Re: [Buildroot] [PATCH 02/11] package/gcc: force --with-arch=cf on m68k MCF5441x

From: Thomas Petazzoni via buildroot <buildroot@buildroot.org>
To: Jean-Michel Hautbois <jeanmichel.hautbois@yoseli.org>
Cc: buildroot@buildroot.org, Bernd Kuhls <bernd@kuhls.net>,
	 Fabrice Fontaine <fontaine.fabrice@gmail.com>,
	Giulio Benetti <giulio.benetti@benettiengineering.com>,
	 Ismael Luceno <ismael@iodev.co.uk>,
	Romain Naour <romain.naour@gmail.com>
Subject: Re: [Buildroot] [PATCH 02/11] package/gcc: force --with-arch=cf on m68k MCF5441x
Date: Sat, 30 May 2026 10:09:37 +0200	[thread overview]
Message-ID: <ahqbG2noGqK-3bsK@windsurf> (raw)
In-Reply-To: <7257763a-5577-44e0-a12a-e13872c041ad@yoseli.org>

Hello Jean-Michel,

On Sat, May 30, 2026 at 09:31:53AM +0200, Jean-Michel Hautbois wrote:

> You are right, that wording is poor and I will fix it in v2.
> 
> MCF5441x is indeed only a ColdFire (V4e) core.
> The real reason --with-arch=cf is needed is in gcc/config.gcc.
> 
> The gcc m68k backend serves both the 680x0 family (arch "m68k") and the
> ColdFire family (arch "cf") from one tree, with a shared multilib generator
> (gcc/config/m68k/t-mlibs).
> 
> The trigger here is that BR2_m68k_cf5441x selects an MMU target, so the
> tuple is m68k-*-linux* rather than the m68k-*-uclinux* used by the existing
> 5208. In the m68k-*-linux* case, config.gcc does:
> 
>     with_arch=${with_arch:-m68k}
> 
> So, it defaults --with-arch to "m68k" (680x0) when none is given.
> 
> That pulls in config/m68k/t-m68k, which sets M68K_ARCH=m68k and restricts
> the multilib CPU set to non-ColdFire devices (CPU !~ "^mcf"). Buildroot
> passes --with-cpu=54418 (a ColdFire core) via R2_GCC_TARGET_CPU, so t-mlibs
> then trips its own sanity check:
> 
>     $(error Error default cpu '...' is not in multilib set '...')
> 
> because the default CPU is ColdFire while the multilib set was narrowed
> to 680x0.
> 
> Passing --with-arch=cf:
> - overrides the m68k default
> - selects config/m68k/t-cf
> - the ColdFire default CPU is back in the set.
> 
> This is also why 5208 does not need it: as a no-MMU m68k-*-uclinux*
> target it does not get the with_arch=m68k default, so its multilib set
> spans all devices and the ColdFire default is accepted.
> 
> The change itself is unchanged. I will just rewrite that paragraph in
> v2 to describe the m68k-*-linux* with_arch default instead of the
> "disambiguate" phrasing, if you are ok with that ?

Thanks for the detailed explanation, makes sense!

> PS: Sorry for the long detailed explanation, but I spent quite a bit of time
> on this one so I must be certain everything is really like I understood it
> :-)

Long detailed explanations are very very good, no need to apologize!

Best regards,

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
_______________________________________________
buildroot mailing list
buildroot@buildroot.org
https://lists.buildroot.org/mailman/listinfo/buildroot