177 lines
4.7 KiB
Groff
177 lines
4.7 KiB
Groff
.\" $NetBSD: brk.2,v 1.24 2000/04/04 08:41:45 fvdl Exp $
|
|
.\"
|
|
.\" 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
|
|
.\"
|
|
.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
|
|
.Fd #include <unistd.h>
|
|
.Ft int
|
|
.Fn brk "void *addr"
|
|
.Ft void *
|
|
.Fn sbrk "intptr_t incr"
|
|
.Sh DESCRIPTION
|
|
.Bf -symbolic
|
|
The brk and 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
|
|
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
|
|
.Fn brk
|
|
function sets the break to
|
|
.Fa addr .
|
|
.Pp
|
|
The
|
|
.Fn sbrk
|
|
function raises the break by at least
|
|
.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.
|
|
.Pp
|
|
.Fn sbrk
|
|
returns the prior address of the break.
|
|
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
|
|
.Em data
|
|
segment;
|
|
it will not be possible to set the break
|
|
beyond the
|
|
.Dv RLIMIT_DATA
|
|
.Em rlim_max
|
|
value returned from a call to
|
|
.Xr getrlimit 2 ,
|
|
e.g.
|
|
.Dq etext + rlim.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.
|
|
.Pp
|
|
The
|
|
.Fn sbrk
|
|
function returns the prior break value if successful;
|
|
otherwise ((void *)-1) is returned and
|
|
.Va errno
|
|
is 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 Er
|
|
.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 mmap 2 ,
|
|
.Xr end 3 ,
|
|
.Xr free 3 ,
|
|
.Xr malloc 3 ,
|
|
.Xr sysconf 3
|
|
.Sh BUGS
|
|
Note that
|
|
mixing
|
|
.Fn brk
|
|
and
|
|
.Fn sbrk
|
|
with
|
|
.Xr malloc 3 ,
|
|
.Xr free 3 ,
|
|
and similar functions may result in non-portable program
|
|
behavior. Caution is advised.
|
|
.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 .
|