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From: Rod Pemberton <donthave AT noreply DOT bit>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Need to hook INT 21h from a DJGPP TSR
Date: Fri, 7 Oct 2005 20:57:31 +0000 (UTC)
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> But the problem remains, I don't want a hardware interrupt. I was
looking
> for a replacement wrapper for
_go32_dpmi_allocate_real_mode_callback_iret
> since I suspect my problem lies in the fact those wrappers are non
> reentrant.

Sure, you might look at Chris Jones's old LFNDOS driver.  He uses
some assembly to switch out of an interrupt context allowing full
use of C.  I personally found that this didn't work too well, but
it may serve your needs.  This is the only place I could find the
source lfndssrc.zip, so get it quick...

http://csd.lae.pp.ru:8101/pub/msdos/misc/

Also, there were four or five patches posted on www.ezboard.com
which are no longer available, including the assembly code (below).
LFNDOS.CPP shows how to call intwrap.asm.



Rod Pemberton


; INTWRAP.ASM - (c) 1998 Chris Jones
; This procedure is called in an interrupt context.  It then calls
the
; cinthandler function out of interrupt context, which enables
system calls
; to be made.  When the C function finishes, it returns to the
previous
; point of execution.
.model large,c

extrn cinthandler,tempstack
public intpointer,asminthandler

segment _DATA word public 'data'
intpointer dd 0

ends

segment _TEXT word public 'code'
assume cs:_text
asminthandler proc
        pushf
        push ax ; cs
        push ax ; ip
        push ax
        push bx
        push cx
        push dx
        push es
        push ds
        push si
        push di
        push bp
        push ax
        mov ax,DGROUP
        mov ds,ax
        pop ax
        mov word ptr ds:intpointer+2,ss
        mov word ptr ds:intpointer,sp
        mov dx,word ptr ds:tempstack+2
        mov ss,dx
        mov sp,word ptr ds:tempstack
        call far ptr cinthandler
        mov dx,word ptr ds:intpointer+2
        mov ss,dx
        mov sp,word ptr ds:intpointer
        pop bp
        pop di
        pop si
        pop ds
        pop es
        pop dx
        pop cx
        pop bx
        pop ax
        iret
endp

ends

end


--
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