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156 lines
5.4 KiB
C++
156 lines
5.4 KiB
C++
//
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// Decoder.hpp
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// Clock Signal
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//
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// Created by Thomas Harte on 01/01/21.
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// Copyright © 2021 Thomas Harte. All rights reserved.
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//
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#ifndef InstructionSets_x86_Decoder_hpp
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#define InstructionSets_x86_Decoder_hpp
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#include "Instruction.hpp"
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#include <cstddef>
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#include <utility>
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namespace InstructionSet {
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namespace x86 {
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enum class Model {
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i8086,
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};
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/*!
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Implements Intel x86 instruction decoding.
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This is an experimental implementation; it has not yet undergone significant testing.
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*/
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class Decoder {
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public:
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Decoder(Model model);
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/*!
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@returns an @c Instruction plus a size; a positive size to indicate successful decoding; a
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negative size specifies the [negatived] number of further bytes the caller should ideally
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collect before calling again. The caller is free to call with fewer, but may not get a decoded
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instruction in response, and the decoder may still not be able to complete decoding
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even if given that number of bytes.
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*/
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std::pair<int, Instruction> decode(const uint8_t *source, size_t length);
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private:
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enum class Phase {
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/// Captures all prefixes and continues until an instruction byte is encountered.
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Instruction,
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/// Receives a ModRegRM byte and either populates the source_ and dest_ fields appropriately
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/// or completes decoding of the instruction, as per the instruction format.
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ModRegRM,
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/// Waits for sufficiently many bytes to pass for the required displacement and operand to be captured.
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/// Cf. displacement_size_ and operand_size_.
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AwaitingDisplacementOrOperand,
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/// Forms and returns an Instruction, and resets parsing state.
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ReadyToPost
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} phase_ = Phase::Instruction;
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/// During the ModRegRM phase, format dictates interpretation of the ModRegRM byte.
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///
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/// During the ReadyToPost phase, format determines how transiently-recorded fields
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/// are packaged into an Instruction.
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enum class ModRegRMFormat: uint8_t {
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// Parse the ModRegRM for mode, register and register/memory fields
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// and populate the source_ and destination_ fields appropriate.
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MemReg_Reg,
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Reg_MemReg,
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// Parse for mode and register/memory fields, populating both
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// source_ and destination_ fields with the result. Use the 'register'
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// field to pick an operation from the TEST/NOT/NEG/MUL/IMUL/DIV/IDIV group.
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MemRegTEST_to_IDIV,
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// Parse for mode and register/memory fields, populating both
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// source_ and destination_ fields with the result. Use the 'register'
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// field to check for the POP operation.
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MemRegPOP,
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// Parse for mode and register/memory fields, populating both
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// the destination_ field with the result and setting source_ to Immediate.
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// Use the 'register' field to check for the MOV operation.
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MemRegMOV,
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// Parse for mode and register/memory fields, populating the
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// destination_ field with the result. Use the 'register' field
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// to pick an operation from the ROL/ROR/RCL/RCR/SAL/SHR/SAR group.
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MemRegROL_to_SAR,
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// Parse for mode and register/memory fields, populating the
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// destination_ field with the result. Use the 'register' field
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// to pick an operation from the ADD/OR/ADC/SBB/AND/SUB/XOR/CMP group and
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// waits for an operand equal to the operation size.
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MemRegADD_to_CMP,
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// Parse for mode and register/memory fields, populating the
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// source_ field with the result. Fills destination_ with a segment
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// register based on the reg field.
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SegReg,
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// Parse for mode and register/memory fields, populating the
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// source_ and destination_ fields with the result. Uses the
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// 'register' field to pick INC or DEC.
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MemRegINC_DEC,
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// Parse for mode and register/memory fields, populating the
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// source_ and destination_ fields with the result. Uses the
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// 'register' field to pick from INC/DEC/CALL/JMP/PUSH, altering
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// the source to ::Immediate and setting an operand size if necessary.
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MemRegINC_to_PUSH,
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// Parse for mode and register/memory fields, populating the
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// source_ and destination_ fields with the result. Uses the
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// 'register' field to pick from ADD/ADC/SBB/SUB/CMP, altering
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// the source to ::Immediate and setting an appropriate operand size.
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MemRegADC_to_CMP,
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} modregrm_format_ = ModRegRMFormat::MemReg_Reg;
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// Ephemeral decoding state.
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Operation operation_ = Operation::Invalid;
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uint8_t instr_ = 0x00; // TODO: is this desired, versus loading more context into ModRegRMFormat?
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int consumed_ = 0, operand_bytes_ = 0;
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// Source and destination locations.
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Source source_ = Source::None;
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Source destination_ = Source::None;
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// Immediate fields.
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int16_t displacement_ = 0;
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uint16_t operand_ = 0;
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uint64_t inward_data_ = 0;
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// Facts about the instruction.
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int displacement_size_ = 0; // i.e. size of in-stream displacement, if any.
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int operand_size_ = 0; // i.e. size of in-stream operand, if any.
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int operation_size_ = 0; // i.e. size of data manipulated by the operation.
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// Prefix capture fields.
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Repetition repetition_ = Repetition::None;
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bool lock_ = false;
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Source segment_override_ = Source::None;
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/// Resets size capture and all fields with default values.
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void reset_parsing() {
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consumed_ = operand_bytes_ = 0;
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displacement_size_ = operand_size_ = 0;
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displacement_ = operand_ = 0;
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lock_ = false;
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segment_override_ = Source::None;
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repetition_ = Repetition::None;
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phase_ = Phase::Instruction;
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source_ = destination_ = Source::None;
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}
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};
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}
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}
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#endif /* InstructionSets_x86_Decoder_hpp */
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