linux-kernel - [PATCH next 12/14] bits: move the defitions of BIT() and BIT

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Message-Id: <20260121145731.3623-13-david.laight.linux@gmail.com>
Date: Wed, 21 Jan 2026 14:57:29 +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 12/14] bits: move the defitions of BIT() and BIT_ULL() back to linux/bits.h

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

The definition of BIT() was moved from linux/bits.h to vdso/bits.h to
isolate the vdso from 'normal' kernel headers.
BIT_ULL() was then moved to be defined in the same place for consistency.

Since then linux/bits.h had gained BIT_Unn() and it really makes sense
for BIT() and BIT_ULL() to be defined in the same place.

Move BIT_ULL() and make code that include both headers use the definition
of BIT() from linux/bits.h
Add BIT_U128() for completness.

This lets BIT() pick up the extra compile time checks for W=[1c] builds
that detect errors like:
	long foo(void) { int x = 64; return BIT(x); }
For which clang (silently) just generates a 'return' instruction.

Note that nothing the the x86-64 build relies on the definition in
vdso/bits.h, linux/bits.h is always included.

Signed-off-by: David Laight <david.laight.linux@...il.com>
---
 include/linux/bits.h | 7 ++++++-
 include/vdso/bits.h  | 2 +-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/linux/bits.h b/include/linux/bits.h
index 0f559038981d..3dd32b9eef35 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -2,7 +2,6 @@
 #ifndef __LINUX_BITS_H
 #define __LINUX_BITS_H
 
-#include <vdso/bits.h>
 #include <uapi/linux/bits.h>
 
 #define BIT_MASK(nr)		(UL(1) << ((nr) % BITS_PER_LONG))
@@ -89,10 +88,16 @@ int BIT_INPUT_CHECK_FAIL(void) __compiletime_error("Bit number out of range");
 	((unsigned int)BIT_INPUT_CHECK(+(nr), BITS_PER_TYPE(type)) + ((type)1 << (nr)))
 #endif /* defined(__ASSEMBLY__) */
 
+/* Prefer this definition of BIT() to the one in vdso/bits.h */
+#undef BIT
+#define __VDSO_BITS_H
+#define BIT(nr)		BIT_TYPE(unsigned long, nr)
+#define BIT_ULL(nr)	BIT_TYPE(unsigned long long, nr)
 #define BIT_U8(nr)	BIT_TYPE(u8, nr)
 #define BIT_U16(nr)	BIT_TYPE(u16, nr)
 #define BIT_U32(nr)	BIT_TYPE(u32, nr)
 #define BIT_U64(nr)	BIT_TYPE(u64, nr)
+#define BIT_U128(nr)	BIT_TYPE(u128, nr)
 
 #if defined(__ASSEMBLY__)
 
diff --git a/include/vdso/bits.h b/include/vdso/bits.h
index 388b212088ea..a6ac1e6b637c 100644
--- a/include/vdso/bits.h
+++ b/include/vdso/bits.h
@@ -4,7 +4,7 @@
 
 #include <vdso/const.h>
 
+/* Most code picks up BIT() from linux/bits.h */
 #define BIT(nr)			(UL(1) << (nr))
-#define BIT_ULL(nr)		(ULL(1) << (nr))
 
 #endif	/* __VDSO_BITS_H */
-- 
2.39.5