Recently the GENMASK_INPUT_CHECK() was added, aiming to catch cases
where there GENMASK arguments are flipped.
Although it seems to be triggering -Wtype-limits in the following cases:
unsigned foo = (10 + x);
unsigned bar = GENMASK(foo, 0);
const unsigned foo = (10 + x);
unsigned bar = GENMASK(foo, 0);
Here are the warnings, from my GCC 9.2 box.
warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
__builtin_constant_p((l) > (h)), (l) > (h), 0)))
^
warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
__builtin_constant_p((l) > (h)), (l) > (h), 0)))
^
This results in people disabling the warning all together or promoting
foo to signed. Either of which being a sub par option IMHO.
Add a trivial "+ 1" to each h and l in the constant expression.
v2: drop accidental !
Fixes: 295bcca84916 ("linux/bits.h: add compile time sanity check of
GENMASK inputs")
Cc: Rikard Falkeborn <rikard.falkeb...@gmail.com>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Emil Velikov <emil.l.veli...@gmail.com>
Reported-by: kbuild test robot <l...@intel.com>
Reported-by: kbuild test robot <l...@intel.com>
---
include/linux/bits.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/bits.h b/include/linux/bits.h
index 4671fbf28842..02a42866d198 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -23,7 +23,7 @@
#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 + 1) > (h + 1)), (l + 1) > (h + 1), 0)))
#else
/*
* BUILD_BUG_ON_ZERO is not available in h files included from asm files,
--
2.25.1
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