Re: [RFC PATCH v3 0/9] fprobe: Introduce fprobe function entry/exit probe

[Masami Hiramatsu]

On Thu, 20 Jan 2022 14:24:15 -0800
Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:

> On Wed, Jan 19, 2022 at 6:56 AM Masami Hiramatsu <mhiramat@xxxxxxxxxx> 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@xxxxxxxxxx/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@xxxxxxxxxx/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?
> 
> 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;
+				__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@xxxxxxxxxx>


-- 
Masami Hiramatsu <mhiramat@xxxxxxxxxx>