staging: 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 <[e-mail]>
Link: https://lore.kernel.org/r/20200220132908.GA30501@embeddedor
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/gdm724x/gdm_mux.h

···
 	__le32 seq_num;
 	__le32 payload_size;
 	__le16 packet_type;
-	unsigned char data[0];
+	unsigned char data[];
 };
 
 struct mux_tx {

drivers/staging/gdm724x/hci_packet.h

···
 struct hci_packet {
 	__dev16 cmd_evt;
 	__dev16 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct tlv {
···
 	__dev32 dft_eps_ID;
 	__dev32 bearer_ID;
 	__dev32 nic_type;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct multi_sdu {
···
 	__dev16 len;
 	__dev16 num_packet;
 	__dev16 reserved;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct hci_pdn_table_ind {

drivers/staging/greybus/audio_apbridgea.h

···
 struct audio_apbridgea_hdr {
 	__u8	type;
 	__le16	i2s_port;
-	__u8	data[0];
+	__u8	data[];
 } __packed;
 
 struct audio_apbridgea_set_config_request {

drivers/staging/ks7010/ks_hostif.h

···
 #define TYPE_DATA 0x0000
 #define TYPE_AUTH 0x0001
 	__le16 reserved;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 #define TYPE_PMK1 0x0001
···
 struct hostif_mib_value {
 	__le16 size;
 	__le16 type;
-	u8 body[0];
+	u8 body[];
 } __packed;
 
 struct hostif_mib_get_confirm_t {

drivers/staging/media/allegro-dvt/allegro-core.c

···
 struct mcu_msg_push_buffers_internal {
 	struct mcu_msg_header header;
 	u32 channel_id;
-	struct mcu_msg_push_buffers_internal_buffer buffer[0];
+	struct mcu_msg_push_buffers_internal_buffer buffer[];
 } __attribute__ ((__packed__));
 
 struct mcu_msg_put_stream_buffer {

drivers/staging/octeon-usb/octeon-hcd.c

···
  */
 struct octeon_temp_buffer {
 	void *orig_buffer;
-	u8 data[0];
+	u8 data[];
 };
 
 static inline struct usb_hcd *octeon_to_hcd(struct octeon_hcd *p)

drivers/staging/rtl8192e/rtllib.h

···
 struct rtllib_hdr {
 	__le16 frame_ctl;
 	__le16 duration_id;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_hdr_1addr {
 	__le16 frame_ctl;
 	__le16 duration_id;
 	u8 addr1[ETH_ALEN];
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_hdr_2addr {
···
 	__le16 duration_id;
 	u8 addr1[ETH_ALEN];
 	u8 addr2[ETH_ALEN];
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_hdr_3addr {
···
 	u8 addr2[ETH_ALEN];
 	u8 addr3[ETH_ALEN];
 	__le16 seq_ctl;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_hdr_4addr {
···
 	u8 addr3[ETH_ALEN];
 	__le16 seq_ctl;
 	u8 addr4[ETH_ALEN];
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_hdr_3addrqos {
···
 	u8 addr3[ETH_ALEN];
 	__le16 seq_ctl;
 	__le16 qos_ctl;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_hdr_4addrqos {
···
 	__le16 seq_ctl;
 	u8 addr4[ETH_ALEN];
 	__le16 qos_ctl;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtllib_info_element {
 	u8 id;
 	u8 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct rtllib_authentication {
···
 	__le16 transaction;
 	__le16 status;
 	/*challenge*/
-	struct rtllib_info_element info_element[0];
+	struct rtllib_info_element info_element[];
 } __packed;
 
 struct rtllib_disauth {
···
 struct rtllib_probe_request {
 	struct rtllib_hdr_3addr header;
 	/* SSID, supported rates */
-	struct rtllib_info_element info_element[0];
+	struct rtllib_info_element info_element[];
 } __packed;
 
 struct rtllib_probe_response {
···
 	/* SSID, supported rates, FH params, DS params,
 	 * CF params, IBSS params, TIM (if beacon), RSN
 	 */
-	struct rtllib_info_element info_element[0];
+	struct rtllib_info_element info_element[];
 } __packed;
 
 /* Alias beacon for probe_response */
···
 	__le16 capability;
 	__le16 listen_interval;
 	/* SSID, supported rates, RSN */
-	struct rtllib_info_element info_element[0];
+	struct rtllib_info_element info_element[];
 } __packed;
 
 struct rtllib_assoc_response_frame {
···
 	__le16 capability;
 	__le16 status;
 	__le16 aid;
-	struct rtllib_info_element info_element[0]; /* supported rates */
+	struct rtllib_info_element info_element[]; /* supported rates */
 } __packed;
 
 struct rtllib_txb {
···
 	u16 reserved;
 	__le16 frag_size;
 	__le16 payload_size;
-	struct sk_buff *fragments[0];
+	struct sk_buff *fragments[];
 };
 
 #define MAX_SUBFRAME_COUNT		  64
···
 	/* This must be the last item so that it points to the data
 	 * allocated beyond this structure by alloc_rtllib
 	 */
-	u8 priv[0];
+	u8 priv[];
 };
 
 #define IEEE_A	    (1<<0)

drivers/staging/rtl8192u/ieee80211/ieee80211.h

···
 struct rtl_80211_hdr {
 	__le16 frame_ctl;
 	__le16 duration_id;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtl_80211_hdr_1addr {
 	__le16 frame_ctl;
 	__le16 duration_id;
 	u8 addr1[ETH_ALEN];
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtl_80211_hdr_2addr {
···
 	__le16 duration_id;
 	u8 addr1[ETH_ALEN];
 	u8 addr2[ETH_ALEN];
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtl_80211_hdr_3addr {
···
 	u8 addr2[ETH_ALEN];
 	u8 addr3[ETH_ALEN];
 	__le16 seq_ctl;
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtl_80211_hdr_4addr {
···
 	u8 addr3[ETH_ALEN];
 	__le16 seq_ctl;
 	u8 addr4[ETH_ALEN];
-	u8 payload[0];
+	u8 payload[];
 } __packed;
 
 struct rtl_80211_hdr_3addrqos {
···
 struct ieee80211_info_element {
 	u8 id;
 	u8 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct ieee80211_authentication {
···
 	__le16 transaction;
 	__le16 status;
 	/*challenge*/
-	struct ieee80211_info_element info_element[0];
+	struct ieee80211_info_element info_element[];
 } __packed;
 
 struct ieee80211_disassoc {
···
 struct ieee80211_probe_request {
 	struct rtl_80211_hdr_3addr header;
 	/* SSID, supported rates */
-	struct ieee80211_info_element info_element[0];
+	struct ieee80211_info_element info_element[];
 } __packed;
 
 struct ieee80211_probe_response {
···
 	/* SSID, supported rates, FH params, DS params,
 	 * CF params, IBSS params, TIM (if beacon), RSN
 	 */
-	struct ieee80211_info_element info_element[0];
+	struct ieee80211_info_element info_element[];
 } __packed;
 
 /* Alias beacon for probe_response */
···
 	__le16 capability;
 	__le16 listen_interval;
 	/* SSID, supported rates, RSN */
-	struct ieee80211_info_element info_element[0];
+	struct ieee80211_info_element info_element[];
 } __packed;
 
 struct ieee80211_reassoc_request_frame {
···
 	__le16 listen_interval;
 	u8 current_ap[ETH_ALEN];
 	/* SSID, supported rates, RSN */
-	struct ieee80211_info_element info_element[0];
+	struct ieee80211_info_element info_element[];
 } __packed;
 
 struct ieee80211_assoc_response_frame {
···
 	__le16 capability;
 	__le16 status;
 	__le16 aid;
-	struct ieee80211_info_element info_element[0]; /* supported rates */
+	struct ieee80211_info_element info_element[]; /* supported rates */
 } __packed;
 
 struct ieee80211_txb {
···
 	u16 reserved;
 	__le16 frag_size;
 	__le16 payload_size;
-	struct sk_buff *fragments[0];
+	struct sk_buff *fragments[];
 };
 
 #define MAX_TX_AGG_COUNT		  16
···
 	/* This must be the last item so that it points to the data
 	 * allocated beyond this structure by alloc_ieee80211
 	 */
-	u8 priv[0];
+	u8 priv[];
 };
 
 #define IEEE_A            (1<<0)

drivers/staging/rtl8712/ieee80211.h

···
 struct ieee80211_info_element {
 	u8 id;
 	u8 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 /*
···
 	u16 reserved;
 	u16 frag_size;
 	u16 payload_size;
-	struct sk_buff *fragments[0];
+	struct sk_buff *fragments[];
 };
 
 /* SWEEP TABLE ENTRIES NUMBER*/

drivers/staging/rtl8712/rtl871x_mp_ioctl.h

···
 struct EFUSE_ACCESS_STRUCT {
 	u16	start_addr;
 	u16	cnts;
-	u8	data[0];
+	u8	data[];
 };
 
 struct burst_rw_reg {
···
 struct mp_ioctl_param {
 	unsigned int subcode;
 	unsigned int len;
-	unsigned char data[0];
+	unsigned char data[];
 };
 
 #define GEN_MP_IOCTL_SUBCODE(code) _MP_IOCTL_ ## code ## _CMD_

drivers/staging/wilc1000/cfg80211.c

···
 	u8 oui_type;
 	u8 oui_subtype;
 	u8 dialog_token;
-	u8 elem[0];
+	u8 elem[];
 } __packed;
 
 struct wilc_vendor_specific_ie {
···
 	u8 tag_len;
 	u8 oui[3];
 	u8 oui_type;
-	u8 attr[0];
+	u8 attr[];
 } __packed;
 
 struct wilc_attr_entry {
 	u8  attr_type;
 	__le16 attr_len;
-	u8 val[0];
+	u8 val[];
 } __packed;
 
 struct wilc_attr_oper_ch {
···
 	u8 attr_type;
 	__le16 attr_len;
 	u8 country_code[IEEE80211_COUNTRY_STRING_LEN];
-	u8 elem[0];
+	u8 elem[];
 } __packed;
 
 struct wilc_ch_list_elem {
 	u8 op_class;
 	u8 no_of_channels;
-	u8 ch_list[0];
+	u8 ch_list[];
 } __packed;
 
 static void cfg_scan_result(enum scan_event scan_event,

drivers/staging/wilc1000/spi.c

···
 	u8 status;
 	u8 resp_header;
 	u8 resp_data[4];
-	u8 crc[0];
+	u8 crc[];
 } __packed;
 
 struct wilc_spi_rsp_data {

drivers/staging/wlan-ng/hfa384x.h

···
 /* Commonly used basic types */
 struct hfa384x_bytestr {
 	__le16 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct hfa384x_bytestr32 {
···
 /*-- Configuration Record: WPAData       (data portion only) --*/
 struct hfa384x_wpa_data {
 	__le16 datalen;
-	u8 data[0];		/* max 80 */
+	u8 data[];		/* max 80 */
 } __packed;
 
 /*--------------------------------------------------------------------

drivers/staging/wlan-ng/p80211types.h

···
 
 struct p80211pstrd {
 	u8 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 /* Maximum pascal string */
···
 	u32 did;
 	u16 status;
 	u16 len;
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 /* message data item for int, BOUNDEDINT, ENUMINT */