linux-kernel - [PATCH v2] include/uapi/linux/swab.h: move explicit cast outside ternary

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Date:   Tue,  7 Jun 2022 17:14:22 -0700
From:   Justin Stitt <jstitt007@...il.com>
To:     ndesaulniers@...gle.com, akpm@...ux-foundation.org
Cc:     jstitt007@...il.com, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev, nathan@...nel.org, trix@...hat.com
Subject: [PATCH v2] include/uapi/linux/swab.h: move explicit cast outside ternary

A cast inside __builtin_constant_p doesn't do anything since it should evaluate
as constant at compile time irrespective of this cast. Instead, I moved this
cast outside the ternary to ensure the return type is as expected.

For instance, if __HAVE_BUILTIN_BSWAP16__ was not defined then __swab16 is
actually returning an `int` not a `u16` due to integer promotion as described
by Nick in this thread. This has repercussions when building with clang
-Wformat. This fix should solve many of these warnings.

Link: https://github.com/ClangBuiltLinux/linux/issues/378
Suggested-by: Nathan Chancellor <nathan@...nel.org>
Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Signed-off-by: Justin Stitt <jstitt007@...il.com>
---
 include/uapi/linux/swab.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
index f6be3f2e6fee..ab5a1283800c 100644
--- a/include/uapi/linux/swab.h
+++ b/include/uapi/linux/swab.h
@@ -99,10 +99,10 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
  * @x: value to byteswap
  */
 #ifdef __HAVE_BUILTIN_BSWAP16__
-#define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
+#define __swab16(x) (__u16)__builtin_bswap16(x)
 #else
 #define __swab16(x)				\
-	(__u16)(__builtin_constant_p((__u16)(x)) ?	\
+	(__u16)(__builtin_constant_p(x) ?	\
 	___constant_swab16(x) :			\
 	__fswab16(x))
 #endif
@@ -112,10 +112,10 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
  * @x: value to byteswap
  */
 #ifdef __HAVE_BUILTIN_BSWAP32__
-#define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
+#define __swab32(x) (__u32)__builtin_bswap32(x)
 #else
 #define __swab32(x)				\
-	(__builtin_constant_p((__u32)(x)) ?	\
+	(__u32)(__builtin_constant_p(x) ?	\
 	___constant_swab32(x) :			\
 	__fswab32(x))
 #endif
@@ -125,10 +125,10 @@ static inline __attribute_const__ __u32 __fswahb32(__u32 val)
  * @x: value to byteswap
  */
 #ifdef __HAVE_BUILTIN_BSWAP64__
-#define __swab64(x) (__u64)__builtin_bswap64((__u64)(x))
+#define __swab64(x) (__u64)__builtin_bswap64(x)
 #else
 #define __swab64(x)				\
-	(__builtin_constant_p((__u64)(x)) ?	\
+	(__u64)(__builtin_constant_p(x) ?	\
 	___constant_swab64(x) :			\
 	__fswab64(x))
 #endif
-- 
2.30.2