1 //===-- X86Disassembler.h - Disassembler for x86 and x86_64 -----*- C++ -*-===//
2 //
3 //                     The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 //
10 // The X86 disassembler is a table-driven disassembler for the 16-, 32-, and
11 // 64-bit X86 instruction sets.  The main decode sequence for an assembly
12 // instruction in this disassembler is:
13 //
14 // 1. Read the prefix bytes and determine the attributes of the instruction.
15 //    These attributes, recorded in enum attributeBits
16 //    (X86DisassemblerDecoderCommon.h), form a bitmask.  The table CONTEXTS_SYM
17 //    provides a mapping from bitmasks to contexts, which are represented by
18 //    enum InstructionContext (ibid.).
19 //
20 // 2. Read the opcode, and determine what kind of opcode it is.  The
21 //    disassembler distinguishes four kinds of opcodes, which are enumerated in
22 //    OpcodeType (X86DisassemblerDecoderCommon.h): one-byte (0xnn), two-byte
23 //    (0x0f 0xnn), three-byte-38 (0x0f 0x38 0xnn), or three-byte-3a
24 //    (0x0f 0x3a 0xnn).  Mandatory prefixes are treated as part of the context.
25 //
26 // 3. Depending on the opcode type, look in one of four ClassDecision structures
27 //    (X86DisassemblerDecoderCommon.h).  Use the opcode class to determine which
28 //    OpcodeDecision (ibid.) to look the opcode in.  Look up the opcode, to get
29 //    a ModRMDecision (ibid.).
30 //
31 // 4. Some instructions, such as escape opcodes or extended opcodes, or even
32 //    instructions that have ModRM*Reg / ModRM*Mem forms in LLVM, need the
33 //    ModR/M byte to complete decode.  The ModRMDecision's type is an entry from
34 //    ModRMDecisionType (X86DisassemblerDecoderCommon.h) that indicates if the
35 //    ModR/M byte is required and how to interpret it.
36 //
37 // 5. After resolving the ModRMDecision, the disassembler has a unique ID
38 //    of type InstrUID (X86DisassemblerDecoderCommon.h).  Looking this ID up in
39 //    INSTRUCTIONS_SYM yields the name of the instruction and the encodings and
40 //    meanings of its operands.
41 //
42 // 6. For each operand, its encoding is an entry from OperandEncoding
43 //    (X86DisassemblerDecoderCommon.h) and its type is an entry from
44 //    OperandType (ibid.).  The encoding indicates how to read it from the
45 //    instruction; the type indicates how to interpret the value once it has
46 //    been read.  For example, a register operand could be stored in the R/M
47 //    field of the ModR/M byte, the REG field of the ModR/M byte, or added to
48 //    the main opcode.  This is orthogonal from its meaning (an GPR or an XMM
49 //    register, for instance).  Given this information, the operands can be
50 //    extracted and interpreted.
51 //
52 // 7. As the last step, the disassembler translates the instruction information
53 //    and operands into a format understandable by the client - in this case, an
54 //    MCInst for use by the MC infrastructure.
55 //
56 // The disassembler is broken broadly into two parts: the table emitter that
57 // emits the instruction decode tables discussed above during compilation, and
58 // the disassembler itself.  The table emitter is documented in more detail in
59 // utils/TableGen/X86DisassemblerEmitter.h.
60 //
61 // X86Disassembler.h contains the public interface for the disassembler,
62 //   adhering to the MCDisassembler interface.
63 // X86Disassembler.cpp contains the code responsible for step 7, and for
64 //   invoking the decoder to execute steps 1-6.
65 // X86DisassemblerDecoderCommon.h contains the definitions needed by both the
66 //   table emitter and the disassembler.
67 // X86DisassemblerDecoder.h contains the public interface of the decoder,
68 //   factored out into C for possible use by other projects.
69 // X86DisassemblerDecoder.c contains the source code of the decoder, which is
70 //   responsible for steps 1-6.
71 //
72 //===----------------------------------------------------------------------===//
73 
74 #ifndef LLVM_LIB_TARGET_X86_DISASSEMBLER_X86DISASSEMBLER_H
75 #define LLVM_LIB_TARGET_X86_DISASSEMBLER_X86DISASSEMBLER_H
76 
77 #include "X86DisassemblerDecoderCommon.h"
78 #include "llvm/MC/MCDisassembler.h"
79 
80 namespace llvm {
81 
82 class MCInst;
83 class MCInstrInfo;
84 class MCSubtargetInfo;
85 class MemoryObject;
86 class raw_ostream;
87 
88 namespace X86Disassembler {
89 
90 /// Generic disassembler for all X86 platforms. All each platform class should
91 /// have to do is subclass the constructor, and provide a different
92 /// disassemblerMode value.
93 class X86GenericDisassembler : public MCDisassembler {
94   std::unique_ptr<const MCInstrInfo> MII;
95 public:
96   X86GenericDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx,
97                          std::unique_ptr<const MCInstrInfo> MII);
98 public:
99   DecodeStatus getInstruction(MCInst &instr, uint64_t &size,
100                               ArrayRef<uint8_t> Bytes, uint64_t Address,
101                               raw_ostream &vStream,
102                               raw_ostream &cStream) const override;
103 
104 private:
105   DisassemblerMode              fMode;
106 };
107 
108 } // namespace X86Disassembler
109 
110 } // namespace llvm
111 
112 #endif
113