1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
|
.\" Copyright (c) 1993 Michael Haardt, (michael@moria.de)
.\" and Copyright 2006, 2008, Michael Kerrisk <tmk.manpages@gmail.com>
.\" Fri Apr 2 11:32:09 MET DST 1993
.\"
.\" %%%LICENSE_START(GPLv2+_DOC_FULL)
.\" This is free documentation; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License as
.\" published by the Free Software Foundation; either version 2 of
.\" the License, or (at your option) any later version.
.\"
.\" The GNU General Public License's references to "object code"
.\" and "executables" are to be interpreted as the output of any
.\" document formatting or typesetting system, including
.\" intermediate and printed output.
.\"
.\" This manual is distributed in the hope that it will be useful,
.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
.\" GNU General Public License for more details.
.\"
.\" You should have received a copy of the GNU General Public
.\" License along with this manual; if not, see
.\" <http://www.gnu.org/licenses/>.
.\" %%%LICENSE_END
.\"
.\" Modified Wed Jul 21 19:52:58 1993 by Rik Faith <faith@cs.unc.edu>
.\" Modified Sun Aug 21 17:40:38 1994 by Rik Faith <faith@cs.unc.edu>
.\"
.TH BRK 2 2016-03-15 "Linux" "Linux Programmer's Manual"
.SH NAME
brk, sbrk \- change data segment size
.SH SYNOPSIS
.B #include <unistd.h>
.PP
.BI "int brk(void *" addr );
.PP
.BI "void *sbrk(intptr_t " increment );
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR brk (),
.BR sbrk ():
.ad l
.RS 4
.PD 0
.TP 4
Since glibc 2.19:
.nf
_DEFAULT_SOURCE ||
(_XOPEN_SOURCE\ >=\ 500) &&
.\" (_XOPEN_SOURCE\ >=\ 500 ||
.\" _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED) &&
! (_POSIX_C_SOURCE\ >=\ 200112L)
.fi
.TP 4
From glibc 2.12 to 2.19:
.nf
_BSD_SOURCE || _SVID_SOURCE ||
(_XOPEN_SOURCE\ >=\ 500) &&
.\" (_XOPEN_SOURCE\ >=\ 500 ||
.\" _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED) &&
! (_POSIX_C_SOURCE\ >=\ 200112L)
.fi
.TP 4
Before glibc 2.12:
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500
.\" || _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.PD
.RE
.ad b
.SH DESCRIPTION
.BR brk ()
and
.BR sbrk ()
change the location of the
.IR "program break" ,
which defines the end of the process's data segment
(i.e., the program break is the first location after the end of the
uninitialized data segment).
Increasing the program break has the effect of
allocating memory to the process;
decreasing the break deallocates memory.
.PP
.BR brk ()
sets the end of the data segment to the value specified by
.IR addr ,
when that value is reasonable, the system has enough memory,
and the process does not exceed its maximum data size (see
.BR setrlimit (2)).
.PP
.BR sbrk ()
increments the program's data space by
.I increment
bytes.
Calling
.BR sbrk ()
with an
.I increment
of 0 can be used to find the current location of the program break.
.SH RETURN VALUE
On success,
.BR brk ()
returns zero.
On error, \-1 is returned, and
.I errno
is set to
.BR ENOMEM .
.PP
On success,
.BR sbrk ()
returns the previous program break.
(If the break was increased,
then this value is a pointer to the start of the newly allocated memory).
On error,
.I "(void\ *)\ \-1"
is returned, and
.I errno
is set to
.BR ENOMEM .
.SH CONFORMING TO
4.3BSD; SUSv1, marked LEGACY in SUSv2, removed in POSIX.1-2001.
.\"
.\" .BR brk ()
.\" and
.\" .BR sbrk ()
.\" are not defined in the C Standard and are deliberately excluded from the
.\" POSIX.1-1990 standard (see paragraphs B.1.1.1.3 and B.8.3.3).
.SH NOTES
Avoid using
.BR brk ()
and
.BR sbrk ():
the
.BR malloc (3)
memory allocation package is the
portable and comfortable way of allocating memory.
.PP
Various systems use various types for the argument of
.BR sbrk ().
Common are \fIint\fP, \fIssize_t\fP, \fIptrdiff_t\fP, \fIintptr_t\fP.
.\" One sees
.\" \fIint\fP (e.g., XPGv4, DU 4.0, HP-UX 11, FreeBSD 4.0, OpenBSD 3.2),
.\" \fIssize_t\fP (OSF1 2.0, Irix 5.3, 6.5),
.\" \fIptrdiff_t\fP (libc4, libc5, ulibc, glibc 2.0, 2.1),
.\" \fIintptr_t\fP (e.g., XPGv5, AIX, SunOS 5.8, 5.9, FreeBSD 4.7, NetBSD 1.6,
.\" Tru64 5.1, glibc2.2).
.SS C library/kernel differences
The return value described above for
.BR brk ()
is the behavior provided by the glibc wrapper function for the Linux
.BR brk ()
system call.
(On most other implementations, the return value from
.BR brk ()
is the same; this return value was also specified in SUSv2.)
However,
the actual Linux system call returns the new program break on success.
On failure, the system call returns the current break.
The glibc wrapper function does some work
(i.e., checks whether the new break is less than
.IR addr )
to provide the 0 and \-1 return values described above.
.PP
On Linux,
.BR sbrk ()
is implemented as a library function that uses the
.BR brk ()
system call, and does some internal bookkeeping so that it can
return the old break value.
.SH SEE ALSO
.BR execve (2),
.BR getrlimit (2),
.BR end (3),
.BR malloc (3)
.SH COLOPHON
This page is part of release 5.09 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%https://www.kernel.org/doc/man\-pages/.
|
