Return-path: Received: from mail-oi0-f68.google.com ([209.85.218.68]:41790 "EHLO mail-oi0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751029AbeBIQoV (ORCPT ); Fri, 9 Feb 2018 11:44:21 -0500 Subject: Re: [PATCH] rtlwifi: rtl8192cu: remove pointless memcpy To: Arnd Bergmann , Ping-Ke Shih Cc: Kalle Valo , Johannes Berg , linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180209132531.2755482-1-arnd@arndb.de> From: Larry Finger Message-ID: <62048535-6455-e4ac-040a-ca2bf60fc0f7@lwfinger.net> (sfid-20180209_174511_426716_1137B0B1) Date: Fri, 9 Feb 2018 10:44:19 -0600 MIME-Version: 1.0 In-Reply-To: <20180209132531.2755482-1-arnd@arndb.de> Content-Type: text/plain; charset=utf-8; format=flowed Sender: linux-wireless-owner@vger.kernel.org List-ID: On 02/09/2018 07:24 AM, Arnd Bergmann wrote: > gcc-8 points out that source and destination of the memcpy() are > always the same pointer, so the effect of memcpy() is undefined > here (its arguments must not overlap): > > drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c: In function '_rtl_rx_process': > drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c:430:2: error: 'memcpy' source argument is the same as destination [-Werror=restrict] > > Most likely this is harmless, but it's easy to just remove the > line and get rid of the warning. > > Signed-off-by: Arnd Bergmann > --- > drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c | 1 - > 1 file changed, 1 deletion(-) > > diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c b/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c > index ac4a82de40c7..9ab56827124e 100644 > --- a/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c > +++ b/drivers/net/wireless/realtek/rtlwifi/rtl8192cu/trx.c > @@ -427,7 +427,6 @@ static void _rtl_rx_process(struct ieee80211_hw *hw, struct sk_buff *skb) > (u32)hdr->addr1[0], (u32)hdr->addr1[1], > (u32)hdr->addr1[2], (u32)hdr->addr1[3], > (u32)hdr->addr1[4], (u32)hdr->addr1[5]); > - memcpy(IEEE80211_SKB_RXCB(skb), rx_status, sizeof(*rx_status)); > ieee80211_rx(hw, skb); > } No, the warning is pointing to the wrong place. The routine in question does the following: 1. Loads the rx_status struct from skb->cb. 2. Overwrites the contents with 0. 3. Fills various members of the struct. 4. Writes the revised struct back into skb->cb. Thus eliminating step 4 negates all the things done in step 3, and is wrong. The correct fix is to change step 1 to create a NULL-filled rx_status struct, and eliminate step 2. NACK. Larry