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

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Message-ID: <CAEz=LcvVgX8VA4M3TJM38NXrhyx-QohBdSoZOG=p3X9pbTY4pA@mail.gmail.com>
Date: Wed, 24 Dec 2025 00:38:11 +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 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.

>
> I didn't write this patch.
>
> 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 {
>
>