#define WIN32_MEAN_AND_LEAN #define NOMINMAX #include #include #include #include #include typedef struct S86_Buffer S86_Buffer; struct S86_Buffer { char *data; size_t size; }; typedef struct S86_Str8 S86_Str8; struct S86_Str8 { char *data; size_t size; }; typedef struct S86_Globals S86_Globals; struct S86_Globals { HANDLE stdout_handle; bool write_to_console; }; typedef struct S86_BufferIterator { S86_Buffer buffer; size_t index; } S86_BufferIterator; S86_Globals s86_globals; #define S86_STRINGIFY2(token) #token #define S86_STRINGIFY(token) S86_STRINGIFY2(token) #define S86_ASSERT(expr) \ if (!(expr)) { \ S86_PrintLnFmt("Assertion triggered [file=\"" __FILE__ ":" S86_STRINGIFY(__LINE__) "\", expr=\"" #expr "\"]"); \ __debugbreak(); \ } \ #define S86_ARRAY_UCOUNT(array) sizeof((array)) / sizeof((array)[0]) #define S86_STR8(string) (S86_Str8){.data = (string), .size = S86_ARRAY_UCOUNT(string) - 1 } #define S86_STR8_FMT(string) (int)((string).size), (string).data #define S86_CAST(Type) (Type) bool S86_BufferIsValid(S86_Buffer buffer); S86_BufferIterator S86_BufferIteratorInit(S86_Buffer buffer); bool S86_BufferIteratorHasMoreBytes(S86_BufferIterator it); uint8_t S86_BufferIteratorPeekByte(S86_BufferIterator it); uint8_t S86_BufferIteratorNextByte(S86_BufferIterator *it); S86_Buffer S86_FileRead(char const *file_path); void S86_FileFree(S86_Buffer buffer); void S86_PrintLn(S86_Str8 string); void S86_PrintLnFmt(char const *fmt, ...); bool S86_BufferIsValid(S86_Buffer buffer) { bool result = buffer.data && buffer.size; return result; } S86_BufferIterator S86_BufferIteratorInit(S86_Buffer buffer) { S86_BufferIterator result = {0}; result.buffer = buffer; return result; } bool S86_BufferIteratorHasMoreBytes(S86_BufferIterator it) { bool result = S86_BufferIsValid(it.buffer) && it.index < it.buffer.size; return result; } uint8_t S86_BufferIteratorPeekByte(S86_BufferIterator it) { S86_ASSERT(S86_BufferIsValid(it.buffer)); S86_ASSERT(it.index < it.buffer.size); uint8_t result = it.buffer.data[it.index]; return result; } uint8_t S86_BufferIteratorNextByte(S86_BufferIterator *it) { S86_ASSERT(it); S86_ASSERT(S86_BufferIsValid(it->buffer)); S86_ASSERT(it->index < it->buffer.size); uint8_t result = it->buffer.data[it->index++]; return result; } S86_Buffer S86_FileRead(char const *file_path) { S86_Buffer result = {0}; // NOTE: Determine file size // ========================================================================= WIN32_FILE_ATTRIBUTE_DATA file_attrib_data = {0}; if (GetFileAttributesEx(file_path, GetFileExInfoStandard, &file_attrib_data) == 0) return result; // NOTE: Open file // ========================================================================= HANDLE file_handle = CreateFile( /*LPCSTR lpFileName*/ file_path, /*DWORD dwDesiredAccess*/ GENERIC_READ, /*DWORD dwShareMode*/ 0, /*LPSECURITY_ATTRIBUTES lpSecurityAttributes*/ NULL, /*DWORD dwCreationDisposition*/ OPEN_EXISTING, /*DWORD dwFlagsAndAttributes*/ 0, /*HANDLE hTemplateFile*/ NULL ); if (file_handle == INVALID_HANDLE_VALUE) return result; // NOTE: Allocate buffer // ========================================================================= uint64_t file_size = (uint64_t)file_attrib_data.nFileSizeHigh << 32 | (uint64_t)file_attrib_data.nFileSizeLow << 0; S86_ASSERT(file_size < (DWORD)-1); char *buffer = VirtualAlloc( /*LPVOID lpAddress*/ NULL, /*SIZE_T dwSize*/ file_size, /*DWORD flAllocationType*/ MEM_COMMIT | MEM_RESERVE, /*DWORD flProtect*/ PAGE_READWRITE ); if (!buffer) goto end; // NOTE: Read file to buffer // ========================================================================= DWORD bytes_read = 0; BOOL read_file_result = ReadFile( /*HANDLE hFile*/ file_handle, /*LPVOID lpBuffer*/ buffer, /*DWORD nNumberOfBytesToRead*/ S86_CAST(DWORD)file_size, /*LPDWORD lpNumberOfBytesRead*/ &bytes_read, /*LPOVERLAPPED lpOverlapped*/ NULL ); // NOTE: Handle read result // ========================================================================= if (read_file_result == 0) { VirtualFree(buffer, 0, MEM_RELEASE); } else { result.data = buffer; result.size = file_size; } end: CloseHandle(file_handle); return result; }; void S86_FileFree(S86_Buffer buffer) { if (S86_BufferIsValid(buffer)) VirtualFree(buffer.data, 0, MEM_RELEASE); } void S86_PrintLn(S86_Str8 string) { if (s86_globals.stdout_handle == NULL) { s86_globals.stdout_handle = GetStdHandle(STD_OUTPUT_HANDLE); DWORD mode = 0; BOOL get_console_mode_result = GetConsoleMode( /*HANDLE hConsoleHandle*/ s86_globals.stdout_handle, /*LPDWORD lpMode*/ &mode ); s86_globals.write_to_console = get_console_mode_result != 0; } S86_ASSERT(string.size < S86_CAST(DWORD)-1); if (s86_globals.write_to_console) { DWORD chars_written = 0; WriteConsoleA(s86_globals.stdout_handle, string.data, (DWORD)string.size, &chars_written, NULL); WriteConsoleA(s86_globals.stdout_handle, "\n", 1, &chars_written, NULL); } else { DWORD bytes_written = 0; WriteFile(s86_globals.stdout_handle, string.data, (DWORD)string.size, &bytes_written, NULL); WriteFile(s86_globals.stdout_handle, "\n", 1, &bytes_written, NULL); } } void S86_PrintLnFmt(char const *fmt, ...) { va_list args, args_copy; va_start(args, fmt); va_copy(args_copy, args); int string_size = vsnprintf(NULL, 0, fmt, args_copy); va_end(args_copy); char buffer[8192]; S86_ASSERT(string_size >= 0 && string_size < S86_ARRAY_UCOUNT(buffer)); if (string_size) { vsnprintf(buffer, sizeof(buffer), fmt, args); S86_Str8 string = {.data = buffer, .size = string_size}; S86_PrintLn(string); } va_end(args); } typedef enum S86_ModEncoding S86_ModEncoding; enum S86_ModEncoding { S86_ModEncoding_MemModeNoDisplace = 0b00, S86_ModEncoding_MemMode8 = 0b01, S86_ModEncoding_MemMode16 = 0b10, S86_ModEncoding_RegisterMode = 0b11, }; typedef enum S86_InstructionType S86_InstructionType; enum S86_InstructionType { S86_InstructionType_MOVRegOrMemToOrFromReg, S86_InstructionType_MOVImmediateToRegOrMem, S86_InstructionType_MOVImmediateToReg, S86_InstructionType_MOVMemToAccum, S86_InstructionType_MOVAccumToMem, S86_InstructionType_MOVRegOrMemToSegReg, S86_InstructionType_MOVSegRegToRegOrMem, S86_InstructionType_Count, }; typedef struct S86_Instruction S86_Instruction; struct S86_Instruction { uint8_t op_mask0; uint8_t op_bits0; uint8_t op_mask1; uint8_t op_bits1; } S86_INSTRUCTIONS[S86_InstructionType_Count] = { [S86_InstructionType_MOVRegOrMemToOrFromReg] = {.op_mask0 = 0b1111'1100, .op_bits0 = 0b1000'1000, .op_mask1 = 0b0000'0000, .op_bits1 = 0b0000'0000}, [S86_InstructionType_MOVImmediateToRegOrMem] = {.op_mask0 = 0b1111'1110, .op_bits0 = 0b1100'0110, .op_mask1 = 0b0011'1000, .op_bits1 = 0b0000'0000}, [S86_InstructionType_MOVImmediateToReg] = {.op_mask0 = 0b1111'0000, .op_bits0 = 0b1011'0000, .op_mask1 = 0b0000'0000, .op_bits1 = 0b0000'0000}, [S86_InstructionType_MOVMemToAccum] = {.op_mask0 = 0b1111'1110, .op_bits0 = 0b1010'0000, .op_mask1 = 0b0000'0000, .op_bits1 = 0b0000'0000}, [S86_InstructionType_MOVAccumToMem] = {.op_mask0 = 0b1111'1110, .op_bits0 = 0b1010'0010, .op_mask1 = 0b0000'0000, .op_bits1 = 0b0000'0000}, [S86_InstructionType_MOVRegOrMemToSegReg] = {.op_mask0 = 0b1111'1111, .op_bits0 = 0b1000'1110, .op_mask1 = 0b0010'0000, .op_bits1 = 0b0000'0000}, [S86_InstructionType_MOVSegRegToRegOrMem] = {.op_mask0 = 0b1111'1111, .op_bits0 = 0b1000'1100, .op_mask1 = 0b0010'0000, .op_bits1 = 0b0000'0000}, }; int main(int argc, char **argv) { if (argc != 2) { S86_PrintLn(S86_STR8("usage: sim8086.exe ")); return -1; } S86_Str8 const REGISTER_FIELD_ENCODING[2][8] = { [0b0] = { S86_STR8("al"), S86_STR8("cl"), S86_STR8("dl"), S86_STR8("bl"), S86_STR8("ah"), S86_STR8("ch"), S86_STR8("dh"), S86_STR8("bh"), }, [0b1] = { S86_STR8("ax"), S86_STR8("cx"), S86_STR8("dx"), S86_STR8("bx"), S86_STR8("sp"), S86_STR8("bp"), S86_STR8("si"), S86_STR8("di"), }, }; char const *file_path = argv[1]; S86_Buffer buffer = S86_FileRead(file_path); if (!S86_BufferIsValid(buffer)) { S86_PrintLnFmt("File read failed [path=\"%s\"]", argv[1], buffer.size); return -1; } S86_PrintLn(S86_STR8("bits 16")); S86_BufferIterator buffer_it = S86_BufferIteratorInit(buffer); while (S86_BufferIteratorHasMoreBytes(buffer_it)) { char op_code_bytes[2] = {0}; size_t op_code_size = 0; op_code_bytes[op_code_size++] = S86_BufferIteratorNextByte(&buffer_it); // NOTE: Match the assembly bytes to the desired instruction // ===================================================================== S86_InstructionType instruction_type = S86_InstructionType_Count; S86_Instruction const *instruction = NULL; for (size_t instruction_index = 0; instruction_type == S86_InstructionType_Count && instruction_index < S86_ARRAY_UCOUNT(S86_INSTRUCTIONS); instruction_index++) { S86_Instruction *item = S86_INSTRUCTIONS + instruction_index; // NOTE: Check first instruction byte // ================================================================= if ((op_code_bytes[0] & item->op_mask0) != item->op_bits0) continue; // NOTE Check multi-byte instruction // ================================================================= // If the matched instruction has a bit mask for the 2nd byte, this // is a multi-byte instruction. Check if the 2nd byte checks out. bool instruction_matched = true; if (item->op_mask1) { // TODO: This assumes the iterator is valid op_code_bytes[op_code_size++] = S86_BufferIteratorNextByte(&buffer_it); instruction_matched = (op_code_bytes[op_code_size - 1] & item->op_mask1) == item->op_bits1; } if (instruction_matched) { instruction_type = instruction_index; instruction = item; } } // NOTE: Disassemble bytes to assembly mnemonics // ================================================================= S86_ASSERT(op_code_size > 0 && op_code_size <= S86_ARRAY_UCOUNT(op_code_bytes)); S86_ASSERT(instruction_type != S86_InstructionType_Count && "Unknown instruction"); switch (instruction_type) { case S86_InstructionType_MOVRegOrMemToOrFromReg: { // NOTE: Instruction does not have opcode bits in the 2nd byte S86_ASSERT(op_code_size == 1); op_code_bytes[op_code_size++] = S86_BufferIteratorNextByte(&buffer_it); uint8_t d = (op_code_bytes[0] & 0b0000'0010) >> 1; uint8_t w = (op_code_bytes[0] & 0b0000'0001) >> 0; uint8_t mod = (op_code_bytes[1] & 0b1100'0000) >> 6; uint8_t reg = (op_code_bytes[1] & 0b0011'1000) >> 3; uint8_t rm = (op_code_bytes[1] & 0b0000'0111) >> 0; S86_ASSERT(d < 2); S86_ASSERT(w < 2); S86_ASSERT(mod < 4); S86_ASSERT(reg < 8); S86_ASSERT(rm < 8); if (mod == 0b11) { // NOTE: Register-to-register move // ========================================================= S86_Str8 src_op = REGISTER_FIELD_ENCODING[w][d ? rm : reg]; S86_Str8 dest_op = REGISTER_FIELD_ENCODING[w][d ? reg : rm]; S86_PrintLnFmt("mov %.*s, %.*s", S86_STR8_FMT(dest_op), S86_STR8_FMT(src_op)); } else { // NOTE: Memory mode w/ effective address calculation // ========================================================= uint16_t displacement = 0; if (mod == 0b01) { // Mem mode 8 bit displacement displacement = S86_BufferIteratorNextByte(&buffer_it); } else if (mod == 0b10 || (mod == 0b00 && rm == 0b110)) { // Mem mode 16 bit displacement uint8_t disp_lo = S86_BufferIteratorNextByte(&buffer_it); uint8_t disp_hi = S86_BufferIteratorNextByte(&buffer_it); displacement = (uint16_t)disp_lo << 0 | (uint16_t)disp_hi << 8; } else { S86_ASSERT(mod == 0b00 /*Mem mode (no displacement)*/); if (mod == 0b00) S86_ASSERT(rm != 0b110 && "16 bit displacement should be handled in (mod == 0b10) branch"); } // NOTE: Generate the effective address calculation string // ========================================================= char effective_addr_buffer[64] = {0}; int effective_addr_size = 0; effective_addr_buffer[effective_addr_size++] = '['; if (rm == 0b110) { effective_addr_buffer[effective_addr_size++] = 'b'; effective_addr_buffer[effective_addr_size++] = 'p'; if (displacement) { effective_addr_size += snprintf(effective_addr_buffer + effective_addr_size, sizeof(effective_addr_buffer) - effective_addr_size, " + %u", displacement); } } else { S86_Str8 base_calc = {0}; switch (rm) { case 0b000: base_calc = S86_STR8("bx + si"); break; case 0b001: base_calc = S86_STR8("bx + di"); break; case 0b010: base_calc = S86_STR8("bp + si"); break; case 0b011: base_calc = S86_STR8("bp + di"); break; case 0b100: base_calc = S86_STR8("si"); break; case 0b101: base_calc = S86_STR8("di"); break; case 0b111: base_calc = S86_STR8("bx"); break; default: S86_ASSERT(!"Invalid rm value, must be 3 bits"); break; } memcpy(effective_addr_buffer + effective_addr_size, base_calc.data, base_calc.size); effective_addr_size += S86_CAST(int)base_calc.size; if (mod == 0b01 || mod == 0b10) { effective_addr_size += snprintf(effective_addr_buffer + effective_addr_size, sizeof(effective_addr_buffer) - effective_addr_size, " + %u", displacement); } } effective_addr_buffer[effective_addr_size++] = ']'; // NOTE: Disassemble // ========================================================= S86_Str8 effective_addr = { .data = effective_addr_buffer, .size = effective_addr_size }; S86_Str8 dest_op = d ? REGISTER_FIELD_ENCODING[w][reg] : effective_addr; S86_Str8 src_op = d ? effective_addr : REGISTER_FIELD_ENCODING[w][reg]; S86_PrintLnFmt("mov %.*s, %.*s", S86_STR8_FMT(dest_op), S86_STR8_FMT(src_op)); } } break; case S86_InstructionType_MOVImmediateToRegOrMem: { S86_ASSERT(op_code_size == 2); #if 0 uint8_t w = (op_code_bytes[0] & 0b0000'0001) >> 0; uint8_t mod = (op_code_bytes[1] & 0b1100'0000) >> 6; uint8_t rm = (op_code_bytes[1] & 0b0000'0111) >> 0; #endif S86_ASSERT(!"Unhandled instruction"); } break; case S86_InstructionType_MOVImmediateToReg: { // NOTE: Parse opcode control bits // ============================================================= S86_ASSERT(op_code_size == 1); uint8_t w = (op_code_bytes[0] & 0b0000'1000) >> 3; uint8_t reg = (op_code_bytes[0] & 0b0000'0111) >> 0; // NOTE: Parse data payload // ============================================================= uint16_t data = S86_BufferIteratorNextByte(&buffer_it); if (w) { // 16 bit data uint8_t data_hi = S86_BufferIteratorNextByte(&buffer_it); data |= (uint16_t)(data_hi) << 8; } // NOTE: Disassemble // ============================================================= S86_Str8 dest_register = REGISTER_FIELD_ENCODING[w][reg]; S86_PrintLnFmt("mov %.*s, %d", S86_STR8_FMT(dest_register), (int16_t)data); } break; case S86_InstructionType_MOVMemToAccum: { S86_ASSERT(!"Unhandled instruction"); } break; case S86_InstructionType_MOVAccumToMem: { S86_ASSERT(!"Unhandled instruction"); } break; case S86_InstructionType_MOVRegOrMemToSegReg: { S86_ASSERT(!"Unhandled instruction"); } break; case S86_InstructionType_MOVSegRegToRegOrMem: { S86_ASSERT(!"Unhandled instruction"); } break; default: { S86_ASSERT(!"Unknown instruction"); } break; } } }