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Date: Wed, 3 Sep 2025 15:31:31 -0700
From: Nathan Chancellor <nathan@kernel.org>
To: Thomas =?iso-8859-1?Q?Wei=DFschuh?= <thomas.weissschuh@linutronix.de>
Cc: Nicolas Schier <nicolas.schier@linux.dev>, linux-kbuild@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Masahiro Yamada <masahiroy@kernel.org>
Subject: Re: [PATCH 2/2] kbuild: userprogs: also inherit byte order and ABI
 from kernel
Message-ID: <20250903223131.GA2264021@ax162>
References: <20250813-kbuild-userprogs-bits-v1-0-2d9f7f411083@linutronix.de>
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In-Reply-To: <20250828083747-e819430a-986f-4f71-bbc8-e402e339c9a2@linutronix.de>

On Mon, Sep 01, 2025 at 11:51:03AM +0200, Thomas Weißschuh wrote:
> Exactly. The normal cases can be handled generically. For example the kconfig
> below works for architectures which only differ in byte order and 32bit/64bit,
> which are most of them. MIPS should require more logic.
> Also I'm ignoring x32, as it is never the kernel's native ABI.
> 
>  config CC_CAN_LINK
>         bool
> +       default $(cc_can_link_user,$(m64-flag) -mlittle-endian) if 64BIT && CPU_LITTLE_ENDIAN
> +       default $(cc_can_link_user,$(m64-flag) -mbig-endian) if 64BIT && CPU_BIG_ENDIAN
>         default $(cc_can_link_user,$(m64-flag)) if 64BIT
> +       default $(cc_can_link_user,$(m32-flag) -mlittle-endian) if CPU_LITTLE_ENDIAN
> +       default $(cc_can_link_user,$(m32-flag) -mbig-endian) if CPU_BIG_ENDIAN
>         default $(cc_can_link_user,$(m32-flag))
> 
> 
> > Feels like that could get complicated quickly but this would probably be
> > the objectively most robust and "hands off" option.
> 
> Agreed.

Nicolas might feel differently but this does not seem terrible to me,
especially with a macro to wrap the common logic, which is where I felt
like things could get unwieldy. Feel free to send an RFC if it is not
too much work.

Cheers,
Nathan