BRK(2) UNIX Programmer's Manual BRK(2)
brk, sbrk - change data segment size
S
\bSY
\bYN
\bNO
\bOP
\bPS
\bSI
\bIS
\bS
c
\bch
\bha
\bar
\br *
\b*b
\bbr
\brk
\bk(
\b(a
\bad
\bdd
\bdr
\br)
\b)
c
\bch
\bha
\bar
\br *
\b*a
\bad
\bdd
\bdr
\br;
\b;
c
\bch
\bha
\bar
\br *
\b*s
\bsb
\bbr
\brk
\bk(
\b(i
\bin
\bnc
\bcr
\br)
\b)
i
\bin
\bnt
\bt i
\bin
\bnc
\bcr
\br;
\b;
D
\bDE
\bES
\bSC
\bCR
\bRI
\bIP
\bPT
\bTI
\bIO
\bON
\bN
_
\bB_
\br_
\bk sets the system's idea of the lowest data segment loca-
tion not used by the program (called the break) to _
\ba_
\bd_
\bd_
\br
(rounded up to the next multiple of the system's page size).
Locations greater than _
\ba_
\bd_
\bd_
\br and below the stack pointer are
not in the address space and will thus cause a memory viola-
In the alternate function _
\bs_
\bb_
\br_
\bk, _
\bi_
\bn_
\bc_
\br more bytes are added to
the program's data space and a pointer to the start of the
When a program begins execution via _
\be_
\bx_
\be_
\bc_
\bv_
\be the break is set
at the highest location defined by the program and data
storage areas. Ordinarily, therefore, only programs with
growing data areas need to use _
\bs_
\bb_
\br_
\bk.
The current value of the program break is reliably returned
by ``sbrk(0)'' (see also _
\be_
\bn_
\bd(3)). The _
\bg_
\be_
\bt_
\br_
\bl_
\bi_
\bm_
\bi_
\bt(2) system
call may be used to determine the maximum permissible size
of the _
\bd_
\ba_
\bt_
\ba segment; it will not be possible to set the
break beyond the _
\br_
\bl_
\bi_
\bm__
\bm_
\ba_
\bx value returned from a call to
_
\bg_
\be_
\bt_
\br_
\bl_
\bi_
\bm_
\bi_
\bt, e.g. "etext + rlp->rlim_max." (see _
\be_
\bn_
\bd(3) for the
definition of _
\be_
\bt_
\be_
\bx_
\bt).
R
\bRE
\bET
\bTU
\bUR
\bRN
\bN V
\bVA
\bAL
\bLU
\bUE
\bE
Zero is returned if the _
\bb_
\br_
\bk could be set; -1 if the program
requests more memory than the system limit. _
\bS_
\bb_
\br_
\bk returns -1
if the break could not be set.
_
\bS_
\bb_
\br_
\bk will fail and no additional memory will be allocated if
one of the following are true:
[ENOMEM] The limit, as set by _
\bs_
\be_
\bt_
\br_
\bl_
\bi_
\bm_
\bi_
\bt(2), was
[ENOMEM] The maximum possible size of a data segment
(compiled into the system) was exceeded.
Printed 7/9/88 June 17, 1986 1
BRK(2) UNIX Programmer's Manual BRK(2)
[ENOMEM] Insufficient space existed in the swap area
to support the expansion.
S
\bSE
\bEE
\bE A
\bAL
\bLS
\bSO
\bO
execve(2), getrlimit(2), malloc(3), end(3)
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 _
\bg_
\be_
\bt_
\br_
\bl_
\bi_
\bm_
\bi_
\bt.
Printed 7/9/88 June 17, 1986 2
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