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28 .\" @(#)brk.2 8.4 (Berkeley) 5/1/95
37 .Nd change data segment size
43 .Fn brk "const void *addr"
45 .Fn sbrk "intptr_t incr"
52 functions are legacy interfaces from before the
53 advent of modern virtual memory management.
60 functions are used to change the amount of memory allocated in a
61 process's data segment.
62 They do this by moving the location of the
64 The break is the first address after the end of the process's
65 uninitialized data segment (also known as the
76 function raises the break by
78 bytes, thus allocating at least
80 bytes of new memory in the data segment.
84 the break is lowered by
88 While the actual process data segment size maintained by the kernel will only
89 grow or shrink in page sizes, these functions allow setting the break
90 to unaligned values (i.e., it may point to any address inside the last
91 page of the data segment).
93 The current value of the program break may be determined by calling
100 system call may be used to determine
101 the maximum permissible size of the
103 It will not be possible to set the break
105 .Dq Va etext No + Va rlim.rlim_max
108 value is returned from a call to
109 .Fn getrlimit RLIMIT_DATA &rlim .
112 for the definition of
119 function returns the prior break value if successful;
121 .Po Vt "void *" Pc Ns \-1
122 is returned and the global variable
124 is set to indicate the error.
134 The requested break value was beyond the beginning of the data segment.
136 The data segment size limit, as set by
140 Insufficient space existed in the swap area
141 to support the expansion of the data segment.
163 or similar functions will result in non-portable program behavior.
165 Setting the break may fail due to a temporary lack of
167 It is not possible to distinguish this
168 from a failure caused by exceeding the maximum size of
169 the data segment without consulting