Re: [PATCH 1/1] scripts: kstack_erase: use relative stackleak plugin path

[Nathan Chancellor <nathan@kernel.org>]

On Fri, Jul 24, 2026 at 10:18:57PM +0200, Nicolas Schier wrote:
> On Wed, Jul 22, 2026 at 07:00:43PM +0000, Jaihind Yadav wrote:
> > 
> > Hi Nicolas Schier,
> > 
> > Thanks for the suggestion. I tested the proposed change:
> > 
> > -kstack-erase-cflags-y += -fplugin=$(objtree)/scripts/gcc-plugins/stackleak_plugin.so
> > +kstack-erase-cflags-y += -fplugin=scripts/gcc-plugins/stackleak_plugin.so
> > 
> > 
> > Unfortunately, it does not work for the out-of-tree module builds in
> > my environment.
> 
> Thanks for checking; and yes I forgot out-of-tree modules.  When
> building them, Kbuild changes to their respective output directory so my
> suggestion had to fail for oot kmods.

Technically, this is only a problem for out of tree kernel modules,
right? When building in-tree kernel modules, objtree is always '.', so
we will never have the output directory path in the debug information
(at least based on my brief testing).

> > Given that the proposed relative path breaks out-of-tree module
> > builds, could you please take a look at the patch I posted? If the
> > approach looks reasonable, I would appreciate your review and
> > consideration for merging it.
> 
> I am not sure, if we can take your path, as 'readlink --relative-to' is
> only available in coreutils/Linux but coreutils are not a documented
> requirement for Linux builds (cp. Documentation/process/changes.rst),
> thus this would probably kill Linux builds on BSDs and Darwin/MacOS.
> 
> But let me think about that a few days;  and perhaps someone else comes
> up with an idea.

Yeah, I don't really like 'realpath --relative-to' either, it feels a
bit like a hack since it will only avoid including a full path if the
module output directory includes part of the build directory. For
example:

  O=/mnt/build/kernel
  MO=/mnt/build/extmod

$ realpath -m --relative-to /mnt/build/extmod /mnt/build/kernel
../kernel

vs.

  O=/home/nathan/build/kernel
  MO=/mnt/build/extmod

$ realpath -m --relative-to /mnt/build/extmod /home/nathan/build/kernel
../../../home/nathan/build/kernel

Furthermore, this patch only fixes KSTACK_ERASE but we have other GCC
plugins that presumably have the same problem.

I do not have a good solution for this either but since it only affects
external kernel modules, I am not particularly inclined to think too
hard about it.

-- 
Cheers,
Nathan