On Mon, Jun 12, 2023 at 1:25 PM Jiri Olsa <olsajiri@xxxxxxxxx> wrote: > > On Mon, Jun 12, 2023 at 11:02:22AM -0400, Steven Rostedt wrote: > > On Mon, 12 Jun 2023 07:49:53 -0700 > > Yonghong Song <yhs@xxxxxxxx> wrote: > > > > > I am actually interested in how available_filter_functions_addrs > > > will be used. For example, bpf_program__attach_kprobe_multi_opts() > > > can already take addresses from kallsyms. How to use > > > available_filter_functions_addrs to facilitate kprobe_multi? > > the problem is that we need to do 2 passes: > > - through available_filter_functions and find out if the function is traceable > - through /proc/kallsyms to get the address for traceable function > > having available_filter_functions symbols together with addresses allow > us to skip the kallsyms step > > and we are ok with the address in available_filter_functions_addr not being the > function entry, because kprobe_multi uses fprobe and that handles both entry and > patch-site address properly > > > > Do we need to change kernel APIs? It would be great at least we > > > got a RFC patch to answer these questions. > > > > I agree, having that information would also be useful to me. > > > > Jiri? Andrii? > > so we have 2 interfaces how to create kprobe_multi link: > > a) passing symbols to kernel > > 1) user gathers symbols and need to ensure that they are > trace-able -> pass through available_filter_functions file > > 2) kernel takes those symbols and translates them to addresses > through kallsyms api > > 3) addresses are passed to fprobe/ftrace through: > > register_fprobe_ips > -> ftrace_set_filter_ips > > b) passing addresses to kernel > > 1) user gathers symbols and needs to ensure that they are > trace-able -> pass through available_filter_functions file > > 2) user takes those symbols and translates them to addresses > through /proc/kallsyms > > 3) addresses are passed to the kernel and kernel calls: > > register_fprobe_ips > -> ftrace_set_filter_ips > > > The new available_filter_functions_addrs file helps us with option b), > because we can make 'b 1' and 'b 2' in one step - while filtering traceable > functions, we get the address directly. > > I tested the new available_filter_functions_addrs changes with some hacked > selftest changes, you can check it in here [1]. > > I assume Jackie Liu will send new version of her patchset [2] based on this > new available_filter_functions_addrs file. > > I think we should have these changes coming together and add some perf > measurements from before and after to make the benefit apparent. > If Steven would be ok with it, can we land this change through the bpf-next tree? Then we can have BPF selftest added in the same patch set that parses a new file and uses bpf_program__attach_kprobe_multi() to attach using explicit addresses. This should make it clear to everyone how this is meant to be used and will be a good test that everything works end-to-end. > jirka > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git/commit/?h=bpf/avail_addrs&id=fecaeeaf40bae034715ab2e9a46ca1dc16371e8e > [2] https://lore.kernel.org/bpf/20230526155026.1419390-1-liu.yun@xxxxxxxxx/#r
