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From:   Christian Lamparter <chunkeey@gmail.com>
To:     Arnd Bergmann <arnd@arndb.de>, Kalle Valo <kvalo@codeaurora.org>
Cc:     "David S. Miller" <davem@davemloft.net>,
        clang-built-linux@googlegroups.com,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>,
        linux-wireless@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] wireless: carl9170: fix clang build warning
Date:   Mon, 25 Mar 2019 15:20:02 +0100
Message-ID: <10158331.jkizvXajyz@debian64>
In-Reply-To: <20190325124354.1413529-1-arnd@arndb.de>
References: <20190325124354.1413529-1-arnd@arndb.de>
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Sender: linux-kernel-owner@vger.kernel.org
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On Monday, March 25, 2019 1:43:44 PM CET Arnd Bergmann wrote:
> clang fails to eliminate some dead code with always-taken branches
> when CONFIG_PROFILE_ANNOTATED_BRANCHES is set, leading to a false-positive
> warning:
> 
> drivers/net/wireless/ath/carl9170/mac.c:522:3: error: variable 'power' is used uninitialized whenever 'if' condition is
>       false [-Werror,-Wsometimes-uninitialized]
>                 BUG_ON(1);
>                 ^~~~~~~~~
> 
> Change both instances of BUG_ON(1) in carl9170 to the simpler BUG()
> to avoid the warning.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Heh, I added these "default:" cases back in the day to make gcc
shut-up about "switch is missing cases" warnings. And now I
guess it's clangs time to complain. (-; 

Especially the "default case" in carl9170_rx_untie_data is hilarious.
Since all the possible cases (just 4!) have been addressed and the
"default" is deadcode. I think gcc did not consider the
AR9170_RX_STATUS_MPDU mask in the 
| switch (mac_status & AR9170_RX_STATUS_MPDU) {

statement. However I'll be waiting for the day until the deadcode
elimination warnings will show up.

Anyway,

Acked-by: Christian Lamparter <chunkeey@gmail.com>

Regards,
Christian

> ---
>  drivers/net/wireless/ath/carl9170/mac.c | 2 +-
>  drivers/net/wireless/ath/carl9170/rx.c  | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/wireless/ath/carl9170/mac.c b/drivers/net/wireless/ath/carl9170/mac.c
> index 7d4a72dc98db..b2eeb9fd68d2 100644
> --- a/drivers/net/wireless/ath/carl9170/mac.c
> +++ b/drivers/net/wireless/ath/carl9170/mac.c
> @@ -519,7 +519,7 @@ int carl9170_set_mac_tpc(struct ar9170 *ar, struct ieee80211_channel *channel)
>  		power = ar->power_5G_leg[0] & 0x3f;
>  		break;
>  	default:
> -		BUG_ON(1);
> +		BUG();
>  	}
>  
>  	power = min_t(unsigned int, power, ar->hw->conf.power_level * 2);
> diff --git a/drivers/net/wireless/ath/carl9170/rx.c b/drivers/net/wireless/ath/carl9170/rx.c
> index 8e154f6364a3..23ab8a80c18c 100644
> --- a/drivers/net/wireless/ath/carl9170/rx.c
> +++ b/drivers/net/wireless/ath/carl9170/rx.c
> @@ -795,7 +795,7 @@ static void carl9170_rx_untie_data(struct ar9170 *ar, u8 *buf, int len)
>  		break;
>  
>  	default:
> -		BUG_ON(1);
> +		BUG();
>  		break;
>  	}
>  
>