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

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Message-ID: <ad8987ae-b7fe-47af-a1d2-5055749011c0@embeddedor.com>
Date: Fri, 19 Dec 2025 18:55:01 +0900
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Zhu Yanjun <mounter625@....com>, Zhu Yanjun <yanjun.zhu@...ux.dev>,
 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

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.

-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
>