Message-ID: <37533A3A.B6A84588@hitech.net.au>
From: leroy <leroy AT hitech DOT net DOT au>
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Subject: DJGPP - real mode procedures.
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Date: Tue, 01 Jun 1999 11:41:15 +1000
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I've found some strange anomolies when calling a real mode procedure in
DJGPP.

Tell me if this is the wrong way to do things.

unsigned char *code[] = {0x5b, 0xb8, 0x10, 0x00, 0x01, 0xd8, 0xcf};

According to debug that is
pop bx
mov ax, 10
add ax, bx
iret

Now, I allocate dos memory using the dpmi function, allocating 1 more
paragraph than I need (just for safety).

I move the code to that allocated memory using the dosmemput() routine.
I checked using _farpokeb() routines that the transfer worked.

I set up the registers using
__dpmi_regs r;
r.x.ss = 0; r.x.sp = 0;
r.x.cs = seg; // the value returned from the dos allocation routine
r.x.ip = 0;

I have a variable called stack that is initialised like so
int stack[] = {0x10};

I then call the function
__dpmi_simulate_real_mode_procedure_retf_stack(&r, 4, &stack);

I'm not so sure how the values for the stack should be passed, so I did
some assumed values, like 4.  Is this right?

Next thing was that when this is run, Windows says that an illegal
instruction was encountered.

It did this even when I ran a smaller procedure that was this
mov ax, 13
retf

When I changed the retf to an iret it worked.

Any ideas what's wrong?

Cheers,

leroy.