linux-kernel - Re: [PATCH] b43: shut up clang -Wuninitialized variable warning

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Message-ID: <758d6087-bd8c-a60f-919a-40c170f7b23c@lwfinger.net>
Date:   Fri, 22 Mar 2019 10:47:10 -0500
From:   Larry Finger <Larry.Finger@...inger.net>
To:     Arnd Bergmann <arnd@...db.de>, Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Priit Laes <plaes@...es.org>
Cc:     clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        linux-wireless@...r.kernel.org, b43-dev@...ts.infradead.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] b43: shut up clang -Wuninitialized variable warning

On 3/22/19 9:37 AM, Arnd Bergmann wrote:
> Clang warns about what is clearly a case of passing an uninitalized
> variable into a static function:
> 
> drivers/net/wireless/broadcom/b43/phy_lp.c:1852:23: error: variable 'gains' is uninitialized when used here
>        [-Werror,-Wuninitialized]
>                  lpphy_papd_cal(dev, gains, 0, 1, 30);
>                                      ^~~~~
> drivers/net/wireless/broadcom/b43/phy_lp.c:1838:2: note: variable 'gains' is declared here
>          struct lpphy_tx_gains gains, oldgains;
>          ^
> 1 error generated.
> 
> However, this function is empty, and its arguments are never evaluated,
> so gcc in contrast does not warn here. Both compilers behave in a
> reasonable way as far as I can tell, so we should change the code
> to avoid the warning everywhere.
> 
> We could just eliminate the lpphy_papd_cal() function entirely,
> given that it has had the TODO comment in it for 10 years now
> and is rather unlikely to ever get done. I'm doing a simpler
> change here, and just pass the 'oldgains' variable in that has
> been initialized, based on the guess that this is what was
> originally meant.
> 
> Fixes: 2c0d6100da3e ("b43: LP-PHY: Begin implementing calibration & software RFKILL support")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>   drivers/net/wireless/broadcom/b43/phy_lp.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/wireless/broadcom/b43/phy_lp.c b/drivers/net/wireless/broadcom/b43/phy_lp.c
> index 46408a560814..aedee026c5e2 100644
> --- a/drivers/net/wireless/broadcom/b43/phy_lp.c
> +++ b/drivers/net/wireless/broadcom/b43/phy_lp.c
> @@ -1835,7 +1835,7 @@ static void lpphy_papd_cal(struct b43_wldev *dev, struct lpphy_tx_gains gains,
>   static void lpphy_papd_cal_txpwr(struct b43_wldev *dev)
>   {
>   	struct b43_phy_lp *lpphy = dev->phy.lp;
> -	struct lpphy_tx_gains gains, oldgains;
> +	struct lpphy_tx_gains oldgains;
>   	int old_txpctl, old_afe_ovr, old_rf, old_bbmult;
>   
>   	lpphy_read_tx_pctl_mode_from_hardware(dev);
> @@ -1849,9 +1849,9 @@ static void lpphy_papd_cal_txpwr(struct b43_wldev *dev)
>   	lpphy_set_tx_power_control(dev, B43_LPPHY_TXPCTL_OFF);
>   
>   	if (dev->dev->chip_id == 0x4325 && dev->dev->chip_rev == 0)
> -		lpphy_papd_cal(dev, gains, 0, 1, 30);
> +		lpphy_papd_cal(dev, oldgains, 0, 1, 30);
>   	else
> -		lpphy_papd_cal(dev, gains, 0, 1, 65);
> +		lpphy_papd_cal(dev, oldgains, 0, 1, 65);
>   
>   	if (old_afe_ovr)
>   		lpphy_set_tx_gains(dev, oldgains);
> 

Acked-by: Larry Finger <Larry.Finger@...inger.net>

Thanks. I will submit a patch that removes lpphy_papd_cal(). You are correct 
that it is unlikely ever to be implemented.

Larry