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

[Zhu Yanjun <yanjun.zhu@linux.dev>]

在 2025/12/19 1:55, Gustavo A. R. Silva 写道:
> 
> 
> On 12/19/25 15:59, Zhu Yanjun wrote:
>>
>> 在 2025/12/18 21:48, Gustavo A. R. Silva 写道:
>>>
>>>> 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;
>>>
>>> Expand struct rxe_dma_info here.
>>
>> Thanks. In struct rxe_dma_info, the struct is
>>
>> struct rxe_sge {
>>         __aligned_u64 addr;
>>         __u32   length;
>>         __u32   lkey;
>> };
>>
>> But in your commit, struct ib_sge is used.
>>
>> struct ib_sge {
>>      u64 addr;
>>      u32 length;
>>      u32 lkey;
>> };
>> __aligned_u64 is a 64-bit integer with a guaranteed 8-byte alignment,
>>
>> used to preserve ABI correctness across architectures and between
>>
>> userspace and kernel, while u64 has architecture-dependent alignment.
>>
>> I am not sure if we can treate "struct rxe_sge" as the same with 
>> "struct ib_sge".
> 
> Just notice that the original code is the one actually doing that.
> See my response in this same thread:
> 
> https://lore.kernel.org/linux-hardening/d3336e9d-2b84-4698-a799- 
> b49e3845f38f@embeddedor.com/
> 
> So, if that code is fine, this is fine. If the original code is wrong,
> then that code should be fixed first.

Thanks a lot. Because struct ib_sge and struct ib_sge is different,
struct ib_sge {
     u64 addr; <--- u64 has architecture-dependent alignment
     u32 length;
     u32 lkey;
};

struct rxe_sge {
        __aligned_u64 addr;   <---guaranteed 8-byte alignment,

used to preserve ABI correctness across architectures and between

userspace and kernel

        __u32   length;
        __u32   lkey;
};

and struct rxe_sge is used in rxe_mr, it is working between userspace 
and kernel, thus, I want to keep struct rxe_mr in rxe_mr.

But in other places, I want to replace struct rxe_sge with struct 
ib_sge. The commit is as below.

In short, the commit "RDMA/rxe: Avoid -Wflex-array-member-not-at-end 
warnings" && the following commit will work well. I have made tests in 
my local host. It can work well.

Please Leon and Jason comment.

diff --git a/drivers/infiniband/sw/rxe/rxe_mr.c 
b/drivers/infiniband/sw/rxe/rxe_mr.c
index b1df05238848..390ae01f549d 100644
--- a/drivers/infiniband/sw/rxe/rxe_mr.c
+++ b/drivers/infiniband/sw/rxe/rxe_mr.c
@@ -341,7 +341,7 @@ int copy_data(
         enum rxe_mr_copy_dir    dir)
  {
         int                     bytes;
-       struct rxe_sge          *sge    = &dma->sge[dma->cur_sge];
+       struct ib_sge *sge      = &dma->sge[dma->cur_sge];
         int                     offset  = dma->sge_offset;
         int                     resid   = dma->resid;
         struct rxe_mr           *mr     = NULL;
@@ -580,7 +580,7 @@ enum resp_states rxe_mr_do_atomic_write(struct 
rxe_mr *mr, u64 iova, u64 value)

  int advance_dma_data(struct rxe_dma_info *dma, unsigned int length)
  {
-       struct rxe_sge          *sge    = &dma->sge[dma->cur_sge];
+       struct ib_sge *sge      = &dma->sge[dma->cur_sge];
         int                     offset  = dma->sge_offset;
         int                     resid   = dma->resid;

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c 
b/drivers/infiniband/sw/rxe/rxe_resp.c
index 711f73e0bbb1..74f5b695da7a 100644
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -283,7 +283,7 @@ static enum resp_states get_srq_wqe(struct rxe_qp *qp)
                 rxe_dbg_qp(qp, "invalid num_sge in SRQ entry\n");
                 return RESPST_ERR_MALFORMED_WQE;
         }
-       size = sizeof(*wqe) + wqe->dma.num_sge*sizeof(struct rxe_sge);
+       size = sizeof(*wqe) + wqe->dma.num_sge*sizeof(struct ib_sge);
         memcpy(&qp->resp.srq_wqe, wqe, size);

         qp->resp.wqe = &qp->resp.srq_wqe.wqe;
diff --git a/include/uapi/rdma/rdma_user_rxe.h 
b/include/uapi/rdma/rdma_user_rxe.h
index bb092fccb813..360839498441 100644
--- a/include/uapi/rdma/rdma_user_rxe.h
+++ b/include/uapi/rdma/rdma_user_rxe.h
@@ -154,7 +154,7 @@ struct rxe_dma_info {
         union {
                 __DECLARE_FLEX_ARRAY(__u8, inline_data);
                 __DECLARE_FLEX_ARRAY(__u8, atomic_wr);
-               __DECLARE_FLEX_ARRAY(struct rxe_sge, sge);
+               __DECLARE_FLEX_ARRAY(struct ib_sge, sge);
         };
  };


To this commit, plus the above commit, it should work well.

Yanjun.Zhu

> 
> -Gustavo
> 
>>
>>
>> Leon and Jason, please comment on it.
>>
>>
>> Yanjun.Zhu
>>
>>>
>>>> };
>>>>
>>>> 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?
>>>
>>> This is clearly explained in the changelog text. I think what you're
>>> missing will be clear once you understand how nested structures
>>> work. See my comment above.
>>>
>>> -Gustavo
>>
>