linux-kernel - [PATCH][next] net/mlx5e: Replace zero-length array with flexible-array member

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Message-ID: <20200218203114.GA27096@embeddedor>
Date:   Tue, 18 Feb 2020 14:31:14 -0600
From:   "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        Leon Romanovsky <leon@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Boris Pismenny <borisp@...lanox.com>
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH][next] net/mlx5e: Replace zero-length array with
 flexible-array member

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@...eddedor.com>
---
 drivers/net/ethernet/mellanox/mlx5/core/en.h          | 2 +-
 drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c  | 2 +-
 drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c | 2 +-
 drivers/net/ethernet/mellanox/mlx5/core/ipoib/ipoib.h | 4 ++--
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h b/drivers/net/ethernet/mellanox/mlx5/core/en.h
index 220ef9f06f84..a960099cd7aa 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
@@ -204,7 +204,7 @@ struct mlx5e_tx_wqe {
 
 struct mlx5e_rx_wqe_ll {
 	struct mlx5_wqe_srq_next_seg  next;
-	struct mlx5_wqe_data_seg      data[0];
+	struct mlx5_wqe_data_seg      data[];
 };
 
 struct mlx5e_rx_wqe_cyc {
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c b/drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c
index 4c61d25d2e88..b794888fa3ba 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fpga/ipsec.c
@@ -57,7 +57,7 @@ struct mlx5_fpga_ipsec_cmd_context {
 	struct completion complete;
 	struct mlx5_fpga_device *dev;
 	struct list_head list; /* Item in pending_cmds */
-	u8 command[0];
+	u8 command[];
 };
 
 struct mlx5_fpga_esp_xfrm;
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c b/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c
index ab69effb056d..f43caefd07a1 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/fs_counters.c
@@ -470,7 +470,7 @@ struct mlx5_fc_bulk {
 	u32 base_id;
 	int bulk_len;
 	unsigned long *bitmask;
-	struct mlx5_fc fcs[0];
+	struct mlx5_fc fcs[];
 };
 
 static void mlx5_fc_init(struct mlx5_fc *counter, struct mlx5_fc_bulk *bulk,
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/ipoib/ipoib.h b/drivers/net/ethernet/mellanox/mlx5/core/ipoib/ipoib.h
index c87962cab921..de7e01a027bb 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/ipoib/ipoib.h
+++ b/drivers/net/ethernet/mellanox/mlx5/core/ipoib/ipoib.h
@@ -56,7 +56,7 @@ struct mlx5i_priv {
 	u32    qkey;
 	u16    pkey_index;
 	struct mlx5i_pkey_qpn_ht *qpn_htbl;
-	char  *mlx5e_priv[0];
+	char  *mlx5e_priv[];
 };
 
 int mlx5i_create_tis(struct mlx5_core_dev *mdev, u32 underlay_qpn, u32 *tisn);
@@ -107,7 +107,7 @@ struct mlx5i_tx_wqe {
 	struct mlx5_wqe_datagram_seg datagram;
 	struct mlx5_wqe_eth_pad      pad;
 	struct mlx5_wqe_eth_seg      eth;
-	struct mlx5_wqe_data_seg     data[0];
+	struct mlx5_wqe_data_seg     data[];
 };
 
 static inline void mlx5i_sq_fetch_wqe(struct mlx5e_txqsq *sq,
-- 
2.25.0