difference between win32,dos and linux assembly

[lepricaun]

hi guys,

i've just started to learn assembly, i've got a couple of tutorials and a couple of assemblers (Tasm,Masm32,LZasm,Goasm,Nasm) , but somehow i've started with one tutorial, written a program, try to assemble it, and all i got was a bunch of errors...

.model small
.stack
.data
message   db "Hello world, I'm learning Assembly !!!", "$"

.code

main   proc
   mov   ax,seg message
   mov   ds,ax

   mov   ah,09
   lea   dx,message
   int   21h

   mov   ax,4c00h
   int   21h
main   endp
end main

this was the source. i've tried assembling it on linux --> no good, try do do it with masm32,LZasm,GoAsm,Tasm on Windows --> no good either...

so i guess this is a DOS tutorial, but how can i see the difference?? i eventually want to learn assembly for win32 and linux, mostly because i would like to use a debugger if necessary, and so i must be able to read/understand assembly...

this is the tutorial i've found for win32 here, great tutorial b.t.w., but like i said, how can i see in the code if a program is written for DOS assembly, Linux or win32 ???

i've tried google for this, but none of the things i've found were very clear

[jdenny]

Well, int 21h was originally a DOS interrupt call, so it can't be used in Linux. But you can still use it on the DOS/Command Prompt in Windows. (See below note).

how can i see in the code if a program is written for DOS assembly, Linux or win32 ???

I think the author should've explicitly explained it, since assembly language is always architecture (hardware and OS) specific.

Note:
Here's how I test the int 21h function call on my XP box. I open a command prompt then use the good ol' debug command:

C:\>debug
-a100
1389:0100 jmp 110
1389:0102 db "Test INT 21h$"
1389:010F nop
1389:0110 mov dx,102
1389:0113 mov ah,9
1389:0115 int 21
1389:0117 int 20
1389:0119
-g
Test INT 21h
Program terminated normally
-q
C:\>


Peace always,
<jdenny>

[cacosapo]

you can see the diference between the code looking for system calls or HL API.
as Jdenny stated, assembly is hardware oriented. So you are programming at your pc, you are using IA-32 archicteture (a.k.a. Intel 32-bits). Basic instructions are connected to what Intel has specified on that (you can get book from Intel side).
--- there is some extensions to that archicture that arent present on every machine, such as SSE2 (intel) or 3DNow (AMD) ---
If u look thru the code, you will see eventually a system call/API. On that, you can identify the target platform (Win/*nix).

[lepricaun]

thanks, this will surely help me

[SerpentSin]

lepricaun, complementing what everyone else said, I consider the best way to find out what architecture the source file is designed for is to analyse the program structure, because, like jdenny said, different archictures require assembly programs to be built in different ways, and that could be a difficult task for beginners. I recommend you stick with DOS for a while (because that's the system most beginner tutorials use) and then move to a more complicated platform when you're used to all the assembly mnemonics, syntax and paradigm.

There are excellent free assembly tutorials and resources by Randall Hyde available here:
http://webster.cs.ucr.edu

Start on Art Of Assembly and then move on to your architecture of choice.
Have fun!

and yet some more excellent assembly for win32 tutorials and resources available here:
http://www.win32asm.cjb.net

[el-half]

C:\>debug
-a100
1389:0100 jmp 110
1389:0102 db "Test INT 21h$"
1389:010F nop
1389:0110 mov dx,102
1389:0113 mov ah,9
1389:0115 int 21
1389:0117 int 20
1389:0119
-g
Test INT 21h
Program terminated normally
-q
C:\>

Lol, that's funny, I always found coding assembly annoying in debug because I had to count on which offset I would declare something. That jump in the beginning solves that. Lol, that I never thought of that.

[lepricaun]

thanks for the links, i'll go and check it out...