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] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Link: https://lore.kernel.org/r/20200213010425.GA13068@embeddedor.com
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com> # added a few more

6 files changed, 9 insertions, 9 deletions

diff --git a/drivers/infiniband/hw/hfi1/mad.c b/drivers/infiniband/hw/hfi1/mad.c
index a51bcd2b4391..7073f237a949 100644
--- a/drivers/infiniband/hw/hfi1/mad.c
+++ b/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
diff --git a/drivers/infiniband/hw/hfi1/mad.h b/drivers/infiniband/hw/hfi1/mad.h
index 2f48e6953629..889e63d3f2cc 100644
--- a/drivers/infiniband/hw/hfi1/mad.h
+++ b/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
diff --git a/drivers/infiniband/hw/hfi1/pio.h b/drivers/infiniband/hw/hfi1/pio.h
index c9a58b642bdd..0102262343c0 100644
--- a/drivers/infiniband/hw/hfi1/pio.h
+++ b/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,
diff --git a/drivers/infiniband/hw/hfi1/sdma.c b/drivers/infiniband/hw/hfi1/sdma.c
index a51525647ac8..c93ea021cf49 100644
--- a/drivers/infiniband/hw/hfi1/sdma.c
+++ b/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 {
diff --git a/drivers/infiniband/hw/hfi1/sdma.h b/drivers/infiniband/hw/hfi1/sdma.h
index 1e2e40f79cb2..7a851191f987 100644
--- a/drivers/infiniband/hw/hfi1/sdma.h
+++ b/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(
diff --git a/drivers/infiniband/hw/hfi1/user_exp_rcv.h b/drivers/infiniband/hw/hfi1/user_exp_rcv.h
index 6257eee083a1..332abb446861 100644
--- a/drivers/infiniband/hw/hfi1/user_exp_rcv.h
+++ b/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,