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 ankitkhushwaha.linux@gmail.com --- 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;
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 ankitkhushwaha.linux@gmail.com
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.
On Tue, Oct 28, 2025 at 05:23:12PM +0000, Simon Horman wrote:
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 ankitkhushwaha.linux@gmail.com
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.
Hi Simon, So if buf and control providing the buffer space, then i think it is better to suppress `-Wgnu-variable-sized-type-not-at-end` warning within this block of code.
#pragma GCC diagnostic push #pragma GCC diagnostic ignored "-Wgnu-variable-sized-type-not-at-end"
struct { union { struct xfrm_algo alg; struct xfrm_algo_aead aead; struct xfrm_algo_auth auth; } u; char buf[XFRM_ALGO_KEY_BUF_SIZE]; } alg = {};
#pragma GCC diagnostic pop
I think this would be fine.
Thanks -- Ankit
On Sat, Nov 08, 2025 at 10:59:59PM +0530, Ankit Khushwaha wrote:
On Tue, Oct 28, 2025 at 05:23:12PM +0000, Simon Horman wrote:
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 ankitkhushwaha.linux@gmail.com
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.
Hi Simon, So if buf and control providing the buffer space, then i think it is better to suppress `-Wgnu-variable-sized-type-not-at-end` warning within this block of code.
#pragma GCC diagnostic push #pragma GCC diagnostic ignored "-Wgnu-variable-sized-type-not-at-end"
I'm unsure of the attitude towards using #pragma like this in kernel code, but certainly it would be a new one for me.
struct { union { struct xfrm_algo alg; struct xfrm_algo_aead aead; struct xfrm_algo_auth auth; } u; char buf[XFRM_ALGO_KEY_BUF_SIZE]; } alg = {};
#pragma GCC diagnostic pop
I think this would be fine.
In my view, the most promising approach I am aware of is using TRAILING_OVERLAP(), as illustrated in [1]. However, that approach was recently rejected, so I guess that means it doesn't have much promise after all.
linux-kselftest-mirror@lists.linaro.org
-
Ankit Khushwaha -
Simon Horman