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

[Christophe Leroy]

Le 19/03/2020 Ã 14:35, Andy Shevchenko a ÃcritÂ:
> 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:

I prefer this one.

>    unsigned long align = is_32bit_task() ? 3 : 7;

I would call it mask instead of align

>    unsigned long top = STACK_TOP - (is_32bit_task() ? 16 : 32);
>
>    return !(!sp || (sp & align) || sp > top);

Christophe