brk(2) [v7 man page]

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.   Ordinar-
       ily, 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 regis-
       ters 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)

brk(2)								System Calls Manual							    brk(2)

Name
       brk, sbrk - change data segment space allocation

Syntax
       #include <sys/types.h>

       char *brk(addr)
       char *addr;

       char *sbrk(incr)
       int incr;

Description
       The  system  call sets the system's idea of the lowest data segment location not used by the program (called the break) to addr (rounded up
       to the next multiple of the system's page size).  Locations greater than addr and below the stack pointer are not in the address space  and
       thus will cause a memory violation if accessed.

       In the alternate function 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 by 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

       The system call may be used to determine the maximum permissible size of the data segment; it will not be possible to set the break  beyond
       the rlim_max value returned from a call to For example:
       0x10000000 + rlp -> rlim_max

Return Values
       Upon successful completion, the system call returns a value of 0 or -1 if the program requests more memory than the system limit.  The sys-
       tem call returns -1 if the break could not be set.

Restrictions
       Setting the break may fail due to a temporary lack of swap space.  It is not possible to distinguish this from a failure caused by  exceed-
       ing the maximum size of the data segment without consulting

Diagnostics
       The system call fails and no additionally memory is allocated if one of the following is true:

	      [ENOMEM]	   The limit, as set by was exceeded.

	      [ENOMEM]	   The maximum possible size a data segment (compiled into the system) was exceeded.

	      [ENOMEM]	   Insufficient space existed in the swap area to support the expansion.

See Also
       execve(2), getrlimit(2), setrlimit(2), ulimit(2)

								       RISC								    brk(2)