netdev - Re: [PATCH bpf-next v3 07/10] samples/bpf: install libbpf headers when building

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Message-ID: <CAEf4BzaCCf7BEbL6MWWFJnThcR0jZ8VxsVvha2KHfzoJZFCzqA@mail.gmail.com>
Date:   Wed, 6 Oct 2021 11:23:17 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Quentin Monnet <quentin@...valent.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v3 07/10] samples/bpf: install libbpf headers
 when building

On Sun, Oct 3, 2021 at 12:22 PM Quentin Monnet <quentin@...valent.com> wrote:
>
> API headers from libbpf should not be accessed directly from the source
> directory. Instead, they should be exported with "make install_headers".
> Make sure that samples/bpf/Makefile installs the headers properly when
> building.
>
> The object compiled from and exported by libbpf are now placed into a
> subdirectory of sample/bpf/ instead of remaining in tools/lib/bpf/. We
> attempt to remove this directory on "make clean". However, the "clean"
> target re-enters the samples/bpf/ directory from the root of the
> repository ("$(MAKE) -C ../../ M=$(CURDIR) clean"), in such a way that
> $(srctree) and $(src) are not defined, making it impossible to use
> $(LIBBPF_OUTPUT) and $(LIBBPF_DESTDIR) in the recipe. So we only attempt
> to clean $(CURDIR)/libbpf, which is the default value.
>
> Add a dependency on libbpf's headers for the $(TRACE_HELPERS).
>
> We also change the output directory for bpftool, to place the generated
> objects under samples/bpf/bpftool/ instead of building in bpftool's
> directory directly. Doing so, we make sure bpftool reuses the libbpf
> library previously compiled and installed.
>
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> ---
>  samples/bpf/Makefile | 41 +++++++++++++++++++++++++++++++----------
>  1 file changed, 31 insertions(+), 10 deletions(-)
>

[...]

> +
> +$(LIBBPF_OUTPUT) $(BPFTOOL_OUTPUT):
> +       $(call msg,MKDIR,$@)
> +       $(Q)mkdir -p $@
>
>  $(obj)/syscall_nrs.h:  $(obj)/syscall_nrs.s FORCE
>         $(call filechk,offsets,__SYSCALL_NRS_H__)
> @@ -309,6 +325,11 @@ verify_target_bpf: verify_cmds
>  $(BPF_SAMPLES_PATH)/*.c: verify_target_bpf $(LIBBPF)
>  $(src)/*.c: verify_target_bpf $(LIBBPF)
>
> +libbpf_hdrs: $(LIBBPF)
> +$(obj)/$(TRACE_HELPERS): libbpf_hdrs

same problem

> +
> +.PHONY: libbpf_hdrs
> +
>  $(obj)/xdp_redirect_cpu_user.o: $(obj)/xdp_redirect_cpu.skel.h
>  $(obj)/xdp_redirect_map_multi_user.o: $(obj)/xdp_redirect_map_multi.skel.h
>  $(obj)/xdp_redirect_map_user.o: $(obj)/xdp_redirect_map.skel.h
> @@ -367,7 +388,7 @@ $(obj)/%.bpf.o: $(src)/%.bpf.c $(obj)/vmlinux.h $(src)/xdp_sample.bpf.h $(src)/x
>         $(Q)$(CLANG) -g -O2 -target bpf -D__TARGET_ARCH_$(SRCARCH) \
>                 -Wno-compare-distinct-pointer-types -I$(srctree)/include \
>                 -I$(srctree)/samples/bpf -I$(srctree)/tools/include \
> -               -I$(srctree)/tools/lib $(CLANG_SYS_INCLUDES) \
> +               -I$(LIBBPF_INCLUDE) $(CLANG_SYS_INCLUDES) \
>                 -c $(filter %.bpf.c,$^) -o $@
>
>  LINKED_SKELS := xdp_redirect_cpu.skel.h xdp_redirect_map_multi.skel.h \
> @@ -404,7 +425,7 @@ $(obj)/%.o: $(src)/%.c
>         @echo "  CLANG-bpf " $@
>         $(Q)$(CLANG) $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(BPF_EXTRA_CFLAGS) \
>                 -I$(obj) -I$(srctree)/tools/testing/selftests/bpf/ \
> -               -I$(srctree)/tools/lib/ \
> +               -I$(LIBBPF_INCLUDE) \
>                 -D__KERNEL__ -D__BPF_TRACING__ -Wno-unused-value -Wno-pointer-sign \
>                 -D__TARGET_ARCH_$(SRCARCH) -Wno-compare-distinct-pointer-types \
>                 -Wno-gnu-variable-sized-type-not-at-end \
> --
> 2.30.2
>