netdev - Re: [RFC PATCH bpf-next 1/2] libbpf: Add support for dynamic tracepoint

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Message-ID: <CAADnVQ+Cbq99wpNoijyJbvtqaMTAxQF_S-n8yf9+0JGHJnShLw@mail.gmail.com>
Date: Mon, 6 Jan 2025 14:33:40 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Yafang Shao <laoar.shao@...il.com>, Daniel Xu <dxu@...uu.xyz>
Cc: Andrii Nakryiko <andrii@...nel.org>, Eddy Z <eddyz87@...il.com>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, Eric Dumazet <edumazet@...gle.com>, bpf <bpf@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>
Subject: Re: [RFC PATCH bpf-next 1/2] libbpf: Add support for dynamic tracepoint

On Sun, Jan 5, 2025 at 6:32 PM Yafang Shao <laoar.shao@...il.com> wrote:
>
> On Mon, Jan 6, 2025 at 8:16 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Sun, Jan 5, 2025 at 4:44 AM Yafang Shao <laoar.shao@...il.com> wrote:
> > >
> > > Dynamic tracepoints can be created using debugfs. For example:
> > >
> > >    echo 'p:myprobe kernel_clone args' >> /sys/kernel/debug/tracing/kprobe_events
> > >
> > > This command creates a new tracepoint under debugfs:
> > >
> > >   $ ls /sys/kernel/debug/tracing/events/kprobes/myprobe/
> > >   enable  filter  format  hist  id  trigger
> > >
> > > Although this dynamic tracepoint appears as a tracepoint, it is internally
> > > implemented as a kprobe. However, it must be attached as a tracepoint to
> > > function correctly in certain contexts.
> >
> > Nack.
> > There are multiple mechanisms to create kprobe/tp via text interfaces.
> > We're not going to mix them with the programmatic libbpf api.
>
> It appears that bpftrace still lacks support for adding a kprobe/tp
> and then attaching to it directly. Is that correct?

what do you mean?
bpftrace supports both kprobe attaching and tp too.

> What do you think about introducing this mechanism into bpftrace? With
> such a feature, we could easily attach to inlined kernel functions
> using bpftrace.

Attaching to inlined funcs also sort-of works. It relies on dwarf,
and there is work in progress to add a special section to vmlinux
to annotate inlined sites, so it can work without dwarf.