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+.\" Copyright (c) 1980, 1991 Regents of the University of California.
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)brk.2	6.5 (Berkeley) 3/10/91
+.\"
+.Dd March 10, 1991
+.Dt BRK 2
+.Os BSD 4
+.Sh NAME
+.Nm brk ,
+.Nm sbrk
+.Nd change data segment size
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Ft char
+.Fn *brk "const char *addr"
+.Ft char *
+.Fn *sbrk "int incr"
+.Sh DESCRIPTION
+.Bf -symbolic
+The brk and sbrk functions are historical curiosities
+left over from earlier days before the advent of virtual memory management.
+.Ef
+The
+.Fn brk
+function
+sets the break or lowest address
+of a process's data segment (unilitialized data) to
+.Fa addr
+(immediately above bss).
+Data addressing is restricted between
+.Fa addr
+and the lowest stack pointer to the stack segment.
+Memory is allocated by
+.Fa brk
+in page size pieces;
+if
+.Fa addr
+is not evenly divisible by the system page size, it is
+increased to the next page boundary.
+.Pp
+.\" The
+.\" .Nm sbrk
+.\" function
+.\" allocates chunks of
+.\" .Fa incr
+.\" bytes
+.\" to the process's data space
+.\" and returns an address pointer.
+.\" The
+.\" .Xr malloc 3
+.\" function utilizes
+.\" .Nm sbrk .
+.\" .Pp
+The current value of the program break is reliably returned by
+.Dq Li sbrk(0)
+(see also 
+.Xr end 3 ) .
+The
+.Xr getrlimit 2
+system call may be used to determine
+the maximum permissible size of the
+.Em data
+segment;
+it will not be possible to set the break
+beyond the
+.Em rlim_max
+value returned from a call to
+.Xr getrlimit ,
+e.g.
+.Dq qetext + rlp\(->rlim_max.
+(see
+.Xr end 3
+for the definition of
+.Em etext ) .
+.Sh RETURN VALUES
+.Nm Brk
+returns 0 if successful; -1 if the process requests more memory than
+than allowed by the system limit.
+The
+.Nm sbrk
+function returns 0 if successful, otherwise the error
+.Er EOPNOTSUPP
+is returned.
+.\" .Sh ERRORS
+.\" .Xr Sbrk
+.\" returns -1 if the break could not be set.
+.\" will fail and no additional memory will be allocated if
+.\" one of the following are true:
+.\" .Bl -tag -width [ENOMEM]
+.\" .It Bq Er ENOMEM
+.\" The limit, as set by
+.\" .Xr setrlimit 2 ,
+.\" was exceeded.
+.\" .It Bq Er ENOMEM
+.\" The maximum possible size of a data segment (compiled into the
+.\" system) was exceeded.
+.\" .It Bq Er ENOMEM
+.\" Insufficient space existed in the swap area
+.\" to support the expansion.
+.\" .El
+.Sh SEE ALSO
+.Xr execve 2 ,
+.Xr getrlimit 2 ,
+.Xr malloc 3 ,
+.Xr end 3
+.Sh 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 
+.Xr getrlimit .
+.Sh HISTORY
+A
+.Nm
+function call appeared in Version 7 AT&T UNIX.