NAME
sigvec - software signal facilities

SYNOPSIS
#include <signal.h>

struct sigvec {
void (*sv_handler)();
int sv_mask;
int sv_flags;
};

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 occurence 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 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(2) or sigsetmask(2) call, or when a
signal is delivered to the process.

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 or’ing in the signal mask associated with the handler to be
invoked.

Sigvec assigns a handler for a specific signal. If vec is non-
zero, it specifies a handler routine and mask to be used when
delivering the specified signal. Further, if the SV_ONSTACK bit is
set in sv_flags, the system will deliver the signal to the process
on a signal stack, specified with sigstack(2). If ovec is non-
zero, the previous handling information for the signal is returned
to the user.

The following is a list of all signals with names as in the include
file <signal.h>:

SIGHUP 1 hangup
SIGINT 2 interrupt
SIGQUIT 3* quit
SIGILL 4* illegal instruction
SIGTRAP 5* trace trap
SIGIOT 6* IOT instruction
SIGEMT 7* EMT instruction
SIGFPE 8* floating point exception
SIGKILL 9 kill (cannot be caught, blocked, or ignored)
SIGBUS 10* bus error
SIGSEGV 11* segmentation violation
SIGSYS 12* bad argument to system call
SIGPIPE 13 write on a pipe with no one to read it
SIGALRM 14 alarm clock
SIGTERM 15 software termination signal
SIGURG 16@ urgent condition present on socket
SIGSTOP 17+ stop (cannot be caught, blocked, or ignored)
SIGTSTP 18+ stop signal generated from keyboard
SIGCONT 19@ continue after stop (cannot be blocked)
SIGCHLD 20@ child status has changed
SIGTTIN 21+ background read attempted from control terminal
SIGTTOU 22+ background write attempted to control terminal
SIGIO 23@ i/o is possible on a descriptor (see fcntl(2))
SIGXCPU 24 cpu time limit exceeded (see setrlimit(2)*)
SIGXFSZ 25 file size limit exceeded (see setrlimit(2)*)
SIGVTALRM 26 virtual time alarm (see setitimer(2))
SIGPROF 27 profiling timer alarm (see setitimer(2))
SIGWINCH 28@ window size change
SIGUSR1 30 user defined signal 1
SIGUSR2 31 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. The
default action for a signal may be reinstated by setting sv_handler
to SIG_DFL; this default is termination (with a core image for
starred signals) 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 sv_handler 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 sv_flags. The affected system calls are read(2) or write(2)
on a slow device (such as a terminal; 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 flags.

Execve(2) 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.

NOTES
The mask specified in vec is not allowed to block SIGKILL, SIGSTOP,
or SIGCONT. This is done silently by the system.

The SV_INTERRUPT flag is not available in 4.2BSD, hence it should
not be used if backward compatibility is needed.

RETURN VALUE
A 0 value indicated that the call succeeded. A -1 return value
indicates an error occurred and errno is set to indicated 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 points to memory that is not a
valid part of the process address space.

[EINVAL] Sig is not a valid signal number.

[EINVAL] An attempt is made to ignore or supply a handler for
SIGKILL or SIGSTOP.

[EINVAL] An attempt is made to ignore SIGCONT (by default
SIGCONT is ignored).

SEE ALSO
kill(1), ptrace(2)*, kill(2), sigblock(2), sigsetmask(2),
sigpause(2), sigstack(2), sigvec(2), setjmp(3), siginterrupt(3),
tty(4)

NOTES
The handler routine can be declared:

void handler(sig, code, scp)
int sig, code;
struct sigcontext *scp;

Here sig is the signal number, into which the hardware faults and
traps are mapped as defined below. Code is a parameter that 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 SIGILL traps by having PSL_CM set in
the psl). Scp is a pointer to the sigcontext structure (defined in
<signal.h>), used to restore the context from before the signal.

The following defines the mapping of hardware traps to signals and
codes. All of these symbols are defined in <signal.h>:

Hardware condition Signal Code

Arithmetic traps:
Integer overflow SIGFPE FPE_INTOVF_TRAP
Integer division by zero SIGFPE FPE_INTDIV_TRAP
Floating overflow trap SIGFPE FPE_FLTOVF_TRAP
Floating/decimal division by zero SIGFPE FPE_FLTDIV_TRAP
Floating underflow trap SIGFPE FPE_FLTUND_TRAP
CHK or CHK2 instruction SIGFPE FPE_CHKINST_TRAP
Branch or set on unordered cond SIGFPE FPE_FLTBSUN_TRAP
Floating Not-a-Number SIGFPE FPE_FLTNAN_TRAP
Length access control SIGSEGV
Protection violation SIGBUS
Trace pending SIGTRAP
Bpt instruction SIGTRAP
Compatibility-mode SIGILL hardware supplied code
Trap #n (1 <= n <= 14) SIGILL ILL_TRAPn_FAULT

BUGS
This manual page is still confusing.

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* Not currently supported under MachTen Personal Unix