8b5179c21c
Due to limitations in the current pthread implementation, makecontext(3) and sigaltstack(2) should not be used in programs which link against libpthread (whether threads are used or not). Wording from drochner@ and ad@ Bump date for man pages. Add note in libpthread/README so it's not forgotten to update the man pages when the problem is fixed.
179 lines
5.5 KiB
Groff
179 lines
5.5 KiB
Groff
.\" $NetBSD: sigaltstack.2,v 1.22 2009/04/16 18:37:29 wiz Exp $
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.\"
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.\" 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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.\" 3. 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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.\"
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.Dd April 16, 2009
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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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.Pp
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.Bd -literal
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typedef struct sigaltstack {
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void *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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.Fn sigaltstack
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allows users to define an alternative stack on which signals
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are to be processed.
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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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and tells the system if the process is currently executing
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on that stack.
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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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call), the system checks to see
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if the process is currently executing on that stack.
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If the process 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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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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Trying to disable an active stack will cause
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.Nm
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to return \-1 with
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.Va errno
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set to
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.Er EINVAL .
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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 alternative 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 process 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 alternative stack area.
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The following code fragment is typically used to allocate an alternative 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(\*[Am]sigstk,0) \*[Lt] 0)
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perror("sigaltstack");
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.Ed
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.Pp
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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 alternative stack feature.
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In computing an alternative 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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Upon successful completion, a value of 0 is returned.
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Otherwise, a value of \-1 is returned and
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.Va errno
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is set to indicate the error.
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.Sh ERRORS
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.Fn sigaltstack
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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 EINVAL
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An attempt was made to disable an active stack.
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.It Bq Er ENOMEM
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Size of alternative stack area is less than
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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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.Xr signal 7
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.Sh STANDARDS
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The
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.Fn sigaltstack
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function conforms to
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.St -xpg4.2 .
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.Sh HISTORY
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The predecessor to
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.Nm 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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.Sh CAVEATS
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Due to limitations in the current pthread implementation,
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.Nm
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should not be used in programs which link against the
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.Xr pthread 3
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library (whether threads are used or not).
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