linux-kernel - Re: [PATCH] samples: run headers_install for host arch instead of target arch

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Message-ID: <CAK8P3a16pR5e1js7JiGreqHqxv5RNJZZY=JLFwLRE8i3nbg5hQ@mail.gmail.com>
Date:   Fri, 28 Sep 2018 21:36:14 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Masahiro Yamada <yamada.masahiro@...ionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Richard Weinberger <richard@....at>,
        Jeff Dike <jdike@...toit.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Andy Gross <andy.gross@...aro.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Gerd Hoffmann <kraxel@...hat.com>
Subject: Re: [PATCH] samples: run headers_install for host arch instead of
 target arch

On Fri, Sep 28, 2018 at 8:51 AM Masahiro Yamada
<yamada.masahiro@...ionext.com> wrote:
>
> Some samples search headers in $(objtree)/usr/include, which is made
> available by "make headers_install".  It is not kernel-space code but
> host programs that need this header search path.
>
> Commit 3fca1700c4c3 ("kbuild: make samples really depend on
> headers_install") is wrong because it installs headers of the target
> architecture.  Besides, UML fails to build with CONFIG_SAMPLES=y
> because UML does not support headers_install.
>
> Invoke "make headers_install" for the _host_ architecture in the
> prepare stage.  Introduce CONFIG_HOST_HEADERS_INSTALL so that this
> happens only for samples that need it.
>
> I also removed 'Documentation/: headers_install', which I guess is
> stale code.
>
> Fixes: 3fca1700c4c3 ("kbuild: make samples really depend on headers_install")
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> Cc: David Howells <dhowells@...hat.com>

I don't understand this one. Why would we want to build the samples for
the host architecture rather than the target architecture?

I would think that the bug is that we try to build them using
HOSTCC, and they end up being unusable on the target as
a consequence.

        Arnd