siginfo.h, siginfo - signal generation information

#include <siginfo.h>

If a process is catching a signal, it might request information that tells why the system generated that signal. See sigaction(2). If a process is monitoring its children, it might receive information that tells why a child changed state. See waitid(2). In either case, the system returns the information in a structure of type siginfo_t, which includes the following information:

int            si_signo        /* signal number */
int            si_errno        /* error number */
int            si_code         /* signal code */
union sigval   si_value        /* signal value */

si_signo contains the system-generated signal number. For the waitid(2) function, si_signo is always SIGCHLD.

If si_errno is non-zero, it contains an error number associated with this signal, as defined in <errno.h>.

si_code contains a code identifying the cause of the signal.

If the value of the si_code member is SI_NOINFO, only the si_signo member of siginfo_t is meaningful, and the value of all other members is unspecified.

If the value of si_code is less than or equal to 0, then the signal was generated by a user process (see kill(2), _lwp_kill(2), sigqueue(3C), sigsend(2), abort(3C), and raise(3C)) and the siginfo structure contains the following additional information:

pid_t        si_pid      /* sending process ID */
uid_t        si_uid      /* sending user ID */
ctid_t       si_ctid     /* sending contract ID */
zoneid_t     si_zoneid   /* sending zone ID */S

If the signal was generated by a user process, the following values are defined for si_code:


The implementation sets si_code to SI_USER if the signal was sent by kill(2), sigsend(2), raise(3C) or abort(3C).


The signal was sent by _lwp_kill(2).


The signal was sent by sigqueue(3C).


The signal was generated by the expiration of a timer created by timer_settime(3C).


The signal was generated by the completion of an asynchronous I/O request.


The signal was generated by the arrival of a message on an empty message queue. See mq_notify(3C).

si_value contains the application specified value, which is passed to the application's signal-catching function at the time of the signal delivery if si_code is any of SI_QUEUE, SI_TIMER, SI_ASYNCHIO, or SI_MESGQ.

Non-user generated signals can arise for a number of reasons. For all of these cases, si_code contains a positive value reflecting the reason why the system generated the signal:

Signal Code Reason
SIGILL ILL_ILLOPC illegal opcode
ILL_ILLOPN illegal operand
ILL_ILLADR illegal addressing mode
ILL_ILLTRP illegal trap
ILL_PRVOPC privileged opcode
ILL_PRVREG privileged register
ILL_COPROC co-processor error
ILL_BADSTK internal stack error
SIGFPE FPE_INTDIV integer divide by zero
FPE_INTOVF integer overflow
FPE_FLTDIV floating point divide by zero
FPE_FLTOVF floating point overflow
FPE_FLTUND floating point underflow
FPE_FLTRES floating point inexact result
FPE_FLTINV invalid floating point operation
FPE_FLTSUB subscript out of range
SIGSEGV SEGV_MAPERR address not mapped to object
SEGV_ACCERR invalid permissions for mapped object
SIGBUS BUS_ADRALN invalid address alignment
BUS_ADRERR non-existent physical address
BUS_OBJERR object specific hardware error
SIGTRAP TRAP_BRKPT process breakpoint
TRAP_TRACE process trace trap
SIGCHLD CLD_EXITED child has exited
CLD_KILLED child was killed
CLD_DUMPED child terminated abnormally
CLD_TRAPPED traced child has trapped
CLD_STOPPED child has stopped
CLD_CONTINUED stopped child had continued
SIGPOLL POLL_IN data input available
POLL_OUT output buffers available
POLL_MSG input message available
POLL_ERR I/O error
POLL_PRI high priority input available
POLL_HUP device disconnected

Signals can also be generated from the resource control subsystem. Where these signals do not already possess kernel-level siginfo codes, the siginfo si_code will be filled with SI_RCTL to indicate a kernel-generated signal from an established resource control value.

Signal Code Reason
SIGXRES SI_RCTL resource-control generated signal

The uncatchable signals SIGSTOP and SIGKILL have undefined siginfo codes.

Signals sent with a siginfo code of SI_RCTL contain code-dependent information for kernel-generated signals:

Code Field Value
SI_RCTL hr_time si_entity process-model entity of control

In addition, the following signal-dependent information is available for kernel-generated signals:

Signal Field Value
SIGILL caddr_t si_addr address of faulting instruction
SIGSEGV caddr_t si_addr address of faulting memory reference
SIGCHLD pid_t si_pid child process ID
int si_status exit value or signal
SIGPOLL long si_band band event for POLL_IN, POLL_OUT, or POLL_MSG

_lwp_kill(2), kill(2), setrctl(2), sigaction(2), sigsend(2), waitid(2), abort(3C), aio_read(3C), mq_notify(3C), raise(3C), sigqueue(3C), timer_create(3C), timer_settime(3C), signal.h(3HEAD)

For SIGCHLD signals, if si_code is equal to CLD_EXITED, then si_status is equal to the exit value of the process; otherwise, it is equal to the signal that caused the process to change state. For some implementations, the exact value of si_addr might not be available; in that case, si_addr is guaranteed to be on the same page as the faulting instruction or memory reference.

February 5, 2008 OmniOS