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

From: Ivan Khoronzhuk <[email-masked]>
Date: Sat, 14 Sep 2019 01:33:13 +0300

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 <[email-masked]>
>> ---
>>   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