The .test.d dependency files are generated by the C preprocessor and list the headers each test file actually #includes. Skeleton headers appear in those generated lists, so the .test.o -> .skel.h dependency is already tracked by the .d file content.
Making skeletons order-only prerequisites of .test.d means that a missing or skipped skeleton does not prevent .test.d generation, and regenerating a skeleton does not force .test.d to be recreated. This avoids unnecessary recompilation and, more importantly, avoids build errors when a skeleton was intentionally skipped due to a BPF compilation failure. $$(BPFOBJ) is intentionally kept as a normal prerequisite: a libbpf rebuild legitimately invalidates .test.d, since libbpf header changes can affect the headers .test.o sees. Only the skeleton headers are moved to order-only. Note that adding a new BPF skeleton via a modified existing local header still works correctly: GNU make builds order-only prerequisites that do not exist (the order-only qualifier only suppresses timestamp-driven rebuilds, not existence-driven builds), so a brand-new .skel.h listed in TRUNNER_BPF_SKELS is generated even when .test.d is otherwise up to date. The modified local header invalidates .test.o through the previously included .d content, forcing a recompile that regenerates .test.d with the new .skel.h dependency captured by gcc -MMD. Signed-off-by: Ricardo B. Marlière <[email protected]> --- tools/testing/selftests/bpf/Makefile | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile index 9a4d8bea0c18..608e6dff0392 100644 --- a/tools/testing/selftests/bpf/Makefile +++ b/tools/testing/selftests/bpf/Makefile @@ -726,11 +726,11 @@ $(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o: \ $(TRUNNER_TEST_OBJS:.o=.d): $(TRUNNER_OUTPUT)/%.test.d: \ $(TRUNNER_TESTS_DIR)/%.c \ $(TRUNNER_EXTRA_HDRS) \ + $$(BPFOBJ) | $(TRUNNER_OUTPUT) \ $(TRUNNER_BPF_SKELS) \ $(TRUNNER_BPF_LSKELS) \ $(TRUNNER_BPF_LSKELS_SIGNED) \ - $(TRUNNER_BPF_SKELS_LINKED) \ - $$(BPFOBJ) | $(TRUNNER_OUTPUT) + $(TRUNNER_BPF_SKELS_LINKED) ifeq ($(filter clean docs-clean emit_tests,$(MAKECMDGOALS)),) include $(wildcard $(TRUNNER_TEST_OBJS:.o=.d)) -- 2.54.0
