Re: Imminent bugfix release (1.97.1)

[Bean]

On Tue, Nov 10, 2009 at 4:28 PM, Bean <address@hidden> wrote:
> On Tue, Nov 10, 2009 at 1:39 PM, Bean <address@hidden> wrote:
>> On Tue, Nov 10, 2009 at 5:34 AM, Vladimir 'phcoder' Serbinenko
>> <address@hidden> wrote:
>>> But now it has a technical problem: it may read post array definitions.
>>> If any of post-array memory is MMIO or absent reading from it may have
>>> peculiar consequences
>>>>     Also, because s1 and s2 have two differents roles, I think it would be
>>>> best to give them names that better suits them. ;)
>>
>> Hi,
>>
>> Right, I think it'd be better to use fixed size array, perhaps we can
>> define a type grub_password_t for it.
>>
>> BTW, with fixed size array, the following algorithm should run exactly
>> the same amount of instruction each time:
>>
>> typedef char grub_password_t[1024];
>>
>> int
>> grub_auth_strcmp (const grub_password_t s1, const grub_password_t s2)
>> {
>>  int r1 = 0;
>>  int r2 = 0;
>>  int i, *p;
>>
>>  p = &r1;
>>  for (i = 0; i < sizeof (grub_password_t); i++, s1++, s2++)
>>    {
>>      *p |= (*s1 ^ *s2);
>>      if (*s1 == '\0')
>>        p = &r2;
>>    }
>>
>>  return (r1 != 0);
>> }
>
> Hi,
>
> Oh sorry, this one still have some issue, this should work:
>
> typedef char grub_password_t[1024];
>
> int
> grub_auth_strcmp (const grub_password_t s1, const grub_password_t s2)
> {
>  int r1 = 0;
>  int r2 = 0;
>  int i, *p1, *p2;
>
>  p1 = p2 = &r1;
>  for (i = 0; i < sizeof (grub_password_t); i++, s1++, s2++)
>    {
>      *p1 |= (*s1 ^ *s2);
>      if (*s1 == '\0')
>        p1 = &r2;
>      else
>        p2 = &r2;
>    }
>
>  return (r1 != 0);
> }


Hi,

Just in case p2 is optimized out by gcc:

typedef char grub_password_t[1024];

int
grub_auth_strcmp (const grub_password_t s1, const grub_password_t s2)
{
  char r1 = 0;
  char r2 = 0;
  char r3 = 0;
  char *p1, *p2;
  int i;

  p1 = &r1;
  p2 = &r3;
  for (i = 0; i < sizeof (grub_password_t); i++, s1++, s2++)
    {
      *p1 |= (*s1 ^ *s2);
      if (*s1 == '\0')
        p1 = &r2;
      else
        p2 = &r2;
     (*p2)++;
    }

  return (r1 != 0);
}


-- 
Bean

My repository: https://launchpad.net/burg
Document: https://help.ubuntu.com/community/Burg