linux-kernel - Re: [PATCH 3/3] kbuild: show hint if subdir-y/m is used to visit module Makefile

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Date:   Thu, 8 Aug 2019 15:29:52 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc:     Jan Kiszka <jan.kiszka@...mens.com>,
        Tom Stonecypher <thomas.edwardx.stonecypher@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: Re: [PATCH 3/3] kbuild: show hint if subdir-y/m is used to visit
 module Makefile

On Tue, Aug 6, 2019 at 7:03 PM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
>
> Since commit ff9b45c55b26 ("kbuild: modpost: read modules.order instead
> of $(MODVERDIR)/*.mod"), a module is no longer built in the following
> pattern:
>
>   [Makefile]
>   subdir-y := some-module
>
>   [some-module/Makefile]
>   obj-m := some-module.o
>
> You cannot write Makefile this way in upstream because modules.order is
> not correctly generated. subdir-y is used to descend to a sub-directory
> that builds tools, device trees, etc.
>
> For external modules, the modules order does not matter. So, the
> Makefile above was known to work.
>
> I believe the Makefile should be re-written as follows:
>
>   [Makefile]
>   obj-m := some-module/
>
>   [some-module/Makefile]
>   obj-m := some-module.o
>
> However, people will have no idea if their Makefile suddenly stops
> working. In fact, I received questions from multiple people.
>
> Show a warning if obj-m is specified in a Makefile visited by subdir-y
> or subdir-m.
>
> Cc: Jan Kiszka <jan.kiszka@...mens.com>
> Cc: Tom Stonecypher <thomas.edwardx.stonecypher@...el.com>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---

This produces false-positive warnings for single-targets.
I will fix up as follows:


diff --git a/Makefile b/Makefile
index 0e37ad2f77bf..fac25e279da6 100644
--- a/Makefile
+++ b/Makefile
@@ -1783,7 +1783,7 @@ PHONY += /
 /: ./

 %/: prepare FORCE
-       $(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir)
+       $(Q)$(MAKE) KBUILD_MODULES=1 $(build)=$(build-dir) need-modorder=1

 # FIXME Should go into a make.lib or something
 # ===========================================================================



>
>  scripts/Makefile.build | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 37a1d2cd49d4..4a26c7ed9198 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -52,6 +52,13 @@ ifndef obj
>  $(warning kbuild: Makefile.build is included improperly)
>  endif
>
> +ifeq ($(need-modorder),)
> +ifneq ($(obj-m),)
> +$(warning $(patsubst %.o,'%.ko',$(obj-m)) will not be built even though obj-m is specified.)
> +$(warning You cannot use subdir-y/m to visit a module Makefile. Use obj-y/m instead.)
> +endif
> +endif
> +
>  # ===========================================================================
>
>  ifneq ($(strip $(lib-y) $(lib-m) $(lib-)),)
> --
> 2.17.1
>


-- 
Best Regards
Masahiro Yamada