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Tue, 24 Feb 2026 05:10:40 -0800 (PST) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Tue, 24 Feb 2026 14:10:37 +0100 To: Andrey Grodzovsky Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, rostedt@goodmis.org, linux-trace-kernel@vger.kernel.org, linux-open-source@crowdstrike.com Subject: Re: [RFC PATCH bpf-next 1/3] libbpf: Optimize kprobe.session attachment for exact function names Message-ID: References: <20260223215113.924599-1-andrey.grodzovsky@crowdstrike.com> <20260223215113.924599-2-andrey.grodzovsky@crowdstrike.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260223215113.924599-2-andrey.grodzovsky@crowdstrike.com> On Mon, Feb 23, 2026 at 04:51:11PM -0500, Andrey Grodzovsky wrote: > Implement dual-path optimization in attach_kprobe_session(): > - Fast path: Use syms[] array for exact function names > (no kallsyms parsing) > - Slow path: Use pattern matching with kallsyms only for > wildcards > > This avoids expensive kallsyms file parsing (~150ms) when function names > are specified exactly, improving attachment time 50x (~3-5ms). > > Error code normalization: The fast path returns ESRCH from kernel's > ftrace_lookup_symbols(), while slow path returns ENOENT from userspace > kallsyms parsing. Convert ESRCH to ENOENT in fast path to maintain API > consistency - both paths now return identical error codes for "symbol > not found". > > Signed-off-by: Andrey Grodzovsky > --- > tools/lib/bpf/libbpf.c | 32 +++++++++++++++++++++++++++----- > 1 file changed, 27 insertions(+), 5 deletions(-) > > diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c > index 0be7017800fe..87a71eab4308 100644 > --- a/tools/lib/bpf/libbpf.c > +++ b/tools/lib/bpf/libbpf.c > @@ -12192,7 +12192,7 @@ static int attach_kprobe_session(const struct bpf_program *prog, long cookie, > { > LIBBPF_OPTS(bpf_kprobe_multi_opts, opts, .session = true); > const char *spec; > - char *pattern; > + char *func_name; > int n; > > *link = NULL; > @@ -12202,14 +12202,36 @@ static int attach_kprobe_session(const struct bpf_program *prog, long cookie, > return 0; > > spec = prog->sec_name + sizeof("kprobe.session/") - 1; > - n = sscanf(spec, "%m[a-zA-Z0-9_.*?]", &pattern); > + n = sscanf(spec, "%m[a-zA-Z0-9_.*?]", &func_name); > if (n < 1) { > - pr_warn("kprobe session pattern is invalid: %s\n", spec); > + pr_warn("kprobe session function name is invalid: %s\n", spec); > return -EINVAL; > } > > - *link = bpf_program__attach_kprobe_multi_opts(prog, pattern, &opts); > - free(pattern); > + /* Check if pattern contains wildcards */ > + if (strpbrk(func_name, "*?")) { > + /* Wildcard pattern - use pattern matching path with kallsyms parsing */ > + *link = bpf_program__attach_kprobe_multi_opts(prog, func_name, &opts); > + } else { > + /* Exact function name - use syms array path (fast, no kallsyms parsing) */ > + const char *syms[1]; > + > + syms[0] = func_name; > + opts.syms = syms; > + opts.cnt = 1; > + *link = bpf_program__attach_kprobe_multi_opts(prog, NULL, &opts); hi, good idea, could we do this directly in bpf_program__attach_kprobe_multi_opts ? seems like it's not drectly related to session jirka > + if (!*link && errno == ESRCH) { > + /* > + * Normalize error code for API consistency: fast path returns ESRCH > + * from kernel's ftrace_lookup_symbols(), while slow path returns ENOENT > + * from userspace kallsyms parsing. Convert ESRCH to ENOENT so both paths > + * return the same error for "symbol not found". > + */ > + errno = ENOENT; > + } > + } > + > + free(func_name); > return *link ? 0 : -errno; > } > > -- > 2.34.1 >