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Re: [RFC] Get rid of SUBARCH

To: David Daney <ddaney.cavm@gmail.com>
Subject: Re: [RFC] Get rid of SUBARCH
From: Rob Landley <rob@landley.net>
Date: Thu, 22 Aug 2013 16:32:55 -0500
Cc: Richard Weinberger <richard@nod.at>, 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>, linux-kbuild <linux-kbuild@vger.kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, linux-m68k <linux-m68k@lists.linux-m68k.org>, Linux MIPS Mailing List <linux-mips@linux-mips.org>, Linux-sh list <linux-sh@vger.kernel.org>, uml-devel <user-mode-linux-devel@lists.sourceforge.net>
In-reply-to: <52167AB8.4060206@gmail.com> (from ddaney.cavm@gmail.com on Thu Aug 22 15:55:20 2013)
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On 08/22/2013 03:55:20 PM, David Daney wrote:
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

Agreed. Expecting the build to guess the right $CROSS_COMPILE is like expecting it to guess the right $PATH. It should be specified, not heuristically probed.

Rob
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