On 12/13/19 4:47 PM, Martin KaFai Lau wrote:
> This patch allows bitfield access as a scalar. It currently limits
> the access to sizeof(u64) and upto the end of the struct. It is needed
> in a later bpf-tcp-cc example that reads bitfield from
> inet_connection_sock and tcp_sock.
>
> Signed-off-by: Martin KaFai Lau <kafai@xxxxxx>
> ---
> kernel/bpf/btf.c | 13 +++++++++----
> 1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 6e652643849b..011194831499 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -3744,10 +3744,6 @@ int btf_struct_access(struct bpf_verifier_log *log,
> }
>
> for_each_member(i, t, member) {
> - if (btf_member_bitfield_size(t, member))
> - /* bitfields are not supported yet */
> - continue;
> -
> /* offset of the field in bytes */
> moff = btf_member_bit_offset(t, member) / 8;
> if (off + size <= moff)
> @@ -3757,6 +3753,15 @@ int btf_struct_access(struct bpf_verifier_log *log,
> if (off < moff)
> continue;
>
> + if (btf_member_bitfield_size(t, member)) {
> + if (off == moff &&
> + !(btf_member_bit_offset(t, member) % 8) &&
This check '!(btf_member_bit_offset(t, member) % 8)' is not needed.
> + size <= sizeof(u64) &&
This one is not needed since verifier gets 'size' from load/store
instructions which is guaranteed to be <= sizeof(u64).
> + off + size <= t->size)
> + return SCALAR_VALUE;
> + continue;
> + }
> +
> /* type of the field */
> mtype = btf_type_by_id(btf_vmlinux, member->type);
> mname = __btf_name_by_offset(btf_vmlinux, member->name_off);
>
