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Manual page for siginfo(5)

siginfo - signal generation information

SYNOPSIS

#include <siginfo.h>

DESCRIPTION

If a process is catching a signal, it may request information that tells why the system generated that signal (see sigaction.2 If a process is monitoring its children, it may 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.

User Signals

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.3r sigsend.2 abort.3c and raise.3c and the siginfo structure contains the following additional information:

typedef long pid_t	si_pid	/* sending process ID */
typedef long uid_t	si_uid	/* sending user ID */

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

SI_USER: the implementation sets si_code to SI_USER if the signal was sent by kill.2 sigsend.2 raise.3c or abort.3c
SI_LWP: the signal was sent by _lwp_kill.2
SI_QUEUE: the signal was sent by sigqueue.3r
SI_TIMER: the signal was generated by the expiration of a timer created by timer_settime.3r
SI_ASYNCIO: the signal was generated by the completion of an asynchronous I/O request.
SI_MESGQ: the signal was generated by the arrival of a message on an empty message queue. (see mq_notify.3r

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.

System Signals

Otherwise, 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

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
SIGFPE
-----------------------------------------------------------------
SIGSEGV   caddr_t si_addr   address of faulting memory reference
SIGBUS
-----------------------------------------------------------------
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

NOTES

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 may not be available; in that case, si_addr is guaranteed to be on the same page as the faulting instruction or memory reference.