linux-kernel - [PATCH next 09/14] bits: Change BIT_U8/16() and GENMASK

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Message-Id: <20260121145731.3623-10-david.laight.linux@gmail.com>
Date: Wed, 21 Jan 2026 14:57:26 +0000
From: david.laight.linux@...il.com
To: Nathan Chancellor <nathan@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Arnd Bergmann <arnd@...db.de>,
	linux-arch@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Yury Norov <yury.norov@...il.com>,
	Lucas De Marchi <lucas.demarchi@...el.com>,
	Jani Nikula <jani.nikula@...el.com>,
	Vincent Mailhol <mailhol.vincent@...adoo.fr>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Kees Cook <keescook@...omium.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: David Laight <david.laight.linux@...il.com>
Subject: [PATCH next 09/14] bits: Change BIT_U8/16() and GENMASK_U8/16() to have unsigned values

From: David Laight <david.laight.linux@...il.com>

Casting the value of BIT_U*() and GENMASK_U8() to (u8) is pointless.
Although it changes what typeof(BIT_U8()) returns the value will
always be promoted to 'signed int' before it is used.
Instead force the expression to be an unsigned type.

Avoids unexpected sign extension from, for example:
	u64 v = BIT_U8(7) << 24;

Fix the KUNIT tests to match.

Signed-off-by: David Laight <david.laight.linux@...il.com>
---
 include/linux/bits.h  |  6 +++---
 lib/tests/test_bits.c | 12 ++++++------
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/include/linux/bits.h b/include/linux/bits.h
index 697318f2a47d..23bc94815569 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -44,8 +44,8 @@
  * - GENMASK_U32(33, 15): doesn't fit in a u32
  */
 #define GENMASK_TYPE(t, h, l)					\
-	((t)(GENMASK_INPUT_CHECK(h, l) +			\
-	     ((t)-1 << (l) & (t)-1 >> (BITS_PER_TYPE(t) - 1 - (h)))))
+	((unsigned int)GENMASK_INPUT_CHECK(h, l) +		\
+	 ((t)-1 << (l) & (t)-1 >> (BITS_PER_TYPE(t) - 1 - (h))))
 
 #define GENMASK(h, l)		GENMASK_TYPE(unsigned long, h, l)
 #define GENMASK_ULL(h, l)	GENMASK_TYPE(unsigned long long, h, l)
@@ -67,7 +67,7 @@
 #define BIT_INPUT_CHECK(type, nr) \
 	BUILD_BUG_ON_ZERO(const_true((nr) >= BITS_PER_TYPE(type)))
 
-#define BIT_TYPE(type, nr) ((type)(BIT_INPUT_CHECK(type, nr) + BIT_ULL(nr)))
+#define BIT_TYPE(type, nr) ((unsigned int)BIT_INPUT_CHECK(type, nr) + ((type)1 << (nr)))
 
 #define BIT_U8(nr)	BIT_TYPE(u8, nr)
 #define BIT_U16(nr)	BIT_TYPE(u16, nr)
diff --git a/lib/tests/test_bits.c b/lib/tests/test_bits.c
index ab88e50d2edf..55be8230f9e7 100644
--- a/lib/tests/test_bits.c
+++ b/lib/tests/test_bits.c
@@ -9,20 +9,20 @@
 
 #define assert_type(t, x) _Generic(x, t: x, default: 0)
 
-static_assert(assert_type(u8, BIT_U8(0)) == 1u);
-static_assert(assert_type(u16, BIT_U16(0)) == 1u);
+static_assert(assert_type(unsigned int, BIT_U8(0)) == 1u);
+static_assert(assert_type(unsigned int, BIT_U16(0)) == 1u);
 static_assert(assert_type(u32, BIT_U32(0)) == 1u);
 static_assert(assert_type(u64, BIT_U64(0)) == 1ull);
 
-static_assert(assert_type(u8, BIT_U8(7)) == 0x80u);
-static_assert(assert_type(u16, BIT_U16(15)) == 0x8000u);
+static_assert(assert_type(unsigned int, BIT_U8(7)) == 0x80u);
+static_assert(assert_type(unsigned int, BIT_U16(15)) == 0x8000u);
 static_assert(assert_type(u32, BIT_U32(31)) == 0x80000000u);
 static_assert(assert_type(u64, BIT_U64(63)) == 0x8000000000000000ull);
 
 static_assert(assert_type(unsigned long, GENMASK(31, 0)) == U32_MAX);
 static_assert(assert_type(unsigned long long, GENMASK_ULL(63, 0)) == U64_MAX);
-static_assert(assert_type(u8, GENMASK_U8(7, 0)) == U8_MAX);
-static_assert(assert_type(u16, GENMASK_U16(15, 0)) == U16_MAX);
+static_assert(assert_type(unsigned int, GENMASK_U8(7, 0)) == U8_MAX);
+static_assert(assert_type(unsigned int, GENMASK_U16(15, 0)) == U16_MAX);
 static_assert(assert_type(u32, GENMASK_U32(31, 0)) == U32_MAX);
 static_assert(assert_type(u64, GENMASK_U64(63, 0)) == U64_MAX);
 
-- 
2.39.5