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163 lines
5.0 KiB
Groff
163 lines
5.0 KiB
Groff
.\" Copyright (c) 1983, 1991, 1992, 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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.\" 4. 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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.\" @(#)sigaltstack.2 8.2 (Berkeley) 5/1/95
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.\" $FreeBSD$
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.\"
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.Dd May 6, 2010
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.Dt SIGALTSTACK 2
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.Os
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.Sh NAME
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.Nm sigaltstack
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.Nd set and/or get signal stack context
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In signal.h
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.Bd -literal
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typedef struct {
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char *ss_sp;
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size_t ss_size;
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int ss_flags;
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} stack_t;
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.Ed
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.Ft int
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.Fn sigaltstack "const stack_t * restrict ss" "stack_t * restrict oss"
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.Sh DESCRIPTION
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The
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.Fn sigaltstack
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system call
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allows defining an alternate stack on which signals
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are to be processed for the current thread.
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If
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.Fa ss
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is non-zero,
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it specifies a pointer to and the size of a
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.Em "signal stack"
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on which to deliver signals.
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When a signal's action indicates its handler
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should execute on the signal stack (specified with a
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.Xr sigaction 2
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system call), the system checks to see
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if the thread is currently executing on that stack.
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If the thread is not currently executing on the signal stack,
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the system arranges a switch to the signal stack for the
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duration of the signal handler's execution.
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.Pp
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An active stack cannot be modified.
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.Pp
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If
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.Dv SS_DISABLE
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is set in
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.Fa ss_flags ,
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.Fa ss_sp
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and
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.Fa ss_size
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are ignored and the signal stack will be disabled.
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A disabled stack will cause all signals to be
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taken on the regular user stack.
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If the stack is later re-enabled then all signals that were specified
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to be processed on an alternate stack will resume doing so.
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.Pp
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If
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.Fa oss
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is non-zero, the current signal stack state is returned.
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The
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.Fa ss_flags
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field will contain the value
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.Dv SS_ONSTACK
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if the thread is currently on a signal stack and
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.Dv SS_DISABLE
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if the signal stack is currently disabled.
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.Sh NOTES
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The value
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.Dv SIGSTKSZ
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is defined to be the number of bytes/chars that would be used to cover
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the usual case when allocating an alternate stack area.
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The following code fragment is typically used to allocate an alternate stack.
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.Bd -literal -offset indent
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if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
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/* error return */
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sigstk.ss_size = SIGSTKSZ;
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sigstk.ss_flags = 0;
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if (sigaltstack(&sigstk, NULL) < 0)
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perror("sigaltstack");
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.Ed
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An alternative approach is provided for programs with signal handlers
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that require a specific amount of stack space other than the default size.
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The value
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.Dv MINSIGSTKSZ
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is defined to be the number of bytes/chars that is required by
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the operating system to implement the alternate stack feature.
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In computing an alternate stack size,
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programs should add
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.Dv MINSIGSTKSZ
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to their stack requirements to allow for the operating system overhead.
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.Pp
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Signal stacks are automatically adjusted for the direction of stack
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growth and alignment requirements.
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Signal stacks may or may not be protected by the hardware and
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are not ``grown'' automatically as is done for the normal stack.
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If the stack overflows and this space is not protected
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unpredictable results may occur.
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.Sh RETURN VALUES
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.Rv -std sigaltstack
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.Sh ERRORS
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The
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.Fn sigaltstack
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system call
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will fail and the signal stack context will remain unchanged
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if one of the following occurs.
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.Bl -tag -width Er
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.It Bq Er EFAULT
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Either
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.Fa ss
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or
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.Fa oss
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points to memory that is not a valid part of the process
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address space.
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.It Bq Er EPERM
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An attempt was made to modify an active stack.
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.It Bq Er EINVAL
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The
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.Fa ss_flags
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field was invalid.
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.It Bq Er ENOMEM
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Size of alternate stack area is less than or equal to
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.Dv MINSIGSTKSZ .
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.El
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.Sh SEE ALSO
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.Xr sigaction 2 ,
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.Xr setjmp 3
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.Sh HISTORY
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The predecessor to
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.Fn sigaltstack ,
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the
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.Fn sigstack
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system call, appeared in
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.Bx 4.2 .
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