brk(2)                     DG/UX 4.30                      brk(2)



     NAME
          brk - Change data segment space allocation

     SYNOPSIS
          int       brk  (endds)
          char *    endds;

     PARAMETERS
          endds     The address of the first byte beyond the new end
                    of the data area.

     DESCRIPTION
          The brk system call dynamically changes the amount of space
          allocated for the calling process's data segment; see
          exec(2).  The change is made by resetting the process's
          break value and allocating or deallocating the appropriate
          amount of space.  The break value is the address of the
          first byte beyond the end of the data segment.  The amount
          of allocated space increases as the break value increases.
          If endds is greater than the current break value, the newly
          allocated space is set to zero; i.e., if these addresses are
          read before they are written, the contents will be zero.  If
          endds is less than the current break value, space is
          deallocated from the data segment.  The contents of
          addresses from endds to the current break value become
          undefined.

          There is a maximum possible break value for a process; this
          value may be determined with the ulimit(2) call.  An
          implementation or machine architecture-dependent minimum
          value exists; this address is one byte greater than the
          ending address of a data area which contains one page, as
          defined by the implementation.

          The brk system call will fail without making any change in
          the allocated space if an error occurs.

     ACCESS CONTROL
          No access check is made.

     RETURN VALUE
          0              The brk operation was successful.

          -1             An error occurred.  Errno is set to indicate
                         the error.

     EXCEPTIONS
          Errno may be set to one of the following error codes:

          ENOMEM         The change would allocate more space than is
                         allowed by a system-imposed maximum (see
                         ulimit(2)).



     Licensed material--property of copyright holder(s)         Page 1

     brk(2)                     DG/UX 4.30                      brk(2)



          ENOMEM         The change would allocate more space than is
                         allowed by the current data resource limit
                         (see getrlimit(2)).

          ENOMEM         The change would make the break value greater
                         than or equal to the start address of an
                         attached shared memory segment (see
                         shmat(2)).

          EFAULT         The change would make the break value less
                         than the system-imposed minimum.

          EFAULT         The new break value is not a valid user
                         address.

          EAGAIN         The change would allocate more space than the
                         available physical memory and swap space.

          EAGAIN         The system-imposed limit on space locked into
                         physical memory would be exceeded; the
                         MCL_FUTURE memory locking option is in effect
                         for the calling process (see memcntl(2)).

     SEE ALSO
          exec(2), ulimit(2), getrlimit(2), memcntl(2).






























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