Is there a boot sector guru in the house?

John Baldwin jhb at FreeBSD.org
Thu Jan 6 13:21:21 PST 2005


On Tuesday 04 January 2005 08:36 pm, Peter Edwards wrote:
> I don't have a box I can test this on, but this looks like a definite
> candidate to get
> 3 more bytes:
>
> --- boot0.S     24 Nov 2004 15:39:04 -0000      1.12
> +++ boot0.S     5 Jan 2005 01:27:31 -0000
> @@ -314,8 +314,7 @@
>                 cmpw $MAGIC,0x1fe(%bx)          # Bootable?
>                 jne main.10                     # No
>                 pushw %si                       # Save
> -               movw $crlf,%si                  # Leave some
> -               callw puts                      #  space
> +               callw putn                      # Leave space
>                 popw %si                        # Restore
>                 jmp *%bx                        # Invoke bootstrap
>
> If my arithmetic is correct, that leaves us wanting one more byte.
> I don't get the save/restore of %si at the end, and judging by the
> comment, someone else didn't either. It could be of some use to the
> chained loader, but our  boot1.S doesn't do anything with it.

This actually changes behavior I think (the earlier code outputs two blank 
lines, the second only one).  However, the push and pop of %si probably can 
go.  I think the save/restore there is just pedantic save/restore around 
puts.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org


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