linux-kernel - Re: [PATCH] include/uapi/linux/swab.h: add __u16 cast to _

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Date:   Tue, 7 Jun 2022 16:20:17 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Justin Stitt <jstitt007@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Nathan Chancellor <nathan@...nel.org>, Tom Rix <trix@...hat.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] include/uapi/linux/swab.h: add __u16 cast to __swab16 conditional

On Tue, Jun 7, 2022 at 3:20 PM Justin Stitt <jstitt007@...il.com> wrote:
>
> if __HAVE_BUILTIN_BSWAP16__ is defined then __swab16 utilizes a __u16 cast.
> This same cast should be used if __HAVE_BUILTIN_BSWAP16__ is not defined as
> well. This should fix loads (at least a few) clang -Wformat warnings
> specifically with `ntohs()`
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Signed-off-by: Justin Stitt <jstitt007@...il.com>

I wonder why there's a cast inside the __builtin_constant_p parameter
list? Can't imagine that changing anything. I wonder if this should
be:

diff --git a/include/uapi/linux/swab.h b/include/uapi/linux/swab.h
index 7272f85d6d6a..0723a9cce747 100644
--- a/include/uapi/linux/swab.h
+++ b/include/uapi/linux/swab.h
@@ -102,7 +102,7 @@ static inline __attribute_const__ __u32
__fswahb32(__u32 val)
 #define __swab16(x) (__u16)__builtin_bswap16((__u16)(x))
 #else
 #define __swab16(x)                            \
-       (__builtin_constant_p((__u16)(x)) ?     \
+       (__u16)(__builtin_constant_p(x) ?       \
        ___constant_swab16(x) :                 \
        __fswab16(x))
 #endif
@@ -115,7 +115,7 @@ static inline __attribute_const__ __u32
__fswahb32(__u32 val)
 #define __swab32(x) (__u32)__builtin_bswap32((__u32)(x))
 #else
 #define __swab32(x)                            \
-       (__builtin_constant_p((__u32)(x)) ?     \
+       (__u32)(__builtin_constant_p(x) ?       \
        ___constant_swab32(x) :                 \
        __fswab32(x))
 #endif
@@ -128,7 +128,7 @@ static inline __attribute_const__ __u32
__fswahb32(__u32 val)
 #define __swab64(x) (__u64)__builtin_bswap64((__u64)(x))
 #else
 #define __swab64(x)                            \
-       (__builtin_constant_p((__u64)(x)) ?     \
+       (__u64)(__builtin_constant_p(x) ?       \
        ___constant_swab64(x) :                 \
        __fswab64(x))
 #endif
--
Thanks,
~Nick Desaulniers