[PATCH bpf-next v3 0/3] selftests/bpf: Improve building with extra

[Viktor Malik <vmalik@redhat.com>]

When trying to build BPF selftests with additional compiler and linker
flags, we're running into multiple problems. This series addresses all
of them:

- CFLAGS are not passed to sub-makes of bpftool and libbpf. This is a
  problem when compiling with PIE as libbpf.a ends up being non-PIE and
  cannot be linked with other binaries (patch #1).

- bpftool Makefile runs `llvm-config --cflags` and appends the result to
  CFLAGS. The result typically contains `-D_GNU_SOURCE` which may be
  already set in CFLAGS. That causes a compilation error (patch #2).

- Some GCC flags are not supported by Clang but there are binaries which
  are always built with Clang but reuse user-defined CFLAGS. When CFLAGS
  contain such flags, compilation fails (patch #3).

Changelog:
----------
v2 -> v3:
- resolve conflicts between patch #1 and 4192bb294f80 ("selftests/bpf:
  Provide a generic [un]load_module helper")
- add Quentin's and Jiri's acks for patches #2 and #3

v1 -> v2:
- cover forgotten case in patch#1 (noted by Eduard)
- remove -D_GNU_SOURCE unconditionally in patch#2 (suggested by Andrii)
- rewrite patch#3 to just add -Wno-unused-command-line-argument
  (suggested by Andrii)

Viktor Malik (3):
  selftests/bpf: Allow building with extra flags
  bpftool: Prevent setting duplicate _GNU_SOURCE in Makefile
  selftests/bpf: Disable warnings on unused flags for Clang builds

 tools/bpf/bpftool/Makefile           |  6 ++++-
 tools/testing/selftests/bpf/Makefile | 36 +++++++++++++++++++---------
 2 files changed, 30 insertions(+), 12 deletions(-)

-- 
2.47.0