This is a note to let you know that I've just added the patch titled include/linux/bitrev.h: fix constant bitrev to the 5.0-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: include-linux-bitrev.h-fix-constant-bitrev.patch and it can be found in the queue-5.0 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 6147e136ff5071609b54f18982dea87706288e21 Mon Sep 17 00:00:00 2001 From: Arnd Bergmann <arnd@xxxxxxxx> Date: Fri, 5 Apr 2019 18:38:53 -0700 Subject: include/linux/bitrev.h: fix constant bitrev From: Arnd Bergmann <arnd@xxxxxxxx> 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@xxxxxxxx Fixes: 556d2f055bf6 ("ARM: 8187/1: add CONFIG_HAVE_ARCH_BITREVERSE to support rbit instruction") Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Cc: Zhao Qiang <qiang.zhao@xxxxxxx> Cc: Yalin Wang <yalin.wang@xxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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) \ Patches currently in stable-queue which might be from arnd@xxxxxxxx are queue-5.0/lib-string.c-implement-a-basic-bcmp.patch queue-5.0/include-linux-bitrev.h-fix-constant-bitrev.patch