On Wed, May 24, 2023 at 04:41:54PM +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 > > Signed-off-by: Jackie Liu <liuyun01@xxxxxxxxxx> > --- > v1: 0.27s user 5.09s system 99% cpu 5.392 total > v2: 0.37s user 1.54s system 98% cpu 1.947 total > v3: 0.10s user 0.98s system 97% cpu 1.107 total > > I saw that reading available_filter_functions takes 0.98s and kallsyms only > takes 0.12s. There is a big difference in performance between them. > > tools/lib/bpf/libbpf.c | 80 ++++++++++++++++++++++++++++++--- > tools/lib/bpf/libbpf_internal.h | 4 +- > 2 files changed, 77 insertions(+), 7 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index ad1ec893b41b..f3e3c92bdf8a 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -10417,13 +10417,14 @@ 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 +10441,69 @@ resolve_kprobe_multi_cb(unsigned long long sym_addr, char sym_type, > return 0; > } > > +static int resolve_kprobe_multi_cb(const char *sym_name, void *ctx) > +{ > + struct kprobe_multi_resolve *res = ctx; > + int err; > + > + 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; > + > + res->syms[res->cnt++] = strdup(sym_name); we need to check the strdup return value > + return 0; > +} > + > +int libbpf_available_filter_functions_parse(available_filter_functions_cb_t cb, > + void *ctx) might be too long, maybe we could just use 'ftrace' instead, so we'd have: libbpf_ftrace_parse libbpf_kallsyms_parse that might be too terse, but AFAIK we don't parse any other ftrace file > +{ > + char sym_name[256]; > + FILE *f; > + int ret, err = 0; > + > + f = fopen("/sys/kernel/debug/tracing/available_filter_functions", "r"); > + if (!f) { > + pr_warn("failed to open available_filter_functions, fallback to /proc/kallsyms.\n"); > + goto fallback; > + } > + > + while (true) { > + ret = fscanf(f, "%s%*[^\n]\n", sym_name); > + if (ret == EOF && feof(f)) > + break; > + if (ret != 1) { > + pr_warn("failed to read available_filter_functions entry: %d\n", > + ret); > + break; > + } > + > + err = cb(sym_name, ctx); > + if (err) > + break; > + } > + > + fclose(f); > + return err; > + > +fallback: > + return libbpf_kallsyms_parse(kallsyms_resolve_kprobe_multi_cb, ctx); let's do the kallsyms fallback in bpf_program__attach_kprobe_multi_opts, something like: err = libbpf_available_filter_functions_parse(resolve_kprobe_multi_cb, &res); if (err) err = libbpf_kallsyms_parse(kallsyms_resolve_kprobe_multi_cb, &res); if (err) goto error; > +} > + > +static void kprobe_multi_resolve_resource_free(struct kprobe_multi_resolve *res) s/kprobe_multi_resolve_resource_free/kprobe_multi_resolve_free/ > +{ > + if (res->syms) { > + while (res->cnt) > + free((char *)res->syms[--res->cnt]); > + free(res->syms); > + } else { > + free(res->addrs); > + } > +} > + > struct bpf_link * > bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, > const char *pattern, > @@ -10476,14 +10540,18 @@ 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); > + err = libbpf_available_filter_functions_parse(resolve_kprobe_multi_cb, > + &res); > if (err) > goto error; > if (!res.cnt) { > err = -ENOENT; > goto error; > } > - addrs = res.addrs; > + if (res.syms) > + syms = res.syms; > + else > + addrs = res.addrs; this could be just: syms = res.syms; addrs = res.addrs; once (cnt > 0) then we have either syms or addrs defined and the other is NULL > cnt = res.cnt; > } > > @@ -10511,12 +10579,12 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog, > goto error; > } > link->fd = link_fd; > - free(res.addrs); > + kprobe_multi_resolve_resource_free(&res); > return link; > > error: > free(link); > - free(res.addrs); > + kprobe_multi_resolve_resource_free(&res); > return libbpf_err_ptr(err); > } > > diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h > index e4d05662a96c..fdf6b464481f 100644 > --- a/tools/lib/bpf/libbpf_internal.h > +++ b/tools/lib/bpf/libbpf_internal.h > @@ -481,8 +481,10 @@ __s32 btf__find_by_name_kind_own(const struct btf *btf, const char *type_name, > > typedef int (*kallsyms_cb_t)(unsigned long long sym_addr, char sym_type, > const char *sym_name, void *ctx); > - > int libbpf_kallsyms_parse(kallsyms_cb_t cb, void *arg); > +typedef int (*available_filter_functions_cb_t)(const char *sym_name, void *ctx); > +int libbpf_available_filter_functions_parse(available_filter_functions_cb_t cb, > + void *arg); let's kee it static, we don't have any other callers thanks, jirka
