Re: NASM HelloWorld - DOS

On Jul 30, 9:35 pm, "Jim Carlock" <anonym...@xxxxxxxxx> wrote:

Are there any other things that might be a little more interesting that
can be added and/or changed in any way without getting too much
more complicated?

<code>
;
; Hello world! example.
; Subsystem: DOS
;
; COMPILE_1: nasmw.exe -fbin -ohellow.com hello.asm
; COMPILE_2: nasmw.exe -fbin -ohellow.exe hello.asm
; LINK_1: NOT REQUIRED FOR .com or DOS .exe
; LINK_2:
;

Just because you give the file an "exe" extension does not
automatically make it into a standard DOS executable. Since it
doesn't contain the proper header, the OS loader will assume it to be
a typical "com" program and treat it as such.

If you go here:

http://sourceforge.net/project/showfiles.php?group_id=6208

....scroll down to the "DOS 16-bit binaries (OBSOLETE)" heading and get
the 0.98.38 archive (the newer 0.98.39 lacks this for some reason)
which contains a "misc" directory with a few useful include files that
define macros and such. The "exebin.mac" provides the needed header
to create a proper DOS "*.exe" program using NASM. It is reprinted
below:

; -*- nasm -*-

; NASM macro file to allow the `bin' output format to generate

; simple .EXE files by constructing the EXE header by hand.

; Adapted from a contribution by Yann Guidon <whygee_corp@xxxxxx>



%define EXE_stack_size EXE_realstacksize



%macro EXE_begin 0

ORG 0E0h

section .text



header_start:

db 4Dh,5Ah ; EXE file signature

dw EXE_allocsize % 512

dw (EXE_allocsize + 511) / 512

dw 0 ; relocation information: none

dw (header_end-header_start)/16 ; header size in paragraphs

dw (EXE_absssize + EXE_realstacksize) / 16 ; min extra mem

dw (EXE_absssize + EXE_realstacksize) / 16 ; max extra mem

dw -10h ; Initial SS (before fixup)

dw EXE_endbss + EXE_realstacksize ; Initial SP (1K DPMI+1K STACK)

dw 0 ; (no) Checksum

dw 100h ; Initial IP - start just after the header

dw -10h ; Initial CS (before fixup)

dw 0 ; file offset to relocation table: none

dw 0 ; (no overlay)

align 16,db 0

header_end:



EXE_startcode:

section .data

EXE_startdata:

section .bss

EXE_startbss:

%endmacro



%macro EXE_stack 1

EXE_realstacksize equ %1

%define EXE_stack_size EXE_bogusstacksize ; defeat EQU in EXE_end

%endmacro



%macro EXE_end 0

section .text

EXE_endcode:

section .data

EXE_enddata:

section .bss

alignb 4

EXE_endbss:



EXE_acodesize equ (EXE_endcode-EXE_startcode+3) & (~3)

EXE_datasize equ EXE_enddata-EXE_startdata

EXE_absssize equ (EXE_endbss-EXE_startbss+3) & (~3)

EXE_allocsize equ EXE_acodesize + EXE_datasize



EXE_stack_size equ 0x800 ; default if nothing else was used

%endmacro


As far as I can tell, the GNU LESSER GENERAL PUBLIC LICENSE Version
2.1 applies to the above code snippet.

Nathan.

.

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