Re: [Intel-xe] [PATCH 2/3] linux/bits.h: Add fixed-width GENMASK and BIT macros
From: Lucas De Marchi
Date: Tue May 09 2023 - 17:35:57 EST
On Tue, May 09, 2023 at 11:00:36AM -0300, Gustavo Sousa wrote:
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@xxxxxxxxx>
---
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))))
the boundary for h and l are already covered here because (32 - 1 - (h))
would lead to a negative value if h >= 32. Similar reason for l
Doing ~U32(0) didn't work for me as it wouldn't catch the invalid values
due to expanding to U32_MAX
#define GENMASK_U32(h, l) \
(GENMASK_INPUT_CHECK(h, l) + __GENMASK_U32(BIT_U32(h), BIT_U32(l)))
^^^^
that doesn't really work as BIT_U32(h) would expand here,
creating the equivalent of
~U32(0) >> (32 - 1 - (BIT_U32(h))),
which is not what we want
#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)?
ugh, good catch. Thanks
I will think if I can come up with something that reuses a single
__GENMASK_U(). Meanwhile I improved my negative tests to cover more
cases.
Lucas De Marchi
--
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