On Fri, May 26, 2023 at 11:50:26PM +0800, Jackie Liu 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 check first, if failed, fallback to > kallsyms. > > Here is the test eBPF program [1]. > [1] https://github.com/JackieLiu1/ketones/commit/a9e76d1ba57390e533b8b3eadde97f7a4535e867 > > Suggested-by: Jiri Olsa <olsajiri@xxxxxxxxx> > Signed-off-by: Jackie Liu <liuyun01@xxxxxxxxxx> > --- > tools/lib/bpf/libbpf.c | 100 ++++++++++++++++++++++++++++++++++++++--- > 1 file changed, 93 insertions(+), 7 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index ad1ec893b41b..0914b7e98e30 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -10106,6 +10106,12 @@ static const char *tracefs_uprobe_events(void) > return use_debugfs() ? DEBUGFS"/uprobe_events" : TRACEFS"/uprobe_events"; > } > > +static const char *tracefs_available_filter_functions(void) > +{ > + return use_debugfs() ? DEBUGFS"/available_filter_functions" : > + TRACEFS"/available_filter_functions"; > +} > + > static void gen_kprobe_legacy_event_name(char *buf, size_t buf_sz, > const char *kfunc_name, size_t offset) > { > @@ -10417,13 +10423,14 @@ static bool glob_match(const char *str, const char *pat) > struct kprobe_multi_resolve { > const char *pattern; > unsigned long *addrs; > + const char **syms; > size_t cap; > size_t cnt; > }; > > static int > -resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > - const char *sym_name, void *ctx) > +kallsyms_resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > + const char *sym_name, void *ctx) > { > struct kprobe_multi_resolve *res = ctx; > int err; > @@ -10440,6 +10447,77 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > return 0; > } > > +static int ftrace_resolve_kprobe_multi_cb(const char *sym_name, void *ctx) > +{ > + struct kprobe_multi_resolve *res = ctx; > + int err; > + char *name; > + > + if (!glob_match(sym_name, res->pattern)) > + return 0; > + > + err = libbpf_ensure_mem((void **) &res->syms, &res->cap, > + sizeof(const char *), res->cnt + 1); > + if (err) > + return err; > + > + name = strdup(sym_name); > + if (!name) > + return -errno; > + > + res->syms[res->cnt++] = name; > + return 0; > +} > + > +typedef int (*available_kprobe_cb_t)(const char *sym_name, void *ctx); > + > +static int > +libbpf_available_kprobes_parse(available_kprobe_cb_t cb, void *ctx) > +{ > + char sym_name[256]; > + FILE *f; > + int ret, err = 0; > + const char *available_path = tracefs_available_filter_functions(); > + > + f = fopen(available_path, "r"); > + if (!f) { > + err = -errno; > + pr_warn("failed to open %s, fallback to /proc/kallsyms.\n", > + available_path); > + return err; > + } > + > + while (true) { > + ret = fscanf(f, "%255s%*[^\n]\n", sym_name); > + if (ret == EOF && feof(f)) > + break; > + if (ret != 1) { > + pr_warn("failed to read available kprobe entry: %d\n", > + ret); > + err = -EINVAL; > + break; > + } > + > + err = cb(sym_name, ctx); > + if (err) > + break; > + } > + > + fclose(f); > + return err; > +} > + > +static void kprobe_multi_resolve_free(struct kprobe_multi_resolve *res) > +{ > + while (res->syms && res->cnt) > + free((char *)res->syms[--res->cnt]); > + > + free(res->syms); > + free(res->addrs); I think we also need to zero the res->syms pointer, so the final kprobe_multi_resolve_free won't try to release it again perhaps use zfree for both syms and addrs other than this it looks ok to me: Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx> thanks, jirka > + /* reset cap to zero, when fallback */ > + res->cap = 0; > +} > + > struct bpf_link * > bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, > const char *pattern, > @@ -10476,13 +10554,21 @@ 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_free(&res); > + err = libbpf_kallsyms_parse(kallsyms_resolve_kprobe_multi_cb, > + &res); > + if (err) > + goto error; > + } > if (!res.cnt) { > err = -ENOENT; > goto error; > } > + syms = res.syms; > addrs = res.addrs; > cnt = res.cnt; > } > @@ -10511,12 +10597,12 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, > goto error; > } > link->fd = link_fd; > - free(res.addrs); > + kprobe_multi_resolve_free(&res); > return link; > > error: > free(link); > - free(res.addrs); > + kprobe_multi_resolve_free(&res); > return libbpf_err_ptr(err); > } > > -- > 2.25.1 >
