linux-kernel - Re: [PATCH v3 1/1] RDMA/rxe: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <ea716013-0149-40fa-b781-b0968980b7bd@embeddedor.com>
Date: Tue, 23 Dec 2025 14:03:06 +0900
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>, zyjzyj2000@...il.com, jgg@...pe.ca,
 leon@...nel.org, linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH v3 1/1] RDMA/rxe: Avoid -Wflex-array-member-not-at-end
 warnings



On 12/23/25 13:41, Zhu Yanjun wrote:
> From: "Gustavo A. R. Silva" <gustavoars@...nel.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@...ux.dev>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>
> ---
> V2->V3: Replace struct ib_sge with struct rxe_sge

What are you doing?

You're making a mess of this whole thing. Please, don't make changes
to my patches on your own.

-Gustavo

> ---
>   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..3ffd7be8e7b1 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 rxe_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 {