| 1 | .\" Copyright (c) 1980 Regents of the University of California.
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| 2 | .\" All rights reserved. The Berkeley software License Agreement
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| 3 | .\" specifies the terms and conditions for redistribution.
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| 4 | .\"
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| 5 | .\" @(#)brk.2 6.3 (Berkeley) 5/22/86
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| 6 | .\"
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| 7 | .TH BRK 2 "May 22, 1986"
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| 8 | .UC 4
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| 9 | .SH NAME
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| 10 | brk, sbrk \- change data segment size
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| 11 | .SH SYNOPSIS
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| 12 | .nf
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| 13 | #include <unistd.h>
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| 14 | .PP
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| 15 | .ft B
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| 16 | int brk(char *\fIaddr\fP)
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| 17 | .PP
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| 18 | .ft B
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| 19 | char *sbrk(int \fIincr\fP)
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| 20 | .fi
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| 21 | .SH DESCRIPTION
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| 22 | .B Brk
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| 23 | sets the system's idea of the lowest data segment
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| 24 | location not used by the program (called the break)
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| 25 | to
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| 26 | .IR addr .
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| 27 | Locations greater than
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| 28 | .I addr
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| 29 | and below the stack pointer
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| 30 | are not in the address space and will thus
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| 31 | cause a memory violation if accessed.
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| 32 | .PP
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| 33 | In the alternate function
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| 34 | .BR sbrk ,
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| 35 | .I incr
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| 36 | more bytes are added to the
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| 37 | program's data space and a pointer to the
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| 38 | start of the new area is returned.
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| 39 | .PP
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| 40 | When a program begins execution via
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| 41 | .B execve
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| 42 | the break is set at the
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| 43 | highest location defined by the program
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| 44 | and data storage areas.
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| 45 | Ordinarily, therefore, only programs with growing
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| 46 | data areas need to use
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| 47 | .BR sbrk .
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| 48 | .SH "RETURN VALUE
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| 49 | The address of the new break is returned if
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| 50 | .B brk
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| 51 | succeeds;
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| 52 | .B \-1
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| 53 | if the program requests more
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| 54 | memory than the system limit.
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| 55 | .B Sbrk
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| 56 | returns
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| 57 | .B \-1
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| 58 | if the break could not be set.
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| 59 | .SH ERRORS
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| 60 | .B Sbrk
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| 61 | will fail and no additional memory will be allocated if
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| 62 | one of the following are true:
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| 63 | .TP 15
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| 64 | [ENOMEM]
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| 65 | The maximum possible size of a data segment (as set by
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| 66 | .BR chmem (1))
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| 67 | was exceeded.
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| 68 | .TP 15
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| 69 | [ENOMEM]
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| 70 | Insufficient virtual memory space existed
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| 71 | to support the expansion. (Minix-vmd)
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| 72 | .SH "SEE ALSO"
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| 73 | .BR chmem (1),
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| 74 | .BR execve (2),
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| 75 | .BR malloc (3),
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| 76 | .BR end (3).
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| 77 | .SH NOTES
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| 78 | Minix-vmd rounds a small data segment limit up to 3 megabytes.
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| 79 | .SH BUGS
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| 80 | Setting the break may fail due to a temporary lack of
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| 81 | virtual memory under Minix-vmd. It is not possible to distinguish this
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| 82 | from a failure caused by exceeding the maximum size of
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| 83 | the data segment.
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| 84 |
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| 85 | .\"
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| 86 | .\" $PchId: brk.2,v 1.2 2000/08/11 20:05:51 philip Exp $
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