[PATCH] x86: Support BHI_CTRL instruction

[Jiang, Haochen]

> From: Christian Ludloff <ludloff@gmail.com>
> Sent: Friday, June 5, 2026 2:25 PM
> To: Jiang, Haochen <haochen.jiang@intel.com>
> Cc: Beulich, Jan <JBeulich@suse.com>; hjl.tools@gmail.com;
> binutils@sourceware.org
> Subject: Re: [PATCH] x86: Support BHI_CTRL instruction
> 
> On Thu, Jun 4, 2026 at 11:02 PM Jiang, Haochen <haochen.jiang@intel.com>
> wrote:
> > > > > Arguably RDSSP{D,Q} is a litmus test – can it REX2 or EVEX?
> > > >
> > > > I suppose it should be a REX2, not EVEX MAP4.
> > >
> > > From the perspective of the ISA, the W for D-vs-Q
> > > can come from REX or REX2 or EVEX – it should
> > > not matter which of the three encodings gets used
> > > for RDSSP. If that is not the case, then please get
> > > it documented too, together with IBHF behavior.
> >
> > APX documentation has mentioned which instructions could be
> > promoted to EVEX MAP4. Only the inst mentioned in chart could
> > use EVEX MAP4. Actually, those EVEX MAP4 insts are all listed
> > one by one in EAS since the encoding are quite different.
> 
> Sure, MAP4 is documented as a "no".
> 
> But MAP1 otoh...  :-)
> 
> 0x62,0xF9,0x7E,0x08,0x1E,0xC8
> 0x62,0xF9,0xFE,0x08,0x1E,0xC8
> 

RDSSP{D,Q} are only legacy encodings, they have nothing to do with
EVEX encoding. So, they should obey legacy space rule, not EVEX space
rule in APX. Those rules are quite clear in documentation. I did not quite
get your confusion here.

Thx,
Haochen