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Flow Diagram:

Flow Diagram:. Push AX,BX,CX,DX,ES,DS,SI,DI,BP. Push flags, CS, IP. POP BP,DI,SI,DS,ES,DX,CX,BX,AX. Pop IP,CS,flags. Typical Reentrant Routine:. Push AX, Push BX, Push CX, Push DX, Push ES, Push DS, Push SI, Push DI, Push BP ---------- ---------- ---------- ----------

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Flow Diagram:

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  1. Flow Diagram: Push AX,BX,CX,DX,ES,DS,SI,DI,BP Push flags, CS, IP POP BP,DI,SI,DS,ES,DX,CX,BX,AX Pop IP,CS,flags

  2. Typical Reentrant Routine: Push AX, Push BX, Push CX, Push DX, Push ES, Push DS, Push SI, Push DI, Push BP ---------- ---------- ---------- ---------- Pop BP, Pop DI, Pop SI , Pop DS, Pop ES, Pop DX, Pop CX, Pop BX, Pop AX, IRET -------------------- Int --------------------

  3. BP DI SI DS ES DX CX BX AX IP CS Flags Animation:

  4. Example: void main (){ x = sum(4, 5); printf (“%d”, x); a = 10; b = 20; x = sum(a, b); printf (“%d”, x);}int sum (int i, int j){ return i+j;} SP 4 5 RP SP a b RP

  5. Accessing Stack Example: void interrupt newint ( unsigned int BP, unsigned int DI, unsigned int SI, unsigned int DS, unsigned int ES, unsigned int DX, unsigned int CX, unsigned int BX, unsigned int AX, unsigned int CS, unsigned int IP, unsigned int flags){ a = AX; b = BX; d = ES;}

  6. Example: void main ( ) {setvect(0x65,newint); _AX = 0x1234; Geninterrupt (0x65); a = _AX; Printf (“%x”, a); } void interrupt newint( unsigned int BP, unsigned int DI, unsigned int SI, unsigned int DS, unsigned int ES, unsigned int DX, unsigned int CX, unsigned int BX, unsigned int AX, unsigned int CS, unsigned int IP, unsigned int flags){ AX = 0xF00F; }

  7. Disk Interrupt ( int# 13H Service# 3) On Entry AH = Service # = 03AL = No of Blocks to write BX = Offset Address of Data CH = Track No. , CL = Sector DH = Head # DL = Drive #(Starts from 0x80 for fixed disk & 0 for removable disks) ES = Segment Address of data buffer. On Exit AH = return Code Carry flag = 0 ( No Error AH = 0) Carry flag = 1 ( Error AH = Error Code)

  8. Addressing of Block Specified: Head, Sec, Track #pragma inline #include <dos.h> #include <bios.h> void interrupt (*oldtsr) ( ); void interrupt newtsr (unsigned int BP, …, flags); void main ( ) { oldtsr = getvect (0x13); setvect = (0x13, newtsr); keep (0, 1000); }

  9. void interrupt newtsr(unsigned int BP, unsigned int DI, unsigned int SI, unsigned int DS, unsigned int ES, unsigned int DX, unsigned int CX, unsigned int BX, unsigned int AX, unsigned int CS, unsigned int IP, unsigned int flags){ _ES = ES; _DX = DX;if ( _AH = = 0x03) _CX = CX; _BX = BX; if(( _DH= =1 && _CH= =0 _AX = AX; && _CL= =1)&& _DL>=0x80) *oldtsr; { asm pushf; asm clc; asm pop flags; asm pushf; AX = _AX; BX = _BX; asm pop flags; CX = _CX; DX = _DX; return; ES = _ES; } }

  10. Keyboard Interrupt Hook (int# 15H Service# 4FH) Move Scan Code from 60H port to AL Int 15H Service 4FH Key Pressed Convert to ASCII & place it in keyboard buffer

  11. Example: #include <dos.h> #include <bios.h> #include <stdio.h> void interrupt (*oldint15) ( ); void interrupt newint15(unsigned int BP, …, flags); void main ( ) { oldint15 = getvect (0x15); setvect (0x15, newint15); keep (0, 1000); }

  12. void interrupt newint15(unsigned int BP, unsigned int DI, unsigned int SI, unsigned int DS, unsigned int ES, unsigned int DX, unsigned int CX, unsigned int BX, unsigned int AX, unsigned int CS, unsigned int IP, unsigned int flags){ if (*(((char*)&AX) + 1) = = 0x4F ) { if (*((char*)&AX) = = 0x2C) *(((char*)&AX)) = 0x1E; else if (*((char*)&AX) = = 0x1E) *((char*)&AX) = = 0x2C; } }

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