Re: [PATCH v4] ELF: AT_PAGE_SHIFT_MASK -- supply userspace with available page shifts

Alexey Dobriyan
2024-02-09T12:30:46Z

On Mon, Feb 05, 2024 at 04:48:08AM -0800, Kees Cook wrote:
> On Mon, Feb 05, 2024 at 12:51:43PM +0300, Alexey Dobriyan wrote:
> > +#define ARCH_AT_PAGE_SHIFT_MASK \
> > + do { \
> > + u32 val = 1 << 12; \
> > + if (boot_cpu_has(X86_FEATURE_PSE)) { \
> > + val |= 1 << 21; \
> > + } \
> > + if (boot_cpu_has(X86_FEATURE_GBPAGES)) { \
> > + val |= 1 << 30; \
> > + } \
>
> Can we use something besides literal "12", "21", and "30" values here?

Ehh, no, why? Inside x86_64 the page shifts are very specific numbers,
they won't change.