From:	"Patrick Hogan" <rubberwall AT iname DOT com>
Newsgroups:	comp.os.msdos.djgpp
Subject:	djgpp, assembler, dos interrupts and buffers
Date:	Mon, 9 Aug 1999 19:33:38 -0000
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Hi,

I'm trying to convert some C/C++ code (djgpp) into assembler for a project
I'm working on. I've come across a major problem, djgpp doesen't like dos
interrupts when dos buffers are involved. I do understand the difference
between protected mode linear memory and the real mode memory but even
compensating for this by providing the proper segment and offset, refuses to
work. Let me provide an example :

One function looks like this in C :
_go32_dpmi_registers r;
memset( &r, 0, sizeof(r) );
r.x.bx = 0x0009;
r.x.es = segment_of_dos_buffer;
r.x.si = offset_of_dos_buffer;
_go32_dpmi_simulate_int( 0x7a, &r );

In NASM I tried :
; prototype: void _get_local_address(long dosseg, long dosofs);
__get_local_address:
          push ebp
          mov ebp,esp
          mov es,[ebp+8]
          mov si,[ebp+12]
          mov bx, 0009h
          int 07Ah
          mov esp,ebp
          pop ebp
          ret

Which compiles perfectly but crashes the program, so does inline AT&T (gas).
I gather the problem is that calling int 07Ah is not the equivalent of
_go32_dpmi_simulate_int( 0x7a, &r ), or it IS but somehow it screws up
because of real/protected mode clashes.

Could someone PLEASE point me to some documentation on real mode interrupts
in protected mode programs. Or maybe help me in this headache?

Thanks,
Patrick Hogan
logiknet AT iname DOT com
http://come.to/logiknet

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