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sbrk(2) [bsd man page]

BRK(2)								System Calls Manual							    BRK(2)

NAME
brk, sbrk - change data segment size SYNOPSIS
#include <sys/types.h> char *brk(addr) char *addr; char *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 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 via execve the break is set at the highest location defined by the program and data storage areas. Ordi- narily, 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, e.g. "etext + rlp->rlim_max." (see end(3) for the definition of etext). 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. ERRORS
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. SEE ALSO
execve(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 exceed- ing the maximum size of the data segment without consulting getrlimit. 4th Berkeley Distribution May 22, 1986 BRK(2)

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BRK(2)							      BSD System Calls Manual							    BRK(2)

NAME
brk, sbrk -- change data segment size SYNOPSIS
#include <unistd.h> char * brk(const char *addr); char * sbrk(int incr); DESCRIPTION
The brk and sbrk functions are historical curiosities left over from earlier 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 segment. 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). RETURN VALUES
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 function returns a pointer to the base of the new storage if successful; otherwise -1 with errno set to indicate why the allocation failed. ERRORS
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. SEE ALSO
execve(2), getrlimit(2), malloc(3), mmap(2), 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. HISTORY
A brk() function call appeared in Version 7 AT&T UNIX. 4th Berkeley Distribution December 11, 1993 4th Berkeley Distribution

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