Re: [PATCH v1] samples/bpf: Fix build out of source tree - Stanislav Fomichev via Linux-kernel-mentees

From: Stanislav Fomichev via Linux-kernel-mentees <linux-kernel-mentees@lists.linuxfoundation.org>
To: Anh Tuan Phan <tuananhlfc@gmail.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: Thu, 6 Jul 2023 11:09:56 -0700	[thread overview]
Message-ID: <ZKcDdIYOUQuPP5Px@google.com> (raw)
In-Reply-To: <67bec6a9-af59-d6f9-2630-17280479a1f7@gmail.com>

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?

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