[RFC PATCH bpf-next v5 1/8] selftests/bpf: keep headers off the generic link command line

The generic '$(OUTPUT)/%:%.c' rule links with '$(LINK.c) $^', so
every prerequisite of such a binary lands on the compiler driver's
command line. That only works while none of them is a header: gcc
tolerates a stray .h argument on a link line, but clang treats it as
a request to precompile the header and fails with "cannot specify -o
when generating multiple output files".

Filter headers out of the recipe, with a comment: header
prerequisites on these targets are useful for dependency tracking -
the next patch declares one - and the constraint is easy to
rediscover the hard way.

Signed-off-by: Mykola Lysenko <[email protected]>
---
 tools/testing/selftests/bpf/Makefile | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 55d394438..65c702613 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -258,9 +258,12 @@ $(OUTPUT)/%.o: %.c
 	$(call msg,CC,,$@)
 	$(Q)$(CC) $(CFLAGS) -c $(filter %.c,$^) $(LDLIBS) -o $@
 
+# Headers may appear among the prerequisites for dependency tracking;
+# they must not reach the clang/gcc command line (clang treats a bare .h
+# argument as a precompiled-header job and refuses -o).
 $(OUTPUT)/%:%.c
 	$(call msg,BINARY,,$@)
-	$(Q)$(LINK.c) $^ $(LDLIBS) -o $@
+	$(Q)$(LINK.c) $(filter-out %.h,$^) $(LDLIBS) -o $@
 
 # LLVM's ld.lld doesn't support all the architectures, so use it only on x86
 ifeq ($(SRCARCH),$(filter $(SRCARCH),x86 riscv))
-- 
2.43.0