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@(#)brk.2 4.1 (Berkeley) 05/09/85

C 4 brk, sbrk, break - change core allocation char *brk(addr)

char *sbrk(incr)

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, and 1024 bytes on a VAX-11). 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 .

The vlimit (2) system call may be used to determine the maximum permissible size of the data region; it will not be possible to set the break beyond \*(lqetext + vlimit(LIM_DATA, -1).\*(rq (See end (3) for the definition of etext .)

exec(2), vlimit(2), malloc(3), end(3) Zero is returned if the brk 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. Sbrk returns -1 if the break could not be set. Setting the break in the range 0177701 to 0177777 (on the PDP11) is the same as setting it to zero. (break = 17.)

sys break; addr

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