NAME

brk, sbrk − change data segment size

SYNOPSIS

caddr_t brk(addr)
caddr_t addr;

caddr_t sbrk(incr)
int incr;

DESCRIPTION

Brk 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 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(2) 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 sbrk.

The getrlimit(2) 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 getrlimit. See end(3) for the definition of etext. See getrlimit(2) for the definition of the rlimit structure. 

RETURN VALUE

Zero is returned if the brk could be set; −1 if the program requests more memory than the system limit.  Sbrk returns −1 if the break could not be set. 

SEE ALSO

exec(2), getrlimit(2), malloc(3), end(3)

BUGS

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 exceeding the maximum size of the data segment without consulting getrlimit.

Sun System Release 0.3  —  25 April 1983