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

From: Yonghong Song <yhs@fb.com>
To: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>,
	"ast@kernel.org" <ast@kernel.org>,
	"daniel@iogearbox.net" <daniel@iogearbox.net>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"jakub.kicinski@netronome.com" <jakub.kicinski@netronome.com>,
	"hawk@kernel.org" <hawk@kernel.org>,
	"john.fastabend@gmail.com" <john.fastabend@gmail.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"clang-built-linux@googlegroups.com" 
	<clang-built-linux@googlegroups.com>
Subject: Re: [PATCH bpf-next 10/11] libbpf: makefile: add C/CXX/LDFLAGS to libbpf.so and test_libpf targets
Date: Fri, 13 Sep 2019 21:43:22 +0000	[thread overview]
Message-ID: <0ad42019-2614-b70c-f93e-527c136bba83@fb.com> (raw)
In-Reply-To: <20190910103830.20794-11-ivan.khoronzhuk@linaro.org>

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@linaro.org>
> ---
>   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.

> 
> 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)|" \
> 