send-pr this?

Jaromir

David Laight wrote:
> I've found a bug in the sbin/fdisk/mbr_bootsel/mbr_bootsel.S timeout code.
> 
> If you specify a timeout of 1801 or larger (in fdisk) then the timer
> expires immediately.
> 
> I'm fairly sure that the problem is either that the:
>     movw_mem_ax(timeout)
> instruction will sign extend the 16bit value to 32 bits
> or that the:
>     cmpl    %rax,%edx
> instruction is only doing a 16 bit compare and is followed by
> a signed jump.
> 
> The code can also be simplified - saving some vital bytes!
> If the sums are correctly done modulo 2^16 the high part of the
> counter can be ignored.
> 
> I haven't test this - anyone who has done it before or feels brave?
> (I suppose you can boot from CD to put the MBR back...)
> But I think the following is right - assuming I've not mistyped it.
> 
>     xorb    %ah,%ah
>     int     $0x1a
>     movl    %edx,%edi
> 3:
>     movb    $1,%ah
>     int     $0x16
>     jnz     4f
>     xor     %ah,%ah
>     int     $0x1a
>     subl    %edi,%edx
>     movw_mem_ax(timeout)
>     cmpl    %eax,%edx
>     jb      3b
> 
> Hard to count how many bytes this saves...
> 
> I don't have a system that can reference the CVS tree.....
> Anyone fancy the dirty work?
> 
>     David
> 


-- 
Jaromir Dolecek <jdolecek@NetBSD.org> http://www.NetBSD.org/Ports/i386/ps2.html
-=  Those who would give up liberty for a little temporary safety deserve  =-
-=  neither liberty nor safety, and will lose both.  -- Benjamin Franklin  =-