X86Disassembler.h

Go to the documentation of this file.

//===-- X86Disassembler.h - Disassembler for x86 and x86_64 -----*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// The X86 disassembler is a table-driven disassembler for the 16-, 32-, and
// 64-bit X86 instruction sets.  The main decode sequence for an assembly
// instruction in this disassembler is:
//
// 1. Read the prefix bytes and determine the attributes of the instruction.
//    These attributes, recorded in enum attributeBits
//    (X86DisassemblerDecoderCommon.h), form a bitmask.  The table CONTEXTS_SYM
//    provides a mapping from bitmasks to contexts, which are represented by
//    enum InstructionContext (ibid.).
//
// 2. Read the opcode, and determine what kind of opcode it is.  The
//    disassembler distinguishes four kinds of opcodes, which are enumerated in
//    OpcodeType (X86DisassemblerDecoderCommon.h): one-byte (0xnn), two-byte
//    (0x0f 0xnn), three-byte-38 (0x0f 0x38 0xnn), or three-byte-3a
//    (0x0f 0x3a 0xnn).  Mandatory prefixes are treated as part of the context.
//
// 3. Depending on the opcode type, look in one of four ClassDecision structures
//    (X86DisassemblerDecoderCommon.h).  Use the opcode class to determine which
//    OpcodeDecision (ibid.) to look the opcode in.  Look up the opcode, to get
//    a ModRMDecision (ibid.).
//
// 4. Some instructions, such as escape opcodes or extended opcodes, or even
//    instructions that have ModRM*Reg / ModRM*Mem forms in LLVM, need the
//    ModR/M byte to complete decode.  The ModRMDecision's type is an entry from
//    ModRMDecisionType (X86DisassemblerDecoderCommon.h) that indicates if the
//    ModR/M byte is required and how to interpret it.
//
// 5. After resolving the ModRMDecision, the disassembler has a unique ID
//    of type InstrUID (X86DisassemblerDecoderCommon.h).  Looking this ID up in
//    INSTRUCTIONS_SYM yields the name of the instruction and the encodings and
//    meanings of its operands.
//
// 6. For each operand, its encoding is an entry from OperandEncoding
//    (X86DisassemblerDecoderCommon.h) and its type is an entry from
//    OperandType (ibid.).  The encoding indicates how to read it from the
//    instruction; the type indicates how to interpret the value once it has
//    been read.  For example, a register operand could be stored in the R/M
//    field of the ModR/M byte, the REG field of the ModR/M byte, or added to
//    the main opcode.  This is orthogonal from its meaning (an GPR or an XMM
//    register, for instance).  Given this information, the operands can be
//    extracted and interpreted.
//
// 7. As the last step, the disassembler translates the instruction information
//    and operands into a format understandable by the client - in this case, an
//    MCInst for use by the MC infrastructure.
//
// The disassembler is broken broadly into two parts: the table emitter that
// emits the instruction decode tables discussed above during compilation, and
// the disassembler itself.  The table emitter is documented in more detail in
// utils/TableGen/X86DisassemblerEmitter.h.
//
// X86Disassembler.h contains the public interface for the disassembler,
//   adhering to the MCDisassembler interface.
// X86Disassembler.cpp contains the code responsible for step 7, and for
//   invoking the decoder to execute steps 1-6.
// X86DisassemblerDecoderCommon.h contains the definitions needed by both the
//   table emitter and the disassembler.
// X86DisassemblerDecoder.h contains the public interface of the decoder,
//   factored out into C for possible use by other projects.
// X86DisassemblerDecoder.c contains the source code of the decoder, which is
//   responsible for steps 1-6.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_LIB_TARGET_X86_DISASSEMBLER_X86DISASSEMBLER_H
#define LLVM_LIB_TARGET_X86_DISASSEMBLER_X86DISASSEMBLER_H

#include "X86DisassemblerDecoderCommon.h"
#include "llvm/MC/MCDisassembler.h"

namespace llvm {

class MCInst;
class MCInstrInfo;
class MCSubtargetInfo;
class MemoryObject;
class raw_ostream;

namespace X86Disassembler {

/// X86GenericDisassembler - Generic disassembler for all X86 platforms.
///   All each platform class should have to do is subclass the constructor, and
///   provide a different disassemblerMode value.
class X86GenericDisassembler : public MCDisassembler {
  std::unique_ptr<const MCInstrInfo> MII;
public:
  /// Constructor     - Initializes the disassembler.
  ///
  X86GenericDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
                         std::unique_ptr<const MCInstrInfo> MII);
public:

  /// getInstruction - See MCDisassembler.
  DecodeStatus getInstruction(MCInst &instr, uint64_t &size,
                              const MemoryObject &region, uint64_t address,
                              raw_ostream &vStream,
                              raw_ostream &cStream) const override;

private:
  DisassemblerMode              fMode;
};

} // namespace X86Disassembler

} // namespace llvm

#endif