Subject: Re: [PATCH] selftest: net: fix variable sized type not at the end of struct warnings

From: Simon Horman <[email-masked]>
Date: Tue, 28 Oct 2025 17:23:12 +0000

On Mon, Oct 27, 2025 at 10:38:56AM +0530, Ankit Khushwaha wrote:
> Some network selftests defined variable-sized types defined at the end of
> struct causing -Wgnu-variable-sized-type-not-at-end warning.
> 
> warning:
> timestamping.c:285:18: warning: field 'cm' with variable sized type 
> 'struct cmsghdr' not at the end of a struct or class is a GNU 
> extension [-Wgnu-variable-sized-type-not-at-end]
>   285 |                 struct cmsghdr cm;
>       |                                ^
> 
> ipsec.c:835:5: warning: field 'u' with variable sized type 'union 
> (unnamed union at ipsec.c:831:3)' not at the end of a struct or class 
> is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
>   835 |                 } u;
>       |                   ^
> 
> This patch move these field at the end of struct to fix these warnings.
> 
> Signed-off-by: Ankit Khushwaha <[email-masked]>

Hi Ankit,

I don't believe this change is correct.

I think that the intention of the code is the char arrays (buf and control)
provide the buffer space for the variable-length trailing field
of the preceding structure. Where we basically have a header followed
by data. But your patch would place the before the header.

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