On Fri, Jan 14, 2022 at 05:08:32PM -0800, Andrii Nakryiko wrote: > 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. ok, that seems doable, we should be able to get the link struct in bpf_get_attach_cookie_trace and reach both ips and cookies jirka > > > > > 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> >
