Re: [RFC] Get rid of SUBARCH

[Rob Landley <rob@landley.net>]

On 08/22/2013 07:58:26 AM, Geert Uytterhoeven wrote:
> On Wed, Aug 21, 2013 at 9:51 PM, Sam Ravnborg <sam@ravnborg.org>  
> wrote:
> >> > The series touches also m68k, sh, mips and unicore32.
> >> > These architectures magically select a cross compiler if ARCH !=  
> SUBARCH.
> >> > Do really need that behavior?
> >>
> >> This does remove functionality.
> >> It allows to build a kernel using e.g. "make ARCH=m68k".
> >>
> >> Perhaps this can be moved to generic code? Most (not all!)  
> cross-toolchains
> >> are called $ARCH-{unknown-,}linux{,-gnu}.
> >> Exceptions are e.g. am33_2.0-linux and bfin-uclinux.
> >
> > Today you can specify CROSS_COMPILE in Kconfig.
> > With this we should be able to remove these hacks.
> 
> The correct CROSS_COMPILE value depends on the host environment, not
> on the target configuration.

Actually it depends on _both_.

Rob
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Date:   Thu, 22 Aug 2013 13:55:20 -0700
From:   David Daney <ddaney.cavm@gmail.com>
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To:     Rob Landley <rob@landley.net>, Richard Weinberger <richard@nod.at>
CC:     Geert Uytterhoeven <geert@linux-m68k.org>,
        Sam Ravnborg <sam@ravnborg.org>,
        Linux-Arch <linux-arch@vger.kernel.org>,
        Michal Marek <mmarek@suse.cz>,
        Ralf Baechle <ralf@linux-mips.org>,
        Paul Mundt <lethal@linux-sh.org>,
        Jeff Dike <jdike@addtoit.com>,
        Guan Xuetao <gxt@mprc.pku.edu.cn>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        the arch/x86 maintainers <x86@kernel.org>,
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        Linux-sh list <linux-sh@vger.kernel.org>,
        uml-devel <user-mode-linux-devel@lists.sourceforge.net>
Subject: Re: [RFC] Get rid of SUBARCH
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On 08/22/2013 01:41 PM, Rob Landley wrote:
> On 08/22/2013 07:58:26 AM, Geert Uytterhoeven wrote:
>> On Wed, Aug 21, 2013 at 9:51 PM, Sam Ravnborg <sam@ravnborg.org> wrote:
>> >> > The series touches also m68k, sh, mips and unicore32.
>> >> > These architectures magically select a cross compiler if ARCH !=
>> SUBARCH.
>> >> > Do really need that behavior?
>> >>
>> >> This does remove functionality.
>> >> It allows to build a kernel using e.g. "make ARCH=m68k".
>> >>
>> >> Perhaps this can be moved to generic code? Most (not all!)
>> cross-toolchains
>> >> are called $ARCH-{unknown-,}linux{,-gnu}.
>> >> Exceptions are e.g. am33_2.0-linux and bfin-uclinux.
>> >
>> > Today you can specify CROSS_COMPILE in Kconfig.
>> > With this we should be able to remove these hacks.
>>
>> The correct CROSS_COMPILE value depends on the host environment, not
>> on the target configuration.
>
> Actually it depends on _both_.
>

I think the important issue is not the exact dependencies of the value 
of CROSS_COMPILE, but rather that it varies enough that automatically 
choosing a value based on SUBARCH often gives the wrong result.

Removing SUBARCH and setting CROSS_COMPILE either from the make command 
line (or environment) or the config file, is a good idea because it 
simplifies the build system, makes things clearer, and yields more 
predictable results.

David Daney