break.2

UNIX v6源代码 这几乎是最经典的unix版本 unix操作系统设计和莱昂氏unix源代码分析都是用的该版

.th BREAK II 8/5/73
.sh NAME
break, brk, sbrk \*- change core allocation
.sh SYNOPSIS
(break = 17.)
.br
.ft B
sys break; addr
.s3
char *brk(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
(called the break)
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,
.it brk
will set the break to
.it addr.
The old break is returned.
.s3
In the alternate entry
.it sbrk,
.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), alloc (III), end (III)
.sh DIAGNOSTICS
The c-bit is set if the program requests more
memory than the system limit
or if more than 8 segmentation
registers would be required to implement the break.
From C, \*-1 is returned for these errors.
.sh BUGS
Setting the break in the range
0177700 to 0177777 is the same as setting it to zero.