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From:   Andy Shevchenko <andy.shevchenko@gmail.com>
Date:   Thu, 19 Mar 2020 15:35:03 +0200
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Subject: Re: [PATCH v11 4/8] powerpc/perf: consolidate valid_user_sp
To:     Michal Suchanek <msuchanek@suse.de>
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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);

-- 
With Best Regards,
Andy Shevchenko