brk(2) [plan9 man page]

BRK(2)								System Calls Manual							    BRK(2)

NAME

       brk, sbrk - change memory allocation

SYNOPSIS

       #include <u.h>
       #include <libc.h>

       int   brk(void *addr)

       void* sbrk(ulong incr)

DESCRIPTION

       Brk sets the system's idea of the lowest bss location not used by the program (called the break) to addr rounded up to the next multiple of
       8 bytes.  Locations not less than addr and below the stack pointer may 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.  Rounding occurs as with brk.

       When  a program begins execution via exec the break is set at the highest location defined by the program and data storage areas.  Ordinar-
       ily, therefore, only programs with growing data areas need to use brk.  A call to sbrk with a zero argument returns the lowest  address	in
       the dynamic segment.

SOURCE

       /sys/src/libc/9sys/sbrk.c

SEE ALSO

       intro(2), malloc(2), segattach(2), segbrk(2)

DIAGNOSTICS

       These functions set errstr.

       The error return from sbrk is (void*)-1.

																	    BRK(2)

BRK(2)								System Calls Manual							    BRK(2)

NAME

       brk, sbrk - change data segment size

SYNOPSIS

       #include <unistd.h>

       char *brk(char *addr)

       char *sbrk(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.  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.

RETURN VALUE

       The address of the new break is returned if brk succeeds; -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 maximum possible size of a data segment (as set by chmem(1)) was exceeded.

       [ENOMEM]       Insufficient virtual memory space existed to support the expansion.  (Minix-vmd)

SEE ALSO

       chmem(1), execve(2), malloc(3), end(3).

NOTES

       Minix-vmd rounds a small data segment limit up to 3 megabytes.

BUGS

       Setting	the break may fail due to a temporary lack of virtual memory under Minix-vmd.  It is not possible to distinguish this from a fail-
       ure caused by exceeding the maximum size of the data segment.

4th Berkeley Distribution					   May 22, 1986 							    BRK(2)