Messages in this thread | | | From | Miguel Ojeda <> | Date | Sat, 5 Oct 2019 19:17:36 +0200 | Subject | Re: [PATCH 2/4] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use |
| |
Hi Joe,
On Sat, Oct 5, 2019 at 6:46 PM Joe Perches <joe@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 <joe@perches.com> > Acked-by: Peter Zijlstra (Intel) <peterz@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
| |