On Wed, Jan 12, 2022 at 6:02 AM Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote: > > Hi Jiri and Alexei, > > Here is the 2nd version of fprobe. This version uses the > ftrace_set_filter_ips() for reducing the registering overhead. > Note that this also drops per-probe point private data, which > is not used anyway. This per-probe private data is necessary for the feature called BPF cookie, in which each attachment has a unique user-provided u64 value associated to it, accessible at runtime through bpf_get_attach_cookie() helper. One way or another we'll need to support this to make these multi-attach BPF programs really useful for generic tracing applications. Jiri, We've discussed with Alexei this week how cookies can be supported for multi-attach fentry (where it seems even more challenging than in kprobe case), and agreed on rather simple solution, which roughly goes like this. When multi-attaching either fentry/fexit program, save sorted array of IP addresses and then sorted in the same order as IPs list of u64 cookies. At runtime, bpf_get_attach_cookie() helper should somehow get access to these two arrays and functions IP (that we already have with bpf_get_func_ip()), perform binary search and locate necessary cookie. This offloads the overhead of finding this cookie to actual call site of bpf_get_attach_cookie() (and it's a log(N), so not bad at all, especially if BPF program can be optimized to call this helper just once). I think something like that should be doable for Masami's fprobe-based multi-attach kprobes, right? That would allow to have super-fast attachment, but still support BPF cookie per each individual IP/kernel function attachment. I haven't looked at code thoroughly, though, please let me know if I'm missing something fundamental. > > This 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 [1/8] and [7/8] are from your 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 > > I also added an out-of-tree (just for testing) patch at the > end of this series ([8/8]) for adding a wildcard support to > the sample program. With that patch, it shows how long the > registration will take; > > # time insmod fprobe_example.ko symbol='btrfs_*' > [ 36.130947] fprobe_init: 1028 symbols found > [ 36.177901] fprobe_init: Planted fprobe at btrfs_* > real 0m 0.08s > user 0m 0.00s > sys 0m 0.07s > > Thank you, > > --- > > Jiri Olsa (2): > ftrace: Add ftrace_set_filter_ips function > bpf: Add kprobe link for attaching raw kprobes > > Masami Hiramatsu (6): > 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 > > > arch/x86/Kconfig | 1 > arch/x86/kernel/Makefile | 1 > arch/x86/kernel/rethook.c | 115 ++++++++++++++++++++ > include/linux/bpf_types.h | 1 > include/linux/fprobe.h | 57 ++++++++++ > include/linux/ftrace.h | 3 + > include/linux/rethook.h | 74 +++++++++++++ > include/linux/sched.h | 3 + > include/uapi/linux/bpf.h | 12 ++ > kernel/bpf/syscall.c | 195 +++++++++++++++++++++++++++++++++- > kernel/exit.c | 2 > kernel/fork.c | 3 + > kernel/kallsyms.c | 1 > kernel/trace/Kconfig | 22 ++++ > kernel/trace/Makefile | 2 > kernel/trace/fprobe.c | 168 +++++++++++++++++++++++++++++ > kernel/trace/ftrace.c | 54 ++++++++- > kernel/trace/rethook.c | 226 +++++++++++++++++++++++++++++++++++++++ > samples/Kconfig | 7 + > samples/Makefile | 1 > samples/fprobe/Makefile | 3 + > samples/fprobe/fprobe_example.c | 154 +++++++++++++++++++++++++++ > tools/include/uapi/linux/bpf.h | 12 ++ > 23 files changed, 1103 insertions(+), 14 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>
