mith College Computer Science CSC231 - Assembly Week #4 Dominique Thiébaut

Transcription

1 mith College Computer Science CSC231 - Assembly Week #4 Dominique Thiébaut dthiebaut@smith.edu

2 Homework Solutions

3 Outline Review Hexdump Pentium Data Registers 32-bit, 16-bit and 8-bit quantities (registers & memory locations)

4 Review

5 Hexdump

6 Hexdump These are the numbers that get loaded into RAM when a program runs.

7 Hexdump The code segment always starts first, at offset

8 Hexdump b are "op codes" or "operation codes" These particular bytes represent "mov eax, 4"

9 Hexdump 11 section.data C6C6F Hello db "Hello there!", 10, A0A 14 HelloLen equ $-Hello section.text 17 global _start 18 _start: ;;; print message B mov eax, 4 ; write BB mov ebx, 1 ; stdout A B9[ ] mov ecx, Hello ; F BA0E mov edx, HelloLen ; CD80 int 0x ;;; exit BB mov ebx, B B mov eax, CD80 int 0x80 b are "op codes" or "operation codes" These particular bytes represent "mov eax, 4"

10 Hexdump The data segment follows the code segment

11 Hexdump The data segment follows the code segment Strings can easily be recognized

12 The Pentium Data Registers

13 Pentium Registers eax ebx ecx edx

14 Pentium Registers 32 bits = 4 bytes eax ebx ecx edx

15 Pentium Registers 11 section.data C6C6F Hello db "Hello there!", 10, A0A 14 HelloLen equ $-Hello section.text 17 global _start 18 _start: ;;; print message B mov eax, 4 ; write BB mov ebx, 1 ; stdout A B9[ ] mov ecx, Hello ; F BA0E mov eax ;;; exit edx, HelloLen ; CD80 int 0x BB mov ebx, B B mov eax, CD80 int 0x80 mov eax, 4 ebx ecx edx B8

16 Pentium Registers mov eax, 4 eax ebx ecx edx B8

17 Pentium Registers eax mov ebx, eax ebx ecx edx

18 Pentium Registers x dd 5 eax ebx x mov ecx, dword[x] ecx edx

19 Pentium Registers x dd 5 eax ebx x add ecx, 1 ecx mov dword[x] edx

20 Code this in assembly: Exercise int z, x = 3, y; y = 10; z = x*2 + y;

21 Pentium Registers The Pentium data registers can also be used to operate on 16-bit quantities (words), as well as 8- bit quantities (bytes)

22 Why 16-bit quantities?

23 Pentium Registers eax ebx ecx edx ax bx cx dx

24 Pentium Registers a dw 9 mov ax, 1 mov bx, word[a] mov cx, bx mov dx, ax eax ebx ecx edx ax bx cx dx

25 Pentium Registers eax ebx ecx edx ah al bh bl ch cl dh dl ax bx cx dx

26 Think of ah and al as boxes inside a bigger one called ax, and ax as half of a bigger box still, called eax.

27 Declaring Variables

28 db, dw, dd db: define byte storage dw: define word storage dd: define double-word storage

29 Examples: db msg db "Hello", 10 a db 0 b db 'H' ; also 72 or 0x48 c db 255 d db 0x80

30 Examples: dw x dw 0 y dw 1 z dw 255 t dw 0x1234

31 We stopped here last time

32 Outline Printing Ints and Strings (needed for HW #4) Difference between binary and text files dd Arithmetic with 8, 16, and 32 bit variables. Step-by-Step Execution of a Program

33 Printing Ints getcopy hw4_1_skel.asm

34 Examples: dd alpha dd 0 beta dd 255 gamma dd 0x

35 Summary of important concepts just seen Numbers Op Codes Machine Language Hexadecimal Executable Files

36 More Examples of The mov Instruction mov dest, source

37 section.data lf db 10 ch db 0 a dw 0x1234 b dw 0 x dd 0 y dd 0x Exercises section.text ; put lf in al eax ebx ecx edx ah al bh bl ch cl dh dl ax bx cx dx

38 section.data lf db 10 ch db 0 a dw 0x1234 b dw 0 x dd 0 y dd 0x Exercises section.text ; put al in ch eax ah al ax ebx bh bl bx ecx ch cl cx edx dh dl dx

39 section.data lf db 10 ch db 0 a dw 0x1234 b dw 0 x dd 0 y dd 0x Exercises section.text ; put a in bx eax ah al ax ; put bx in b ebx bh bl bx ; put bx in ax ecx ch cl cx ; put 0 in cx edx dh dl dx

40 section.data lf db 10 ch db 0 a dw 0x1234 b dw 0 x dd 0 y dd 0x Exercises section.text ; put x in eax eax ah al ax ; put y in ecx ebx bh bl bx ; put ecx in edx ecx ch cl cx ; put ex into y edx dh dl dx

41 section.data lf db 10 ch db 0 a dw 0x1234 b dw 0 x dd 0 y dd 0x Exercises section.text ; put 0 in ah eax ah al ax ; put 3 in cx ebx bh bl bx ; put 5 in edx ecx ch cl cx ; put 0x into eax edx dh dl dx

42 We understand mov!

43 add & sub instructions add dest, source sub dest, source

44 section.data lf db 10 ch db 0 a dw 0x1234 b dw 0 x dd 0 y dd 0x Examples section.text ; add 3 to ch eax ah al ax ; subtract 100 from b ebx bh bl bx ; add -1 to edx ecx ch cl cx ; subtract x from y edx dh dl dx

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46 We stopped here last time (10/3/18)