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libbpf: Optimize kprobe.session attachment for exact function names

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Detect exact function names (no wildcards) in
bpf_program__attach_kprobe_multi_opts() and bypass kallsyms parsing,
passing the symbol directly to the kernel via syms[] array.  This
benefits all callers, not just kprobe.session.

When the pattern contains no '*' or '?' characters, set syms to point
directly at the pattern string and cnt to 1, skipping the expensive
/proc/kallsyms or available_filter_functions parsing (~150ms per
function).

Error code normalization: the fast path returns ESRCH from kernel's
ftrace_lookup_symbols(), while the slow path returns ENOENT from
userspace kallsyms parsing.  Convert ESRCH to ENOENT in the
bpf_link_create error path to maintain API consistency - both paths
now return identical error codes for "symbol not found".

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@crowdstrike.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260302200837.317907-2-andrey.grodzovsky@crowdstrike.com
This commit is contained in:
Andrey Grodzovsky
2026-03-02 15:08:35 -05:00
committed by Andrii Nakryiko
parent ddb0c14f1b
commit e08da3014b
1 changed files with 18 additions and 1 deletions
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19
src/libbpf.c
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@@ -12041,7 +12041,16 @@ bpf_program__attach_kprobe_multi_opts(const struct bpf_program *prog,
if (addrs && syms)
return libbpf_err_ptr(-EINVAL);
if (pattern) {
/*
* Exact function name (no wildcards) without unique_match:
* bypass kallsyms parsing and pass the symbol directly to the
* kernel via syms[] array. When unique_match is set, fall
* through to the slow path which detects duplicate symbols.
*/
if (pattern && !strpbrk(pattern, "*?") && !unique_match) {
syms = &pattern;
cnt = 1;
} else if (pattern) {
if (has_available_filter_functions_addrs())
err = libbpf_available_kprobes_parse(&res);
else
@@ -12084,6 +12093,14 @@ 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;