RDMA: 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] KSPP/linux#21
[3] commit 7649773 ("cxgb3/l2t: Fix undefined behaviour")

Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Gustavo A. R. Silva <[email protected]>
Signed-off-by: Jason Gunthorpe <[email protected]> # added a few more

Author: GustavoARSilva

drivers/infiniband/core/cache.c

@@ -46,7 +46,7 @@
 
 struct ib_pkey_cache {
 	int             table_len;
-	u16             table[0];
+	u16             table[];
 };
 
 struct ib_update_work {

drivers/infiniband/core/cm.c

@@ -197,7 +197,7 @@ struct cm_device {
 	struct ib_device *ib_device;
 	u8 ack_delay;
 	int going_down;
-	struct cm_port *port[0];
+	struct cm_port *port[];
 };
 
 struct cm_av {
@@ -216,7 +216,7 @@ struct cm_work {
 	__be32 local_id;			/* Established / timewait */
 	__be32 remote_id;
 	struct ib_cm_event cm_event;
-	struct sa_path_rec path[0];
+	struct sa_path_rec path[];
 };
 
 struct cm_timewait_info {

drivers/infiniband/core/mad_priv.h

@@ -79,13 +79,13 @@ struct ib_mad_private {
 	struct ib_mad_private_header header;
 	size_t mad_size;
 	struct ib_grh grh;
-	u8 mad[0];
+	u8 mad[];
 } __packed;
 
 struct ib_rmpp_segment {
 	struct list_head list;
 	u32 num;
-	u8 data[0];
+	u8 data[];
 };
 
 struct ib_mad_agent_private {

drivers/infiniband/core/multicast.c

@@ -71,7 +71,7 @@ struct mcast_device {
 	struct ib_event_handler	event_handler;
 	int			start_port;
 	int			end_port;
-	struct mcast_port	port[0];
+	struct mcast_port	port[];
 };
 
 enum mcast_state {

drivers/infiniband/core/sa_query.c

@@ -101,7 +101,7 @@ struct ib_sa_port {
 struct ib_sa_device {
 	int                     start_port, end_port;
 	struct ib_event_handler event_handler;
-	struct ib_sa_port port[0];
+	struct ib_sa_port port[];
 };
 
 struct ib_sa_query {

drivers/infiniband/hw/cxgb4/iw_cxgb4.h

@@ -707,7 +707,7 @@ struct mpa_message {
 	u8 flags;
 	u8 revision;
 	__be16 private_data_size;
-	u8 private_data[0];
+	u8 private_data[];
 };
 
 struct mpa_v2_conn_params {
@@ -719,7 +719,7 @@ struct terminate_message {
 	u8 layer_etype;
 	u8 ecode;
 	__be16 hdrct_rsvd;
-	u8 len_hdrs[0];
+	u8 len_hdrs[];
 };
 
 #define TERM_MAX_LENGTH (sizeof(struct terminate_message) + 2 + 18 + 28)

drivers/infiniband/hw/cxgb4/t4fw_ri_api.h

@@ -123,7 +123,7 @@ struct fw_ri_dsgl {
 	__be32	len0;
 	__be64	addr0;
 #ifndef C99_NOT_SUPPORTED
-	struct fw_ri_dsge_pair sge[0];
+	struct fw_ri_dsge_pair sge[];
 #endif
 };
 
@@ -139,7 +139,7 @@ struct fw_ri_isgl {
 	__be16	nsge;
 	__be32	r2;
 #ifndef C99_NOT_SUPPORTED
-	struct fw_ri_sge sge[0];
+	struct fw_ri_sge sge[];
 #endif
 };
 
@@ -149,7 +149,7 @@ struct fw_ri_immd {
 	__be16	r2;
 	__be32	immdlen;
 #ifndef C99_NOT_SUPPORTED
-	__u8	data[0];
+	__u8	data[];
 #endif
 };
 
@@ -321,7 +321,7 @@ struct fw_ri_res_wr {
 	__be32 len16_pkd;
 	__u64  cookie;
 #ifndef C99_NOT_SUPPORTED
-	struct fw_ri_res res[0];
+	struct fw_ri_res res[];
 #endif
 };
 

drivers/infiniband/hw/hfi1/mad.c

@@ -2381,7 +2381,7 @@ struct opa_port_status_rsp {
 		__be64 port_vl_rcv_bubble;
 		__be64 port_vl_mark_fecn;
 		__be64 port_vl_xmit_discards;
-	} vls[0]; /* real array size defined by # bits set in vl_select_mask */
+	} vls[]; /* real array size defined by # bits set in vl_select_mask */
 };
 
 enum counter_selects {
@@ -2423,7 +2423,7 @@ struct opa_aggregate {
 	__be16 attr_id;
 	__be16 err_reqlength;	/* 1 bit, 8 res, 7 bit */
 	__be32 attr_mod;
-	u8 data[0];
+	u8 data[];
 };
 
 #define MSK_LLI 0x000000f0

drivers/infiniband/hw/hfi1/mad.h

@@ -165,7 +165,7 @@ struct opa_mad_notice_attr {
 		} __packed ntc_2048;
 
 	};
-	u8	class_data[0];
+	u8	class_data[];
 };
 
 #define IB_VLARB_LOWPRI_0_31    1

drivers/infiniband/hw/hfi1/pio.h

@@ -243,7 +243,7 @@ struct sc_config_sizes {
  */
 struct pio_map_elem {
 	u32 mask;
-	struct send_context *ksc[0];
+	struct send_context *ksc[];
 };
 
 /*
@@ -263,7 +263,7 @@ struct pio_vl_map {
 	u32 mask;
 	u8 actual_vls;
 	u8 vls;
-	struct pio_map_elem *map[0];
+	struct pio_map_elem *map[];
 };
 
 int pio_map_init(struct hfi1_devdata *dd, u8 port, u8 num_vls,

drivers/infiniband/hw/hfi1/sdma.c

@@ -833,7 +833,7 @@ struct sdma_engine *sdma_select_engine_sc(
 struct sdma_rht_map_elem {
 	u32 mask;
 	u8 ctr;
-	struct sdma_engine *sde[0];
+	struct sdma_engine *sde[];
 };
 
 struct sdma_rht_node {

drivers/infiniband/hw/hfi1/sdma.h

@@ -1002,7 +1002,7 @@ void sdma_engine_interrupt(struct sdma_engine *sde, u64 status);
  */
 struct sdma_map_elem {
 	u32 mask;
-	struct sdma_engine *sde[0];
+	struct sdma_engine *sde[];
 };
 
 /**
@@ -1024,7 +1024,7 @@ struct sdma_vl_map {
 	u32 mask;
 	u8 actual_vls;
 	u8 vls;
-	struct sdma_map_elem *map[0];
+	struct sdma_map_elem *map[];
 };
 
 int sdma_map_init(

drivers/infiniband/hw/hfi1/user_exp_rcv.h

@@ -73,7 +73,7 @@ struct tid_rb_node {
 	dma_addr_t dma_addr;
 	bool freed;
 	unsigned int npages;
-	struct page *pages[0];
+	struct page *pages[];
 };
 
 static inline int num_user_pages(unsigned long addr,

drivers/infiniband/hw/i40iw/i40iw_cm.h

@@ -85,7 +85,7 @@ struct ietf_mpa_v1 {
 	u8 flags;
 	u8 rev;
 	__be16 priv_data_len;
-	u8 priv_data[0];
+	u8 priv_data[];
 };
 
 #define ietf_mpa_req_resp_frame ietf_mpa_frame
@@ -101,7 +101,7 @@ struct ietf_mpa_v2 {
 	u8 rev;
 	__be16 priv_data_len;
 	struct ietf_rtr_msg rtr_msg;
-	u8 priv_data[0];
+	u8 priv_data[];
 };
 
 struct i40iw_cm_node;

drivers/infiniband/hw/mthca/mthca_memfree.c

@@ -58,7 +58,7 @@ struct mthca_user_db_table {
 		u64                uvirt;
 		struct scatterlist mem;
 		int                refcount;
-	}                page[0];
+	} page[];
 };
 
 static void mthca_free_icm_pages(struct mthca_dev *dev, struct mthca_icm_chunk *chunk)

drivers/infiniband/hw/mthca/mthca_memfree.h

@@ -68,7 +68,7 @@ struct mthca_icm_table {
 	int               lowmem;
 	int               coherent;
 	struct mutex      mutex;
-	struct mthca_icm *icm[0];
+	struct mthca_icm *icm[];
 };
 
 struct mthca_icm_iter {

drivers/infiniband/hw/usnic/usnic_uiom.h

@@ -77,7 +77,7 @@ struct usnic_uiom_reg {
 struct usnic_uiom_chunk {
 	struct list_head		list;
 	int				nents;
-	struct scatterlist		page_list[0];
+	struct scatterlist		page_list[];
 };
 
 struct usnic_uiom_pd *usnic_uiom_alloc_pd(void);

drivers/infiniband/sw/rxe/rxe_queue.h

@@ -63,7 +63,7 @@ struct rxe_queue_buf {
 	__u32			pad_2[31];
 	__u32			consumer_index;
 	__u32			pad_3[31];
-	__u8			data[0];
+	__u8			data[];
 };
 
 struct rxe_queue {

drivers/infiniband/ulp/opa_vnic/opa_vnic_encap.h

@@ -258,7 +258,7 @@ struct opa_veswport_mactable {
 	__be16                              offset;
 	__be16                              num_entries;
 	__be32                              mac_tbl_digest;
-	struct opa_veswport_mactable_entry  tbl_entries[0];
+	struct opa_veswport_mactable_entry  tbl_entries[];
 } __packed;
 
 /**
@@ -440,7 +440,7 @@ struct opa_veswport_iface_macs {
 	__be16 num_macs_in_msg;
 	__be16 tot_macs_in_lst;
 	__be16 gen_count;
-	struct opa_vnic_iface_mac_entry entry[0];
+	struct opa_vnic_iface_mac_entry entry[];
 } __packed;
 
 /**

drivers/infiniband/ulp/srp/ib_srp.h

@@ -309,7 +309,7 @@ struct srp_fr_pool {
 	int			max_page_list_len;
 	spinlock_t		lock;
 	struct list_head	free_list;
-	struct srp_fr_desc	desc[0];
+	struct srp_fr_desc	desc[];
 };
 
 /**

include/rdma/ib_fmr_pool.h

@@ -73,7 +73,7 @@ struct ib_pool_fmr {
 	int                 remap_count;
 	u64                 io_virtual_address;
 	int                 page_list_len;
-	u64                 page_list[0];
+	u64                 page_list[];
 };
 
 struct ib_fmr_pool *ib_create_fmr_pool(struct ib_pd             *pd,

include/rdma/ib_verbs.h

@@ -1876,7 +1876,7 @@ struct ib_flow_eth_filter {
 	__be16	ether_type;
 	__be16	vlan_tag;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_eth {
@@ -1890,7 +1890,7 @@ struct ib_flow_ib_filter {
 	__be16 dlid;
 	__u8   sl;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_ib {
@@ -1915,7 +1915,7 @@ struct ib_flow_ipv4_filter {
 	u8	ttl;
 	u8	flags;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_ipv4 {
@@ -1933,7 +1933,7 @@ struct ib_flow_ipv6_filter {
 	u8	traffic_class;
 	u8	hop_limit;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_ipv6 {
@@ -1947,7 +1947,7 @@ struct ib_flow_tcp_udp_filter {
 	__be16	dst_port;
 	__be16	src_port;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_tcp_udp {
@@ -1959,7 +1959,7 @@ struct ib_flow_spec_tcp_udp {
 
 struct ib_flow_tunnel_filter {
 	__be32	tunnel_id;
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 /* ib_flow_spec_tunnel describes the Vxlan tunnel
@@ -1976,7 +1976,7 @@ struct ib_flow_esp_filter {
 	__be32	spi;
 	__be32  seq;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_esp {
@@ -1991,7 +1991,7 @@ struct ib_flow_gre_filter {
 	__be16 protocol;
 	__be32 key;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_gre {
@@ -2004,7 +2004,7 @@ struct ib_flow_spec_gre {
 struct ib_flow_mpls_filter {
 	__be32 tag;
 	/* Must be last */
-	u8	real_sz[0];
+	u8	real_sz[];
 };
 
 struct ib_flow_spec_mpls {

include/rdma/opa_vnic.h

@@ -75,7 +75,7 @@
 struct opa_vnic_rdma_netdev {
 	struct rdma_netdev rn;  /* keep this first */
 	/* followed by device private data */
-	char *dev_priv[0];
+	char *dev_priv[];
 };
 
 static inline void *opa_vnic_priv(const struct net_device *dev)

include/rdma/rdmavt_mr.h

@@ -85,7 +85,7 @@ struct rvt_mregion {
 	u8  lkey_published;     /* in global table */
 	struct percpu_ref refcount;
 	struct completion comp; /* complete when refcount goes to zero */
-	struct rvt_segarray *map[0];    /* the segments */
+	struct rvt_segarray *map[];    /* the segments */
 };
 
 #define RVT_MAX_LKEY_TABLE_BITS 23

include/rdma/rdmavt_qp.h

@@ -191,7 +191,7 @@ struct rvt_swqe {
 	u32 ssn;                /* send sequence number */
 	u32 length;             /* total length of data in sg_list */
 	void *priv;             /* driver dependent field */
-	struct rvt_sge sg_list[0];
+	struct rvt_sge sg_list[];
 };
 
 /**