Re: [PATCH bpf-next 10/11] libbpf: makefile: add C/CXX/LDFLAGS to libbpf.so and test_libpf targets

[Ivan Khoronzhuk]

On Fri, Sep 13, 2019 at 09:43:22PM +0000, Yonghong Song wrote:
> On 9/10/19 11:38 AM, Ivan Khoronzhuk wrote:
> > 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(-)
>
> Could you separate this patch into two?
> One of libbpf and another for samples.
>
> The subject 'libbpf: ...' is not entirely accurate.
Yes, ofc.
But there is too many patches already, but better a lot of small
changes then couple huge.

> > 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)|" \

--
Regards,
Ivan Khoronzhuk