The document discusses assembly language instruction addressing and execution. It covers loading an *.exe program by accessing it from disk and storing it in memory segments. The boot process and loading of an *.exe file is explained. Examples are provided to illustrate instruction execution and addressing, showing how the instruction address is determined from segment registers and offsets.

1. Assembly Language Instruction Addressing and Execution Motaz K. Saad Spring 2007 Motaz K. Saad, Dept. of CS

3. Recalling main concepts Motaz K. Saad, Dept. of CS

4. Recalling main concepts Motaz K. Saad, Dept. of CS

6. Recalling main concepts Stack Segment Data Segment Code Segment SS DS CS Segment Registers Motaz K. Saad, Dept. of CS

10. PSP Motaz K. Saad, Dept. of CS

11. Assembly directive to define memory model to use in the program . MODEL SMALL, .STACK .DATA MESSAGE DB "HELLO EVERYBODY! I AM LEARNING ASSEMBLY LANGUAGE!","$" .CODE MAIN PROC MOV AX, @DATA MOV DS,AX MOV AH,09 LEA DX,MESSAGE INT 21H MOV AX,4C00H INT 21H MAIN ENDP END MAIN Motaz K. Saad, Dept. of CS

13. Real and Protected mode Motaz K. Saad, Dept. of CS Real Mode 16-bit Protected Mode 32-bit Protected Mode Segment base address 20-bit 24-bit, from descriptor 32-bit, from descriptor Segment size (limit) 16-bit, 64K bytes (fixed) 16-bit, 1-64K bytes 20-bit, 1-1M bytes or 4K-4G bytes Segment protection no yes yes Segment register segment base address / 16 selector selector

21. BIOS Boot process BIOS routine FFFF0H Interrupt Vector Table BIOS Data Areas Access the bootstrap loader Check ports Initialize devices Motaz K. Saad, Dept. of CS

23. Assembly directive to define stack to use in the program . model small . STACK .DATA MESSAGE DB "HELLO EVERYBODY! I AM LEARNING ASSEMBLY LANGUAGE!","$" .CODE MAIN PROC MOV AX, @DATA MOV DS,AX MOV AH,09 LEA DX,MESSAGE INT 21H MOV AX,4C00H INT 21H MAIN ENDP END MAIN Motaz K. Saad, Dept. of CS

27. Loading *.exe file Access *.exe from disk 256-byte Program Segment Prefix (PSP) on a paragraph boundary Store the program immediately following the PSP Load address of PSP in the DS & ES Load code segment in CS, set IP Load address of the stack to SS, set SP Transfer control to the program for execution Motaz K. Saad, Dept. of CS

29. Practice 2B360H PSP Stack Segment Data Segment Code Segment Memory Motaz K. Saad, Dept. of CS

30. Practice 2B360H PSP Stack Segment Data Segment Code Segment Memory PSP 2B360H PSP size 100 H Offset 0H SS 2B460H (stored as 2B46) 2B46H SS Motaz K. Saad, Dept. of CS

31. Practice 2B360H PSP Stack Segment Data Segment Code Segment Memory 2B46H SS PSP 2B360H PSP size 100H Offset 30H 70H CS 2B500H (stored as 2B50) CS 2B50H Motaz K. Saad, Dept. of CS

32. Practice 2B360H PSP Stack Segment Data Segment Code Segment Memory 2B46H SS CS 2B50H 2B36H 2B36H DS ES SP 0030H Motaz K. Saad, Dept. of CS

34. Example 4AF0 CS 0013 IP 4AF13H 04B1 DS Motaz K. Saad, Dept. of CS CS segment address: 4AF00H IP offset: 0013H ________________________ + Instruction address:

35. Example 4AF0 CS 0013 IP 4AF13H A01200 Memory 04B1 DS Decode instruction: AO: MOV [0012] to AL Motaz K. Saad, Dept. of CS

36. Example 4AF0 CS 0013 IP 04B03H A01200 Memory 04B1 DS 04B22H Motaz K. Saad, Dept. of CS DS segment address:04B10H IP offset: 0012H ________________________ + Data address:

37. Example 4AF0 CS 0013 IP 04B03H A01200 1B Memory 04B1 DS 04B22 Data address: 04B22H Motaz K. Saad, Dept. of CS | 1B AX AX AH AL