linux-kernel - Re: [PATCH bpf-next v2 05/13] resolve_btfids: Support for KF_IMPLICIT

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Message-ID: <c370026bdcb3c2684a5c5c5a9e173f8c3e2189e5.camel@gmail.com>
Date: Mon, 19 Jan 2026 16:55:59 -0800
From: Eduard Zingerman <eddyz87@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>, Alexei Starovoitov
 <ast@...nel.org>,  Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>
Cc: Mykyta Yatsenko <yatsenko@...a.com>, Tejun Heo <tj@...nel.org>, Alan
 Maguire <alan.maguire@...cle.com>, Benjamin Tissoires <bentiss@...nel.org>,
 Jiri Kosina	 <jikos@...nel.org>, Amery Hung <ameryhung@...il.com>,
 bpf@...r.kernel.org, 	linux-kernel@...r.kernel.org,
 linux-input@...r.kernel.org, 	sched-ext@...ts.linux.dev
Subject: Re: [PATCH bpf-next v2 05/13] resolve_btfids: Support for
 KF_IMPLICIT_ARGS

On Fri, 2026-01-16 at 12:16 -0800, Ihor Solodrai wrote:
> Implement BTF modifications in resolve_btfids to support BPF kernel
> functions with implicit arguments.
> 
> For a kfunc marked with KF_IMPLICIT_ARGS flag, a new function
> prototype is added to BTF that does not have implicit arguments. The
> kfunc's prototype is then updated to a new one in BTF. This prototype
> is the intended interface for the BPF programs.
> 
> A <func_name>_impl function is added to BTF to make the original kfunc
> prototype searchable for the BPF verifier. If a <func_name>_impl
> function already exists in BTF, its interpreted as a legacy case, and
> this step is skipped.
> 
> Whether an argument is implicit is determined by its type:
> currently only `struct bpf_prog_aux *` is supported.
> 
> As a result, the BTF associated with kfunc is changed from
> 
>     __bpf_kfunc bpf_foo(int arg1, struct bpf_prog_aux *aux);
> 
> into
> 
>     bpf_foo_impl(int arg1, struct bpf_prog_aux *aux);
>     __bpf_kfunc bpf_foo(int arg1);
> 
> For more context see previous discussions and patches [1][2].
> 
> [1] https://lore.kernel.org/dwarves/ba1650aa-fafd-49a8-bea4-bdddee7c38c9@linux.dev/
> [2] https://lore.kernel.org/bpf/20251029190113.3323406-1-ihor.solodrai@linux.dev/
> 
> Signed-off-by: Ihor Solodrai <ihor.solodrai@...ux.dev>
> ---

Patch logic looks good to me, modulo LLM's memory management concern
and nit from Andrii.

Acked-by: Eduard Zingerman <eddyz87@...il.com>

> @@ -837,6 +854,369 @@ static int dump_raw_btf(struct btf *btf, const char *out_path)
>  	return 0;
>  }
>  
> +static const struct btf_type *btf_type_skip_qualifiers(const struct btf *btf, s32 type_id)
> +{
> +	const struct btf_type *t = btf__type_by_id(btf, type_id);
> +
> +	while (btf_is_mod(t))
> +		t = btf__type_by_id(btf, t->type);
> +
> +	return t;
> +}
> +
> +static const struct btf_decl_tag *btf_type_decl_tag(const struct btf_type *t)
> +{
> +	return (const struct btf_decl_tag *)(t + 1);
> +}

Nit: there is a utility function btf_decl_tag() in bpf/btf.h
     which does exactly the same.

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