From: Steven Rostedt <rostedt@goodmis.org>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc: "Jiri Olsa" <jolsa@kernel.org>,
"Alexei Starovoitov" <ast@kernel.org>,
"Daniel Borkmann" <daniel@iogearbox.net>,
"Andrii Nakryiko" <andriin@fb.com>,
Networking <netdev@vger.kernel.org>, bpf <bpf@vger.kernel.org>,
"Martin KaFai Lau" <kafai@fb.com>,
"Song Liu" <songliubraving@fb.com>, "Yonghong Song" <yhs@fb.com>,
"John Fastabend" <john.fastabend@gmail.com>,
"KP Singh" <kpsingh@chromium.org>, "Daniel Xu" <dxu@dxuuu.xyz>,
"Jesper Brouer" <jbrouer@redhat.com>,
"Toke Høiland-Jørgensen" <toke@redhat.com>,
"Viktor Malik" <vmalik@redhat.com>
Subject: Re: [RFC bpf-next 09/16] bpf: Add BPF_TRAMPOLINE_BATCH_ATTACH support
Date: Fri, 23 Oct 2020 16:31:10 -0400 [thread overview]
Message-ID: <20201023163110.54e4a202@gandalf.local.home> (raw)
In-Reply-To: <CAEf4Bzb_HPmGSoUX+9+LvSP2Yb95OqEQKtjpMiW1Um-rixAM8Q@mail.gmail.com>
On Fri, 23 Oct 2020 13:03:22 -0700
Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
> Basically, maybe ftrace subsystem could provide a set of APIs to
> prepare a set of functions to attach to. Then BPF subsystem would just
> do what it does today, except instead of attaching to a specific
> kernel function, it would attach to ftrace's placeholder. I don't know
> anything about ftrace implementation, so this might be far off. But I
> thought that looking at this problem from a bit of a different angle
> would benefit the discussion. Thoughts?
I probably understand bpf internals as much as you understand ftrace
internals ;-)
Anyway, what I'm currently working on, is a fast way to get to the
arguments of a function. For now, I'm just focused on x86_64, and only add
6 argments.
The main issue that Alexei had with using the ftrace trampoline, was that
the only way to get to the arguments was to set the "REGS" flag, which
would give a regs parameter that contained a full pt_regs. The problem with
this approach is that it required saving *all* regs for every function
traced. Alexei felt that this was too much overehead.
Looking at Jiri's patch, I took a look at the creation of the bpf
trampoline, and noticed that it's copying the regs on a stack (at least
what is used, which I think could be an issue).
For tracing a function, one must store all argument registers used, and
restore them, as that's how they are passed from caller to callee. And
since they are stored anyway, I figure, that should also be sent to the
function callbacks, so that they have access to them too.
I'm working on a set of patches to make this a reality.
-- Steve
next prev parent reply other threads:[~2020-10-23 20:31 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-22 8:21 [RFC bpf-next 00/16] bpf: Speed up trampoline attach Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 01/16] ftrace: Add check_direct_entry function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 02/16] ftrace: Add adjust_direct_size function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 03/16] ftrace: Add get/put_direct_func function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 04/16] ftrace: Add ftrace_set_filter_ips function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 05/16] ftrace: Add register_ftrace_direct_ips function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 06/16] ftrace: Add unregister_ftrace_direct_ips function Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 07/16] kallsyms: Use rb tree for kallsyms name search Jiri Olsa
2020-10-28 18:25 ` Jiri Olsa
2020-10-28 21:15 ` Alexei Starovoitov
2020-10-29 9:29 ` Jiri Olsa
2020-10-29 22:45 ` Andrii Nakryiko
2020-10-28 22:40 ` Andrii Nakryiko
2020-10-29 9:33 ` Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 08/16] bpf: Use delayed link free in bpf_link_put Jiri Olsa
2020-10-23 19:46 ` Andrii Nakryiko
2020-10-25 19:02 ` Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 09/16] bpf: Add BPF_TRAMPOLINE_BATCH_ATTACH support Jiri Olsa
2020-10-23 20:03 ` Andrii Nakryiko
2020-10-23 20:31 ` Steven Rostedt [this message]
2020-10-23 22:23 ` Andrii Nakryiko
2020-10-25 19:41 ` Jiri Olsa
2020-10-26 23:19 ` Andrii Nakryiko
2020-10-22 8:21 ` [RFC bpf-next 10/16] bpf: Add BPF_TRAMPOLINE_BATCH_DETACH support Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 11/16] bpf: Sync uapi bpf.h to tools Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 12/16] bpf: Move synchronize_rcu_mult for batch processing (NOT TO BE MERGED) Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 13/16] libbpf: Add trampoline batch attach support Jiri Olsa
2020-10-23 20:09 ` Andrii Nakryiko
2020-10-25 19:11 ` Jiri Olsa
2020-10-26 23:15 ` Andrii Nakryiko
2020-10-27 19:03 ` Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 14/16] libbpf: Add trampoline batch detach support Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 15/16] selftests/bpf: Add trampoline batch test Jiri Olsa
2020-10-22 8:21 ` [RFC bpf-next 16/16] selftests/bpf: Add attach batch test (NOT TO BE MERGED) Jiri Olsa
2020-10-22 13:35 ` [RFC bpf-next 00/16] bpf: Speed up trampoline attach Steven Rostedt
2020-10-22 14:11 ` Jiri Olsa
2020-10-22 14:42 ` Steven Rostedt
2020-10-22 16:21 ` Steven Rostedt
2020-10-22 20:52 ` Steven Rostedt
2020-10-23 6:09 ` Jiri Olsa
2020-10-23 13:50 ` Steven Rostedt
2020-10-25 19:01 ` Jiri Olsa
2020-10-27 4:30 ` Alexei Starovoitov
2020-10-27 13:14 ` Steven Rostedt
2020-10-27 14:28 ` Jiri Olsa
2020-10-28 21:13 ` Alexei Starovoitov
2020-10-29 11:09 ` Jiri Olsa
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