Re: [PATCH v3 1/3] bits: introduce fixed-type genmasks

From: Dmitry Baryshkov
Date: Wed Feb 21 2024 - 15:37:52 EST

On Wed, 21 Feb 2024 at 22:30, Dmitry Baryshkov
<dmitry.baryshkov@xxxxxxxxxx> wrote:
>
> On Thu, 8 Feb 2024 at 09:45, Lucas De Marchi <lucas.demarchi@xxxxxxxxx> wrote:
> >
> > From: Yury Norov <yury.norov@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> > Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> > ---
> > 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:
>

Excuse me, it seems a c&p from gitlab didn't work as expected.

arch/arm64/kernel/entry-fpsimd.S: Assembler messages:
arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:271: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
arch/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)))))'
arch/arm64/kernel/entry-fpsimd.S:66: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
arch/arm64/kernel/entry-fpsimd.S:282: Error: found 'l', expected: ')'
arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
arch/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)))))'
arch/arm64/kernel/entry-fpsimd.S:98: Info: macro invoked from here
make[4]: *** [scripts/Makefile.build:361:
arch/arm64/kernel/entry-fpsimd.o] Error 1
make[3]: *** [scripts/Makefile.build:481: arch/arm64/kernel] Error 2
make[2]: *** [scripts/Makefile.build:481: arch/arm64] Error 2
make[2]: *** Waiting for unfinished jobs...


--
With best wishes
Dmitry