Linking a simple DOS program (ASM), WLINK warns about no stack segment

Question

I'm trying to assemble and link the following program (.EXE, not .COM), based on the example in the NASM manual:

segment data

hello:  db "hello",13,10,"$"

segment code
..start:
        mov ax,data
        mov ds,ax
        mov ax,stack
        mov ss,ax
        mov sp,stacktop
        mov dx,hello
        mov ah,9
        int 0x21
        mov ax,0x4c00
        int 0x21

segment stack stack
        resb 64
stacktop:

I assemble with the following command (which produces nothing on stdout, but generates test.obj):

nasm -Wall -f obj test.asm

and link with the following command (this is OpenWatcom 1.9 WLINK):

wlink name test.exe format dos file test.obj

This gives me the following output (including a warning):

Open Watcom Linker Version 1.9
Portions Copyright (c) 1985-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.
See http://www.openwatcom.org/ for details.
loading object files
Warning! W1014: stack segment not found
creating a DOS executable

The manual states:

The above code declares a stack segment containing 64 bytes of uninitialized stack space, and points `stacktop` at the top of it. The directive segment stack stack defines a segment called `stack`, and also of type `STACK`. The latter is not necessary to the correct running of the program, but linkers are likely to issue warnings or errors if your program has no segment of type `STACK`.

What am I missing?

Answer 1

In NASM code you need to mark the stack segment as having a class of stack.

Also, DOS will load SS and SP for you before your program starts.

Finally, 64 bytes of stack is a little too little. Interrupt service routines use the current stack and if it's too small, they will overwrite some code or data nearby.

This is how you fix it:

segment data

hello:  db "hello",13,10,"$"

segment code
..start:
        mov ax,data
        mov ds,ax

;        mov ax,stack
;        mov ss,ax
;        mov sp,stacktop

        mov dx,hello
        mov ah,9
        int 0x21
        mov ax,0x4c00
        int 0x21

segment stack class=stack
        resb 512 ; 64 is too little for interrupts
;stacktop: