[PATCH net-next v6 4/5] selftests/net: Add a shared BPF skeleton rule

[Bochao Cao via B4 Relay]

From: Bochao Cao <bochaolucky@xxxxxxxxx>

Add a shared skeleton rule and build host bpftool when BPFTOOL is not
supplied. Use host CC/LD and absolute source paths in submakes.

Pass KHDR_INCLUDES to the BPF compiler without overriding it with
source-tree headers. Generate the skeleton through a temporary file.

Tested normal and separate-output builds, inherited relative srctree,
and host bootstrap with unusable target CC/LD. A conflicting source
header no longer overrides the installed header.

Signed-off-by: Bochao Cao <bochaolucky@xxxxxxxxx>
---
 tools/testing/selftests/net/bpf.mk | 33 +++++++++++++++++++++++++++++++--
 1 file changed, 31 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/net/bpf.mk b/tools/testing/selftests/net/bpf.mk
index a4f6755dd8941..016e32960280a 100644
--- a/tools/testing/selftests/net/bpf.mk
+++ b/tools/testing/selftests/net/bpf.mk
@@ -4,12 +4,12 @@ CLANG ?= clang
 SCRATCH_DIR := $(OUTPUT)/tools
 BUILD_DIR := $(SCRATCH_DIR)/build
 BPFDIR := $(top_srcdir)/tools/lib/bpf
 APIDIR := $(top_srcdir)/tools/include/uapi
 
+CCINCLUDE += $(KHDR_INCLUDES)
 CCINCLUDE += -I$(selfdir)/bpf
-CCINCLUDE += -I$(top_srcdir)/usr/include/
 CCINCLUDE += -I$(SCRATCH_DIR)/include
 
 BPFOBJ := $(BUILD_DIR)/libbpf/libbpf.a
 
 MAKE_DIRS := $(BUILD_DIR)/libbpf
@@ -44,10 +44,39 @@ $(BPF_PROG_OBJS): $(OUTPUT)/%.o : %.c $(BPFOBJ) | $(MAKE_DIRS)
 
 $(BPFOBJ): $(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)		       \
 	   $(APIDIR)/linux/bpf.h					       \
 	   | $(BUILD_DIR)/libbpf
 	$(call msg,MAKE,,$@)
-	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) OUTPUT=$(BUILD_DIR)/libbpf/ \
+	$(Q)$(MAKE) $(submake_extras) -C $(BPFDIR) srctree=$(abspath $(top_srcdir)) \
+		    OUTPUT=$(BUILD_DIR)/libbpf/ \
 		    EXTRA_CFLAGS='-g -O0'				       \
 		    DESTDIR=$(SCRATCH_DIR) prefix= all install_headers
 
 EXTRA_CLEAN += $(SCRATCH_DIR)
+
+# Build a host bpftool only when a test needs a generated skeleton.
+HOSTCC ?= gcc
+HOSTLD ?= ld
+BPFTOOL_BUILD := $(BUILD_DIR)/bpftool
+ifeq ($(origin BPFTOOL),undefined)
+BPFTOOL := $(BPFTOOL_BUILD)/bootstrap/bpftool
+BPFTOOL_DEP := $(BPFTOOL)
+else
+BPFTOOL_DEP := $(shell command -v $(BPFTOOL))
+endif
+
+$(BPFTOOL_BUILD)/bootstrap/bpftool: \
+	$(wildcard $(top_srcdir)/tools/bpf/bpftool/*.[ch]) \
+	$(top_srcdir)/tools/bpf/bpftool/Makefile \
+	$(wildcard $(BPFDIR)/*.[ch] $(BPFDIR)/Makefile)
+	$(call msg,MAKE,,$@)
+	$(Q)mkdir -p $(BPFTOOL_BUILD)
+	$(Q)$(MAKE) $(submake_extras) -C $(top_srcdir)/tools/bpf/bpftool \
+		OUTPUT=$(BPFTOOL_BUILD)/ srctree=$(abspath $(top_srcdir)) \
+		ARCH= CROSS_COMPILE= CC="$(HOSTCC)" LD="$(HOSTLD)" bootstrap
+
+$(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o $(BPFTOOL_DEP)
+	$(call msg,GEN-SKEL,,$@)
+	$(Q)$(BPFTOOL) gen skeleton $< name $(notdir $*) > $@.tmp
+	$(Q)mv $@.tmp $@
+
+EXTRA_CLEAN += $(wildcard $(OUTPUT)/*.skel.h $(OUTPUT)/*.skel.h.tmp)

-- 
Git-155)