Re: rex.W prefix in jumps on x86_64

[Paul Cercueil]

Hi Marc,

Le lun. 15 juin 2020 à 10:26, Marc Nieper-Wißkirchen 
<marc.nieper+gnu@gmail.com> a écrit :
> May I check with you whether this issue has reached you, Paulo?

Your message definitely hit the list.

> Thanks,
>
> Marc
>
> Am Sa., 25. Apr. 2020 um 21:02 Uhr schrieb Marc Nieper-Wißkirchen
> <marc.nieper+gnu@gmail.com>:
> >  Hi,
> >
> >  I am currently using the development version of GNU lightning. When 
> > I
> >  look at the disassembly, I see things like
> >
> >  rex.W jmpq *%rax
> >
> >  when an instruction like `jmpr R0' is jitted. I am wondering about 
> > the
> >  REX prefix, which doesn't seem to be necessary. In 64 bit-mode, 
> > where
> >  the operand size is fixed for jumps and calls.

Was that introduced by commit 8dc376f?. This one introduced a bug but I 
can't exactly put my finger on what's going on.

-Paul

> >  Thanks!
> >
> >  Marc