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

[Masahiro Yamada]

On Wed, Dec 18, 2024 at 8:51 PM Mickaël Salaün <mic@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxx>
> Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Nicolas Schier <nicolas@xxxxxxxxx>
> Cc: Richard Weinberger <richard@xxxxxx>
> Fixes: 1b620d539ccc ("kbuild: disable header exports for UML in a straightforward way")
> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
> ---
>  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.

-- 
Best Regards
Masahiro Yamada