[PATCH v2] selftest: net: fix variable sized type issue not at the end of a struct

[PATCH v2] selftest: net: fix variable sized type issue not at the end of a struct

[Ankit Khushwaha]

Some network selftests defined variable-sized types variable at the middle
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 <ankitkhushwaha.linux@gmail.com>
---
Changelog:
v2: https://lore.kernel.org/linux-kselftest/20251027050856.30270-1-ankitkhushwaha.linux@gmail.com/
- fixed typos in the commit msg.

---
 tools/testing/selftests/net/ipsec.c        | 2 +-
 tools/testing/selftests/net/timestamping.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/ipsec.c b/tools/testing/selftests/net/ipsec.c
index 0ccf484b1d9d..36083c8f884f 100644
--- a/tools/testing/selftests/net/ipsec.c
+++ b/tools/testing/selftests/net/ipsec.c
@@ -828,12 +828,12 @@ static int xfrm_state_pack_algo(struct nlmsghdr *nh, size_t req_sz,
 		struct xfrm_desc *desc)
 {
 	struct {
+		char buf[XFRM_ALGO_KEY_BUF_SIZE];
 		union {
 			struct xfrm_algo	alg;
 			struct xfrm_algo_aead	aead;
 			struct xfrm_algo_auth	auth;
 		} u;
-		char buf[XFRM_ALGO_KEY_BUF_SIZE];
 	} alg = {};
 	size_t alen, elen, clen, aelen;
 	unsigned short type;
diff --git a/tools/testing/selftests/net/timestamping.c b/tools/testing/selftests/net/timestamping.c
index 044bc0e9ed81..ad2be2143698 100644
--- a/tools/testing/selftests/net/timestamping.c
+++ b/tools/testing/selftests/net/timestamping.c
@@ -282,8 +282,8 @@ static void recvpacket(int sock, int recvmsg_flags,
 	struct iovec entry;
 	struct sockaddr_in from_addr;
 	struct {
-		struct cmsghdr cm;
 		char control[512];
+		struct cmsghdr cm;
 	} control;
 	int res;
 
-- 
2.51.0

Re: [PATCH v2] selftest: net: fix variable sized type issue not at the end of a struct

[Jason Xing]

On Mon, Oct 27, 2025 at 1:32 PM Ankit Khushwaha
<ankitkhushwaha.linux@gmail.com> wrote:
>
> Some network selftests defined variable-sized types variable at the middle
> 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 <ankitkhushwaha.linux@gmail.com>
> ---
> Changelog:
> v2: https://lore.kernel.org/linux-kselftest/20251027050856.30270-1-ankitkhushwaha.linux@gmail.com/
> - fixed typos in the commit msg.
>
> ---
>  tools/testing/selftests/net/ipsec.c        | 2 +-
>  tools/testing/selftests/net/timestamping.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/net/ipsec.c b/tools/testing/selftests/net/ipsec.c
> index 0ccf484b1d9d..36083c8f884f 100644
> --- a/tools/testing/selftests/net/ipsec.c
> +++ b/tools/testing/selftests/net/ipsec.c
> @@ -828,12 +828,12 @@ static int xfrm_state_pack_algo(struct nlmsghdr *nh, size_t req_sz,
>                 struct xfrm_desc *desc)
>  {
>         struct {
> +               char buf[XFRM_ALGO_KEY_BUF_SIZE];
>                 union {
>                         struct xfrm_algo        alg;
>                         struct xfrm_algo_aead   aead;
>                         struct xfrm_algo_auth   auth;
>                 } u;
> -               char buf[XFRM_ALGO_KEY_BUF_SIZE];
>         } alg = {};
>         size_t alen, elen, clen, aelen;
>         unsigned short type;
> diff --git a/tools/testing/selftests/net/timestamping.c b/tools/testing/selftests/net/timestamping.c
> index 044bc0e9ed81..ad2be2143698 100644
> --- a/tools/testing/selftests/net/timestamping.c
> +++ b/tools/testing/selftests/net/timestamping.c
> @@ -282,8 +282,8 @@ static void recvpacket(int sock, int recvmsg_flags,
>         struct iovec entry;
>         struct sockaddr_in from_addr;
>         struct {
> -               struct cmsghdr cm;
>                 char control[512];
> +               struct cmsghdr cm;
>         } control;
>         int res;

For the timestamping part:

Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>

Thanks,
Jason

Re: [PATCH v2] selftest: net: fix variable sized type issue not at the end of a struct

[Jakub Kicinski]

On Mon, 27 Oct 2025 11:01:56 +0530 Ankit Khushwaha wrote:
> -		struct cmsghdr cm;
>  		char control[512];
> +		struct cmsghdr cm;

This is no longer in the order in which it will appear in the msg.
If the struct placement is not important just use a raw char buffer
for the whole thing.

Before you repost please read at least the TLDR section of:
https://www.kernel.org/doc/html/next/process/maintainer-netdev.html
-- 
pw-bot: cr