Merge branch 'veristat: add better support of freplace programs'

Andrii Nakryiko says:

====================

Teach veristat how to deal with freplace BPF programs. As they can't be
directly loaded by veristat without custom user-space part that sets correct
target program FD, veristat always fails freplace programs. This patch set
teaches veristat to guess target program type that will be inherited by
freplace program itself, and subtitute it for BPF_PROG_TYPE_EXT (freplace) one
for the purposes of BPF verification.

Patch #1 fixes bug in libbpf preventing overriding freplace with specific
program type.

Patch #2 adds convenient -d flag to request veristat to emit libbpf debug
logs. It help debugging why a specific BPF program fails to load, if the
problem is not due to BPF verification itself.

v3->v4:
  - fix optional kern_name check when guessing prog type (Alexei);
v2->v3:
  - fix bpf_obj_id selftest that uses legacy bpf_prog_test_load() helper,
    which always sets program type programmatically; teach the helper to do it
    only if actually necessary (Stanislav);
v1->v2:
  - fix compilation error reported by old GCC (my GCC v11 doesn't produce even
    a warning) and Clang (see CI failure at [0]):

GCC version:

  veristat.c: In function ‘fixup_obj’:
  veristat.c:908:1: error: label at end of compound statement
    908 | skip_freplace_fixup:
        | ^~~~~~~~~~~~~~~~~~~

Clang version:

  veristat.c:909:1: error: label at end of compound statement is a C2x extension [-Werror,-Wc2x-extensions]
  }
  ^
  1 error generated.

  [0] https://github.com/kernel-patches/bpf/actions/runs/4515972059/jobs/7953845335
====================

Acked-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>