linux-kernel - Re: [PATCH RFC bpf-next 5/7] bpf: introduce bpf_arch_text_poke

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Message-ID: <CADxym3a3UCgW1ukK_VZEfqM6YvPT1ZAE=Wd52oq1FhHwdhf4Cg@mail.gmail.com>
Date: Sat, 15 Nov 2025 10:26:22 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, Steven Rostedt <rostedt@...dmis.org>, 
	Daniel Borkmann <daniel@...earbox.net>, John Fastabend <john.fastabend@...il.com>, 
	Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, 
	Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>, KP Singh <kpsingh@...nel.org>, 
	Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, 
	Masami Hiramatsu <mhiramat@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC bpf-next 5/7] bpf: introduce bpf_arch_text_poke_type

On Sat, Nov 15, 2025 at 2:42 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Fri, Nov 14, 2025 at 1:25 AM Menglong Dong <menglong8.dong@...il.com> wrote:
> >
> > Introduce the function bpf_arch_text_poke_type(), which is able to specify
> > both the current and new opcode. If it is not implemented by the arch,
> > bpf_arch_text_poke() will be called directly if the current opcode is the
> > same as the new one. Otherwise, -EOPNOTSUPP will be returned.
> >
> > Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> > ---
> >  include/linux/bpf.h |  4 ++++
> >  kernel/bpf/core.c   | 10 ++++++++++
> >  2 files changed, 14 insertions(+)
> >
> > diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> > index d65a71042aa3..aec7c65539f5 100644
> > --- a/include/linux/bpf.h
> > +++ b/include/linux/bpf.h
> > @@ -3711,6 +3711,10 @@ enum bpf_text_poke_type {
> >         BPF_MOD_JUMP,
> >  };
> >
> > +int bpf_arch_text_poke_type(void *ip, enum bpf_text_poke_type old_t,
> > +                           enum bpf_text_poke_type new_t, void *addr1,
> > +                           void *addr2);
> > +
>
> Instead of adding a new helper, I think, it's cleaner to change
> the existing bpf_arch_text_poke() across all archs in one patch,
> and also do:
>
> enum bpf_text_poke_type {
> +       BPF_MOD_NOP,
>         BPF_MOD_CALL,
>         BPF_MOD_JUMP,
> };
>
> and use that instead of addr[12] = !NULL to indicate
> the transition.
>
> The callsites will be easier to read when they will look like:
> bpf_arch_text_poke(ip, BPF_MOD_CALL, BPF_MOD_CALL, old_addr, new_addr);
>
> bpf_arch_text_poke(ip, BPF_MOD_NOP, BPF_MOD_CALL, NULL, new_addr);
>
> bpf_arch_text_poke(ip, BPF_MOD_JMP, BPF_MOD_CALL, old_addr, new_addr);

Yeah, much clearer. The new helper also makes me feel a bit
dizzy.

Thanks!
Menglong Dong