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 <[email protected]>
---
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;
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));
}
rtl_write_dword(rtlpriv, regaddr, data);
@@ -153,7 +153,7 @@ u32 rtl8821ae_phy_query_rf_reg(struct ieee80211_hw *hw,
original_value = _rtl8821ae_phy_rf_serial_read(hw, rfpath, regaddr);
bitshift = _rtl8821ae_phy_calculate_bit_shift(bitmask);
- readback_value = (original_value & bitmask) >> bitshift;
+ readback_value = (u64)(original_value & bitmask) >> bitshift;
spin_unlock(&rtlpriv->locks.rf_lock);
@@ -181,7 +181,7 @@ void rtl8821ae_phy_set_rf_reg(struct ieee80211_hw *hw,
original_value =
_rtl8821ae_phy_rf_serial_read(hw, rfpath, regaddr);
bitshift = _rtl8821ae_phy_calculate_bit_shift(bitmask);
- data = ((original_value & (~bitmask)) | (data << bitshift));
+ data = ((original_value & (~bitmask)) | ((u64)data << bitshift));
}
_rtl8821ae_phy_rf_serial_write(hw, rfpath, regaddr, data);
--
2.30.2
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 <[email protected]>
> ---
> 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);*/
> -----Original Message-----
> From: Dan Carpenter <[email protected]>
> Sent: Wednesday, November 22, 2023 9:02 PM
> To: Su Hui <[email protected]>
> Cc: Ping-Ke Shih <[email protected]>; [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]
> Subject: Re: [PATCH wireless-next 2/2] rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior
>
> 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...
>
I think the bitmask should not 0, so just replace _rtl8821ae_phy_calculate_bit_shift()
by __ffs(bitmask). To be safer, callers can check bitmask is not 0 before calling.
Ping-Ke
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 <[email protected]>
>> ---
>> 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
On 2023/11/23 08:41, Ping-Ke Shih wrote:
>
>> -----Original Message-----
>> From: Dan Carpenter <[email protected]>
>> Sent: Wednesday, November 22, 2023 9:02 PM
>> To: Su Hui <[email protected]>
>> Cc: Ping-Ke Shih <[email protected]>; [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; [email protected]; [email protected];
>> [email protected]; [email protected]; [email protected];
>> [email protected]
>> Subject: Re: [PATCH wireless-next 2/2] rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior
>>
>> 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...
>>
> I think the bitmask should not 0, so just replace _rtl8821ae_phy_calculate_bit_shift()
> by __ffs(bitmask). To be safer, callers can check bitmask is not 0 before calling.
Thanks for your great suggestion!
I will send v2 soon.
Su Hui
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 <[email protected]>
> > > ---
> > > 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