freebsd-dev/lib/libc/sys/brk.2

.\" 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.
.\" 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 December 15, 2015
.Dt BRK 2
.Os
.Sh NAME
.Nm brk ,
.Nm sbrk
.Nd change data segment size
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.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
The
.Fn brk
and
.Fn sbrk
functions
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 HISTORY
The
.Fn brk
function appeared in
.At v7 .
.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 .
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.\" 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.`
			`.\" 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.`
			`.\"`
Merge from Lite2 onto mainline - - add undelete() and undelete.2 (requires libc minor bump some time) - man page updates 1997-03-11 11:35:56 +00:00			`.\" @(#)brk.2 8.4 (Berkeley) 5/1/95`
$Id$ -> $FreeBSD$ 1999-08-28 00:22:10 +00:00			`.\" $FreeBSD$`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.\"`
Remove sys/types.h due to STANDARDS and unistd.h also includes sys/types.h. 2015-12-15 15:19:06 +00:00			`.Dd December 15, 2015`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Dt BRK 2`
mdoc(7) police: removed HISTORY info from the .Os call. 2001-07-10 13:41:46 +00:00			`.Os`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh NAME`
			`.Nm brk ,`
			`.Nm sbrk`
			`.Nd change data segment size`
Introduce ".Lb" macro to libc manpages. More libraries manpages updates following. 2000-04-21 09:42:15 +00:00			`.Sh LIBRARY`
			`.Lb libc`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh SYNOPSIS`
mdoc(7) police: Use the new .In macro for #include statements. 2001-10-01 16:09:29 +00:00			`.In unistd.h`
Change brk's prototype from char brk(const char ) to int brk(const void ) and sbrk's prototype from char sbrk(int) to void *sbrk(intptr_t). This makes us more consistant with NetBSD and standards which include these functions. Bruce pointed out that ptrdiff_t would probably have been better than intptr_t, but this doesn't match other implimentations. Also remove local declarations of sbrk and unnecessary casting. PR: 32296 Tested by: Harti Brandt <brandt@fokus.gmd.de> MFC after: 1 month 2002-01-24 12:11:31 +00:00			`.Ft int`
			`.Fn brk "const void *addr"`
			`.Ft void *`
			`.Fn sbrk "intptr_t incr"`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh DESCRIPTION`
			`.Bf -symbolic`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`The`
			`.Fn brk`
			`and`
			`.Fn sbrk`
			`functions are legacy interfaces from before the`
			`advent of modern virtual memory management.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Ef`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`.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`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`The`
			`.Fn brk`
			`function`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`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 .`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Pp`
			`The`
			`.Xr getrlimit 2`
			`system call may be used to determine`
			`the maximum permissible size of the`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`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 .`
Prepare for mdoc(7)NG. 2000-12-29 14:08:20 +00:00			`(See`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Xr end 3`
			`for the definition of`
mdoc(7) police: split punctuation characters + misc fixes. 2001-02-01 16:38:02 +00:00			`.Va etext ) .`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh RETURN VALUES`
Change brk's prototype from char brk(const char ) to int brk(const void ) and sbrk's prototype from char sbrk(int) to void *sbrk(intptr_t). This makes us more consistant with NetBSD and standards which include these functions. Bruce pointed out that ptrdiff_t would probably have been better than intptr_t, but this doesn't match other implimentations. Also remove local declarations of sbrk and unnecessary casting. PR: 32296 Tested by: Harti Brandt <brandt@fokus.gmd.de> MFC after: 1 month 2002-01-24 12:11:31 +00:00			`.Rv -std brk`
Use ``.Rv -std'' wherever possible. Submitted by: yar 2001-08-31 09:57:38 +00:00			`.Pp`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`The`
Update a bunch of man pages to use .Fn instead of .Nm when referencing funciton names. 1996-08-22 22:05:59 +00:00			`.Fn sbrk`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`function returns the prior break value if successful;`
			`otherwise the value`
Change brk's prototype from char brk(const char ) to int brk(const void ) and sbrk's prototype from char sbrk(int) to void *sbrk(intptr_t). This makes us more consistant with NetBSD and standards which include these functions. Bruce pointed out that ptrdiff_t would probably have been better than intptr_t, but this doesn't match other implimentations. Also remove local declarations of sbrk and unnecessary casting. PR: 32296 Tested by: Harti Brandt <brandt@fokus.gmd.de> MFC after: 1 month 2002-01-24 12:11:31 +00:00			`.Po Vt "void *" Pc Ns \-1`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`is returned and the global variable`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Va errno`
Use ``.Rv -std'' wherever possible. Submitted by: yar 2001-08-31 09:57:38 +00:00			`is set to indicate the error.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh ERRORS`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`The`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`.Fn brk`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`and`
Merge from Lite2 onto mainline - - add undelete() and undelete.2 (requires libc minor bump some time) - man page updates 1997-03-11 11:35:56 +00:00			`.Fn sbrk`
mdoc(7) police: Tidy up the syscall language. Stop calling system calls "function calls". Use "The .Fn system call" a-la "The .Nm utility". When referring to a non-BSD implementation in the HISTORY section, call syscall a function, to be safe. 2002-12-18 09:22:32 +00:00			`functions`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`will fail if:`
Use `Er' variable to define first column width in ERRORS section. It was initially suggested by mdoc(7) style, but was broken over the years 2000-05-04 13:09:25 +00:00			`.Bl -tag -width Er`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`.It Bq Er EINVAL`
			`The requested break value was beyond the beginning of the data segment.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.It Bq Er ENOMEM`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`The data segment size limit, as set by`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Xr setrlimit 2 ,`
			`was exceeded.`
			`.It Bq Er ENOMEM`
			`Insufficient space existed in the swap area`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`to support the expansion of the data segment.`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.El`
			`.Sh SEE ALSO`
			`.Xr execve 2 ,`
			`.Xr getrlimit 2 ,`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`.Xr mmap 2 ,`
Sort cross references. 1997-01-20 23:23:22 +00:00			`.Xr end 3 ,`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`.Xr free 3 ,`
Sort cross references. 1997-01-20 23:23:22 +00:00			`.Xr malloc 3`
Sort sections. 2005-01-20 09:17:07 +00:00			`.Sh HISTORY`
			`The`
			`.Fn brk`
			`function appeared in`
			`.At v7 .`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`.Sh BUGS`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`Mixing`
			`.Fn brk`
			`or`
			`.Fn sbrk`
			`with`
			`.Xr malloc 3 ,`
			`.Xr free 3 ,`
			`or similar functions will result in non-portable program behavior.`
			`.Pp`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`Setting the break may fail due to a temporary lack of`
Fix all the ambiguous or erroneous statements of the brk(2) manpage by taking its text from NetBSD and editing it further. This also improves the page's mdoc(7) markup style. Reviewed by: ru Obtained from: NetBSD 2001-09-06 12:11:22 +00:00			`swap space.`
			`It is not possible to distinguish this`
BSD 4.4 Lite Lib Sources 1994-05-27 05:00:24 +00:00			`from a failure caused by exceeding the maximum size of`
Remove whitespace at EOL. 2001-07-15 07:53:42 +00:00			`the data segment without consulting`
Added missing section numbers to a bunch of .Xr macros, or converted them into .Fn macros where appropriate. Also fixed up some minor formatting problems. 1996-03-27 20:49:07 +00:00			`.Xr getrlimit 2 .`