[PATCH bpf-next v3 12/14] bpf: Pull tools/build/feature biz into selftests Makefile

[Brendan Jackman]

This is somewhat cargo-culted from the libbpf build. It will be used
in a subsequent patch to query for Clang BPF atomics support.

Change-Id: I9318a1702170eb752acced35acbb33f45126c44c
Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
---
 tools/testing/selftests/bpf/.gitignore |  1 +
 tools/testing/selftests/bpf/Makefile   | 38 ++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
index 395ae040ce1f..3c604dff1e20 100644
--- a/tools/testing/selftests/bpf/.gitignore
+++ b/tools/testing/selftests/bpf/.gitignore
@@ -35,3 +35,4 @@ test_cpp
 /tools
 /runqslower
 /bench
+/FEATURE-DUMP.selftests.bpf
diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
index 894192c319fb..f21c4841a612 100644
--- a/tools/testing/selftests/bpf/Makefile
+++ b/tools/testing/selftests/bpf/Makefile
@@ -104,8 +104,46 @@ OVERRIDE_TARGETS := 1
 override define CLEAN
 	$(call msg,CLEAN)
 	$(Q)$(RM) -r $(TEST_GEN_PROGS) $(TEST_GEN_PROGS_EXTENDED) $(TEST_GEN_FILES) $(EXTRA_CLEAN)
+	$(Q)$(RM) $(OUTPUT)/FEATURE-DUMP.selftests.bpf
 endef
 
+# This will work when bpf is built in tools env. where srctree
+# isn't set and when invoked from selftests build, where srctree
+# is set to ".". building_out_of_srctree is undefined for in srctree
+# builds
+ifeq ($(srctree),)
+update_srctree := 1
+endif
+ifdef building_out_of_srctree
+update_srctree := 1
+endif
+ifeq ($(update_srctree),1)
+srctree := $(patsubst %/,%,$(dir $(CURDIR)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+srctree := $(patsubst %/,%,$(dir $(srctree)))
+endif
+
+FEATURE_USER = .selftests.bpf
+FEATURE_TESTS = clang-bpf-atomics
+FEATURE_DISPLAY = clang-bpf-atomics
+
+check_feat := 1
+NON_CHECK_FEAT_TARGETS := clean
+ifdef MAKECMDGOALS
+ifeq ($(filter-out $(NON_CHECK_FEAT_TARGETS),$(MAKECMDGOALS)),)
+  check_feat := 0
+endif
+endif
+
+ifeq ($(check_feat),1)
+ifeq ($(FEATURES_DUMP),)
+include $(srctree)/tools/build/Makefile.feature
+else
+include $(FEATURES_DUMP)
+endif
+endif
+
 include ../lib.mk
 
 SCRATCH_DIR := $(OUTPUT)/tools
-- 
2.29.2.454.gaff20da3a2-goog