On Tue, Feb 04, 2025 at 01:27:41PM +1030, Gustavo A. R. Silva wrote:
> -Wflex-array-member-not-at-end was introduced in GCC-14, and we are
> getting ready to enable it, globally.
>
> So, in order to avoid ending up with a flexible-array member in the
> middle of other structs, we use the `struct_group_tagged()` helper
> to create a new tagged `struct mlx5e_umr_wqe_hdr`. This structure
> groups together all the members of the flexible `struct mlx5e_umr_wqe`
> except the flexible array.
>
> As a result, the array is effectively separated from the rest of the
> members without modifying the memory layout of the flexible structure.
> We then change the type of the middle struct member currently causing
> trouble from `struct mlx5e_umr_wqe` to `struct mlx5e_umr_wqe_hdr`.
>
> We also want to ensure that when new members need to be added to the
> flexible structure, they are always included within the newly created
> tagged struct. For this, we use `static_assert()`. This ensures that the
> memory layout for both the flexible structure and the new tagged struct
> is the same after any changes.
>
> This approach avoids having to implement `struct mlx5e_umr_wqe_hdr` as
> a completely separate structure, thus preventing having to maintain two
> independent but basically identical structures, closing the door to
> potential bugs in the future.
>
> We also use `container_of()` whenever we need to retrieve a pointer to
> the flexible structure, through which we can access the flexible-array
> member, if necessary.
>
> So, with these changes, fix 124 of the following warnings:
>
> drivers/net/ethernet/mellanox/mlx5/core/en.h:664:48: warning: structure
> containing a flexible array member is not at the end of another structure
> [-Wflex-array-member-not-at-end]
>
> Signed-off-by: Gustavo A. R. Silva <gustavo...@kernel.org>
> ---
> drivers/net/ethernet/mellanox/mlx5/core/en.h | 13 +++++++++----
> drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 4 +++-
> 2 files changed, 12 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en.h
> b/drivers/net/ethernet/mellanox/mlx5/core/en.h
> index 979fc56205e1..c30c64eb346f 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en.h
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en.h
> @@ -233,15 +233,20 @@ struct mlx5e_rx_wqe_cyc {
> };
>
> struct mlx5e_umr_wqe {
> - struct mlx5_wqe_ctrl_seg ctrl;
> - struct mlx5_wqe_umr_ctrl_seg uctrl;
> - struct mlx5_mkey_seg mkc;
> + /* New members MUST be added within the struct_group() macro below. */
> + struct_group_tagged(mlx5e_umr_wqe_hdr, hdr,
> + struct mlx5_wqe_ctrl_seg ctrl;
> + struct mlx5_wqe_umr_ctrl_seg uctrl;
> + struct mlx5_mkey_seg mkc;
> + );
> union {
> DECLARE_FLEX_ARRAY(struct mlx5_mtt, inline_mtts);
> DECLARE_FLEX_ARRAY(struct mlx5_klm, inline_klms);
> DECLARE_FLEX_ARRAY(struct mlx5_ksm, inline_ksms);
> };
> };
> +static_assert(offsetof(struct mlx5e_umr_wqe, inline_mtts) == sizeof(struct
> mlx5e_umr_wqe_hdr),
> + "struct member likely outside of struct_group_tagged()");
>
> enum mlx5e_priv_flag {
> MLX5E_PFLAG_RX_CQE_BASED_MODER,
> @@ -660,7 +665,7 @@ struct mlx5e_rq {
> } wqe;
> struct {
> struct mlx5_wq_ll wq;
> - struct mlx5e_umr_wqe umr_wqe;
> + struct mlx5e_umr_wqe_hdr umr_wqe;
> struct mlx5e_mpw_info *info;
> mlx5e_fp_skb_from_cqe_mpwrq skb_from_cqe_mpwrq;
> __be32 umr_mkey_be;
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> index bd41b75d246e..4ff4ff2342cf 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
> @@ -373,6 +373,8 @@ static void mlx5e_rq_shampo_hd_info_free(struct mlx5e_rq
> *rq)
>
> static int mlx5e_rq_alloc_mpwqe_info(struct mlx5e_rq *rq, int node)
> {
> + struct mlx5e_umr_wqe *umr_wqe =
> + container_of(&rq->mpwqe.umr_wqe, struct mlx5e_umr_wqe, hdr);
> int wq_sz = mlx5_wq_ll_get_size(&rq->mpwqe.wq);
> size_t alloc_size;
>
> @@ -393,7 +395,7 @@ static int mlx5e_rq_alloc_mpwqe_info(struct mlx5e_rq *rq,
> int node)
> bitmap_fill(wi->skip_release_bitmap, rq->mpwqe.pages_per_wqe);
> }
>
> - mlx5e_build_umr_wqe(rq, rq->icosq, &rq->mpwqe.umr_wqe);
> + mlx5e_build_umr_wqe(rq, rq->icosq, umr_wqe);
>
> return 0;
Reviewed-by: Michal Swiatkowski <michal.swiatkow...@linux.intel.com>
> }
> --
> 2.43.0
