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28 .\" @(#)brk.2 8.4 (Berkeley) 5/1/95
37 .Nd change data segment size
44 .Fn brk "const void *addr"
46 .Fn sbrk "intptr_t incr"
53 functions are legacy interfaces from before the
54 advent of modern virtual memory management.
61 functions are used to change the amount of memory allocated in a
62 process's data segment.
63 They do this by moving the location of the
65 The break is the first address after the end of the process's
66 uninitialized data segment (also known as the
77 function raises the break by
79 bytes, thus allocating at least
81 bytes of new memory in the data segment.
85 the break is lowered by
89 While the actual process data segment size maintained by the kernel will only
90 grow or shrink in page sizes, these functions allow setting the break
91 to unaligned values (i.e., it may point to any address inside the last
92 page of the data segment).
94 The current value of the program break may be determined by calling
101 system call may be used to determine
102 the maximum permissible size of the
104 It will not be possible to set the break
106 .Dq Va etext No + Va rlim.rlim_max
109 value is returned from a call to
110 .Fn getrlimit RLIMIT_DATA &rlim .
113 for the definition of
120 function returns the prior break value if successful;
122 .Po Vt "void *" Pc Ns \-1
123 is returned and the global variable
125 is set to indicate the error.
135 The requested break value was beyond the beginning of the data segment.
137 The data segment size limit, as set by
141 Insufficient space existed in the swap area
142 to support the expansion of the data segment.
164 or similar functions will result in non-portable program behavior.
166 Setting the break may fail due to a temporary lack of
168 It is not possible to distinguish this
169 from a failure caused by exceeding the maximum size of
170 the data segment without consulting