Re: [PATCH] vDSO, kbuild: Provide vDSO debug variants at runtime

[Thomas Weißschuh]

On Tue, Oct 27, 2026 at 05:02:52PM -0700, H. Peter Anvin wrote:
> On October 27, 2026 1:22:44 PM PDT, Nicolas Schier <nsc@xxxxxxxxxx> wrote:
> >On 2026-07-08 15:56 +0200, Thomas Weißschuh wrote:
> >> Finding the debug version of the vDSO is not trivial as there is no common
> >> scheme where it is placed. That's especially problematic for CI testing.
> >> 
> >> The vDSO futex unlock mechanism requires for testing to have access to the
> >> inner labels of the unlock assembly, which are only accessible via the
> >> debug so.
> >> 
> >> Also for general debugging purposes it's convenient to have access to the
> >> debug vDSO at a well defined place.
> >> 
> >> The files are placed in /sys/kernel/vdso_debug.tar.xz. They use the
> >> regular 'make vdso_install' layout, including build-id symlinks to find
> >> the correct file for each process.
> >> 
> >> The design is kept close to the ones of the similar IKCONFIG and IKHEADERS.
> >> 
> >> On x86 the x32 vDSO is derived from the x86_64 one, necessitating an
> >> explicit dependency to avoid errors due to concurrent builds.
> >> 
> >> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxx>
> >> Link: https://lore.kernel.org/lkml/20260602090536.045586688@xxxxxxxxxx/
> >> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> >> ---
> >>  Makefile            | 33 ++++++++++++++++++++++++++++++++-
> >>  arch/x86/Makefile   |  3 +++
> >>  init/Kconfig        | 10 ++++++++++
> >>  kernel/Makefile     |  1 +
> >>  kernel/vdso_debug.c | 43 +++++++++++++++++++++++++++++++++++++++++++
> >>  5 files changed, 89 insertions(+), 1 deletion(-)
> >> 
> >
> >This seems to have fallen through the cracks; shall it be considered for
> >kbuild-7.5?

Please don't pick this up just yet. I have a prototype which exposes the
directory through sysfs directly without forcing users to unpack the archive.
If you could take a look at the kbuild bits however, that would be great.

> A thought: most tools support compressed separate debug information. Would it
> make more sense to have the vdso images with separate, compressed debug data
> in a subdirectory?

I want to stick to the 'make vdso_install' layout. Maybe that should be
changed to your proposal, too? But what are the specific advantages?
The files are compressed on disk anyways through the module compression.


Thomas