[PATCH bpf-next v4 7/8] selftests/bpf: Run resolve_btfids only for relevant .test.o objects

[Ihor Solodrai <ihor.solodrai@linux.dev>]

A selftest targeting resolve_btfids functionality relies on a resolved
.BTF_ids section to be available in the TRUNNER_BINARY. The underlying
BTF data is taken from a special BPF program (btf_data.c), and so
resolve_btfids is executed as a part of a TRUNNER_BINARY build recipe
on the final binary.

Subsequent patches in this series allow resolve_btfids to modify BTF
before resolving the symbols, which means that the test needs access
to that modified BTF [1]. Currently the test simply reads in
btf_data.bpf.o on the assumption that BTF hasn't changed.

Implement resolve_btfids call only for particular test objects (just
resolve_btfids.test.o for now). The test objects are linked into the
TRUNNER_BINARY, and so .BTF_ids section will be available there.

This will make it trivial for the resolve_btfids test to access BTF
modified by resolve_btfids.

[1] https://lore.kernel.org/bpf/CAErzpmvsgSDe-QcWH8SFFErL6y3p3zrqNri5-UHJ9iK2ChyiBw@mail.gmail.com/

Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
---
 tools/testing/selftests/bpf/Makefile | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 4aa60e83ff19..ffd0a4c354c7 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -643,6 +643,9 @@ $(TRUNNER_TESTS_HDR): $(TRUNNER_TESTS_DIR)/*.c
 		 ) > $$@)
 endif
 
+$(TRUNNER_OUTPUT)/resolve_btfids.test.o: $(RESOLVE_BTFIDS) $(TRUNNER_OUTPUT)/btf_data.bpf.o
+$(TRUNNER_OUTPUT)/resolve_btfids.test.o: private TEST_NEEDS_BTFIDS = 1
+
 # compile individual test files
 # Note: we cd into output directory to ensure embedded BPF object is found
 $(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o:			\
@@ -650,6 +653,9 @@ $(TRUNNER_TEST_OBJS): $(TRUNNER_OUTPUT)/%.test.o:			\
 		      | $(TRUNNER_OUTPUT)/%.test.d
 	$$(call msg,TEST-OBJ,$(TRUNNER_BINARY),$$@)
 	$(Q)cd $$(@D) && $$(CC) -I. $$(CFLAGS) -MMD -MT $$@ -c $(CURDIR)/$$< $$(LDLIBS) -o $$(@F)
+	$$(if $$(TEST_NEEDS_BTFIDS),					\
+		$$(call msg,BTFIDS,$(TRUNNER_BINARY),$$@)		\
+		$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@)
 
 $(TRUNNER_TEST_OBJS:.o=.d): $(TRUNNER_OUTPUT)/%.test.d:			\
 			    $(TRUNNER_TESTS_DIR)/%.c			\
@@ -695,13 +701,11 @@ $(OUTPUT)/$(TRUNNER_BINARY): | $(TRUNNER_BPF_OBJS)
 $(OUTPUT)/$(TRUNNER_BINARY): $(TRUNNER_TEST_OBJS)			\
 			     $(TRUNNER_EXTRA_OBJS) $$(BPFOBJ)		\
 			     $(TRUNNER_LIB_OBJS)			\
-			     $(RESOLVE_BTFIDS)				\
 			     $(TRUNNER_BPFTOOL)				\
 			     $(OUTPUT)/veristat				\
 			     | $(TRUNNER_BINARY)-extras
 	$$(call msg,BINARY,,$$@)
 	$(Q)$$(CC) $$(CFLAGS) $$(filter %.a %.o,$$^) $$(LDLIBS) $$(LLVM_LDLIBS) $$(LDFLAGS) $$(LLVM_LDFLAGS) -o $$@
-	$(Q)$(RESOLVE_BTFIDS) --btf $(TRUNNER_OUTPUT)/btf_data.bpf.o $$@
 	$(Q)ln -sf $(if $2,..,.)/tools/build/bpftool/$(USE_BOOTSTRAP)bpftool \
 		   $(OUTPUT)/$(if $2,$2/)bpftool
 
-- 
2.52.0