Re: [PATCH v1] samples/bpf: Fix build out of source tree

From: Anh Tuan Phan <tuananhlfc@gmail.com>
To: Stanislav Fomichev <sdf@google.com>
Cc: daniel@iogearbox.net, martin.lau@linux.dev, ast@kernel.org,
	andrii@kernel.org, bpf@vger.kernel.org,
	linux-kernel-mentees@lists.linuxfoundation.org
Subject: Re: [PATCH v1] samples/bpf: Fix build out of source tree
Date: Sun, 9 Jul 2023 12:12:31 +0700	[thread overview]
Message-ID: <38ff5cf8-0f71-a156-d88b-e3ec74897790@gmail.com> (raw)
In-Reply-To: <ZKcDdIYOUQuPP5Px@google.com>

Adding one more discussion around your previous question that I missed.

On 7/7/23 01:09, Stanislav Fomichev wrote:
> On 07/06, Anh Tuan Phan wrote:
>> This commit fixes a few compilation issues when building out of source
>> tree. The command that I used to build samples/bpf:
>>
>> export KBUILD_OUTPUT=/tmp
>> make V=1 M=samples/bpf
>>
>> The compilation failed since it tried to find the header files in the
>> wrong places between output directory and source tree directory
>>
>> Signed-off-by: Anh Tuan Phan <tuananhlfc@gmail.com>
>> ---
>>  samples/bpf/Makefile        | 8 ++++----
>>  samples/bpf/Makefile.target | 2 +-
>>  2 files changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
>> index 615f24ebc49c..32469aaa82d5 100644
>> --- a/samples/bpf/Makefile
>> +++ b/samples/bpf/Makefile
>> @@ -341,10 +341,10 @@ $(obj)/hbm_edt_kern.o: $(src)/hbm.h $(src)/hbm_kern.h
>>  # Override includes for xdp_sample_user.o because $(srctree)/usr/include in
>>  # TPROGS_CFLAGS causes conflicts
>>  XDP_SAMPLE_CFLAGS += -Wall -O2 \
>> -		     -I$(src)/../../tools/include \
>> +		     -I$(srctree)/tools/include \
> 
> [..]
> 
>>  		     -I$(src)/../../tools/include/uapi \
> 
> Does this $(src) need to be changed as well?
> 
> 
>>  		     -I$(LIBBPF_INCLUDE) \
>> -		     -I$(src)/../../tools/testing/selftests/bpf
>> +		     -I$(srctree)/tools/testing/selftests/bpf
>>
>>  $(obj)/$(XDP_SAMPLE): TPROGS_CFLAGS = $(XDP_SAMPLE_CFLAGS)
>>  $(obj)/$(XDP_SAMPLE): $(src)/xdp_sample_user.h $(src)/xdp_sample_shared.h
>> @@ -393,7 +393,7 @@ $(obj)/xdp_router_ipv4.bpf.o: $(obj)/xdp_sample.bpf.o
>>  $(obj)/%.bpf.o: $(src)/%.bpf.c $(obj)/vmlinux.h $(src)/xdp_sample.bpf.h
>> $(src)/xdp_sample_shared.h
>>  	@echo "  CLANG-BPF " $@
>>  	$(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(SRCARCH) \
>> -		-Wno-compare-distinct-pointer-types -I$(srctree)/include \
>> +		-Wno-compare-distinct-pointer-types -I$(obj) -I$(srctree)/include \
>>  		-I$(srctree)/samples/bpf -I$(srctree)/tools/include \
>>  		-I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
>>  		-c $(filter %.bpf.c,$^) -o $@
>> @@ -412,7 +412,7 @@ xdp_router_ipv4.skel.h-deps := xdp_router_ipv4.bpf.o
>> xdp_sample.bpf.o
>>
>>  LINKED_BPF_SRCS := $(patsubst %.bpf.o,%.bpf.c,$(foreach
>> skel,$(LINKED_SKELS),$($(skel)-deps)))
>>
>> -BPF_SRCS_LINKED := $(notdir $(wildcard $(src)/*.bpf.c))
>> +BPF_SRCS_LINKED := $(notdir $(wildcard $(srctree)/$(src)/*.bpf.c))
>>  BPF_OBJS_LINKED := $(patsubst %.bpf.c,$(obj)/%.bpf.o, $(BPF_SRCS_LINKED))
>>  BPF_SKELS_LINKED := $(addprefix $(obj)/,$(LINKED_SKELS))
>>
>> diff --git a/samples/bpf/Makefile.target b/samples/bpf/Makefile.target
>> index 7621f55e2947..86a454cfb080 100644
>> --- a/samples/bpf/Makefile.target
>> +++ b/samples/bpf/Makefile.target
>> @@ -41,7 +41,7 @@ _tprogc_flags   = $(TPROGS_CFLAGS) \
>>                   $(TPROGCFLAGS_$(basetarget).o)
>>
>>  # $(objtree)/$(obj) for including generated headers from checkin source
>> files
> 
> [..]
> 
>> -ifeq ($(KBUILD_EXTMOD),)
>> +ifneq ($(KBUILD_EXTMOD),)
> 
> This parts seems to be copy-pasted all over the place in its 'ifeq'
> form. What is it doing and why is it needed?

Sorry for missing this question. As I understand KBUILD_EXTMOD
corresponding to external module. In my case, it's $M=samples/bpf. I
don't really know why it's needed here.

> 
>>  ifdef building_out_of_srctree
>>  _tprogc_flags   += -I $(objtree)/$(obj)
>>  endif
>> -- 
>> 2.34.1
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