diff options
Diffstat (limited to 'llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp')
| -rw-r--r-- | llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp | 87 |
1 files changed, 84 insertions, 3 deletions
diff --git a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp index 86473347e4b..008dead5d0a 100644 --- a/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp +++ b/llvm/lib/Target/X86/Disassembler/X86Disassembler.cpp @@ -10,11 +10,70 @@ // This file is part of the X86 Disassembler. // It contains code to translate the data produced by the decoder into // MCInsts. -// Documentation for the disassembler can be found in X86Disassembler.h. +// +// +// 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.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. // //===----------------------------------------------------------------------===// -#include "X86Disassembler.h" #include "X86DisassemblerDecoder.h" #include "MCTargetDesc/X86MCTargetDesc.h" #include "llvm/MC/MCContext.h" @@ -67,6 +126,28 @@ static bool translateInstruction(MCInst &target, InternalInstruction &source, const MCDisassembler *Dis); +namespace { + +/// 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: + X86GenericDisassembler(const MCSubtargetInfo &STI, MCContext &Ctx, + std::unique_ptr<const MCInstrInfo> MII); +public: + DecodeStatus getInstruction(MCInst &instr, uint64_t &size, + ArrayRef<uint8_t> Bytes, uint64_t Address, + raw_ostream &vStream, + raw_ostream &cStream) const override; + +private: + DisassemblerMode fMode; +}; + +} + X86GenericDisassembler::X86GenericDisassembler( const MCSubtargetInfo &STI, MCContext &Ctx, @@ -980,7 +1061,7 @@ static MCDisassembler *createX86Disassembler(const Target &T, const MCSubtargetInfo &STI, MCContext &Ctx) { std::unique_ptr<const MCInstrInfo> MII(T.createMCInstrInfo()); - return new X86Disassembler::X86GenericDisassembler(STI, Ctx, std::move(MII)); + return new X86GenericDisassembler(STI, Ctx, std::move(MII)); } extern "C" void LLVMInitializeX86Disassembler() { |
