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From: Joe Perches <joe@perches.com>
To: Linus Torvalds <torvalds@linux-foundation.org>,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cc: Kees Cook <keescook@chromium.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	"Gustavo A . R . Silva" <gustavo@embeddedor.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Kan Liang <kan.liang@linux.intel.com>,
	Namhyung Kim <namhyung@kernel.org>, Jiri Olsa <jolsa@redhat.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Shawn Landden <shawn@git.icu>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use
Date: Tue, 30 Jul 2019 22:35:18 -0700
Message-ID: <1d2830aadbe9d8151728a7df5b88528fc72a0095.1564549413.git.joe@perches.com> (raw)
In-Reply-To: <e0dd3af448e38e342c1ac6e7c0c802696eb77fd6.1564549413.git.joe@perches.com>

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];

fallthough is gcc's __attribute__((__fallthrough__)) which was introduced
in gcc version 7..

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>
---

For allow compilation of a kernel that includes net/sctp, this patch
also requires a rename of the use of fallthrough as a label in
net/sctp/sm_make_chunk.c that was submitted as:

https://lore.kernel.org/lkml/e0dd3af448e38e342c1ac6e7c0c802696eb77fd6.1564549413.git.joe@perches.com/

 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
 #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.
  *
-- 
2.15.0


  reply index

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-31  5:04 [PATCH] net: sctp: Rename fallthrough label to unhandled Joe Perches
2019-07-31  5:35 ` Joe Perches [this message]
2019-07-31  9:02   ` [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use Peter Zijlstra
2019-07-31  9:34     ` Joe Perches
2019-07-31 17:14   ` Pavel Machek
2019-07-31 17:51     ` Joe Perches
2019-07-31 18:24       ` hpa
2019-07-31 18:48         ` Peter Zijlstra
2019-07-31 20:02           ` Kees Cook
2019-07-31 20:59             ` Miguel Ojeda
2019-07-31 22:07               ` Joe Perches
2019-08-01  0:00                 ` Miguel Ojeda
2019-08-01 12:25             ` Peter Zijlstra
2019-08-15 18:15             ` Kees Cook
2019-08-15 22:31               ` Kees Cook
2019-09-16 22:19               ` treewide replacement of fallthrough comments with "fallthrough" macro (was Re: [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use) Kees Cook
2019-09-17 22:26                 ` Joe Perches
2019-09-17 23:38                   ` Kees Cook
2019-07-31 21:01           ` [RFC PATCH] compiler_attributes.h: Add 'fallthrough' pseudo keyword for switch/case use hpa
2019-07-31 23:55             ` Miguel Ojeda
2019-08-01  6:10               ` hpa
2019-08-01  7:52                 ` Joe Perches
2019-08-01 12:24                 ` Peter Zijlstra
2019-08-01 20:09                   ` hpa
2019-08-01 20:26                     ` Miguel Ojeda
2019-08-01 20:47                       ` Joe Perches
2019-08-02 11:00                       ` Neil Horman
2019-08-02 12:34                         ` Pavel Machek
2019-08-02 16:09                           ` Kees Cook
2019-08-02 16:16                             ` Joe Perches
2019-08-04 18:01   ` Joe Perches
2019-08-04 18:09     ` Linus Torvalds
2019-08-04 19:38       ` Miguel Ojeda
2019-08-05  0:39       ` Joe Perches
2019-08-05  1:18         ` Nathan Chancellor
2019-08-05  2:01           ` Joe Perches
2019-07-31 11:19 ` [PATCH] net: sctp: Rename fallthrough label to unhandled Neil Horman
2019-07-31 11:32   ` Joe Perches
2019-07-31 12:16     ` Neil Horman
2019-07-31 16:35       ` Joe Perches
2019-07-31 20:58         ` Neil Horman
2019-07-31 22:23           ` Joe Perches
2019-08-01 10:50             ` Neil Horman
2019-08-01 17:42               ` Joe Perches
2019-08-01 20:48                 ` Neil Horman
2019-08-05 11:49                 ` David Laight
2019-08-02 17:47       ` Joe Perches
2019-08-02 23:19         ` David Miller
2019-08-02 23:26           ` Joe Perches
2019-08-03 18:01           ` Joe Perches
2019-08-04 19:26           ` Neil Horman
2019-08-02 17:50 ` Neil Horman

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