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 */

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 si_code is less than or equal to 0, then the signal was generated by a user process [see kill(2) and sigsend(2)] and the siginfo structure contains the following additional information:

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

Otherwise, si_code contains a signal-specific reason why the signal was generated, as follows:

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

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
SIGFPE caddr_t si_addr address of faulting instruction

SIGSEGV
SIGBUS caddr_t si_addr address of faulting memory reference

SIGCHLD pid_t si_pid
int si_status child process ID
exit value or signal

SIGPOLL long si_band band event for POLL_IN, POLL_OUT, or POLL_MSG

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

References

sigaction(2), signal(5), waitid(2)

Notices

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.