NAME
brk, sbrk - change data segment size

SYNOPSIS
#include <sys/types.h>

char *brk(addr)
const 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.
Ordinarily, therefore, only programs with growing data areas need
to use sbrk.

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. "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.

NOTES
When MachTen is not running in virtual memory mode, all memory
references are by actual physical addresses. Thus, when sbrk
allocates additional data space (out of the application heap), it
will be disjoint from the original data space and any prior sbrk.
There is also no linear ordering of consecutive sbrks.

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
exceeding the maximum size of the data segment without consulting
getrlimit*.

__________
* Not currently supported under MachTen