From: DavMac AT iname DOT com (Davin McCall)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: DJGPP - real mode procedures.
Date: Wed, 02 Jun 1999 08:00:32 GMT
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Well then, change the "iret" to "retf" and the "pop bx" to "mov bx,
[sp+4]" (or else, "mov bp, sp" followed by "mov bx, [bp+4]").

In case I didn't explain clearly, the arguments are normally pushed
*before* the return address. That means that your "pop bx" is
destroying the return address.

Davin.

On Wed, 02 Jun 1999 17:39:36 +1000, leroy <leroy AT hitech DOT net DOT au> wrote:

>Actually it was just my rushed attempt at rebuilding the routine I had. :)
>
>Also I tried for ages to get the routine to work, thinking that it was my
>C code that was wrong.  It was only when AS said that retf was an unknown
>386 instruction that I changed it to ret, then to iret when that didn't
>work.
>
>Heres the program that technically should run, but prefers to lock up
>Windows/DOS instead.
>
>/* Attempt at getting a real mode machine code call to work */
>
>#include <stdio.h>
>#include <go32.h>
>#include <dpmi.h>
>
>int main()
>{
> unsigned char asmroutine[] = {0x5b, 0xb8, 0x10, 0x00, 0x01, 0xd8, 0xcf};
> int stack[1];
> /* pop bx
>  * mov ax, 13h
>  * add ax, bx
>  * iret
>  */
> int sel = 0, seg = 0;
> __dpmi_regs r;
>
> seg = __dpmi_allocate_dos_memory(2, &sel);
> dosmemput(asmroutine, 4, (seg * 16));
>
> memset(&r, 0, sizeof(r));
>
> r.x.cs = seg;
> /* I'm not sure about the stack[0] << 8 part, but it shouldn't matter */
> stack[0] = 0x10 << 8;
> __dpmi_simulate_real_mode_procedure_retf_stack(&r, 2, stack);
>
> printf("Value of ax now: 0x%s\n", itoa(r.x.ax, NULL, 16));
>}
>
>Cheers,
>
>leroy.

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