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Chapter 4: Using the Assembler

Chapter 4: Using the Assembler. Slides to Accompany Assembly Language for Intel-Based Computers, Third Edition. Overview. More about the assembler and linker Operators and expressions JMP and LOOP instructions Indirect addressing Debugging workshop More 80386 and 80486 instructions

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Chapter 4: Using the Assembler

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  1. Chapter 4: Using the Assembler Slides to Accompany Assembly Language for Intel-Based Computers, Third Edition Irvine, Kip R. Assembly Language For Intel-Based Computers

  2. Overview • More about the assembler and linker • Operators and expressions • JMP and LOOP instructions • Indirect addressing • Debugging workshop • More 80386 and 80486 instructions • Using a link library Irvine, Kip R. Assembly Language For Intel-Based Computers

  3. More About the Assembler and Linker Topics: • Source Listing • Map File • Memory models • Overlapping segments • Target processor directives Irvine, Kip R. Assembly Language For Intel-Based Computers

  4. Source Listing • Exchange Two Variables                       (SAMPLE.ASM) • 3 0000 .model small • 4 0000 .stack 100h • 5 • 6 0000 .code • 7 0000 main proc • 8 0000  B8 0000s mov   ax,@data ; initialize DS register • 9 0003  8E D8 mov   ds,ax • 10 0005 swap: • 11 0005  A0 0000r mov   al,value1 ; load the AL register • 12 0008  86 06 0001r xchg  al,value2 ; exchange AL, value2 • 13 000C  A2 0000r mov   value1,al ; store new value of AL • 14 000F  B8 4C00 mov   ax,4C00h ; return to DOS • 15 0012  CD 21 int   21h • 16 0014 main endp • 17 • 18 0014 .data • 19 0000  0A value1  db 0Ah • 20 0001  14 value2  db 14h • 21 • 22 end main Irvine, Kip R. Assembly Language For Intel-Based Computers

  5. Map File Segments always begin on even-paragraph boundaries. • Start Stop Length Name Class • 00000H   00013H  00014H  _TEXT CODE • 00020H   00021H  00002H    _DATA      DATA • 00030H   0012FH  00100H    STACK      STACK • Program entry point at 0000:0000 Irvine, Kip R. Assembly Language For Intel-Based Computers

  6. Memory Models Irvine, Kip R. Assembly Language For Intel-Based Computers

  7. Overlapping Segments Start Stop Length Name Class 00000 00010 00011 _TEXT CODE 00020 0002F 00010 _DATA DATA 00030 0012F 00100 STACK STACK Program entry point at 0000:0000 Irvine, Kip R. Assembly Language For Intel-Based Computers

  8. Target Processor Directives Irvine, Kip R. Assembly Language For Intel-Based Computers

  9. Assembler Operators Irvine, Kip R. Assembly Language For Intel-Based Computers

  10. Assembler Operators(continued) Irvine, Kip R. Assembly Language For Intel-Based Computers

  11. Operator Precedence Table Irvine, Kip R. Assembly Language For Intel-Based Computers

  12. Offset, Seg, Ptr, Label, and Even • OFFSET returns the 16-bit address (offset) of a label • SEG returns the segment portion of a label's address • PTR overrides the default size of an operand • LABEL redefines the size attribute of a data label • EVEN aligns the next instruction to a 16-bit boundary • EVENDATA aligns the next data label on a 16-bit boundary Irvine, Kip R. Assembly Language For Intel-Based Computers

  13. TYPE and SIZE Operators • TYPE • returns the size, in bytes of a single element of a data label (variable) • LENGTH • returns a count of the number of individual elements in a data label that uses the DUP operator • SIZE • returns the product of TYPE * LENGTH Irvine, Kip R. Assembly Language For Intel-Based Computers

  14. TYPE TYPE returns the size attribute: .data myByte db 1,2,3,4 myWord dw 1000h,2000h,3000h myDouble dd 12345678h myQuad dq 1,2,3 .code mov ax,TYPE myByte ; 1 mov ax,TYPE myWord ; 2 mov ax,TYPE myDouble ; 4 mov ax,TYPE myQuad ; 8 Irvine, Kip R. Assembly Language For Intel-Based Computers

  15. LENGTH Returns a count of the number of individual elements in a data label that uses the DUP operator: .data myByte db 20 dup(?) myWord dw 5 dup(0) .code mov ax,LENGTH myByte ; 20 mov ax,LENGTH myWord ; 5 Irvine, Kip R. Assembly Language For Intel-Based Computers

  16. SIZE Returns TYPE multiplied by LENGTH: .data myByte db 20 dup(?) myWord dw 5 dup(0) .code mov ax,SIZE myByte ; 20 (20 * 1) mov ax,SIZE myWord ; 10 (5 * 2) Irvine, Kip R. Assembly Language For Intel-Based Computers

  17. JMP and LOOP Instructions • JMP is an unconditional jump to a code label • LOOP creates a counting loop, using CX as the default counter • LOOPD uses ECX as the counter register • LOOPW uses CX as the counter register • (only necessary in 32-bit mode programming) Irvine, Kip R. Assembly Language For Intel-Based Computers

  18. JMP: Distance Modifiers • JMP SHORT destination • +/- 127 bytes • JMP NEAR PTR destination • same code segment • (default in the small and compact memory models) • JMP FAR PTR destination • different code segment • (default in the large, medium, and huge memory models) Irvine, Kip R. Assembly Language For Intel-Based Computers

  19. JMP Example Label1: . . jmp Label1 Unconditional Transfer of control to a label: Irvine, Kip R. Assembly Language For Intel-Based Computers

  20. LOOP Instruction • Automatically uses CX as the counter • decrements it automatically • If CX > 0, LOOP transfers control to a label • otherwise, excecution drops through Irvine, Kip R. Assembly Language For Intel-Based Computers

  21. LOOP Example Task: sum the integers { 1,2,3,4,5 } mov cx,5 ; loop counter mov bx,1 ; value to be added mov ax,0 ; holds the sum L1: add ax,bx inc bx Loop L1 ; AX=000F, BX=0006, CX=0000 Irvine, Kip R. Assembly Language For Intel-Based Computers

  22. Indirect Addressing • Indirect Operands [si]. [di], [bx], [bp] • Based and Indexed Operands array[si], array[di], array[bx] • Base-Index Operands [bx+si], [bx+di] • Base-Index with Displacement array[bx+si], array[bx+di] Irvine, Kip R. Assembly Language For Intel-Based Computers

  23. Indirect Operand Example .data aString db "ABCDEFG“ .code mov bx,offset aString add bx,5 mov dl,[bx] Irvine, Kip R. Assembly Language For Intel-Based Computers

  24. Adding 8-bit Integers .data aList db 10h,20h,30h sum   db 0 .code mov bx,offset aList    mov al,[bx] ; AL = 10h inc bx add al,[bx] ; AL = 30h inc bx add al,[bx] ; AL = 60h mov si,offset sum ; get offset of sum mov [si],al ; store the sum If you want to paste a code example such as this into a program, remember that the code segment must always begin with the following statements: mov ax,@data mov ds,ax Irvine, Kip R. Assembly Language For Intel-Based Computers

  25. Adding 16-bit Integers .data wordList dw 1000h,2000h,3000h, 0 .code mov bx,offset wordList mov ax,[bx] ; first number add ax,[bx+2] ; second number add ax,[bx+4] ; third number mov [bx+6],ax ; store the sum Irvine, Kip R. Assembly Language For Intel-Based Computers

  26. 32-Bit Registers The .386 directive permits any of the following registers to be used as indirect operands: EAX, EBX, ECX, EDX, ESI, EDI, EBP .386 mov ax,[ebx+3] mov dl,string[edx] mov ecx,[esi] mov ebx,[eax] Irvine, Kip R. Assembly Language For Intel-Based Computers

  27. Displaying a String .data string db "This is a string." COUNT = ($–string)  ; calculate string length .code mov   cx,COUNT ; loop counter mov   si,offset string  L1:  mov   ah,2 ; DOS function: display char mov   dl,[si] ; get character from array int   21h ; display it now inc   si ; point to next character Loop  L1 ; decrement CX, repeat until 0 Irvine, Kip R. Assembly Language For Intel-Based Computers

  28. Summing an Integer Array .data intarray dw 0100h,0200h,0300h,0400h COUNT = ($ – intarray) / (TYPE intarray) .code mov   ax,0 ; zero accumulator mov   di,offset intarray ; address of array mov   cx,COUNT ; loop counter L1:  add   ax,[di] ; add an integer add   di,TYPE intarray ; point to next integer Loop  L1 ; repeat until CX = 0 Irvine, Kip R. Assembly Language For Intel-Based Computers

  29. Based and Indexed Operands The microsoft assembler permits the same address expression to be notated in various ways: Irvine, Kip R. Assembly Language For Intel-Based Computers

  30. Two-Dimensional Array Example Each row of this table contains five bytes. BX points to the beginning of the second row: .data ROWSIZE = 5 array  db  2h, 16h, 4h, 22h, 13h db 19h, 42h, 64h, 44h, 88h .code mov bx,ROWSIZE mov al,array[bx]     ; AL = 19h Irvine, Kip R. Assembly Language For Intel-Based Computers

  31. Based-Index Operands Add the value of a base register to an index register, producing an effective address of 0157: BX = 0155, SI = 0002 Example... Irvine, Kip R. Assembly Language For Intel-Based Computers

  32. Base-Index Example .data ROWSIZE = 5 array  db  10h, 20h, 30h, 40h, 50h db 60h, 70h, 80h, 90h,0A0h        db 0B0h,0C0h,0D0h,0E0h,0F0h .code mov  bx,offset array ; point to the array at 0150 add  bx,ROWSIZE ; choose second row mov  si,2 ; choose third column mov  al,[bx + si] ; get the value at 0157 Irvine, Kip R. Assembly Language For Intel-Based Computers

  33. Base-Index with Displacement .data ROWSIZE = 5 array db  10h, 20h, 30h, 40h, 50h db 60h, 70h, 80h, 90h,0A0h       db 0B0h,0C0h,0D0h,0E0h,0F0h .code mov bx,ROWSIZE ; row 1 mov si,2 ; column 2 mov dl,array[bx + si] ; DL = 80h Irvine, Kip R. Assembly Language For Intel-Based Computers

  34. Debugging Workshop Irvine, Kip R. Assembly Language For Intel-Based Computers

  35. Mismatching Operand Sizes 1:    title Mismatching Operand Sizes  2:     3:    .model small 4:    .stack 100h 5:    .code 6:    main proc 7: mov   ax,@data 8: mov   ds,ax 9: mov   ax,value1     10: mov   ah,value2 11: mov   ax,4C00h 12: int   21h 13: main endp 14: 15:   .data 16:  value1   db    0Ah 17:  value2   dw    1000h 18:  end  main  (9): warning A4031: Operand types must match (10): warning A4031: Operand types must match Irvine, Kip R. Assembly Language For Intel-Based Computers

  36. Miscellaneous Errors  1:   title Miscellaneous Errors Program  2:     3:   .model small  4:   .stack 100h  5:   .code  6:   main proc  7:        mov   ax,@data  8:        mov   ds,ax  9:        mov   ax,bx * cx 10:        mov   bx,value1 * 2 11:        mov   byte ptr value3,al 12:        mov   cx,ax 13:        mov   cs,ds 14:        mov   ax,4C00h 15:        int   21h 16:    main endp 17:   .data 18:   value1   db    0Ah 19:   value2   db    14h 20:   value3   dw    1000h 21:   end main Irvine, Kip R. Assembly Language For Intel-Based Computers

  37. Intel386 and Intel486 Instructions • MOVZX - Move with zero-extend • moves 8-bit operand into a 16-bit register, fills upper bits with zeros • moves 16-bit operand into a 32-bit register, fills upper bits with zeros • MOVSX - Move with sign-extend • moves 8-bit operand into a 16-bit register, sign extends into upper bits • moves 16-bit operand into a 32-bit register, sign extends into upper bits Irvine, Kip R. Assembly Language For Intel-Based Computers

  38. MOVZX and MOVSX Examples .data var16 dw 1234h var8 db -2 ; FEh .code mov bl,22h movzx ax,bl ; AX = 0022h movzx edx,var16 ; EDX = 00001234h movsx cx,var8 ; CX = FFFEh Irvine, Kip R. Assembly Language For Intel-Based Computers

  39. XADD Instruction .code mov   ax,1000h  mov   bx,2000h ; AX = 1000h, BX = 2000h xadd  ax,bx ; AX = 3000h, BX = 1000h XADD op-left, op-right Adds operands and stores sum in op-left. Saves the starting value of op-left and stores it in op-right. Irvine, Kip R. Assembly Language For Intel-Based Computers

  40. Using a Link Library • IRVINE.LIB is supplied with the book's sample programs • Complete list of procedures is in Appendix E • EXTRN directive • notifies the assembler that a procedure, constant, or variable is located outside the current program module • EXTRN name:type Irvine, Kip R. Assembly Language For Intel-Based Computers

  41. Data Types for the EXTRN Directive Irvine, Kip R. Assembly Language For Intel-Based Computers

  42. Selected Procedures in the Link Library Irvine, Kip R. Assembly Language For Intel-Based Computers

  43. Selected Procedures in the Link Library Irvine, Kip R. Assembly Language For Intel-Based Computers

  44. Link Library Demo Program Title Link Library Demo Program        (lnkdemo.asm) ; This program calls various I/O procedures ; in the link library. .model small .stack 100h WhiteOnBlue = 1Fh GreetingLoc = 0400h .data greeting db "Link Library Demo Program" db 0dh,0ah,0dh,0ah db "What is your name? ",0   numberPrompt db 0dh,0ah db "Please enter a 16–bit integer: ",0 userName db 50 dup(0) pressAnyKey  db 0dh,0ah,0dh,0ah db "Press any key...",0 .code extrn Clrscr:proc, Crlf:proc, Gotoxy:proc, \   Readint:proc, Readstring:proc, Scroll:proc, \   Readkey:proc, Writeint:proc, Writestring:proc Irvine, Kip R. Assembly Language For Intel-Based Computers

  45. Link Library Demo, continued main proc    mov ax,@data    mov ds,ax ; Clear the screen, scroll a blue window.    call Clrscr    mov  cx,0400h ; upper–left corner    mov  dx,0B28h ; lower–right corner    mov  bh,WhiteOnBlue    call Scroll ; Display a greeting and ask for the  ; user’s name.    mov  dx,GreetingLoc    call Gotoxy    mov  dx,offset greeting    call Writestring    mov  dx,offset userName    call Readstring Irvine, Kip R. Assembly Language For Intel-Based Computers

  46. Link Library Demo, continued ; Ask the user to enter a signed decimal integer. ; Redisplay the number in hexadecimal and binary.    mov  dx,offset numberPrompt    call Writestring    call Readint ; input an integer    call Crlf    mov  bx,16 ; display in hexadecimal    call Writeint    call Crlf    mov  bx,2 ; display in binary    call Writeint       mov  dx,offset pressAnyKey    call Writestring    call Readkey    call Clrscr    mov ax,4c00h ; end program    int 21h main endp    end main Irvine, Kip R. Assembly Language For Intel-Based Computers

  47. Generating Random Integers Generate 20 random integers between 0 and 999. .code     extrn Randomize:proc, Random_range:proc extrn WriteInt:proc, Crlf:proc     call Randomize     mov  cx,20 L1: mov  eax,1000     call Random_range  ; EAX = random integer     mov  bx,10         ; decimal radix     call WriteInt         call Crlf     Loop L1 Irvine, Kip R. Assembly Language For Intel-Based Computers

  48. Delay_seconds Procedure Pause for a specified number of seconds. extrn Seconds_today:proc Delay_seconds proc    pusha    mov  ecx,eax          ; delay, in seconds    call Seconds_today    mov  ebx,eax          ; save start time DLY1:     call Seconds_today    ; get the time    sub  eax,ebx          ; subtract from start    cmp  eax,ecx          ; delay finished yet?    jb   DLY1             ; if not, continue loop    popa    ret Delay_seconds endp Irvine, Kip R. Assembly Language For Intel-Based Computers

  49. The End Irvine, Kip R. Assembly Language For Intel-Based Computers

  50. title text .code Irvine, Kip R. Assembly Language For Intel-Based Computers

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