From: Darrick J. Wong <djw...@kernel.org> Back in mid-2021, Kees and Gustavo rammed into the kernel a bunch of static checker "improvements" that redefined '/* fallthrough */' comments for switch statements as a macro that virtualizes either that same comment, a do-while loop, or a compiler __attribute__. This was necessary to work around the poor decision-making of the clang, gcc, and C language standard authors, who collectively came up with four mutually incompatible ways to document a lack of branching in a code flow.
Having received ZERO HELP porting this to userspace, Eric and I foolishly dumped that crap into linux.h, which was a poor decision because we keep forgetting that linux.h is exported as a userspace header. This has now caused downstream regressions in Debian[1] and will probably cause more problems in the other distros. Move it to platform_defs.h since that's not shipped publicly and leave a warning to anyone else who dare modify linux.h. [1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1000974 Fixes: df9c7d8d ("xfs: Fix fall-through warnings for Clang") Cc: 1000...@bugs.debian.org, gustavo...@kernel.org, keesc...@chromium.org Signed-off-by: Darrick J. Wong <djw...@kernel.org> --- include/linux.h | 20 ++------------------ include/platform_defs.h.in | 21 +++++++++++++++++++++ 2 files changed, 23 insertions(+), 18 deletions(-) diff --git a/include/linux.h b/include/linux.h index 24650228..054117aa 100644 --- a/include/linux.h +++ b/include/linux.h @@ -360,24 +360,8 @@ fsmap_advance( #endif /* HAVE_MAP_SYNC */ /* - * Add the pseudo keyword 'fallthrough' so case statement blocks - * must end with any of these keywords: - * break; - * fallthrough; - * continue; - * goto <label>; - * return [expression]; - * - * gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes + * Reminder: anything added to this file will be compiled into downstream + * userspace projects! */ -#if defined __has_attribute -# if __has_attribute(__fallthrough__) -# define fallthrough __attribute__((__fallthrough__)) -# else -# define fallthrough do {} while (0) /* fallthrough */ -# endif -#else -# define fallthrough do {} while (0) /* fallthrough */ -#endif #endif /* __XFS_LINUX_H__ */ diff --git a/include/platform_defs.h.in b/include/platform_defs.h.in index 7c6b3ada..6e6f26ef 100644 --- a/include/platform_defs.h.in +++ b/include/platform_defs.h.in @@ -113,4 +113,25 @@ static inline size_t __ab_c_size(size_t a, size_t b, size_t c) sizeof(*(p)->member) + __must_be_array((p)->member), \ sizeof(*(p))) +/* + * Add the pseudo keyword 'fallthrough' so case statement blocks + * must end with any of these keywords: + * break; + * fallthrough; + * continue; + * goto <label>; + * return [expression]; + * + * gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes + */ +#if defined __has_attribute +# if __has_attribute(__fallthrough__) +# define fallthrough __attribute__((__fallthrough__)) +# else +# define fallthrough do {} while (0) /* fallthrough */ +# endif +#else +# define fallthrough do {} while (0) /* fallthrough */ +#endif + #endif /* __XFS_PLATFORM_DEFS_H__ */
