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Date: Mon, 24 Jan 2022 00:50:13 +0100
From: Jiri Olsa <jolsa@...hat.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>,
Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
lkml <linux-kernel@...r.kernel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
"Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
"David S . Miller" <davem@...emloft.net>
Subject: Re: [RFC PATCH v3 0/9] fprobe: Introduce fprobe function entry/exit
probe
On Fri, Jan 21, 2022 at 09:29:00AM -0800, Andrii Nakryiko wrote:
> On Thu, Jan 20, 2022 at 8:55 PM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> >
> > On Thu, 20 Jan 2022 14:24:15 -0800
> > Andrii Nakryiko <andrii.nakryiko@...il.com> wrote:
> >
> > > On Wed, Jan 19, 2022 at 6:56 AM Masami Hiramatsu <mhiramat@...nel.org> wrote:
> > > >
> > > > Hello Jiri,
> > > >
> > > > Here is the 3rd version of fprobe. I added some comments and
> > > > fixed some issues. But I still saw some problems when I add
> > > > your selftest patches.
> > > >
> > > > This series introduces the fprobe, the function entry/exit probe
> > > > with multiple probe point support. This also introduces the rethook
> > > > for hooking function return as same as kretprobe does. This
> > > > abstraction will help us to generalize the fgraph tracer,
> > > > because we can just switch it from rethook in fprobe, depending
> > > > on the kernel configuration.
> > > >
> > > > The patch [1/9] and [7/9] are from Jiri's series[1]. Other libbpf
> > > > patches will not be affected by this change.
> > > >
> > > > [1] https://lore.kernel.org/all/20220104080943.113249-1-jolsa@kernel.org/T/#u
> > > >
> > > > However, when I applied all other patches on top of this series,
> > > > I saw the "#8 bpf_cookie" test case has been stacked (maybe related
> > > > to the bpf_cookie issue which Andrii and Jiri talked?) And when I
> > > > remove the last selftest patch[2], the selftest stopped at "#112
> > > > raw_tp_test_run".
> > > >
> > > > [2] https://lore.kernel.org/all/20220104080943.113249-1-jolsa@kernel.org/T/#m242d2b3a3775eeb5baba322424b15901e5e78483
> > > >
> > > > Note that I used tools/testing/selftests/bpf/vmtest.sh to check it.
> > > >
> > > > This added 2 more out-of-tree patches. [8/9] is for adding wildcard
> > > > support to the sample program, [9/9] is a testing patch for replacing
> > > > kretprobe trampoline with rethook.
> > > > According to this work, I noticed that using rethook in kretprobe
> > > > needs 2 steps.
> > > > 1. port the rethook on all architectures which supports kretprobes.
> > > > (some arch requires CONFIG_KPROBES for rethook)
> > > > 2. replace kretprobe trampoline with rethook for all archs, at once.
> > > > This must be done by one treewide patch.
> > > >
> > > > Anyway, I'll do the kretprobe update in the next step as another series.
> > > > (This testing patch is just for confirming the rethook is correctly
> > > > implemented.)
> > > >
> > > > BTW, on the x86, ftrace (with fentry) location address is same as
> > > > symbol address. But on other archs, it will be different (e.g. arm64
> > > > will need 2 instructions to save link-register and call ftrace, the
> > > > 2nd instruction will be the ftrace location.)
> > > > Does libbpf correctly handle it?
hm, I'm probably missing something, but should this be handled by arm
specific kernel code? user passes whatever is found in kallsyms, right?
> > >
> > > libbpf doesn't do anything there. The interface for kprobe is based on
> > > function name and kernel performs name lookups internally to resolve
> > > IP. For fentry it's similar (kernel handles IP resolution), but
> > > instead of function name we specify BTF ID of a function type.
> >
> > Hmm, according to Jiri's original patch, it seems to pass an array of
> > addresses. So I thought that has been resolved by libbpf.
> >
> > + struct {
> > + __aligned_u64 addrs;
>
> I think this is a pointer to an array of pointers to zero-terminated C strings
I used direct addresses, because bpftrace already has them, so there was
no point passing strings, I cann add support for that
jirka
>
> > + __u32 cnt;
> > + __u64 bpf_cookie;
> > + } kprobe;
> >
> > Anyway, fprobe itself also has same issue. I'll try to fix it.
> >
> > Thank you!
> >
> > >
> > > >
> > > > Thank you,
> > > >
> > > > ---
> > > >
> > > > Jiri Olsa (2):
> > > > ftrace: Add ftrace_set_filter_ips function
> > > > bpf: Add kprobe link for attaching raw kprobes
> > > >
> > > > Masami Hiramatsu (7):
> > > > fprobe: Add ftrace based probe APIs
> > > > rethook: Add a generic return hook
> > > > rethook: x86: Add rethook x86 implementation
> > > > fprobe: Add exit_handler support
> > > > fprobe: Add sample program for fprobe
> > > > [DO NOT MERGE] Out-of-tree: Support wildcard symbol option to sample
> > > > [DO NOT MERGE] out-of-tree: kprobes: Use rethook for kretprobe
> > > >
> > > >
> > > > arch/x86/Kconfig | 1
> > > > arch/x86/include/asm/unwind.h | 8 +
> > > > arch/x86/kernel/Makefile | 1
> > > > arch/x86/kernel/kprobes/core.c | 106 --------------
> > > > arch/x86/kernel/rethook.c | 115 +++++++++++++++
> > > > include/linux/bpf_types.h | 1
> > > > include/linux/fprobe.h | 84 +++++++++++
> > > > include/linux/ftrace.h | 3
> > > > include/linux/kprobes.h | 85 +----------
> > > > include/linux/rethook.h | 99 +++++++++++++
> > > > include/linux/sched.h | 4 -
> > > > include/uapi/linux/bpf.h | 12 ++
> > > > kernel/bpf/syscall.c | 195 +++++++++++++++++++++++++-
> > > > kernel/exit.c | 3
> > > > kernel/fork.c | 4 -
> > > > kernel/kallsyms.c | 1
> > > > kernel/kprobes.c | 265 +++++------------------------------
> > > > kernel/trace/Kconfig | 22 +++
> > > > kernel/trace/Makefile | 2
> > > > kernel/trace/fprobe.c | 179 ++++++++++++++++++++++++
> > > > kernel/trace/ftrace.c | 54 ++++++-
> > > > kernel/trace/rethook.c | 295 +++++++++++++++++++++++++++++++++++++++
> > > > kernel/trace/trace_kprobe.c | 4 -
> > > > kernel/trace/trace_output.c | 2
> > > > samples/Kconfig | 7 +
> > > > samples/Makefile | 1
> > > > samples/fprobe/Makefile | 3
> > > > samples/fprobe/fprobe_example.c | 154 ++++++++++++++++++++
> > > > tools/include/uapi/linux/bpf.h | 12 ++
> > > > 29 files changed, 1283 insertions(+), 439 deletions(-)
> > > > create mode 100644 arch/x86/kernel/rethook.c
> > > > create mode 100644 include/linux/fprobe.h
> > > > create mode 100644 include/linux/rethook.h
> > > > create mode 100644 kernel/trace/fprobe.c
> > > > create mode 100644 kernel/trace/rethook.c
> > > > create mode 100644 samples/fprobe/Makefile
> > > > create mode 100644 samples/fprobe/fprobe_example.c
> > > >
> > > > --
> > > > Masami Hiramatsu (Linaro) <mhiramat@...nel.org>
> >
> >
> > --
> > Masami Hiramatsu <mhiramat@...nel.org>
>
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