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From: Ping-Ke Shih <pkshih@realtek.com>
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Subject: RE: [PATCH wireless-next v3 2/2] wifi: rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior
Thread-Topic: [PATCH wireless-next v3 2/2] wifi: rtlwifi: rtl8821ae: phy: fix
 an undefined bitwise shift behavior
Thread-Index: AQHaINIRUzT9Mv+uykSNp3dE8RYddbCNaTqA
Date: Mon, 27 Nov 2023 02:04:14 +0000
Message-ID: <daf6238559114e50a673d97b3f1bab4e@realtek.com>
References: <20231127013511.26694-1-suhui@nfschina.com>
 <20231127013511.26694-2-suhui@nfschina.com>
In-Reply-To: <20231127013511.26694-2-suhui@nfschina.com>
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> -----Original Message-----
> From: Su Hui <suhui@nfschina.com>
> Sent: Monday, November 27, 2023 9:35 AM
> To: Ping-Ke Shih <pkshih@realtek.com>; dan.carpenter@linaro.org; kvalo@ke=
rnel.org; nathan@kernel.org;
> ndesaulniers@google.com; trix@redhat.com
> Cc: Su Hui <suhui@nfschina.com>; lizetao1@huawei.com; linville@tuxdriver.=
com; Larry.Finger@lwfinger.net;
> linux-wireless@vger.kernel.org; linux-kernel@vger.kernel.org; llvm@lists.=
linux.dev;
> kernel-janitors@vger.kernel.org
> Subject: [PATCH wireless-next v3 2/2] wifi: rtlwifi: rtl8821ae: phy: fix =
an undefined bitwise shift behavior
>=20
> 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]
>=20
> 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]
>=20
> 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. Let _rtl8821ae_phy_calculate_bit_shift()'s
> return value less than 32 to fix this problem. Warn if bitmask is zero.
>=20
> [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
>=20
> Fixes: 21e4b0726dc6 ("rtlwifi: rtl8821ae: Move driver from staging to reg=
ular tree")
> Signed-off-by: Su Hui <suhui@nfschina.com>

Acked-by: Ping-Ke Shih <pkshih@realtek.com>

> +       if (WARN_ON_ONCE(!bitmask))

I test this patch with real hardware to connect 2GHz and 5GHz AP
respectively and keep ping for a while. It doesn't throw warning
by this statement.=20