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().
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| @@ -1,13 +1,15 @@ | ||
| 1 | 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
| 2 | 2 | #ifndef __LINUX_BITS_H |
| 3 | 3 | #define __LINUX_BITS_H |
| 4 | + | |
| 5 | +#include <linux/const.h> | |
| 4 | 6 | #include <asm/bitsperlong.h> |
| 5 | 7 | |
| 6 | −#define BIT(nr) (1UL << (nr)) | |
| 7 | −#define BIT_ULL(nr) (1ULL << (nr)) | |
| 8 | −#define BIT_MASK(nr) (1UL << ((nr) % BITS_PER_LONG)) | |
| 8 | +#define BIT(nr) (UL(1) << (nr)) | |
| 9 | +#define BIT_ULL(nr) (ULL(1) << (nr)) | |
| 10 | +#define BIT_MASK(nr) (UL(1) << ((nr) % BITS_PER_LONG)) | |
| 9 | 11 | #define BIT_WORD(nr) ((nr) / BITS_PER_LONG) |
| 10 | −#define BIT_ULL_MASK(nr) (1ULL << ((nr) % BITS_PER_LONG_LONG)) | |
| 12 | +#define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG)) | |
| 11 | 13 | #define BIT_ULL_WORD(nr) ((nr) / BITS_PER_LONG_LONG) |
| 12 | 14 | #define BITS_PER_BYTE 8 |
| 13 | 15 | |
| @@ -17,10 +19,11 @@ · 3 unmodified lines | ||
| 17 | 19 | * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. |
| 18 | 20 | */ |
| 19 | 21 | #define GENMASK(h, l) \ |
| 20 | − (((~0UL) - (1UL << (l)) + 1) & (~0UL >> (BITS_PER_LONG - 1 - (h)))) | |
| 22 | + (((~UL(0)) - (UL(1) << (l)) + 1) & \ | |
| 23 | + (~UL(0) >> (BITS_PER_LONG - 1 - (h)))) | |
| 21 | 24 | |
| 22 | 25 | #define GENMASK_ULL(h, l) \ |
| 23 | − (((~0ULL) - (1ULL << (l)) + 1) & \ | |
| 24 | − (~0ULL >> (BITS_PER_LONG_LONG - 1 - (h)))) | |
| 26 | + (((~ULL(0)) - (ULL(1) << (l)) + 1) & \ | |
| 27 | + (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h)))) | |
| 25 | 28 | |
| 26 | 29 | #endif /* __LINUX_BITS_H */ |