138 lines
4.2 KiB
Groff
138 lines
4.2 KiB
Groff
.\" $NetBSD: ucontext.2,v 1.10 2018/02/27 10:09:42 uwe Exp $
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.\"
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.\" Copyright (c) 2001 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 Klaus Klein.
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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 February 25, 2018
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.Dt UCONTEXT 2
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.Os
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.Sh NAME
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.Nm ucontext
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.Nd user context
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.Sh SYNOPSIS
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.In ucontext.h
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.Fn _UC_MACHINE_SP "&uc"
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.Fn _UC_MACHINE_FP "&uc"
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.Fn _UC_MACHINE_PC "&uc"
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.Fn _UC_MACHINE_INTRV "&uc"
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.Fn _UC_MACHINE_SET_PC "&uc"
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.Sh DESCRIPTION
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The
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.Vt ucontext_t
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is a structure type which is used to describe the context of a
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thread of control within the execution of a process.
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A thread's context includes its stack, saved registers, and list of
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blocked signals.
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.Pp
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The
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.Vt ucontext_t
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structure includes the following members:
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.Bd -literal -offset indent
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ucontext_t *uc_link
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sigset_t uc_sigmask
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stack_t uc_stack
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mcontext_t uc_mcontext
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.Ed
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.Pp
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The
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.Fa uc_link
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member points to the context that will be resumed after the function
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specified when modifying a context using
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.Xr makecontext 3
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has returned.
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If
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.Fa uc_link
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is a
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.Dv NULL
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pointer, then the context is the main context,
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and the process will exit with an exit status of 0 upon return.
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.Pp
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The
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.Fa uc_sigmask
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member is the set of signals that are blocked when the context is
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activated.
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Further information can be found in
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.Xr sigprocmask 2 .
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.Pp
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The
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.Fa uc_stack
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member defines the stack used by the context.
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Further information can be found in
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.Xr sigaltstack 2 .
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.Pp
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The
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.Fa uc_mcontext
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member defines the machine state associated with the context;
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it may consist of general registers, floating point registers
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and other machine-specific information.
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Its description is beyond the scope of this manual page;
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portable applications should not access this structure member.
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.Pp
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The following auxiliary macros are available to access some of that
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machine-specific information:
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.Bl -tag -width ".Fn _UC_MACHINE_SET_PC" -offset indent
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.It Fn _UC_MACHINE_SP
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\(em read stack pointer,
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.It Fn _UC_MACHINE_FP
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\(em read frame pointer (base pointer),
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.It Fn _UC_MACHINE_PC
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\(em read program counter,
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.It Fn _UC_MACHINE_INTRV
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\(em read integer return value,
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.It Fn _UC_MACHINE_SET_PC
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\(em write program counter.
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.El
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.Pp
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The frame pointer macro does not guarantee to retrieve a reliable value
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and should not be used in a code unless no other debugging format is
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easily accessible.
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A compiler might optimize the frame pointer register in a function,
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reusing it as a general purpose register storage
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.Fl ( fomit-frame-pointer )
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or emit function prologues only before parts that need them
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.Fl ( fshrink-wrap ) .
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.Sh SEE ALSO
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.Xr _exit 2 ,
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.Xr getcontext 2 ,
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.Xr setcontext 2 ,
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.Xr sigaltstack 2 ,
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.Xr sigprocmask 2 ,
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.Xr makecontext 3 ,
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.Xr swapcontext 3
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.Sh STANDARDS
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The
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.Vt ucontext_t
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type conforms to
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.St -xsh5
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and
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.St -p1003.1-2001 .
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The
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.St -p1003.1-2008
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revision removed the
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.Vt ucontext_t
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from the specification.
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