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 >>. > > rtl_dbg(rtlpriv, COMP_RF, DBG_TRACE, > "BBR MASK=0x%x Addr[0x%x]=0x%x\n", > @@ -128,7 +128,7 @@ void rtl8821ae_phy_set_bb_reg(struct ieee80211_hw *hw, > originalvalue = rtl_read_dword(rtlpriv, regaddr); > bitshift = _rtl8821ae_phy_calculate_bit_shift(bitmask); > data = ((originalvalue & (~bitmask)) | > - ((data << bitshift) & bitmask)); > + (((u64)data << bitshift) & bitmask)); The checker is printing an accurate warning, however, I'm not sure the fix is correct. Obviously, shift wrapping is bad and your patch would eliminate that possibility. However, data is a u32 so we end up discarding the high 32 bits. I can imagine a different static checker would complain about that. Perhaps, a better way to silence the warning is to just change _rtl8821ae_phy_calculate_bit_shift() to not return 32 bits? Do we really ever pass bitmask 0? No idea... regards, dan carpenter diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c index 5323ead30db0..42885e3a458f 100644 --- a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c +++ b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c @@ -29,9 +29,7 @@ static void _rtl8821ae_phy_rf_serial_write(struct ieee80211_hw *hw, u32 data); static u32 _rtl8821ae_phy_calculate_bit_shift(u32 bitmask) { - u32 i = ffs(bitmask); - - return i ? i - 1 : 32; + return ffs(bitmask) - 1; } static bool _rtl8821ae_phy_bb8821a_config_parafile(struct ieee80211_hw *hw); /*static bool _rtl8812ae_phy_config_mac_with_headerfile(struct ieee80211_hw *hw);*/
