mlxsw: 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@embeddedor.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Tested-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.h b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.h
index 5965913565a5..96437992b102 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.h
+++ b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.h
@@ -20,7 +20,7 @@ struct mlxsw_sp_acl_tcam {
 	struct mutex lock; /* guards vregion list */
 	struct list_head vregion_list;
 	u32 vregion_rehash_intrvl;   /* ms */
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };
 
@@ -86,7 +86,7 @@ struct mlxsw_sp_acl_tcam_region {
 	char tcam_region_info[MLXSW_REG_PXXX_TCAM_REGION_INFO_LEN];
 	struct mlxsw_afk_key_info *key_info;
 	struct mlxsw_sp *mlxsw_sp;
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };