lecture (05) x86 programming 4 - draelshafee.net fileassembler directives directives are...

Lecture (05)x86 programming ‐ 4

By:

Dr. Ahmed ElShafee

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١

TOC

• IA32 cont,..

• Segmentation

• Assembler Directives

• Format of console programs

• Practical deliverable 01

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢

•

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٣

Simple Memory Addressing Modes

• Normal (R) Mem[Reg[R]]

– Register R specifies memory address

mov eax, [ecx]

• Displacement D(R) Mem[Reg[R]+D]

– Register R specifies start of memory region

– Constant displacement D specifies offset

mov edx, 8[ebp]

•

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٤

Example 06

int _tmain(int argc, _TCHAR* argv[]){unsigned int src_arr[4]={12,34,56,78};unsigned int x1,x2,x3,x4;unsigned int des_arr[4];_asm{lea ebx,src_arrmov edx,[ebx]mov x1,edxmov edx,4[ebx]mov x2,edxmov edx,8[ebx]mov x3,edxmov edx,12[ebx]mov x4,edx

lea ebx,des_arrmov edx,x4mov [ebx],edxmov edx,x3mov 4[ebx],edxmov edx,x2mov 8[ebx],edx

mov edx,x1mov 12[ebx],edx}printf("x1=%d\n",x1);printf("x2=%d\n",x2);printf("x3=%d\n",x3);printf("x4=%d\n",x4);printf("des_arr[0]=%d\n",des_arr[0]);printf("des_arr[1]=%d\n",des_arr[1]);printf("des_arr[2]=%d\n",des_arr[2]);printf("des_arr[3]=%d\n",des_arr[3]);printf("Press any key to continue,...");char ch = getch();return 0;}

•

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٥

int _tmain(int argc, _TCHAR* argv[]){unsigned int x,y,z;printf("Enter X=");scanf("%d",&x);printf("Enter y=");scanf("%d",&y);_asm{push xpush ypop eaxpop edxadd eax,edxpush eaxpop z}printf("z=%d\n",z);printf("Press any key to continue,...");getch();return 0;}

Example 07

Segmentation

• Segmentation is used to allow relocation of programs, i.e. programs can be loaded on different memory areas and still run correctly.

• Segmentation is used in the 8088/8086 microprocessors to allow the generation of 20‐bit addresses using 16‐bit registers.

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٦

• In the Real Mode Operation a 20‐bit address (effective address) is obtained by shifting the segment address 4 bits to the left (X10H) and then adding the offset address

• The offset address is specified in the program. The segment address is specified by the operating system whenever the program is loaded.

• The code segment holds the machine codes of the program. The Instruction Pointer specifies the offset address in the code segment.Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٧

• The data segment holds the data used by the program. Most data references are specified in the data segment.

• The stack segment holds the stack of the program. The offset address in the stack segment is specified with the registers SP and BP.

• The extra segment is used as a data segment by some data movement instructions.

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٨

Example 01

If DS =1600H find the maximum area occupied by the data segment. Find also the effective address, if the offset address is 1F00H.

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٩

Solution 01

Starting address = DS X 10H = 1600H X 10H

= 16000H

Ending address = Starting address + FFFF

= 16000H + FFFFH = 25FFFH

Effective address= Segment:Offset = 1600:1F00

= Segment address X 10H + Offset

= 1600H X 10H + 1F00H

= 16000H + 1F00H = 17F00H

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٠

Assembler Directives

Directives are instructions given by the programmer to the assembler on how to assemble the program.

Directives are not part of the instruction set of the microprocessor.

The use of directives might vary from assembler to assembler.

Some of the MASM 32 assembler directives are:

– ORG (Origin): Tells the assembler where to store the machine code of the next instruction.

– EQU (Equate): Tells the assembler to assign a value to an identifier.

– SEGMENT: Tells the assembler to begin a new segment.

– ASSUME: Tell the assembler to associate a segment with a segment register.

– PROC (Procedure): Tells the assembler to begin a new procedure.

– MACRO: Assigns the sequence of instructions to an identifier.

– END: Ends a program, segment (ENDS), a procedure (ENDP), or a macro (ENDM).Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١١

> Data Definition Directives

• Data Definition directives tell the assembler to store the specified data in the next memory locations. Data that occupies more than one location is stored with the LSByte in the lower address.

• (DB) Define Byte (1 byte or 8 bits ‐ Same as BYTE)

• (DW) Define Word (2 bytes or 16 bits ‐ Same as WORD)

• (DD) Define Double Word (4 bytes or 32 bits ‐ Same as DWORD)

• (DQ) Define Quad Word (8 bytes or 64 bits ‐ Same as QWORD)

• (DT) Define Ten Bytes (10 bytes or 80 bits ‐ Same as TBYTE)

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٢

Code 01

Examples:

• ABC DB 26H ;ABC=26H

• XYZ DB 35H,87H,0A4H ;XYZ= {35H,87H,A4H}

• YOU DB ‘ahmd’ ;YOU = ahmd’

• VAL DW 1254H ;VAL = 1254H

• X1 DB ? ;X1 = UNSPECIFIED

• X4 DB 3 DUP(20H) ;X4 = {20H,20H,20H}

• N1 DB 123H ;INVALID

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٣

Code 02

• Show the content of the memory based on the following data definitions:

ORG 100H

VAL1 EQU 21H

AB10 DB 37

NEW DB 23H,56H,’$’

LOT DW 1245H

XY11 DB ‘NEXT’

A123 DD 123H

B561 DB 4 DUP(40H)

VAL2 DB VAL1

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٤

AB10

Label

NEW+0

NEW+1

NEW+2

LOT

XY11+0

XY11+1

XY11+2

A123

XY11+3

B561+1

B561+0

B561+2

B561+3

VAL2

DS:0100

Address

DS:0101

DS:0102

DS:0103

DS:0105

DS:0104

DS:0106

DS:0107

DS:0108

DS:010A

DS:0109

DS:010B

DS:010C

DS:010D

DS:010F

DS:010E

DS:0110

DS:0111

DS:0112

Content

solution

• Show the content of the memory based on the following data definitions:

ORG 100H

VAL1 EQU 21H

AB10 DB 37

NEW DB 23H,56H,’$’

LOT DW 1245H

XY11 DB ‘NEXT’

A123 DD 123H

B561 DB 4 DUP(40H)

VAL2 DB VAL1

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٥

Code 03; data definition; emu86

ORG 100H

JMP START

VAL1 EQU 21H

AB10 DB 37

NEW DB 23H,56H,’$’

LOT DW 1245H

XY11 DB ‘NEXT’

A123 DD 123H

B561 DB 4 DUP(40H)

VAL2 DB VAL1

START:

nop

END

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٦

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٧

Format of DOS programs

• All programs must have a code and a stack.

– Code is the part of the program that contains the instructions of the program.

– Stack is an area in the RAM used by the system to store return addresses, and by the programmer to store temporarily data. It is a Last In First Out (LIFO) buffer.

• Programs can also have a data area, where all data (variables) is stored.

• There are two basic types of programs:

– Commands (.COM). The data and the stack of the program are part of the Code segment. The stack is always located at the end of the segment. The first 256 bytes of the segment are reserved.

– Executable (.EXE). The code and stack and data of the program are located in different segments.

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٨

Format of the .COM programs

.MODEL SMALL

CSEG SEGMENT PARA 'CODE’ ;Start a Code segment

ASSUME CS:CSEG, DS:CSEG, SS:CSEG

ORG 100H ;Reserve first 256 locations

START: JMP MAIN ;Skip data area

{Place the data of the program here}

MAIN PROC NEAR ;Beginning of main procedure

{Place the code of the

program here}

RET ;Get return DOS address

MAIN ENDP ;End of main procedure

CSEG ENDS ;End of the segment

END START ;End of the program

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1١٩

Format of the .COM programs

.MODEL SMALL

.CODE



{Place the data of the program here}


{Place the code of the

program here}

RET ;Get return DOS address



Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢٠

Example 01.01; hello world; masm

CSEG SEGMENT PARA ‘CODE’ ;Start a Code segment

ASSUME CS:CSEG, DS:CSEG, SS:CSEG



MSG DB "Hello World 01",'$‘


LEA DX,MSG

MOV AH,9

INT 21H

INT 20H

RET


CSEG ENDS ;End of the segment


Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢١

Example 01; hello world; masm

.MODEL SMALL

.CODE



MSG DB "Hello World 01",'$‘


LEA DX,MSG

MOV AH,9

INT 21H

INT 20H

RET



Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢٢

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢٣

Compiling and linking

Masm 01.asm

ML –AT 01.obj

01.com

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢٤

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢٥

Thanks,..

Dr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1٢٦

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