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

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Date:	Wed, 2 Mar 2016 10:39:15 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Andreas Schwab <schwab@...ux-m68k.org>
Cc:	Arnd Bergmann <arnd@...db.de>,
	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 Wed, Mar 2, 2016 at 10:28 AM, Andreas Schwab <schwab@...ux-m68k.org> wrote:
> Geert Uytterhoeven <geert@...ux-m68k.org> writes:
>
>>> +#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?
>
> Yes, that is guaranteed, the operations cancel each other (6.5.3.2#3: If
> the operand is the result of a unary * operator, neither that operator
> nor the & operator is evaluated and the result is as if both were
> omitted).

Thanks for confirming.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds