Hi Kirill,
On Wed, 9 Jul 2025 at 11:31, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> On Tue, Jul 08, 2025 at 07:40:35PM -0700, Sohil Mehta wrote:
> > > @@ -664,14 +673,23 @@ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs,
> > > return GP_NO_HINT;
> > >
> > > #ifdef CONFIG_X86_64
> >
> > Might as well get rid of the #ifdef in C code, if possible.
> >
> > if (!IS_ENABLED(CONFIG_X86_64)
> > return GP_CANONICAL;
> >
> > or combine it with the next check.
>
> I tried this before. It triggers compiler error on 32-bit:
>
> arch/x86/kernel/traps.c:673:16: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
> 673 | if (*addr >= ~__VIRTUAL_MASK)
> | ^~~~~~~~~~~~~~
>
> __VIRTUAL_MASK is not usable on 32-bit configs.
arch/x86/include/asm/page_32_types.h:#define __VIRTUAL_MASK_SHIFT 32
arch/x86/include/asm/page_32_types.h:#define __VIRTUAL_MASK_SHIFT 32
arch/x86/include/asm/page_64_types.h:#define __VIRTUAL_MASK_SHIFT
(pgtable_l5_enabled() ? 56 : 47)
arch/x86/include/asm/page_types.h:#define __VIRTUAL_MASK
((1UL << __VIRTUAL_MASK_SHIFT) - 1)
Given __VIRTUAL_MASK_SHIFT is 32 on 32-bit platforms, perhaps
__VIRTUAL_MASK should just be changed to shift 1ULL instead?
Or better, use GENMASK(__VIRTUAL_MASK_SHIFT - 1, 0), so the
resulting type is still unsigned long.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
