linux-kernel - Re: [PATCH v2 09/29] kbuild: disallow multi-word in M= or KBUILD

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Date:   Mon, 1 Jun 2020 03:31:05 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Cc:     Michal Marek <michal.lkml@...kovi.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 09/29] kbuild: disallow multi-word in M= or KBUILD_EXTMOD

On Mon, May 25, 2020 at 12:43 AM Masahiro Yamada <masahiroy@...nel.org> wrote:
>
> $(firstword ...) in scripts/Makefile.modpost was added by commit
> 3f3fd3c05585 ("[PATCH] kbuild: allow multi-word $M in Makefile.modpost")
> to build multiple external module directories.
>
> It was a solution to resolve symbol dependencies when an external
> module depends on another external module.
>
> Commit 0d96fb20b7ed ("kbuild: Add new Kbuild variable
> KBUILD_EXTRA_SYMBOLS") introduced another solution by passing symbol
> info via KBUILD_EXTRA_SYMBOLS, then broke the multi-word M= support.
>
>   include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>                $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
>
> ... does not work if KBUILD_EXTMOD contains multiple words.
>
> This feature has been broken for more than a decade. Remove the
> bitrotten code, and stop parsing if M or KBUILD_EXTMOD contains
> multiple words.
>
> As Documentation/kbuild/modules.rst explains, if your module depends
> on another one, there are two solutions:
>   - add a common top-level Kbuild file
>   - use KBUILD_EXTRA_SYMBOLS
>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

This patch, applied to linux-kbuild.



> ---
>
> Changes in v2:
>   - Add more commit log
>
>  Makefile                 | 3 +++
>  scripts/Makefile.modpost | 2 +-
>  2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 72eb55a36545..48a2dfaf3bf3 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -218,6 +218,9 @@ ifeq ("$(origin M)", "command line")
>    KBUILD_EXTMOD := $(M)
>  endif
>
> +$(if $(word 2, $(KBUILD_EXTMOD)), \
> +       $(error building multiple external modules is not supported))
> +
>  export KBUILD_CHECKSRC KBUILD_EXTMOD
>
>  extmod-prefix = $(if $(KBUILD_EXTMOD),$(KBUILD_EXTMOD)/)
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index 957eed6a17a5..b79bf0e30d32 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -44,7 +44,7 @@ include include/config/auto.conf
>  include scripts/Kbuild.include
>
>  kernelsymfile := $(objtree)/Module.symvers
> -modulesymfile := $(firstword $(KBUILD_EXTMOD))/Module.symvers
> +modulesymfile := $(KBUILD_EXTMOD)/Module.symvers
>
>  MODPOST = scripts/mod/modpost                                                          \
>         $(if $(CONFIG_MODVERSIONS),-m)                                                  \
> --
> 2.25.1
>


-- 
Best Regards
Masahiro Yamada