My 8-Line program wont run!

Index > Main > My 8-Line program wont run!

Author

Thread

quddusaliquddus

Joined: 18 May 2009
Posts: 3

quddusaliquddus 19 May 2009, 00:01

Quote:

DOSSEG
.MODEL SMALL
.STACK 200h
.DATA
.CODE
START:
INT 20
END START

Why?

19 May 2009, 00:01

bitRAKE

Joined: 21 Jul 2003
Posts: 4181
Location: vpcmpistri

bitRAKE 19 May 2009, 01:03

That isn't FASM syntax - looks like MASM?

19 May 2009, 01:03

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20531
Location: In your JS exploiting you and your system

revolution 19 May 2009, 03:17

In fasm you can just do this:

Code:

int 0x20

7 of those lines are MASM bloat.

19 May 2009, 03:17

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 19 May 2009, 03:27

Or maybe:

Code:

format MZ
stack $200

; int $20 ; Not int $20

mov ax, $4C00
int $21

Unless it is OK to generate a COM executable.

[edit]Code corrected according to Japheth's post below[/edit]

Last edited by LocoDelAssembly on 20 May 2009, 16:19; edited 1 time in total

19 May 2009, 03:27

quddusaliquddus

Joined: 18 May 2009
Posts: 3

quddusaliquddus 19 May 2009, 03:35

Thanks for the replies.

Im new to all things assembly, and I am following an example of x86 assembly language code.

Are there big differences between different assembly compilers?

19 May 2009, 03:35

quddusaliquddus

Joined: 18 May 2009
Posts: 3

quddusaliquddus 19 May 2009, 03:37

And also - how would I prevent the above-generated program from quitting so quickly?

19 May 2009, 03:37

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20531
Location: In your JS exploiting you and your system

revolution 19 May 2009, 05:39

Have a look at the "examples" folder in the download zip file. Those files are already in fasm syntax.

19 May 2009, 05:39

Borsuc

Joined: 29 Dec 2005
Posts: 2465
Location: Bucharest, Romania

Borsuc 20 May 2009, 00:50

revolution wrote:

Have a look at the "examples" folder in the download zip file. Those files are already in fasm syntax.

To add to what revolution said: you don't have to understand the whole example! You only have to see the relevant parts (e.g the beginning) to get an idea Wink

_________________
Previously known as The_Grey_Beast

20 May 2009, 00:50

Japheth

Joined: 26 Oct 2004
Posts: 151

Japheth 20 May 2009, 10:21

LocoDelAssembly wrote:

Or maybe:
Code:
format MZ
stack $200

int $20
; Or:
; mov ax, $4C00
; int $21
    
Unless it is OK to generate a COM executable.

Actually, format MZ combined with INT $20 is a bug. Because to terminate a DOS program with INT 20h "requires" CS==PSP segment, which usually is true for .COM files only.

20 May 2009, 10:21

LocoDelAssembly
Your code has a bug

Joined: 06 May 2005
Posts: 4624
Location: Argentina

LocoDelAssembly 20 May 2009, 16:19

Corrected, thanks.

20 May 2009, 16:19

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8367
Location: Kraków, Poland

Tomasz Grysztar 20 May 2009, 18:54

Japheth wrote:

Actually, format MZ combined with INT $20 is a bug. Because to terminate a DOS program with INT 20h "requires" CS==PSP segment, which usually is true for .COM files only.

Good that you added "usually", because you can get the same thing with MZ format, too:

Code:

format MZ

segment main
PSP = main - 10h
entry PSP:100h
org 100h

        mov     ah,9
        mov     dx,_hello
        int     21h

        int     20h

_hello db "Hello, guys!",24h

Actually, this is the kind of "emulation" that fasm does when you specify binary .com file as a stub for PE executable.

20 May 2009, 18:54

DOS386

Joined: 08 Dec 2006
Posts: 1905

DOS386 21 May 2009, 13:41

quddusaliquddus wrote:

My 8-Line program wont run!
Why?
And also - how would I prevent the above-generated program from quitting so quickly?

It seems to be MASM syntax and 7 of the 8 lines don't do anything, there is just 1 ( ONE ) instruction, as pointed above Smile

Also, numbers are decimal by default in FASM so your "INT 20" becomes INT $14 - serial port: http://www.ctyme.com/intr/int-14.htm

INT $20 would be a bad (see above) way to exit, the safest one (see also above) is:

Code:

  mov ax, $4C00
  int $21

To prevent from "quitting so quickly", you have to do something before you exit Wink

Also INT $21 is DOS only code, so for DOS examples check the DOS subforum, OTOH for Win32 forget INT $21 and check the Win32 subforum and included examples using format PE Idea

21 May 2009, 13:41

< Last Thread | Next Thread >

Forum Rules:

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum