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call a interrupt by number stored in a variable

 
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danrevella
Master Cheater
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Joined: 11 Jun 2008
Posts: 292
PostPosted: Thu Jul 14, 2016 10:44 am    Post subject: call a interrupt by number stored in a variable Reply with quote
Hi!!
Under dos, using TASM i'm actually writing a little dos TSR to help me to get work the old dos utility Game Wizard32 (an old dos program cheat) with the game Quake (the first dos version).
For this purpose I need invoke an interrupt that I have just elaborated and stored in a variable (1 byte)
figure the follows:
CHEAT_INT_X0H db 50h (here is the int number I must call)
.some code
.
.
int CHEAT_INT_X0H
but this does not work,
so I have rearranged the code:
Code:
;call the interrupt with self modifying code
push ax
push si
   mov al,CHEAT_INT_X0H
   mov si,offset intr_C0h; abbreviazione per interrupt CHEAT_INT_X0H
   mov [si+1],al   ;change the 00 below to the contents of AL
pop si
pop ax
intr_C0h:   int 00h   ;call the interrupt (00 will be changed above)

I don't like this solution, maybe does exist another (simplest) way?
Many Thanks
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kantoboy69
Advanced Cheater
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Joined: 31 Mar 2010
Posts: 71
Location: Manila
PostPosted: Fri Aug 05, 2016 2:20 am    Post subject: Reply with quote
You can't do that

Code:
intx:
   db 21h

mov ah, 40h
mov al, 21h
int intx


instead you can find out the address of the interrupt by using
get interrupt vector and call it directly like a normal sub/func
That's a proper way or a messy way

modify the offset where the interrupt should be before executing interrupt which is not a good idea and very tedious to do so



http://www.fysnet.net/ivect.htm
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danrevella
Master Cheater
Reputation: 2

Joined: 11 Jun 2008
Posts: 292
PostPosted: Fri Aug 05, 2016 2:49 am    Post subject: Reply with quote
Many thanks, I understand the way you have proposed is the best.
Now Game wizard may work with Quake(dos) Very Happy
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