[PATCH bpf-next 1/3] samples: bpf: Fix cross-compiling error by using bootstrap bpftool

[Pu Lehui]

Currently, when cross compiling bpf samples, the host side cannot
use arch-specific bpftool to generate vmlinux.h or skeleton. Since
samples/bpf use bpftool for vmlinux.h, skeleton, and static linking
only, we can use lightweight bootstrap version of bpftool to handle
these, and it's always host-native.

Signed-off-by: Pu Lehui <pulehui@xxxxxxxxxx>
Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
---
 samples/bpf/Makefile | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 5002a5b9a7da..57012b8259d2 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -282,12 +282,18 @@ $(LIBBPF): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
 
 BPFTOOLDIR := $(TOOLS_PATH)/bpf/bpftool
 BPFTOOL_OUTPUT := $(abspath $(BPF_SAMPLES_PATH))/bpftool
-BPFTOOL := $(BPFTOOL_OUTPUT)/bpftool
+BPFTOOL := $(BPFTOOL_OUTPUT)/bootstrap/bpftool
+ifeq ($(CROSS_COMPILE),)
 $(BPFTOOL): $(LIBBPF) $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) | $(BPFTOOL_OUTPUT)
-	    $(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../ \
-		OUTPUT=$(BPFTOOL_OUTPUT)/ \
-		LIBBPF_OUTPUT=$(LIBBPF_OUTPUT)/ \
-		LIBBPF_DESTDIR=$(LIBBPF_DESTDIR)/
+	$(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../		\
+		OUTPUT=$(BPFTOOL_OUTPUT)/ 					\
+		LIBBPF_BOOTSTRAP_OUTPUT=$(LIBBPF_OUTPUT)/ 			\
+		LIBBPF_BOOTSTRAP_DESTDIR=$(LIBBPF_DESTDIR)/ bootstrap
+else
+$(BPFTOOL): $(wildcard $(BPFTOOLDIR)/*.[ch] $(BPFTOOLDIR)/Makefile) | $(BPFTOOL_OUTPUT)
+	$(MAKE) -C $(BPFTOOLDIR) srctree=$(BPF_SAMPLES_PATH)/../../ 		\
+		OUTPUT=$(BPFTOOL_OUTPUT)/ bootstrap
+endif
 
 $(LIBBPF_OUTPUT) $(BPFTOOL_OUTPUT):
 	$(call msg,MKDIR,$@)
-- 
2.25.1