[PATCH bpf-next 10/11] 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 is used for samples/bpf cross-compiling allowing to
get elf lib from sysroot.

Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@xxxxxxxxxx>
---
 samples/bpf/Makefile   |  8 +++++++-
 tools/lib/bpf/Makefile | 11 ++++++++---
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 79c9aa41832e..4edc5232cfc1 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -186,6 +186,10 @@ ccflags-y += -I$(srctree)/tools/perf
 ccflags-y += $(D_OPTIONS)
 ccflags-y += -Wall
 ccflags-y += -fomit-frame-pointer
+
+EXTRA_CXXFLAGS := $(ccflags-y)
+
+# options not valid for C++
 ccflags-y += -Wmissing-prototypes
 ccflags-y += -Wstrict-prototypes
 
@@ -252,7 +256,9 @@ clean:
 
 $(LIBBPF): FORCE
 # Fix up variables inherited from Kbuild that tools/ build system won't like
-	$(MAKE) -C $(dir $@) RM='rm -rf' LDFLAGS= srctree=$(BPF_SAMPLES_PATH)/../../ O=
+	$(MAKE) -C $(dir $@) RM='rm -rf' EXTRA_CFLAGS="$(PROGS_CFLAGS)" \
+		EXTRA_CXXFLAGS="$(EXTRA_CXXFLAGS)" LDFLAGS=$(PROGS_LDFLAGS) \
+		srctree=$(BPF_SAMPLES_PATH)/../../ O=
 
 $(obj)/syscall_nrs.h:	$(obj)/syscall_nrs.s FORCE
 	$(call filechk,offsets,__SYSCALL_NRS_H__)
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