SecurityEmulator/src/CPU.cpp

#include "CPU.h"

#include <stdexcept>
#include <iostream>
#include <iomanip>
#include <stdlib.h>
#include <array>
#include <cassert>

CPU::CPU(std::shared_ptr<Bus> bus) : m_Bus(bus), m_IsHalted(false), m_Context({m_Instruction, m_InstructionPointer, m_Flags, m_Registers, m_Bus, m_IsHalted}) {
  m_InstructionPointer = 0x00008000;

  for(int i = 0; i < 16; i++)
  {
    m_Registers[i] = 0;
  }
}

void CPU::Step() {
  FetchDecode();
  Execute();
}

void CPU::FetchDecode() {
  uint8_t opcode_raw = m_Bus->AccessX<uint8_t>(m_InstructionPointer);
  Opcode opcode = static_cast<Opcode>(opcode_raw);

  switch(opcode_raw) {
  case Opcode::MOV_R_IMM32 ... 0xBF: // 0xB8 to 0xBF
    m_Instruction.m_Opcode = Opcode::MOV_R_IMM32;
    m_Instruction.m_Operand1 = opcode_raw - 0xB8;
    m_Instruction.m_Operand2 = m_Bus->AccessX<uint32_t>(m_InstructionPointer + 1);
    m_Instruction.m_Length = 5;
    break;
  case Opcode::NOP:
  case Opcode::HLT:
    m_Instruction.m_Opcode = opcode;
    m_Instruction.m_Length = 1;
    break;
  case Opcode::ADD_RM32_R32:
    m_Instruction.m_Opcode = opcode;
    m_Instruction.optional.m_ModRM = x86::process_modrm(m_Bus->AccessX<uint8_t>(m_InstructionPointer + 1));
    m_Instruction.m_Length = 2;
    FetchModRMFields();
    break;
  }

  m_InstructionPointer += m_Instruction.m_Length;
}

void CPU::Execute() {
  std::cout << "Executing... \n";
  uint8_t opcode_value = static_cast<uint8_t>(m_Instruction.m_Opcode);
  auto& exec_table = GetExecutorTable();
  if(exec_table[opcode_value])
  {
    exec_table[opcode_value](m_Context);
    return;
  }
  throw std::runtime_error("Opcode not found!");
}

void CPU::FetchModRMFields() {
  assert(m_Instruction.m_Length != 0); // FetchDecode() must set m_Length before calling FetchModRMFields()
  x86::ModRMState state = m_Instruction.optional.m_ModRM.m_State;
  switch(state) {
  case x86::ModRMState::LR:
  case x86::ModRMState::R:
    break;
  case x86::ModRMState::DISP32:
  case x86::ModRMState::LR_DISP32:
    m_Instruction.m_Operand1 = m_Bus->AccessX<uint32_t>(m_InstructionPointer + m_Instruction.m_Length);      
    m_Instruction.m_Length += 4;
    break;
  case x86::ModRMState::LR_DISP8:
    m_Instruction.m_Operand1 = m_Bus->AccessX<uint8_t>(m_InstructionPointer + m_Instruction.m_Length);      
    m_Instruction.m_Length += 1;
    break;
  default:
    throw std::runtime_error("Instruction could not be modified according to the modrm field!");
  }
}