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cglibcsbrk

can sbrk(0) fail?

I'd like to know if someone already seen sbrk(0) fail ?

I mean, if you can reach this function you obviously had the rights to access the memory before, so to check the current break location should be ok, right ?

EDIT : Should I consider an error exception for example ?

Solution

  • The documents states that:

       sbrk() increments the program's data space by increment bytes.
   Calling sbrk() with an increment of 0 can be used to find the current
   location of the program break.

  ...

   On success, sbrk() returns the previous program break.  (If the break
   was increased, then this value is a pointer to the start of the newly
   allocated memory).  On error, (void *) -1 is returned, and errno is
   set to ENOMEM.

    If you look at glibc implementation you will see:

    extern void *__curbrk;
  ...
void *
__sbrk (intptr_t increment)
{
  ...
  if (increment == 0)
    return __curbrk; 
  ...

    there is no way it will fail since it just returns the current value of __curbrk if increment is zero.