Re: [PATCH] net/mlx5: Replace zero-length array with flexible-array
From: Saeed Mahameed
Date: Sat May 09 2020 - 23:51:02 EST
On Thu, 2020-05-07 at 13:59 -0500, Gustavo A. R. Silva wrote:
> The current codebase makes use of the zero-length array language
> extension to the C90 standard, but the preferred mechanism to declare
> variable-length types such as these ones is a flexible array
> member[1][2],
> introduced in C99:
>
> struct foo {
> int stuff;
> struct boo array[];
> };
>
> By making use of the mechanism above, we will get a compiler warning
> in case the flexible array does not occur last in the structure,
> which
> will help us prevent some kind of undefined behavior bugs from being
> inadvertently introduced[3] to the codebase from now on.
>
> Also, notice that, dynamic memory allocations won't be affected by
> this change:
>
> "Flexible array members have incomplete type, and so the sizeof
> operator
> may not be applied. As a quirk of the original implementation of
> zero-length arrays, sizeof evaluates to zero."[1]
>
> sizeof(flexible-array-member) triggers a warning because flexible
> array
> members have incomplete type[1]. There are some instances of code in
> which the sizeof operator is being incorrectly/erroneously applied to
> zero-length arrays and the result is zero. Such instances may be
> hiding
hmmm, we actually have some tooling that rely on this to identify such
0 length fields .. since the structs in this file are usually auto-
generated from the hw sepcs .. now i see that these tools are broken in
our CI with this patch applied.
I guess we will need to fix them, and fix our code auto-generation
tools.
overall i am ok with this patch. I will apply it to mlx5-next.
and submit it upstream soom.
> some bugs. So, this work (flexible-array member conversions) will
> also
> help to get completely rid of those sorts of issues.
>
> This issue was found with the help of Coccinelle.
>
> [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [2] https://github.com/KSPP/linux/issues/21
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
> ---
> include/linux/mlx5/driver.h | 2 -
> include/linux/mlx5/mlx5_ifc.h | 66 +++++++++++++++++++++--------
> -------------
> include/linux/mlx5/qp.h | 2 -
> 3 files changed, 35 insertions(+), 35 deletions(-)
>
> diff --git a/include/linux/mlx5/driver.h
> b/include/linux/mlx5/driver.h
> index 6f8f79ef829b..1a4ba36275de 100644
> --- a/include/linux/mlx5/driver.h
> +++ b/include/linux/mlx5/driver.h
> @@ -200,7 +200,7 @@ struct mlx5_rsc_debug {
> void *object;
> enum dbg_rsc_type type;
> struct dentry *root;
> - struct mlx5_field_desc fields[0];
> + struct mlx5_field_desc fields[];
> };
>
> enum mlx5_dev_event {
> diff --git a/include/linux/mlx5/mlx5_ifc.h
> b/include/linux/mlx5/mlx5_ifc.h
> index 69b27c7dfc3e..c55686ff6504 100644
> --- a/include/linux/mlx5/mlx5_ifc.h
> +++ b/include/linux/mlx5/mlx5_ifc.h
> @@ -1677,7 +1677,7 @@ struct mlx5_ifc_wq_bits {
>
> u8 reserved_at_140[0x4c0];
>
> - struct mlx5_ifc_cmd_pas_bits pas[0];
> + struct mlx5_ifc_cmd_pas_bits pas[];
> };
>
> struct mlx5_ifc_rq_num_bits {
> @@ -1895,7 +1895,7 @@ struct mlx5_ifc_resource_dump_menu_segment_bits
> {
> u8 reserved_at_20[0x10];
> u8 num_of_records[0x10];
>
> - struct mlx5_ifc_resource_dump_menu_record_bits record[0];
> + struct mlx5_ifc_resource_dump_menu_record_bits record[];
> };
>
> struct mlx5_ifc_resource_dump_resource_segment_bits {
> @@ -1907,7 +1907,7 @@ struct
> mlx5_ifc_resource_dump_resource_segment_bits {
>
> u8 index2[0x20];
>
> - u8 payload[0][0x20];
> + u8 payload[][0x20];
> };
>
> struct mlx5_ifc_resource_dump_terminate_segment_bits {
> @@ -2984,7 +2984,7 @@ struct mlx5_ifc_flow_context_bits {
>
> u8 reserved_at_1200[0x600];
>
> - union mlx5_ifc_dest_format_struct_flow_counter_list_auto_bits
> destination[0];
> + union mlx5_ifc_dest_format_struct_flow_counter_list_auto_bits
> destination[];
> };
>
> enum {
> @@ -3276,7 +3276,7 @@ struct mlx5_ifc_rqtc_bits {
>
> u8 reserved_at_e0[0x6a0];
>
> - struct mlx5_ifc_rq_num_bits rq_num[0];
> + struct mlx5_ifc_rq_num_bits rq_num[];
> };
>
> enum {
> @@ -3388,7 +3388,7 @@ struct mlx5_ifc_nic_vport_context_bits {
>
> u8 reserved_at_7e0[0x20];
>
> - u8 current_uc_mac_address[0][0x40];
> + u8 current_uc_mac_address[][0x40];
> };
>
> enum {
> @@ -4310,7 +4310,7 @@ struct mlx5_ifc_query_xrc_srq_out_bits {
>
> u8 reserved_at_280[0x600];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_query_xrc_srq_in_bits {
> @@ -4588,7 +4588,7 @@ struct mlx5_ifc_query_srq_out_bits {
>
> u8 reserved_at_280[0x600];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_query_srq_in_bits {
> @@ -4799,7 +4799,7 @@ struct mlx5_ifc_query_qp_out_bits {
>
> u8 reserved_at_800[0x80];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_query_qp_in_bits {
> @@ -5132,7 +5132,7 @@ struct mlx5_ifc_query_hca_vport_pkey_out_bits {
>
> u8 reserved_at_40[0x40];
>
> - struct mlx5_ifc_pkey_bits pkey[0];
> + struct mlx5_ifc_pkey_bits pkey[];
> };
>
> struct mlx5_ifc_query_hca_vport_pkey_in_bits {
> @@ -5168,7 +5168,7 @@ struct mlx5_ifc_query_hca_vport_gid_out_bits {
> u8 gids_num[0x10];
> u8 reserved_at_70[0x10];
>
> - struct mlx5_ifc_array128_auto_bits gid[0];
> + struct mlx5_ifc_array128_auto_bits gid[];
> };
>
> struct mlx5_ifc_query_hca_vport_gid_in_bits {
> @@ -5436,7 +5436,7 @@ struct mlx5_ifc_query_flow_counter_out_bits {
>
> u8 reserved_at_40[0x40];
>
> - struct mlx5_ifc_traffic_counter_bits flow_statistics[0];
> + struct mlx5_ifc_traffic_counter_bits flow_statistics[];
> };
>
> struct mlx5_ifc_query_flow_counter_in_bits {
> @@ -5530,7 +5530,7 @@ struct mlx5_ifc_query_eq_out_bits {
>
> u8 reserved_at_300[0x580];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_query_eq_in_bits {
> @@ -5555,7 +5555,7 @@ struct mlx5_ifc_packet_reformat_context_in_bits
> {
> u8 reserved_at_20[0x10];
> u8 reformat_data[2][0x8];
>
> - u8 more_reformat_data[0][0x8];
> + u8 more_reformat_data[][0x8];
> };
>
> struct mlx5_ifc_query_packet_reformat_context_out_bits {
> @@ -5566,7 +5566,7 @@ struct
> mlx5_ifc_query_packet_reformat_context_out_bits {
>
> u8 reserved_at_40[0xa0];
>
> - struct mlx5_ifc_packet_reformat_context_in_bits
> packet_reformat_context[0];
> + struct mlx5_ifc_packet_reformat_context_in_bits
> packet_reformat_context[];
> };
>
> struct mlx5_ifc_query_packet_reformat_context_in_bits {
> @@ -5805,7 +5805,7 @@ struct mlx5_ifc_query_cq_out_bits {
>
> u8 reserved_at_280[0x600];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_query_cq_in_bits {
> @@ -6412,7 +6412,7 @@ struct mlx5_ifc_modify_cq_in_bits {
>
> u8 reserved_at_300[0x580];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_modify_cong_status_out_bits {
> @@ -6476,7 +6476,7 @@ struct mlx5_ifc_manage_pages_out_bits {
>
> u8 reserved_at_60[0x20];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> enum {
> @@ -6498,7 +6498,7 @@ struct mlx5_ifc_manage_pages_in_bits {
>
> u8 input_num_entries[0x20];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_mad_ifc_out_bits {
> @@ -7453,7 +7453,7 @@ struct mlx5_ifc_create_xrc_srq_in_bits {
>
> u8 reserved_at_300[0x580];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_create_tis_out_bits {
> @@ -7529,7 +7529,7 @@ struct mlx5_ifc_create_srq_in_bits {
>
> u8 reserved_at_280[0x600];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_create_sq_out_bits {
> @@ -7690,7 +7690,7 @@ struct mlx5_ifc_create_qp_in_bits {
> u8 wq_umem_valid[0x1];
> u8 reserved_at_861[0x1f];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_create_psv_out_bits {
> @@ -7761,7 +7761,7 @@ struct mlx5_ifc_create_mkey_in_bits {
>
> u8 reserved_at_320[0x560];
>
> - u8 klm_pas_mtt[0][0x20];
> + u8 klm_pas_mtt[][0x20];
> };
>
> enum {
> @@ -7894,7 +7894,7 @@ struct mlx5_ifc_create_eq_in_bits {
>
> u8 reserved_at_3c0[0x4c0];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_create_dct_out_bits {
> @@ -7951,7 +7951,7 @@ struct mlx5_ifc_create_cq_in_bits {
> u8 cq_umem_valid[0x1];
> u8 reserved_at_2e1[0x59f];
>
> - u8 pas[0][0x40];
> + u8 pas[][0x40];
> };
>
> struct mlx5_ifc_config_int_moderation_out_bits {
> @@ -8307,7 +8307,7 @@ struct mlx5_ifc_access_register_out_bits {
>
> u8 reserved_at_40[0x40];
>
> - u8 register_data[0][0x20];
> + u8 register_data[][0x20];
> };
>
> enum {
> @@ -8327,7 +8327,7 @@ struct mlx5_ifc_access_register_in_bits {
>
> u8 argument[0x20];
>
> - u8 register_data[0][0x20];
> + u8 register_data[][0x20];
> };
>
> struct mlx5_ifc_sltp_reg_bits {
> @@ -9344,7 +9344,7 @@ struct mlx5_ifc_cmd_in_bits {
> u8 reserved_at_20[0x10];
> u8 op_mod[0x10];
>
> - u8 command[0][0x20];
> + u8 command[][0x20];
> };
>
> struct mlx5_ifc_cmd_if_box_bits {
> @@ -9638,7 +9638,7 @@ struct mlx5_ifc_mcqi_reg_bits {
> u8 reserved_at_a0[0x10];
> u8 data_size[0x10];
>
> - union mlx5_ifc_mcqi_reg_data_bits data[0];
> + union mlx5_ifc_mcqi_reg_data_bits data[];
> };
>
> struct mlx5_ifc_mcc_reg_bits {
> @@ -10200,7 +10200,7 @@ struct mlx5_ifc_umem_bits {
>
> u8 num_of_mtt[0x40];
>
> - struct mlx5_ifc_mtt_bits mtt[0];
> + struct mlx5_ifc_mtt_bits mtt[];
> };
>
> struct mlx5_ifc_uctx_bits {
> @@ -10325,7 +10325,7 @@ struct mlx5_ifc_mtrc_stdb_bits {
> u8 reserved_at_4[0x4];
> u8 read_size[0x18];
> u8 start_offset[0x20];
> - u8 string_db_data[0];
> + u8 string_db_data[];
> };
>
> struct mlx5_ifc_mtrc_ctrl_bits {
> @@ -10379,7 +10379,7 @@ struct mlx5_ifc_query_esw_functions_out_bits
> {
> struct mlx5_ifc_host_params_context_bits host_params_context;
>
> u8 reserved_at_280[0x180];
> - u8 host_sf_enable[0][0x40];
> + u8 host_sf_enable[][0x40];
> };
>
> struct mlx5_ifc_sf_partition_bits {
> @@ -10399,7 +10399,7 @@ struct mlx5_ifc_query_sf_partitions_out_bits
> {
>
> u8 reserved_at_60[0x20];
>
> - struct mlx5_ifc_sf_partition_bits sf_partition[0];
> + struct mlx5_ifc_sf_partition_bits sf_partition[];
> };
>
> struct mlx5_ifc_query_sf_partitions_in_bits {
> diff --git a/include/linux/mlx5/qp.h b/include/linux/mlx5/qp.h
> index ae63b1ae9004..4e684298d1de 100644
> --- a/include/linux/mlx5/qp.h
> +++ b/include/linux/mlx5/qp.h
> @@ -402,7 +402,7 @@ struct mlx5_wqe_signature_seg {
>
> struct mlx5_wqe_inline_seg {
> __be32 byte_count;
> - __be32 data[0];
> + __be32 data[];
> };
>
> enum mlx5_sig_type {
>