From: Mathieu Desnoyers <mathieu.desnoyers@polymtl•ca>
To: Paul Mackerras <paulus@samba•org>
Cc: Andrew Morton <akpm@osdl•org>,
Greg Kroah-Hartman <gregkh@suse•de>,
linux-kernel@vger•kernel.org,
"Martin J. Bligh" <mbligh@mbligh•org>,
Christoph Hellwig <hch@infradead•org>,
linuxppc-dev@ozlabs•org, Douglas Niehaus <niehaus@eecs•ku.edu>,
Ingo Molnar <mingo@redhat•com>,
ltt-dev@shafik•org, systemtap@sources•redhat.com,
Thomas Gleixner <tglx@linutronix•de>
Subject: Re: [PATCH 7/10] local_t : powerpc
Date: Wed, 24 Jan 2007 12:00:22 -0500 [thread overview]
Message-ID: <20070124170022.GE4979@Krystal> (raw)
In-Reply-To: <17847.8700.118329.777644@cargo.ozlabs.ibm.com>
* Paul Mackerras (paulus@samba•org) wrote:
> Mathieu Desnoyers writes:
>
> > +static __inline__ int local_dec_if_positive(local_t *l)
> > +{
> > + int t;
> > +
> > + __asm__ __volatile__(
> > +"1: lwarx %0,0,%1 # local_dec_if_positive\n\
> > + addic. %0,%0,-1\n\
> > + blt- 2f\n"
> > + PPC405_ERR77(0,%1)
> > +" stwcx. %0,0,%1\n\
> > + bne- 1b"
>
> This has the same bugs that we fixed recently in atomic_dec_if_positive;
> first, on 64-bit machines, the lwarx will zero-extend the word loaded
> from memory, and so the result of the addic will be negative only if
> the word was originally 0. Secondly, even on 32-bit machines,
> 0x80000000 will be considered positive since decrementing it gives
> 0x7fffffff, which is positive.
>
Hi Paul,
Thanks, will fix.
Mathieu
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prev parent reply other threads:[~2007-01-24 17:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20061221001545.GP28643@Krystal>
2006-12-21 0:27 ` [PATCH 7/10] local_t : powerpc Mathieu Desnoyers
2006-12-21 3:34 ` [Ltt-dev] " Mathieu Desnoyers
2007-01-24 9:08 ` Paul Mackerras
2007-01-24 10:43 ` Gabriel Paubert
2007-01-24 17:00 ` Mathieu Desnoyers [this message]
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