f19351aad8
The previous misuse of sys_sigqueue() was sending random register or stack garbage to 64-bit targets. The freebsd32 implementation preserves the sival_int member of value when signaling a 64-bit process. Document the mixed ABI implementation of union sigval and the incompability of sival_ptr with pointer integrity schemes. Reviewed by: kib, wblock MFC after: 1 week Sponsored by: DARPA, AFRL Differential Revision: https://reviews.freebsd.org/D10605
164 lines
4.4 KiB
Groff
164 lines
4.4 KiB
Groff
.\" Copyright (c) 2005 David Xu <davidxu@FreeBSD.org>
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.\" 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(s), this list of conditions and the following disclaimer as
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.\" the first lines of this file unmodified other than the possible
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.\" addition of one or more copyright notices.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice(s), this list of conditions and the following disclaimer in
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.\" the documentation and/or other materials provided with the
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.\" distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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.\" EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE
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.\" 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
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.\" BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
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.\" WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
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.\" OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
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.\" EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 5, 2017
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.Dt SIGQUEUE 2
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.Os
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.Sh NAME
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.Nm sigqueue
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.Nd "queue a signal to a process (REALTIME)"
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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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.Ft int
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.Fn sigqueue "pid_t pid" "int signo" "const union sigval value"
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.Sh DESCRIPTION
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The
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.Fn sigqueue
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system call causes the signal specified by
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.Fa signo
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to be sent with the value specified by
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.Fa value
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to the process specified by
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.Fa pid .
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If
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.Fa signo
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is zero (the null signal), error checking is performed but
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no signal is actually sent.
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The null signal can be used to check the
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validity of PID.
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.Pp
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The conditions required for a process to have permission to queue a
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signal to another process are the same as for the
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.Xr kill 2
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system call.
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The
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.Fn sigqueue
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system call queues a signal to a single process specified by the
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.Fa pid
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argument.
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.Pp
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The
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.Fn sigqueue
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system call returns immediately.
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If the resources were
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available to queue the signal, the signal will be queued and sent to
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the receiving process.
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.Pp
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If the value of
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.Fa pid
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causes
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.Fa signo
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to be generated for the sending process, and if
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.Fa signo
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is not blocked for the calling thread and if no other thread has
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.Fa signo
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unblocked or is waiting in a
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.Fn sigwait
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system call for
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.Fa signo ,
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either
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.Fa signo
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or at least the pending, unblocked signal will be delivered to the
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calling thread before
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.Fn sigqueue
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returns.
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Should any multiple pending signals in the range
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.Dv SIGRTMIN
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to
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.Dv SIGRTMAX
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be selected for delivery, it is the lowest numbered
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one.
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The selection order between realtime and non-realtime signals, or
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between multiple pending non-realtime signals, is unspecified.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn sigqueue
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system call
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EAGAIN
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No resources are available to queue the signal.
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The process has already
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queued
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.Brq Dv SIGQUEUE_MAX
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signals that are still pending at the receiver(s),
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or a system-wide resource limit has been exceeded.
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.It Bq Er EINVAL
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The value of the
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.Fa signo
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argument is an invalid or unsupported signal number.
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.It Bq Er EPERM
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The process does not have the appropriate privilege to send the signal
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to the receiving process.
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.It Bq Er ESRCH
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The process
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.Fa pid
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does not exist.
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.El
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.Sh SEE ALSO
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.Xr kill 2 ,
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.Xr sigaction 2 ,
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.Xr sigpending 2 ,
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.Xr sigsuspend 2 ,
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.Xr sigtimedwait 2 ,
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.Xr sigwait 2 ,
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.Xr sigwaitinfo 2 ,
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.Xr pause 3 ,
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.Xr pthread_sigmask 3 ,
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.Xr siginfo 3
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.Sh STANDARDS
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The
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.Fn sigqueue
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system call conforms to
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.St -p1003.1-2004 .
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.Sh HISTORY
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Support for
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.Tn POSIX
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realtime signal queue first appeared in
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.Fx 7.0 .
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.Sh CAVEATS
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When using
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.Nm
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to send signals to a process which might have a different ABI
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(for instance, one is 32-bit and the other 64-bit),
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the
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.Va sival_int
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member of
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.Fa value
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can be delivered reliably, but the
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.Va sival_ptr
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may be truncated in endian dependent ways and must not be relied on.
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Further, many pointer integrity schemes disallow sending pointers to other
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processes, and this technique should not be used in programs intended to
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be portable.
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