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Re: [PATCH 7/10] local_t : powerpc
- From: Mathieu Desnoyers <mathieu dot desnoyers at polymtl dot ca>
- To: Paul Mackerras <paulus at samba dot org>
- Cc: linux-kernel at vger dot kernel dot org, Andrew Morton <akpm at osdl dot org>, Ingo Molnar <mingo at redhat dot com>, Greg Kroah-Hartman <gregkh at suse dot de>, Christoph Hellwig <hch at infradead dot org>, "Martin J. Bligh" <mbligh at mbligh dot org>, linuxppc-dev at ozlabs dot org, Douglas Niehaus <niehaus at eecs dot ku dot edu>, ltt-dev at shafik dot org, systemtap at sources dot redhat dot com, Thomas Gleixner <tglx at linutronix dot de>
- Date: Wed, 24 Jan 2007 12:00:22 -0500
- Subject: Re: [PATCH 7/10] local_t : powerpc
- References: <20061221001545.GP28643@Krystal> <20061221002705.GW28643@Krystal> <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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