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Date:   Tue, 18 Feb 2020 14:57:05 -0600
From:   "Gustavo A. R. Silva" <gustavo@embeddedor.com>
To:     Jiri Pirko <jiri@mellanox.com>, Ido Schimmel <idosch@mellanox.com>,
        "David S. Miller" <davem@davemloft.net>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: [PATCH][next] mlxsw: Replace zero-length array with flexible-array
 member
Message-ID: <20200218205705.GA29805@embeddedor>
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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/mlxsw/core.c                    | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_keys.c      | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum1_kvdl.c          | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum2_kvdl.c          | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum_acl.c            | 4 ++--
 .../net/ethernet/mellanox/mlxsw/spectrum_acl_bloom_filter.c   | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.c       | 4 ++--
 drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.h       | 4 ++--
 drivers/net/ethernet/mellanox/mlxsw/spectrum_kvdl.c           | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c             | 2 +-
 drivers/net/ethernet/mellanox/mlxsw/spectrum_nve.c            | 2 +-
 11 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlxsw/core.c b/drivers/net/ethernet/mellanox/mlxsw/core.c
index e9f791c43f20..0d630096a28c 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/core.c
+++ b/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 */
 };
 
diff --git a/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_keys.c b/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_keys.c
index feb4672a5ac0..bd2207f60722 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/core_acl_flex_keys.c
+++ b/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
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum1_kvdl.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum1_kvdl.c
index 09ee0a807747..a9fff8adc75e 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum1_kvdl.c
+++ b/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 {
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum2_kvdl.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum2_kvdl.c
index 8d14770766b4..3a73d654017f 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum2_kvdl.c
+++ b/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 {
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl.c
index 3d3cca596116..9368b93dab38 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl.c
+++ b/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 */
 };
 
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_bloom_filter.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_bloom_filter.c
index 3a2de13fcb68..dbd3bebf11ec 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_bloom_filter.c
+++ b/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
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.c
index e993159e8e4c..430da69003d8 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_acl_tcam.c
+++ b/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 */
 };
 
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 */
 };
 
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_kvdl.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_kvdl.c
index 1e4cdee7bcd7..715ec8ecacba 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_kvdl.c
+++ b/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 */
 };
 
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c
index 54275624718b..423eedebcd22 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_mr.c
+++ b/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 */
 };
 
diff --git a/drivers/net/ethernet/mellanox/mlxsw/spectrum_nve.c b/drivers/net/ethernet/mellanox/mlxsw/spectrum_nve.c
index 2153bcc4b585..16a130c2f21c 100644
--- a/drivers/net/ethernet/mellanox/mlxsw/spectrum_nve.c
+++ b/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 {
-- 
2.25.0