wireless: marvell: 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: NGustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: NGanapathi Bhat <ganapathi.bhat@nxp.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200225020413.GA8057@embeddedor

drivers/net/wireless/marvell/libertas_tf/if_usb.h

@@ -81,7 +81,7 @@ struct fwheader {
 struct fwdata {
 	struct fwheader hdr;
 	__le32 seqnum;
-	uint8_t data[0];
+	uint8_t data[];
 };
 
 /** fwsyncheader */

drivers/net/wireless/marvell/mwifiex/fw.h

@@ -846,7 +846,7 @@ struct mwifiex_ie_types_random_mac {
 
 struct mwifiex_ietypes_chanstats {
 	struct mwifiex_ie_types_header header;
-	struct mwifiex_fw_chan_stats chanstats[0];
+	struct mwifiex_fw_chan_stats chanstats[];
 } __packed;
 
 struct mwifiex_ie_types_wildcard_ssid_params {
@@ -1082,7 +1082,7 @@ struct host_cmd_ds_get_hw_spec {
 	__le32 reserved_6;
 	__le32 dot_11ac_dev_cap;
 	__le32 dot_11ac_mcs_support;
-	u8 tlvs[0];
+	u8 tlvs[];
 } __packed;
 
 struct host_cmd_ds_802_11_rssi_info {
@@ -1140,7 +1140,7 @@ struct ieee_types_assoc_rsp {
 	__le16 cap_info_bitmap;
 	__le16 status_code;
 	__le16 a_id;
-	u8 ie_buffer[0];
+	u8 ie_buffer[];
 } __packed;
 
 struct host_cmd_ds_802_11_associate_rsp {
@@ -1455,7 +1455,7 @@ struct host_cmd_ds_chan_rpt_event {
 	__le32 result;
 	__le64 start_tsf;
 	__le32 duration;
-	u8 tlvbuf[0];
+	u8 tlvbuf[];
 } __packed;
 
 struct host_cmd_sdio_sp_rx_aggr_cfg {
@@ -1625,7 +1625,7 @@ struct host_cmd_ds_802_11_bg_scan_config {
 	__le32 reserved2;
 	__le32 report_condition;
 	__le16 reserved3;
-	u8 tlv[0];
+	u8 tlv[];
 } __packed;
 
 struct host_cmd_ds_802_11_bg_scan_query {
@@ -1720,7 +1720,7 @@ struct mwifiex_ie_types_sta_info {
 
 struct host_cmd_ds_sta_list {
 	__le16 sta_count;
-	u8 tlv[0];
+	u8 tlv[];
 } __packed;
 
 struct mwifiex_ie_types_pwr_capability {
@@ -1743,7 +1743,7 @@ struct mwifiex_ie_types_wmm_param_set {
 struct mwifiex_ie_types_mgmt_frame {
 	struct mwifiex_ie_types_header header;
 	__le16 frame_control;
-	u8 frame_contents[0];
+	u8 frame_contents[];
 };
 
 struct mwifiex_ie_types_wmm_queue_status {
@@ -1861,7 +1861,7 @@ struct mwifiex_ie_types_2040bssco {
 
 struct mwifiex_ie_types_extcap {
 	struct mwifiex_ie_types_header header;
-	u8 ext_capab[0];
+	u8 ext_capab[];
 } __packed;
 
 struct host_cmd_ds_mem_access {
@@ -1918,12 +1918,12 @@ struct mwifiex_assoc_event {
 	__le16 frame_control;
 	__le16 cap_info;
 	__le16 listen_interval;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct host_cmd_ds_sys_config {
 	__le16 action;
-	u8 tlv[0];
+	u8 tlv[];
 };
 
 struct host_cmd_11ac_vht_cfg {
@@ -1956,7 +1956,7 @@ struct host_cmd_tlv_gwk_cipher {
 
 struct host_cmd_tlv_passphrase {
 	struct mwifiex_ie_types_header header;
-	u8 passphrase[0];
+	u8 passphrase[];
 } __packed;
 
 struct host_cmd_tlv_wep_key {
@@ -1978,12 +1978,12 @@ struct host_cmd_tlv_encrypt_protocol {
 
 struct host_cmd_tlv_ssid {
 	struct mwifiex_ie_types_header header;
-	u8 ssid[0];
+	u8 ssid[];
 } __packed;
 
 struct host_cmd_tlv_rates {
 	struct mwifiex_ie_types_header header;
-	u8 rates[0];
+	u8 rates[];
 } __packed;
 
 struct mwifiex_ie_types_bssid_list {
@@ -2100,13 +2100,13 @@ struct mwifiex_fw_mef_entry {
 	u8 mode;
 	u8 action;
 	__le16 exprsize;
-	u8 expr[0];
+	u8 expr[];
 } __packed;
 
 struct host_cmd_ds_mef_cfg {
 	__le32 criteria;
 	__le16 num_entries;
-	struct mwifiex_fw_mef_entry mef_entry[0];
+	struct mwifiex_fw_mef_entry mef_entry[];
 } __packed;
 
 #define CONNECTION_TYPE_INFRA   0
@@ -2169,7 +2169,7 @@ struct mwifiex_radar_det_event {
 struct mwifiex_ie_types_multi_chan_info {
 	struct mwifiex_ie_types_header header;
 	__le16 status;
-	u8 tlv_buffer[0];
+	u8 tlv_buffer[];
 } __packed;
 
 struct mwifiex_ie_types_mc_group_info {
@@ -2185,7 +2185,7 @@ struct mwifiex_ie_types_mc_group_info {
 		u8 usb_ep_num;
 	} hid_num;
 	u8 intf_num;
-	u8 bss_type_numlist[0];
+	u8 bss_type_numlist[];
 } __packed;
 
 struct meas_rpt_map {
@@ -2250,13 +2250,13 @@ struct coalesce_receive_filt_rule {
 	u8 num_of_fields;
 	u8 pkt_type;
 	__le16 max_coalescing_delay;
-	struct coalesce_filt_field_param params[0];
+	struct coalesce_filt_field_param params[];
 } __packed;
 
 struct host_cmd_ds_coalesce_cfg {
 	__le16 action;
 	__le16 num_of_rules;
-	struct coalesce_receive_filt_rule rule[0];
+	struct coalesce_receive_filt_rule rule[];
 } __packed;
 
 struct host_cmd_ds_multi_chan_policy {
@@ -2295,7 +2295,7 @@ struct host_cmd_ds_pkt_aggr_ctrl {
 
 struct host_cmd_ds_sta_configure {
 	__le16 action;
-	u8 tlv_buffer[0];
+	u8 tlv_buffer[];
 } __packed;
 
 struct host_cmd_ds_command {

drivers/net/wireless/marvell/mwl8k.c

@@ -592,7 +592,7 @@ struct mwl8k_cmd_pkt {
 	__u8	seq_num;
 	__u8	macid;
 	__le16	result;
-	char	payload[0];
+	char	payload[];
 } __packed;
 
 /*
@@ -806,7 +806,7 @@ static int mwl8k_load_firmware(struct ieee80211_hw *hw)
 struct mwl8k_dma_data {
 	__le16 fwlen;
 	struct ieee80211_hdr wh;
-	char data[0];
+	char data[];
 } __packed;
 
 /* Routines to add/remove DMA header from skb.  */
@@ -2955,7 +2955,7 @@ mwl8k_cmd_rf_antenna(struct ieee80211_hw *hw, int antenna, int mask)
 struct mwl8k_cmd_set_beacon {
 	struct mwl8k_cmd_pkt header;
 	__le16 beacon_len;
-	__u8 beacon[0];
+	__u8 beacon[];
 };
 
 static int mwl8k_cmd_set_beacon(struct ieee80211_hw *hw,