V4/man/man2/break.2

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.th BREAK II 8/5/73
.sh NAME
break \*- set program break
.sh SYNOPSIS
(break = 17.)
.br
.ft B
sys break; addr
.s3
char *sbrk(incr)
.ft R
.sh DESCRIPTION
.it Break
sets the system's idea of the lowest location not used by the program
to
.it addr
(rounded up to the next multiple of 64 bytes).
Locations not less than
.it addr
and below the stack pointer
are not in the address space and will thus
cause a memory violation if accessed.
.s3
From C, the calling sequence is different;
.it incr
more bytes are added to the
program's data space and a pointer to the
start of the new area is returned.
.s3
When a program begins execution via
.it 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
.it break.
.sh "SEE ALSO"
exec(II)
.sh DIAGNOSTICS
The c-bit is set if the program requests more
memory than the system limit
(currently 20K words),
or if more than 8 segmentation
registers would be required to implement the break.
From C, \*-1 is returned for these errors.