linux-hardening - Re: [PATCH][next] RDMA/rxe: Avoid -Wflex-array-member-not-at-end warnings

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Message-ID: <01b419f6-264e-4faa-b4df-480fdf952d14@linux.dev>
Date: Thu, 18 Dec 2025 21:27:30 -0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
 Leon Romanovsky <leon@...nel.org>
Cc: Jason Gunthorpe <jgg@...dia.com>,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Zhu Yanjun <zyjzyj2000@...il.com>, linux-rdma@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH][next] RDMA/rxe: Avoid -Wflex-array-member-not-at-end
 warnings

在 2025/12/18 20:35, Gustavo A. R. Silva 写道:
> 
> 
> On 12/19/25 13:29, Zhu Yanjun wrote:
>>
>> 在 2025/12/18 18:51, Gustavo A. R. Silva 写道:
>>>
>>>
>>> On 12/19/25 04:22, Yanjun.Zhu wrote:
>>>>
>>>> On 12/18/25 7:56 AM, Leon Romanovsky wrote:
>>>>> On Sun, Dec 14, 2025 at 09:00:51PM -0800, Zhu Yanjun wrote:
>>>>>>
>>>>>> 在 2025/12/5 20:41, Zhu Yanjun 写道:
>>>>>>>
>>>>>>> 在 2025/12/4 9:48, yanjun.zhu 写道:
>>>>>>>> On 12/4/25 5:05 AM, Jason Gunthorpe wrote:
>>>>>>>>> On Wed, Dec 03, 2025 at 09:08:45PM -0800, Zhu Yanjun wrote:
>>>>>>>>>>>         unsigned int res_head;
>>>>>>>>>>>         unsigned int        res_tail;
>>>>>>>>>>>         struct resp_res        *res;
>>>>>>>>>>> +
>>>>>>>>>>> +    /* SRQ only. srq_wqe.dma.sge is a flex array */
>>>>>>>>>>> +    struct rxe_recv_wqe srq_wqe;
>>>>>>>>>> drivers/infiniband/sw/rxe/rxe_resp.c: In function get_srq_wqe:
>>>>>>>>>> drivers/infiniband/sw/rxe/rxe_resp.c:289:41: error: struct
>>>>>>>>>> rxe_recv_wqe has
>>>>>>>>>> no member named wqe
>>>>>>>>>>     289 |         qp->resp.wqe = &qp->resp.srq_wqe.wqe;
>>>>>>>>>>         |                                         ^
>>>>>>>>> I didn't try to fix all the typos, you will need to do that.
>>>>>>>> Exactly. I will fix this problem. This weekend, I will send out an
>>>>>>>> official commit.
>>>>>>> Hi, Jason
>>>>>>>
>>>>>>> The followings are based on your commits and Leon's commits. And 
>>>>>>> it can
>>>>>>> pass the rdma-core tests.
>>>>>>>
>>>>>>> I am not sure if this commit is good or not.
>>>>>> Hi, Jason && Leon
>>>>>>
>>>>>> Any update? If this looks good to you, I will send out an official 
>>>>>> commit
>>>>>> based on the following commit.
>>>>> You are RXE maintainer, send the official patch.
>>>>
>>>> Will do. I will send it out very soon.
>>>
>>> I don't see how this addresses the flex-array in the middle issue that
>>> originated this discussion.
>>
>> Could you please explain this in more detail?
>> Also, if you have a better approach, would you mind sending a new 
>> commit for discussion?
> 
> This is exactly what my original patch is about. I've explained this a 
> couple of times
> in this thread already.

In your original patch, I have the following problem. I read all your 
replies.  But I can not find your answers to my problem.

My problem is as below:

1. The followings are the declaration of __TRAILING_OVERLAP

/**
  * __TRAILING_OVERLAP() - Overlap a flexible-array member with trailing
  *            members.
  *
  * Creates a union between a flexible-array member (FAM) in a struct 
and a set
  * of additional members that would otherwise follow it.
  *
  * @TYPE: Flexible structure type name, including "struct" keyword.
  * @NAME: Name for a variable to define.
  * @FAM: The flexible-array member within @TYPE          <----- Here
  * @ATTRS: Any struct attributes (usually empty)
  * @MEMBERS: Trailing overlapping members.
  */
#define __TRAILING_OVERLAP(TYPE, NAME, FAM, ATTRS, MEMBERS)         \
     union {                                 \
         TYPE NAME;                          \
         struct {                            \
             unsigned char __offset_to_FAM[offsetof(TYPE, FAM)]; \
             MEMBERS                         \
         } ATTRS;                            \
     }

2. I expanded the above MACRO __TRAILING_OVERLAP into the following 
following the definition in your commit.

union {

         struct rxe_recv_wqe wqe;

         struct {
             unsigned char __offset_to_FAM[offsetof(struct rxe_recv_wqe, 
dma.sge)]; \
             struct ib_sge sge[RXE_MAX_SGE];
         } ;

     }srq_wqe;

3. In your original commit, dma.sge should be the member of struct 
rxe_recv_wqe. The struct rxe_recv_wqe is as below.


"@FAM: The flexible-array member within @TYPE"


The struct rxe_recv_wqe is as below.

struct rxe_recv_wqe {
     __aligned_u64       wr_id;
     __u32           reserved;
     __u32           padding;
     struct rxe_dma_info dma;
};

But I can not find dma.sge in the above struct. Can you explain it?

To be honest, I read your original commit for several times, but I can 
not get it.  Can you explain the MACRO TRAILING_OVERLAP? And how can it 
replace the following struct?

struct {
       struct rxe_recv_wqe    wqe;
       struct ib_sge        sge[RXE_MAX_SGE];
} srq_wqe;

Thanks a lot.

Yanjun.Zhu

> 
> -Gustavo