Re: [PATCH bpf 2/2] bpf: enforce usage of __aligned_u64 in the UAPI header

[Song Liu]

On Sun, May 27, 2018 at 4:28 AM, Eugene Syromiatnikov <esyr@xxxxxxxxxx> wrote:
> Use __aligned_u64 instead of __u64 everywhere in the UAPI header,
> similarly to v4.17-rc1~94^2~58^2 "RDMA: Change all uapi headers to use
> __aligned_u64 instead of __u64".
>
> This commit doesn't change structure layouts, but imposes additional
> alignment requirements on struct bpf_stack_build_id, struct
> bpf_sock_ops, struct bpf_perf_event_value, and struct
> bpf_raw_tracepoint_args; of them only struct bpf_sock_ops and struct
> bpf_perf_event_value have 64-bit fields that were present in a released
> kernel without this additional alignment requirement (bytes_received
> and bytes_acked were added to struct bpf_sock_ops in commit
> v4.16-rc1~123^2~33^2~5^2~4, struct bpf_perf_event_value was added
> in commit v4.15-rc1~84^2~532^2~3).
>
> Signed-off-by: Eugene Syromiatnikov <esyr@xxxxxxxxxx>
> ---
>  include/uapi/linux/bpf.h       | 22 +++++++++++-----------
>  tools/include/uapi/linux/bpf.h | 22 +++++++++++-----------
>  2 files changed, 22 insertions(+), 22 deletions(-)
>
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 903010a..174e99a 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -259,8 +259,8 @@ struct bpf_stack_build_id {
>         __s32           status;
>         unsigned char   build_id[BPF_BUILD_ID_SIZE];
>         union {
> -               __u64   offset;
> -               __u64   ip;
> +               __aligned_u64   offset;
> +               __aligned_u64   ip;
>         };
>  };
>
> @@ -288,7 +288,7 @@ union bpf_attr {
>                         __aligned_u64 value;
>                         __aligned_u64 next_key;
>                 };
> -               __u64           flags;
> +               __aligned_u64   flags;
>         };
>
>         struct { /* anonymous struct used by BPF_PROG_LOAD command */
> @@ -360,7 +360,7 @@ union bpf_attr {
>         } query;
>
>         struct {
> -               __u64 name;
> +               __aligned_u64 name;
>                 __u32 prog_fd;
>         } raw_tracepoint;
>  } __attribute__((aligned(8)));
> @@ -1011,7 +1011,7 @@ struct bpf_prog_info {
>         __u32 xlated_prog_len;
>         __aligned_u64 jited_prog_insns;
>         __aligned_u64 xlated_prog_insns;
> -       __u64 load_time;        /* ns since boottime */
> +       __aligned_u64 load_time;        /* ns since boottime */
>         __u32 created_by_uid;
>         __u32 nr_map_ids;
>         __aligned_u64 map_ids;
> @@ -1101,8 +1101,8 @@ struct bpf_sock_ops {
>         __u32 lost_out;
>         __u32 sacked_out;
>         __u32 sk_txhash;
> -       __u64 bytes_received;
> -       __u64 bytes_acked;
> +       __aligned_u64 bytes_received;
> +       __aligned_u64 bytes_acked;
>  };
>
>  /* Definitions for bpf_sock_ops_cb_flags */
> @@ -1189,9 +1189,9 @@ enum {
>  #define TCP_BPF_SNDCWND_CLAMP  1002    /* Set sndcwnd_clamp */
>
>  struct bpf_perf_event_value {
> -       __u64 counter;
> -       __u64 enabled;
> -       __u64 running;
> +       __aligned_u64 counter;
> +       __aligned_u64 enabled;
> +       __aligned_u64 running;
>  };
>
>  #define BPF_DEVCG_ACC_MKNOD    (1ULL << 0)
> @@ -1209,7 +1209,7 @@ struct bpf_cgroup_dev_ctx {
>  };
>
>  struct bpf_raw_tracepoint_args {
> -       __u64 args[0];
> +       __aligned_u64 args[0];
>  };
>
>  #endif /* _UAPI__LINUX_BPF_H__ */
> diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> index 903010a..174e99a 100644
> --- a/tools/include/uapi/linux/bpf.h
> +++ b/tools/include/uapi/linux/bpf.h
> @@ -259,8 +259,8 @@ struct bpf_stack_build_id {
>         __s32           status;
>         unsigned char   build_id[BPF_BUILD_ID_SIZE];
>         union {
> -               __u64   offset;
> -               __u64   ip;
> +               __aligned_u64   offset;
> +               __aligned_u64   ip;
>         };
>  };
>
> @@ -288,7 +288,7 @@ union bpf_attr {
>                         __aligned_u64 value;
>                         __aligned_u64 next_key;
>                 };
> -               __u64           flags;
> +               __aligned_u64   flags;
>         };
>
>         struct { /* anonymous struct used by BPF_PROG_LOAD command */
> @@ -360,7 +360,7 @@ union bpf_attr {
>         } query;
>
>         struct {
> -               __u64 name;
> +               __aligned_u64 name;
>                 __u32 prog_fd;
>         } raw_tracepoint;
>  } __attribute__((aligned(8)));
> @@ -1011,7 +1011,7 @@ struct bpf_prog_info {
>         __u32 xlated_prog_len;
>         __aligned_u64 jited_prog_insns;
>         __aligned_u64 xlated_prog_insns;
> -       __u64 load_time;        /* ns since boottime */
> +       __aligned_u64 load_time;        /* ns since boottime */
>         __u32 created_by_uid;
>         __u32 nr_map_ids;
>         __aligned_u64 map_ids;
> @@ -1101,8 +1101,8 @@ struct bpf_sock_ops {
>         __u32 lost_out;
>         __u32 sacked_out;
>         __u32 sk_txhash;
> -       __u64 bytes_received;
> -       __u64 bytes_acked;
> +       __aligned_u64 bytes_received;
> +       __aligned_u64 bytes_acked;
>  };
>
>  /* Definitions for bpf_sock_ops_cb_flags */
> @@ -1189,9 +1189,9 @@ enum {
>  #define TCP_BPF_SNDCWND_CLAMP  1002    /* Set sndcwnd_clamp */
>
>  struct bpf_perf_event_value {
> -       __u64 counter;
> -       __u64 enabled;
> -       __u64 running;
> +       __aligned_u64 counter;
> +       __aligned_u64 enabled;
> +       __aligned_u64 running;
>  };
>
>  #define BPF_DEVCG_ACC_MKNOD    (1ULL << 0)
> @@ -1209,7 +1209,7 @@ struct bpf_cgroup_dev_ctx {
>  };
>
>  struct bpf_raw_tracepoint_args {
> -       __u64 args[0];
> +       __aligned_u64 args[0];
>  };
>
>  #endif /* _UAPI__LINUX_BPF_H__ */
> --
> 2.1.4
>

I think these changes are not necessary. Is it a general guidance to
only use 64-bit aligned
variables in UAPI headers?

Thanks,
Song