Re: [PATCH v5 12/24] vdso: Add the vdsocheck tool

On Tue, Sep 08, 2026 at 09:19:11AM +0200, Peter Zijlstra wrote:

On Tue, Sep 08, 2026 at 08:33:46AM +0200, Thomas Weißschuh wrote:

quoted

All vDSO code needs to be completely position independent. Symbol
references are marked as hidden so the compiler emits PC-relative
relocations. However there are cases where the compiler may still
emit absolute relocations, as they are valid in regular PIC DSO code.
These would be resolved by the linker and will break at runtime.
This has been observed on arm64, see commit 0c314cda9325 ("arm64: vdso:
Work around invalid absolute relocations from GCC")

Introduce a tool to check for absolute relocations during the build,
as the current inline-shell logic is not expressive enough.
The check is done on the object files as the relocations will not exist
anymore in the final DSO. As there is no extension point for the
compilation of each object file, perform the validation in vdso_check.

Signed-off-by: Thomas Weißschuh <redacted>
---
 Makefile                    |  19 ++
 lib/vdso/Kconfig            |   5 +
 lib/vdso/Makefile           |   2 +
 lib/vdso/Makefile.include   |  14 ++
 lib/vdso/check/.gitignore   |   3 +
 lib/vdso/check/Makefile     |  34 +++
 lib/vdso/check/elf.rs       | 498 ++++++++++++++++++++++++++++++++++++++++++++
 lib/vdso/check/vdsocheck.rs | 154 ++++++++++++++
 8 files changed, 729 insertions(+)

Urgh, does this mean I have to have rust installed just to build a
kernel now?

No.

If you don't have rust installed the build will instead use the existing shell
script for a less thorough check. We only need one build machine at some point
to have rust installed to report issues and this check to be useful.


Thomas