bsd man page for brk

BRK(2)								System Calls Manual							    BRK(2)

NAME
       brk, sbrk - change data segment size

SYNOPSIS
       #include <sys/types.h>

       char *brk(addr)
       char *addr;

       char *sbrk(incr)
       int incr;

DESCRIPTION
       Brk  sets  the system's idea of the lowest data segment location not used by the program (called the break) to addr (rounded up to the next
       multiple of the system's page size).  Locations greater than addr and below the stack pointer are not in the address space  and	will  thus
       cause a memory violation if accessed.

       In  the	alternate  function  sbrk,  incr  more	bytes  are added to the program's data space and a pointer to the start of the new area is
       returned.

       When a program begins execution via execve the break is set at the highest location defined by the program and data storage  areas.   Ordi-
       narily, therefore, only programs with growing data areas need to use sbrk.

       The  getrlimit(2) system call may be used to determine the maximum permissible size of the data segment; it will not be possible to set the
       break beyond the rlim_max value returned from a call to getrlimit, e.g. "etext + rlp->rlim_max."  (see end(3) for the definition of etext).

RETURN VALUE
       Zero is returned if the brk could be set; -1 if the program requests more memory than the system limit.	Sbrk returns -1 if the break could
       not be set.

ERRORS
       Sbrk will fail and no additional memory will be allocated if one of the following are true:

       [ENOMEM]       The limit, as set by setrlimit(2), was exceeded.

       [ENOMEM]       The maximum possible size of a data segment (compiled into the system) was exceeded.

       [ENOMEM]       Insufficient space existed in the swap area to support the expansion.

SEE ALSO
       execve(2), getrlimit(2), malloc(3), end(3)

BUGS
       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 exceed-
       ing the maximum size of the data segment without consulting getrlimit.

4th Berkeley Distribution					   May 22, 1986 							    BRK(2)