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From: "Rod Pemberton" <do_not_have AT havenone DOT cmm>
Newsgroups: comp.os.msdos.djgpp,comp.os.msdos.programmer
Subject: NASM version of John Santic's stderr to stdout TSR
Date: Wed, 14 Apr 2010 14:25:49 -0400
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The code below is a binary compatible NASM conversion
of John Santic's stderr to stdout TSR from:
http://johnsantic.com/comp/tsr.html


Rod Pemberton


; STDERROR.ASM

BITS 16
ORG 0x100                                 ; require for .COM file
SECTION .text

start:  jmp      short start1
        nop

old_vector: dw   00h,00h                  ; save old DOS int 21 vector

start1:
        mov      ax, 0
        mov      es, ax
        les      bx, [es:21h * 4]         ; read the vector for DOS int 21
        mov      [old_vector], bx         ; save it so we can chain to it
        mov      [old_vector + 2], es
        mov      ax, 0
        mov      es, ax
        cli                            ; disable interrupts while we write

        mov      word [es:21h * 4], isr   ; chain our handler to DOS int 21
        mov      [es:(21h * 4) + 2], cs
        sti                               ; enable interrupts
        mov      ax, 3100h                ; function code to become resident
        mov      dx, last / 16 + 11h      ; reserve memory paragraphs for us
        int      21h                   ; return to DOS but remain resident

; This interrupt service routine is chained to the main DOS int 21 vector.

isr:    cmp      ah, 40h                  ; function code = write to file?
        jne      exit                     ; jump if no, don't do anything
        cmp      bx, byte 2               ; handle = stderr?
        jne      exit                     ; jump if no, don't do anything
        dec      bx                       ; force handle to stdout
exit:   jmp      far [cs:old_vector]      ; let DOS do its thing

last    equ      $ - start                ; how much memory we use