Re: [Intel-xe] [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros

Gustavo Sousa
2023-05-09T14:01:26Z

Quoting Lucas De Marchi (2023-05-09 02:14:02)
>Add GENMASK_U32(), GENMASK_U16() and GENMASK_U8() macros to create
>masks for fixed-width types and also the corresponding BIT_U32(),
>BIT_U16() and BIT_U8().
>
>All of those depend on a new "U" suffix added to the integer constant.
>Due to naming clashes it's better to call the macro U32. Since C doesn't
>have a proper suffix for short and char types, the U16 and U18 variants
>just use U32 with one additional check in the BIT_* macros to make
>sure the compiler gives an error when the those types overflow.
>The BIT_U16() and BIT_U8() need the help of GENMASK_INPUT_CHECK(),
>as otherwise they would allow an invalid bit to be passed. Hence
>implement them in include/linux/bits.h rather than together with
>the other BIT* variants.
>
>The following test file is is used to test this:
>
> $ cat mask.c
> #include <linux/types.h>
> #include <linux/bits.h>
>
> static const u32 a = GENMASK_U32(31, 0);
> static const u16 b = GENMASK_U16(15, 0);
> static const u8 c = GENMASK_U8(7, 0);
> static const u32 x = BIT_U32(31);
> static const u16 y = BIT_U16(15);
> static const u8 z = BIT_U8(7);
>
> #if FAIL
> static const u32 a2 = GENMASK_U32(32, 0);
> static const u16 b2 = GENMASK_U16(16, 0);
> static const u8 c2 = GENMASK_U8(8, 0);
> static const u32 x2 = BIT_U32(32);
> static const u16 y2 = BIT_U16(16);
> static const u8 z2 = BIT_U8(8);
> #endif
>
>Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
>---
> include/linux/bits.h | 22 ++++++++++++++++++++++
> include/uapi/linux/const.h | 2 ++
> include/vdso/const.h | 1 +
> 3 files changed, 25 insertions(+)
>
>diff --git a/include/linux/bits.h b/include/linux/bits.h
>index 7c0cf5031abe..ff4786c99b8c 100644
>--- a/include/linux/bits.h
>+++ b/include/linux/bits.h
>@@ -42,4 +42,26 @@
> #define GENMASK_ULL(h, l) \
> (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l))
>
>+#define __GENMASK_U32(h, l) \
>+ (((~U32(0)) - (U32(1) << (l)) + 1) & \
>+ (~U32(0) >> (32 - 1 - (h))))
>+#define GENMASK_U32(h, l) \
>+ (GENMASK_INPUT_CHECK(h, l) + __GENMASK_U32(h, l))
>+
>+#define __GENMASK_U16(h, l) \
>+ ((U32(0xffff) - (U32(1) << (l)) + 1) & \
>+ (U32(0xffff) >> (16 - 1 - (h))))
>+#define GENMASK_U16(h, l) \
>+ (GENMASK_INPUT_CHECK(h, l) + __GENMASK_U16(h, l))
>+
>+#define __GENMASK_U8(h, l) \
>+ (((U32(0xff)) - (U32(1) << (l)) + 1) & \
>+ (U32(0xff) >> (8 - 1 - (h))))
>+#define GENMASK_U8(h, l) \
>+ (GENMASK_INPUT_CHECK(h, l) + __GENMASK_U8(h, l))

I wonder if we should use BIT_U* variants in the above to ensure the values are
valid. If so, we get a nice boundary check and we also can use a single
definition for the mask generation:

#define __GENMASK_U32(h, l) \
(((~U32(0)) - (U32(1) << (l)) + 1) & \
(~U32(0) >> (32 - 1 - (h))))
#define GENMASK_U32(h, l) \
(GENMASK_INPUT_CHECK(h, l) + __GENMASK_U32(BIT_U32(h), BIT_U32(l)))
#define GENMASK_U16(h, l) \
(GENMASK_INPUT_CHECK(h, l) + __GENMASK_U32(BIT_U16(h), BIT_U16(l)))
#define GENMASK_U8(h, l) \
(GENMASK_INPUT_CHECK(h, l) + __GENMASK_U32(BIT_U8(h), BIT_U8(l)))

>+
>+#define BIT_U32(nr) _BITU32(nr)
>+#define BIT_U16(nr) (GENMASK_INPUT_CHECK(16 - 1, nr) + (U32(1) << (nr)))
>+#define BIT_U8(nr) (GENMASK_INPUT_CHECK(32 - 1, nr) + (U32(1) << (nr)))

Shouldn't this be GENMASK_INPUT_CHECK(8 - 1, nr)?

--
Gustavo Sousa

>+
> #endif /* __LINUX_BITS_H */
>diff --git a/include/uapi/linux/const.h b/include/uapi/linux/const.h
>index a429381e7ca5..3a4e152520f4 100644
>--- a/include/uapi/linux/const.h
>+++ b/include/uapi/linux/const.h
>@@ -22,9 +22,11 @@
> #define _AT(T,X) ((T)(X))
> #endif
>
>+#define _U32(x) (_AC(x, U))
> #define _UL(x) (_AC(x, UL))
> #define _ULL(x) (_AC(x, ULL))
>
>+#define _BITU32(x) (_U32(1) << (x))
> #define _BITUL(x) (_UL(1) << (x))
> #define _BITULL(x) (_ULL(1) << (x))
>
>diff --git a/include/vdso/const.h b/include/vdso/const.h
>index 94b385ad438d..417384a9795b 100644
>--- a/include/vdso/const.h
>+++ b/include/vdso/const.h
>@@ -4,6 +4,7 @@
>
> #include <uapi/linux/const.h>
>
>+#define U32(x) (_U32(x))
> #define UL(x) (_UL(x))
> #define ULL(x) (_ULL(x))
>
>--
>2.40.1
>