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28 .\" @(#)brk.2 8.4 (Berkeley) 5/1/95
29 .\" $FreeBSD: src/lib/libc/sys/brk.2,v 1.13.2.10 2002/03/04 12:00:31 dwmalone Exp $
36 .Nd change data segment size (obsolete)
43 .Fn sbrk "intptr_t incr"
48 function is a legacy interface from before the
49 advent of modern virtual memory management.
51 has only limited functionality due to having to play nice with
52 modern system calls such as
58 function is used to change the amount of memory allocated in a
59 process's data segment.
60 It does this by moving the location of the
62 The break is the first address after the end of the process's
63 uninitialized data segment (also known as the
66 The break range is limited by the
68 resource limit applied to the process.
72 function raises the break by
74 bytes, returning a pointer to the base of the new memory.
75 Any attempt to lower the break point will return
76 .Po Vt "void *" Pc Ns \-1
80 While the actual process data segment size maintained by the kernel will only
81 grow or shrink in page sizes, this function allows setting the break
82 to unaligned values (i.e., it may point to any address inside the last
83 page of the data segment).
85 The current value of the program break may be determined by calling
90 function is thread-safe.
96 system call may be used to determine
97 the maximum permissible size of the
99 It will not be possible to set the break
101 .Dq Va etext No + Va rlim.rlim_max
104 value is returned from a call to
105 .Fn getrlimit RLIMIT_DATA &rlim .
108 for the definition of
113 function returns the prior break pointer if successful;
115 .Po Vt "void *" Pc Ns \-1
116 is returned and the global variable
118 is set to indicate the error.
124 The requested break value was beyond the beginning of the data segment.
126 The data segment size limit, as set by
130 Insufficient space existed in the swap area
131 to support the expansion of the data segment.
133 An attempt has been made to perform an action that is no longer supported
149 or similar functions will result in non-portable program behavior.
151 Setting the break may fail due to a temporary lack of
153 It is not possible to distinguish this
154 from a failure caused by exceeding the maximum size of
155 the data segment without consulting