Subject: [PATCH][next] intel: Replace zero-length array with flexible-array member

From: "Gustavo A. R. Silva" <[email-masked]>
Date: Mon, 24 Feb 2020 10:41:06 -0600

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 <[email-masked]>
---
 drivers/net/ethernet/intel/fm10k/fm10k.h | 6 +++---
 drivers/net/ethernet/intel/i40e/i40e.h   | 4 ++--
 drivers/net/ethernet/intel/igb/igb.h     | 2 +-
 drivers/net/ethernet/intel/igc/igc.h     | 2 +-
 drivers/net/ethernet/intel/ixgbe/ixgbe.h | 2 +-
 5 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/intel/fm10k/fm10k.h b/drivers/net/ethernet/intel/fm10k/fm10k.h
index f306084ca12c..5b78362b82ac 100644
--- a/drivers/net/ethernet/intel/fm10k/fm10k.h
+++ b/drivers/net/ethernet/intel/fm10k/fm10k.h
@@ -41,7 +41,7 @@ struct fm10k_l2_accel {
 	u16 count;
 	u16 dglort;
 	struct rcu_head rcu;
-	struct net_device *macvlan[0];
+	struct net_device *macvlan[];
 };
 
 enum fm10k_ring_state_t {
@@ -198,7 +198,7 @@ struct fm10k_q_vector {
 	struct rcu_head rcu;	/* to avoid race with update stats on free */
 
 	/* for dynamic allocation of rings associated with this q_vector */
-	struct fm10k_ring ring[0] ____cacheline_internodealigned_in_smp;
+	struct fm10k_ring ring[] ____cacheline_internodealigned_in_smp;
 };
 
 enum fm10k_ring_f_enum {
@@ -218,7 +218,7 @@ struct fm10k_iov_data {
 	unsigned int		num_vfs;
 	unsigned int		next_vf_mbx;
 	struct rcu_head		rcu;
-	struct fm10k_vf_info	vf_info[0];
+	struct fm10k_vf_info	vf_info[];
 };
 
 struct fm10k_udp_port {
diff --git a/drivers/net/ethernet/intel/i40e/i40e.h b/drivers/net/ethernet/intel/i40e/i40e.h
index 4833187bd259..e95b8da45e07 100644
--- a/drivers/net/ethernet/intel/i40e/i40e.h
+++ b/drivers/net/ethernet/intel/i40e/i40e.h
@@ -334,13 +334,13 @@ int i40e_ddp_flash(struct net_device *netdev, struct ethtool_flash *flash);
 
 struct i40e_ddp_profile_list {
 	u32 p_count;
-	struct i40e_profile_info p_info[0];
+	struct i40e_profile_info p_info[];
 };
 
 struct i40e_ddp_old_profile_list {
 	struct list_head list;
 	size_t old_ddp_size;
-	u8 old_ddp_buf[0];
+	u8 old_ddp_buf[];
 };
 
 /* macros related to FLX_PIT */
diff --git a/drivers/net/ethernet/intel/igb/igb.h b/drivers/net/ethernet/intel/igb/igb.h
index 49b5fa9d4783..0c9282e2aaec 100644
--- a/drivers/net/ethernet/intel/igb/igb.h
+++ b/drivers/net/ethernet/intel/igb/igb.h
@@ -306,7 +306,7 @@ struct igb_q_vector {
 	char name[IFNAMSIZ + 9];
 
 	/* for dynamic allocation of rings associated with this q_vector */
-	struct igb_ring ring[0] ____cacheline_internodealigned_in_smp;
+	struct igb_ring ring[] ____cacheline_internodealigned_in_smp;
 };
 
 enum e1000_ring_flags_t {
diff --git a/drivers/net/ethernet/intel/igc/igc.h b/drivers/net/ethernet/intel/igc/igc.h
index 0014828eec46..a1f845a2aa80 100644
--- a/drivers/net/ethernet/intel/igc/igc.h
+++ b/drivers/net/ethernet/intel/igc/igc.h
@@ -326,7 +326,7 @@ struct igc_q_vector {
 	struct net_device poll_dev;
 
 	/* for dynamic allocation of rings associated with this q_vector */
-	struct igc_ring ring[0] ____cacheline_internodealigned_in_smp;
+	struct igc_ring ring[] ____cacheline_internodealigned_in_smp;
 };
 
 #define MAX_ETYPE_FILTER		(4 - 1)
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index 39e73ad60352..2833e4f041ce 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -462,7 +462,7 @@ struct ixgbe_q_vector {
 	char name[IFNAMSIZ + 9];
 
 	/* for dynamic allocation of rings associated with this q_vector */
-	struct ixgbe_ring ring[0] ____cacheline_internodealigned_in_smp;
+	struct ixgbe_ring ring[] ____cacheline_internodealigned_in_smp;
 };
 
 #ifdef CONFIG_IXGBE_HWMON
-- 
2.25.0