On Thu, 2017-10-05 at 15:12 +0000, David Laight wrote: > From: Joe Perches > > Sent: 05 October 2017 13:19 > > On Thu, 2017-10-05 at 14:05 +0200, Arnd Bergmann wrote: > > > gcc produces a harmless warning about a recently introduced > > > signed integer overflow: > > > > > > drivers/net/wireless/rsi/rsi_91x_hal.c: In function > > > 'rsi_prepare_mgmt_desc': > > > include/uapi/linux/swab.h:13:15: error: integer overflow in expression > > > [-Werror=overflow] > > > (((__u16)(x) & (__u16)0x00ffU) << 8) | \ > > > ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~ > > > include/uapi/linux/swab.h:104:2: note: in expansion of macro > > > '___constant_swab16' > > > ___constant_swab16(x) : \ > > > ^~~~~~~~~~~~~~~~~~ > > > include/uapi/linux/byteorder/big_endian.h:34:43: note: in expansion of > > > macro '__swab16' > > > #define __cpu_to_le16(x) ((__force __le16)__swab16((x))) > > > > [] > > > > > The problem is that the 'mask' value is a signed integer that gets > > > turned into a negative number when truncated to 16 bits. Making it > > > an unsigned constant avoids this. > > > > I would expect there are more of these. > > > > Perhaps this define in include/uapi/linux/swab.h: > > > > #define __swab16(x) \ > > (__builtin_constant_p((__u16)(x)) ? \ > > ___constant_swab16(x) : \ > > __fswab16(x)) > > > > should be > > > > #define __swab16(x) \ > > (__builtin_constant_p((__u16)(x)) ? \ > > ___constant_swab16((__u16)(x)) : \ > > __fswab16((__u16)(x))) > > You probably don't want the cast in the call to __fswab16() since > that is likely to generate an explicit and with 0xffff. > You will likely also get one if the argument is _u16 (not unsigned int).
It would just an explicit vs implicit cast as __fswab16 is a static inline with a __u16 argument
