Using brk() and sbrk()

A break is the greatest valid data address in the process image that is not in the stack. When a program starts executing, the break value is normally set by the execve() function to the greatest address defined by the program and its data storage.

Use the brk() function to set the break to a greater address. You can also use the sbrk() function to add an increment of storage to the data segment of a process. You can get the maximum possible size of the data segment by a call to the getrlimit() function.

caddr_t
brk(caddr_t addr);

caddr_t
sbrk(intptr_t incr);

brk() identifies the lowest data segment location not used by the caller as addr. This location is rounded up to the next multiple of the system page size.

sbrk(), the alternate interface, adds incr bytes to the caller data space and returns a pointer to the start of the new data area.

For more information, see the brk(2), sbrk(2), execve(2), and getrlimit(2) man pages.