On Thu, Nov 23, 2023 at 09:33:06AM +0800, Su Hui wrote: > On 2023/11/22 21:02, Dan Carpenter wrote: > > On Wed, Nov 22, 2023 at 05:02:12PM +0800, Su Hui wrote: > > > Clang staic checker warning: > > > drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c:184:49: > > > The result of the left shift is undefined due to shifting by '32', > > > which is greater or equal to the width of type 'u32'. > > > [core.UndefinedBinaryOperatorResult] > > > > > > If the value of the right operand is negative or is greater than or > > > equal to the width of the promoted left operand, the behavior is > > > undefined.[1][2] > > > > > > For example, when using different gcc's compilation optimizaation options > > > (-O0 or -O2), the result of '(u32)data << 32' is different. One is 0, the > > > other is old value of data. Adding an u64 cast to fix this problem. > > > > > > [1]:https://stackoverflow.com/questions/11270492/what-does-the-c- > > > standard-say-about-bitshifting-more-bits-than-the-width-of-type > > > [2]:https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf > > > > > > Fixes: 21e4b0726dc6 ("rtlwifi: rtl8821ae: Move driver from staging to regular tree") > > > Signed-off-by: Su Hui <suhui@xxxxxxxxxxxx> > > > --- > > > drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c | 8 ++++---- > > > 1 file changed, 4 insertions(+), 4 deletions(-) > > > > > > diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c > > > index 6df270e29e66..89713e0587b5 100644 > > > --- a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c > > > +++ b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c > > > @@ -106,7 +106,7 @@ u32 rtl8821ae_phy_query_bb_reg(struct ieee80211_hw *hw, u32 regaddr, > > > regaddr, bitmask); > > > originalvalue = rtl_read_dword(rtlpriv, regaddr); > > > bitshift = _rtl8821ae_phy_calculate_bit_shift(bitmask); > > > - returnvalue = (originalvalue & bitmask) >> bitshift; > > > + returnvalue = (u64)(originalvalue & bitmask) >> bitshift; > > This is a right shift, not a left shift. << vs >>. > > Hi, > > It's same for right shift and having a really weird result. > > The result of '(u32)data >> 32' is different when using different compiler. > Clang: "(unsigned int)41 >> 32" = 2077469672 > Gcc: "(unsigned int)41 >> 32" = 0 Ah. Sorry. I had forgotten that it was undefined either way... regards, dan carpenter
