[PATCH 1/1] x86: add "udb" opcode (permanent official #UD in 64-bit mode)

[Jiang, Haochen]

> From: H.J. Lu <hjl.tools@gmail.com>
> Sent: Tuesday, August 12, 2025 2:31 AM
> 
> On Mon, Aug 11, 2025 at 10:48 AM H. Peter Anvin <hpa@zytor.com> wrote:
> >
> > The opcode D6 has been officially reserved as a single-byte permanent
> > undefined (#UD) opcode in 64-bit mode with the mnemonic UDB.  This is
> > already the behavior of all known 64-bit implementations; this is thus
> > merely an official statement of forward compatibility and the
> > assignment of a mnemonic.
> >
> > This will be documented in the next version of the Intel Software
> > Developer's Manual; in the meantime I DO speak officially for Intel on

If you do think we need to hurry this patch in before next SDM published,
which should happen at the end of September, please make sure you add
this into the patch note since it is not released yet.

Thx,
Haochen

> > this issue.
> >
> > The x86 Advisory Council has ratified this decision, and so it is
> > expected to be honored across vendors, but I obviously cannot make any
> > official statement on any other vendor's behalf.
> >
> > I am covered by the Intel-FSF copyright assignment for binutils.
> >
> > Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>