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

[H. Peter Anvin]

On October 27, 2026 10:55:04 PM PDT, "Thomas Weißschuh" <thomas.weissschuh@xxxxxxxxxxxxx> wrote:
>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

The nice thing would be that it would let debug tools use them as-is, and after all we need to make the vdso itself available anyway. As a possible side benefit the user would be able to see the post-patch vdso.