linux-kernel - Re: [PATCH v3] kbuild: Set KBUILD_CFLAGS before incl. arch Makefile

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Date:   Tue, 28 Nov 2017 20:27:43 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Linux MIPS Mailing List <linux-mips@...ux-mips.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Greg Hackmann <ghackmann@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Openrisc <openrisc@...ts.librecores.org>,
        Michal Marek <mmarek@...e.com>,
        Matthias Kaehlcke <mka@...omium.org>,
        Jan-Simon Möller <dl9pf@....de>,
        Chris Fries <cfries@...gle.com>,
        Mark Charlebois <charlebm@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3] kbuild: Set KBUILD_CFLAGS before incl. arch Makefile

Hi Nick,

On Tue, Nov 28, 2017 at 7:18 PM, Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> Thanks for merging Chris' patch, and sorry for taking so long to respond.
>
> On Wed, Nov 22, 2017 at 8:24 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> Linus suggests to move compiler flag testing to Kconfig.
>
> Do you have an LKML link for context?
>
> On Wed, Nov 15, 2017 at 6:32 PM, Masahiro Yamada
> <yamada.masahiro@...ionext.com> wrote:
>> BTW, I notice another issue.
>>
>> If we move clang settings before including arch Makefile,
>> "ifneq ($(CROSS_COMPILE),)" comes early.
>>
>> Some arch Makefiles (arch/mips/Makefile, arch/blackfin/Makefile, etc.)
>> set CROSS_COMPILE there if CROSS_COMPILE is not given.
>>
>> Then, we have a conflict between two requirements among arch.
>>
>> [1] arm64, powerpc use ld-option in their Makefile.
>>     So, clang flags must be set before inc. arch Makefile.
>> [2] mips, blackfin, etc. may set CROSS_COMPILE in their Makefile.
>>     So, we want to reference CROSS_COMPILE only after inc. arch Makefile
>>
>> I have no idea how to solve it.
>>
>> At this moment, I guess clang is intended to support
>> only limited architectures.
>>
>> It might be OK to be compromised here.
>
> I definitely find it curious that certain arch's define CROSS_COMPILE
> themselves.  The benefit is one less argument to supply at compile
> time, but it assumes that the toolchain always has a certain prefix.
> This makes sense to me when cross compiling, but seems odd when
> compiling natively on that arch as the host and target.  Maybe those
> arch's use that convention, or simply are always cross compiled for?
>
> Taking a survey of all arch's currently in the kernel via `cd arch; ag
> CROSS_COMPILE` and quickly eyeballing the result:
>
> m68k if not set

And inside "ifneq ($(SUBARCH),$(ARCH))", so the prefix is not used for
native compilation.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds