RE: [PATCH] x86: Remove unnecessary vex.w check for xh_mode in disassembler

["Jiang, Haochen" <haochen.jiang@intel.com>]

> -----Original Message-----
> From: H.J. Lu <hjl.tools@gmail.com>
> Sent: Tuesday, December 6, 2022 11:40 AM
> To: Jiang, Haochen <haochen.jiang@intel.com>
> Cc: Beulich, Jan <JBeulich@suse.com>; binutils@sourceware.org
> Subject: Re: [PATCH] x86: Remove unnecessary vex.w check for xh_mode in
> disassembler
> 
> On Mon, Dec 5, 2022 at 5:36 PM Jiang, Haochen <haochen.jiang@intel.com>
> wrote:
> >
> > > > Another reason for removing this check is because xh_mode with
> > > > broadcast usage should not indicate the vex.w bit. Instead it
> > > > should be handled by a W table entry.
> > >
> > > There are no broadcast insns using xh_mode, and you can't really
> > > mean embedded broadcast (because EVEX.W needs to be properly
> encoded
> > > there).
> > > Hence I don't follow what you're talking about here.
> >
> > Maybe this part is a little misleading. I will delete that in commit message.
> > What I actually mean is just like what you commented.
> >
> > I suppose using a W table entry in the future to encode here if not
> > using something like %XH.
> 
> If vex.w == 1 check is removed, disassembler will display the wrong
> instruction.

No, it will still print "{bad}" for all instructions currently since all of them are
using %XH, which will do this thing.

Maybe you are concerned about future instruction behavior w/o using %XH?

Haochen

> 
> > Haochen
> >
> > >
> > > The code change is okay, but if the above is to become the commit
> > > message, the raised question will need addressing first.
> > >
> > > Jan
> 
> 
> 
> --
> H.J.