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.Dd February 17, 2021
.Dt SIGINFO 3
.Os
.Sh NAME
.Nm siginfo
.Nd "signal generation information"
.Sh SYNOPSIS
.In signal.h
.Sh DESCRIPTION
A process may request signal information when it is catching a signal.
The information specifies why the system generated that signal.
To request signal information in a signal handler, the user can set
.Dv SA_SIGINFO
in
.Va sa_flags
before
.Xr sigaction 2
is called,
otherwise the user can use
.Xr sigwaitinfo 2
and
.Xr sigtimedwait 2
to get signal information.
In either case, the system returns the information in a structure of type
.Vt siginfo_t ,
which includes the following information:
.Bl -column ".Vt union signal" ".Va si_overrun"
.It Sy Type Ta Sy Member Ta Sy Description
.It Vt int Ta Va si_signo Ta
signal number
.It Vt int Ta Va si_errno Ta
error number
.It Vt int Ta Va si_code Ta
signal code
.It Vt union sigval Ta Va si_value Ta
signal value
.It Vt pid_t Ta Va si_pid Ta
sending process ID
.It Vt uid_t Ta Va si_uid Ta
sending process's real user ID
.It Vt void Ta Va *si_addr Ta
virtual address
.It Vt int Ta Va si_status Ta
exit value or signal
.It Vt long Ta Va si_band Ta
band event for
.Dv SIGPOLL
.It Vt int Ta Va si_trapno Ta
machine trap code
.It Vt int Ta Va si_timerid Ta
.Tn POSIX
timer ID
.It Vt int Ta Va si_overrun Ta
.Tn POSIX
timer overrun count
.It Vt int Ta Va si_mqd Ta
.Tn POSIX
message queue ID
.El
.Pp
The
.Va si_signo
member contains the signal number.
.Pp
The
.Va si_errno
member contains an error number defined in the file
.In errno.h .
.Pp
The
.Va si_code
member contains a code which describes the cause of the signal.
The macros specified in the
.Sy Code
column of the following table are defined
for use as values of
.Va si_code
that are signal-specific or non-signal-specific reasons why the signal was
generated:
.Bl -column ".Dv SIGPOLL" ".Dv CLD_CONTINUED"
.It Sy Signal Ta Sy Code Ta Sy Reason
.It Dv SIGILL Ta Dv ILL_ILLOPC Ta
illegal opcode
.It Ta Dv ILL_ILLOPN Ta
illegal operand
.It Ta Dv ILL_ILLADR Ta
illegal addressing mode
.It Ta Dv ILL_ILLTRP Ta
illegal trap
.It Ta Dv ILL_PRVOPC Ta
illegal privileged opcode
.It Ta Dv ILL_PRVREG Ta
illegal privileged register
.It Ta Dv ILL_COPROC Ta
coprocessor error
.It Ta Dv ILL_BADSTK Ta
internal stack error
.It Dv SIGFPE Ta Dv FPE_INTDIV Ta
integer divide by zero
.It Ta Dv FPE_INTOVF Ta
integer overflow
.It Ta Dv FPE_FLTDIV Ta
floating-point divide by zero
.It Ta Dv FPE_FLTOVF Ta
floating-point overflow
.It Ta Dv FPE_FLTUND Ta
floating-point underflow
.It Ta Dv FPE_FLTRES Ta
floating-point inexact result
.It Ta Dv FPE_FLTINV Ta
invalid floating-point operation
.It Ta Dv FPE_FLTSUB Ta
subscript out of range
.It Dv SIGSEGV Ta Dv SEGV_MAPERR Ta
address not mapped to object
.It Ta Dv SEGV_ACCERR Ta
invalid permissions for mapped object
.It Dv SIGBUS Ta Dv BUS_ADRALN Ta
invalid address alignment
.It Ta Dv BUS_ADRERR Ta
nonexistent physical address
.It Ta Dv BUS_OBJERR Ta
object-specific hardware error
.It Ta Dv BUS_OOMERR Ta
cannot alloc a page to map at fault
.It Dv SIGTRAP Ta Dv TRAP_BRKPT Ta
process breakpoint
.It Ta Dv TRAP_TRACE Ta
process trace trap
.It Ta Dv TRAP_DTRACE Ta
DTrace induced trap
.It Ta Dv TRAP_CAP Ta
capabilities protective trap
.It Dv SIGCHLD Ta Dv CLD_EXITED Ta
child has exited
.It Ta Dv CLD_KILLED Ta
child has terminated abnormally and did not create a core file
.It Ta Dv CLD_DUMPED Ta
child has terminated abnormally and created a core file
.It Ta Dv CLD_TRAPPED Ta
traced child has trapped
.It Ta Dv CLD_STOPPED Ta
child has stopped
.It Ta Dv CLD_CONTINUED Ta
stopped child has continued
.It Dv SIGPOLL Ta Dv POLL_IN Ta
data input available
.It Ta Dv POLL_OUT Ta
output buffers available
.It Ta Dv POLL_MSG Ta
input message available
.It Ta Dv POLL_ERR Ta
I/O error
.It Ta Dv POLL_PRI Ta
high priority input available
.It Ta Dv POLL_HUP Ta
device disconnected
.It Any Ta Dv SI_NOINFO Ta
Only the
.Va si_signo
member is meaningful; the value of all other members is unspecified.
.It Ta Dv SI_USER Ta
signal sent by
.Xr kill 2
.It Ta Dv SI_QUEUE Ta
signal sent by
.Xr sigqueue 2
.It Ta Dv SI_TIMER Ta
signal generated by expiration of a timer set by
.Xr timer_settime 2
.It Ta Dv SI_ASYNCIO Ta
signal generated by completion of an asynchronous I/O request
.It Ta Dv SI_MESGQ Ta
signal generated by arrival of a message on an empty message queue
.It Ta Dv SI_KERNEL Ta
signal generated by miscellaneous parts of the kernel
.It Ta Dv SI_LWP Ta
signal sent by
.Xr pthread_kill 3
.El
.Pp
For synchronous signals,
.Va si_addr
is generally set to the address of the faulting instruction.
However, synchronous signals raised by a faulting memory access such as
.Dv SIGSEGV
and
.Dv SIGBUS
may report the address of the faulting memory access (if available) in
.Va si_addr
instead.
Additionally
.Dv SIGTRAP
raised by a hardware watchpoint exception may report the data address that
triggered the watchpoint in
.Va si_addr .
.Pp
Sychronous signals set
.Va si_trapno
to a machine-dependent trap number.
.Pp
In addition, the following signal-specific information is available:
.Bl -column ".Dv SIGPOLL" ".Dv CLD_CONTINUED"
.It Sy Signal Ta Sy Member Ta Sy Value
.It Dv SIGCHLD Ta Va si_pid Ta
child process ID
.It Ta Va si_status Ta
exit value or signal; if
.Va si_code
is equal to
.Dv CLD_EXITED ,
then it is equal to the exit value of the child process, otherwise,
it is equal to a signal that caused the child process to change state.
.It Ta Va si_uid Ta "real user ID of the process that sent the signal"
.It Dv SIGPOLL Ta Va si_band Ta "band event for"
.Dv POLL_IN , POLL_OUT ,
or
.Dv POLL_MSG
.El
.Pp
Finally, the following code-specific information is available:
.Bl -column ".Dv SI_ASYNCIO" ".Va si_overrun"
.It Sy Code Ta Sy Member Ta Sy Value
.It Dv SI_USER Ta Va si_pid Ta
the process ID that sent the signal
.It Ta Va si_uid Ta
real user ID of the process that sent the signal
.It Dv SI_QUEUE Ta Va si_value Ta
the value passed to
.Xr sigqueue 2
system call
.It Ta Va si_pid Ta
the process ID that sent the signal
.It Ta Va si_uid Ta
real user ID of the process that sent the signal
.It Dv SI_TIMER Ta Va si_value Ta
the value passed to
.Xr timer_create 2
system call
.It Ta Va si_timerid Ta
the timer ID returned by
.Xr timer_create 2
system call
.It Ta Va si_overrun Ta
timer overrun count corresponding to the signal
.It Ta Va si_errno Ta
If timer overrun will be
.Brq Dv DELAYTIMER_MAX ,
an error code defined in
.In errno.h
is set
.It Dv SI_ASYNCIO Ta Va si_value Ta
the value passed to aio system calls
.It Dv SI_MESGQ Ta Va si_value Ta
the value passed to
.Xr mq_notify 2
system call
.It Ta Va si_mqd Ta
the ID of the message queue which generated the signal
.It Dv SI_LWP Ta Va si_pid Ta
the process ID that sent the signal
.It Ta Va si_uid Ta
real user ID of the process that sent the signal
.El
.Sh NOTES
Currently, the kernel never generates the
.Dv SIGPOLL
signal.
.Dv SIGCHLD
signal is queued when a process changed its status or exited.
.Tn POSIX
Realtime Extensions like aio, timer, and message queue also queue
signals.
Signals with code
.Dv SI_USER ,
.Dv SI_KERNEL
or
.Dv SI_LWP
are only queued if there are sufficient resources;
otherwise,
.Dv SI_NOINFO
results.
For some hardware architectures, the exact value of
.Va si_addr
might not be available.
.Sh SEE ALSO
.Xr aio_read 2 ,
.Xr kill 2 ,
.Xr mq_notify 2 ,
.Xr sigaction 2 ,
.Xr sigqueue 2 ,
.Xr sigwaitinfo 2 ,
.Xr timer_create 2 ,
.Xr timer_settime 2 ,
.Xr waitpid 2 ,
.Xr pthread_kill 3
.Sh STANDARDS
The
.Vt siginfo_t
type conforms to
.St -p1003.1-2004 .
.Sh HISTORY
Full support for
.Tn POSIX
signal information first appeared in
.Fx 7.0 .
The codes
.Dv SI_USER
and
.Dv SI_KERNEL
can be generated as of
.Fx 8.1 .
The code
.Dv SI_LWP
can be generated as of
.Fx 9.0 .
.Sh AUTHORS
This manual page was written by
.An David Xu Aq Mt davidxu@FreeBSD.org .