Question

I have a problem correctly terminating a 16bit DOS program written in Assembly. Here’s part of code:

.386P
.model flat

stack_s segment stack 'stack' 
        db 256 dup(0)
stack_s ends

data segment use16
data ends

code segment 'code' use16
assume cs:code, ds:data

main proc
    mov ax, data
    mov ds, ax

    iretd
main endp

code ends
end main

The problem is, that the program doesn’t terminate in a correct way. DOSBox just freezes. I tried to understand what happens using debugger, and it seems the program just ends up in an infinite loop after iretd is performed. Why does this happen? How can do I terminate a 16bit DOS app correctly?

Answer 1

The most correct way to end a DOS program is to use the “terminate” DOS function; followed by adequate comments so that people understand that this function won’t return.

For example:

pleaseKillMeNow:
    mov ah,0x4C          ;DOS "terminate" function
    int 0x21