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
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.
Oh, it's my negligence...
Su Hui
