instruction, consuming the ModR/M byte as
 *   appropriate for extended and escape opcodes.  Determines the attributes and
 *   context for the instruction before doing so.
 *
 * @param insn  - The instruction whose ID is to be determined.
 * @return      - 0 if the ModR/M could be read when needed or was not needed;
 *                nonzero otherwise.
 */
static int getID(struct InternalInstruction *insn)
{
  uint16_t attrMask;
  uint16_t instructionID;

  attrMask = ATTR_NONE;

  if (insn->mode == MODE_64BIT)
    attrMask |= ATTR_64BIT;

  if (insn->vectorExtensionType != TYPE_NO_VEX_XOP) {
    attrMask |= (insn->vectorExtensionType == TYPE_EVEX) ?
            ATTR_EVEX :
            ATTR_VEX;

    if (insn->vectorExtensionType == TYPE_EVEX) {
      switch (ppFromEVEX3of4(
        insn->vectorExtensionPrefix[2])) {
      case VEX_PREFIX_66:
        attrMask |= ATTR_OPSIZE;
        break;
      case VEX_PREFIX_F3:
        attrMask |= ATTR_XS;
        break;
      case VEX_PREFIX_F2:
        attrMask |= ATTR_XD;
        break;
      }

      if (zFromEVEX4of4(insn->vectorExtensionPrefix[3]))
        attrMask |= ATTR_EVEXKZ;
      if (bFromEVEX4of4(insn->vectorExtensionPrefix[3]))
        attrMask |= ATTR_EVEXB;
      if (aaaFromEVEX4of4(insn->vectorExtensionPrefix[3]))
        attrMask |= ATTR_EVEXK;
      if (lFromEVEX4of4(insn->vectorExtensionPrefix[3]))
        attrMask |= ATTR_EVEXL;
      if (l2FromEVEX4of4(insn->vectorExtensionPrefix[3]))
        attrMask |= ATTR_EVEXL2;
    } else if (insn->vectorExtensionType == TYPE_VEX_3B) {
      switch (ppFromVEX3of3(insn->vectorExtensionPrefix[2])) {
      case VEX_PREFIX_66:
        attrMask |= ATTR_OPSIZE;
        break;
      case VEX_PREFIX_F3:
        attrMask |= ATTR_XS;
        break;
      case VEX_PREFIX_F2:
        attrMask |= ATTR_XD;
        break;
      }

      if (lFromVEX3of3(insn->vectorExtensionPrefix[2]))
        attrMask |= ATTR_VEXL;
    } else if (insn->vectorExtensionType == TYPE_VEX_2B) {
      switch (ppFromVEX2of2(insn->vectorExtensionPrefix[1])) {
      case VEX_PREFIX_66:
        attrMask |= ATTR_OPSIZE;
        break;
      case VEX_PREFIX_F3:
        attrMask |= ATTR_XS;
        break;
      case VEX_PREFIX_F2:
        attrMask |= ATTR_XD;
        break;
      }

      if (lFromVEX2of2(insn->vectorExtensionPrefix[1]))
        attrMask |= ATTR_VEXL;
    } else if (insn->vectorExtensionType == TYPE_XOP) {
      switch (ppFromXOP3of3(insn->vectorExtensionPrefix[2])) {
      case VEX_PREFIX_66:
        attrMask |= ATTR_OPSIZE;
        break;
      case VEX_PREFIX_F3:
        attrMask |= ATTR_XS;
        break;
      case VEX_PREFIX_F2:
        attrMask |= ATTR_XD;
        break;
      }

      if (lFromXOP3of3(insn->vectorExtensionPrefix[2]))
        attrMask |= ATTR_VEXL;
    } else {
      return -1;
    }
  } else {
    if (insn->hasOpSize && insn->mode != MODE_16BIT) {
      attrMask |= ATTR_OPSIZE;
    }
    if (insn->hasAdSize)
      attrMask |= ATTR_ADSIZE;
    if (insn->opcodeType == ONEBYTE) {
      if (insn->repeatPrefix == 0xf3 &&
          (insn->opcode == 0x90))
        // Special support for PAUSE
        attrMask |= ATTR_XS;
    } else {
      if (insn->repeatPrefix == 0xf2)
        attrMask |= ATTR_XD;
      else if (insn->repeatPrefix == 0xf3)
        attrMask |= ATTR_XS;
    }

    if ((attrMask & ATTR_OPSIZE) &&
        (attrMask & (ATTR_XD | ATTR_XS))) {
      attrMask =
        resolveMandatoryPrefixConflict(insn, attrMask);
    }
  }

  if (insn->rexPrefix & 0x08) {
    attrMask |= ATTR_REXW;
    attrMask &= ~ATTR_ADSIZE;
  }

  /*
   * JCXZ/JECXZ need special handling for 16-bit mode because the meaning
   * of the AdSize prefix is inverted w.r.t. 32-bit mode.
   */
  if (insn->mode == MODE_16BIT && insn->opcodeType == ONEBYTE &&
      insn->opcode == 0xE3)
    attrMask ^= ATTR_ADSIZE;

  /*
   * In 64-bit mode all f64 superscripted opcodes ignore opcode size prefix
   * CALL/JMP/JCC instructions need to ignore 0x66 and consume 4 bytes
   */
  if ((insn->mode == MODE_64BIT) && insn->hasOpSize) {
    switch (insn->opcode) {
    case 0xE8:
    case 0xE9:
      // Take care of psubsb and other mmx instructions.
      if (insn->opcodeType == ONEBYTE) {
        attrMask ^= ATTR_OPSIZE;
        insn->immediateSize = 4;
        insn->displacementSize = 4;
      }
      break;
    case 0x82:
    case 0x83:
    case 0x84:
    case 0x85:
    case 0x86:
    case 0x87:
    case 0x88:
    case 0x89:
    case 0x8A:
    case 0x8B:
    case 0x8C:
    case 0x8D:
    case 0x8E:
    case 0x8F:
      // Take care of lea and three byte ops.
      if (insn->opcodeType == TWOBYTE) {
        attrMask ^= ATTR_OPSIZE;
        insn->immediateSize = 4;
        insn->displacementSize = 4;
      }
      break;
    }
  }

  /* The following clauses compensate for limitations of the tables. */
  if (insn->mode != MODE_64BIT &&
      insn->vectorExtensionType != TYPE_NO_VEX_XOP) {
    if (getIDWithAttrMask(&instructionID, insn, attrMask)) {
      return -1;
    }

    /*
     * The tables can't distinguish between cases where the W-bit is used to
     * select register size and cases where it's a required part of the opcode.
     */
    if ((insn->vectorExtensionType == TYPE_EVEX &&
         wFromEVEX3of4(insn->vectorExtensionPrefix[2])) ||
        (insn->vectorExtensionType == TYPE_VEX_3B &&
         wFromVEX3of3(insn->vectorExtensionPrefix[2])) ||
        (insn->vectorExtensionType == TYPE_XOP &&
         wFromXOP3of3(insn->vectorExtensionPrefix[2]))) {
      uint16_t instructionIDWithREXW;

      if (getIDWithAttrMask(&instructionIDWithREXW, insn,
                attrMask | ATTR_REXW)) {
        insn->instructionID = instructionID;
        insn->spec = specifierForUID(instructionID);
        return 0;
      }

      // If not a 64-bit instruction. Switch the opcode.
      if (!is64Bit(instructionIDWithREXW)) {
        insn->instructionID = instructionIDWithREXW;
        insn->spec =
          specifierForUID(instructionIDWithREXW);

        return 0;
      }
    }
  }

  /*
   * Absolute moves, umonitor, and movdir64b need special handling.
   * -For 16-bit mode because the meaning of the AdSize and OpSize prefixes are
   *  inverted w.r.t.
   * -For 32-bit mode we need to ensure the ADSIZE prefix is observed in
   *  any position.
   */
  if ((insn->opcodeType == ONEBYTE && ((insn->opcode & 0xFC) == 0xA0)) ||
      (insn->opcodeType == TWOBYTE && (insn->opcode == 0xAE)) ||
      (insn->opcodeType == THREEBYTE_38 && insn->opcode == 0xF8)) {
    /* Make sure we observed the prefixes in any position. */
    if (insn->hasAdSize)
      attrMask |= ATTR_ADSIZE;

    if (insn->hasOpSize)
      attrMask |= ATTR_OPSIZE;

    /* In 16-bit, invert the attributes. */
    if (insn->mode == MODE_16BIT) {
      attrMask ^= ATTR_ADSIZE;

      /* The OpSize attribute is only valid with the absolute moves. */
      if (insn->opcodeType == ONEBYTE &&
          ((insn->opcode & 0xFC) == 0xA0))
        attrMask ^= ATTR_OPSIZE;
    }

    if (getIDWithAttrMask(&instructionID, insn, attrMask)) {
      return -1;
    }

    insn->instructionID = instructionID;
    insn->spec = specifierForUID(instructionID);

    return 0;
  }
  if (getIDWithAttrMask(&instructionID, insn, attrMask)) {
    return -1;
  }

  if ((insn->mode == MODE_16BIT || insn->hasOpSize) &&
      !(attrMask & ATTR_OPSIZE)) {
    /*
     * The instruction tables make no distinction between instructions that
     * allow OpSize anywhere (i.e., 16-bit operations) and that need it in a
     * particular spot (i.e., many MMX operations).  In general we're
     * conservative, but in the specific case where OpSize is present but not
     * in the right place we check if there's a 16-bit operation.
     */
    const struct InstructionSpecifier *spec;
    uint16_t instructionIDWithOpsize;

    spec = specifierForUID(instructionID);

    if (getIDWithAttrMask(&instructionIDWithOpsize, insn,
              attrMask | ATTR_OPSIZE)) {
      /*
       * ModRM required with OpSize but not present; give up and return version
       * without OpSize set
       */
      insn->instructionID = instructionID;
      insn->spec = spec;

      return 0;
    }

    if (is16BitEquivalent(instructionID, instructionIDWithOpsize) &&
        (insn->mode == MODE_16BIT) ^ insn->hasOpSize) {
      insn->instructionID = instructionIDWithOpsize;
      insn->spec = specifierForUID(instructionIDWithOpsize);
    } else {
      insn->instructionID = instructionID;
      insn->spec = spec;
    }

    return 0;
  }

  if (insn->opcodeType == ONEBYTE && insn->opcode == 0x90 &&
      insn->rexPrefix & 0x01) {
    /*
     * NOOP shouldn't decode as NOOP if REX.b is set. Instead
     * it should decode as XCHG %r8, %eax.
     */
    const struct InstructionSpecifier *spec;
    uint16_t instructionIDWithNewOpcode;
    const struct InstructionSpecifier *specWithNewOpcode;

    spec = specifierForUID(instructionID);

    /* Borrow opcode from one of the other XCHGar opcodes */
    insn->opcode = 0x91;

    if (getIDWithAttrMask(&instructionIDWithNewOpcode, insn,
              attrMask)) {
      insn->opcode = 0x90;

      insn->instructionID = instructionID;
      insn->spec = spec;

      return 0;
    }

    specWithNewOpcode = specifierForUID(instructionIDWithNewOpcode);

    /* Change back */
    insn->opcode = 0x90;

    insn->instructionID = instructionIDWithNewOpcode;
    insn->spec = specWithNewOpcode;

    return 0;
  }

  insn->instructionID = instructionID;
  insn->spec = specifierForUID(insn->instructionID);

  return 0;
}

/*
 * readSIB - Consumes the SIB byte to determine addressing information for an
 *   instruction.
 *
 * @param insn  - The instruction whose SIB byte is to be read.
 * @return      - 0 if the SIB byte was successfully read; nonzero otherwise.
 */
static int readSIB(struct InternalInstruction *insn)
{
  SIBBase sibBaseBase = SIB_BASE_NONE;
  uint8_t index, base;

  // dbgprintf(insn, "readSIB()");

  if (insn->consumedSIB)
    return 0;

  insn->consumedSIB = true;

  switch (insn->addressSize) {
  case 2:
    // dbgprintf(insn, "SIB-based addressing doesn't work in 16-bit mode");
    return -1;
  case 4:
    insn->sibIndexBase = SIB_INDEX_EAX;
    sibBaseBase = SIB_BASE_EAX;
    break;
  case 8:
    insn->sibIndexBase = SIB_INDEX_RAX;
    sibBaseBase = SIB_BASE_RAX;
    break;
  }

  if (consumeByte(insn, &insn->sib))
    return -1;

  index = indexFromSIB(insn->sib) | (xFromREX(insn->rexPrefix) << 3);

  if (index == 0x4) {
    insn->sibIndex = SIB_INDEX_NONE;
  } else {
    insn->sibIndex = (SIBIndex)(insn->sibIndexBase + index);
  }

  insn->sibScale = 1 << scaleFromSIB(insn->sib);

  base = baseFromSIB(insn->sib) | (bFromREX(insn->rexPrefix) << 3);

  switch (base) {
  case 0x5:
  case 0xd:
    switch (modFromModRM(insn->modRM)) {
    case 0x0:
      insn->eaDisplacement = EA_DISP_32;
      insn->sibBase = SIB_BASE_NONE;
      break;
    case 0x1:
      insn->eaDisplacement = EA_DISP_8;
      insn->sibBase = (SIBBase)(sibBaseBase + base);
      break;
    case 0x2:
      insn->eaDisplacement = EA_DISP_32;
      insn->sibBase = (SIBBase)(sibBaseBase + base);
      break;
    case 0x3:
      // debug("Cannot have Mod = 0b11 and a SIB byte");
      return -1;
    }
    break;
  default:
    insn->sibBase = (SIBBase)(sibBaseBase + base);
    break;
  }

  return 0;
}

/*
 * readDisplacement - Consumes the displacement of an instruction.
 *
 * @param insn  - The instruction whose displacement is to be read.
 * @return      - 0 if the displacement byte was successfully read; nonzero
 *                otherwise.
 */
static int readDisplacement(struct InternalInstruction *insn)
{
  int8_t d8;
  int16_t d16;
  int32_t d32;

  // dbgprintf(insn, "readDisplacement()");

  if (insn->consumedDisplacement)
    return 0;

  insn->consumedDisplacement = true;
  insn->displacementOffset = insn->readerCursor - insn->startLocation;

  switch (insn->eaDisplacement) {
  case EA_DISP_NONE:
    insn->consumedDisplacement = false;
    break;
  case EA_DISP_8:
    if (consumeInt8(insn, &d8))
      return -1;
    insn->displacement = d8;
    break;
  case EA_DISP_16:
    if (consumeInt16(insn, &d16))
      return -1;
    insn->displacement = d16;
    break;
  case EA_DISP_32:
    if (consumeInt32(insn, &d32))
      return -1;
    insn->displacement = d32;
    break;
  }

  return 0;
}

/*
 * readModRM - Consumes all addressing information (ModR/M byte, SIB byte, and
 *   displacement) for an instruction and interprets it.
 *
 * @param insn  - The instruction whose addressing information is to be read.
 * @return      - 0 if the information was successfully read; nonzero otherwise.
 */
static int readModRM(struct InternalInstruction *insn)
{
  uint8_t mod, rm, reg, evexrm;

  // dbgprintf(insn, "readModRM()");

  if (insn->consumedModRM)
    return 0;

  insn->modRMOffset = (uint8_t)(insn->readerCursor - insn->startLocation);

  if (consumeByte(insn, &insn->modRM))
    return -1;

  insn->consumedModRM = true;

  // save original ModRM for later reference
  insn->orgModRM = insn->modRM;

  // handle MOVcr, MOVdr, MOVrc, MOVrd by pretending they have MRM.mod = 3
  if ((insn->firstByte == 0x0f && insn->opcodeType == TWOBYTE) &&
      (insn->opcode >= 0x20 && insn->opcode <= 0x23))
    insn->modRM |= 0xC0;

  mod = modFromModRM(insn->modRM);
  rm = rmFromModRM(insn->modRM);
  reg = regFromModRM(insn->modRM);

  /*
   * This goes by insn->registerSize to pick the correct register, which messes
   * up if we're using (say) XMM or 8-bit register operands.  That gets fixed in
   * fixupReg().
   */
  switch (insn->registerSize) {
  case 2:
    insn->regBase = MODRM_REG_AX;
    insn->eaRegBase = EA_REG_AX;
    break;
  case 4:
    insn->regBase = MODRM_REG_EAX;
    insn->eaRegBase = EA_REG_EAX;
    break;
  case 8:
    insn->regBase = MODRM_REG_RAX;
    insn->eaRegBase = EA_REG_RAX;
    break;
  }

  reg |= rFromREX(insn->rexPrefix) << 3;
  rm |= bFromREX(insn->rexPrefix) << 3;

  evexrm = 0;
  if (insn->vectorExtensionType == TYPE_EVEX &&
      insn->mode == MODE_64BIT) {
    reg |= r2FromEVEX2of4(insn->vectorExtensionPrefix[1]) << 4;
    evexrm = xFromEVEX2of4(insn->vectorExtensionPrefix[1]) << 4;
  }

  insn->reg = (Reg)(insn->regBase + reg);

  switch (insn->addressSize) {
  case 2: {
    EABase eaBaseBase = EA_BASE_BX_SI;

    switch (mod) {
    case 0x0:
      if (rm == 0x6) {
        insn->eaBase = EA_BASE_NONE;
        insn->eaDisplacement = EA_DISP_16;
        if (readDisplacement(insn))
          return -1;
      } else {
        insn->eaBase = (EABase)(eaBaseBase + rm);
        insn->eaDisplacement = EA_DISP_NONE;
      }
      break;
    case 0x1:
      insn->eaBase = (EABase)(eaBaseBase + rm);
      insn->eaDisplacement = EA_DISP_8;
      insn->displacementSize = 1;
      if (readDisplacement(insn))
        return -1;
      break;
    case 0x2:
      insn->eaBase = (EABase)(eaBaseBase + rm);
      insn->eaDisplacement = EA_DISP_16;
      if (readDisplacement(insn))
        return -1;
      break;
    case 0x3:
      insn->eaBase = (EABase)(insn->eaRegBase + rm);
      if (readDisplacement(insn))
        return -1;
      break;
    }
    break;
  }

  case 4:
  case 8: {
    EABase eaBaseBase =
      (insn->addressSize == 4 ? EA_BASE_EAX : EA_BASE_RAX);

    switch (mod) {
    default:
      break;
    case 0x0:
      insn->eaDisplacement =
        EA_DISP_NONE; /* readSIB may override this */
      // In determining whether RIP-relative mode is used (rm=5),
      // or whether a SIB byte is present (rm=4),
      // the extension bits (REX.b and EVEX.x) are ignored.
      switch (rm & 7) {
      case 0x4: // SIB byte is present
        insn->eaBase = (insn->addressSize == 4 ?
              EA_BASE_sib :
              EA_BASE_sib64);
        if (readSIB(insn) || readDisplacement(insn))
          return -1;
        break;
      case 0x5: // RIP-relative
        insn->eaBase = EA_BASE_NONE;
        insn->eaDisplacement = EA_DISP_32;
        if (readDisplacement(insn))
          return -1;
        break;
      default:
        insn->eaBase = (EABase)(eaBaseBase + rm);
        break;
      }
      break;
    case 0x1:
      insn->displacementSize = 1;
      /* FALLTHROUGH */
    case 0x2:
      insn->eaDisplacement =
        (mod == 0x1 ? EA_DISP_8 : EA_DISP_32);
      switch (rm & 7) {
      case 0x4: // SIB byte is present
        insn->eaBase = EA_BASE_sib;
        if (readSIB(insn) || readDisplacement(insn))
          return -1;
        break;
      default:
        insn->eaBase = (EABase)(eaBaseBase + rm);
        if (readDisplacement(insn))
          return -1;
        break;
      }
      break;
    case 0x3:
      insn->eaDisplacement = EA_DISP_NONE;
      insn->eaBase = (EABase)(insn->eaRegBase + rm + evexrm);
      break;
    }

    break;
  }
  } /* switch (insn->addressSize) */

  return 0;
}

#define GENERIC_FIXUP_FUNC(name, base, prefix, mask) \
  static uint16_t name(struct InternalInstruction *insn, \
           OperandType type, uint8_t index, uint8_t *valid) \
  { \
    *valid = 1; \
    switch (type) { \
    default: \
      *valid = 0; \
      return 0; \
    case TYPE_Rv: \
      return base + index; \
    case TYPE_R8: \
      index &= mask; \
      if (index > 0xf) \
        *valid = 0; \
      if (insn->rexPrefix && index >= 4 && index <= 7) { \
        return prefix##_SPL + (index - 4); \
      } else { \
        return prefix##_AL + index; \
      } \
    case TYPE_R16: \
      index &= mask; \
      if (index > 0xf) \
        *valid = 0; \
      return prefix##_AX + index; \
    case TYPE_R32: \
      index &= mask; \
      if (index > 0xf) \
        *valid = 0; \
      return prefix##_EAX + index; \
    case TYPE_R64: \
      index &= mask; \
      if (index > 0xf) \
        *valid = 0; \
      return prefix##_RAX + index; \
    case TYPE_ZMM: \
      return prefix##_ZMM0 + index; \
    case TYPE_YMM: \
      return prefix##_YMM0 + index; \
    case TYPE_XMM: \
      return prefix##_XMM0 + index; \
    case TYPE_VK: \
      index &= 0xf; \
      if (index > 7) \
        *valid = 0; \
      return prefix##_K0 + index; \
    case TYPE_MM64: \
      return prefix##_MM0 + (index & 0x7); \
    case TYPE_SEGMENTREG: \
      if ((index & 7) > 5) \
        *valid = 0; \
      return prefix##_ES + (index & 7); \
    case TYPE_DEBUGREG: \
      return prefix##_DR0 + index; \
    case TYPE_CONTROLREG: \
      return prefix##_CR0 + index; \
    case TYPE_BNDR: \
      if (index > 3) \
        *valid = 0; \
      return prefix##_BND0 + index; \
    case TYPE_MVSIBX: \
      return prefix##_XMM0 + index; \
    case TYPE_MVSIBY: \
      return prefix##_YMM0 + index; \
    case TYPE_MVSIBZ: \
      return prefix##_ZMM0 + index; \
    } \
  }

/*
 * fixup*Value - Consults an operand type to determine the meaning of the
 *   reg or R/M field.  If the operand is an XMM operand, for example, an
 *   operand would be XMM0 instead of AX, which readModRM() would otherwise
 *   misinterpret it as.
 *
 * @param insn  - The instruction containing the operand.
 * @param type  - The operand type.
 * @param index - The existing value of the field as reported by readModRM().
 * @param valid - The address of a uint8_t.  The target is set to 1 if the
 *                field is valid for the register class; 0 if not.
 * @return      - The proper value.
 */
GENERIC_FIXUP_FUNC(fixupRegValue, insn->regBase, MODRM_REG, 0x1f)
GENERIC_FIXUP_FUNC(fixupRMValue, insn->eaRegBase, EA_REG, 0xf)

/*
 * fixupReg - Consults an operand specifier to determine which of the
 *   fixup*Value functions to use in correcting readModRM()'ss interpretation.
 *
 * @param insn  - See fixup*Value().
 * @param op    - The operand specifier.
 * @return      - 0 if fixup was successful; -1 if the register returned was
 *                invalid for its class.
 */
static int fixupReg(struct InternalInstruction *insn,
        const struct OperandSpecifier *op)
{
  uint8_t valid;

  switch ((OperandEncoding)op->encoding) {
  default:
    // debug("Expected a REG or R/M encoding in fixupReg");
    return -1;
  case ENCODING_VVVV:
    insn->vvvv = (Reg)fixupRegValue(insn, (OperandType)op->type,
            insn->vvvv, &valid);
    if (!valid)
      return -1;
    break;
  case ENCODING_REG:
    insn->reg = (Reg)fixupRegValue(insn, (OperandType)op->type,
                 insn->reg - insn->regBase,
                 &valid);
    if (!valid)
      return -1;
    break;
CASE_ENCODING_RM:
    if (insn->eaBase >= insn->eaRegBase) {
      insn->eaBase = (EABase)fixupRMValue(
        insn, (OperandType)op->type,
        insn->eaBase - insn->eaRegBase, &valid);
      if (!valid)
        return -1;
    }
    break;
  }

  return 0;
}

/*
 * readOpcodeRegister - Reads an operand from the opcode field of an
 *   instruction and interprets it appropriately given the operand width.
 *   Handles AddRegFrm instructions.
 *
 * @param insn  - the instruction whose opcode field is to be read.
 * @param size  - The width (in bytes) of the register being specified.
 *                1 means AL and friends, 2 means AX, 4 means EAX, and 8 means
 *                RAX.
 * @return      - 0 on success; nonzero otherwise.
 */
static int readOpcodeRegister(struct InternalInstruction *insn, uint8_t size)
{
  if (size == 0)
    size = insn->registerSize;

  switch (size) {
  case 1:
    insn->opcodeRegister =
      (Reg)(MODRM_REG_AL + ((bFromREX(insn->rexPrefix) << 3) |
                (insn->opcode & 7)));
    if (insn->rexPrefix &&
        insn->opcodeRegister >= MODRM_REG_AL + 0x4 &&
        insn->opcodeRegister < MODRM_REG_AL + 0x8) {
      insn->opcodeRegister =
        (Reg)(MODRM_REG_SPL + (insn->opcodeRegister -
                   MODRM_REG_AL - 4));
    }

    break;
  case 2:
    insn->opcodeRegister =
      (Reg)(MODRM_REG_AX + ((bFromREX(insn->rexPrefix) << 3) |
                (insn->opcode & 7)));
    break;
  case 4:
    insn->opcodeRegister = (Reg)(MODRM_REG_EAX +
               ((bFromREX(insn->rexPrefix) << 3) |
                (insn->opcode & 7)));
    break;
  case 8:
    insn->opcodeRegister = (Reg)(MODRM_REG_RAX +
               ((bFromREX(insn->rexPrefix) << 3) |
                (insn->opcode & 7)));
    break;
  }

  return 0;
}

/*
 * readImmediate - Consumes an immediate operand from an instruction, given the
 *   desired operand size.
 *
 * @param insn  - The instruction whose operand is to be read.
 * @param size  - The width (in bytes) of the operand.
 * @return      - 0 if the immediate was successfully consumed; nonzero
 *                otherwise.
 */
static int readImmediate(struct InternalInstruction *insn, uint8_t size)
{
  uint8_t imm8;
  uint16_t imm16;
  uint32_t imm32;
  uint64_t imm64;

  if (insn->numImmediatesConsumed == 2) {
    // debug("Already consumed two immediates");
    return -1;
  }

  if (size == 0)
    size = insn->immediateSize;
  else
    insn->immediateSize = size;

  insn->immediateOffset = insn->readerCursor - insn->startLocation;

  switch (size) {
  case 1:
    if (consumeByte(insn, &imm8))
      return -1;

    insn->immediates[insn->numImmediatesConsumed] = imm8;
    break;
  case 2:
    if (consumeUInt16(insn, &imm16))
      return -1;

    insn->immediates[insn->numImmediatesConsumed] = imm16;
    break;
  case 4:
    if (consumeUInt32(insn, &imm32))
      return -1;

    insn->immediates[insn->numImmediatesConsumed] = imm32;
    break;
  case 8:
    if (consumeUInt64(insn, &imm64))
      return -1;
    insn->immediates[insn->numImmediatesConsumed] = imm64;
    break;
  }

  insn->numImmediatesConsumed++;

  return 0;
}

/*
 * readVVVV - Consumes vvvv from an instruction if it has a VEX prefix.
 *
 * @param insn  - The instruction whose operand is to be read.
 * @return      - 0 if the vvvv was successfully consumed; nonzero
 *                otherwise.
 */
static int readVVVV(struct InternalInstruction *insn)
{
  int vvvv;

  if (insn->vectorExtensionType == TYPE_EVEX)
    vvvv = (v2FromEVEX4of4(insn->vectorExtensionPrefix[3]) << 4 |
      vvvvFromEVEX3of4(insn->vectorExtensionPrefix[2]));
  else if (insn->vectorExtensionType == TYPE_VEX_3B)
    vvvv = vvvvFromVEX3of3(insn->vectorExtensionPrefix[2]);
  else if (insn->vectorExtensionType == TYPE_VEX_2B)
    vvvv = vvvvFromVEX2of2(insn->vectorExtensionPrefix[1]);
  else if (insn->vectorExtensionType == TYPE_XOP)
    vvvv = vvvvFromXOP3of3(insn->vectorExtensionPrefix[2]);
  else
    return -1;

  if (insn->mode != MODE_64BIT)
    vvvv &= 0xf; // Can only clear bit 4. Bit 3 must be cleared later.

  insn->vvvv = (Reg)vvvv;

  return 0;
}

/*
 * readMaskRegister - Reads an mask register from the opcode field of an
 *   instruction.
 *
 * @param insn    - The instruction whose opcode field is to be read.
 * @return        - 0 on success; nonzero otherwise.
 */
static int readMaskRegister(struct InternalInstruction *insn)
{
  if (insn->vectorExtensionType != TYPE_EVEX)
    return -1;

  insn->writemask =
    (Reg)(aaaFromEVEX4of4(insn->vectorExtensionPrefix[3]));

  return 0;
}

/*
 * readOperands - Consults the specifier for an instruction and consumes all
 *   operands for that instruction, interpreting them as it goes.
 *
 * @param insn  - The instruction whose operands are to be read and interpreted.
 * @return      - 0 if all operands could be read; nonzero otherwise.
 */
static int readOperands(struct InternalInstruction *insn)
{
  int hasVVVV, needVVVV;
  int sawRegImm = 0;
  int i;

  /* If non-zero vvvv specified, need to make sure one of the operands
     uses it. */
  hasVVVV = !readVVVV(insn);
  needVVVV = hasVVVV && (insn->vvvv != 0);

  for (i = 0; i < X86_MAX_OPERANDS; ++i) {
    const OperandSpecifier *op =
      &x86OperandSets[insn->spec->operands][i];
    switch (op->encoding) {
    case ENCODING_NONE:
    case ENCODING_SI:
    case ENCODING_DI:
      break;

CASE_ENCODING_VSIB:
      // VSIB can use the V2 bit so check only the other bits.
      if (needVVVV)
        needVVVV = hasVVVV & ((insn->vvvv & 0xf) != 0);

      if (readModRM(insn))
        return -1;

      // Reject if SIB wasn't used.
      if (insn->eaBase != EA_BASE_sib &&
          insn->eaBase != EA_BASE_sib64)
        return -1;

      // If sibIndex was set to SIB_INDEX_NONE, index offset is 4.
      if (insn->sibIndex == SIB_INDEX_NONE)
        insn->sibIndex =
          (SIBIndex)(insn->sibIndexBase + 4);

      // If EVEX.v2 is set this is one of the 16-31 registers.
      if (insn->vectorExtensionType == TYPE_EVEX &&
          insn->mode == MODE_64BIT &&
          v2FromEVEX4of4(insn->vectorExtensionPrefix[3]))
        insn->sibIndex =
          (SIBIndex)(insn->sibIndex + 16);

      // Adjust the index register to the correct size.
      switch (op->type) {
      default:
        // debug("Unhandled VSIB index type");
        return -1;
      case TYPE_MVSIBX:
        insn->sibIndex =
          (SIBIndex)(SIB_INDEX_XMM0 +
               (insn->sibIndex -
                insn->sibIndexBase));
        break;
      case TYPE_MVSIBY:
        insn->sibIndex =
          (SIBIndex)(SIB_INDEX_YMM0 +
               (insn->sibIndex -
                insn->sibIndexBase));
        break;
      case TYPE_MVSIBZ:
        insn->sibIndex =
          (SIBIndex)(SIB_INDEX_ZMM0 +
               (insn->sibIndex -
                insn->sibIndexBase));
        break;
      }

      // Apply the AVX512 compressed displacement scaling factor.
      if (op->encoding != ENCODING_REG &&
          insn->eaDisplacement == EA_DISP_8)
        insn->displacement *=
          1 << (op->encoding - ENCODING_VSIB);
      break;

    case ENCODING_REG:
CASE_ENCODING_RM:
      if (readModRM(insn))
        return -1;

      if (fixupReg(insn, op))
        return -1;

      // Apply the AVX512 compressed displacement scaling factor.
      if (op->encoding != ENCODING_REG &&
          insn->eaDisplacement == EA_DISP_8)
        insn->displacement *=
          1 << (op->encoding - ENCODING_RM);
      break;

    case ENCODING_IB:
      if (sawRegImm) {
        /* Saw a register immediate so don't read again and instead split the
             previous immediate.  FIXME: This is a hack. */
        insn->immediates[insn->numImmediatesConsumed] =
          insn->immediates
            [insn->numImmediatesConsumed -
             1] &
          0xf;
        ++insn->numImmediatesConsumed;
        break;
      }
      if (readImmediate(insn, 1))
        return -1;
      if (op->type == TYPE_XMM || op->type == TYPE_YMM)
        sawRegImm = 1;
      break;

    case ENCODING_IW:
      if (readImmediate(insn, 2))
        return -1;
      break;

    case ENCODING_ID:
      if (readImmediate(insn, 4))
        return -1;
      break;

    case ENCODING_IO:
      if (readImmediate(insn, 8))
        return -1;
      break;

    case ENCODING_Iv:
      if (readImmediate(insn, insn->immediateSize))
        return -1;
      break;

    case ENCODING_Ia:
      if (readImmediate(insn, insn->addressSize))
        return -1;
      /* Direct memory-offset (moffset) immediate will get mapped
           to memory operand later. We want the encoding info to
           reflect that as well. */
      insn->displacementOffset = insn->immediateOffset;
      insn->consumedDisplacement = true;
      insn->displacementSize = insn->immediateSize;
      insn->displacement =
        insn->immediates[insn->numImmediatesConsumed -
             1];
      insn->immediateOffset = 0;
      insn->immediateSize = 0;
      break;

    case ENCODING_IRC:
      insn->RC =
        (l2FromEVEX4of4(insn->vectorExtensionPrefix[3])
         << 1) |
        lFromEVEX4of4(insn->vectorExtensionPrefix[3]);
      break;

    case ENCODING_RB:
      if (readOpcodeRegister(insn, 1))
        return -1;
      break;

    case ENCODING_RW:
      if (readOpcodeRegister(insn, 2))
        return -1;
      break;

    case ENCODING_RD:
      if (readOpcodeRegister(insn, 4))
        return -1;
      break;

    case ENCODING_RO:
      if (readOpcodeRegister(insn, 8))
        return -1;
      break;

    case ENCODING_Rv:
      if (readOpcodeRegister(insn, 0))
        return -1;
      break;

    case ENCODING_FP:
      break;

    case ENCODING_VVVV:
      if (!hasVVVV)
        return -1;

      needVVVV =
        0; /* Mark that we have found a VVVV operand. */

      if (insn->mode != MODE_64BIT)
        insn->vvvv = (Reg)(insn->vvvv & 0x7);

      if (fixupReg(insn, op))
        return -1;
      break;

    case ENCODING_WRITEMASK:
      if (readMaskRegister(insn))
        return -1;
      break;

    case ENCODING_DUP:
      break;

    default:
      // dbgprintf(insn, "Encountered an operand with an unknown encoding.");
      return -1;
    }
  }

  /* If we didn't find ENCODING_VVVV operand, but non-zero vvvv present, fail */
  if (needVVVV)
    return -1;

  return 0;
}

// return True if instruction is illegal to use with prefixes
// This also check & fix the isPrefixNN when a prefix is irrelevant.
static bool checkPrefix(struct InternalInstruction *insn)
{
  // LOCK prefix
  if (insn->hasLockPrefix) {
    switch (insn->instructionID) {
    default:
      // invalid LOCK
      return true;

    // nop dword [rax]
    case X86_NOOPL:

    // DEC
    case X86_DEC16m:
    case X86_DEC32m:
    case X86_DEC64m:
    case X86_DEC8m:

    // ADC
    case X86_ADC16mi:
    case X86_ADC16mi8:
    case X86_ADC16mr:
    case X86_ADC32mi:
    case X86_ADC32mi8:
    case X86_ADC32mr:
    case X86_ADC64mi32:
    case X86_ADC64mi8:
    case X86_ADC64mr:
    case X86_ADC8mi:
    case X86_ADC8mi8:
    case X86_ADC8mr:
    case X86_ADC8rm:
    case X86_ADC16rm:
    case X86_ADC32rm:
    case X86_ADC64rm:

    // ADD
    case X86_ADD16mi:
    case X86_ADD16mi8:
    case X86_ADD16mr:
    case X86_ADD32mi:
    case X86_ADD32mi8:
    case X86_ADD32mr:
    case X86_ADD64mi32:
    case X86_ADD64mi8:
    case X86_ADD64mr:
    case X86_ADD8mi:
    case X86_ADD8mi8:
    case X86_ADD8mr:
    case X86_ADD8rm:
    case X86_ADD16rm:
    case X86_ADD32rm:
    case X86_ADD64rm:

    // AND
    case X86_AND16mi:
    case X86_AND16mi8:
    case X86_AND16mr:
    case X86_AND32mi:
    case X86_AND32mi8:
    case X86_AND32mr:
    case X86_AND64mi32:
    case X86_AND64mi8:
    case X86_AND64mr:
    case X86_AND8mi:
    case X86_AND8mi8:
    case X86_AND8mr:
    case X86_AND8rm:
    case X86_AND16rm:
    case X86_AND32rm:
    case X86_AND64rm:

    // BTC
    case X86_BTC16mi8:
    case X86_BTC16mr:
    case X86_BTC32mi8:
    case X86_BTC32mr:
    case X86_BTC64mi8:
    case X86_BTC64mr:

    // BTR
    case X86_BTR16mi8:
    case X86_BTR16mr:
    case X86_BTR32mi8:
    case X86_BTR32mr:
    case X86_BTR64mi8:
    case X86_BTR64mr:

    // BTS
    case X86_BTS16mi8:
    case X86_BTS16mr:
    case X86_BTS32mi8:
    case X86_BTS32mr:
    case X86_BTS64mi8:
    case X86_BTS64mr:

    // CMPXCHG
    case X86_CMPXCHG16B:
    case X86_CMPXCHG16rm:
    case X86_CMPXCHG32rm:
    case X86_CMPXCHG64rm:
    case X86_CMPXCHG8rm:
    case X86_CMPXCHG8B:

    // INC
    case X86_INC16m:
    case X86_INC32m:
    case X86_INC64m:
    case X86_INC8m:

    // NEG
    case X86_NEG16m:
    case X86_NEG32m:
    case X86_NEG64m:
    case X86_NEG8m:

    // NOT
    case X86_NOT16m:
    case X86_NOT32m:
    case X86_NOT64m:
    case X86_NOT8m:

    // OR
    case X86_OR16mi:
    case X86_OR16mi8:
    case X86_OR16mr:
    case X86_OR32mi:
    case X86_OR32mi8:
    case X86_OR32mr:
    case X86_OR64mi32:
    case X86_OR64mi8:
    case X86_OR64mr:
    case X86_OR8mi8:
    case X86_OR8mi:
    case X86_OR8mr:
    case X86_OR8rm:
    case X86_OR16rm:
    case X86_OR32rm:
    case X86_OR64rm:

    // SBB
    case X86_SBB16mi:
    case X86_SBB16mi8:
    case X86_SBB16mr:
    case X86_SBB32mi:
    case X86_SBB32mi8:
    case X86_SBB32mr:
    case X86_SBB64mi32:
    case X86_SBB64mi8:
    case X86_SBB64mr:
    case X86_SBB8mi:
    case X86_SBB8mi8:
    case X86_SBB8mr:

    // SUB
    case X86_SUB16mi:
    case X86_SUB16mi8:
    case X86_SUB16mr:
    case X86_SUB32mi:
    case X86_SUB32mi8:
    case X86_SUB32mr:
    case X86_SUB64mi32:
    case X86_SUB64mi8:
    case X86_SUB64mr:
    case X86_SUB8mi8:
    case X86_SUB8mi:
    case X86_SUB8mr:
    case X86_SUB8rm:
    case X86_SUB16rm:
    case X86_SUB32rm:
    case X86_SUB64rm:

    // XADD
    case X86_XADD16rm:
    case X86_XADD32rm:
    case X86_XADD64rm:
    case X86_XADD8rm:

    // XCHG
    case X86_XCHG16rm:
    case X86_XCHG32rm:
    case X86_XCHG64rm:
    case X86_XCHG8rm:

    // XOR
    case X86_XOR16mi:
    case X86_XOR16mi8:
    case X86_XOR16mr:
    case X86_XOR32mi:
    case X86_XOR32mi8:
    case X86_XOR32mr:
    case X86_XOR64mi32:
    case X86_XOR64mi8:
    case X86_XOR64mr:
    case X86_XOR8mi8:
    case X86_XOR8mi:
    case X86_XOR8mr:
    case X86_XOR8rm:
    case X86_XOR16rm:
    case X86_XOR32rm:
    case X86_XOR64rm:

      // this instruction can be used with LOCK prefix
      return false;
    }
  }

#if 0
  // REPNE prefix
  if (insn->repeatPrefix) {
    // 0xf2 can be a part of instruction encoding, but not really a prefix.
    // In such a case, clear it.
    if (insn->twoByteEscape == 0x0f) {
      insn->prefix0 = 0;
    }
  }
#endif

  // no invalid prefixes
  return false;
}

/*
 * decodeInstruction - Reads and interprets a full instruction provided by the
 *   user.
 *
 * @param insn      - A pointer to the instruction to be populated.  Must be
 *                    pre-allocated.
 * @param reader    - The function to be used to read the instruction's bytes.
 * @param readerArg - A generic argument to be passed to the reader to store
 *                    any internal state.
 * @param startLoc  - The address (in the reader's address space) of the first
 *                    byte in the instruction.
 * @param mode      - The mode (real mode, IA-32e, or IA-32e in 64-bit mode) to
 *                    decode the instruction in.
 * @return          - 0 if instruction is valid; nonzero if not.
 */
int decodeInstruction(struct InternalInstruction *insn, byteReader_t reader,
          const void *readerArg, uint64_t startLoc,
          DisassemblerMode mode)
{
  insn->reader = reader;
  insn->readerArg = readerArg;
  insn->startLocation = startLoc;
  insn->readerCursor = startLoc;
  insn->mode = mode;
  insn->numImmediatesConsumed = 0;

  if (readPrefixes(insn) || readOpcode(insn) || getID(insn) ||
      insn->instructionID == 0 || checkPrefix(insn) || readOperands(insn))
    return -1;

  insn->length = (size_t)(insn->readerCursor - insn->startLocation);

  // instruction length must be <= 15 to be valid
  if (insn->length > 15)
    return -1;

  if (insn->operandSize == 0)
    insn->operandSize = insn->registerSize;

  insn->operands = &x86OperandSets[insn->spec->operands][0];

  return 0;
}

#endif

Coverage Report

Created: 2026-04-29 06:06