linux-kernel - Re: [PATCH] GICv3: Fixing 32 bit compatibility

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Date:	Tue, 9 Sep 2014 11:19:12 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Robert Richter <rric@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Robert Richter <rrichter@...ium.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] GICv3: Fixing 32 bit compatibility

On Tue, Sep 09, 2014 at 11:12:01AM +0200, Robert Richter wrote:
> On 09.09.14 10:00:42, Uwe Kleine-König wrote:
> > On Mon, Sep 08, 2014 at 04:11:19PM +0200, Robert Richter wrote:
> 
> > > @@ -479,7 +479,7 @@ static void gic_raise_softirq(const struct cpumask *mask, unsigned int irq)
> > >     smp_wmb();
> > >  
> > >     for_each_cpu_mask(cpu, *mask) {
> > > -           u64 cluster_id = cpu_logical_map(cpu) & ~0xffUL;
> > > +           u64 cluster_id = cpu_logical_map(cpu) & ~0xffULL;
> > This doesn't change anything, does it?
> 
> It does, not in 64 bit but in 32 bit there unsigned long is 32
> bit. So, bit masks are broken if you compile a 32 bit kernel.
Can you make an example where the result actually changes?

> > I wonder if it would be cleaner to use (u64)0xff here.
> 
> No, that's ULL for. This is commonly used in x86 too.
I don't care much here, but I'd say ULL is to force an unsigned long
long. If you want to make it obvious that you want a 64bit value, a cast
to u64 makes this more clear.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
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