linux-kernel - Re: [PATCH v3 04/16] kbuild: userprogs: add nolibc support

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Message-ID: <20250611-horned-prudent-saluki-b5a5df@l-nschier-aarch64>
Date: Wed, 11 Jun 2025 16:09:01 +0200
From: Nicolas Schier <nicolas.schier@...ux.dev>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, Willy Tarreau <w@....eu>,
	Thomas Weißschuh <linux@...ssschuh.net>,
	Brendan Higgins <brendan.higgins@...ux.dev>,
	David Gow <davidgow@...gle.com>, Rae Moar <rmoar@...gle.com>,
	Shuah Khan <shuah@...nel.org>, Jonathan Corbet <corbet@....net>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, kunit-dev@...glegroups.com,
	linux-doc@...r.kernel.org, linux-riscv@...ts.infradead.org,
	workflows@...r.kernel.org
Subject: Re: [PATCH v3 04/16] kbuild: userprogs: add nolibc support

On Wed, Jun 11, 2025 at 09:38:10AM +0200, Thomas Weißschuh wrote:
> Userprogs are built with the regular kernel compiler $CC.
> A kernel compiler does not necessarily contain a libc which is required
> for a normal userspace application.
> However the kernel tree does contain a minimal libc implementation
> "nolibc" which can be used to build userspace applications.
> 
> Introduce support to build userprogs against nolibc instead of the
> default libc of the compiler, which may not exist.
> 
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> 
> ---
> This could probably be moved out of the generic kbuild makefiles.
> I think the ergonimics would suffer and this functionality could be
> used by other users of userprogs.
> 
> Also this does currently not support out-of-tree builds.
> For that tools/include/nolibc/*.h and usr/include/*.h would need to be
> installed into the build directory.

Thanks!

Reviewed-by: Nicolas Schier <n.schier@....de>

Probably overkill, but might it make sense to abort *-nolibc compilation 
requests for out-of-tree builds?

Kind regards,
Nicolas