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brk(2)                           System Calls                           brk(2)

       brk,  sbrk  -  change  the  amount  of  space allocated for the calling
       process's data segment

       #include <unistd.h>

       int brk(void *endds);

       void *sbrk(intptr_t incr);

       The brk() and sbrk() functions  are  used  to  change  dynamically  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  the  appropriate  amount  of  space. The break value is the
       address of the first location beyond the end of the data  segment.  The
       amount of allocated space increases as the break value increases. Newly
       allocated space is set to zero. If, however, the same memory  space  is
       reallocated to the same process its contents are undefined.

       When  a program begins execution using execve() the break is set at the
       highest location defined by the program and data storage areas.

       The getrlimit(2) function may be used to determine the maximum  permis‐
       sible  size  of  the  data segment; it is not possible to set the break
       beyond the rlim_max value returned from a call to getrlimit(), that  is
       to say, "end + rlim.rlim_max." See end(3C).

       The  brk() function sets the break value to endds and changes the allo‐
       cated space accordingly.

       The sbrk() function adds incr function bytes to  the  break  value  and
       changes the allocated space accordingly. The incr function can be nega‐
       tive, in which case the amount of allocated space is decreased.

       Upon successful completion, brk() returns 0. Otherwise, it  returns  −1
       and sets errno to indicate the error.

       Upon  successful completion, sbrk() returns the prior break value. Oth‐
       erwise, it returns (void *)−1 and sets errno to indicate the error.

       The brk() and sbrk() functions will fail and no additional memory  will
       be allocated if:

       ENOMEM    The  data segment size limit as set by setrlimit() (see getr‐
                 limit(2)) would be exceeded; the maximum possible size  of  a
                 data  segment  (compiled  into the system) would be exceeded;
                 insufficient space exists in the swap  area  to  support  the
                 expansion;  or  the new break value would extend into an area
                 of the address space defined by some  previously  established
                 mapping (see mmap(2)).

       EAGAIN    Total  amount of system memory available for private pages is
                 temporarily insufficient. This  may  occur  even  though  the
                 space  requested  was less than the maximum data segment size
                 (see ulimit(2)).

       The behavior of brk() and sbrk() is unspecified if an application  also
       uses   any   other  memory  functions  (such  as  malloc(3C),  mmap(2),
       free(3C)). The brk() and sbrk() functions have been used in specialized
       cases where no other memory allocation function provided the same capa‐
       bility. The use of mmap(2) is now preferred  because  it  can  be  used
       portably  with all other memory allocation functions and with any func‐
       tion that uses other allocation functions.

       It is unspecified whether the pointer returned  by  sbrk()  is  aligned
       suitably for any purpose.

       See attributes(7) for descriptions of the following attributes:

       tab()  box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
       TRIBUTE VALUE _ MT-LevelMT-Safe

       exec(2), getrlimit(2), mmap(2), shmop(2), ulimit(2), end(3C), free(3C),

       The  value of incr may be adjusted by the system before setting the new
       break value. Upon successful completion, the implementation  guarantees
       a  minimum of incr bytes will be added to the data segment if incr is a
       positive value. If incr is a negative value, a maximum  of  incr  bytes
       will  be removed from the data segment. This adjustment may not be nec‐
       essary for all machine architectures.

       The value of the arguments to both brk() and sbrk() are rounded up  for
       alignment with eight-byte boundaries.

       Setting the break may fail due to a temporary lack of swap space. It is
       not possible to distinguish this from a failure caused by exceeding the
       maximum size of the data segment without consulting getrlimit().

Oracle Solaris 11.4               14 Jan 1997                           brk(2)
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