svcrdma: 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 <[email protected]>

---
 net/sunrpc/xprtrdma/svc_rdma_rw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

net/sunrpc/xprtrdma/svc_rdma_rw.c +1 -1

index 48fe3b16b0d9..003610ce00bc 100644
@@ -41,7 +41,7 @@ struct svc_rdma_rw_ctxt {
 	struct rdma_rw_ctx	rw_ctx;
 	int			rw_nents;
 	struct sg_table		rw_sg_table;
-	struct scatterlist	rw_first_sgl[0];
+	struct scatterlist	rw_first_sgl[];
 };
 
 static inline struct svc_rdma_rw_ctxt *

Signature · 1 line

2.25.0