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32 .\" @(#)brk.2 8.4 (Berkeley) 5/1/95
33 .\" $FreeBSD: src/lib/libc/sys/brk.2,v 1.13.2.10 2002/03/04 12:00:31 dwmalone Exp $
34 .\" $DragonFly: src/lib/libc/sys/brk.2,v 1.3 2006/02/17 19:35:06 swildner Exp $
42 .Nd change data segment size
49 .Fn brk "const void *addr"
51 .Fn sbrk "intptr_t incr"
58 functions are legacy interfaces from before the
59 advent of modern virtual memory management.
66 functions are used to change the amount of memory allocated in a
67 process's data segment.
68 They do this by moving the location of the
70 The break is the first address after the end of the process's
71 uninitialized data segment (also known as the
82 function raises the break by
84 bytes, thus allocating at least
86 bytes of new memory in the data segment.
90 the break is lowered by
94 While the actual process data segment size maintained by the kernel will only
95 grow or shrink in page sizes, these functions allow setting the break
96 to unaligned values (i.e., it may point to any address inside the last
97 page of the data segment).
99 The current value of the program break may be determined by calling
106 system call may be used to determine
107 the maximum permissible size of the
109 It will not be possible to set the break
111 .Dq Va etext No + Va rlim.rlim_max
114 value is returned from a call to
115 .Fn getrlimit RLIMIT_DATA &rlim .
118 for the definition of
125 function returns the prior break value if successful;
127 .Po Vt "void *" Pc Ns \-1
128 is returned and the global variable
130 is set to indicate the error.
138 The requested break value was beyond the beginning of the data segment.
140 The data segment size limit, as set by
144 Insufficient space existed in the swap area
145 to support the expansion of the data segment.
157 function call appeared in
167 or similar functions will result in non-portable program behavior.
169 Setting the break may fail due to a temporary lack of
171 It is not possible to distinguish this
172 from a failure caused by exceeding the maximum size of
173 the data segment without consulting