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Man Pages
SIGINFO(3) FreeBSD Library Functions Manual SIGINFO(3)

siginfo
signal generation information

#include <signal.h>

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 SA_SIGINFO in sa_flags before sigaction(2) is called, otherwise the user can use sigwaitinfo(2) and sigtimedwait(2) to get signal information. In either case, the system returns the information in a structure of type siginfo_t, which includes the following information:
Type Member Description
int si_signo signal number
int si_errno error number
int si_code signal code
union sigval si_value signal value
pid_t si_pid sending process ID
uid_t si_uid sending process's real user ID
void *si_addr address of faulting instruction
int si_status exit value or signal
long si_band band event for SIGPOLL
int si_trapno machine trap code
int si_timerid POSIX timer ID
int si_overrun POSIX timer overrun count
int si_mqd POSIX message queue ID
The si_signo member contains the signal number.
The si_errno member contains an error number defined in the file <errno.h>.
The si_code member contains a code which describes the cause of the signal. The macros specified in the Code column of the following table are defined for use as values of si_code that are signal-specific or non-signal-specific reasons why the signal was generated:
Signal Code Reason
illegal opcode
illegal operand
illegal addressing mode
illegal trap
illegal privileged opcode
illegal privileged register
coprocessor error
internal stack error
integer divide by zero
integer overflow
floating-point divide by zero
floating-point overflow
floating-point underflow
floating-point inexact result
invalid floating-point operation
subscript out of range
address not mapped to object
invalid permissions for mapped object
invalid address alignment
nonexistent physical address
object-specific hardware error
process breakpoint
process trace trap
DTrace induced trap
capabilities protective trap
child has exited
child has terminated abnormally and did not create a core file
child has terminated abnormally and created a core file
traced child has trapped
child has stopped
stopped child has continued
data input available
output buffers available
input message available
I/O error
high priority input available
device disconnected
Any Only the si_signo member is meaningful; the value of all other members is unspecified.
signal sent by kill(2)
signal sent by sigqueue(2)
signal generated by expiration of a timer set by timer_settime(2)
signal generated by completion of an asynchronous I/O request
signal generated by arrival of a message on an empty message queue
signal generated by miscellaneous parts of the kernel
signal sent by pthread_kill(3)
In addition, the following signal-specific information is available:
Signal Member Value
si_addr address of faulting instruction
si_trapno machine dependent of trap code
si_addr address of faulting instruction
si_trapno machine dependent of trap code
si_addr address of faulting memory reference
si_trapno machine dependent of trap code
si_addr address of faulting instruction
si_trapno machine dependent of trap code
si_pid child process ID
si_status exit value or signal; if si_code is equal to 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.
si_uid real user ID of the process that sent the signal
si_band band event for POLL_IN, POLL_OUT, or POLL_MSG
Finally, the following code-specific information is available:
Code Member Value
si_pid the process ID that sent the signal
si_uid real user ID of the process that sent the signal
si_value the value passed to sigqueue(2) system call
si_pid the process ID that sent the signal
si_uid real user ID of the process that sent the signal
si_value the value passed to timer_create(2) system call
si_timerid the timer ID returned by timer_create(2) system call
si_overrun timer overrun count corresponding to the signal
si_errno If timer overrun will be {DELAYTIMER_MAX}, an error code defined in <errno.h> is set
si_value the value passed to aio system calls
si_value the value passed to mq_notify(2) system call
si_mqd the ID of the message queue which generated the signal
si_pid the process ID that sent the signal
si_uid real user ID of the process that sent the signal

Currently, the kernel never generates the SIGPOLL signal. SIGCHLD signal is queued when a process changed its status or exited. POSIX Realtime Extensions like aio, timer, and message queue also queue signals. Signals with code SI_USER, SI_KERNEL or SI_LWP are only queued if there are sufficient resources; otherwise, SI_NOINFO results. For some hardware architectures, the exact value of si_addr might not be available.

aio_read(2), kill(2), mq_notify(2), sigaction(2), sigqueue(2), sigwaitinfo(2), timer_create(2), timer_settime(2), waitpid(2), pthread_kill(3)

The siginfo_t type conforms to IEEE Std 1003.1-2004 (“POSIX.1”).

Full support for POSIX signal information first appeared in FreeBSD 7.0. The codes SI_USER and SI_KERNEL can be generated as of FreeBSD 8.1. The code SI_LWP can be generated as of FreeBSD 9.0.

This manual page was written by David Xu <davidxu@FreeBSD.org>.
April 24, 2018 FreeBSD 12.0-RELEASE

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