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

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

[Gustavo A. R. Silva]

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@embeddedor.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

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

[Leon Romanovsky]

On Tue, Feb 18, 2020 at 02:31:14PM -0600, Gustavo A. R. Silva wrote:
> 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@embeddedor.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(-)
>

Thanks, applied to mlx5-next.

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

[Gustavo A. R. Silva]

On 2/19/20 01:14, Leon Romanovsky wrote:

>>
>> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.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(-)
>>
> 
> Thanks, applied to mlx5-next.
> 

Thank you.

--
Gustavo

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

[Gustavo A. R. Silva]

Zero-length arrays are deprecated[1] and we are moving towards
adopting C99 flexible-array members instead. So, replace zero-length
array declaration in struct mlx5e_flow_meter_aso_obj with flex-array
member.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
routines on memcpy() and help us make progress towards globally
enabling -fstrict-flex-arrays=3 [2].

Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays [1]
Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [2]
Link: https://github.com/KSPP/linux/issues/78
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/net/ethernet/mellanox/mlx5/core/en/tc/meter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/tc/meter.c b/drivers/net/ethernet/mellanox/mlx5/core/en/tc/meter.c
index 78af8a3175bf..7758a425bfa8 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en/tc/meter.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en/tc/meter.c
@@ -28,7 +28,7 @@ struct mlx5e_flow_meter_aso_obj {
 	int base_id;
 	int total_meters;
 
-	unsigned long meters_map[0]; /* must be at the end of this struct */
+	unsigned long meters_map[]; /* must be at the end of this struct */
 };
 
 struct mlx5e_flow_meters {
-- 
2.34.1

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

[Saeed Mahameed]

On 09 Jan 19:39, Gustavo A. R. Silva wrote:
>Zero-length arrays are deprecated[1] and we are moving towards
>adopting C99 flexible-array members instead. So, replace zero-length
>array declaration in struct mlx5e_flow_meter_aso_obj with flex-array
>member.
>
>This helps with the ongoing efforts to tighten the FORTIFY_SOURCE
>routines on memcpy() and help us make progress towards globally
>enabling -fstrict-flex-arrays=3 [2].
>
>Link: https://www.kernel.org/doc/html/latest/process/deprecated.html#zero-length-and-one-element-arrays [1]
>Link: https://gcc.gnu.org/pipermail/gcc-patches/2022-October/602902.html [2]
>Link: https://github.com/KSPP/linux/issues/78
>Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Applied to net-next-mlx5, Thanks!