87 lines
2 KiB
Groff
87 lines
2 KiB
Groff
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.\" Copyright (c) 1980 Regents of the University of California.
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.\" All rights reserved. The Berkeley software License Agreement
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.\" specifies the terms and conditions for redistribution.
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.\"
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.\" @(#)brk.2 6.3 (Berkeley) 5/22/86
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.\"
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.TH BRK 2 "May 22, 1986"
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.UC 4
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.SH NAME
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brk, sbrk \- change data segment size
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.SH SYNOPSIS
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.nf
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#include <unistd.h>
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.PP
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.ft B
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int brk(char *\fIaddr\fP)
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.PP
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.ft B
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char *sbrk(int \fIincr\fP)
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.fi
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.SH DESCRIPTION
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.B Brk
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sets the system's idea of the lowest data segment
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location not used by the program (called the break)
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to
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.IR addr .
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Locations greater than
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.I addr
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and below the stack pointer
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are not in the address space and will thus
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cause a memory violation if accessed.
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.PP
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In the alternate function
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.BR sbrk ,
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.I incr
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more bytes are added to the
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program's data space and a pointer to the
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start of the new area is returned.
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.PP
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When a program begins execution via
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.B execve
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the break is set at the
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highest location defined by the program
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and data storage areas.
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Ordinarily, therefore, only programs with growing
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data areas need to use
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.BR sbrk .
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.SH "RETURN VALUE
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The address of the new break is returned if
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.B brk
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succeeds;
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.B \-1
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if the program requests more
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memory than the system limit.
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.B Sbrk
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returns
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.B \-1
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if the break could not be set.
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.SH ERRORS
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.B Sbrk
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will fail and no additional memory will be allocated if
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one of the following are true:
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.TP 15
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[ENOMEM]
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The maximum possible size of a data segment (as set by
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.BR chmem (1))
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was exceeded.
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.TP 15
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[ENOMEM]
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Insufficient virtual memory space existed
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to support the expansion. (Minix-vmd)
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.SH "SEE ALSO"
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.BR chmem (1),
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.BR execve (2),
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.BR malloc (3),
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.BR end (3).
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.SH NOTES
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Minix-vmd rounds a small data segment limit up to 3 megabytes.
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.SH BUGS
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Setting the break may fail due to a temporary lack of
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virtual memory under Minix-vmd. It is not possible to distinguish this
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from a failure caused by exceeding the maximum size of
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the data segment.
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.\"
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.\" $PchId: brk.2,v 1.2 2000/08/11 20:05:51 philip Exp $
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