SIGVEC(2) —

NAME

sigvec − software signal facilities

SYNOPSIS

#include <signal.h>

struct sigvec {
int(∗sv_handler)();
intsv_mask;
intsv_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 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 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, 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 defined in the include file <signal.h>:

SIGHUP1hangup
SIGINT2interrupt
SIGQUIT3∗quit
SIGILL4∗illegal instruction
SIGTRAP5∗trace trap
SIGIOT6∗IOT instruction
SIGEMT7∗EMT instruction
SIGFPE8∗floating point exception
SIGKILL9kill (cannot be caught, blocked, or ignored)
SIGBUS10∗bus error
SIGSEGV11∗segmentation violation
SIGSYS12∗bad argument to system call
SIGPIPE13write on a pipe with no one to read it
SIGALRM14alarm clock
SIGTERM15software termination signal
SIGURG16•urgent condition present on socket
SIGSTOP17†stop (cannot be caught, blocked, or ignored)
SIGTSTP18†stop signal generated from keyboard
SIGCONT19•continue after stop (cannot be blocked)
SIGCHLD20•child status has changed
SIGTTIN21†background read attempted from control terminal
SIGTTOU22†background write attempted to control terminal
SIGIO23•I/O is possible on a descriptor (see fcntl(2))
SIGXCPU24cpu time limit exceeded (see setrlimit(2))
SIGXFSZ25file size limit exceeded (see setrlimit(2))
SIGVTALRM26virtual time alarm (see setitimer(2))
SIGPROF27profiling timer alarm (see setitimer(2))
SIGWINCH28•window size change
SIGUSR130user defined signal 1
SIGUSR231user defined signal 2

The starred (∗) signals in the list above cause a core dump 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 zero value means that the call succeeded. A −1 return value means an error occurred and errno is set to show the reason.

ERRORS

Sigvec fails with no new signal handler installed when 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).

NOTES FOR THE IBM RT PC

The handler routine can be declared:

    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 further defines the signal on SIGILL or SIGFPE; it is zero in all other cases. For SIGILL, code is the value of the hardware machine/program check register (mcs_pcs) at the time of the trap; the code for SIGFPE is as given below. Scp is a pointer to the sigcontext structure (defined in <signal.h>), used to restore the context from before the signal. It contains all the context information needed to resume execution at the point that the signal was delivered.

This context includes the general registers (in sc_regs[0] through sc_regs[15]), the Instruction Address Register (IAR) in sc_iar, the Interrupt Status and Condition Code (ICSCS) in sc_icscs, the Multiply Quotient register (MQ) (in sc_regs[17]), and if the SC_EXCEPTION bit is set in sc_flags, the exception packets that caused the program check that generated in this signal are stored in sc_regs.

The definitions in the include file <machine/reg.h>), may be used to examine the exception packets. The value in sc_regs[ECR_COUNT] is the number of exception packets (zero, one or two), which are in sc_regs[EX1_CTL...EX1_RSV] and sc_regs[EX2_CTL...EX2_RSV]. Upon return from the signal handler these packets will be re-issued unless the SC_EXCEPTION bit in sc_flags has been reset.

If the SC_ONSTACK bit in sc_flags is set the program was executing on the signal stack.

The SIGFPE signal (other than for integer divide) will cause the SC_FLOATSAVED bit to be set in sc_flags and floating point information to be stored in the region pointed to by sc_floatsave, the structure of this region is discussed in “Floating Point Arithmetic Linkage” in “IBM/4.3 Linkage Convention” in Volume II, Supplementary Documents.

The following defines the mapping of hardware traps to signals and codes. The SIGxxx symbols are defined in <signal.h>; SIGFPE codes are defined in <machine/fp.h>:

     Hardware conditionSignalCode
Program TrapSIGTRAP
Privileged Instruction ExceptionSIGILLmcs_pcs
Illegal Operation CodeSIGILLmcs_pcs
Instruction or Data Address Exception:
   Page Fault (unresolvable)SIGSEGV
   ProtectionSIGSEGV
   OtherSIGBUS
Arithmetic traps (simulated):
   Floating operation invalidSIGFPEFP_INV_OPER
   Floating division by zeroSIGFPEFP_DIVIDE
   Floating underflowSIGFPEFP_UNDERFLOW
   Floating overflowSIGFPEFP_OVERFLOW
   Floating inexact resultSIGFPEFP_INEXACT
   Integer division by zeroSIGFPEFP_INT_DIVIDE

BUGS

This manual page is confusing.

PRPQs 5799-WZQ/5799-PFF: IBM/4.3 — July 1987

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