[PATCH] x86/APX: limit printing of REX2 payload

[H.J. Lu]

On Wed, Sep 9, 2026 at 1:52 PM Jan Beulich <jbeulich@suse.com> wrote:
>
> On 09.09.2026 07:50, Jiang, Haochen wrote:
> >> From: Jan Beulich <jbeulich@suse.com>
> >> Sent: Tuesday, September 8, 2026 11:11 PM
> >>
> >> When set bits were properly consumed (and hence all we want is an
> >> indication that REX2-encoding is in use), print merely {rex2}, thus also
> >> better matching original input.
> >>
> >> While effectively copying parts of an existing conditional, also simplify
> >> the original: There's no need to apply the 3-bit mask twice.
> >>
> >> While adjusting testcases, also escape curly braces.
> >
> > Actually, when I am working on BHI_CTRL patch, I have the same question
> > for why we are printing {rex2 0x88}. Thus, I asked Lili for that. Lili told me
> > that back to the very beginning, it is H.J requested to add those additional
> > info to express the rex2 prefix.
>
> And we still do when there are unconsumed bits.
>
> > Maybe we need H.J's input on this.
>
> Sure, I'm not going to commit right away.
>

{rex} and {rex2} are different.

[hjl@gnu-tgl-3 tmp]$ cat x.s
{rex} movl %eax,%ebx
{rex2} movl %eax,%ebx
[hjl@gnu-tgl-3 tmp]$ gcc -c x.s
[hjl@gnu-tgl-3 tmp]$ objdump -dw x.o

x.o:     file format elf64-x86-64


Disassembly of section .text:

0000000000000000 <.text>:
   0: 40 89 c3             rex mov %eax,%ebx
   3: d5 00 89 c3           {rex2 0x0} mov %eax,%ebx
[hjl@gnu-tgl-3 tmp]$

{rex} maps to 0x40.  But {rex2} maps to different 2 bytes.
{rex2 0x0} tells what these 2 bytes are.   I prefer to
keep it ASIS.

-- 
H.J.