selftests/bpf: Run resolve_btfids only for relevant .test.o objects

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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Tested-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/bpf/20251219181825.1289460-2-ihor.solodrai@linux.dev

diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 4aa60e83ff191a9664c3e4c3d315e4310b0c3c0b..ffd0a4c354c74debb3a81ec7a88665cead00a5fe 100644 (file)
--- 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