Currently the BPF selftests can only be built by using the minimum kernel
configuration defined in tools/testing/selftests/bpf/config*. This poses a
problem in distribution kernels that may have some of the flags disabled or
set as module. For example, we have been running the tests regularly in
openSUSE Tumbleweed [1] [2] but to work around this fact we created a
special package [3] that build the tests against an auxiliary vmlinux with
the BPF Kconfig. We keep a list of known issues that may happen due to,
amongst other things, configuration mismatches [4] [5].

The maintenance of this package is far from ideal, especially for
enterprise kernels. The goal of this series is to enable the common usecase
of running the following in any system:

```sh
make -C tools/testing/selftests install \
        SKIP_TARGETS= \
        TARGETS=bpf \
        O=/lib/modules/$(uname -r)/build
```

As an example, the following script targeting a minimal config can be used
for testing:

```sh
make defconfig
scripts/config --file .config \
               --enable DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT \
               --enable DEBUG_INFO_BTF \
               --enable BPF_SYSCALL \
               --enable BPF_JIT
make olddefconfig
make -j$(nproc)
make -j$(nproc) -C tools/testing/selftests SKIP_TARGETS= TARGETS=bpf install
```

This produces a test_progs binary with 579 subtests, against the total of
708. Many of them will still fail or be skipped at runtime due to lack of
symbols, but at least there will be a clear way of building the tests.

[1]: https://openqa.opensuse.org/tests/5811715
[2]: https://openqa.opensuse.org/tests/5811730
[3]: https://src.opensuse.org/rmarliere/kselftests
[4]: https://github.com/openSUSE/kernel-qe/blob/main/kselftests_known_issues.yaml
[5]: https://openqa.opensuse.org/tests/5811730/logfile?filename=run_kselftests-config_mismatches.txt

Assisted-by: {codex,claude}
Signed-off-by: Ricardo B. Marlière <rbm@suse.com>
---
Ricardo B. Marlière (10):
      selftests/bpf: Fall back to distro build directory for test_kmods
      selftests/bpf: Tolerate BPF and skeleton generation failures
      selftests/bpf: Avoid rebuilds when running emit_tests
      selftests/bpf: Make skeleton headers order-only prerequisites of .test.d
      selftests/bpf: Tolerate test file compilation failures
      selftests/bpf: Allow test_progs to link with a partial object set
      selftests/bpf: Tolerate benchmark build failures
      selftests/bpf: Provide weak definitions for cross-test uprobe functions
      selftests/bpf: Skip tests whose objects were not built
      selftests/bpf: Tolerate missing files during install

 tools/testing/selftests/bpf/Makefile               | 107 ++++++++++++++-------
 .../testing/selftests/bpf/prog_tests/bpf_cookie.c  |  11 ++-
 tools/testing/selftests/bpf/test_kmods/Makefile    |   6 +-
 tools/testing/selftests/bpf/test_progs.c           |   7 +-
 4 files changed, 88 insertions(+), 43 deletions(-)
---
base-commit: 0eeb0094ba0321f0927806857b5f01c1577bc245
change-id: 20260401-selftests-bpf_misconfig-4c33ef5c56da

Best regards,
--  
Ricardo B. Marlière <rbm@suse.com>