Re: [PATCH RESEND] kbuild: Stop modifying $(objtree)/Makefile when building oot-kmods oos

[Nicolas Schier <nsc@kernel.org>]

On Thu, Jul 23, 2026 at 04:16:22PM -0700, Nathan Chancellor wrote:
> > Update output Makefile in the corresponding tree only: for out-of-source
> > in-tree builds update $(objtree)/Makefile, for out-of-source out-of-tree
> > module builds update $(KBUILD_EXTMOD_OUTPUT)/Makefile instead.
> > 
> > In-source builds are not affected.
> > 
> > Since commit c9bb03ac2c66 ("kbuild: reduce output spam when building out
> > of tree"), building out-of-tree kernel modules out-of-source (make M=...
> > MO=...) causes a rewrite of $(objtree)/Makefile with KBUILD_EXTMOD and
> > KBUILD_EXTMOD_OUTPUT being set.  That is problematic:
> > 
> >  * $(objtree)/ must not be changed in any way when building out-of-tree
> >    modules as it breaks other uses of $(objtree).
> > 
> >  * Setting KBUILD_EXTMOD and KBUILD_EXTMOD_OUTPUT in $(objtree)/Makefile
> >    kills the tree for incremental builds that start right there
> >    ('make -C $(objtree)'); builds starting in $(srctree) reset
> >    $(objtree)/Makefile to its original content.
> > 
> > Further, $(KBUILD_EXTMOD_OUTPUT)/Makefile was not generated any more at
> > all.
> > 
> > This commit restores the previous kbuild behaviour prior to commit
> > c9bb03ac2c66 ("kbuild: reduce output spam when building out of tree")
> > but leaves in-place the use of filechk for output spam reduction.
> > 
> > Fixes: c9bb03ac2c66 ("kbuild: reduce output spam when building out of tree")
> > Reported-by: Anish Rashinkar <rashinkar.anish@gmail.com>
> > Closes: https://lore.kernel.org/r/CAOESE2Q2-0KUDaM0mUo+c_F-tMaUsBZ-gpnhdoe0rmYdgnnuJQ@mail.gmail.com
> > Cc: stable@vger.kernel.org
> > Tested-by: Philipp Hahn <p.hahn@avm.de>
> > Reviewed-by: Philipp Hahn <p.hahn@avm.de>
> > Signed-off-by: Nicolas Schier <n.schier@fritz.com>
> > Signed-off-by: Nicolas Schier <nsc@kernel.org>
> 
> Thanks!
> 
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Tested-by: Nathan Chancellor <nathan@kernel.org>
> 
> Do you want me to take this via kbuild-fixes?

Yes, please take it via kbuild-fixes, as it actually breaks build trees.

Thanks!

-- 
Nicolas