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From:   Masahiro Yamada <yamada.masahiro@socionext.com>
Date:   Tue, 13 Feb 2018 17:59:25 +0900
Message-ID: <CAK7LNARXz-SYZrnyWedh6nxLYS-T18RdEPFsmBxHUW_4jQERPA@mail.gmail.com>
Subject: Re: [RFC PATCH 4/7] kconfig: support new special property shell=
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Randy Dunlap <rdunlap@infradead.org>,
        Kees Cook <keescook@chromium.org>,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        "Luis R . Rodriguez" <mcgrof@suse.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Pavel Machek <pavel@ucw.cz>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Jiri Kosina <jkosina@suse.cz>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Tejun Heo <tj@kernel.org>, Ingo Molnar <mingo@kernel.org>,
        "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>
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2018-02-13 17:35 GMT+09:00 Arnd Bergmann <arnd@arndb.de>:
> On Tue, Feb 13, 2018 at 2:53 AM, Randy Dunlap <rdunlap@infradead.org> wrote:
>> On 02/12/2018 05:41 PM, Masahiro Yamada wrote:
>>> 2018-02-13 8:48 GMT+09:00 Randy Dunlap <rdunlap@infradead.org>:
>>>> On 02/12/2018 07:24 AM, Kees Cook wrote:
>>>>> On Mon, Feb 12, 2018 at 6:39 AM, Masahiro Yamada
>>>>> <yamada.masahiro@socionext.com> wrote:
>>>>
>>>>>>> (And in thinking about this, does Kconfig know the true $CC in use?
>>>>>>> i.e. the configured cross compiler, etc?)
>>>>>>
>>>>>> I was thinking of removing CONFIG_CROSS_COMPILE.
>>>>>>
>>>>>> A user can dynamically change CROSS_COMPILE from
>>>>>> "make menuconfig".
>>>>>
>>>>> Most builds I've seen implement cross compilers as an environment
>>>>> variable during all "make" invocations.
>>>>
>>>> I agree. I think you would break a bunch of build bots if you remove that.
>>>
>>>
>>> For clarification, I suggested to remove CONFIG_CROSS_COMPILE.
>>>
>>> The following code:
>>> https://github.com/torvalds/linux/blob/v4.16-rc1/Makefile#L315
>>> https://github.com/torvalds/linux/blob/v4.16-rc1/init/Kconfig#L58
>>>
>>> I hope build bots are not using this.
>>>
>>>
>>> Passing CROSS_COMPILE via the command line, environment
>>> is still supported.
>>
>> OK, I misunderstood.  That one can go away IMO.
>
> Removing it will break the workflow for some people in a minor way
> though. Could we have the top-level Makefile try to detect the
> CROSS_COMPILE? Instead of just using CC=gcc as the default,
> we could check for ${ARCH}!=`uname -m` and then see if $PATH
> contains a ${ARCH}-linux-gcc, ${ARCH}-elf-gcc or ${ARCH}-gcc.
>
> it will need slightly more complexity to deal with architectures
> that have different identifiers in linux and gcc, but I think it would
> be a nice feature anyway.
>
>      Arnd

Some architectures such as m68k, mips, etc.
do this in their arch/*/Makefile
by using $(call cc-cross-prefix, ...)

But, currently we do not do this globally.

It would be possible to do it, but it does not mean
backward-compatible with CONFIG_CROSS_COMPILE.


-- 
Best Regards
Masahiro Yamada