[PATCH 5.0 070/117] include/linux/bitrev.h: fix constant bitrev

Greg Kroah-Hartman
2019-04-15T19:12:17Z

From: Arnd Bergmann <arnd@arndb.de>

commit 6147e136ff5071609b54f18982dea87706288e21 upstream.

clang points out with hundreds of warnings that the bitrev macros have a
problem with constant input:

drivers/hwmon/sht15.c:187:11: error: variable '__x' is uninitialized when used within its own initialization
[-Werror,-Wuninitialized]
u8 crc = bitrev8(data->val_status & 0x0F);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/bitrev.h:102:21: note: expanded from macro 'bitrev8'
__constant_bitrev8(__x) : \
~~~~~~~~~~~~~~~~~~~^~~~
include/linux/bitrev.h:67:11: note: expanded from macro '__constant_bitrev8'
u8 __x = x; \
~~~ ^

Both the bitrev and the __constant_bitrev macros use an internal
variable named __x, which goes horribly wrong when passing one to the
other.

The obvious fix is to rename one of the variables, so this adds an extra
'_'.

It seems we got away with this because

- there are only a few drivers using bitrev macros

- usually there are no constant arguments to those

- when they are constant, they tend to be either 0 or (unsigned)-1
(drivers/isdn/i4l/isdnhdlc.o, drivers/iio/amplifiers/ad8366.c) and
give the correct result by pure chance.

In fact, the only driver that I could find that gets different results
with this is drivers/net/wan/slic_ds26522.c, which in turn is a driver
for fairly rare hardware (adding the maintainer to Cc for testing).

Link: http://lkml.kernel.org/r/20190322140503.123580-1-arnd@arndb.de
Fixes: 556d2f055bf6 ("ARM: 8187/1: add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Cc: Zhao Qiang <qiang.zhao@nxp.com>
Cc: Yalin Wang <yalin.wang@sonymobile.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
include/linux/bitrev.h | 46 +++++++++++++++++++++++-----------------------
1 file changed, 23 insertions(+), 23 deletions(-)

--- a/include/linux/bitrev.h
+++ b/include/linux/bitrev.h
@@ -34,41 +34,41 @@ static inline u32 __bitrev32(u32 x)

#define __constant_bitrev32(x) \
({ \
- u32 __x = x; \
- __x = (__x >> 16) | (__x << 16); \
- __x = ((__x & (u32)0xFF00FF00UL) >> 8) | ((__x & (u32)0x00FF00FFUL) << 8); \
- __x = ((__x & (u32)0xF0F0F0F0UL) >> 4) | ((__x & (u32)0x0F0F0F0FUL) << 4); \
- __x = ((__x & (u32)0xCCCCCCCCUL) >> 2) | ((__x & (u32)0x33333333UL) << 2); \
- __x = ((__x & (u32)0xAAAAAAAAUL) >> 1) | ((__x & (u32)0x55555555UL) << 1); \
- __x; \
+ u32 ___x = x; \
+ ___x = (___x >> 16) | (___x << 16); \
+ ___x = ((___x & (u32)0xFF00FF00UL) >> 8) | ((___x & (u32)0x00FF00FFUL) << 8); \
+ ___x = ((___x & (u32)0xF0F0F0F0UL) >> 4) | ((___x & (u32)0x0F0F0F0FUL) << 4); \
+ ___x = ((___x & (u32)0xCCCCCCCCUL) >> 2) | ((___x & (u32)0x33333333UL) << 2); \
+ ___x = ((___x & (u32)0xAAAAAAAAUL) >> 1) | ((___x & (u32)0x55555555UL) << 1); \
+ ___x; \
})

#define __constant_bitrev16(x) \
({ \
- u16 __x = x; \
- __x = (__x >> 8) | (__x << 8); \
- __x = ((__x & (u16)0xF0F0U) >> 4) | ((__x & (u16)0x0F0FU) << 4); \
- __x = ((__x & (u16)0xCCCCU) >> 2) | ((__x & (u16)0x3333U) << 2); \
- __x = ((__x & (u16)0xAAAAU) >> 1) | ((__x & (u16)0x5555U) << 1); \
- __x; \
+ u16 ___x = x; \
+ ___x = (___x >> 8) | (___x << 8); \
+ ___x = ((___x & (u16)0xF0F0U) >> 4) | ((___x & (u16)0x0F0FU) << 4); \
+ ___x = ((___x & (u16)0xCCCCU) >> 2) | ((___x & (u16)0x3333U) << 2); \
+ ___x = ((___x & (u16)0xAAAAU) >> 1) | ((___x & (u16)0x5555U) << 1); \
+ ___x; \
})

#define __constant_bitrev8x4(x) \
({ \
- u32 __x = x; \
- __x = ((__x & (u32)0xF0F0F0F0UL) >> 4) | ((__x & (u32)0x0F0F0F0FUL) << 4); \
- __x = ((__x & (u32)0xCCCCCCCCUL) >> 2) | ((__x & (u32)0x33333333UL) << 2); \
- __x = ((__x & (u32)0xAAAAAAAAUL) >> 1) | ((__x & (u32)0x55555555UL) << 1); \
- __x; \
+ u32 ___x = x; \
+ ___x = ((___x & (u32)0xF0F0F0F0UL) >> 4) | ((___x & (u32)0x0F0F0F0FUL) << 4); \
+ ___x = ((___x & (u32)0xCCCCCCCCUL) >> 2) | ((___x & (u32)0x33333333UL) << 2); \
+ ___x = ((___x & (u32)0xAAAAAAAAUL) >> 1) | ((___x & (u32)0x55555555UL) << 1); \
+ ___x; \
})

#define __constant_bitrev8(x) \
({ \
- u8 __x = x; \
- __x = (__x >> 4) | (__x << 4); \
- __x = ((__x & (u8)0xCCU) >> 2) | ((__x & (u8)0x33U) << 2); \
- __x = ((__x & (u8)0xAAU) >> 1) | ((__x & (u8)0x55U) << 1); \
- __x; \
+ u8 ___x = x; \
+ ___x = (___x >> 4) | (___x << 4); \
+ ___x = ((___x & (u8)0xCCU) >> 2) | ((___x & (u8)0x33U) << 2); \
+ ___x = ((___x & (u8)0xAAU) >> 1) | ((___x & (u8)0x55U) << 1); \
+ ___x; \
})

#define bitrev32(x) \