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| | siginfo - signal generation information |
SYNOPSIS
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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:
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int si_signo /* signal number */
int si_errno /* error number */
int si_code /* signal code */
union sigval si_value /* signal value */
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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
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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(3RT), sigsend(2), abort(3C), and raise(3C)) and the siginfo structure contains the following additional information:
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typedef long pid_t si_pid /* sending process ID */
typedef long uid_t si_uid /* sending user ID */
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If the signal was generated by a user process, the following values are defined for si_code:
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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).
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SI_LWP
- The signal was sent by _lwp_kill(2).
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SI_QUEUE
- The signal was sent by sigqueue(3RT).
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SI_TIMER
- The signal was generated by the expiration of a timer created by timer_settime(3RT).
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SI_ASYNCIO
- The signal was generated by the completion of an asynchronous I/O request.
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SI_MESGQ
- The signal was generated by the arrival of a message on an empty message queue. See mq_notify(3RT).
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.
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System Signals
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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 |
| SIGHUP | | |
| SIGTERM | | |
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 |
| 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 |
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_lwp_kill(2), kill(2), setrctl(2), sigaction(2), sigsend(2), waitid(2), abort(3C), aio_read(3RT), mq_notify(3RT), raise(3C), signal(3HEAD), sigqueue(3RT), timer_create(3RT), timer_settime(3RT)
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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.
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