From: Alan Maguire <alan.maguire@oracle.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: "Alan Maguire" <alan.maguire@oracle.com>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
andrii@kernel.org, "Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>,
yhs@fb.com, "John Fastabend" <john.fastabend@gmail.com>,
kpsingh@kernel.org,
"Nathan Chancellor" <natechancellor@gmail.com>,
"Nick Desaulniers" <ndesaulniers@google.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
jean-philippe@linaro.org, bpf <bpf@vger.kernel.org>,
"Linux Kernel Network Developers" <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH bpf-next] ksnoop: kernel argument/return value tracing/display using BTF
Date: Tue, 5 Jan 2021 22:44:29 +0000 (GMT) [thread overview]
Message-ID: <alpine.LRH.2.23.451.2101052209360.30305@localhost> (raw)
In-Reply-To: <CAM_iQpW5ajiTTW7HBZiK+n_F1MhGyzzD+OWExns1YbejHRsy5A@mail.gmail.com>
On Tue, 5 Jan 2021, Cong Wang wrote:
> On Mon, Jan 4, 2021 at 7:29 AM Alan Maguire <alan.maguire@oracle.com> wrote:
> >
> > BPF Type Format (BTF) provides a description of kernel data structures
> > and of the types kernel functions utilize as arguments and return values.
> >
> > A helper was recently added - bpf_snprintf_btf() - that uses that
> > description to create a string representation of the data provided,
> > using the BTF id of its type. For example to create a string
> > representation of a "struct sk_buff", the pointer to the skb
> > is provided along with the type id of "struct sk_buff".
> >
> > Here that functionality is utilized to support tracing kernel
> > function entry and return using k[ret]probes. The "struct pt_regs"
> > context can be used to derive arguments and return values, and
> > when the user supplies a function name we
> >
> > - look it up in /proc/kallsyms to find its address/module
> > - look it up in the BTF kernel data to get types of arguments
> > and return value
> > - store a map representation of the trace information, keyed by
> > instruction pointer
> > - on function entry/return we look up the map to retrieve the BTF
> > ids of the arguments/return values and can call bpf_snprintf_btf()
> > with these argument/return values along with the type ids to store
> > a string representation in the map.
> > - this is then sent via perf event to userspace where it can be
> > displayed.
> >
> > ksnoop can be used to show function signatures; for example:
>
> This is definitely quite useful!
>
> Is it possible to integrate this with bpftrace? That would save people
> from learning yet another tool. ;)
>
I'd imagine (and hope!) other tracing tools will do this, but right
now the aim is to make the task of tracing kernel data structures simpler,
so having a tool dedicated to just that can hopefully help those
discussions. There's a bit more work to be done to simplify that task, for
example implementing Alexei's suggestion to support pretty-printing of
data structures using BTF in libbpf.
My hope is that we can evolve this tool - or something like it - to the
point where we can solve that one problem easily, and that other more
general tracers can then make use of that solution. I probably should
have made all of this clearer in the patch submission, sorry about that.
Alan
prev parent reply other threads:[~2021-01-05 22:45 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-04 15:26 [RFC PATCH bpf-next] ksnoop: kernel argument/return value tracing/display using BTF Alan Maguire
2021-01-05 1:57 ` Alexei Starovoitov
2021-01-05 20:48 ` Cong Wang
2021-01-05 22:44 ` Alan Maguire [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=alpine.LRH.2.23.451.2101052209360.30305@localhost \
--to=alan.maguire@oracle.com \
--cc=andrii@kernel.org \
--cc=ast@kernel.org \
--cc=bpf@vger.kernel.org \
--cc=daniel@iogearbox.net \
--cc=jean-philippe@linaro.org \
--cc=john.fastabend@gmail.com \
--cc=kafai@fb.com \
--cc=kpsingh@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=natechancellor@gmail.com \
--cc=ndesaulniers@google.com \
--cc=netdev@vger.kernel.org \
--cc=songliubraving@fb.com \
--cc=toke@redhat.com \
--cc=xiyou.wangcong@gmail.com \
--cc=yhs@fb.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).