Re: Build failure for R3000 DECstation

[Ralf Baechle <ralf@oss.sgi.com>]

On Wed, Nov 15, 2000 at 01:58:21AM +0100, Maciej W. Rozycki wrote:

> > In any case, for uniprocessor non-ll/sc machines there is also a better
> > solution availble with no syscalls at all.  It's easy to implement, just
> > use the fact that any exception will change the values of k0/k1.  That of
> > course breaks silently on SMP.
> 
>  Can you guarantee it???  Well I can guarantee k0 and k1 won't change when
> least expected. ;-)  AFAIK, the only fact guaranteed is that exception
> handlers do not preserve the values of the scratch registers, but it does
> not mean the last value written there is always different from what was
> there upon a handler's entry... 

Make that change k0 to a non-zero value.  So a R3000 UP spinlock can look
like:

        move    k0, zero
        li      t0, 1
0:      sw      t0, spin
        bnez    k0, 0b

        [critical section]

        sw      zero, spin

  Ralf

(Who should write thousant times ``I shall not post with a phone in my hand'')