netdev - Re: [PATCH bpf-next 3/6] bpftool: Use $(OUTPUT) and not $(O) for VMLINUX_BTF

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Date:   Thu, 11 Nov 2021 10:59:20 -0800
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 3/6] bpftool: Use $(OUTPUT) and not $(O) for
 VMLINUX_BTF_PATHS in Makefile

On Wed, Nov 10, 2021 at 3:46 AM Quentin Monnet <quentin@...valent.com> wrote:
>
> The Makefile for bpftool relies on $(OUTPUT), and not on $(O), for
> passing the output directory. So $(VMLINUX_BTF_PATHS), used for
> searching for kernel BTF info, should use the same variable.
>
> Fixes: 05aca6da3b5a ("tools/bpftool: Generalize BPF skeleton support and generate vmlinux.h")
> Signed-off-by: Quentin Monnet <quentin@...valent.com>
> ---
>  tools/bpf/bpftool/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> index 2a846cb92120..40abf50b59d4 100644
> --- a/tools/bpf/bpftool/Makefile
> +++ b/tools/bpf/bpftool/Makefile
> @@ -150,7 +150,7 @@ $(BOOTSTRAP_OBJS): $(LIBBPF_BOOTSTRAP)
>  OBJS = $(patsubst %.c,$(OUTPUT)%.o,$(SRCS)) $(OUTPUT)disasm.o
>  $(OBJS): $(LIBBPF) $(LIBBPF_INTERNAL_HDRS)
>
> -VMLINUX_BTF_PATHS ?= $(if $(O),$(O)/vmlinux)                           \
> +VMLINUX_BTF_PATHS ?= $(if $(OUTPUT),$(OUTPUT)/vmlinux)                 \
>                      $(if $(KBUILD_OUTPUT),$(KBUILD_OUTPUT)/vmlinux)    \

But you still check KBUILD_OUTPUT? O overrides KBUILD_OUTPUT as far as
kernel build goes. So if you still support KBUILD_OUTPUT, you should
support O. And the $(OUTPUT) seems to be completely unrelated, as that
defines the output of bpftool build files, not the vmlinux image. Or
am I missing something?

>                      ../../../vmlinux                                   \
>                      /sys/kernel/btf/vmlinux                            \
> --
> 2.32.0
>