linux-kernel - Re: [PATCH v1] kbuild: Allow building of samples with UML

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Message-ID: <20250211-efficient-pink-dolphin-dcfd4d@l-nschier-z2>
Date: Tue, 11 Feb 2025 11:50:18 +0100
From: Nicolas Schier <nicolas@...sle.eu>
To: Masahiro Yamada <masahiroy@...nel.org>
Cc: linux-kbuild@...r.kernel.org, linux-um@...ts.infradead.org,
	linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org,
	Günther Noack <gnoack@...gle.com>,
	Anton Ivanov <anton.ivanov@...bridgegreys.com>,
	Johannes Berg <johannes@...solutions.net>,
	Nathan Chancellor <nathan@...nel.org>,
	Richard Weinberger <richard@....at>,
	Nicolas Schier <nicolas@...sle.eu>,
	Mickaël Salaün <mic@...ikod.net>
Subject: Re: [PATCH v1] kbuild: Allow building of samples with UML

On Tue, Feb 11, 2025 at 06:44:30PM +0900, Masahiro Yamada wrote:
> On Wed, Dec 18, 2024 at 8:51 PM Mickaël Salaün <mic@...ikod.net> wrote:
> >
> > It's useful to build samples/* with UML and the only blocker is the
> > artificial incompatibility with CONFIG_HEADERS_INSTALL.
> >
> > Allow the headers_install target with ARCH=um, which then allow building
> > samples (and tests using them) with UML too:
> >
> >   printf 'CONFIG_SAMPLES=y\nCONFIG_HEADERS_INSTALL=y\nCONFIG_SAMPLE_LANDLOCK=y\n' >.config
> >   make ARCH=um olddefconfig headers_install
> >   make ARCH=um samples/landlock/
> >
> > Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
> > Cc: Johannes Berg <johannes@...solutions.net>
> > Cc: Masahiro Yamada <masahiroy@...nel.org>
> > Cc: Nathan Chancellor <nathan@...nel.org>
> > Cc: Nicolas Schier <nicolas@...sle.eu>
> > Cc: Richard Weinberger <richard@....at>
> > Fixes: 1b620d539ccc ("kbuild: disable header exports for UML in a straightforward way")
> > Signed-off-by: Mickaël Salaün <mic@...ikod.net>
> > ---
> >  Makefile          | 1 -
> >  lib/Kconfig.debug | 1 -
> >  2 files changed, 2 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index e5b8a8832c0c..6e2cce16a2a3 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1355,7 +1355,6 @@ hdr-inst := -f $(srctree)/scripts/Makefile.headersinst obj
> >
> >  PHONY += headers
> >  headers: $(version_h) scripts_unifdef uapi-asm-generic archheaders archscripts
> > -       $(if $(filter um, $(SRCARCH)), $(error Headers not exportable for UML))
> >         $(Q)$(MAKE) $(hdr-inst)=include/uapi
> >         $(Q)$(MAKE) $(hdr-inst)=arch/$(SRCARCH)/include/uapi
> >
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index f3d723705879..fac1208f48e4 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -473,7 +473,6 @@ config READABLE_ASM
> >
> >  config HEADERS_INSTALL
> >         bool "Install uapi headers to usr/include"
> > -       depends on !UML
> >         help
> >           This option will install uapi headers (headers exported to user-space)
> >           into the usr/include directory for use during the kernel build.
> > --
> > 2.47.1
> >
> 
> This patch was not even compile-tested.
> 
> Apply this patch.
> Enable CONFIG_HEADERS_INSTALL and CONFIG_UAPI_HEADERS_TEST.
> "make ARCH=um" and see the errors.
> 
> The reason is obvious, UML is a kernel. No such userspace.

oh, I sorry.  I should have seen that when reviewing, but confused
myself as I missed the UAPI_HEADERS_TEST and just looked at a
"successful" run of 'make headers_install'.

Kind regards,
Nicolas