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

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Message-ID: <CAEz=LcsLXuAiQ0Rv0Z7E9mV35Qd92xxGsoSdDFBT8F1AdfZcoA@mail.gmail.com>
Date: Wed, 24 Dec 2025 01:19:14 +0800
From: Greg Sword <gregsword0@...il.com>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Cc: 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, 
	"Gustavo A. R. Silva" <gustavoars@...nel.org>
Subject: Re: [PATCH v3 1/1] RDMA/rxe: Avoid -Wflex-array-member-not-at-end warnings

On Wed, Dec 24, 2025 at 12:59 AM Gustavo A. R. Silva
<gustavo@...eddedor.com> wrote:
>
>
>
> On 12/24/25 01:38, Greg Sword wrote:
> > On Tue, Dec 23, 2025 at 5:35 PM Gustavo A. R. Silva
> > <gustavo@...eddedor.com> wrote:
> >>
> >>
> >>
> >> 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>
> >>
> >> NACK.
> >
> > Just a small reminder about community conventions: reviewers can NACK
> > a patch, but authors generally should not NACK their own patches.
>
> It's obvious that you don't understand what's going on here.

I’ve read through the full discussion and understand how this evolved.
Based on that, I believe there may be a misunderstanding on your side.

>
> >> I didn't write this patch.
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This line should've given you a clue.
>
> -Gustavo
>
> >>
> >> Please, don't ever submit modified patches on my behalf.
> >>
> >>> ---
> >>> V2->V3: Replace struct ib_sge with struct rxe_sge
> >>
> >> Patch granularity is a fundamental thing. Changes addressing different
> >> issues should not be mixed together. Previously existing issues (if any)
> >> must be addressed in separate patches.
> >>
> >> -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 {
> >>
> >>
>