linux-kernel - Re: [PATCH 1/6] rtc: generic: allow building on all architectures

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Message-ID: <1620536.OtjnSSLgCT@wuerfel>
Date:	Wed, 02 Mar 2016 10:05:18 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Kyle McMartin <kyle@...artin.ca>,
	RTCLINUX <rtc-linux@...glegroups.com>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Linux-sh list <linux-sh@...r.kernel.org>,
	Parisc List <linux-parisc@...r.kernel.org>,
	linux-m68k <linux-m68k@...ts.linux-m68k.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] rtc: generic: allow building on all architectures

On Wednesday 02 March 2016 09:57:27 Geert Uytterhoeven wrote:
> > @@ -33,13 +35,21 @@ static const struct rtc_class_ops generic_rtc_ops = {
> >         .read_time = generic_get_time,
> >         .set_time = generic_set_time,
> >  };
> > +#else
> > +#define generic_rtc_ops *(struct rtc_class_ops*)NULL
> > +#endif
> >
> >  static int __init generic_rtc_probe(struct platform_device *dev)
> >  {
> >         struct rtc_device *rtc;
> > +       const struct rtc_class_ops *ops;
> > +
> > +       ops = dev_get_platdata(&dev->dev);
> > +       if (!ops)
> > +               ops = &generic_rtc_ops;
> 
> I hope no compiler version treats "&*(struct rtc_class_ops*)NULL" as
> undefined behavior?

It's a bit odd, but I think it's syntactically correct C, and not
much too different from 

#define offsetof(TYPE, MEMBER)  ((size_t)&((TYPE *)0)->MEMBER)

is it? My last patch gets rid of it again.

	Arnd