Commit 294f69e6 authored Oct 05, 2019 by Joe Perches Committed by Linus Torvalds Oct 11, 2019

compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use



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 should end in one of:

	break;
	fallthrough;
	goto <label>;
	return [expression];
	continue;

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: Joe Perches <joe@perches.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 48f9bcf9

include/linux/compiler_attributes.h

+17 −0

Original line number	Diff line number	Diff line
		@@ -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
		#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
		*/
		#if __has_attribute(__fallthrough__)
		# define fallthrough __attribute__((__fallthrough__))
		#else
		# define fallthrough do {} while (0) /* fallthrough */
		#endif

		/*
		* Note the missing underscores.
		*

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