signal.9

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.Dd July 14, 2023
.Dt SIGNAL 9
.Os
.Sh NAME
.Nm signal ,
.Nm SIGADDSET ,
.Nm SIGDELSET ,
.Nm SETEMPTYSET ,
.Nm SIGFILLSET ,
.Nm SIGISMEMBER ,
.Nm SIGISEMPTY ,
.Nm SIGNOTEMPTY ,
.Nm SIGSETEQ ,
.Nm SIGSETNEQ ,
.Nm SIGSETOR ,
.Nm SIGSETAND ,
.Nm SIGSETNAND ,
.Nm SIGSETCANTMASK ,
.Nm SIG_STOPSIGMASK ,
.Nm SIG_CONTSIGMASK ,
.Nm SIGPENDING ,
.Nm cursig ,
.Nm execsigs ,
.Nm issignal ,
.Nm killproc ,
.Nm pgsigio ,
.Nm postsig ,
.Nm sigexit ,
.Nm siginit ,
.Nm signotify ,
.Nm trapsignal
.Nd "kernel signal functions"
.Sh SYNOPSIS
.In sys/param.h
.In sys/proc.h
.In sys/signalvar.h
.Ft void
.Fn SIGADDSET "sigset_t set" "int signo"
.Ft void
.Fn SIGDELSET "sigset_t set" "int signo"
.Ft void
.Fn SIGEMPTYSET "sigset_t set"
.Ft void
.Fn SIGFILLSET "sigset_t set"
.Ft int
.Fn SIGISMEMBER "sigset_t set" "int signo"
.Ft int
.Fn SIGISEMPTY "sigset_t set"
.Ft int
.Fn SIGNOTEMPTY "sigset_t set"
.Ft int
.Fn SIGSETEQ "sigset_t set1" "sigset_t set2"
.Ft int
.Fn SIGSETNEQ "sigset_t set1" "sigset_t set2"
.Ft void
.Fn SIGSETOR "sigset_t set1" "sigset_t set2"
.Ft void
.Fn SIGSETAND "sigset_t set1" "sigset_t set2"
.Ft void
.Fn SIGSETNAND "sigset_t set1" "sigset_t set2"
.Ft void
.Fn SIG_CANTMASK "sigset_t set"
.Ft void
.Fn SIG_STOPSIGMASK "sigset_t set"
.Ft void
.Fn SIG_CONTSIGMASK "sigset_t set"
.Ft int
.Fn SIGPENDING "struct proc *p"
.Ft int
.Fn cursig "struct thread *td"
.Ft void
.Fn execsigs "struct proc *p"
.Ft int
.Fn issignal "struct thread *td"
.Ft void
.Fn killproc "struct proc *p" "char *why"
.Ft void
.Fn pgsigio "struct sigio **sigiop" "int sig" "int checkctty"
.Ft void
.Fn postsig "int sig"
.Ft void
.Fn sigexit "struct thread *td" "int signum"
.Ft void
.Fn siginit "struct proc *p"
.Ft void
.Fn signotify "struct thread *td"
.Ft void
.Fn trapsignal "struct thread *td" "int sig" "u_long code"
.Sh DESCRIPTION
The
.Fn SIGADDSET
macro adds
.Fa signo
to
.Fa set .
No effort is made to ensure that
.Fa signo
is a valid signal number.
.Pp
The
.Fn SIGDELSET
macro removes
.Fa signo
from
.Fa set .
No effort is made to ensure that
.Fa signo
is a valid signal number.
.Pp
The
.Fn SIGEMPTYSET
macro clears all signals in
.Fa set .
.Pp
The
.Fn SIGFILLSET
macro sets all signals in
.Fa set .
.Pp
The
.Fn SIGISMEMBER
macro determines if
.Fa signo
is set in
.Fa set .
.Pp
The
.Fn SIGISEMPTY
macro determines if
.Fa set
does not have any signals set.
.Pp
The
.Fn SIGNOTEMPTY
macro determines if
.Fa set
has any signals set.
.Pp
The
.Fn SIGSETEQ
macro determines if two signal sets are equal; that is, the same signals
are set in both.
.Pp
The
.Fn SIGSETNEQ
macro determines if two signal sets differ; that is, if any signal set in
one is not set in the other.
.Pp
The
.Fn SIGSETOR
macro ORs the signals set in
.Fa set2
into
.Fa set1 .
.Pp
The
.Fn SIGSETAND
macro ANDs the signals set in
.Fa set2
into
.Fa set1 .
.Pp
The
.Fn SIGSETNAND
macro NANDs the signals set in
.Fa set2
into
.Fa set1 .
.Pp
The
.Fn SIG_CANTMASK
macro clears the
.Dv SIGKILL
and
.Dv SIGSTOP
signals from
.Fa set .
These two signals cannot be blocked or caught and
.Fn SIG_CANTMASK
is used in code where signals are manipulated to ensure this policy
is enforced.
.Pp
The
.Fn SIG_STOPSIGMASK
macro clears the
.Dv SIGSTOP ,
.Dv SIGTSTP ,
.Dv SIGTTIN ,
and
.Dv SIGTTOU
signals from
.Fa set .
.Fn SIG_STOPSIGMASK
is used to clear stop signals when a process is waiting for a child to
exit or exec, and when a process is continuing after having been
suspended.
.Pp
The
.Fn SIG_CONTSIGMASK
macro clears the
.Dv SIGCONT
signal from
.Fa set .
.Fn SIG_CONTSIGMASK
is called when a process is stopped.
.Pp
The
.Fn SIGPENDING
macro determines if the given process has any pending signals that are
not masked.
If the process has a pending signal and the process is currently being
traced,
.Fn SIGPENDING
will return true even if the signal is masked.
.Pp
The
.Fn cursig
function returns the signal number that should be delivered to process
.Fa td->td_proc .
If there are no signals pending, zero is returned.
.Pp
The
.Fn execsigs
function resets the signal set and signal stack of a process in preparation
for an
.Xr execve 2 .
The process lock for
.Fa p
must be held before
.Fn execsigs
is called.
.Pp
The
.Fn issignal
function determines if there are any pending signals for process
.Fa td->td_proc
that should be caught, or cause this process to terminate or interrupt its
current system call.
If process
.Fa td->td_proc
is currently being traced, ignored signals will be handled and the process
is always stopped.
Stop signals are handled and cleared right away by
.Fn issignal
unless the process is a member of an orphaned process group and the stop
signal originated from a TTY.
The process spin lock for
.Fa td->td_proc
may be acquired and released.
The
.Vt sigacts
structure
.Fa td->td_proc->p_sigacts
must be locked before calling
.Fn issignal
and may be released and reacquired during the call.
The process lock for
.Fa td->td_proc
must be acquired before calling
.Fn issignal
and may be released and reacquired during the call.
Default signal actions are not taken for system processes and init.
.Pp
The
.Fn killproc
function delivers
.Dv SIGKILL
to
.Fa p .
.Fa why
is logged as the reason
.Em why
the process was killed.
.Pp
The
.Fn pgsigio
function sends the signal
.Fa sig
to the process or process group
.Fa sigiop->sio_pgid .
If
.Fa checkctty
is non-zero, the signal is only delivered to processes in the process group
that have a controlling terminal.
If
.Fa sigiop->sio_pgid
is for a process (> 0), the lock for
.Fa sigiop->sio_proc
is acquired and released.
If
.Fa sigiop->sio_pgid
is for a process group (< 0), the process group lock for
.Fa sigiop->sio_pgrp
is acquired and released.
The lock
.Va sigio_lock
is acquired and released.
.Pp
The
.Fn postsig
function handles the actual delivery of the signal
.Fa sig .
.Fn postsig
is called from
.Fn ast
after the kernel has been notified that a signal should be delivered
(via a call to
.Fn signotify ,
which causes the flag
.Dv PS_NEEDSIGCHK
to be set).
The process lock for process that owns
.Va curthread
must be held before
.Fn postsig
is called, and the current process cannot be 0.
The lock for the
.Va p_sigacts
field of the current process must be held before
.Fn postsig
is called, and may be released and reacquired.
.Pp
The
.Fn sigexit
function causes the process that owns
.Fa td
to exit with a return value of signal number
.Fa sig .
If required, the process will dump core.
The process lock for the process that owns
.Fa td
must be held before
.Fn sigexit
is called.
.Pp
The
.Fn siginit
function is called during system initialization to cause every signal with
a default property of
.Dv SA_IGNORE
(except
.Dv SIGCONT )
to be ignored by
.Fa p .
The process lock for
.Fa p
is acquired and released, as is the lock for sigacts structure
.Fa p->p_sigacts .
The only process that
.Fn siginit
is ever called for
is
.Va proc0 .
.Pp
The
.Fn signotify
function flags that there are unmasked signals pending that
.Fn ast
should handle.
The process lock for process
.Fa td->td_proc
must be held before
.Fn signotify
is called, and the thread lock is acquired and released.
.Pp
The
.Fn trapsignal
function sends a signal that is the result of a trap to process
.Fa td->td_proc .
If the process is not being traced and the signal can be delivered
immediately,
.Fn trapsignal
will deliver it directly; otherwise,
.Fn trapsignal
will call
.Xr psignal 9
to cause the signal to be delivered.
The process lock for
.Fa td->td_proc
is acquired and released.
The lock for the
.Va p_sigacts
field of
.Fa td->td_proc
is acquired and released.
.Sh RETURN VALUES
The
.Fn SIGISMEMBER ,
.Fn SIGISEMPTY ,
.Fn SIGNOTEMPTY ,
.Fn SIGSETEQ ,
.Fn SIGSETNEQ ,
and
.Fn SIGPENDING
macros all return non-zero (true) if the condition they are checking
is found to be true; otherwise, zero (false) is returned.
.Pp
The
.Fn cursig
function returns either a valid signal number or zero.
.Pp
.Fn issignal
returns either a valid signal number or zero.
.Sh SEE ALSO
.Xr pgsignal 9 ,
.Xr psignal 9
.Sh AUTHORS
This manual page was written by
.An Chad David Aq Mt davidc@FreeBSD.org .