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Message-ID: <ZddfF7kb54o2c/QR@yury-ThinkPad> Date: Thu, 22 Feb 2024 06:49:59 -0800 From: Yury Norov <yury.norov@...il.com> To: Lucas De Marchi <lucas.demarchi@...el.com> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, Jani Nikula <jani.nikula@...ux.intel.com>, intel-xe@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org, Jani Nikula <jani.nikula@...el.com> Subject: Re: Re: [PATCH v3 1/3] bits: introduce fixed-type genmasks On Wed, Feb 21, 2024 at 03:59:06PM -0600, Lucas De Marchi wrote: > On Wed, Feb 21, 2024 at 11:04:22PM +0200, Andy Shevchenko wrote: > > On Wed, Feb 21, 2024 at 10:30:02PM +0200, Dmitry Baryshkov wrote: > > > On Thu, 8 Feb 2024 at 09:45, Lucas De Marchi <lucas.demarchi@...el.com> wrote: > > > > ... > > > > > > +#define BITS_PER_TYPE(type) (sizeof(type) * BITS_PER_BYTE) > > > > Can sizeof() be used in assembly? > > > > ... > > > > > > -#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)) > > > > > > +#define __GENMASK(t, h, l) \ > > > > + (GENMASK_INPUT_CHECK(h, l) + \ > > > > + (((t)~0ULL - ((t)(1) << (l)) + 1) & \ > > > > + ((t)~0ULL >> (BITS_PER_TYPE(t) - 1 - (h))))) > > > > Nevertheless, the use ~0ULL is not proper assembly, this broke initial > > implementation using UL() / ULL(). > > indeed. > > > > > > > > > -#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)) > > > > Ditto. > > problem here seems actually because of the cast to the final type. My > previous impl was avoiding that, but was too verbose compared to this. > > I will look at reverting this. > > Lucas De Marchi The fix is quite straightforward. Can you consider the following patch? I tested it for C and x86_64 asm parts, and it compiles well. Thanks, Yury >From 78b2887eea26f208aac50ae283ba9a4d062bb997 Mon Sep 17 00:00:00 2001 From: Yury Norov <yury.norov@...il.com> Date: Wed, 7 Feb 2024 23:45:19 -0800 Subject: [PATCH v2] bits: introduce fixed-type GENMASKs 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) & \ | ^~ CC: Dmitry Baryshkov <dmitry.baryshkov@...aro.org> Signed-off-by: Yury Norov <yury.norov@...il.com> Acked-by: Jani Nikula <jani.nikula@...el.com> Reviewed-by: Andi Shyti <andi.shyti@...ux.intel.com> --- include/linux/bitops.h | 1 - include/linux/bits.h | 41 ++++++++++++++++++++++++++++------------- 2 files changed, 28 insertions(+), 14 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..f3cf8d5f2b55 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)) @@ -22,24 +24,37 @@ #define GENMASK_INPUT_CHECK(h, l) \ (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ __is_constexpr((l) > (h)), (l) > (h), 0))) +#define __GENMASK(t, h, l) \ + (GENMASK_INPUT_CHECK(h, l) + \ + (((t)~0ULL - ((t)(1) << (l)) + 1) & \ + ((t)~0ULL >> (BITS_PER_TYPE(t) - 1 - (h))))) #else /* - * BUILD_BUG_ON_ZERO is not available in h files included from asm files, - * disable the input check if that is the case. + * BUILD_BUG_ON_ZERO is not available in h files included from asm files. + * Similarly, assembler lacks for C types. So no parameters check in asm. + * It's users' responsibility to provide bitranges within a machine word + * boundaries. */ #define GENMASK_INPUT_CHECK(h, l) 0 +#define __GENMASK(t, h, l) \ + ((~0 - (1 << (l)) + 1) & (~0 >> (BITS_PER_LONG - 1 - (h)))) #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)) - -#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)) +/* + * 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(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) #endif /* __LINUX_BITS_H */ -- 2.40.1
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