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

On Thu, Mar 19, 2020 at 03:35:03PM +0200, Andy Shevchenko wrote:

On Thu, Mar 19, 2020 at 1:54 PM Michal Suchanek [off-list ref] wrote:

quoted

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

...

quoted

+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