linux-mips
[Top] [All Lists]

Re: Build failure for R3000 DECstation

To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Subject: Re: Build failure for R3000 DECstation
From: Ralf Baechle <ralf@oss.sgi.com>
Date: Wed, 15 Nov 2000 02:43:58 +0100
Cc: Harald Koerfgen <Harald.Koerfgen@home.ivm.de>, linux-mips@oss.sgi.com
In-reply-to: <Pine.GSO.3.96.1001115014410.11897A-100000@delta.ds2.pg.gda.pl>; from macro@ds2.pg.gda.pl on Wed, Nov 15, 2000 at 01:58:21AM +0100
References: <20001115004122.G927@bacchus.dhis.org> <Pine.GSO.3.96.1001115014410.11897A-100000@delta.ds2.pg.gda.pl>
Sender: owner-linux-mips@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'')

<Prev in Thread] Current Thread [Next in Thread>