sigvec(3) (BSD Compatibility Package) sigvec(3)
NAME
sigvec - software signal facilities
SYNOPSIS
cc [ flag... ] file ... -lucb
#include <signal.h>
int sigvec(sig, vec, ovec)
int sig;
struct sigvec *vec, *ovec;
DESCRIPTION
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 handler to which a signal is delivered, or specify that
a signal is to be blocked or 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 signal stack.
All signals have the same priority. Signal routines execute with the
signal that caused their invocation to be blocked, but other signals
may yet occur. A global 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 sigblock(3) or sigsetmask(3) call, or when a signal
is delivered to the process.
A process may also specify a set of flags for a signal that affect
the delivery of that signal.
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 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.
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
sigblock or sigsetmask call is made). This mask is formed by taking
the current signal mask, adding the signal to be delivered, and ORing
in the signal mask associated with the handler to be invoked.
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sigvec(3) (BSD Compatibility Package) sigvec(3)
The action to be taken when the signal is delivered is specified by a
sigvec structure, which includes the following members:
void (*sv_handler)(); /* signal handler */
int sv_mask; /* signal mask to apply */
int sv_flags; /* see signal options */
#define SV_ONSTACK /* take signal on signal stack */
#define SV_INTERRUPT /* do not restart system on signal return */
#define SV_RESETHAND /* reset handler to SIG_DFL when signal taken */
If the SV_ONSTACK bit is set in the flags for that signal, the system
will deliver the signal to the process on the signal stack specified
with sigstack(2), rather than delivering the signal on the current
stack.
If vec is not a NULL pointer, sigvec assigns the handler specified by
sv_handler, the mask specified by sv_mask, and the flags specified by
sv_flags to the specified signal. If vec is a NULL pointer, sigvec
does not change the handler, mask, or flags for the specified signal.
The mask specified in vec is not allowed to block SIGKILL, SIGSTOP,
or SIGCONT. The system enforces this restriction silently.
If ovec is not a NULL pointer, the handler, mask, and flags in effect
for the signal before the call to sigvec are returned to the user. A
call to sigvec with vec a NULL pointer and ovec not a NULL pointer
can be used to determine the handling information currently in effect
for a signal without changing that information.
The following is a list of all signals with names as in the include
file /usr/include/signal.h:
SIGHUP hangup
SIGINT interrupt
SIGQUIT * quit
SIGILL * illegal instruction
SIGTRAP * trace trap
SIGABRT * abort (generated by abort(3) routine)
SIGEMT * emulator trap
SIGFPE * arithmetic exception
SIGKILL kill (cannot be caught, blocked, or ignored)
SIGBUS * bus error
SIGSEGV * segmentation violation
SIGSYS * bad argument to system call
SIGPIPE write on a pipe or other socket with no one to read it
SIGALRM alarm clock
SIGTERM software termination signal
SIGURG @ urgent condition present on socket
SIGSTOP † stop (cannot be caught, blocked, or ignored)
SIGTSTP † stop signal generated from keyboard
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sigvec(3) (BSD Compatibility Package) sigvec(3)
SIGCONT @ continue after stop (cannot be blocked)
SIGCHLD @ child status has changed
SIGTTIN † background read attempted from control terminal
SIGTTOU † background write attempted to control terminal
SIGIO @ I/O is possible on a descriptor [see fcntl(2)]
SIGXCPU cpu time limit exceeded [see setrlimit(2)]
SIGXFSZ file size limit exceeded [see setrlimit(2)]
SIGVTALRM virtual time alarm [see setitimer(2)]
SIGPROF profiling timer alarm [see setitimer(2)]
SIGWINCH @ window changed [see termio(4)]
SIGUSR1 user-defined signal 1
SIGUSR2 user-defined signal 2
The starred signals in the list above cause a core image if not
caught or ignored.
Once a signal handler is installed, it remains installed until
another sigvec call is made, or an execve(2) is performed, unless the
SV_RESETHAND bit is set in the flags for that signal. In that case,
the value of the handler for the caught signal will be set to SIG_DFL
before entering the signal-catching function, unless the signal is
SIGILL, SIGPWR, or SIGTRAP. Also, if this bit is set, the bit for
that signal in the signal mask will not be set; unless the signal
mask associated with that signal blocks that signal, further
occurrences of that signal will not be blocked. The SV_RESETHAND
flag is not available in 4.2BSD, hence it should not be used if
backward compatibility is needed.
The default action for a signal may be reinstated by setting the
signal's handler to SIG_DFL; this default is termination except for
signals marked with @ or †. Signals marked with @ are discarded if
the action is SIG_DFL; signals marked with † cause the process to
stop. If the process is terminated, a ``core image'' will be made in
the current working directory of the receiving process if the signal
is one for which an asterisk appears in the above list [see core(4)].
If the handler for that signal is SIG_IGN, the signal is subsequently
ignored, and pending instances of the signal are discarded.
If a caught signal occurs during certain system calls, the call is
normally restarted. The call can be forced to terminate prematurely
with an EINTR error return by setting the SV_INTERRUPT bit in the
flags for that signal. The SV_INTERRUPT flag is not available in
4.2BSD, hence it should not be used if backward compatibility is
needed. The affected system calls are read(2) or write(2) on a slow
device (such as a terminal or pipe or other socket, but not a file)
and during a wait(2).
After a fork(2) or vfork(2) the child inherits all signals, the
signal mask, the signal stack, and the restart/interrupt and reset-
signal-handler flags.
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sigvec(3) (BSD Compatibility Package) sigvec(3)
The execve(2) call resets all caught signals to default action 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.
The accuracy of addr is machine dependent. For example, certain
machines may supply an address that is on the same page as the
address that caused the fault. If an appropriate addr cannot be
computed it will be set to SIG_NOADDR.
RETURN VALUE
A 0 value indicates that the call succeeded. A -1 return value
indicates that an error occurred and errno is set to indicate the
reason.
ERRORS
sigvec will fail and no new signal handler will be installed if one
of the following occurs:
EFAULT Either vec or ovec is not a NULL pointer and points to
memory that is not a valid part of the process address
space.
EINVAL Sig is not a valid signal number, or, SIGKILL, or
SIGSTOP.
SEE ALSO
signal(3), sigpause(3), sigsetmask(3), wait(3).
exec(2), fcntl(2), fork(2), getrlimit(2), getitimer(2), ioctl(2),
kill(2), ptrace(2), read(2), sigblock(2), signal(2), sigstack(2),
umask(2), wait(2), write(2), setjmp(3) in the Programmer's Reference
Manual.
streamio(7), termio(7) in the System Administrator's Reference
Manual.
NOTES
SIGPOLL is a synonym for SIGIO. A SIGIO will be issued when a file
descriptor corresponding to a STREAMS [see intro(2)] file has a
``selectable'' event pending. Unless that descriptor has been put
into asynchronous mode [see fcntl(2)], a process must specifically
request that this signal be sent using the I_SETSIG ioctl call [see
streamio(4)]. Otherwise, the process will never receive SIGPOLL.
The handler routine can be declared:
void handler(sig, code, scp, addr)
int sig, code;
struct sigcontext *scp;
char *addr;
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sigvec(3) (BSD Compatibility Package) sigvec(3)
Here sig is the signal number; code is a parameter of certain signals
that provides additional detail; scp is a pointer to the sigcontext
structure (defined in signal.h), used to restore the context from
before the signal; and addr is additional address information.
The signals SIGKILL, SIGSTOP, and SIGCONT cannot be ignored.
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