[PATCH] um: let 'make clean' properly clean underlying SUBARCH as well

[Johannes Berg]

On Wed, 2025-05-07 at 16:49 +0900, Masahiro Yamada wrote:
> Building the kernel with O= is affected by stale in-tree build artifacts.
> 
> So, if the source tree is not clean, Kbuild displays the following:
> 
>   $ make ARCH=um O=build defconfig
>   make[1]: Entering directory '/.../linux/build'
>   ***
>   *** The source tree is not clean, please run 'make ARCH=um mrproper'
>   *** in /.../linux
>   ***
>   make[2]: *** [/.../linux/Makefile:673: outputmakefile] Error 1
>   make[1]: *** [/.../linux/Makefile:248: __sub-make] Error 2
>   make[1]: Leaving directory '/.../linux/build'
>   make: *** [Makefile:248: __sub-make] Error 2
> 
> Usually, running 'make mrproper' is sufficient for cleaning the source
> tree for out-of-tree builds.
> 
> However, building UML generates build artifacts not only in arch/um/,
> but also in the SUBARCH directory (i.e., arch/x86/). If in-tree stale
> files remain under arch/x86/, Kbuild will reuse them instead of creating
> new ones under the specified build directory.
> 
> This commit makes 'make ARCH=um clean' recurse into the SUBARCH directory.

Do you want to take that through your tree? I'm not sure we'd get it
into 6.15 at this point via uml, if you have some other material feel
free to take it:

Acked-by: Johannes Berg <johannes at sipsolutions.net>

Otherwise we can take it via uml tree for 6.16 too, let us know.

johannes