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

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Message-ID: <CAADnVQ+VfT8nQA4eFec2Q7Fga0_2sbYmdaJffSbKpFmTwsE8eg@mail.gmail.com>
Date: Tue, 6 Jan 2026 10:40:25 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Amery Hung <ameryhung@...il.com>
Cc: Jakub Sitnicki <jakub@...udflare.com>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	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 Tue, Jan 6, 2026 at 9:47 AM Amery Hung <ameryhung@...il.com> wrote:
>
> > diff --git a/net/core/filter.c b/net/core/filter.c
> > index 7f5bc6a505e1..53993c2c492d 100644
> > --- a/net/core/filter.c
> > +++ b/net/core/filter.c
> > @@ -9082,8 +9082,7 @@ static int bpf_unclone_prologue(struct bpf_insn *insn_buf, u32 pkt_access_flags,
> >         /* ret = bpf_skb_pull_data(skb, 0); */
> >         *insn++ = BPF_MOV64_REG(BPF_REG_6, BPF_REG_1);
> >         *insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_2, BPF_REG_2);
> > -       *insn++ = BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
> > -                              BPF_FUNC_skb_pull_data);
>
> This is why I was suggesting setting off = 1 in BPF_EMIT_CALL to mark
> a call as finalized. So that we can continue to support using
> BPF_RAW_INSN to emit a helper call in prologue and epilogue.

That's the only place in the code where BPF_RAW_INSN(CALL, BPF_FUNC_xxx)
is used, and it was done this way only because we didn't think
of finalized_call concept.
So I don't think we should introduce more corner cases with off=1.