The patch titled
Subject: linux/bits.h: fix unsigned less than zero warnings
has been added to the -mm tree. Its filename is
linux-bitsh-fix-unsigned-less-than-zero-warnings.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/linux-bitsh-fix-unsigned-less-than-zero-warnings.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/linux-bitsh-fix-unsigned-less-than-zero-warnings.patch
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------------------------------------------------------
From: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx>
Subject: linux/bits.h: fix unsigned less than zero warnings
When calling the GENMASK and GENMASK_ULL macros with zero lower bit and an
unsigned unknown high bit, some gcc versions warn due to the comparisons
of the high and low bit in GENMASK_INPUT_CHECK.
To silence the warnings, only perform the check if both inputs are known.
This does not trigger any warnings, from the Wtype-limits help:
Warn if a comparison is always true or always false due to the
limited range of the data type, but do not warn for constant
expressions.
As an example of the warning, kindly reported by the kbuild test robot:
from drivers/mfd/atmel-smc.c:11:
drivers/mfd/atmel-smc.c: In function 'atmel_smc_cs_encode_ncycles':
include/linux/bits.h:26:28: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
26 | __builtin_constant_p((l) > (h)), (l) > (h), 0)))
| ^
include/linux/build_bug.h:16:62: note: in definition of macro 'BUILD_BUG_ON_ZERO'
16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))
| ^
include/linux/bits.h:39:3: note: in expansion of macro 'GENMASK_INPUT_CHECK'
39 | (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
| ^~~~~~~~~~~~~~~~~~~
>> drivers/mfd/atmel-smc.c:49:25: note: in expansion of macro 'GENMASK'
49 | unsigned int lsbmask = GENMASK(msbpos - 1, 0);
| ^~~~~~~
Link: http://lkml.kernel.org/r/20200608221823.35799-1-rikard.falkeborn@xxxxxxxxx
Fixes: 295bcca84916 ("linux/bits.h: add compile time sanity check of GENMASK inputs")
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx>
Reported-by: kbuild test robot <lkp@xxxxxxxxx>
Reported-by: Emil Velikov <emil.l.velikov@xxxxxxxxx>
Reported-by: Syed Nayyar Waris <syednwaris@xxxxxxxxx>
Reviewed-by: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Emil Velikov <emil.l.velikov@xxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Walleij <linus.walleij@xxxxxxxxxx>
Cc: William Breathitt Gray <vilhelm.gray@xxxxxxxxx>
Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/bits.h | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/include/linux/bits.h~linux-bitsh-fix-unsigned-less-than-zero-warnings
+++ a/include/linux/bits.h
@@ -23,7 +23,8 @@
#include <linux/build_bug.h>
#define GENMASK_INPUT_CHECK(h, l) \
(BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
- __builtin_constant_p((l) > (h)), (l) > (h), 0)))
+ __builtin_constant_p(l) && __builtin_constant_p(h), \
+ (l) > (h), 0)))
#else
/*
* BUILD_BUG_ON_ZERO is not available in h files included from asm files,
_
Patches currently in -mm which might be from rikard.falkeborn@xxxxxxxxx are
linux-bitsh-fix-unsigned-less-than-zero-warnings.patch
bits-add-tests-of-genmask.patch
