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.Dd April 2, 2022
.Dt SIGVEC 2
.Os
.Sh NAME
.Nm sigvec
.Nd software signal facilities
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In signal.h
.Bd -literal
struct sigvec {
        void     (*sv_handler)();
	int      sv_mask;
	int      sv_flags;
};
.Ed
.Ft int
.Fn sigvec "int sig" "struct sigvec *vec" "struct sigvec *ovec"
.Sh DESCRIPTION
.Bf -symbolic
This interface is made obsolete by
.Xr sigaction 2 .
.Ef
.Pp
The system defines a set of signals that may be delivered to a process.
Signal delivery resembles the occurrence of a hardware interrupt:
the signal is blocked from further occurrence, the current process
context is saved, and a new one is built.
A process may specify a
.Em handler
to which a signal is delivered, or specify that a signal is to be
.Em blocked
or
.Em ignored .
A process may also specify that a default action is to be taken
by the system when a signal occurs.
Normally, signal handlers execute on the current stack
of the process.
This may be changed, on a per-handler basis,
so that signals are taken on a special
.Em "signal stack" .
.Pp
All signals have the same
.Em priority .
Signal routines execute with the signal that caused their
invocation
.Em blocked ,
but other signals may yet occur.
A global
.Em "signal mask"
defines the set of signals currently blocked from delivery
to a process.
The signal mask for a process is initialized
from that of its parent (normally 0).
It
may be changed with a
.Xr sigblock 2
or
.Xr sigsetmask 2
call, or when a signal is delivered to the process.
.Pp
When a signal
condition arises for a process, the signal is added to a set of
signals pending for the process.
If the signal is not currently
.Em blocked
by the process then it is delivered to the process.
When a signal
is delivered, the current state of the process is saved,
a new signal mask is calculated (as described below),
and the signal handler is invoked.
The call to the handler
is arranged so that if the signal handling routine returns
normally the process will resume execution in the context
from before the signal's delivery.
If the process wishes to resume in a different context, then it
must arrange to restore the previous context itself.
.Pp
When a signal is delivered to a process a new signal mask is
installed for the duration of the process' signal handler
(or until a
.Xr sigblock 2
or
.Xr sigsetmask 2
call is made).
This mask is formed by taking the current signal mask,
adding the signal to be delivered, and
.Em or Ns 'ing
in the signal mask associated with the handler to be invoked.
.Pp
The
.Fn sigvec
function
assigns a handler for a specific signal.
If
.Fa vec
is non-zero, it
specifies a handler routine and mask
to be used when delivering the specified signal.
Further, if the
.Dv SV_ONSTACK
bit is set in
.Fa sv_flags ,
the system will deliver the signal to the process on a
.Em "signal stack" ,
specified with
.Xr sigaltstack 2 .
If
.Fa ovec
is non-zero, the previous handling information for the signal
is returned to the user.
.Pp
The following is a list of all signals
with names as in the include file
.In signal.h :
.Bl -column SIGVTALARMXX "create core imagexxx"
.It Sy "NAME	Default Action	Description"
.It Dv SIGHUP No "	terminate process" "	terminal line hangup"
.It Dv SIGINT No "	terminate process" "	interrupt program"
.It Dv SIGQUIT No "	create core image" "	quit program"
.It Dv SIGILL No "	create core image" "	illegal instruction"
.It Dv SIGTRAP No "	create core image" "	trace trap"
.It Dv SIGABRT No "	create core image" Ta Xr abort 3
call (formerly
.Dv SIGIOT )
.It Dv SIGEMT No "	create core image" "	emulate instruction executed"
.It Dv SIGFPE No "	create core image" "	floating-point exception"
.It Dv SIGKILL No "	terminate process" "	kill program"
.It Dv SIGBUS No "	create core image" "	bus error"
.It Dv SIGSEGV No "	create core image" "	segmentation violation"
.It Dv SIGSYS No "	create core image" "	non-existent system call invoked"
.It Dv SIGPIPE No "	terminate process" "	write on a pipe with no reader"
.It Dv SIGALRM No "	terminate process" "	real-time timer expired"
.It Dv SIGTERM No "	terminate process" "	software termination signal"
.It Dv SIGURG No "	discard signal" "	urgent condition present on socket"
.It Dv SIGSTOP No "	stop process" "	stop (cannot be caught or ignored)"
.It Dv SIGTSTP No "	stop process" "	stop signal generated from keyboard"
.It Dv SIGCONT No "	discard signal" "	continue after stop"
.It Dv SIGCHLD No "	discard signal" "	child status has changed"
.It Dv SIGTTIN No "	stop process" "	background read attempted from control terminal"
.It Dv SIGTTOU No "	stop process" "	background write attempted to control terminal"
.It Dv SIGIO No "	discard signal" Tn "	I/O"
is possible on a descriptor (see
.Xr fcntl 2 )
.It Dv SIGXCPU No "	terminate process" "	cpu time limit exceeded (see"
.Xr setrlimit 2 )
.It Dv SIGXFSZ No "	terminate process" "	file size limit exceeded (see"
.Xr setrlimit 2 )
.It Dv SIGVTALRM No "	terminate process" "	virtual time alarm (see"
.Xr setitimer 2 )
.It Dv SIGPROF No "	terminate process" "	profiling timer alarm (see"
.Xr setitimer 2 )
.It Dv SIGWINCH No "	discard signal" "	Window size change"
.It Dv SIGINFO No "	discard signal" "	status request from keyboard"
.It Dv SIGUSR1 No "	terminate process" "	User defined signal 1"
.It Dv SIGUSR2 No "	terminate process" "	User defined signal 2"
.El
.Pp
Once a signal handler is installed, it remains installed
until another
.Fn sigvec
call is made, or an
.Xr execve 2
is performed.
A signal-specific default action may be reset by
setting
.Fa sv_handler
to
.Dv SIG_DFL .
The defaults are process termination, possibly with core dump;
no action; stopping the process; or continuing the process.
See the above signal list for each signal's default action.
If
.Fa sv_handler
is
.Dv SIG_IGN
current and pending instances
of the signal are ignored and discarded.
.Pp
If a signal is caught during the system calls listed below,
the call is normally restarted.
The call can be forced to terminate prematurely with an
.Er EINTR
error return by setting the
.Dv SV_INTERRUPT
bit in
.Fa sv_flags .
The affected system calls include
.Xr read 2 ,
.Xr write 2 ,
.Xr sendto 2 ,
.Xr recvfrom 2 ,
.Xr sendmsg 2
and
.Xr recvmsg 2
on a communications channel or a slow device (such as a terminal,
but not a regular file)
and during a
.Xr wait 2
or
.Xr ioctl 2 .
However, calls that have already committed are not restarted,
but instead return a partial success (for example, a short read count).
.Pp
After a
.Xr fork 2
or
.Xr vfork 2
all signals, the signal mask, the signal stack,
and the restart/interrupt flags are inherited by the child.
.Pp
The
.Xr execve 2
system call reinstates the default
action for all signals which were caught and
resets all signals to be caught on the user stack.
Ignored signals remain ignored;
the signal mask remains the same;
signals that interrupt system calls continue to do so.
.Sh NOTES
The mask specified in
.Fa vec
is not allowed to block
.Dv SIGKILL
or
.Dv SIGSTOP .
This is done silently by the system.
.Pp
The
.Dv SV_INTERRUPT
flag is not available in
.Bx 4.2 ,
hence it should not be used if backward compatibility is needed.
.Sh RETURN VALUES
.Rv -std sigvec
.Sh EXAMPLES
On the
.Tn VAX\-11
The handler routine can be declared:
.Bd -literal -offset indent
void handler(sig, code, scp)
int sig, code;
struct sigcontext *scp;
.Ed
.Pp
Here
.Fa sig
is the signal number, into which the hardware faults and traps are
mapped as defined below.
The
.Fa code
argument
is either a constant
as given below or, for compatibility mode faults, the code provided by
the hardware (Compatibility mode faults are distinguished from the
other
.Dv SIGILL
traps by having
.Dv PSL_CM
set in the psl).
The
.Fa scp
argument
is a pointer to the
.Fa sigcontext
structure (defined in
.In signal.h ) ,
used to restore the context from before the signal.
.Sh ERRORS
The
.Fn sigvec
function
will fail and no new signal handler will be installed if one
of the following occurs:
.Bl -tag -width Er
.It Bq Er EFAULT
Either
.Fa vec
or
.Fa ovec
points to memory that is not a valid part of the process
address space.
.It Bq Er EINVAL
The
.Fa sig
argument
is not a valid signal number.
.It Bq Er EINVAL
An attempt is made to ignore or supply a handler for
.Dv SIGKILL
or
.Dv SIGSTOP .
.El
.Sh SEE ALSO
.Xr kill 1 ,
.Xr kill 2 ,
.Xr ptrace 2 ,
.Xr sigaction 2 ,
.Xr sigaltstack 2 ,
.Xr sigblock 2 ,
.Xr sigpause 2 ,
.Xr sigprocmask 2 ,
.Xr sigsetmask 2 ,
.Xr sigsuspend 2 ,
.Xr setjmp 3 ,
.Xr siginterrupt 3 ,
.Xr signal 3 ,
.Xr sigsetops 3 ,
.Xr tty 4
.Sh HISTORY
A
.Fn sigvec
system call first appeared in
.Bx 4.2 .
It was reimplemented as a wrapper around
.Xr sigaction 2
in
.Bx 4.3 Reno .
.Sh BUGS
This manual page is still confusing.