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Date:   Thu, 19 Mar 2020 15:04:16 +0100
From:   Michal =?iso-8859-1?Q?Such=E1nek?= <msuchanek@suse.de>
To:     Andy Shevchenko <andy.shevchenko@gmail.com>
Cc:     "open list:LINUX FOR POWERPC PA SEMI PWRFICIENT" 
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Subject: Re: [PATCH v11 4/8] powerpc/perf: consolidate valid_user_sp
Message-ID: <20200319140416.GK25468@kitsune.suse.cz>
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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@suse.de> 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