Merge branch 'libbpf-make-optimized-uprobes-backward-compatible'

Merge branch 'libbpf-make-optimized-uprobes-backward-compatible'

Jiri Olsa says:

====================
libbpf: Make optimized uprobes backward compatible

hi,
we can currently optimize uprobes on top of nop5 instructions,
so application can define USDT_NOP to nop5 and use USDT macro
to define optimized usdt probes.

This works fine on new kernels, but could have performance penalty
on older kernels, that do not have the support to optimize and to
emulate nop5 instruction.

This patchset adds support to workaround the performance penalty
on older kernels that do not support uprobe optimization, please
see detailed description in patch 2.

v1: https://lore.kernel.org/bpf/20251117083551.517393-1-jolsa@kernel.org/
v2: https://lore.kernel.org/bpf/20260210133649.524292-1-jolsa@kernel.org/
v3: https://lore.kernel.org/bpf/20260211084858.750950-1-jolsa@kernel.org/T/#t
v4: https://lore.kernel.org/bpf/20260220104220.634154-1-jolsa@kernel.org/

v5 changes:
- keep nop_combo on stack and levae buf uninitialized
  in has_nop_combo function [David]

v4 changes:
- rebased on latest bpf-next/master
- use pread for nop combo read [Andrii]
- renamed usdt triger benchmark names [Andrii]
- added more ip address checks to tests [Andrii]

v3 changes:
- fix __x86_64 define and other typos [CI]
- add missing '?' to usdt trigger program [CI]

v2 changes:
- after more investigation we realized there are some versions of
  bpftrace and stap that does not work with solution suggested in
  version 1, so we decided to switch to following solution:

  - change USDT macro [1] emits nop,nop5 instructions combo by
    default
  - libbpf detects nop,nop5 instructions combo for USDT probe,
    if there is and if uprobe syscall is detected libbpf installs
    usdt probe on top of nop5 instruction to get it optimized

- added usdt trigger benchmarks [Andrii]
- several small fixes on uprobe syscall detection, tests and other places [Andrii]
- true usdt.h source [1] updated [Andrii]
- compile usdt_* objects unconditionally [Andrii]

thanks,
jirka

[1] https://github.com/libbpf/usdt
---
====================

Link: https://patch.msgid.link/20260224103915.1369690-1-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>