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 76497732 ("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>

drivers/net/ethernet/mellanox/mlxsw/core.c

@@ -82,7 +82,7 @@ struct mlxsw_core {
 	struct mlxsw_core_port *ports;
 	unsigned int max_ports;
 	bool fw_flash_in_progress;
-	unsigned long driver_priv[0];
+	unsigned long driver_priv[];
 	/* driver_priv has to be always the last item */
 };
 

drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_keys.c

@@ -72,7 +72,7 @@ struct mlxsw_afk_key_info {
 						      * is index inside "blocks"
 						      */
 	struct mlxsw_afk_element_usage elusage;
-	const struct mlxsw_afk_block *blocks[0];
+	const struct mlxsw_afk_block *blocks[];
 };
 
 static bool

drivers/net/ethernet/mellanox/mlxsw/spectrum1_kvdl.c

@@ -60,7 +60,7 @@ static const struct mlxsw_sp1_kvdl_part_info mlxsw_sp1_kvdl_parts_info[] = {
 
 struct mlxsw_sp1_kvdl_part {
 	struct mlxsw_sp1_kvdl_part_info info;
-	unsigned long usage[0];	/* Entries */
+	unsigned long usage[];	/* Entries */
 };
 
 struct mlxsw_sp1_kvdl {

drivers/net/ethernet/mellanox/mlxsw/spectrum2_kvdl.c

@@ -45,7 +45,7 @@ struct mlxsw_sp2_kvdl_part {
 	unsigned int usage_bit_count;
 	unsigned int indexes_per_usage_bit;
 	unsigned int last_allocated_bit;
-	unsigned long usage[0];	/* Usage bits */
+	unsigned long usage[];	/* Usage bits */
 };
 
 struct mlxsw_sp2_kvdl {

drivers/net/ethernet/mellanox/mlxsw/spectrum_acl.c

@@ -58,7 +58,7 @@ struct mlxsw_sp_acl_ruleset {
 	struct mlxsw_sp_acl_ruleset_ht_key ht_key;
 	struct rhashtable rule_ht;
 	unsigned int ref_count;
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };
 
@@ -71,7 +71,7 @@ struct mlxsw_sp_acl_rule {
 	u64 last_used;
 	u64 last_packets;
 	u64 last_bytes;
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };
 

drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_bloom_filter.c

@@ -13,7 +13,7 @@
 struct mlxsw_sp_acl_bf {
 	struct mutex lock; /* Protects Bloom Filter updates. */
 	unsigned int bank_size;
-	refcount_t refcnt[0];
+	refcount_t refcnt[];
 };
 
 /* Bloom filter uses a crc-16 hash over chunks of data which contain 4 key

drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.c

@@ -224,7 +224,7 @@ struct mlxsw_sp_acl_tcam_vchunk;
 struct mlxsw_sp_acl_tcam_chunk {
 	struct mlxsw_sp_acl_tcam_vchunk *vchunk;
 	struct mlxsw_sp_acl_tcam_region *region;
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };
 
@@ -243,7 +243,7 @@ struct mlxsw_sp_acl_tcam_vchunk {
 struct mlxsw_sp_acl_tcam_entry {
 	struct mlxsw_sp_acl_tcam_ventry *ventry;
 	struct mlxsw_sp_acl_tcam_chunk *chunk;
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };
 

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 */
 };
 

drivers/net/ethernet/mellanox/mlxsw/spectrum_kvdl.c

@@ -8,7 +8,7 @@
 
 struct mlxsw_sp_kvdl {
 	const struct mlxsw_sp_kvdl_ops *kvdl_ops;
-	unsigned long priv[0];
+	unsigned long priv[];
 	/* priv has to be always the last item */
 };
 

drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c

@@ -68,7 +68,7 @@ struct mlxsw_sp_mr_table {
 	struct list_head route_list;
 	struct rhashtable route_ht;
 	const struct mlxsw_sp_mr_table_ops *ops;
-	char catchall_route_priv[0];
+	char catchall_route_priv[];
 	/* catchall_route_priv has to be always the last item */
 };
 

drivers/net/ethernet/mellanox/mlxsw/spectrum_nve.c

@@ -67,7 +67,7 @@ struct mlxsw_sp_nve_mc_record {
 	struct mlxsw_sp_nve_mc_list *mc_list;
 	const struct mlxsw_sp_nve_mc_record_ops *ops;
 	u32 kvdl_index;
-	struct mlxsw_sp_nve_mc_entry entries[0];
+	struct mlxsw_sp_nve_mc_entry entries[];
 };
 
 struct mlxsw_sp_nve_mc_list {