| Message ID | 20250322-fixed-type-genmasks-v7-1-da380ff1c5b9@wanadoo.fr (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | bits: Fixed-type GENMASK_U*() and BIT_U*() | expand |
On Sat, Mar 22, 2025 at 06:23:12PM +0900, Vincent Mailhol via B4 Relay wrote: > > Add GENMASK_TYPE() which generalizes __GENMASK() to support different > types, and implement fixed-types versions of GENMASK() based on it. > The fixed-type version allows more strict checks to the min/max values > accepted, which is useful for defining registers like implemented by > i915 and xe drivers with their REG_GENMASK*() macros. > > The strict checks rely on shift-count-overflow compiler check to fail > the build if a number outside of the range allowed is passed. > Example: > > #define FOO_MASK GENMASK_U32(33, 4) > > will generate a warning like: > > include/linux/bits.h:51:27: error: right shift count >= width of type [-Werror=shift-count-overflow] > 51 | type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h))))) > | ^~ > > While GENMASK_TYPE() is crafted to cover all variants, including the > already existing GENMASK(), GENMASK_ULL() and GENMASK_U128(), for the > moment, only use it for the newly introduced GENMASK_U*(). The > consolidation will be done in a separate change. ... > #if !defined(__ASSEMBLY__) > + > -#else > +#else /* defined(__ASSEMBLY__) */ > -#endif > + > +#endif /* !defined(__ASSEMBLY__) */ Up to you, but if new version is needed or maintainer require, I would move the above changes either to a separate patch (prerequisite) or dropped them at all. These are not big but unneeded churn,
On 24/03/2025 at 16:22, Andy Shevchenko wrote: > On Sat, Mar 22, 2025 at 06:23:12PM +0900, Vincent Mailhol via B4 Relay wrote: >> >> Add GENMASK_TYPE() which generalizes __GENMASK() to support different >> types, and implement fixed-types versions of GENMASK() based on it. >> The fixed-type version allows more strict checks to the min/max values >> accepted, which is useful for defining registers like implemented by >> i915 and xe drivers with their REG_GENMASK*() macros. >> >> The strict checks rely on shift-count-overflow compiler check to fail >> the build if a number outside of the range allowed is passed. >> Example: >> >> #define FOO_MASK GENMASK_U32(33, 4) >> >> will generate a warning like: >> >> include/linux/bits.h:51:27: error: right shift count >= width of type [-Werror=shift-count-overflow] >> 51 | type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h))))) >> | ^~ >> >> While GENMASK_TYPE() is crafted to cover all variants, including the >> already existing GENMASK(), GENMASK_ULL() and GENMASK_U128(), for the >> moment, only use it for the newly introduced GENMASK_U*(). The >> consolidation will be done in a separate change. > > ... > >> #if !defined(__ASSEMBLY__) >> + > >> -#else > >> +#else /* defined(__ASSEMBLY__) */ > >> -#endif >> + >> +#endif /* !defined(__ASSEMBLY__) */ > > Up to you, but if new version is needed or maintainer require, I would move the > above changes either to a separate patch (prerequisite) or dropped them at all. > These are not big but unneeded churn, I do not want to drop this. After all the changes, there is a lot of scrolling between the #if, #else and #endif, and the comments helps to keep track of which context we are in. As for putting this into another patch, OK but only if there is a need for new version for other reasons. Yours sincerely, Vincent Mailhol
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index c1cb53cf2f0f8662ed3e324578f74330e63f935d..9be2d50da09a417966b3d11c84092bb2f4cd0bef 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -8,7 +8,6 @@ #include <uapi/linux/kernel.h> -#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) #define BITS_TO_LONGS(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(long)) #define BITS_TO_U64(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u64)) #define BITS_TO_U32(nr) __KERNEL_DIV_ROUND_UP(nr, BITS_PER_TYPE(u32)) diff --git a/include/linux/bits.h b/include/linux/bits.h index 14fd0ca9a6cd17339dd2f69e449558312a8a001b..beb3ee2f1bc74a9346dd72eb06c722a9bc536051 100644 --- a/include/linux/bits.h +++ b/include/linux/bits.h @@ -12,6 +12,7 @@ #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 +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) /* * Create a contiguous bitmask starting at bit position @l and ending at @@ -19,16 +20,50 @@ * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000. */ #if !defined(__ASSEMBLY__) + +/* + * Missing asm support + * + * GENMASK_U*() depend on BITS_PER_TYPE() which relies on sizeof(), + * something not available in asm. Nevertheless, fixed width integers is a C + * concept. Assembly code can rely on the long and long long versions instead. + */ + #include <linux/build_bug.h> #include <linux/compiler.h> +#include <linux/overflow.h> + #define GENMASK_INPUT_CHECK(h, l) BUILD_BUG_ON_ZERO(const_true((l) > (h))) -#else + +/* + * Generate a mask for the specified type @t. Additional checks are made to + * guarantee the value returned fits in that type, relying on + * shift-count-overflow compiler check to detect incompatible arguments. + * For example, all these create build errors or warnings: + * + * - GENMASK(15, 20): wrong argument order + * - GENMASK(72, 15): doesn't fit unsigned long + * - GENMASK_U32(33, 15): doesn't fit in a u32 + */ +#define GENMASK_TYPE(t, h, l) \ + ((t)(GENMASK_INPUT_CHECK(h, l) + \ + (type_max(t) << (l) & \ + type_max(t) >> (BITS_PER_TYPE(t) - 1 - (h))))) + +#define GENMASK_U8(h, l) GENMASK_TYPE(u8, h, l) +#define GENMASK_U16(h, l) GENMASK_TYPE(u16, h, l) +#define GENMASK_U32(h, l) GENMASK_TYPE(u32, h, l) +#define GENMASK_U64(h, l) GENMASK_TYPE(u64, h, l) + +#else /* defined(__ASSEMBLY__) */ + /* * BUILD_BUG_ON_ZERO is not available in h files included from asm files, * disable the input check if that is the case. */ #define GENMASK_INPUT_CHECK(h, l) 0 -#endif + +#endif /* !defined(__ASSEMBLY__) */ #define GENMASK(h, l) \ (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))