Re: 6.18.14: VirtualBox modules don't build anymore; bisected

[Nathan Chancellor <nathan@kernel.org>]

On Fri, Feb 27, 2026 at 08:29:05PM -0500, Greg KH wrote:
> On Sat, Feb 28, 2026 at 12:30:29AM +0100, Rainer Fiebig wrote:
> > Am 27.02.26 um 21:12 schrieb Greg KH:
> > > On Fri, Feb 27, 2026 at 04:33:34PM +0100, Rainer Fiebig wrote:
> > >> In case this hasn't been reported already: with 6.18.14 the
> > >> VirtualBox-7.1.16 modules won't build during the boot process, as they
> > >> usually do.  Bisecting between 6.18.13/14 led to this:
> > >>
> > >> f056c340b73962ebaffe93997b582bdf16dc6270 is the first bad commit
> > >> commit f056c340b73962ebaffe93997b582bdf16dc6270 (HEAD)
> > >> Author: Josh Poimboeuf <jpoimboe@kernel.org>
> > >> Date:   Tue Feb 10 13:45:22 2026 -0800
> > >>
> > >>     kbuild: Add objtool to top-level clean target
> > >>
> > >>     [ Upstream commit 68b4fe32d73789dea23e356f468de67c8367ef8f ]
> > >>
> > >>     Objtool is an integral part of the build, make sure it gets cleaned
> > >>     by "make clean" and "make mrproper".
> > >> [...]
> > >>
> > >>
> > >> The script I use for building my kernels includes "make mrproper" before
> > >> compiling and "make clean" after the kernel and modules have been
> > >> installed.
> > >>
> > >> Perhaps it would be more appropriate to report this to the
> > >> VirtualBox-devs but I won't do that because the registration procedure
> > >> asks for too many private data.
> > > 
> > > We obviously can not do anything about external modules, so if you rely
> > > on these, you are going to have to work with them on this, sorry.
> > 
> > Alright, tough luck.  But that a patch-release of an LTS-kernel breaks
> > VirtualBox is really a first - at least as far as I can remember.
> 
> Then they have gotten really lucky :)

I think this is firmly a Kbuild bug, as we broke the contract of
'make clean' leaving around enough to build external modules:

  https://lore.kernel.org/20260227-avoid-objtool-binary-removal-clean-v1-1-122f3e55eae9@kernel.org/

Kbuild is what runs objtool, not the external module itself. I don't
care much for external modules but this does not appear to be something
they have done or relied on.

Cheers,
Nathan