[PATCH v2 1/2] RDMA/rxe: Avoid -Wflex-array-member-not-at-end warnings

[Zhu Yanjun <yanjun.zhu@linux.dev>]

From: "Gustavo A. R. Silva" <gustavoars@kernel.org>

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the new TRAILING_OVERLAP() helper to fix the following warning:

21 drivers/infiniband/sw/rxe/rxe_verbs.h:271:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM) and a
set of MEMBERS that would otherwise follow it.

This overlays the trailing MEMBER struct ib_sge sge[RXE_MAX_SGE]; onto
the FAM struct rxe_recv_wqe::dma.sge, while keeping the FAM and the
start of MEMBER aligned.

The static_assert() ensures this alignment remains, and it's
intentionally placed inmediately after the related structure --no
blank line in between.

Lastly, move the conflicting declaration struct rxe_resp_info resp;
to the end of the corresponding structure.

Reviewed-by: Zhu Yanjun <yanjun.zhu@linux.dev>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
V1->V2: Replace struct rxe_sge with struct ib_sge
---
 drivers/infiniband/sw/rxe/rxe_verbs.h | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_verbs.h b/drivers/infiniband/sw/rxe/rxe_verbs.h
index fd48075810dd..6498d61e8956 100644
--- a/drivers/infiniband/sw/rxe/rxe_verbs.h
+++ b/drivers/infiniband/sw/rxe/rxe_verbs.h
@@ -219,12 +219,6 @@ struct rxe_resp_info {
 	u32			rkey;
 	u32			length;
 
-	/* SRQ only */
-	struct {
-		struct rxe_recv_wqe	wqe;
-		struct ib_sge		sge[RXE_MAX_SGE];
-	} srq_wqe;
-
 	/* Responder resources. It's a circular list where the oldest
 	 * resource is dropped first.
 	 */
@@ -232,7 +226,15 @@ struct rxe_resp_info {
 	unsigned int		res_head;
 	unsigned int		res_tail;
 	struct resp_res		*res;
+
+	/* SRQ only */
+	/* Must be last as it ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct rxe_recv_wqe, wqe, dma.sge,
+		struct ib_sge		sge[RXE_MAX_SGE];
+	) srq_wqe;
 };
+static_assert(offsetof(struct rxe_resp_info, srq_wqe.wqe.dma.sge) ==
+	      offsetof(struct rxe_resp_info, srq_wqe.sge));
 
 struct rxe_qp {
 	struct ib_qp		ibqp;
@@ -269,7 +271,6 @@ struct rxe_qp {
 
 	struct rxe_req_info	req;
 	struct rxe_comp_info	comp;
-	struct rxe_resp_info	resp;
 
 	atomic_t		ssn;
 	atomic_t		skb_out;
@@ -289,6 +290,9 @@ struct rxe_qp {
 	spinlock_t		state_lock; /* guard requester and completer */
 
 	struct execute_work	cleanup_work;
+
+	/* Must be last as it ends in a flexible-array member. */
+	struct rxe_resp_info	resp;
 };
 
 enum {
-- 
2.39.5