[RFC PATCH bpf-next v3 0/3] Optimize kprobe.session attachment for exact function names

When libbpf attaches kprobe.session programs with exact function names
(the common case: SEC("kprobe.session/vfs_read")), the current code path
has two independent performance bottlenecks:

1. Userspace (libbpf): attach_kprobe_session() always parses
/proc/kallsyms to resolve function names, even when the name is exact
(no wildcards).  This takes ~150ms per function.

2. Kernel (ftrace): ftrace_lookup_symbols() does a full O(N) linear scan
over ~200K kernel symbols via kallsyms_on_each_symbol(), decompressing
every symbol name, even when resolving a single symbol (cnt == 1).

This series optimizes both layers:

- Patch 1: libbpf detects exact function names (no wildcards) in
bpf_program__attach_kprobe_multi_opts() and bypasses kallsyms parsing,
passing the symbol directly to the kernel via syms[] array.
ESRCH is normalized to ENOENT for API consistency.

- Patch 2: ftrace_lookup_symbols() uses kallsyms_lookup_name() for
O(log N) binary search when cnt == 1, with fallback to linear scan for
duplicate symbols. Included here for context; this patch is destined
for the tracing tree via linux-trace-kernel (Steven Rostedt).

- Patch 3: Selftests validating exact-name attachment via
kprobe_multi_session.c and error consistency between wildcard and exact
paths in test_attach_api_fails.

Changes since v2 [2]:
- Use if/else-if instead of goto (Jiri Olsa)
- Use syms = &pattern directly (Jiri Olsa)
- Drop unneeded pattern = NULL (Jiri Olsa)
- Revert cosmetic rename in attach_kprobe_session (Jiri Olsa)
- Remove "module symbols" from ftrace comment (CI bot)

Changes since v1 [1]:
- Move optimization into attach_kprobe_multi_opts (Jiri Olsa)
- Use ftrace_location as boolean check only (Jiri Olsa)
- Remove verbose perf rationale from comment (Steven Rostedt)
- Consolidate tests into existing subtests (Jiri Olsa)
- Delete standalone _syms.c and _errors.c files

[1] https://lore.kernel.org/bpf/20260223215113.924599-1-andrey.grodzovsky@crowdstrike.com/ (local)
[2] https://lore.kernel.org/bpf/20260226173342.3565919-1-andrey.grodzovsky@crowdstrike.com/ (local)

Andrey Grodzovsky (3):
  libbpf: Optimize kprobe.session attachment for exact function names
  ftrace: Use kallsyms binary search for single-symbol lookup
  selftests/bpf: add tests for kprobe.session optimization

 kernel/trace/ftrace.c                         | 22 +++++++++++++
 tools/lib/bpf/libbpf.c                        | 18 +++++++++-
 .../bpf/prog_tests/kprobe_multi_test.c        | 33 +++++++++++++++++--
 .../bpf/progs/kprobe_multi_session.c          | 10 ++++++
 4 files changed, 80 insertions(+), 3 deletions(-)

-- 
2.34.1