Subject: Re: [PATCH bpf-next 2/2] bpf: treewide: Annotate BPF kfuncs in BTF

From: Jiri Olsa <[email-masked]>
Date: Thu, 4 Jan 2024 12:41:51 +0100

On Wed, Jan 03, 2024 at 04:31:56PM -0700, Daniel Xu wrote:

SNIP

> diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
> index 88f914579fa1..771e29762a2d 100644
> --- a/include/linux/btf_ids.h
> +++ b/include/linux/btf_ids.h
> @@ -8,6 +8,9 @@ struct btf_id_set {
>  	u32 ids[];
>  };
>  
> +/* This flag implies BTF_SET8 holds kfunc(s) */
> +#define BTF_SET8_KFUNC		(1 << 0)
> +
>  struct btf_id_set8 {
>  	u32 cnt;
>  	u32 flags;
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 51e8b4bee0c8..b8ba00a4179f 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -7769,6 +7769,9 @@ static int __register_btf_kfunc_id_set(enum btf_kfunc_hook hook,
>  	struct btf *btf;
>  	int ret, i;
>  
> +	/* All kfuncs need to be tagged as such in BTF */
> +	WARN_ON(!(kset->set->flags & BTF_SET8_KFUNC));

__register_btf_kfunc_id_set gets called also from the 'hooks' path:

  bpf_mptcp_kfunc_init
    register_btf_fmodret_id_set
      __register_btf_kfunc_id_set

so it will hit the warn.. it should be probably in the register_btf_kfunc_id_set ?

also given that we can have modules calling register_btf_kfunc_id_set,
should we just return error instead of the warn?

SNIP

> diff --git a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> index 91907b321f91..32972334cd50 100644
> --- a/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> +++ b/tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c
> @@ -341,7 +341,7 @@ static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {
>  	.write = bpf_testmod_test_write,
>  };
>  
> -BTF_SET8_START(bpf_testmod_common_kfunc_ids)
> +BTF_SET8_START(bpf_testmod_common_kfunc_ids, BTF_SET8_KFUNC)
>  BTF_ID_FLAGS(func, bpf_iter_testmod_seq_new, KF_ITER_NEW)
>  BTF_ID_FLAGS(func, bpf_iter_testmod_seq_next, KF_ITER_NEXT | KF_RET_NULL)
>  BTF_ID_FLAGS(func, bpf_iter_testmod_seq_destroy, KF_ITER_DESTROY)

we need to change also bpf_testmod_check_kfunc_ids set

jirka

> -- 
> 2.42.1