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Unix Version 7 - man page for brk (v7 section 2)

BRK(2)				       System Calls Manual				   BRK(2)

NAME
       brk, sbrk, break - change core allocation

SYNOPSIS
       char *brk(addr)

       char *sbrk(incr)

DESCRIPTION
       Brk  sets  the  system's  idea  of the lowest location not used by the program (called the
       break) to addr (rounded up to the next multiple of 64 bytes on the PDP11, 256 bytes on the
       Interdata  8/32, 512 bytes on the VAX-11/780).  Locations not less than addr and below the
       stack pointer are not in the address space and will  thus  cause  a  memory  violation  if
       accessed.

       In  the alternate function sbrk, incr more bytes are added to the program's data space and
       a pointer to the start of the new area is returned.

       When a program begins execution via 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 break.

SEE ALSO
       exec(2), malloc(3), end(3)

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.

BUGS
       Setting the break in the range 0177701 to 0177777 (on the PDP11) is the same as setting it
       to zero.

ASSEMBLER
       (break = 17.)
       sys break; addr

       Break  performs	the  function of brk.  The name of the routine differs from that in C for
       historical reasons.

											   BRK(2)


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