[unix-history] / usr / man / man2 / brk.2

.TH BRK 2 
.SH NAME
brk, sbrk, break \- change core allocation
.SH SYNOPSIS
.B char *brk(addr)
.PP
.B char *sbrk(incr)
.SH DESCRIPTION
.I Brk
sets the system's idea of the lowest location not used by the program
(called the break)
to
.I addr
(rounded up to the next multiple of 64 bytes
on the PDP11, 256 bytes on the Interdata 8/32,
and 512 bytes on a VAX-11).
Locations not less than
.I addr
and below the stack pointer
are not in the address space and will thus
cause a memory violation if accessed.
.PP
In the alternate function
.I sbrk,
.I incr
more bytes are added to the
program's data space and a pointer to the
start of the new area is returned.
.PP
When a program begins execution via
.I exec
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
.IR break .
.SH "SEE ALSO"
exec(2),
malloc(3),
end(3)
.SH DIAGNOSTICS
Zero is returned if the break could be set;
\-1 if the program requests more
memory than the system limit
or if too many segmentation
registers would be required to implement the break.
.SH BUGS
Setting the break in the range
0177701 to 0177777 (on the PDP11) is the same as setting it to zero.
.SH "ASSEMBLER (PDP-11)"
(break = 17.)
.br
.B sys break; addr
.PP
.I Break
performs the function of
.IR brk .
The name of the routine differs from that in C
for historical reasons.
Commit	Line	Data
cb67878b TL	1	.TH BRK 2
	2	.SH NAME
	3	brk, sbrk, break \- change core allocation
	4	.SH SYNOPSIS
	5	.B char *brk(addr)
	6	.PP
	7	.B char *sbrk(incr)
	8	.SH DESCRIPTION
	9	.I Brk
	10	sets the system's idea of the lowest location not used by the program
	11	(called the break)
	12	to
	13	.I addr
	14	(rounded up to the next multiple of 64 bytes
	15	on the PDP11, 256 bytes on the Interdata 8/32,
	16	and 512 bytes on a VAX-11).
	17	Locations not less than
	18	.I addr
	19	and below the stack pointer
	20	are not in the address space and will thus
	21	cause a memory violation if accessed.
	22	.PP
	23	In the alternate function
	24	.I sbrk,
	25	.I incr
	26	more bytes are added to the
	27	program's data space and a pointer to the
	28	start of the new area is returned.
	29	.PP
	30	When a program begins execution via
	31	.I exec
	32	the break is set at the
	33	highest location defined by the program
	34	and data storage areas.
	35	Ordinarily, therefore, only programs with growing
	36	data areas need to use
	37	.IR break .
	38	.SH "SEE ALSO"
	39	exec(2),
	40	malloc(3),
	41	end(3)
	42	.SH DIAGNOSTICS
	43	Zero is returned if the break could be set;
	44	\-1 if the program requests more
	45	memory than the system limit
	46	or if too many segmentation
	47	registers would be required to implement the break.
	48	.SH BUGS
	49	Setting the break in the range
	50	0177701 to 0177777 (on the PDP11) is the same as setting it to zero.
	51	.SH "ASSEMBLER (PDP-11)"
	52	(break = 17.)
	53	.br
	54	.B sys break; addr
	55	.PP
	56	.I Break
	57	performs the function of
	58	.IR brk .
	59	The name of the routine differs from that in C
	60	for historical reasons.