[apple/xnu.git] / libsyscall / mach / brk.2

.\"	$NetBSD: brk.2,v 1.7 1995/02/27 12:31:57 cgd 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	8.2 (Berkeley) 12/11/93
.\"
.Dd December 11, 1993
.Dt BRK 2
.Os BSD 4
.Sh NAME
.Nm brk ,
.Nm sbrk
.Nd change data segment size
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft void *
.Fn brk "const void *addr"
.Ft void *
.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 ,
e.g.
.Dq qetext + rlp\(->rlim_max.
(see
.Xr end 3
for the definition of
.Em etext ) .
.Sh RETURN VALUES
.Nm Brk
returns a pointer to the new end of memory if successful;
otherwise -1 with
.Va errno
set to indicate why the allocation failed.
The
.Nm 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
.Xr 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 malloc 3 ,
.Xr mmap 2 ,
.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
.Fn brk
function call appeared in 
.At v7 .
Commit	Line	Data
2d21ac55 A	1	.\" $NetBSD: brk.2,v 1.7 1995/02/27 12:31:57 cgd Exp $
	2	.\"
	3	.\" Copyright (c) 1980, 1991, 1993
	4	.\" The Regents of the University of California. All rights reserved.
	5	.\"
	6	.\" Redistribution and use in source and binary forms, with or without
	7	.\" modification, are permitted provided that the following conditions
	8	.\" are met:
	9	.\" 1. Redistributions of source code must retain the above copyright
	10	.\" notice, this list of conditions and the following disclaimer.
	11	.\" 2. Redistributions in binary form must reproduce the above copyright
	12	.\" notice, this list of conditions and the following disclaimer in the
	13	.\" documentation and/or other materials provided with the distribution.
	14	.\" 3. All advertising materials mentioning features or use of this software
	15	.\" must display the following acknowledgement:
	16	.\" This product includes software developed by the University of
	17	.\" California, Berkeley and its contributors.
	18	.\" 4. Neither the name of the University nor the names of its contributors
	19	.\" may be used to endorse or promote products derived from this software
	20	.\" without specific prior written permission.
	21	.\"
	22	.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
	23	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	24	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	25	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	26	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	27	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	28	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	29	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	30	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	31	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	32	.\" SUCH DAMAGE.
	33	.\"
	34	.\" @(#)brk.2 8.2 (Berkeley) 12/11/93
	35	.\"
	36	.Dd December 11, 1993
	37	.Dt BRK 2
	38	.Os BSD 4
	39	.Sh NAME
	40	.Nm brk ,
	41	.Nm sbrk
	42	.Nd change data segment size
	43	.Sh SYNOPSIS
	44	.Fd #include <unistd.h>
	45	.Ft void *
	46	.Fn brk "const void *addr"
	47	.Ft void *
	48	.Fn sbrk "int incr"
	49	.Sh DESCRIPTION
	50	.Bf -symbolic
	51	The brk and sbrk functions are historical curiosities
	52	left over from earlier days before the advent of virtual memory management.
	53	.Ef
	54	The
	55	.Fn brk
	56	function
	57	sets the break or lowest address
	58	of a process's data segment (uninitialized data) to
	59	.Fa addr
	60	(immediately above bss).
	61	Data addressing is restricted between
	62	.Fa addr
	63	and the lowest stack pointer to the stack segment.
	64	Memory is allocated by
65	.Fa brk
66	in page size pieces;
67	if
68	.Fa addr
69	is not evenly divisible by the system page size, it is
70	increased to the next page boundary.
71	.Pp
72	.\" The
73	.\" .Nm sbrk
74	.\" function
75	.\" allocates chunks of
76	.\" .Fa incr
77	.\" bytes
78	.\" to the process's data space
79	.\" and returns an address pointer.
80	.\" The
81	.\" .Xr malloc 3
82	.\" function utilizes
83	.\" .Nm sbrk .
84	.\" .Pp
85	The current value of the program break is reliably returned by
86	.Dq Li sbrk(0)
87	(see also
88	.Xr end 3 ) .
89	The
90	.Xr getrlimit 2
91	system call may be used to determine
92	the maximum permissible size of the
93	.Em data
94	segment;
95	it will not be possible to set the break
96	beyond the
97	.Em rlim_max
98	value returned from a call to
99	.Xr getrlimit ,
100	e.g.
101	.Dq qetext + rlp\(->rlim_max.
102	(see
103	.Xr end 3
104	for the definition of
105	.Em etext ) .
106	.Sh RETURN VALUES
107	.Nm Brk
108	returns a pointer to the new end of memory if successful;
109	otherwise -1 with
110	.Va errno
111	set to indicate why the allocation failed.
112	The
113	.Nm sbrk
114	function returns a pointer to the base of the new storage if successful;
115	otherwise -1 with
116	.Va errno
117	set to indicate why the allocation failed.
118	.Sh ERRORS
119	.Xr Sbrk
120	will fail and no additional memory will be allocated if
121	one of the following are true:
122	.Bl -tag -width Er
123	.It Bq Er ENOMEM
124	The limit, as set by
125	.Xr setrlimit 2 ,
126	was exceeded.
127	.It Bq Er ENOMEM
128	The maximum possible size of a data segment (compiled into the
129	system) was exceeded.
130	.It Bq Er ENOMEM
131	Insufficient space existed in the swap area
132	to support the expansion.
133	.El
134	.Sh SEE ALSO
135	.Xr execve 2 ,
136	.Xr getrlimit 2 ,
137	.Xr malloc 3 ,
138	.Xr mmap 2 ,
139	.Xr end 3
140	.Sh BUGS
141	Setting the break may fail due to a temporary lack of
142	swap space. It is not possible to distinguish this
143	from a failure caused by exceeding the maximum size of
144	the data segment without consulting
145	.Xr getrlimit .
146	.Sh HISTORY
147	A
148	.Fn brk
149	function call appeared in
150	.At v7 .