sigaction(2) - Linux manual page (original) (raw)
sigaction(2) System Calls Manual sigaction(2)
NAME top
sigaction, rt_sigaction - examine and change a signal actionLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <signal.h>**
**int sigaction(int** _signum_**,**
**const struct sigaction *_Nullable restrict** _act_**,**
**struct sigaction *_Nullable restrict** _oldact_**);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**sigaction**():
_POSIX_C_SOURCE
_siginfot_:
_POSIX_C_SOURCE >= 199309LDESCRIPTION top
The **sigaction**() system call is used to change the action taken by
a process on receipt of a specific signal. (See [signal(7)](../man7/signal.7.html) for an
overview of signals.)
_signum_ specifies the signal and can be any valid signal except
**SIGKILL** and **SIGSTOP**.
If _act_ is non-NULL, the new action for signal _signum_ is installed
from _act_. If _oldact_ is non-NULL, the previous action is saved in
_oldact_.
The _sigaction_ structure is defined as something like:
struct sigaction {
void (*sa_handler)(int);
void (*sa_sigaction)(int, siginfo_t *, void *);
sigset_t sa_mask;
int sa_flags;
void (*sa_restorer)(void);
};
On some architectures a union is involved: do not assign to both
_sahandler_ and _sasigaction_.
The _sarestorer_ field is not intended for application use. (POSIX
does not specify a _sarestorer_ field.) Some further details of
the purpose of this field can be found in [sigreturn(2)](../man2/sigreturn.2.html).
_sahandler_ specifies the action to be associated with _signum_ and
can be one of the following:
• **SIG_DFL** for the default action.
• **SIG_IGN** to ignore this signal.
• A pointer to a signal handling function. This function
receives the signal number as its only argument.
If **SA_SIGINFO** is specified in _saflags_, then _sasigaction_ (instead
of _sahandler_) specifies the signal-handling function for _signum_.
This function receives three arguments, as described below.
_samask_ specifies a mask of signals which should be blocked (i.e.,
added to the signal mask of the thread in which the signal handler
is invoked) during execution of the signal handler. In addition,
the signal which triggered the handler will be blocked, unless the
**SA_NODEFER** flag is used.
_saflags_ specifies a set of flags which modify the behavior of the
signal. It is formed by the bitwise OR of zero or more of the
following:
**SA_NOCLDSTOP**
If _signum_ is **SIGCHLD**, do not receive notification when
child processes stop (i.e., when they receive one of
**SIGSTOP**, **SIGTSTP**, **SIGTTIN**, or **SIGTTOU**) or resume (i.e.,
they receive **SIGCONT**) (see [wait(2)](../man2/wait.2.html)). This flag is
meaningful only when establishing a handler for **SIGCHLD**.
**SA_NOCLDWAIT** (since Linux 2.6)
If _signum_ is **SIGCHLD**, do not transform children into
zombies when they terminate. See also [waitpid(2)](../man2/waitpid.2.html). This
flag is meaningful only when establishing a handler for
**SIGCHLD**, or when setting that signal's disposition to
**SIG_DFL**.
If the **SA_NOCLDWAIT** flag is set when establishing a handler
for **SIGCHLD**, POSIX.1 leaves it unspecified whether a
**SIGCHLD** signal is generated when a child process
terminates. On Linux, a **SIGCHLD** signal is generated in
this case; on some other implementations, it is not.
**SA_NODEFER**
Do not add the signal to the thread's signal mask while the
handler is executing, unless the signal is specified in
_act.samask_. Consequently, a further instance of the
signal may be delivered to the thread while it is executing
the handler. This flag is meaningful only when
establishing a signal handler.
**SA_NOMASK** is an obsolete, nonstandard synonym for this
flag.
**SA_ONSTACK**
Call the signal handler on an alternate signal stack
provided by [sigaltstack(2)](../man2/sigaltstack.2.html). If an alternate stack is not
available, the default stack will be used. This flag is
meaningful only when establishing a signal handler.
**SA_RESETHAND**
Restore the signal action to the default upon entry to the
signal handler. This flag is meaningful only when
establishing a signal handler.
**SA_ONESHOT** is an obsolete, nonstandard synonym for this
flag.
**SA_RESTART**
Provide behavior compatible with BSD signal semantics by
making certain system calls restartable across signals.
This flag is meaningful only when establishing a signal
handler. See [signal(7)](../man7/signal.7.html) for a discussion of system call
restarting.
**SA_RESTORER**
_Not intended for application use_. This flag is used by C
libraries to indicate that the _sarestorer_ field contains
the address of a "signal trampoline". See [sigreturn(2)](../man2/sigreturn.2.html) for
more details.
**SA_SIGINFO** (since Linux 2.2)
The signal handler takes three arguments, not one. In this
case, _sasigaction_ should be set instead of _sahandler_.
This flag is meaningful only when establishing a signal
handler.
**SA_UNSUPPORTED** (since Linux 5.11)
Used to dynamically probe for flag bit support.
If an attempt to register a handler succeeds with this flag
set in _act->saflags_ alongside other flags that are
potentially unsupported by the kernel, and an immediately
subsequent **sigaction**() call specifying the same signal
number and with a non-NULL _oldact_ argument yields
**SA_UNSUPPORTED** _clear_ in _oldact->saflags_, then
_oldact->saflags_ may be used as a bitmask describing which
of the potentially unsupported flags are, in fact,
supported. See the section "Dynamically probing for flag
bit support" below for more details.
**SA_EXPOSE_TAGBITS** (since Linux 5.11)
Normally, when delivering a signal, an architecture-
specific set of tag bits are cleared from the _siaddr_ field
of _siginfot_. If this flag is set, an architecture-
specific subset of the tag bits will be preserved in
_siaddr_.
Programs that need to be compatible with Linux versions
older than 5.11 must use **SA_UNSUPPORTED** to probe for
support.The siginfo_t argument to a SA_SIGINFO handler When the SA_SIGINFO flag is specified in act.saflags, the signal handler address is passed via the act.sasigaction field. This handler takes three arguments, as follows:
void
handler(int sig, siginfo_t *info, void *ucontext)
{
...
}
These three arguments are as follows
_sig_ The number of the signal that caused invocation of the
handler.
_info_ A pointer to a _siginfot_, which is a structure containing
further information about the signal, as described below.
_ucontext_
This is a pointer to a _ucontextt_ structure, cast to
_void *_. The structure pointed to by this field contains
signal context information that was saved on the user-space
stack by the kernel; for details, see [sigreturn(2)](../man2/sigreturn.2.html).
Further information about the _ucontextt_ structure can be
found in [getcontext(3)](../man3/getcontext.3.html) and [signal(7)](../man7/signal.7.html). Commonly, the
handler function doesn't make any use of the third
argument.
The _siginfot_ data type is a structure with the following fields:
siginfo_t {
int si_signo; /* Signal number */
int si_errno; /* An errno value */
int si_code; /* Signal code */
int si_trapno; /* Trap number that caused
hardware-generated signal
(unused on most architectures) */
pid_t si_pid; /* Sending process ID */
uid_t si_uid; /* Real user ID of sending process */
int si_status; /* Exit value or signal */
clock_t si_utime; /* User time consumed */
clock_t si_stime; /* System time consumed */
union sigval si_value; /* Signal value */
int si_int; /* POSIX.1b signal */
void *si_ptr; /* POSIX.1b signal */
int si_overrun; /* Timer overrun count;
POSIX.1b timers */
int si_timerid; /* Timer ID; POSIX.1b timers */
void *si_addr; /* Memory location which caused fault */
long si_band; /* Band event (was _int_ in
glibc 2.3.2 and earlier) */
int si_fd; /* File descriptor */
short si_addr_lsb; /* Least significant bit of address
(since Linux 2.6.32) */
void *si_lower; /* Lower bound when address violation
occurred (since Linux 3.19) */
void *si_upper; /* Upper bound when address violation
occurred (since Linux 3.19) */
int si_pkey; /* Protection key on PTE that caused
fault (since Linux 4.6) */
void *si_call_addr; /* Address of system call instruction
(since Linux 3.5) */
int si_syscall; /* Number of attempted system call
(since Linux 3.5) */
unsigned int si_arch; /* Architecture of attempted system call
(since Linux 3.5) */
}
_sisigno_, _sierrno_ and _sicode_ are defined for all signals.
(_sierrno_ is generally unused on Linux.) The rest of the struct
may be a union, so that one should read only the fields that are
meaningful for the given signal:
• Signals sent with [kill(2)](../man2/kill.2.html) and [sigqueue(3)](../man3/sigqueue.3.html) fill in _sipid_ and
_siuid_. In addition, signals sent with [sigqueue(3)](../man3/sigqueue.3.html) fill in
_siint_ and _siptr_ with the values specified by the sender of
the signal; see [sigqueue(3)](../man3/sigqueue.3.html) for more details.
• Signals sent by POSIX.1b timers (since Linux 2.6) fill in
_sioverrun_ and _sitimerid_. The _sitimerid_ field is an internal
ID used by the kernel to identify the timer; it is not the same
as the timer ID returned by [timer_create(2)](../man2/timer%5Fcreate.2.html). The _sioverrun_
field is the timer overrun count; this is the same information
as is obtained by a call to [timer_getoverrun(2)](../man2/timer%5Fgetoverrun.2.html). These fields
are nonstandard Linux extensions.
• Signals sent for message queue notification (see the
description of **SIGEV_SIGNAL** in [mq_notify(3)](../man3/mq%5Fnotify.3.html)) fill in
_siint_/_siptr_, with the _sigevvalue_ supplied to [mq_notify(3)](../man3/mq%5Fnotify.3.html);
_sipid_, with the process ID of the message sender; and _siuid_,
with the real user ID of the message sender.
• **SIGCHLD** fills in _sipid_, _siuid_, _sistatus_, _siutime_, and
_sistime_, providing information about the child. The _sipid_
field is the process ID of the child; _siuid_ is the child's
real user ID. The _sistatus_ field contains the exit status of
the child (if _sicode_ is **CLD_EXITED**), or the signal number that
caused the process to change state. The _siutime_ and _sistime_
contain the user and system CPU time used by the child process;
these fields do not include the times used by waited-for
children (unlike [getrusage(2)](../man2/getrusage.2.html) and [times(2)](../man2/times.2.html)). Up to Linux 2.6,
and since Linux 2.6.27, these fields report CPU time in units
of _sysconf(SCCLKTCK)_. In Linux 2.6 kernels before Linux
2.6.27, a bug meant that these fields reported time in units of
the (configurable) system jiffy (see [time(7)](../man7/time.7.html)).
• **SIGILL**, **SIGFPE**, **SIGSEGV**, **SIGBUS**, and **SIGTRAP** fill in _siaddr_
with the address of the fault. On some architectures, these
signals also fill in the _sitrapno_ field.
Some suberrors of **SIGBUS**, in particular **BUS_MCEERR_AO** and
**BUS_MCEERR_AR**, also fill in _siaddrlsb_. This field indicates
the least significant bit of the reported address and therefore
the extent of the corruption. For example, if a full page was
corrupted, _siaddrlsb_ contains _log2(sysconf(SCPAGESIZE))_.
When **SIGTRAP** is delivered in response to a [ptrace(2)](../man2/ptrace.2.html) event
(PTRACE_EVENT_foo), _siaddr_ is not populated, but _sipid_ and
_siuid_ are populated with the respective process ID and user ID
responsible for delivering the trap. In the case of
[seccomp(2)](../man2/seccomp.2.html), the tracee will be shown as delivering the event.
**BUS_MCEERR_*** and _siaddrlsb_ are Linux-specific extensions.
The **SEGV_BNDERR** suberror of **SIGSEGV** populates _silower_ and
_siupper_.
The **SEGV_PKUERR** suberror of **SIGSEGV** populates _sipkey_.
• **SIGIO**/**SIGPOLL** (the two names are synonyms on Linux) fills in
_siband_ and _sifd_. The _siband_ event is a bit mask containing
the same values as are filled in the _revents_ field by [poll(2)](../man2/poll.2.html).
The _sifd_ field indicates the file descriptor for which the I/O
event occurred; for further details, see the description of
**F_SETSIG** in [fcntl(2)](../man2/fcntl.2.html).
• **SIGSYS**, generated (since Linux 3.5) when a seccomp filter
returns **SECCOMP_RET_TRAP**, fills in _sicalladdr_, _sisyscall_,
_siarch_, _sierrno_, and other fields as described in [seccomp(2)](../man2/seccomp.2.html).The si_code field The sicode field inside the siginfot argument that is passed to a SA_SIGINFO signal handler is a value (not a bit mask) indicating why this signal was sent. For a ptrace(2) event, sicode will contain SIGTRAP and have the ptrace event in the high byte:
(SIGTRAP | PTRACE_EVENT_foo << 8).
For a non-[ptrace(2)](../man2/ptrace.2.html) event, the values that can appear in _sicode_
are described in the remainder of this section. Since glibc 2.20,
the definitions of most of these symbols are obtained from
_<signal.h>_ by defining feature test macros (before including _any_
header file) as follows:
• **_XOPEN_SOURCE** with the value 500 or greater;
• **_XOPEN_SOURCE** and **_XOPEN_SOURCE_EXTENDED**; or
• **_POSIX_C_SOURCE** with the value 200809L or greater.
For the **TRAP_*** constants, the symbol definitions are provided only
in the first two cases. Before glibc 2.20, no feature test macros
were required to obtain these symbols.
For a regular signal, the following list shows the values which
can be placed in _sicode_ for any signal, along with the reason
that the signal was generated.
**SI_USER**
[kill(2)](../man2/kill.2.html).
**SI_KERNEL**
Sent by the kernel.
**SI_QUEUE**
[sigqueue(3)](../man3/sigqueue.3.html).
**SI_TIMER**
POSIX, or [setitimer(2)](../man2/setitimer.2.html) or [alarm(2)](../man2/alarm.2.html) timer expired.
**SI_MESGQ** (since Linux 2.6.6)
POSIX message queue state changed; see [mq_notify(3)](../man3/mq%5Fnotify.3.html).
**SI_ASYNCIO**
AIO completed.
**SI_SIGIO**
Queued **SIGIO** (only up to Linux 2.2; from Linux 2.4
onward **SIGIO**/**SIGPOLL** fills in _sicode_ as described
below).
**SI_TKILL** (since Linux 2.4.19)
[tkill(2)](../man2/tkill.2.html) or [tgkill(2)](../man2/tgkill.2.html).
The following values can be placed in _sicode_ for a **SIGILL** signal:
**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**
Coprocessor error.
**ILL_BADSTK**
Internal stack error.
The following values can be placed in _sicode_ for a **SIGFPE** signal:
**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**
Floating-point invalid operation.
**FPE_FLTSUB**
Subscript out of range.
The following values can be placed in _sicode_ for a **SIGSEGV**
signal:
**SEGV_MAPERR**
Address not mapped to object.
**SEGV_ACCERR**
Invalid permissions for mapped object.
**SEGV_BNDERR** (since Linux 3.19)
Failed address bound checks.
**SEGV_PKUERR** (since Linux 4.6)
Access was denied by memory protection keys. See
[pkeys(7)](../man7/pkeys.7.html). The protection key which applied to this
access is available via _sipkey_.
The following values can be placed in _sicode_ for a **SIGBUS** signal:
**BUS_ADRALN**
Invalid address alignment.
**BUS_ADRERR**
Nonexistent physical address.
**BUS_OBJERR**
Object-specific hardware error.
**BUS_MCEERR_AR** (since Linux 2.6.32)
Hardware memory error consumed on a machine check;
action required.
**BUS_MCEERR_AO** (since Linux 2.6.32)
Hardware memory error detected in process but not
consumed; action optional.
The following values can be placed in _sicode_ for a **SIGTRAP**
signal:
**TRAP_BRKPT**
Process breakpoint.
**TRAP_TRACE**
Process trace trap.
**TRAP_BRANCH** (since Linux 2.4, IA64 only)
Process taken branch trap.
**TRAP_HWBKPT** (since Linux 2.4, IA64 only)
Hardware breakpoint/watchpoint.
The following values can be placed in _sicode_ for a **SIGCHLD**
signal:
**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** (since Linux 2.6.9)
Stopped child has continued.
The following values can be placed in _sicode_ for a **SIGIO**/**SIGPOLL**
signal:
**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.
The following value can be placed in _sicode_ for a **SIGSYS** signal:
**SYS_SECCOMP** (since Linux 3.5)
Triggered by a [seccomp(2)](../man2/seccomp.2.html) filter rule.Dynamically probing for flag bit support The sigaction() call on Linux accepts unknown bits set in act->saflags without error. The behavior of the kernel starting with Linux 5.11 is that a second sigaction() will clear unknown bits from oldact->saflags. However, historically, a second sigaction() call would typically leave those bits set in oldact->saflags.
This means that support for new flags cannot be detected simply by
testing for a flag in _saflags_, and a program must test that
**SA_UNSUPPORTED** has been cleared before relying on the contents of
_saflags_.
Since the behavior of the signal handler cannot be guaranteed
unless the check passes, it is wise to either block the affected
signal while registering the handler and performing the check in
this case, or where this is not possible, for example if the
signal is synchronous, to issue the second **sigaction**() in the
signal handler itself.
In kernels that do not support a specific flag, the kernel's
behavior is as if the flag was not set, even if the flag was set
in _act->saflags_.
The flags **SA_NOCLDSTOP**, **SA_NOCLDWAIT**, **SA_SIGINFO**, **SA_ONSTACK**,
**SA_RESTART**, **SA_NODEFER**, **SA_RESETHAND**, and, if defined by the
architecture, **SA_RESTORER** may not be reliably probed for using
this mechanism, because they were introduced before Linux 5.11.
However, in general, programs may assume that these flags are
supported, since they have all been supported since Linux 2.6,
which was released in the year 2003.
See EXAMPLES below for a demonstration of the use of
**SA_UNSUPPORTED**.RETURN VALUE top
**sigaction**() returns 0 on success; on error, -1 is returned, and
_[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
**EFAULT** _act_ or _oldact_ points to memory which is not a valid part of
the process address space.
**EINVAL** An invalid signal was specified. This will also be
generated if an attempt is made to change the action for
**SIGKILL** or **SIGSTOP**, which cannot be caught or ignored.VERSIONS top
C library/kernel differences The glibc wrapper function for sigaction() gives an error (EINVAL) on attempts to change the disposition of the two real-time signals used internally by the NPTL threading implementation. See nptl(7) for details.
On architectures where the signal trampoline resides in the C
library, the glibc wrapper function for **sigaction**() places the
address of the trampoline code in the _act.sarestorer_ field and
sets the **SA_RESTORER** flag in the _act.saflags_ field. See
[sigreturn(2)](../man2/sigreturn.2.html).
The original Linux system call was named **sigaction**(). However,
with the addition of real-time signals in Linux 2.2, the fixed-
size, 32-bit _sigsett_ type supported by that system call was no
longer fit for purpose. Consequently, a new system call,
**rt_sigaction**(), was added to support an enlarged _sigsett_ type.
The new system call takes a fourth argument, _sizet sigsetsize_,
which specifies the size in bytes of the signal sets in
_act.samask_ and _oldact.samask_. This argument is currently
required to have the value _sizeof(sigsett)_ (or the error **EINVAL**
results). The glibc **sigaction**() wrapper function hides these
details from us, transparently calling **rt_sigaction**() when the
kernel provides it.STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001, SVr4.
POSIX.1-1990 disallowed setting the action for **SIGCHLD** to **SIG_IGN**.
POSIX.1-2001 and later allow this possibility, so that ignoring
**SIGCHLD** can be used to prevent the creation of zombies (see
[wait(2)](../man2/wait.2.html)). Nevertheless, the historical BSD and System V behaviors
for ignoring **SIGCHLD** differ, so that the only completely portable
method of ensuring that terminated children do not become zombies
is to catch the **SIGCHLD** signal and perform a [wait(2)](../man2/wait.2.html) or similar.
POSIX.1-1990 specified only **SA_NOCLDSTOP**. POSIX.1-2001 added
**SA_NOCLDWAIT**, **SA_NODEFER**, **SA_ONSTACK**, **SA_RESETHAND**, **SA_RESTART**,
and **SA_SIGINFO** as XSI extensions. POSIX.1-2008 moved **SA_NODEFER**,
**SA_RESETHAND**, **SA_RESTART**, and **SA_SIGINFO** to the base
specifications. Use of these latter values in _saflags_ may be
less portable in applications intended for older UNIX
implementations.
The **SA_RESETHAND** flag is compatible with the SVr4 flag of the same
name.
The **SA_NODEFER** flag is compatible with the SVr4 flag of the same
name under kernels 1.3.9 and later. On older kernels the Linux
implementation allowed the receipt of any signal, not just the one
we are installing (effectively overriding any _samask_ settings).NOTES top
A child created via [fork(2)](../man2/fork.2.html) inherits a copy of its parent's signal
dispositions. During an [execve(2)](../man2/execve.2.html), the dispositions of handled
signals are reset to the default; the dispositions of ignored
signals are left unchanged.
According to POSIX, the behavior of a process is undefined after
it ignores a **SIGFPE**, **SIGILL**, or **SIGSEGV** signal that was not
generated by [kill(2)](../man2/kill.2.html) or [raise(3)](../man3/raise.3.html). Integer division by zero has
undefined result. On some architectures it will generate a **SIGFPE**
signal. (Also dividing the most negative integer by -1 may
generate **SIGFPE**.) Ignoring this signal might lead to an endless
loop.
**sigaction**() can be called with a NULL second argument to query the
current signal handler. It can also be used to check whether a
given signal is valid for the current machine by calling it with
NULL second and third arguments.
It is not possible to block **SIGKILL** or **SIGSTOP** (by specifying them
in _samask_). Attempts to do so are silently ignored.
See [sigsetops(3)](../man3/sigsetops.3.html) for details on manipulating signal sets.
See [signal-safety(7)](../man7/signal-safety.7.html) for a list of the async-signal-safe functions
that can be safely called inside from inside a signal handler.
POSIX only guarantees **SI_TIMER** for signals created by
[timer_create(2)](../man2/timer%5Fcreate.2.html). Implementations are free to also provide it for
other types of timers. The Linux behaviour matches NetBSD.Undocumented Before the introduction of SA_SIGINFO, it was also possible to get some additional information about the signal. This was done by providing an sahandler signal handler with a second argument of type struct sigcontext, which is the same structure as the one that is passed in the ucmcontext field of the ucontext structure that is passed (via a pointer) in the third argument of the sasigaction handler. See the relevant Linux kernel sources for details. This use is obsolete now.
BUGS top
When delivering a signal resulting from a hardware exception with
a **SA_SIGINFO** handler, the kernel does not always provide
meaningful values for all of the fields of the _siginfot_ that are
relevant for that signal. For example, when the x86 _int_
instruction is called with a forbidden argument (any number other
than 3 or 128), a **SIGSEGV** signal is delivered, but the _siginfot_
passed to the signal handler has all its fields besides _sisigno_
and _sicode_ set to zero, even if other fields should be set (as an
example, _siaddr_ should be non-zero for all **SIGSEGV** signals).
Up to and including Linux 2.6.13, specifying **SA_NODEFER** in
_saflags_ prevents not only the delivered signal from being masked
during execution of the handler, but also the signals specified in
_samask_. This bug was fixed in Linux 2.6.14.EXAMPLES top
See [mprotect(2)](../man2/mprotect.2.html).Probing for flag support The following example program exits with status EXIT_SUCCESS if SA_EXPOSE_TAGBITS is determined to be supported, and EXIT_FAILURE otherwise.
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
void
handler(int signo, siginfo_t *info, void *context)
{
struct sigaction oldact;
if (sigaction(SIGSEGV, NULL, &oldact) == -1
|| (oldact.sa_flags & SA_UNSUPPORTED)
|| !(oldact.sa_flags & SA_EXPOSE_TAGBITS))
{
_exit(EXIT_FAILURE);
}
_exit(EXIT_SUCCESS);
}
int
main(void)
{
struct sigaction act = { 0 };
act.sa_flags = SA_SIGINFO | SA_UNSUPPORTED | SA_EXPOSE_TAGBITS;
act.sa_sigaction = &handler;
if (sigaction(SIGSEGV, &act, NULL) == -1) {
perror("sigaction");
exit(EXIT_FAILURE);
}
raise(SIGSEGV);
}SEE ALSO top
[kill(1)](../man1/kill.1.html), [kill(2)](../man2/kill.2.html), [pause(2)](../man2/pause.2.html), [pidfd_send_signal(2)](../man2/pidfd%5Fsend%5Fsignal.2.html),
[restart_syscall(2)](../man2/restart%5Fsyscall.2.html), [seccomp(2)](../man2/seccomp.2.html), [sigaltstack(2)](../man2/sigaltstack.2.html), [signal(2)](../man2/signal.2.html),
[signalfd(2)](../man2/signalfd.2.html), [sigpending(2)](../man2/sigpending.2.html), [sigprocmask(2)](../man2/sigprocmask.2.html), [sigreturn(2)](../man2/sigreturn.2.html),
[sigsuspend(2)](../man2/sigsuspend.2.html), [wait(2)](../man2/wait.2.html), [killpg(3)](../man3/killpg.3.html), [raise(3)](../man3/raise.3.html), [siginterrupt(3)](../man3/siginterrupt.3.html),
[sigqueue(3)](../man3/sigqueue.3.html), [sigsetops(3)](../man3/sigsetops.3.html), [sigvec(3)](../man3/sigvec.3.html), [core(5)](../man5/core.5.html), [signal(7)](../man7/signal.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-08-21 sigaction(2)
Pages that refer to this page:env(1), kill(1), kill(1@@procps-ng), pgrep(1), alarm(2), clock_nanosleep(2), clone(2), fcntl(2), getitimer(2), pidfd_open(2), pidfd_send_signal(2), PR_MCE_KILL_SET(2const), PR_SET_PDEATHSIG(2const), PR_SET_SYSCALL_USER_DISPATCH(2const), ptrace(2), restart_syscall(2), rt_sigqueueinfo(2), seccomp(2), seccomp_unotify(2), semop(2), send(2), sigaltstack(2), signal(2), signalfd(2), sigpending(2), sigprocmask(2), sigreturn(2), sigsuspend(2), sigwaitinfo(2), syscalls(2), timer_getoverrun(2), wait(2), wait4(2), abort(3), bsd_signal(3), getcontext(3), makecontext(3), posix_spawn(3), profil(3), psignal(3), pthread_kill(3), pthread_sigmask(3), pthread_sigqueue(3), raise(3), seccomp_init(3), sigevent(3type), siginterrupt(3), sigpause(3), sigqueue(3), sigset(3), sigsetops(3), sigvec(3), sigwait(3), system(3), sysv_signal(3), core(5), proc_pid_timers(5), proc_sys_vm(5), fifo(7), inotify(7), nptl(7), pid_namespaces(7), pkeys(7), signal(7), signal-safety(7), socket(7), system_data_types(7), user_namespaces(7)