linux-kernel - [PATCH] mwifiex: avoid null-pointer-subtraction warning

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Date:   Mon, 27 Sep 2021 14:16:35 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Amitkumar Karwar <amitkarwar@...il.com>,
        Ganapathi Bhat <ganapathi017@...il.com>,
        Sharvari Harisangam <sharvari.harisangam@....com>,
        Xinming Hu <huxinming820@...il.com>,
        Kalle Valo <kvalo@...eaurora.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH] mwifiex: avoid null-pointer-subtraction warning

From: Arnd Bergmann <arnd@...db.de>

clang complains about some NULL pointer arithmetic in this driver:

drivers/net/wireless/marvell/mwifiex/sta_tx.c:65:59: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
        pad = ((void *)skb->data - (sizeof(*local_tx_pd) + hroom)-
                                                                 ^
drivers/net/wireless/marvell/mwifiex/uap_txrx.c:478:53: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
        pad = ((void *)skb->data - (sizeof(*txpd) + hroom) - NULL) &

Rework that expression to do the same thing using a uintptr_t.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/net/wireless/marvell/mwifiex/sta_tx.c   | 4 ++--
 drivers/net/wireless/marvell/mwifiex/uap_txrx.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/marvell/mwifiex/sta_tx.c b/drivers/net/wireless/marvell/mwifiex/sta_tx.c
index 241305377e20..a9b5eb992220 100644
--- a/drivers/net/wireless/marvell/mwifiex/sta_tx.c
+++ b/drivers/net/wireless/marvell/mwifiex/sta_tx.c
@@ -62,8 +62,8 @@ void *mwifiex_process_sta_txpd(struct mwifiex_private *priv,
 
 	pkt_type = mwifiex_is_skb_mgmt_frame(skb) ? PKT_TYPE_MGMT : 0;
 
-	pad = ((void *)skb->data - (sizeof(*local_tx_pd) + hroom)-
-			 NULL) & (MWIFIEX_DMA_ALIGN_SZ - 1);
+	pad = ((uintptr_t)skb->data - (sizeof(*local_tx_pd) + hroom)) &
+	       (MWIFIEX_DMA_ALIGN_SZ - 1);
 	skb_push(skb, sizeof(*local_tx_pd) + pad);
 
 	local_tx_pd = (struct txpd *) skb->data;
diff --git a/drivers/net/wireless/marvell/mwifiex/uap_txrx.c b/drivers/net/wireless/marvell/mwifiex/uap_txrx.c
index 9bbdb8dfce62..245ff644f81e 100644
--- a/drivers/net/wireless/marvell/mwifiex/uap_txrx.c
+++ b/drivers/net/wireless/marvell/mwifiex/uap_txrx.c
@@ -475,8 +475,8 @@ void *mwifiex_process_uap_txpd(struct mwifiex_private *priv,
 
 	pkt_type = mwifiex_is_skb_mgmt_frame(skb) ? PKT_TYPE_MGMT : 0;
 
-	pad = ((void *)skb->data - (sizeof(*txpd) + hroom) - NULL) &
-			(MWIFIEX_DMA_ALIGN_SZ - 1);
+	pad = ((uintptr_t)skb->data - (sizeof(*txpd) + hroom)) &
+	       (MWIFIEX_DMA_ALIGN_SZ - 1);
 
 	skb_push(skb, sizeof(*txpd) + pad);
 
-- 
2.29.2