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Annotation of 43BSDReno/lib/libc/sys/brk.2, revision 1.1

1.1     ! root        1: .\" Copyright (c) 1980 Regents of the University of California.
        !             2: .\" All rights reserved.  The Berkeley software License Agreement
        !             3: .\" specifies the terms and conditions for redistribution.
        !             4: .\"
        !             5: .\"    @(#)brk.2       6.4 (Berkeley) 6/17/86
        !             6: .\"
        !             7: .TH BRK 2 "June 17, 1986"
        !             8: .UC 4
        !             9: .SH NAME
        !            10: brk, sbrk \- change data segment size
        !            11: .SH SYNOPSIS
        !            12: .nf
        !            13: #include <sys/types.h>
        !            14: .PP
        !            15: .ft B
        !            16: char *brk(addr)
        !            17: char *addr;
        !            18: .PP
        !            19: .ft B
        !            20: char *sbrk(incr)
        !            21: int incr;
        !            22: .fi
        !            23: .SH DESCRIPTION
        !            24: .I Brk
        !            25: sets the system's idea of the lowest data segment 
        !            26: location not used by the program (called the break)
        !            27: to
        !            28: .I addr
        !            29: (rounded up to the next multiple of the system's page size).
        !            30: Locations greater than
        !            31: .I addr
        !            32: and below the stack pointer
        !            33: are not in the address space and will thus
        !            34: cause a memory violation if accessed.
        !            35: .PP
        !            36: In the alternate function
        !            37: .IR sbrk ,
        !            38: .I incr
        !            39: more bytes are added to the
        !            40: program's data space and a pointer to the
        !            41: start of the new area is returned.
        !            42: .PP
        !            43: When a program begins execution via
        !            44: .I execve
        !            45: the break is set at the
        !            46: highest location defined by the program
        !            47: and data storage areas.
        !            48: Ordinarily, therefore, only programs with growing
        !            49: data areas need to use
        !            50: .IR sbrk .
        !            51: .PP
        !            52: The current value of the program break is reliably returned by
        !            53: ``sbrk(0)'' (see also 
        !            54: .IR end (3)).
        !            55: The
        !            56: .IR getrlimit (2)
        !            57: system call may be used to determine
        !            58: the maximum permissible size of the
        !            59: .I data
        !            60: segment;
        !            61: it will not be possible to set the break
        !            62: beyond the
        !            63: .I rlim_max
        !            64: value returned from a call to
        !            65: .IR getrlimit ,
        !            66: e.g. \*(lqetext + rlp\(->rlim_max.\*(rq
        !            67: (see
        !            68: .IR end (3)
        !            69: for the definition of
        !            70: .IR etext ).
        !            71: .SH "RETURN VALUE
        !            72: Zero is returned if the 
        !            73: .I brk
        !            74: could be set;
        !            75: \-1 if the program requests more
        !            76: memory than the system limit.
        !            77: .I Sbrk
        !            78: returns \-1 if the break could not be set.
        !            79: .SH ERRORS
        !            80: .I Sbrk
        !            81: will fail and no additional memory will be allocated if
        !            82: one of the following are true:
        !            83: .TP 15
        !            84: [ENOMEM]
        !            85: The limit, as set by
        !            86: .IR setrlimit (2),
        !            87: was exceeded.
        !            88: .TP 15
        !            89: [ENOMEM]
        !            90: The maximum possible size of a data segment (compiled into the
        !            91: system) was exceeded.
        !            92: .TP 15
        !            93: [ENOMEM]
        !            94: Insufficient space existed in the swap area
        !            95: to support the expansion.
        !            96: .SH "SEE ALSO"
        !            97: execve(2), getrlimit(2), malloc(3), end(3)
        !            98: .SH BUGS
        !            99: Setting the break may fail due to a temporary lack of
        !           100: swap space.  It is not possible to distinguish this
        !           101: from a failure caused by exceeding the maximum size of
        !           102: the data segment without consulting 
        !           103: .IR getrlimit .

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