[PATCH v3 1/3] bits: introduce fixed-type genmasks
Dmitry Baryshkov
dmitry.baryshkov at linaro.org
Wed Feb 21 20:30:02 UTC 2024
On Thu, 8 Feb 2024 at 09:45, Lucas De Marchi <lucas.demarchi at intel.com> wrote:
>
> From: Yury Norov <yury.norov at gmail.com>
>
> Generalize __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:41:31: error: left shift count >= width of type [-Werror=shift-count-overflow]
> 41 | (((t)~0ULL - ((t)(1) << (l)) + 1) & \
> | ^~
>
> Signed-off-by: Yury Norov <yury.norov at gmail.com>
> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
> Acked-by: Jani Nikula <jani.nikula at intel.com>
> ---
> include/linux/bitops.h | 1 -
> include/linux/bits.h | 32 ++++++++++++++++++++++----------
> 2 files changed, 22 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/bitops.h b/include/linux/bitops.h
> index 2ba557e067fe..1db50c69cfdb 100644
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -15,7 +15,6 @@
> # define aligned_byte_mask(n) (~0xffUL << (BITS_PER_LONG - 8 - 8*(n)))
> #endif
>
> -#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 7c0cf5031abe..bd56f32de44e 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -6,6 +6,8 @@
> #include <vdso/bits.h>
> #include <asm/bitsperlong.h>
>
> +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE)
> +
> #define BIT_MASK(nr) (UL(1) << ((nr) % BITS_PER_LONG))
> #define BIT_WORD(nr) ((nr) / BITS_PER_LONG)
> #define BIT_ULL_MASK(nr) (ULL(1) << ((nr) % BITS_PER_LONG_LONG))
> @@ -30,16 +32,26 @@
> #define GENMASK_INPUT_CHECK(h, l) 0
> #endif
>
> -#define __GENMASK(h, l) \
> - (((~UL(0)) - (UL(1) << (l)) + 1) & \
> - (~UL(0) >> (BITS_PER_LONG - 1 - (h))))
> -#define GENMASK(h, l) \
> - (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
> +/*
> + * 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(t, h, l) \
> + (GENMASK_INPUT_CHECK(h, l) + \
> + (((t)~0ULL - ((t)(1) << (l)) + 1) & \
> + ((t)~0ULL >> (BITS_PER_TYPE(t) - 1 - (h)))))
>
> -#define __GENMASK_ULL(h, l) \
> - (((~ULL(0)) - (ULL(1) << (l)) + 1) & \
> - (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))
> -#define GENMASK_ULL(h, l) \
> - (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l))
> +#define GENMASK(h, l) __GENMASK(unsigned long, h, l)
> +#define GENMASK_ULL(h, l) __GENMASK(unsigned long long, h, l)
> +#define GENMASK_U8(h, l) __GENMASK(u8, h, l)
> +#define GENMASK_U16(h, l) __GENMASK(u16, h, l)
> +#define GENMASK_U32(h, l) __GENMASK(u32, h, l)
> +#define GENMASK_U64(h, l) __GENMASK(u64, h, l)
This breaks drm-tip on arm64 architecture:
arch/arm64/kernel/entry-fpsimd.S: Assembler messages:
465arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
466arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
467arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
468arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
469arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
470arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
471arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
472arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
473arch/arm64/kernel/entry-fpsimd.S:271: Error: unexpected characters
following instruction at operand 3 -- `bic x2,x1,(0+(((unsigned
long)~0ULL-((unsigned long)(1)<<(0))+1)&((unsigned
long)~0ULL>>((sizeof(unsigned long)*8)-1-(3)))))'
474arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
475arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
476arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
477arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
478arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
479arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
480arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
481arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
482arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
483arch/arm64/kernel/entry-fpsimd.S:282: Error: unexpected characters
following instruction at operand 3 -- `bic x2,x1,(0+(((unsigned
long)~0ULL-((unsigned long)(1)<<(0))+1)&((unsigned
long)~0ULL>>((sizeof(unsigned long)*8)-1-(3)))))'
484arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
>
> #endif /* __LINUX_BITS_H */
> --
> 2.43.0
>
--
With best wishes
Dmitry
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