linux-kernel - [PATCH 1/2] linux/bits.h: make BIT(), GENMASK(), and friends available in assembly

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Date:   Mon, 10 Jun 2019 00:39:40 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-s390@...r.kernel.org, linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: [PATCH 1/2] linux/bits.h: make BIT(), GENMASK(), and friends available in assembly

BIT(), GENMASK(), etc. are useful to define register bits of hardware.
However, low-level code is often written in assembly, where they are
not available due to the hard-coded 1UL, 0UL.

In fact, in-kernel headers such as arch/arm64/include/asm/sysreg.h
use _BITUL() instead of BIT() so that the register bit macros are
available in assembly.

Using macros in include/uapi/linux/const.h have two reasons:

[1] For use in uapi headers
  We should use underscore-prefixed variants for user-space.

[2] For use in assembly code
  Since _BITUL() uses UL(1) instead of 1UL, it can be used as an
  alternative of BIT().

For [2], it is pretty easy to change BIT() etc. for use in assembly.

This allows to replace _BUTUL() in kernel-space headers with BIT().

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 include/linux/bits.h | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/linux/bits.h b/include/linux/bits.h
index 2b7b532c1d51..669d69441a62 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -1,13 +1,15 @@
 /* SPDX-License-Identifier: GPL-2.0 */
 #ifndef __LINUX_BITS_H
 #define __LINUX_BITS_H
+
+#include <linux/const.h>
 #include <asm/bitsperlong.h>
 
-#define BIT(nr)			(1UL << (nr))
-#define BIT_ULL(nr)		(1ULL << (nr))
-#define BIT_MASK(nr)		(1UL << ((nr) % BITS_PER_LONG))
+#define BIT(nr)			(UL(1) << (nr))
+#define BIT_ULL(nr)		(ULL(1) << (nr))
+#define BIT_MASK(nr)		(UL(1) << ((nr) % BITS_PER_LONG))
 #define BIT_WORD(nr)		((nr) / BITS_PER_LONG)
-#define BIT_ULL_MASK(nr)	(1ULL << ((nr) % BITS_PER_LONG_LONG))
+#define BIT_ULL_MASK(nr)	(ULL(1) << ((nr) % BITS_PER_LONG_LONG))
 #define BIT_ULL_WORD(nr)	((nr) / BITS_PER_LONG_LONG)
 #define BITS_PER_BYTE		8
 
@@ -17,10 +19,11 @@
  * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
  */
 #define GENMASK(h, l) \
-	(((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h))))
+	(((~UL(0)) - (UL(1) << (l)) + 1) & \
+	 (~UL(0) >> (BITS_PER_LONG - 1 - (h))))
 
 #define GENMASK_ULL(h, l) \
-	(((~0ULL) - (1ULL << (l)) + 1) & \
-	 (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h))))
+	(((~ULL(0)) - (ULL(1) << (l)) + 1) & \
+	 (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))
 
 #endif	/* __LINUX_BITS_H */
-- 
2.17.1