linux-kernel - [PATCH 4.9 029/102] mac80211: Fix clang warning about constant operand in logical operation

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Date:   Fri,  6 Apr 2018 15:23:10 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Matthias Kaehlcke <mka@...omium.org>,
        Johannes Berg <johannes.berg@...el.com>,
        Nathan Chancellor <natechancellor@...il.com>
Subject: [PATCH 4.9 029/102] mac80211: Fix clang warning about constant operand in logical operation

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Matthias Kaehlcke <mka@...omium.org>

commit 93f56de259376d7e4fff2b2d104082e1fa66e237 upstream.

When clang detects a non-boolean constant in a logical operation it
generates a 'constant-logical-operand' warning. In
ieee80211_try_rate_control_ops_get() the result of strlen(<const str>)
is used in a logical operation, clang resolves the expression to an
(integer) constant at compile time when clang's builtin strlen function
is used.

Change the condition to check for strlen() > 0 to make the constant
operand boolean and thus avoid the warning.

Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Cc: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/mac80211/rate.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/mac80211/rate.c
+++ b/net/mac80211/rate.c
@@ -173,9 +173,11 @@ ieee80211_rate_control_ops_get(const cha
 		/* try default if specific alg requested but not found */
 		ops = ieee80211_try_rate_control_ops_get(ieee80211_default_rc_algo);
 
-	/* try built-in one if specific alg requested but not found */
-	if (!ops && strlen(CONFIG_MAC80211_RC_DEFAULT))
+	/* Note: check for > 0 is intentional to avoid clang warning */
+	if (!ops && (strlen(CONFIG_MAC80211_RC_DEFAULT) > 0))
+		/* try built-in one if specific alg requested but not found */
 		ops = ieee80211_try_rate_control_ops_get(CONFIG_MAC80211_RC_DEFAULT);
+
 	kernel_param_unlock(THIS_MODULE);
 
 	return ops;