From eff7d1d2dcca4a5749454d956bc317e1b4c37a18 Mon Sep 17 00:00:00 2001 From: Andrew Rybchenko Date: Wed, 25 Apr 2018 18:51:37 +0100 Subject: [PATCH] net/sfc/base: cope with clang warning on negative shift clang 4.0.1-6 on Ubuntu generates false positive warning that shift is negative. It is done regardless of the fact that the branch is not taken because of previous check. The warning is generate in EFX_INSERT_NATIVE32 used by EFX_INSERT_FIELD_NATIVE32. All similar cases are fixed as well. It is undesirable to suppress the warning completely. Signed-off-by: Andrew Rybchenko --- drivers/net/sfc/base/efx_types.h | 38 ++++++++++++++++++++------------ 1 file changed, 24 insertions(+), 14 deletions(-) diff --git a/drivers/net/sfc/base/efx_types.h b/drivers/net/sfc/base/efx_types.h index 0581f67f44..65168ab79a 100644 --- a/drivers/net/sfc/base/efx_types.h +++ b/drivers/net/sfc/base/efx_types.h @@ -328,6 +328,16 @@ extern int fix_lint; #define FIX_LINT(_x) (_x) #endif +/* + * Saturation arithmetic subtract with minimum equal to zero. + * + * Use saturating arithmetic to ensure a non-negative result. This + * avoids undefined behaviour (and compiler warnings) when used as a + * shift count. + */ +#define EFX_SSUB(_val, _sub) \ + ((_val) > (_sub) ? ((_val) - (_sub)) : 0) + /* * Extract bit field portion [low,high) from the native-endian element * which contains bits [min,max). @@ -347,8 +357,8 @@ extern int fix_lint; ((FIX_LINT(_low > _max) || FIX_LINT(_high < _min)) ? \ 0U : \ ((_low > _min) ? \ - ((_element) >> (_low - _min)) : \ - ((_element) << (_min - _low)))) + ((_element) >> EFX_SSUB(_low, _min)) : \ + ((_element) << EFX_SSUB(_min, _low)))) /* * Extract bit field portion [low,high) from the 64-bit little-endian @@ -537,29 +547,29 @@ extern int fix_lint; (((_low > _max) || (_high < _min)) ? \ 0U : \ ((_low > _min) ? \ - (((uint64_t)(_value)) << (_low - _min)) : \ - (((uint64_t)(_value)) >> (_min - _low)))) + (((uint64_t)(_value)) << EFX_SSUB(_low, _min)) :\ + (((uint64_t)(_value)) >> EFX_SSUB(_min, _low)))) #define EFX_INSERT_NATIVE32(_min, _max, _low, _high, _value) \ (((_low > _max) || (_high < _min)) ? \ 0U : \ ((_low > _min) ? \ - (((uint32_t)(_value)) << (_low - _min)) : \ - (((uint32_t)(_value)) >> (_min - _low)))) + (((uint32_t)(_value)) << EFX_SSUB(_low, _min)) :\ + (((uint32_t)(_value)) >> EFX_SSUB(_min, _low)))) #define EFX_INSERT_NATIVE16(_min, _max, _low, _high, _value) \ (((_low > _max) || (_high < _min)) ? \ 0U : \ (uint16_t)((_low > _min) ? \ - ((_value) << (_low - _min)) : \ - ((_value) >> (_min - _low)))) + ((_value) << EFX_SSUB(_low, _min)) : \ + ((_value) >> EFX_SSUB(_min, _low)))) #define EFX_INSERT_NATIVE8(_min, _max, _low, _high, _value) \ (((_low > _max) || (_high < _min)) ? \ 0U : \ (uint8_t)((_low > _min) ? \ - ((_value) << (_low - _min)) : \ - ((_value) >> (_min - _low)))) + ((_value) << EFX_SSUB(_low, _min)) : \ + ((_value) >> EFX_SSUB(_min, _low)))) /* * Construct bit field portion @@ -1288,22 +1298,22 @@ extern int fix_lint; #define EFX_SHIFT64(_bit, _base) \ (((_bit) >= (_base) && (_bit) < (_base) + 64) ? \ - ((uint64_t)1 << ((_bit) - (_base))) : \ + ((uint64_t)1 << EFX_SSUB((_bit), (_base))) : \ 0U) #define EFX_SHIFT32(_bit, _base) \ (((_bit) >= (_base) && (_bit) < (_base) + 32) ? \ - ((uint32_t)1 << ((_bit) - (_base))) : \ + ((uint32_t)1 << EFX_SSUB((_bit),(_base))) : \ 0U) #define EFX_SHIFT16(_bit, _base) \ (((_bit) >= (_base) && (_bit) < (_base) + 16) ? \ - (uint16_t)(1 << ((_bit) - (_base))) : \ + (uint16_t)(1 << EFX_SSUB((_bit), (_base))) : \ 0U) #define EFX_SHIFT8(_bit, _base) \ (((_bit) >= (_base) && (_bit) < (_base) + 8) ? \ - (uint8_t)(1 << ((_bit) - (_base))) : \ + (uint8_t)(1 << EFX_SSUB((_bit), (_base))) : \ 0U) #define EFX_SET_OWORD_BIT64(_oword, _bit) \ -- 2.20.1