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OpenDarwin 7.2.1 - man page for sbrk (opendarwin section 2)

BRK(2)				     BSD System Calls Manual				   BRK(2)

NAME
     brk, sbrk -- change data segment size

SYNOPSIS
     #include <unistd.h>

     char *
     brk(const char *addr);

     char *
     sbrk(int incr);

DESCRIPTION
     The brk and sbrk functions are historical curiosities left over from earlier days before the
     advent of virtual memory management.  The brk() function sets the break or lowest address of
     a process's data segment (uninitialized data) to addr (immediately above bss).  Data
     addressing is restricted between addr and the lowest stack pointer to the stack segment.
     Memory is allocated by brk in page size pieces; if addr is not evenly divisible by the sys-
     tem page size, it is increased to the next page boundary.

     The current value of the program break is reliably returned by ``sbrk(0)'' (see also
     end(3)).  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.  ``qetext + rlp->rlim_max.'' (see end(3) for the
     definition of etext).

RETURN VALUES
     Brk returns a pointer to the new end of memory if successful; otherwise -1 with errno set to
     indicate why the allocation failed.  The sbrk function returns a pointer to the base of the
     new storage if successful; otherwise -1 with errno set to indicate why the allocation
     failed.

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), mmap(2), 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 exceeding the maximum size of the data segment
     without consulting getrlimit.

HISTORY
     A brk() function call appeared in Version 7 AT&T UNIX.

4th Berkeley Distribution		December 11, 1993		4th Berkeley Distribution


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