linux-kernel - Re: [PATCH 1/2] kbuild: create built-in.o automatically if parent directory wants it

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Message-ID: <CAK7LNASt+4oNw3niSOcM=++Z8D0CF5jy8z1d2oz7Lp=CT2b6tg@mail.gmail.com>
Date:   Sat, 18 Nov 2017 13:06:24 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        devicetree@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Linux-MIPS <linux-mips@...ux-mips.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>
Subject: Re: [PATCH 1/2] kbuild: create built-in.o automatically if parent
 directory wants it

2017-11-08 1:31 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> "obj-y += foo/" syntax requires Kbuild to visit the "foo" subdirectory
> and link built-in.o from that directory.  This means foo/Makefile is
> responsible for creating built-in.o even if there is no object to
> link (in this case, built-in.o is an empty archive).
>
> We have had several fixups like commit 4b024242e8a4 ("kbuild: Fix
> linking error built-in.o no such file or directory"), then ended up
> with a complex condition as follows:
>
>   ifneq ($(strip $(obj-y) $(obj-m) $(obj-) $(subdir-m) $(lib-target)),)
>   builtin-target := $(obj)/built-in.o
>   endif
>
> We still have more cases not covered by the above, so we need to add
>   obj- := dummy.o
> in several places just for creating empty built-in.o.
>
> A key point is, the parent Makefile knows whether built-in.o is needed
> or not.  If a subdirectory needs to create built-in.o, its parent can
> tell the fact when Kbuild descends into it.
>
> If non-empty $(need-builtin) flag is passed from the parent, built-in.o
> should be created.  $(obj-y) should be still checked to support the
> single target "%/".  All of ugly tricks will go away.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>

Applied to linux-kbuild/kbuild.



-- 
Best Regards
Masahiro Yamada