151 lines
4.3 KiB
Groff
151 lines
4.3 KiB
Groff
.\" 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 May 1, 1995
|
|
.Dt BRK 2
|
|
.Os BSD 4
|
|
.Sh NAME
|
|
.Nm brk ,
|
|
.Nm sbrk
|
|
.Nd change data segment size
|
|
.Sh SYNOPSIS
|
|
.Fd #include <unistd.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 (uninitialized 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 2 ,
|
|
e.g.
|
|
.Dq etext + rlp\(->rlim_max.
|
|
(see
|
|
.Xr end 3
|
|
for the definition of
|
|
.Em etext ) .
|
|
.Sh RETURN VALUES
|
|
.Fn Brk
|
|
returns 0 if successful;
|
|
otherwise -1 with
|
|
.Va errno
|
|
set to indicate why the allocation failed.
|
|
The
|
|
.Fn sbrk
|
|
function returns a pointer to the base of the new storage if successful;
|
|
otherwise -1 with
|
|
.Va errno
|
|
set to indicate why the allocation failed.
|
|
.Sh ERRORS
|
|
.Fn Brk
|
|
or
|
|
.Fn sbrk
|
|
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 end 3 ,
|
|
.Xr malloc 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 2 .
|
|
.Sh HISTORY
|
|
A
|
|
.Fn brk
|
|
function call appeared in
|
|
.At v7 .
|