Re: [PATCH v11 4/8] powerpc/perf: consolidate valid_user_sp

From: Michal Suchánek
Date: Thu Mar 19 2020 - 10:04:23 EST


On Thu, Mar 19, 2020 at 03:35:03PM +0200, Andy Shevchenko wrote:
> On Thu, Mar 19, 2020 at 1:54 PM Michal Suchanek <msuchanek@xxxxxxx> wrote:
> >
> > Merge the 32bit and 64bit version.
> >
> > Halve the check constants on 32bit.
> >
> > Use STACK_TOP since it is defined.
> >
> > Passing is_64 is now redundant since is_32bit_task() is used to
> > determine which callchain variant should be used. Use STACK_TOP and
> > is_32bit_task() directly.
> >
> > This removes a page from the valid 32bit area on 64bit:
> > #define TASK_SIZE_USER32 (0x0000000100000000UL - (1 * PAGE_SIZE))
> > #define STACK_TOP_USER32 TASK_SIZE_USER32
>
> ...
>
> > +static inline int valid_user_sp(unsigned long sp)
> > +{
> > + bool is_64 = !is_32bit_task();
> > +
> > + if (!sp || (sp & (is_64 ? 7 : 3)) || sp > STACK_TOP - (is_64 ? 32 : 16))
> > + return 0;
> > + return 1;
> > +}
>
> Perhaps better to read
>
> if (!sp)
> return 0;
>
> if (is_32bit_task()) {
> if (sp & 0x03)
> return 0;
> if (sp > STACK_TOP - 16)
> return 0;
> } else {
> ...
> }
>
> return 1;
>
> Other possibility:
>
> unsigned long align = is_32bit_task() ? 3 : 7;
> unsigned long top = STACK_TOP - (is_32bit_task() ? 16 : 32);
>
> return !(!sp || (sp & align) || sp > top);
Sounds reasonale.

Thanks

Michal
>
> --
> With Best Regards,
> Andy Shevchenko