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

Geert Uytterhoeven [off-list ref] writes:

quoted

+#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).

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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On Wed, Mar 2, 2016 at 10:28 AM, Andreas Schwab [off-list ref] wrote:

Geert Uytterhoeven [off-list ref] writes:

quoted

quoted

+#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@linux-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