brk(2) BSD System Calls Manual brk(2)
brk, sbrk -- change data segment size
#include <unistd.h> void * brk(const void *addr); void * sbrk(int incr);
The brk and sbrk functions are historical curiosities left over from ear- lier days before the advent of virtual memory management. The brk() function sets the break or lowest address of a process's data segment (uninitialized data) to addr (immediately above bss). Data addressing is restricted between addr and the lowest stack pointer to the stack seg- ment. Memory is allocated by brk in page size pieces; if addr is not evenly divisible by the system page size, it is increased to the next page boundary. The current value of the program break is reliably returned by ``sbrk(0)'' (see also end(3)). 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, e.g. ``qetext + rlp->rlim_max.'' (see end(3) for the definition of etext).
Brk returns a pointer to the new end of memory if successful; otherwise -1 with errno set to indicate why the allocation failed. The sbrk func- tion returns a pointer to the base of the new storage if successful; oth- erwise -1 with errno set to indicate why the allocation failed.
Sbrk will fail and no additional memory will be allocated if one of the following are true: [ENOMEM] The limit, as set by setrlimit(2), was exceeded. [ENOMEM] The maximum possible size of a data segment (compiled into the system) was exceeded. [ENOMEM] Insufficient space existed in the swap area to support the expansion.
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.
A brk() function call appeared in Version 7 AT&T UNIX. 4th Berkeley Distribution December 11, 1993 4th Berkeley Distribution
Mac OS X 10.8 - Generated Sat Aug 25 05:51:19 CDT 2012