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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.
54 They are deprecated and not present on the arm64 or riscv architectures.
57 interface should be used to allocate pages instead.
64 functions are used to change the amount of memory allocated in a
65 process's data segment.
66 They do this by moving the location of the
68 The break is the first address after the end of the process's
69 uninitialized data segment (also known as the
80 function raises the break by
82 bytes, thus allocating at least
84 bytes of new memory in the data segment.
88 the break is lowered by
92 While the actual process data segment size maintained by the kernel will only
93 grow or shrink in page sizes, these functions allow setting the break
94 to unaligned values (i.e., it may point to any address inside the last
95 page of the data segment).
97 The current value of the program break may be determined by calling
104 system call may be used to determine
105 the maximum permissible size of the
107 It will not be possible to set the break
109 .Dq Va etext No + Va rlim.rlim_max
112 value is returned from a call to
113 .Fn getrlimit RLIMIT_DATA &rlim .
116 for the definition of
123 function returns the prior break value if successful;
125 .Po Vt "void *" Pc Ns \-1
126 is returned and the global variable
128 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.
160 introduced the arm64 and riscv architectures which do not support
172 or similar functions will result in non-portable program behavior.
174 Setting the break may fail due to a temporary lack of
176 It is not possible to distinguish this
177 from a failure caused by exceeding the maximum size of
178 the data segment without consulting
182 is sometimes used to monitor heap use by calling with an argument of 0.
183 The result is unlikely to reflect actual utilization in combination with an