brk(2) — VAX
Name
brk, sbrk − change core allocation
Syntax
#include <sys/types.h>
caddr_t brk(addr)
caddr_t addr;
caddr_t sbrk(incr)
int incr;
Description
The brk system call 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 greater 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 using execve, 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 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, for example, etext + rlp −rlim_max. See end() for the definition of etext.
Return Values
If the call is successful, brk returns a 0 value. If the program requests more memory than the system limit, brk returns −1. If the break could not be set, brk returns −1.
Restrictions
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.
Diagnostics
The sbrk call fails and no additional memory is allocated under the following conditions:
[ENOMEM] The limit, as set by setrlimit, is exceeded.
[ENOMEM] The maximum possible size of a data segment (compiled into the system) is exceeded.
[ENOMEM] Insufficient space exists in the swap area to support the expansion.