From: Emil Velikov <emil.l.velikov@gmail.com>
To: dri-devel@lists.freedesktop.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
emil.l.velikov@gmail.com,
Rikard Falkeborn <rikard.falkeborn@gmail.com>,
Chris Wilson <chris@chris-wilson.co.uk>
Subject: [PATCH] linux/bits.h: adjust GENMASK_INPUT_CHECK() check
Date: Tue, 19 May 2020 11:13:20 +0100 [thread overview]
Message-ID: <20200519101320.33495-1-emil.l.velikov@gmail.com> (raw)
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.
Fixes: 295bcca84916 ("linux/bits.h: add compile time sanity check of
GENMASK inputs")
Cc: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
---
From some quick testing, this works as expected although I could be
wrong.
-Emil
---
include/linux/bits.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/bits.h b/include/linux/bits.h
index 4671fbf28842..5e3ca57adc20 100644
--- a/include/linux/bits.h
+++ b/include/linux/bits.h
@@ -22,8 +22,8 @@
(!defined(CONFIG_CC_IS_GCC) || CONFIG_GCC_VERSION >= 49000)
#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)))
+ (BUILD_BUG_ON_ZERO(!__builtin_choose_expr( \
+ __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,
--
2.23.0
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next reply other threads:[~2020-05-19 10:13 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-19 10:13 Emil Velikov [this message]
2020-05-19 14:46 ` [PATCH] linux/bits.h: adjust GENMASK_INPUT_CHECK() check kbuild test robot
2020-05-19 15:04 ` kbuild test robot
2020-05-19 21:14 ` [PATCH v2] " Emil Velikov
2020-05-19 21:28 ` Rikard Falkeborn
2020-05-22 18:50 ` Emil Velikov
2020-05-23 19:35 ` Rikard Falkeborn
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