2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
174 lines
4.5 KiB
Groff
174 lines
4.5 KiB
Groff
.\" $NetBSD: brk.2,v 1.32 2004/05/13 10:20:57 wiz Exp $
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.\"
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.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)brk.2 8.4 (Berkeley) 5/1/95
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.\"
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.Dd July 12, 1999
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.Dt BRK 2
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.Os
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.Sh NAME
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.Nm brk ,
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.Nm sbrk
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.Nd change data segment size
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In unistd.h
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.Ft int
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.Fn brk "void *addr"
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.Ft void *
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.Fn sbrk "intptr_t incr"
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.Sh DESCRIPTION
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.Bf -symbolic
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The brk and sbrk functions are legacy interfaces from before the
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advent of modern virtual memory management.
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.Ef
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.Pp
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The
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.Fn brk
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and
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.Fn sbrk
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functions are used to change the amount of memory allocated in a
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process's data segment.
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They do this by moving the location of the
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.Dq break .
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The break is the first address after the end of the process's
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uninitialized data segment (also known as the
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.Dq BSS ) .
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.Pp
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While the actual process data segment size maintained by the kernel will only
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grow or shrink in page sizes, these functions allow setting the break
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to unaligned values (i.e. it may point to any address inside the last
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page of the data segment).
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.Pp
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The
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.Fn brk
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function sets the break to
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.Fa addr .
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.Pp
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The
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.Fn sbrk
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function raises the break by at least
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.Fa incr
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bytes, thus allocating at least
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.Fa incr
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bytes of new memory in the data segment.
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If
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.Fa incr
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is negative,
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the break is lowered by
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.Fa incr
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bytes.
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.Pp
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.Fn sbrk
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returns the prior address of the break.
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The current value of the program break may be determined by calling
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.Fn sbrk 0 .
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(See also
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.Xr end 3 ) .
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.Pp
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The
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.Xr getrlimit 2
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system call may be used to determine
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the maximum permissible size of the
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.Em data
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segment;
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it will not be possible to set the break
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beyond the
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.Dv RLIMIT_DATA
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.Em rlim_max
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value returned from a call to
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.Xr getrlimit 2 ,
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e.g.
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.Dq etext + rlim.rlim_max .
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(see
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.Xr end 3
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for the definition of
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.Em etext ) .
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.Sh RETURN VALUES
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.Fn brk
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returns 0 if successful;
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otherwise \-1 with
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.Va errno
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set to indicate why the allocation failed.
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.Pp
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The
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.Fn sbrk
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function returns the prior break value if successful;
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otherwise ((void *)\-1) is returned and
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.Va errno
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is set to indicate why the allocation failed.
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.Sh ERRORS
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.Fn brk
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or
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.Fn 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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.Bl -tag -width Er
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.It Bq Er ENOMEM
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The limit, as set by
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.Xr setrlimit 2 ,
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was exceeded.
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.It Bq Er ENOMEM
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The maximum possible size of a data segment (compiled into the
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system) was exceeded.
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.It Bq Er ENOMEM
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Insufficient space existed in the swap area
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to support the expansion.
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.El
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.Sh SEE ALSO
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.Xr execve 2 ,
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.Xr getrlimit 2 ,
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.Xr mmap 2 ,
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.Xr end 3 ,
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.Xr free 3 ,
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.Xr malloc 3 ,
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.Xr sysconf 3
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.Sh HISTORY
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A
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.Fn brk
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function call appeared in
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.At v7 .
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.Sh BUGS
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Note that
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mixing
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.Fn brk
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and
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.Fn sbrk
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with
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.Xr malloc 3 ,
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.Xr free 3 ,
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and similar functions may result in non-portable program
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behavior.
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Caution is advised.
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.Pp
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Setting the break may fail due to a temporary lack of swap space.
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It is not possible to distinguish this from a failure caused by
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exceeding the maximum size of the data segment without consulting
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.Xr getrlimit 2 .
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