Re: [PATCH v4 08/11] xen/compiler: import 'fallthrough' keyword from linux

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi,

> On 8 Jan 2021, at 14:46, Rahul Singh <Rahul.Singh@xxxxxxx> wrote:
> 
> -Wimplicit-fallthrough warns when a switch case falls through. Warning
> can be suppress by either adding a /* fallthrough */ comment, or by
> using a null statement: __attribute__ ((fallthrough))
> 
> Define the pseudo keyword 'fallthrough' for the ability to convert the
> various case block /* fallthrough */ style comments to null statement
> "__attribute__((__fallthrough__))"
> 
> In C mode, GCC supports the __fallthrough__ attribute since 7.1,
> the same time the warning and the comment parsing were introduced.
> 
> fallthrough devolves to an empty "do {} while (0)" if the compiler
> version (any version less than gcc 7) does not support the attribute.
> 
> Signed-off-by: Rahul Singh <rahul.singh@xxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Cheers
Bertrand

> ---
> Changes in V4:
> - This patch is introduce in this verison.
> ---
> xen/include/xen/compiler.h | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
> 
> diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
> index e643e69128..0ec0b4698e 100644
> --- a/xen/include/xen/compiler.h
> +++ b/xen/include/xen/compiler.h
> @@ -33,6 +33,22 @@
> #define unreachable() __builtin_unreachable()
> #endif
> 
> +/*
> + * Add the pseudo keyword 'fallthrough' so case statement blocks
> + * must end with any of these keywords:
> + *   break;
> + *   fallthrough;
> + *   goto <label>;
> + *   return [expression];
> + *
> + *  gcc: 
> https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
> + */
> +#if (!defined(__clang__) && (__GNUC__ >= 7))
> +# define fallthrough        __attribute__((__fallthrough__))
> +#else
> +# define fallthrough        do {} while (0)  /* fallthrough */
> +#endif
> +
> #ifdef __clang__
> /* Clang can replace some vars with new automatic ones that go in .data;
>  * mark all explicit-segment vars 'used' to prevent that. */
> -- 
> 2.17.1
>