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+.\" Copyright (c) 1980, 1991, 1993
+.\"	The 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	8.4 (Berkeley) 5/1/95
+.\" $FreeBSD$
+.\"
+.Dd July 12, 1999
+.Dt BRK 2
+.Os
+.Sh NAME
+.Nm brk ,
+.Nm sbrk
+.Nd change data segment size
+.Sh LIBRARY
+.Lb libc
+.Sh SYNOPSIS
+.In sys/types.h
+.In unistd.h
+.Ft int
+.Fn brk "const void *addr"
+.Ft void *
+.Fn sbrk "intptr_t incr"
+.Sh DESCRIPTION
+.Bf -symbolic
+The
+.Fn brk
+and
+.Fn sbrk
+functions are legacy interfaces from before the
+advent of modern virtual memory management.
+.Ef
+.Pp
+The
+.Fn brk
+and
+.Fn sbrk
+functions are used to change the amount of memory allocated in a
+process's data segment.
+They do this by moving the location of the
+.Dq break .
+The break is the first address after the end of the process's
+uninitialized data segment (also known as the
+.Dq BSS ) .
+.Pp
+The
+.Fn brk
+function
+sets the break to
+.Fa addr .
+.Pp
+The
+.Fn sbrk
+function raises the break by
+.Fa incr
+bytes, thus allocating at least
+.Fa incr
+bytes of new memory in the data segment.
+If
+.Fa incr
+is negative,
+the break is lowered by
+.Fa incr
+bytes.
+.Sh NOTES
+While the actual process data segment size maintained by the kernel will only
+grow or shrink in page sizes, these functions allow setting the break
+to unaligned values (i.e., it may point to any address inside the last
+page of the data segment).
+.Pp
+The current value of the program break may be determined by calling
+.Fn sbrk 0 .
+See also
+.Xr end 3 .
+.Pp
+The
+.Xr 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
+.Dq Va etext No + Va rlim.rlim_max
+where the
+.Va rlim.rlim_max
+value is returned from a call to
+.Fn getrlimit RLIMIT_DATA &rlim .
+(See
+.Xr end 3
+for the definition of
+.Va etext ) .
+.Sh RETURN VALUES
+.Rv -std brk
+.Pp
+The
+.Fn sbrk
+function returns the prior break value if successful;
+otherwise the value
+.Po Vt "void *" Pc Ns \-1
+is returned and the global variable
+.Va errno
+is set to indicate the error.
+.Sh ERRORS
+.Fn brk
+or
+.Fn sbrk
+will fail if:
+.Bl -tag -width Er
+.It Bq Er EINVAL
+The requested break value was beyond the beginning of the data segment.
+.It Bq Er ENOMEM
+The data segment size limit, as set by
+.Xr setrlimit 2 ,
+was exceeded.
+.It Bq Er ENOMEM
+Insufficient space existed in the swap area
+to support the expansion of the data segment.
+.El
+.Sh SEE ALSO
+.Xr execve 2 ,
+.Xr getrlimit 2 ,
+.Xr mmap 2 ,
+.Xr end 3 ,
+.Xr free 3 ,
+.Xr malloc 3
+.Sh BUGS
+Mixing
+.Fn brk
+or
+.Fn sbrk
+with
+.Xr malloc 3 ,
+.Xr free 3 ,
+or similar functions will result in non-portable program behavior.
+.Pp
+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 2 .
+.Sh HISTORY
+A
+.Fn brk
+function call appeared in
+.At v7 .