netdev - Re: [PATCH bpf-next v2 15/16] bpf: Realign skb metadata for TC progs using data

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Message-ID: <CAADnVQJ=kmVAZsgkG9P2nEBTUG3E4PrDG=Yz8tfeFysH4ZBqVw@mail.gmail.com>
Date: Mon, 5 Jan 2026 18:04:28 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Amery Hung <ameryhung@...il.com>
Cc: Martin KaFai Lau <martin.lau@...ux.dev>, Jakub Sitnicki <jakub@...udflare.com>, 
	Martin KaFai Lau <martin.lau@...nel.org>, bpf <bpf@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Jesper Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>, 
	Stanislav Fomichev <sdf@...ichev.me>, Simon Horman <horms@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	kernel-team <kernel-team@...udflare.com>
Subject: Re: [PATCH bpf-next v2 15/16] bpf: Realign skb metadata for TC progs
 using data_meta

On Mon, Jan 5, 2026 at 3:19 PM Amery Hung <ameryhung@...il.com> wrote:
>
> >
> > >
> > > I guess we can mark such emitted call in insn_aux_data as finalized
> > > and get_func_proto() isn't needed.
> >
> > It is a good idea.
> >
>
> Hmm, insn_aux_data has to be marked in gen_{pro,epi}logue since this
> is the only place we know whether the call needs fixup or not. However
> insn_aux_data is not available yet in gen_{pro,epi}logue because we
> haven't resized insn_aux_data.
>
> Can we do some hack based on the fact that calls emitted by
> BPF_EMIT_CALL() are finalized while calls emitted by BPF_RAW_INSN()
> most likely are not?
> Let BPF_EMIT_CALL() mark the call insn as finalized temporarily (e.g.,
> .off = 1). Then, when do_misc_fixups() encounters it just reset off to
> 0 and don't call get_func_proto().

marking inside insn via off=1 or whatever is an option,
but once we remove BPF_CALL_KFUNC from gen_prologue we can
delete add_kfunc_in_insns() altogether and replace it with
a similar loop that does
if (bpf_helper_call()) mark insn_aux_data.

That would be a nice benefit, since add_kfunc_call() from there
was always a bit odd, since we're adding kfuncs early before the main
verifier pass and after, because of gen_prologue.