Re: Redirecting a DOS interrupt call out to Linux

[Stas Sergeev <stsp@list.ru>]

18.07.2013 20:35, Andrew Bird (Sphere Systems) пишет:
> Hi all,
> 	I've been playing with the Dosemu source code with the hope of replacing
> an old TSR with a native Linux daemon. Currently a DOS app I have no source
> for makes an interrupt call to a TSR with data, the TSR works with it and the
> result is returned.
>
> I had in mind to replace it with something like this:
> 1/ Old DOS app makes call to interrupt
> 2/ New Dosemu interrupt handler that collects the data given to it by the DOS
> app and pushes it into a message queue on the host.
> 3/ A Linux daemon that reads the incoming message, does the processing and
> returns the result via a second message queue.
> 4/ The new Dosemu interrupt handler then reads the result from the second
> message queue, places it in memory and returns.
> 5/ The DOS app sees the result and is unaware of any difference.
>
> My first step was to hook in a new skeleton Dosemu interrupt handler, but it
> doesn't seem to be being called and the DOS app thinks the TSR is not
> installed. I'm using Dosemu 1.2.2 for historical reasons, but I expect the
> problem is similar on 1.4.0 etc.
>
> I figured all I'd need to do would be to add a new function to
> src/base/async/int.c and reference it.
>
> /* this is the handler for INT 76 calls from DOS to the test interface */
> int test_int (void) {
> 	ds_printf("INT76: we have been called\n");
> 	return 1;
> }
>
> /* add reference to it in setup_interrupts() */
> interrupt_function[0x76] = test_int;
>
> Can anybody tell me what I'm missing? How does the interrupt vector table get
> built?
Firstly, the interrupt handling is much different in 1.2
and 1.4. Secondly, you need to make sure the interrupt
vector points to BIOSSEG:INT_OFF(i) (see bios_setup() in setup.c)
and that no one have hooked it from DOS (or, at least, chains
it back to the original address).
Alternatively you can make dosemu to try and intercept the int0xNN
instruction. In this case you won't need to worry if someone have
hooked that vector under DOS. For that you will need to modify
the can_revector() function.
Note that this all applies to 1.4. I have no idea how 1.2 worked,
this was too long ago.
Additionally, curent git allows you to sleep inside the interrupt
handler of dosemu, while the DOS is still running. This will likely
allow you to do the thing within one interrupt call, instead of 2.
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