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[xen master] xen/compiler: import 'fallthrough' keyword from linux
commit be5dc0b90db68df57925ee951ccc480fcab14192
Author: Rahul Singh <rahul.singh@arm.com>
AuthorDate: Wed Jan 20 14:52:41 2021 +0000
Commit: Julien Grall <jgrall@amazon.com>
CommitDate: Sat Jan 23 11:48:33 2021 +0000

xen/compiler: import 'fallthrough' keyword from linux

-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@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
---
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. */
--
generated by git-patchbot for /home/xen/git/xen.git#master