Category : Assembly Language Source Code
Archive   : BREAKPT.ZIP
Filename : BREAKPT.ASM

PAGE 60,132
; BREAKPT.ASM: A DEBUGGING UTILITY
; TO BE USED IN CONJUNCTION WITH THE DOS DEBUG UTILITY OR ANY DEBUGGER
; WHICH CAN INTERCEPT THE BREAKPOINT INTERRUPT.
; USAGE: RUN BREAKPT.COM ONCE UNDER DOS TO INSTALL.
; LOAD DEBUGGER WITH PROGRAM TO BE DEBUGGED.
; SET A BREAKPOINT (ANY BREAKPOINT) AND EXECUTE PROGRAM.
; WHILE PROGRAM RUNS, HITTING CTRL-ESC JUMPS TO THIS ROUTINE,
; WHICH HANDS CONTROL TO DEBUGGER.
; NOTE THIS METHOD CAN BE USED TO INTERRUPT BOTH ROM
; AND RAM EXECUTION.
; PROGRAM BY RICH WINKEL
BOTTOM SEGMENT AT 0H
ORG 024H
KBDIP DW ? ;IP FOR KBD INT
KBDCS DW ? ;CS FOR KBD INT
ORG 0417H
KB_FLAG DB ? ;ROM BIOS DATA
BOTTOM ENDS
;
BREAKPT SEGMENT
ASSUME CS:BREAKPT,DS:BOTTOM
ORG 100H
MAIN PROC NEAR
JMP INIT
;
; KEYBOARD INTERRUPT INTERCEPT ROUTINE
;
CATCH: STI ;INTERRUPTS BACK ON
PUSH AX
IN AL,60H ;CHECK SCAN CODE
CMP AL,01H ;IS IT ESC KEY?
JNZ L2 ;NO, ON TO KEYBOARD ROUTINE
PUSH DS ;OTHERWISE, CHECK FOR
XOR AX,AX ;CONTROL KEY SHIFT
MOV DS,AX ;GET DOWN TO THE BOTTOM
MOV AL,KB_FLAG ;GET KEYBOARD FLAG BYTE FROM ROM DATA
TEST AL,04H ;CTRL SHIFT?
JZ L1 ;NO, ON TO KEYBOARD ROUTINE
IN AL,61H ;OTHERWISE, WE TAKE IT FROM HERE
MOV AH,AL ;RESET
OR AL,80H ;THE
OUT 61H,AL ;KEYBOARD
MOV AL,AH ;CONTROL
OUT 61H,AL ;PORT
CLI ;TURN OFF INTERRUPTS
MOV AL,20H ;RESET INTERRUPT CONTROLLER (8259)
OUT 20H,AL
POP DS
POP AX
STI ;LET PENDING INTERRUPTS EXECUTE
NOP
INT 03H ;NOW GIVE DEBUG CONTROL
IRET ;SINGLE STEP BACK TO INTERRUPTED PGM
L1: POP DS ;ONWARD TO KBD ROUTINE
L2: POP AX
DB 0EAH ;PREFIX BYTE FOR FAR JUMP
JFARIP DW 0H ;IP FOR KBD ROUTINE
JFARCS DW 0H ;CS FOR KBD ROUTINE
INIT: XOR AX,AX ;GET INTO
MOV DS,AX ;BOTTOM SEGMENT
MOV AX,KBDIP ;GET IP FOR KBD INTERRUPT
MOV CS:JFARIP,AX ;PUT IN OUR FAR JUMP
MOV AX,KBDCS ;GET CS FOR KBD INTERRUPT
MOV CS:JFARCS,AX ;PUT IN OUR FAR JUMP
MOV AX,CS ;BACK TO
MOV DS,AX ;OUR SEGMENT
MOV DX,OFFSET CATCH ;USE DOS TO POINT KBD INT TO US
MOV AX,2509H ;'RESET INT 9H VECTOR TO DS:DX'
INT 21H ;DO IT
MOV AH,09H ;PRINT MESSAGE
MOV DX,OFFSET MSG ;POINT TO MESSAGE
INT 21H ;DO IT
MOV DX,OFFSET INIT ;GET LAST ADDRESS OF RESIDENT CODE
INT 27H ;TERMINATE AND STAY RESIDENT
;
MSG DB 'Breakpoint debugging utility.',0DH,0AH
DB 'Load a program under DEBUG, '
DB 'set a breakpoint, (any breakpoint) and go.',0DH,0AH
DB 'To stop the program for debugging, hit Ctrl-Esc, then type:',0DH,0AH
DB 09H,'RIP 12D T ',0DH,0AH
DB 'to jump over the INT 3, execute an IRET, and',0DH,0AH
DB 'get back to where your program was executing.',0DH,0AH
DB "WARNING: Don't hit Ctrl-Esc except while under DEBUG!$"
;
MAIN ENDP
BREAKPT ENDS
END MAIN
P
BREAKPT ENDS
END MAIN