Hi Joe,
On Sat, Oct 5, 2019 at 6:46 PM Joe Perches <j...@perches.com> wrote:
>
> Reserve the pseudo keyword 'fallthrough' for the ability to convert the
> various case block /* fallthrough */ style comments to appear to be an
> actual reserved word with the same gcc case block missing fallthrough
> warning capability.
>
> All switch/case blocks now must end in one of:
>
> break;
> fallthrough;
> goto <label>;
> return [expression];
> continue;
>
> fallthough is gcc's __attribute__((__fallthrough__)) which was introduced
> in gcc version 7..
Nits: double period, missing "r" in fallthough.
> fallthrough devolves to an empty "do {} while (0)" if the compiler
> version (any version less than gcc 7) does not support the attribute.
Perhaps add a short note why (empty statement warnings maybe? I don't
remember them but it was months ago so maybe it changed).
> Signed-off-by: Joe Perches <j...@perches.com>
> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
Please add Dan's Suggested-by and copy the things I wrote in the
commit message when I proposed this:
https://github.com/ojeda/linux/commit/668f011a2706ea555987e263f609a5deba9c7fc4
> ---
> include/linux/compiler_attributes.h | 17 +++++++++++++++++
> 1 file changed, 17 insertions(+)
>
> diff --git a/include/linux/compiler_attributes.h
> b/include/linux/compiler_attributes.h
> index 6b318efd8a74..cdf016596659 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -40,6 +40,7 @@
> # define __GCC4_has_attribute___noclone__ 1
> # define __GCC4_has_attribute___nonstring__ 0
> # define __GCC4_has_attribute___no_sanitize_address__ (__GNUC_MINOR__ >= 8)
> +# define __GCC4_has_attribute___fallthrough__ 0
This goes after __externally_visible__.
> #endif
>
> /*
> @@ -185,6 +186,22 @@
> # define __noclone
> #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
This also goes after __externally_visible__.
Please add:
* Optional: only supported since gcc >= 7.1
* Optional: only supported since clang >= 10
* Optional: not supported by icc
As well as:
clang: https://clang.llvm.org/docs/AttributeReference.html#fallthrough
See how I did it in the link above:
https://github.com/ojeda/linux/commit/668f011a2706ea555987e263f609a5deba9c7fc4
> + */
> +#if __has_attribute(__fallthrough__)
> +# define fallthrough __attribute__((__fallthrough__))
> +#else
> +# define fallthrough do {} while (0) /* fallthrough */
> +#endif
> +
> /*
> * Note the missing underscores.
> *
> --
> 2.15.0
>
Cheers,
Miguel
