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

[Shuah Khan]

On 5/7/25 01:49, 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.
> 
> Reported-by: Shuah Khan <skhan at linuxfoundation.org>
> Closes: https://lore.kernel.org/lkml/20250502172459.14175-1-skhan@linuxfoundation.org/
> Signed-off-by: Masahiro Yamada <masahiroy at kernel.org>

It doesn't solve the problem. I still see arch/x86/realmode/rm/pasyms.h
after running make ARCH=um mrproper

A subsequent kunit run on x86_64 fails. make ARCH=x86_64 mrproper
will remove the headers for x86_64 properly. The patch I proposed
prompts user run mrproper on the arch in compile.h - It works now
for the case where compile.h doesn't exist. I can send that out
unless you have other ideas on how to fix this.

My workflow:

- Build kernel on x86_64 with CONFIG_AMD_MEM_ENCRYPT enabled

- Check for arch/x86/realmode/rm/pasyms.h
   ls arch/x86/realmode/rm/pasyms.h
      arch/x86/realmode/rm/pasyms.h

- make ARCH=um O=/linux/build
   
   This patch cleans the source tree, but doesn't remove
   arch/x86/realmode/rm/pasyms.h

- ls arch/x86/realmode/rm/pasyms.h
      arch/x86/realmode/rm/pasyms.h

- ./tools/testing/kunit/kunit.py run --alltests --arch x86_64
[15:26:35] Configuring KUnit Kernel ...
Regenerating .config ...
Populating config with:
$ make ARCH=x86_64 O=.kunit olddefconfig
[15:26:37] Building KUnit Kernel ...
Populating config with:
$ make ARCH=x86_64 O=.kunit olddefconfig
Building with:
$ make all compile_commands.json scripts_gdb ARCH=x86_64 O=.kunit --jobs=16
ERROR:root:ld:arch/x86/realmode/rm/realmode.lds:236: undefined symbol `sev_es_trampoline_start' referenced in expression
make[6]: *** [../arch/x86/realmode/rm/Makefile:49: arch/x86/realmode/rm/realmode.elf] Error 1
make[5]: *** [../arch/x86/realmode/Makefile:22: arch/x86/realmode/rm/realmode.bin] Error 2
make[4]: *** [../scripts/Makefile.build:461: arch/x86/realmode] Error 2
make[4]: *** Waiting for unfinished jobs....
make[3]: *** [../scripts/Makefile.build:461: arch/x86] Error 2
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [/linux/linux_kselftest/Makefile:2009: .] Error 2
make[1]: *** [/linux/linux_kselftest/Makefile:248: __sub-make] Error 2
make: *** [Makefile:248: __sub-make] Error 2

thanks,
-- Shuah