linux-kernel - RE: [PATCH] mac80211: Fix clang warning about constant operand in logical operation

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6DCFFCA9CE@AcuExch.aculab.com>
Date:   Mon, 10 Apr 2017 14:12:00 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Matthias Kaehlcke' <mka@...omium.org>,
        Johannes Berg <johannes@...solutions.net>,
        "David S . Miller" <davem@...emloft.net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Grant Grundler <grundler@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>
Subject: RE: [PATCH] mac80211: Fix clang warning about constant operand in
 logical operation

From: Matthias Kaehlcke
> Sent: 06 April 2017 19:57
> Clang raises a warning about the expression 'strlen(CONFIG_XXX)' being
> used in a logical operation. Clangs' builtin strlen function resolves the
> expression to a constant at compile time, which causes clang to generate
> a 'constant-logical-operand' warning.
> 
> Split the if statement in two to avoid using the const expression in a
> logical operation.
> 
> Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
> ---
>  net/mac80211/rate.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/net/mac80211/rate.c b/net/mac80211/rate.c
> index 206698bc93f4..68ff202d6380 100644
> --- a/net/mac80211/rate.c
> +++ b/net/mac80211/rate.c
> @@ -173,9 +173,14 @@ ieee80211_rate_control_ops_get(const char *name)
>  		/* try default if specific alg requested but not found */
>  		ops = ieee80211_try_rate_control_ops_get(ieee80211_default_rc_algo);
> 
> +	if (ops)
> +		goto unlock;
> +
>  	/* try built-in one if specific alg requested but not found */
> -	if (!ops && strlen(CONFIG_MAC80211_RC_DEFAULT))
> +	if (strlen(CONFIG_MAC80211_RC_DEFAULT))
>  		ops = ieee80211_try_rate_control_ops_get(CONFIG_MAC80211_RC_DEFAULT);
> +
> +unlock:

Using the result of strlen() as a boolean should itself be a compilation error.
You could change to code to the equivalent:

	if (!ops && CONFIG_MAC80211_RC_DEFAULT[0])
		ops = ...

	David