89 lines
3.3 KiB
Groff
89 lines
3.3 KiB
Groff
.\" $NetBSD: userret.9,v 1.8 2007/02/17 17:29:24 yamt 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 December 20, 2005
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.Dt USERRET 9
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.Os
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.Sh NAME
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.Nm userret
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.Nd return path to user-mode execution
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.Sh SYNOPSIS
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.In sys/lwp.h
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.In sys/sched.h
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.Ft void
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.Fn userret "struct lwp *l"
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.Sh DESCRIPTION
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The
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.Fn userret
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function is executed after processing a trap
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.Pq e.g., a system call or interrupt
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before returning to user-mode execution.
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The implementation is machine dependent and is never invoked from
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machine-independent code.
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The function prototype for each architecture may be different to the
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prototype above, however the functionally provided by the
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.Fn userret
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function on each architecture is essentially the same.
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.Pp
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Specifically, the
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.Fn userret
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function performs the following procedure:
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.Bl -bullet -offset indent
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.It
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Detect a change in the signal disposition of the current process and invoke
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.Xr postsig 9
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to post the signal to the process.
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This may occur when the outcome of the trap or syscall posted a signal
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to the process
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.Pq e.g., invalid instruction trap .
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.It
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Check the
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.Va want_resched
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flag to see if the scheduler requires the current process to be
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preempted by invoking
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.Xr preempt 9
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.Pq see Xr cpu_need_resched 9 .
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This may occur if the clock interrupt causes the scheduler to
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determine that the current process has completed its time slice.
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.It
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Update the scheduler state.
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.El
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.Sh SEE ALSO
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.Xr cpu_need_resched 9 ,
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.Xr postsig 9 ,
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.Xr preempt 9 ,
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.Xr scheduler 9
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