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.
RETURN VALUE
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.
DIAGNOSTICS
Sbrk will fail and no additional memory will be allocated if:
[ENOMEM] The maximum possible size of a data segment (compiled into the system) was exceeded.
[ENOMEM] The maximum available memory for a user process was exceeded. For I/D process, text or data+stack was larger than 64KB. For non-I/D process, text+data+stack was larger than 64KB.
RESTRICTIONS
Setting the break in the range 0177701 to 0177777 (on the PDP11) is the same as setting it to zero.
SEE ALSO
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.