Re: [Nasm-users] [aoaprogramming] Re: boot code

[Frank K. <fbk...@ve...>]

martinknappe wrote:
> 
> 
> Got the error(s)
> 
>  > its still not working, it seems im still in an endless loop
>  > somewhere:
>  >
>  > BITS 16
>  > jmp 07C0h:start
>  >
>  > start:
>  > mov ax, cs
>  > mov ds, ax
>  > push txt
>  > rept:
>  > call print
>  > add sp, 2
>  > jmp rept
> 
> Here I'm jumping back to the procedure call, not to where the
> parameter is pushed...

Yup. Good catch!

>  > print:
>  > push bp
>  > mov bp, sp
>  > push ax
>  > push bx
>  > mov ah, 0Eh
>  > mov bx, [bp+2]
> 
> This needs to read [bp+4].

You had it [bp + 4] originally, no?

> Maybe someone can explain that to me. I
> thought in 16Bit code [bp] is the return address right after calling
> the procedure and [bp+2] is the parameter pushed last unto the stack,
> but it seems I'm wrong here :-(

Correct, so far... but then you "push bp"... Stack looks like:

???
; more parameters?
param0
; return address segment, for a "far" call
return address offset
caller's bp

So [bp + 4] is correct.

Best,
Frank