2.9BSD/usr/man/man2/brk.2

.TH BRK 2 
.UC
.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 PDP-11, 256 bytes on the Interdata 8/32, 512 bytes on the 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
.IR 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 execve
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 RETURN VALUE
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 ERRORS
.I Sbrk
will fail and no additional memory will be allocated if:
.TP 20
[ENOMEM]
The maximum possible size of a data segment (compiled into the system)
was exceeded.
.TP 20
[ENOMEM]
The maximum available memory for a user process was exceeded.
.SH "SEE ALSO"
execve(2), end(3), malloc(3)
.SH BUGS
Setting the break in the range
0177701 to 0177777 (on the PDP-11) is the same as setting it to zero.
.SH ASSEMBLER
(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.