On Thu, Feb 22, 2024 at 06:49:59AM -0800, Yury Norov wrote:
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@xxxxxxxxx> 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@xxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Acked-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Reviewed-by: Andi Shyti <andi.shyti@xxxxxxxxxxxxxxx>
I build-tested this in x86-64, x86-32 and arm64. I didn't like much the
need to fork the __GENMASK() implementation on the 2 sides of the ifdef
since I think the GENMASK_INPUT_CHECK() should be the one covering the
input checks. However to make it common we'd need to solve 2 problems:
the casts and the sizeof. The sizeof can be passed as arg to
__GENMASK(), however the casts I think would need a __CAST_U8(x)
or the like and sprinkle it everywhere, which would hurt readability.
Not pretty. Or go back to the original submission and make it less
horrible :-/
---
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))))
humn... this builds, but does it work if GENMASK_ULL() is used in
assembly? That BITS_PER_LONG does not match the type width.
Lucas De Marchi
#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
