On Sat, Jun 24, 2023 at 6:14 PM Jackie Liu <liu.yun@xxxxxxxxx> wrote: > > From: Jackie Liu <liuyun01@xxxxxxxxxx> > > When using regular expression matching with "kprobe multi", it scans all > the functions under "/proc/kallsyms" that can be matched. However, not all > of them can be traced by kprobe.multi. If any one of the functions fails > to be traced, it will result in the failure of all functions. The best > approach is to filter out the functions that cannot be traced to ensure > proper tracking of the functions. > > Use available_filter_functions_addrs check first, if failed, fallback to > kallsyms. > This is good, but it also doesn't address the original problem. On older kernels that don't have available_filter_functions_addrs, we'll still be trying to attach to non-attachable kprobes? So I think we'll still need to add available_filter_functions-based filtering on top of kallsyms. I guess we'll have to collect all symbols+addr from kallsyms, sort them, then go over available_filter_functions and do binary search. If element is not found, we'll mark it for removal. Then last pass to filter out marked entries to keep only addrs to be passed to kernel? > Here is the test eBPF program [1]. > [1] https://github.com/JackieLiu1/ketones/tree/master/src/funccount > > Suggested-by: Jiri Olsa <jolsa@xxxxxxxxxx> > Signed-off-by: Jackie Liu <liuyun01@xxxxxxxxxx> > --- > tools/lib/bpf/libbpf.c | 81 ++++++++++++++++++++++++++++++++++++++---- > 1 file changed, 75 insertions(+), 6 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index a27f6e9ccce7..fca5d2e412c5 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -10107,6 +10107,12 @@ static const char *tracefs_uprobe_events(void) > return use_debugfs() ? DEBUGFS"/uprobe_events" : TRACEFS"/uprobe_events"; > } > > +static const char *tracefs_available_filter_functions_addrs(void) > +{ > + return use_debugfs() ? DEBUGFS"/available_filter_functions_addrs" : > + TRACEFS"/available_filter_functions_addrs"; > +} > + > static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz, > const char *kfunc_name, size_t offset) > { > @@ -10422,9 +10428,8 @@ struct kprobe_multi_resolve { > size_t cnt; > }; > > -static int > -resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > - const char *sym_name, void *ctx) > +static int ftrace_resolve_kprobe_multi_cb(unsigned long long sym_addr, > + const char *sym_name, void *ctx) > { > struct kprobe_multi_resolve *res = ctx; > int err; > @@ -10441,6 +10446,63 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > return 0; > } > > +static int > +kallsyms_resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > + const char *sym_name, void *ctx) > +{ > + return ftrace_resolve_kprobe_multi_cb(sym_addr, sym_name, ctx); > +} > + > +typedef int (*available_kprobe_cb_t)(unsigned long long sym_addr, > + const char *sym_name, void *ctx); > + > +static int > +libbpf_available_kprobes_parse(available_kprobe_cb_t cb, void *ctx) > +{ > + unsigned long long sym_addr; > + char sym_name[256]; > + FILE *f; > + int ret, err = 0; > + const char *available_path = tracefs_available_filter_functions_addrs(); > + > + f = fopen(available_path, "r"); > + if (!f) { > + err = -errno; > + pr_warn("failed to open %s, fallback to /proc/kallsyms.\n", > + available_path); if this is expected to happen, we shouldn't pr_warn() and pollute log output > + return err; > + } > + > + while (true) { > + ret = fscanf(f, "%llx %255s%*[^\n]\n", &sym_addr, sym_name); > + if (ret == EOF && feof(f)) > + break; > + if (ret != 2) { > + pr_warn("failed to read available kprobe entry: %d\n", > + ret); > + err = -EINVAL; > + break; > + } > + > + err = cb(sym_addr, sym_name, ctx); > + if (err) > + break; > + } > + > + fclose(f); > + return err; > +} > + > +static void kprobe_multi_resolve_reinit(struct kprobe_multi_resolve *res) > +{ > + free(res->addrs); > + > + /* reset to zero, when fallback */ > + res->cap = 0; > + res->cnt = 0; > + res->addrs = NULL; > +} > + > struct bpf_link * > bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, > const char *pattern, > @@ -10477,9 +10539,16 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, > return libbpf_err_ptr(-EINVAL); > > if (pattern) { > - err = libbpf_kallsyms_parse(resolve_kprobe_multi_cb, &res); > - if (err) > - goto error; > + err = libbpf_available_kprobes_parse(ftrace_resolve_kprobe_multi_cb, > + &res); > + if (err) { > + /* fallback to kallsyms */ > + kprobe_multi_resolve_reinit(&res); instead of try, fail, try something else approach, can we check that tracefs_available_filter_functions_addrs() exists and is readable, and if yes -- commit to it. If something fails -- to bad. If it doesn't exist, fallback to kallsyms. And we won't need ugly kprobe_multi_resolve_reinit() hack. > + err = libbpf_kallsyms_parse(kallsyms_resolve_kprobe_multi_cb, > + &res); > + if (err) > + goto error; > + } > if (!res.cnt) { > err = -ENOENT; > goto error; > -- > 2.25.1 > >
