SIGINFO(2)

💖 SIGINFO(2) 💖

okay bestie, this is the System Calls Manual page for siginfo — literally signal information. no cap, it’s the struct that spills the tea about a signal that got delivered to your process 🫶

🌸 NAME 🌸

siginfo — signal information

✨ SYNOPSIS ✨

#include <signal.h>

💅 DESCRIPTION 💅

<hotpink>siginfo</hotpink> is a structure type, and it contains info about a signal delivered to a process. iconic little data container, honestly 💖

<purple>siginfo</purple> includes these members:

int si_signo;
int si_errno;
int si_code;

• si_signo — contains the signal number generated by the system ⭐
• si_errno — if it’s non-zero, then it contains a system specific error number associated with this signal. that number is defined in errno(2).
• si_code — the main-character field that tells you where the signal came from 👑

if si_code is less than or equal to zero, the signal was generated by a user process or a user requested service. it’s giving “user-side origin story” ✨

🫶 SI_USER

the signal was generated via kill(2). the siginfo structure contains these additional members:

pid_t si_pid;
uid_t si_uid;

the si_pid field contains the pid of the sending process, and the si_uid field contains the user id of the sending process 🎀

💌 SI_QUEUE

the signal was generated via sigqueue(2). the siginfo structure contains these additional members:

pid_t si_pid;
uid_t si_uid;
sigval_t si_value;

the si_pid field contains the pid of the sending process, and the si_uid field contains the user id of the sending process. finally, the si_value field contains the value sent via sigqueue(2) 💅

⏰ SI_TIMER

the signal was generated because a timer set by timer_settime(2) has expired. the siginfo structure contains this additional member:

sigval_t si_value;

the si_value field contains the value set via timer_create(2) ⏱️

🦋 SI_ASYNCIO

the signal was generated by completion of an asynchronous I/O operation. the siginfo structure contains these additional members:

int si_fd;
long si_band;

the si_fd argument contains the file descriptor number on which the operation was completed, and the si_band field contains the side and priority of the operation.

if the operation was a normal read, si_band will contain POLLIN | POLLRDNORM; on an out-of-band read it will contain POLLPRI | POLLRDBAND; on a normal write it will contain POLLOUT | POLLWRNORM; on an out-of-band write it will contain POLLPRI | POLLWRBAND. slay, extremely specific 💀✨

📬 SI_MESGQ

the signal was generated because of the arrival of a message on an empty message queue. see mq_notify(3).

🌈 SI_LWP

the signal was generated via _lwp_kill(2). the siginfo structure contains these additional members:

pid_t si_pid;
uid_t si_uid;

the si_pid field contains the pid of the sending process, and the si_uid field contains the user id of the sending process 🫶

💀 SI_NOINFO

the signal was generated without specific info available. mysterious. elusive. no notes.

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if si_code is positive, then it contains a signal specific reason why the signal was generated 👑

🌟 SIGILL

• ILL_BADSTK — Internal stack error
• ILL_COPROC — Coprocessor error
• ILL_ILLADR — Illegal addressing mode
• ILL_ILLOPC — Illegal opcode
• ILL_ILLOPN — Illegal operand
• ILL_ILLTRP — Illegal trap
• ILL_PRVOPC — Privileged opcode
• ILL_PRVREG — Privileged register

🧮 SIGFPE

• FPE_FLTDIV — Floating-point divide by zero
• FPE_FLTINV — Invalid floating-point operation
• FPE_FLTOVF — Floating-point overflow
• FPE_FLTRES — Floating-point inexact result
• FPE_FLTUND — Floating-point underflow
• FPE_FLTSUB — Subscript out of range
• FPE_INTDIV — Integer divide by zero
• FPE_INTOVF — Integer overflow

🧨 SIGSEGV

• SEGV_ACCERR — Invalid permissions for mapped object
• SEGV_MAPERR — Address not mapped to object

🚌 SIGBUS

• BUS_ADRALN — Invalid address alignment
• BUS_ADRERR — Nonexistent physical address
• BUS_OBJERR — Object-specific hardware error

🪤 SIGTRAP

• TRAP_BRKPT — Process breakpoint
• TRAP_CHLD — Process child trap
• TRAP_DBREG — Process hardware debug register trap
• TRAP_EXEC — Process exec trap
• TRAP_LWP — Process LWP trap
• TRAP_SCE — Process syscall entry trap
• TRAP_SCX — Process syscall exit trap
• TRAP_TRACE — Process trace trap

👶 SIGCHLD

• CLD_CONTINUED — Stopped child has continued
• CLD_DUMPED — Child has terminated abnormally and created a core file
• CLD_EXITED — Child has exited
• CLD_KILLED — Child has terminated abnormally but did not create a core file
• CLD_STOPPED — Child has stopped
• CLD_TRAPPED — Traced child has trapped

📡 SIGIO

• POLL_ERR — I/O error
• POLL_HUP — Device disconnected
• POLL_IN — Data input available
• POLL_MSG — Input message available
• POLL_OUT — Output buffers available
• POLL_PRI — High priority input available

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for SIGILL, SIGFPE, SIGBUS and SIGSEGV the siginfo structure contains these additional members:

void *si_addr;
int si_trap;

si_addr contains the address of the faulting instruction or data, and si_trap contains a hardware specific reason 🔥

for SIGTRAP and TRAP_BRKPT, TRAP_TRACE or TRAP_DBREG the siginfo structure contains these additional members:

void *si_addr;
int si_trap;

si_addr contains the address of the faulting data, and si_trap contains a hardware specific reason 🎀

for SIGTRAP and TRAP_SCE or TRAP_SCX the siginfo structure contains these additional members:

int si_sysnum;
int si_retval[2];
int si_error;
uint64_t si_args[8];

si_sysnum contains the syscall number, si_retval contains the syscall return value (meaningful for TRAP_SCX only), si_error contains the syscall error value (meaningful for TRAP_SCX only), and si_args[8] contains the syscall arguments 🧚

for SIGIO the siginfo structure contains these additional members:

int si_fd;
long si_band;

the si_fd argument contains the file descriptor number on which the operation was completed, and the si_band field contains the side and priority of the operation as described above 📡

finally, for SIGCHLD the siginfo structure contains these additional members:

pid_t si_pid;
uid_t si_uid;
int si_status;
clock_t si_utime;
clock_t si_stime;

the si_pid field contains the pid of the process who’s status changed, the si_uid field contains the user id of that process, and the si_status field contains either the exit code of the process (for CLD_EXITED), or the signal number received by the process. waitid(2), waitpid(2), and the si_utime and si_stime fields contain the user and system process accounting time 👑

🦋 STANDARDS 🦋

the <cyan>siginfo</cyan> type conforms to X/Open System Interfaces and Headers Issue 5 (“XSH5”).

signals specifying SI_LWP or SI_NOINFO are NetBSD extensions.

the TRAP_CHLD, TRAP_DBREG, TRAP_EXEC, TRAP_LWP, TRAP_SCE and TRAP_SCX signal specific reasons of SIGTRAP are NetBSD extensions 💜

🎀 HISTORY 🎀

the <lavender>siginfo</lavender> functionality first appeared in AT&T System V Release 4 UNIX.

TRAP_CHLD, TRAP_DBREG, TRAP_EXEC, TRAP_LWP, TRAP_SCE and TRAP_SCX first appeared in NetBSD 8.

the additional parameters with syscall information in TRAP_SCE and TRAP_SCX first appeared in NetBSD 9 🌈

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that’s the whole tea, bestie 🫶 this page is from Debian, dated May 25, 2019, and it’s SIGINFO(2). go decode those signals and absolutely slay 💅✨