Re: [tip: x86/cleanups] x86/segment: Use MOVL when reading segment registers

[Uros Bizjak]

On Thu, Mar 12, 2026 at 8:50 PM Uros Bizjak <ubizjak@xxxxxxxxx> wrote:
>
> On Thu, Mar 12, 2026 at 8:12 PM H. Peter Anvin <hpa@xxxxxxxxx> wrote:
> >
> > Note: I personally *hate* the savesegment() syntax. For one thing, I would
> > much rather see a more C-like syntax, even if that means making a bunch of
> > inline functions. Replacing the macro with something that is actually
> > type-safe would be a bloody good thing, too.
> >
> > Something like:
> >
> > /* Generates register operation */
> > static inline unsigned int ds(void)
> > {
> >         unsigned int v;
> >         asm volatile("mov %%ds,%0" : "=r" (v));
> >         return v;
> > }
>
> Yes, this would be much better, but should be unsigned long, because
> move from segment register zero-extends all the way to 64-bits:
>
> static inline unsigned long read_ds(void)
> {
>          unsigned long v;
>          asm volatile("mov %%ds,%k0" : "=r" (v));
>          return v;
> }

Now implemented at [1].

[1] https://lore.kernel.org/lkml/20260312215916.258176-4-ubizjak@xxxxxxxxx/T/#u

Uros.