COM files in Windows 7 64-bit?

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Falk

Joined: 16 Aug 2011
Posts: 2

Falk 20 Aug 2011, 21:23

I've just started with Assembly, and I found this code in a tutorial:

Code:

org 100h
mov ah,09
msg db "hello world!$"
mov dx,msg
int 21h
mov ah,08
int 21h
int 20h

In Windows XP 32-bit it displayed a nice MSDOS prompt with the text in it.
In Windows 7 64-bit I get this message:

Quote:

This version of the file is not compatible with the version of Windows you're running. Check your computer's system information to see whether you need an x86 (32-bit) or an x64 (64-bit) version of the program

Is there a way to make this code (or something similar) work in 64-bit?
I quite like the simpleness of this code, and I would like to wait a while before I start with all the Windows includes and the PE format.

20 Aug 2011, 21:23

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20425
Location: In your JS exploiting you and your system

revolution 20 Aug 2011, 21:27

You will need something like DOSBOX to run the old DOS programs in Win7. MS removed support for 16-bit programs so there is no other way other than using a DOS emulator.

20 Aug 2011, 21:27

me239

Joined: 06 Jan 2011
Posts: 200

me239 20 Aug 2011, 21:32

revolution wrote:

You will need something like DOSBOX to run the old DOS programs in Win7. MS removed support for 16-bit programs so there is no other way other than using a DOS emulator.

Beware though, DOSBox is meant for DOS gaming so don't be surprised if a lot of your DOS utilities and programs don't work.

20 Aug 2011, 21:32

DOS386

Joined: 08 Dec 2006
Posts: 1903

DOS386 21 Aug 2011, 02:07

Falk wrote:

Code:

org 100h
mov ah,09
msg db "hello world!$" ; !!! BUG !!!
mov dx,msg
int 21h
mov ah,08
int 21h
int 20h

The code is faulty as it
executes data Sad

Quote:

Is there a way to make this code (or something similar) work in
64-bit?

NO.

Quote:

I quite like the simpleness of this code, and I would like to wait a while before I start with all the Windows includes and the PE format.

PE works without includes too
Wink

... Otherweise, I recommend only
PE examples if you don't have DOS.

_________________
Bug Nr.: 12345

Title: Hello World program compiles to 100 KB !!!

Status: Closed: NOT a Bug

21 Aug 2011, 02:07

Falk

Joined: 16 Aug 2011
Posts: 2

Falk 21 Aug 2011, 09:23

I think that I'll just run in Windows XP/Virtual mode on Windows 7.

DOS386 wrote:

The code is faulty as it
executes data

As I understand it too, yes it does.
But it always works, so I let that one slide, as I believe I know what the problem is, and won't really build a major project based on this hello world Smile

Thanks guys.

21 Aug 2011, 09:23

Madis731

Joined: 25 Sep 2003
Posts: 2139
Location: Estonia

Madis731 21 Aug 2011, 14:26

You are *VERY* lucky that your code works, because this is what the CPU sees:

Code:

org 100h
mov ah,09
msg:push 6C65h
    insb
    outsw
    jc $+2+6Ch
    and [fs:si],sp
mov dx,msg
int 21h
mov ah,08
int 21h
int 20h

21 Aug 2011, 14:26

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