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

[Christophe Leroy <christophe.leroy@c-s.fr>]

Le 19/03/2020 à 14:35, Andy Shevchenko a écrit :
> 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:

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