hooking int 21?

hooking int 21?

[Stuart Axon]

Hello, I want to handle a function of int21 in dosemu, but can't see
where to put the code; int21() in int.c is only for when debugging...
but I can't see where for normal execution..?

Re: hooking int 21?

[Bart Oldeman]

On 26 Jan 2003, Stuart Axon wrote:

> Hello, I want to handle a function of int21 in dosemu, but can't see
> where to put the code; int21() in int.c is only for when debugging...
> but I can't see where for normal execution..?

Yes, int21() only traps in DOSEMU for debugging, and some hooks
for the redirector. Everything else is handled by the DOS you're running
in DOSEMU.

But of course you can do what you like in int21() or ms_dos() for that
matter.

Bart

Re: hooking int 21?

[Stuart Axon]

Thanks, discovered the can_revector_int21 too, which seemed to help... 
Now tho, can't seem to return a cleared carry flag: if I temporarily put
 ds_printf("CF=%x\n",REG(eflags)&&CF);
in int21() after my function call I can see
CF=0
so it's still clear, but by the time it gets back to dos its set, is
there anything I need to be aware of in order to preserve CF?

On Sun, 2003-01-26 at 23:07, Bart Oldeman wrote:
> On 26 Jan 2003, Stuart Axon wrote:
> 
> > Hello, I want to handle a function of int21 in dosemu, but can't see
> > where to put the code; int21() in int.c is only for when debugging...
> > but I can't see where for normal execution..?
> 
> Yes, int21() only traps in DOSEMU for debugging, and some hooks
> for the redirector. Everything else is handled by the DOS you're running
> in DOSEMU.
> 
> But of course you can do what you like in int21() or ms_dos() for that
> matter.
> 
> Bart
> 
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Re: hooking int 21?

[Bart Oldeman]

On 26 Jan 2003, Stuart Axon wrote:

> Thanks, discovered the can_revector_int21 too, which seemed to help...
> Now tho, can't seem to return a cleared carry flag: if I temporarily put
>  ds_printf("CF=%x\n",REG(eflags)&&CF);
> in int21() after my function call I can see
> CF=0
> so it's still clear, but by the time it gets back to dos its set, is
> there anything I need to be aware of in order to preserve CF?

That's because it's chained in front of the real DOS int21. If you
implement your function in ms_dos() then you can "return 1" to claim this
case exclusively for you and "return 0" if you want to pass it on to DOS.

Bart