Lecture (05) x86 programming 4

Transcription

1 Lecture (05) x86 programming 4 By: Dr. Ahmed ElShafee ١ TOC IA32 cont,.. Segmentation Assembler Directives Format of console programs Practical deliverable 01 ٢

2 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] ٣ 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_arr mov edx,[ebx] mov x1,edx mov edx,4[ebx] mov x2,edx mov edx,8[ebx] mov x3,edx mov edx,12[ebx] mov x4,edx lea ebx,des_arr mov edx,x4 mov [ebx],edx mov edx,x3 mov 4[ebx],edx mov edx,x2 mov 8[ebx],edx ٤ mov edx,x1 mov 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; } Example 06

3 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 x push y pop eax pop edx add eax,edx push eax pop z } printf("z=%d\n",z); printf("press any key to continue,..."); getch(); return 0; } ٥ 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. ٦

4 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 ٧ offset address in the code segment. 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. ٨

5 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. ٩ 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 ١٠

6 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. ١١ END: Ends a program, segment (ENDS), a procedure (ENDP), or a Ḍr. Ahmed ElShafee, ACU : Fall 2018, Microprocessors 1 macro (ENDM) > 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) ١٢

7 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 ١٣ 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 ١٤

8 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 ١٥ Label Address AB10 DS:0100 NEW+0 DS:0101 NEW+1 DS:0102 NEW+2 DS:0103 LOT DS:0104 DS:0105 XY11+0 DS:0106 XY11+1 DS:0107 XY11+2 DS:0108 XY11+3 DS:0109 A123 DS:010A DS:010B DS:010C DS:010D B561+0 DS:010E B561+1 DS:010F B561+2 DS:0110 B561+3 DS:0111 VAL2 DS:0112 Content 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 ١٦

9 ١٧ 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. ١٨ Executable (.EXE). The code and stack and data of the program are located in different segments.

10 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 ١٩ Format of the.com programs.model SMALL.CODE 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 END START ;End of the program ٢٠

11 Example 01.01; hello world; masm 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 MSG DB "Hello World 01",'$ MAIN PROC NEAR ;Beginning of main procedure LEA DX,MSG MOV AH,9 INT 21H INT 20H RET MAIN ENDP ;End of main procedure CSEG ENDS ;End of the segment END START ;End of the program ٢١ Example 01; hello world; masm.model SMALL.CODE ORG 100H ;Reserve first 256 locations START: JMP MAIN ;Skip data area MSG DB "Hello World 01",'$ MAIN PROC NEAR ;Beginning of main procedure LEA DX,MSG MOV AH,9 INT 21H INT 20H RET MAIN ENDP ;End of main procedure END START ;End of the program ٢٢

12 ٢٣ Compiling and linking Masm 01.asm ML AT 01.obj 01.com ٢٤

13 ٢٥ Thanks,.. ٢٦