[PATCH v3 bpf-next 11/14] libbpf: makefile: add C/CXX/LDFLAGS to libbpf.so and test_libpf targets

[Ivan Khoronzhuk]

In case of LDFLAGS and EXTRA_CC/CXX flags there is no way to pass them
correctly to build command, for instance when --sysroot is used or
external libraries are used, like -lelf, wich can be absent in
toolchain. This can be used for samples/bpf cross-compiling allowing
to get elf lib from sysroot.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
---
 tools/lib/bpf/Makefile | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index c6f94cffe06e..bccfa556ef4e 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -94,6 +94,10 @@ else
   CFLAGS := -g -Wall
 endif
 
+ifdef EXTRA_CXXFLAGS
+  CXXFLAGS := $(EXTRA_CXXFLAGS)
+endif
+
 ifeq ($(feature-libelf-mmap), 1)
   override CFLAGS += -DHAVE_LIBELF_MMAP_SUPPORT
 endif
@@ -176,8 +180,9 @@ $(BPF_IN): force elfdep bpfdep
 $(OUTPUT)libbpf.so: $(OUTPUT)libbpf.so.$(LIBBPF_VERSION)
 
 $(OUTPUT)libbpf.so.$(LIBBPF_VERSION): $(BPF_IN)
-	$(QUIET_LINK)$(CC) --shared -Wl,-soname,libbpf.so.$(LIBBPF_MAJOR_VERSION) \
-				    -Wl,--version-script=$(VERSION_SCRIPT) $^ -lelf -o $@
+	$(QUIET_LINK)$(CC) $(LDFLAGS) \
+		--shared -Wl,-soname,libbpf.so.$(LIBBPF_MAJOR_VERSION) \
+		-Wl,--version-script=$(VERSION_SCRIPT) $^ -lelf -o $@
 	@ln -sf $(@F) $(OUTPUT)libbpf.so
 	@ln -sf $(@F) $(OUTPUT)libbpf.so.$(LIBBPF_MAJOR_VERSION)
 
@@ -185,7 +190,7 @@ $(OUTPUT)libbpf.a: $(BPF_IN)
 	$(QUIET_LINK)$(RM) $@; $(AR) rcs $@ $^
 
 $(OUTPUT)test_libbpf: test_libbpf.cpp $(OUTPUT)libbpf.a
-	$(QUIET_LINK)$(CXX) $(INCLUDES) $^ -lelf -o $@
+	$(QUIET_LINK)$(CXX) $(CXXFLAGS) $(LDFLAGS) $(INCLUDES) $^ -lelf -o $@
 
 $(OUTPUT)libbpf.pc:
 	$(QUIET_GEN)sed -e "s|@PREFIX@|$(prefix)|" \
-- 
2.17.1