Re: [PATCH bpf-next v5 1/2] bpf: Support struct btf_struct_meta via KF_IMPLICIT_ARGS

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Mar 27, 2026 at 01:32:40PM -0700, Ihor Solodrai wrote:
> The following kfuncs currently accept void *meta__ign argument:
>   * bpf_obj_new_impl
>   * bpf_obj_drop_impl
>   * bpf_percpu_obj_new_impl
>   * bpf_percpu_obj_drop_impl
>   * bpf_refcount_acquire_impl
>   * bpf_list_push_back_impl
>   * bpf_list_push_front_impl
>   * bpf_rbtree_add_impl
> 
> The __ign suffix is an indicator for the verifier to skip the argument
> in check_kfunc_args(). Then, in fixup_kfunc_call() the verifier may
> set the value of this argument to struct btf_struct_meta *
> kptr_struct_meta from insn_aux_data.
> 
> BPF programs must pass a dummy NULL value when calling these kfuncs.
> 
> Additionally, the list and rbtree _impl kfuncs also accept an implicit
> u64 argument, which doesn't require __ign suffix because it's a
> scalar, and BPF programs explicitly pass 0.
> 
> Add new kfuncs with KF_IMPLICIT_ARGS [1], that correspond to each
> _impl kfunc accepting meta__ign. The existing _impl kfuncs remain
> unchanged for backwards compatibility.
> 
> To support this, add "btf_struct_meta" to the list of recognized
> implicit argument types in resolve_btfids.
> 
> Implement is_kfunc_arg_implicit() in the verifier, that determines
> implicit args by inspecting both a non-_impl BTF prototype of the
> kfunc.
> 
> Update the special_kfunc_list in the verifier and relevant checks to
> support both the old _impl and the new KF_IMPLICIT_ARGS variants of
> btf_struct_meta users.
> 
> [1] https://lore.kernel.org/bpf/20260120222638.3976562-1-ihor.solodrai@linux.dev/
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka