linux-kernel - Re: [PATCH bpf-next] kbuild: Restore ability to build out-of-tree modules

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Date:   Tue, 1 Dec 2020 10:01:23 -0800
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Leon Romanovsky <leonro@...dia.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Edward Srouji <edwards@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>,
        Networking <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next] kbuild: Restore ability to build out-of-tree modules

On Tue, Dec 1, 2020 at 6:37 AM Leon Romanovsky <leon@...nel.org> wrote:
>
> From: Leon Romanovsky <leonro@...dia.com>
>
> The out-of-tree modules are built without vmlinux target and request
> to recompile that target unconditionally causes to the following
> compilation error.
>
> [root@...ver kernel]# make
> <..>
> make -f ./scripts/Makefile.modpost
> make -f ./scripts/Makefile.modfinal
> make[3]: *** No rule to make target 'vmlinux', needed by '/my_temp/out-of-tree-module/kernel/test.ko'.  Stop.
> make[2]: *** [scripts/Makefile.modpost:117: __modpost] Error 2
> make[1]: *** [Makefile:1703: modules] Error 2
> make[1]: Leaving directory '/usr/src/kernels/5.10.0-rc5_for_upstream_base_2020_11_29_11_34'
> make: *** [Makefile:80: modules] Error 2
>
> As a solution separate between build paths that has vmlinux target and paths without.
>
> Fixes: 5f9ae91f7c0d ("kbuild: Build kernel module BTFs if BTF is enabled and pahole supports it")
> Reported-by: Edward Srouji <edwards@...dia.com>
> Signed-off-by: Leon Romanovsky <leonro@...dia.com>
> ---

e732b538f455 ("kbuild: Skip module BTF generation for out-of-tree
external modules") ([0]) was supposed to take care of this. Did you
try it?

  [0] https://patchwork.kernel.org/project/netdevbpf/patch/20201121070829.2612884-1-andrii@kernel.org/


> Not proficient enough in Makefile, but it fixes the issue.
> ---
>  scripts/Makefile.modfinal | 5 +++++
>  scripts/Makefile.modpost  | 4 ++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 02b892421f7a..8a7d0604e7d0 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -48,9 +48,14 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
>         $(cmd);                                                              \
>         printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
>
> +ifdef MODPOST_VMLINUX
>  # Re-generate module BTFs if either module's .ko or vmlinux changed
>  $(modules): %.ko: %.o %.mod.o scripts/module.lds vmlinux FORCE
>         +$(call if_changed_except,ld_ko_o,vmlinux)
> +else
> +$(modules): %.ko: %.o %.mod.o scripts/module.lds FORCE
> +       +$(call if_changed_except,ld_ko_o)
> +endif
>  ifdef CONFIG_DEBUG_INFO_BTF_MODULES
>         +$(if $(newer-prereqs),$(call cmd,btf_ko))
>  endif
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index f54b6ac37ac2..f5aa5b422ad7 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -114,8 +114,12 @@ targets += $(output-symdump)
>
>  __modpost: $(output-symdump)
>  ifneq ($(KBUILD_MODPOST_NOFINAL),1)
> +ifdef MODPOST_VMLINUX
> +       $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal MODPOST_VMLINUX=1
> +else
>         $(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modfinal
>  endif
> +endif
>
>  PHONY += FORCE
>  FORCE:
> --
> 2.28.0
>