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

From: Michal Suchánek <[email-masked]>
Date: Thu, 19 Mar 2020 15:46:42 +0100

On Thu, Mar 19, 2020 at 03:16:03PM +0100, Christophe Leroy wrote:
> 
> 
> Le 19/03/2020 à 14:35, Andy Shevchenko a écrit :
> > On Thu, Mar 19, 2020 at 1:54 PM Michal Suchanek <[email-masked]> 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;
> > > +}
> > 
> > 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);
And we can avoid the inversion here as well as in !valid_user_sp(sp) by
changing to invalid_user_sp.

Thanks

Michal