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

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Message-ID: <4a8e3365-cb74-4531-99dc-9d2911045d4b@linux.dev>
Date: Mon, 22 Dec 2025 21:10:11 -0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>, 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


在 2025/12/22 21:03, Gustavo A. R. Silva 写道:
>
>
> 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?

Because struct rxe_sge differs from struct ib_sge, I aligned it to use 
the same structure.

Yanjun.Zhu

>
> 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 {
>
-- 
Best Regards,
Yanjun.Zhu