[PATCH] doc: announce changes in structure alignments for UBSan

[Morten Brørup]

> From: David Marchand [mailto:david.marchand at redhat.com]
> Sent: Wednesday, 9 July 2025 14.40
> 
> As part of the effort to limit undefined behaviors in DPDK code, some
> structure alignments revealed not to be accurate enough.
> At the moment two structures have been identified but others may be
> found while running more parts of DPDK with UBSan.
> 
> Though the calling code can explicitly request alignment,
> we would prefer to put the alignment constraints as part of the
> structure definition itself.
> 
> Such changes are ABI breakages.
> 
> Signed-off-by: David Marchand <david.marchand at redhat.com>
> ---
>  doc/guides/rel_notes/deprecation.rst | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/doc/guides/rel_notes/deprecation.rst
> b/doc/guides/rel_notes/deprecation.rst
> index e2d4125308..4ae561d670 100644
> --- a/doc/guides/rel_notes/deprecation.rst
> +++ b/doc/guides/rel_notes/deprecation.rst
> @@ -57,6 +57,10 @@ Deprecation Notices
>    ``__atomic_thread_fence`` must be used for patches that need to be
> merged in
>    20.08 onwards. This change will not introduce any performance
> degradation.
> 
> +* lib: multiple issues relating to unaligned accesses have been
> detected using the UBSan checker.
> +  As part of resolving those issues, alignment in some structures will
> be updated in 25.11,
> +  namely (but not exhaustively): ``struct rte_stack_lf_head`` and
> ``struct rte_mp_msg``.
> +
>  * lib: will fix extending some enum/define breaking the ABI. There are
> multiple
>    samples in DPDK that enum/define terminated with a ``.*MAX.*`` value
> which is
>    used by iterators, and arrays holding these values are sized with
> this
> --
> 2.50.0

Yes, please.

Acked-by: Morten Brørup <mb at smartsharesystems.com>