66 lines
2.3 KiB
Groff
66 lines
2.3 KiB
Groff
.\" $NetBSD: __insn_barrier.3,v 1.2 2011/01/02 07:14:02 jruoho Exp $
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.\"
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.\" Copyright (c) 2010 Jukka Ruohonen <jruohonen@iki.fi>
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.\" 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd January 2, 2011
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.Dt __INSN_BARRIER 3
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.Os
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.Sh NAME
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.Nm __insn_barrier
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.Nd compiler reorder barrier
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.Sh SYNOPSIS
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.In sys/cdefs.h
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.Ft void
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.Fn __insn_barrier
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.Sh DESCRIPTION
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The
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.Fn __insn_barrier
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macro prevents
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.Tn GCC
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from moving code across the barrier.
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In other words, the compiler is not allowed to reorder read and write
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commands below the barrier with the code preceding the barrier.
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Like with the
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.Em volatile
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type qualifier,
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.Fn __insn_barrier
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may be necessary in some corner cases to prevent the compiler
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from misoptimizing.
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.Sh SEE ALSO
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.Xr gcc 1 ,
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.Xr cdefs 3 ,
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.Xr mb 9
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.Rs
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.%A Paul E. McKenney
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.%T Memory Barriers: a Hardware View for Software Hackers
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.%D June 7, 2010
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.%U http://www.rdrop.com/users/paulmck/scalability/paper/whymb.2010.06.07c.pdf
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.Re
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.Sh HISTORY
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The
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.Fn __insn_barrier
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macro first appeared in
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.Nx 2.0 .
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