BSD 2.11 - man page for brk (bsd section 2)

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BRK(2)											   BRK(2)

       brk, sbrk - change data segment size

       #include <sys/types.h>

       char *brk(addr)
       char *addr;

       char *sbrk(incr)
       int incr;

       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.  Ordinarily, 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

       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.

       Sbrk  will  fail  and  no  additional memory will be allocated if one of the following are

       [ENOMEM]       The limit, as set by setrlimit(2), was exceeded.

       [ENOMEM]       The maximum possible size of a data segment (compiled into the system)  was

       [ENOMEM]       Insufficient space existed in the swap area to support the expansion.

       execve(2), getrlimit(2), malloc(3), end(3)

       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.

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