linux-kernel - [PATCH v2 2/2] bitfield: Ensure the return values of helper functions are checked

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Message-ID: <20250709093808.920284-3-ben.horgan@arm.com>
Date: Wed,  9 Jul 2025 10:38:08 +0100
From: Ben Horgan <ben.horgan@....com>
To: catalin.marinas@....com,
	will@...nel.org,
	maz@...nel.org,
	oliver.upton@...ux.dev,
	joey.gouly@....com,
	suzuki.poulose@....com,
	yuzenghui@...wei.com,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	yury.norov@...il.com,
	linux@...musvillemoes.dk,
	linux-kernel@...r.kernel.org
Cc: james.morse@....com,
	Ben Horgan <ben.horgan@....com>
Subject: [PATCH v2 2/2] bitfield: Ensure the return values of helper functions are checked

As type##_replace_bits() has no side effects it is only useful if its
return value is checked. Add __must_check to enforce this usage. To have
the bits replaced in-place typep##_replace_bits() can be used instead.

Although, type_##_get_bits() and type_##_encode_bits() are harder to misuse
they are still only useful if the return value is checked. For
consistency, also add __must_check to these.

Signed-off-by: Ben Horgan <ben.horgan@....com>
---
 include/linux/bitfield.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index 6d9a53db54b6..5355f8f806a9 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -189,14 +189,14 @@ static __always_inline u64 field_mask(u64 field)
 }
 #define field_max(field)	((typeof(field))field_mask(field))
 #define ____MAKE_OP(type,base,to,from)					\
-static __always_inline __##type type##_encode_bits(base v, base field)	\
+static __always_inline __##type __must_check type##_encode_bits(base v, base field)	\
 {									\
 	if (__builtin_constant_p(v) && (v & ~field_mask(field)))	\
 		__field_overflow();					\
 	return to((v & field_mask(field)) * field_multiplier(field));	\
 }									\
-static __always_inline __##type type##_replace_bits(__##type old,	\
-					base val, base field)		\
+static __always_inline __##type __must_check type##_replace_bits(__##type old,	\
+							base val, base field)	\
 {									\
 	return (old & ~to(field)) | type##_encode_bits(val, field);	\
 }									\
@@ -205,7 +205,7 @@ static __always_inline void type##p_replace_bits(__##type *p,		\
 {									\
 	*p = (*p & ~to(field)) | type##_encode_bits(val, field);	\
 }									\
-static __always_inline base type##_get_bits(__##type v, base field)	\
+static __always_inline base __must_check type##_get_bits(__##type v, base field)	\
 {									\
 	return (from(v) & field)/field_multiplier(field);		\
 }
-- 
2.43.0