A crash course in MIPS assembly programming

Transcription

1 A crash course in MIPS assembly programming Computer Architecture 1DT016 distance Fall Per Foyer Mail: 1

2 MIPS Our processor Microprocessor without Interlocking Pipe Stages 2

3 Where in the machine now? Level 5 Problem-oriented language level Translation (compiler) Level 4 Assembly language level Translation (assembler) Level 3 Operating system machine level int addmul( int t ) { return (t + 2) * 2; } addmul: addi $r1, $zero, 2 mul $r1, $r1, 2 jr $ra li $v0, 4 syscall Partial interpretation (OS) Level 2 Conventional machine level Level 1 Microprogramming level Level 0 Digital Logic Level Interpretation (microprogram) 0x x c 0x03E Executed by hardware 3

4 What do we need to know? To program a MIPS, or any processor for that matter, in assembly language we need to know: How many registers are there in the CPU? How does the memory map look like? What assembler instructions does the CPU have? Arithmetic, logic, shift and rotate, jump, What do the addressing modes look like? (in what ways can we reference memory) What assembler directives are there? 4

5 MIPS register names 5

6 MIPS register file 6

7 MIPS registers and usage convention 7

8 MIPS memory 8

9 MIPS memory map 9

10 MIPS CPU blocks Von Neumann? Why or why not? 10

11 MIPS addressing modes 11

12 Registers and arithmetic 12

13 The anatomy (ISA) of a MIPS instruction Machine language: The binary representation for instructions. ISA: Instruction Set Architecture Fixed size (32-bit) instructions Only 3 instruction formats Limited sized immediate fields. Strict Load and Store architecture. RISC! Studying MIPS machine language will also reveal some restrictions in the instruction set architecture (ISA) 13

14 MIPS: register-to-register 14

15 The R-type format Shamt = SHift AMounT 15

16 The I-type format 16

17 The J-type format 17

18 The Arithmetic Logic Unit (ALU) A+B Arithmetic A B A*B A/B A<B A == B Logic ALU A AND B A OR B A XOR B 18

19 Basic arithmetic and logic 19

20 Immediate operands 20

21 Loading and storing bytes 21

22 Loading and storing words 22

23 Limitations: Loads and stores 23

24 Larger constants 24

25 Memory alignment 25

26 Data flow in MIPS 26

27 Function control flow in MIPS 27

28 Pseudo-instructions 28

29 Assembler directives.align Align next data item on specified byte boundary (0=byte, 1=half, 2=word, 3=double).ascii Store the string in the Data segment but do not add null terminator.asciiz Store the string in the Data segment and add null terminator.byte Store the listed value(s) as 8 bit bytes.data Subsequent items stored in Data segment at next available address.end_macro End macro definition..eqv Substitute second operand for first. First operand is symbol, second See.macro operand is expression (like #define).extern Declare the listed label and byte length to be a global data field.globl Declare the listed label(s) as global to enable referencing from other files.half Store the listed value(s) as 16 bit halfwords on halfword boundary.include Insert the contents of the specified file..macro Begin macro definition..set Set assembler variables..space Reserve the next specified number of bytes in Data segment.text Subsequent items (instructions) stored in Text segment at next available address.word Store the listed value(s) as 32 bit words on word boundary Put filename in quotes. See.end_macro Currently ignored but included for SPIM compatability 29

30 SPIM / MARS system calls Example 30

31 Demo: Hello world in Mars After assembling, how do the instructions look like? # helloworld.s # # Print out "Hello World" How about the memory map?.data msg:.asciiz "Hello World".text.globl main main: li $v0, 4 # syscall 4 (print_str) la $a0, msg # argument: string syscall # print the string jr $ra # retrun to caller 31

32 Endianness First word: lleh Big endian Byte 1 Byte 2 Byte 3 Byte 4 Byte 3 Byte 1 Little endian Byte 4 Byte 3 Lowest memory address 32

33 Branches Short conditional jumps 33

34 Larger branch constants 34

35 Nested functions 35

36 Spilling registers 36

37 Who saves the registers? 37

38 The caller? 38

39 The routine that s called? 39

40 or both? 40

41 Register spilling convention 41

42 Demo: stradd.s Simple program that demonstrates single nested functions following the register spilling convention. Uses SPIM / MARS syscalls Test setting breakpoints Test single backstepping 42

43 Function calls and stacks 43

44 Stacks and function calls 44

45 The MIPS stack 45

46 Pushing elements 46

47 Accessing and popping elements 47

48 Summary: Calls, Registers and Stack Function (subroutine) calls in MIPS: Functions are called using jal, passing arguments in registers $a0-$a3 Functions place results in registers $v0-$v1 and return using $ra Assembly programmers must follow many conventions. Nothing prevents a rogue program from overwriting registers or stack memory used by some other function. 48

49 Decoding Machine Language A form of reverse engineering, Disassembling machine code 49

50 Finito la musica! 50