Re: [PATCH 2/2] alpha: read $gp and $sp explicitly for clang

On Tue, Aug 11, 2026 at 1:10 PM Maciej W. Rozycki <[email protected]> wrote:
>
> On Mon, 3 Aug 2026, Magnus Lindholm wrote:
>
> > > diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
> > > index 7631129ac914..5b4f1ae2b74b 100644
> > > --- a/arch/alpha/kernel/traps.c
> > > +++ b/arch/alpha/kernel/traps.c
> > > @@ -925,7 +925,9 @@ void
> > >  trap_init(void)
> > >  {
> > >         /* Tell PAL-code what global pointer we want in the kernel.  */
> > > -       register unsigned long gptr __asm__("$29");
> > > +       unsigned long gptr;
> > > +
> > > +       __asm__ volatile("mov $29, %0" : "=r"(gptr));
> > >         wrkgp(gptr);
> > >
> > >         wrent(entArith, 1);
> >
> > This looks good to me. The explicit $gp read and use of
> > current_stack_pointer avoid relying on the unsupported local
> > register-asm behavior.
>
>  It could have been worth mentioning in the change description that no
> code quality regression results here with GCC:
>
> --- arch/alpha/kernel/traps-0.dump      2026-08-11 11:57:59.895247441 +0100
> +++ arch/alpha/kernel/traps-1.dump      2026-08-11 11:56:31.788713285 +0100
> @@ -2223,8 +2223,8 @@
>                         1b70: GPDISP    .text+0x4
>      1b74:      00 00 bd 23     lda     gp,0(gp)
>      1b78:      f0 ff de 23     lda     sp,-16(sp)
> -    1b7c:      10 04 fd 47     mov     gp,a0
> -    1b80:      00 00 5e b7     stq     ra,0(sp)
> +    1b7c:      00 00 5e b7     stq     ra,0(sp)
> +    1b80:      10 04 fd 47     mov     gp,a0
>      1b84:      37 00 00 00     call_pal        0x37
>      1b88:      04 00 00 c2     br      a0,1b9c <trap_init+0x2c>
>      1b8c:      08 00 1e a6     ldq     a0,8(sp)
>
>  Also I think our coding style would rather see the asm written as:
>
>         __asm__ __volatile__("mov $29, %0" : "=r" (gptr));
>
>  Otherwise:
>
> Reviewed-by: Maciej W. Rozycki <[email protected]>
>
>   Maciej

Hi Matt,

Given Maciej's comment on the inline asm style, do you want to send a v2
of this patch, or are you happy for me to fold the

__asm__ volatile(...)

to

__asm__ __volatile__(...)

style change in when I apply it to the Alpha tree?

Either is fine with me.

Thanks,
Magnus