Our website uses cookies to enhance your browsing experience.
Accept
to the top
close form

Fill out the form in 2 simple steps below:

Your contact information:

Step 1
Congratulations! This is your promo code!

Desired license type:

Step 2
Team license
Enterprise license
** By clicking this button you agree to our Privacy Policy statement
close form
Request our prices
New License
License Renewal
--Select currency--
USD
EUR
* By clicking this button you agree to our Privacy Policy statement

close form
Free PVS‑Studio license for Microsoft MVP specialists
* By clicking this button you agree to our Privacy Policy statement

close form
To get the licence for your open-source project, please fill out this form
* By clicking this button you agree to our Privacy Policy statement

close form
I am interested to try it on the platforms:
* By clicking this button you agree to our Privacy Policy statement

close form
check circle
Message submitted.

Your message has been sent. We will email you at


If you do not see the email in your inbox, please check if it is filtered to one of the following folders:

  • Promotion
  • Updates
  • Spam

>
>
>
Atavisms in large systems

Atavisms in large systems

Aug 06 2009
Author:

Large old program systems developing for tens of years contain a lot of various atavisms and code sections which have been simply written with the use of popular paradigms and styles of different ages. You can watch evolution of programming languages - the oldest code sections are written in C and the most recent contain complex templates in Alexandrescu style.

There are atavisms relating to 64-bit mode as well. To be more exact, they are atavisms which prevent modern 64-bit code from correct operation. I will give you two examples I have learned recently.

The interesting error relates to an old version of macOS system and is situated inside the function malloc_zone_calloc:

// beyond this, assume a programming error
#define MAX_ALLOCATION 0xc0000000 
// Allocate cleared (zero-filled) memory from
// the given zone for num_items objects,
// each of which is size bytes large
void *malloc_zone_calloc(malloc_zone_t *zone,
  size_t num_items, size_t size)
{
  void  *ptr;
  if (malloc_check_start &&
      (malloc_check_counter++ >= malloc_check_start))
  {
    internal_check();
  }
  if (((unsigned)num_items >= MAX_ALLOCATION) ||
      ((unsigned)size >= MAX_ALLOCATION) ||
      ((long long)size * num_items >=
       (long long) MAX_ALLOCATION))
  {
    /* Probably a programming error */
    fprintf(stderr,
      "*** malloc_zone_calloc[%d]: arguments too large: %d,%d\n",
      getpid(), (unsigned)num_items, (unsigned)size);
    return NULL;
  }
  ptr = zone->calloc(zone, num_items, size);
  if (malloc_logger)
    malloc_logger(MALLOC_LOG_TYPE_ALLOCATE |
                  MALLOC_LOG_TYPE_HAS_ZONE |
                  MALLOC_LOG_TYPE_CLEARED,
                  (unsigned)zone,
                  num_items * size, 0,
                  (unsigned)ptr, 0);
  return ptr;
}

Firstly, the function's code contains check of the sizes of memory being allocated strange for the 64-bit system. And secondly, the diagnostic warning you see is incorrect for if we ask to allocate memory for 4 400 000 000 items, due to explicit conversion of the type to unsigned, we will see a strange diagnostic warning about impossibility to allocate memory only for 105 032 704 items.

As far as I understood the note, this strange check was removed from the function only in 2006. Although I may be wrong about the date of correction, this example shows rather well how easy it is to forget about something old.



Comments (0)

Next comments next comments
close comment form