selftests, bpf: Fix makefile dependencies on libbpf

When building bpf selftest with make -j, I'm randomly getting build failures
such as this one:

  In file included from progs/bpf_flow.c:19:
  [...]/tools/testing/selftests/bpf/tools/include/bpf/bpf_helpers.h:11:10: fatal error: 'bpf_helper_defs.h' file not found
  #include "bpf_helper_defs.h"
           ^~~~~~~~~~~~~~~~~~~

The file that fails the build varies between runs but it's always in the
progs/ subdir.

The reason is a missing make dependency on libbpf for the .o files in
progs/. There was a dependency before commit a3a7627d1c522 but that commit
removed it to prevent unneeded rebuilds. However, that only works if libbpf
has been built already; the 'wildcard' prerequisite does not trigger when
there's no bpf_helper_defs.h generated yet.

Keep the libbpf as an order-only prerequisite to satisfy both goals. It is
always built before the progs/ objects but it does not trigger unnecessary
rebuilds by itself.

Fixes: a3a7627d1c522 ("selftests/bpf: BPF object files should depend only on libbpf headers")
Signed-off-by: Jiri Benc <jbenc@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/ee84ab66436fba05a197f952af23c98d90eb6243.1632758415.git.jbenc@redhat.com

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 866531c08e4f9da1e892b1c7cd15e24552774b81..799b88152e9e8d95fbd89da55f77a7b3247aba65 100644 (file)
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -375,7 +375,8 @@ $(TRUNNER_BPF_OBJS): $(TRUNNER_OUTPUT)/%.o:                         \
                     $(TRUNNER_BPF_PROGS_DIR)/%.c                       \
                     $(TRUNNER_BPF_PROGS_DIR)/*.h                       \
                     $$(INCLUDE_DIR)/vmlinux.h                          \
-                    $(wildcard $(BPFDIR)/bpf_*.h) | $(TRUNNER_OUTPUT)
+                    $(wildcard $(BPFDIR)/bpf_*.h)                      \
+                    | $(TRUNNER_OUTPUT) $$(BPFOBJ)
        $$(call $(TRUNNER_BPF_BUILD_RULE),$$<,$$@,                      \
                                          $(TRUNNER_BPF_CFLAGS))