On Thu, Feb 26, 2026 at 12:33:40PM -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 <[email protected]>
> ---
> tools/lib/bpf/libbpf.c | 34 ++++++++++++++++++++++++++++------
> 1 file changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
> index 0be7017800fe..0ba8aa2c5fd2 100644
> --- a/tools/lib/bpf/libbpf.c
> +++ b/tools/lib/bpf/libbpf.c
> @@ -12042,6 +12042,20 @@ bpf_program__attach_kprobe_multi_opts(const struct
> bpf_program *prog,
> return libbpf_err_ptr(-EINVAL);
>
> if (pattern) {
> + /*
> + * Exact function name (no wildcards): bypass kallsyms parsing
> + * and pass the symbol directly to the kernel via syms[] array.
> + * The kernel's ftrace_lookup_symbols() resolves it efficiently.
> + */
> + if (!strpbrk(pattern, "*?")) {
> + const char *sym = pattern;
> +
> + syms = &sym;
why not use pattern ndirectly?
> + cnt = 1;
> + pattern = NULL;
not sure why we need this
> + goto attach;
> + }
I wonder we could just another if path and avoid the goto, like:
- if (pattern) {
+ /*
+ * Exact function name (no wildcards): bypass kallsyms parsing
+ * and pass the symbol directly to the kernel via syms[] array.
+ * The kernel's ftrace_lookup_symbols() resolves it efficiently.
+ */
+ if (pattern && !strpbrk(pattern, "*?")) {
+ syms = &pattern;
+ cnt = 1;
+ } else if (pattern) {
if (has_available_filter_functions_addrs())
err = libbpf_available_kprobes_parse(&res);
wdyt?
> +
> if (has_available_filter_functions_addrs())
> err = libbpf_available_kprobes_parse(&res);
> else
> @@ -12060,6 +12074,7 @@ bpf_program__attach_kprobe_multi_opts(const struct
> bpf_program *prog,
> cnt = res.cnt;
> }
>
> +attach:
> retprobe = OPTS_GET(opts, retprobe, false);
> session = OPTS_GET(opts, session, false);
>
> @@ -12067,7 +12082,6 @@ bpf_program__attach_kprobe_multi_opts(const struct
> bpf_program *prog,
> return libbpf_err_ptr(-EINVAL);
>
> attach_type = session ? BPF_TRACE_KPROBE_SESSION :
> BPF_TRACE_KPROBE_MULTI;
> -
not needed
> lopts.kprobe_multi.syms = syms;
> lopts.kprobe_multi.addrs = addrs;
> lopts.kprobe_multi.cookies = cookies;
> @@ -12084,6 +12098,14 @@ bpf_program__attach_kprobe_multi_opts(const struct
> bpf_program *prog,
> link_fd = bpf_link_create(prog_fd, 0, attach_type, &lopts);
> if (link_fd < 0) {
> err = -errno;
> + /*
> + * Normalize error code: when exact name bypasses kallsyms
> + * parsing, kernel returns ESRCH from ftrace_lookup_symbols().
> + * Convert to ENOENT for API consistency with the pattern
> + * matching path which returns ENOENT from userspace.
> + */
> + if (err == -ESRCH)
> + err = -ENOENT;
> pr_warn("prog '%s': failed to attach: %s\n",
> prog->name, errstr(err));
> goto error;
> @@ -12192,7 +12214,7 @@ 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;
I don't think we need the change, it's jus for the different pr_warn
below right? let's keep pattern
thanks,
jirka
> int n;
>
> *link = NULL;
> @@ -12202,14 +12224,14 @@ 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);
> + *link = bpf_program__attach_kprobe_multi_opts(prog, func_name, &opts);
> + free(func_name);
> return *link ? 0 : -errno;
> }
>
> --
> 2.34.1
>
