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.\" $NetBSD: ras.9,v 1.5 2003/04/16 13:35:33 wiz Exp $
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.\"
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.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Gregory McGarry.
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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. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the NetBSD
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.\" Foundation, Inc. and its contributors.
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.\" 4. Neither the name of The NetBSD Foundation nor the names of its
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.\" contributors may be used to endorse or promote products derived
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.\" from this software without specific prior written permission.
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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 August 12, 2002
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.Dt RAS 9
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.Os
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.Sh NAME
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.Nm ras_lookup ,
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.Nm ras_fork ,
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.Nm ras_purgeall
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.Nd restartable atomic sequences
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/proc.h
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.In sys/ras.h
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.Ft caddr_t
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.Fn ras_lookup "struct proc *p" "caddr_t addr"
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.Ft int
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.Fn ras_fork "struct proc *p1" "struct proc *p2"
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.Ft int
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.Fn ras_purgeall "struct proc *p"
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.Sh DESCRIPTION
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Restartable atomic sequences are user code sequences which are
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guaranteed to execute without preemption.
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This property is assured by checking the set of restartable atomic
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sequences registered for a process during
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.Xr cpu_switch 9 .
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If a process is found to have been preempted during a restartable
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sequence, then its execution is rolled-back to the start of the
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sequence by resetting its program counter saved in its process control
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block (PCB).
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.Pp
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The RAS functionality is provided by a combination of the
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machine-independent routines discussed in this page and
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a machine-dependent component in
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.Xr cpu_switch 9 .
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A port which supports restartable atomic sequences will define
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__HAVE_RAS in
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.Pa machine/types.h
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for machine-independent code to conditionally provide RAS support.
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.Pp
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A complicated side-effect of restartable atomic sequences is their
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interaction with the machine-dependent
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.Xr ptrace 2
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support.
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Specifically, single-step traps and/or the emulation of single-stepping
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must carefully consider the effect on restartable atomic sequences.
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A general solution is to ignore these traps or disable them within
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restartable atomic sequences.
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.Sh FUNCTIONS
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The functions which operate on restartable atomic sequences are:
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.Pp
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.Bl -tag -width compact
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.It Fn ras_lookup "p" "addr"
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This function searches the registered restartable atomic sequences for
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process
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.Fa p
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which contain the user address
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.Fa addr .
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If the address
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.Fa addr
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is found within a RAS, then the restart address of the RAS is
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returned, otherwise \-1 is returned.
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.It Fn ras_fork "p1" "p2"
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This function is used to copy all registered restartable atomic
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sequences for process
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.Fa p1
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to process
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.Fa p2 .
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It is primarily called from
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.Xr fork1 9
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when the sequences are inherited from the parent by the child.
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.It Fn ras_purgeall "p"
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This function is used to remove all registered restartable atomic
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sequences for process
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.Fa p .
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It is primarily used to remove all registered restartable atomic
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sequences for a process during
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.Xr exec 3
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and by
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.Xr rasctl 2 .
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.El
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.Sh CODE REFERENCES
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This section describes places within the
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.Nx
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source tree where actual code implementing or using the RAS
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functionality can be found.
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All pathnames are relative to
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.Pa /usr/src .
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.Pp
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The RAS framework itself is implemented within the file
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.Pa sys/kern/kern_ras.c .
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Data structures and function prototypes for the framework are located
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in
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.Pa sys/sys/ras.h .
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Machine-dependent portions are implemented within
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.Xr cpu_switch 9
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in the machine-dependent file
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.Pa sys/arch/\*[Lt]arch\*[Gt]/\*[Lt]arch\*[Gt]/locore.S .
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.Sh SEE ALSO
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.Xr rasctl 2 ,
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.Xr cpu_switch 9 ,
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.Xr fork1 9
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.Sh HISTORY
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The RAS functionality first appeared in
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.Nx 2.0 .
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