Merging upstream version 6.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 0 insertions, 1210 deletions

diff --git a/man2/sigaction.2 b/man2/sigaction.2
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-.\" Copyright (c) 1994,1995 Mike Battersby <mib@deakin.edu.au>
-.\" and Copyright 2004, 2005 Michael Kerrisk <mtk.manpages@gmail.com>
-.\" based on work by faith@cs.unc.edu
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.\" Modified, aeb, 960424
-.\" Modified Fri Jan 31 17:31:20 1997 by Eric S. Raymond <esr@thyrsus.com>
-.\" Modified Thu Nov 26 02:12:45 1998 by aeb - add SIGCHLD stuff.
-.\" Modified Sat May  8 17:40:19 1999 by Matthew Wilcox
-.\"	add POSIX.1b signals
-.\" Modified Sat Dec 29 01:44:52 2001 by Evan Jones <ejones@uwaterloo.ca>
-.\"	SA_ONSTACK
-.\" Modified 2004-11-11 by Michael Kerrisk <mtk.manpages@gmail.com>
-.\"	Added mention of SIGCONT under SA_NOCLDSTOP
-.\"	Added SA_NOCLDWAIT
-.\" Modified 2004-11-17 by Michael Kerrisk <mtk.manpages@gmail.com>
-.\"	Updated discussion for POSIX.1-2001 and SIGCHLD and sa_flags.
-.\"	Formatting fixes
-.\" 2004-12-09, mtk, added SI_TKILL + other minor changes
-.\" 2005-09-15, mtk, split sigpending(), sigprocmask(), sigsuspend()
-.\"	out of this page into separate pages.
-.\" 2010-06-11 Andi Kleen, add hwpoison signal extensions
-.\" 2010-06-11 mtk, improvements to discussion of various siginfo_t fields.
-.\" 2015-01-17, Kees Cook <keescook@chromium.org>
-.\"	Added notes on ptrace SIGTRAP and SYS_SECCOMP.
-.\"
-.TH sigaction 2 2024-02-25 "Linux man-pages 6.7"
-.SH NAME
-sigaction, rt_sigaction \- examine and change a signal action
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.B #include <signal.h>
-.P
-.BI "int sigaction(int " signum ,
-.BI "              const struct sigaction *_Nullable restrict " act ,
-.BI "              struct sigaction *_Nullable restrict " oldact );
-.fi
-.P
-.RS -4
-Feature Test Macro Requirements for glibc (see
-.BR feature_test_macros (7)):
-.RE
-.P
-.BR sigaction ():
-.nf
-    _POSIX_C_SOURCE
-.fi
-.P
-.IR siginfo_t :
-.nf
-    _POSIX_C_SOURCE >= 199309L
-.fi
-.SH DESCRIPTION
-The
-.BR sigaction ()
-system call is used to change the action taken by a process on
-receipt of a specific signal.
-(See
-.BR signal (7)
-for an overview of signals.)
-.P
-.I signum
-specifies the signal and can be any valid signal except
-.B SIGKILL
-and
-.BR SIGSTOP .
-.P
-If
-.I act
-is non-NULL, the new action for signal
-.I signum
-is installed from
-.IR act .
-If
-.I oldact
-is non-NULL, the previous action is saved in
-.IR oldact .
-.P
-The
-.I sigaction
-structure is defined as something like:
-.P
-.in +4n
-.EX
-struct sigaction {
-    void     (*sa_handler)(int);
-    void     (*sa_sigaction)(int, siginfo_t *, void *);
-    sigset_t   sa_mask;
-    int        sa_flags;
-    void     (*sa_restorer)(void);
-};
-.EE
-.in
-.P
-On some architectures a union is involved: do not assign to both
-.I sa_handler
-and
-.IR sa_sigaction .
-.P
-The
-.I sa_restorer
-field is not intended for application use.
-(POSIX does not specify a
-.I sa_restorer
-field.)
-Some further details of the purpose of this field can be found in
-.BR sigreturn (2).
-.P
-.I sa_handler
-specifies the action to be associated with
-.I signum
-and can be one of the following:
-.IP \[bu] 3
-.B SIG_DFL
-for the default action.
-.IP \[bu]
-.B SIG_IGN
-to ignore this signal.
-.IP \[bu]
-A pointer to a signal handling function.
-This function receives the signal number as its only argument.
-.P
-If
-.B SA_SIGINFO
-is specified in
-.IR sa_flags ,
-then
-.I sa_sigaction
-(instead of
-.IR sa_handler )
-specifies the signal-handling function for
-.IR signum .
-This function receives three arguments, as described below.
-.P
-.I sa_mask
-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
-.B SA_NODEFER
-flag is used.
-.P
-.I sa_flags
-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:
-.TP
-.B SA_NOCLDSTOP
-If
-.I signum
-is
-.BR SIGCHLD ,
-do not receive notification when child processes stop (i.e., when they
-receive one of
-.BR SIGSTOP ", " SIGTSTP ", " SIGTTIN ,
-or
-.BR SIGTTOU )
-or resume (i.e., they receive
-.BR SIGCONT )
-(see
-.BR wait (2)).
-This flag is meaningful only when establishing a handler for
-.BR SIGCHLD .
-.TP
-.BR SA_NOCLDWAIT " (since Linux 2.6)"
-.\" To be precise: Linux 2.5.60 -- MTK
-If
-.I signum
-is
-.BR SIGCHLD ,
-do not transform children into zombies when they terminate.
-See also
-.BR waitpid (2).
-This flag is meaningful only when establishing a handler for
-.BR SIGCHLD ,
-or when setting that signal's disposition to
-.BR SIG_DFL .
-.IP
-If the
-.B SA_NOCLDWAIT
-flag is set when establishing a handler for
-.BR SIGCHLD ,
-POSIX.1 leaves it unspecified whether a
-.B SIGCHLD
-signal is generated when a child process terminates.
-On Linux, a
-.B SIGCHLD
-signal is generated in this case;
-on some other implementations, it is not.
-.TP
-.B SA_NODEFER
-Do not add the signal to the thread's signal mask while the
-handler is executing, unless the signal is specified in
-.IR act.sa_mask .
-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.
-.IP
-.B SA_NOMASK
-is an obsolete, nonstandard synonym for this flag.
-.TP
-.B SA_ONSTACK
-Call the signal handler on an alternate signal stack provided by
-.BR sigaltstack (2).
-If an alternate stack is not available, the default stack will be used.
-This flag is meaningful only when establishing a signal handler.
-.TP
-.B 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.
-.IP
-.B SA_ONESHOT
-is an obsolete, nonstandard synonym for this flag.
-.TP
-.B 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
-.BR signal (7)
-for a discussion of system call restarting.
-.TP
-.B SA_RESTORER
-.IR "Not intended for application use" .
-This flag is used by C libraries to indicate that the
-.I sa_restorer
-field contains the address of a "signal trampoline".
-See
-.BR sigreturn (2)
-for more details.
-.TP
-.BR SA_SIGINFO " (since Linux 2.2)"
-The signal handler takes three arguments, not one.
-In this case,
-.I sa_sigaction
-should be set instead of
-.IR sa_handler .
-This flag is meaningful only when establishing a signal handler.
-.\" (The
-.\" .I sa_sigaction
-.\" field was added in Linux 2.1.86.)
-.\"
-.TP
-.BR SA_UNSUPPORTED " (since Linux 5.11)"
-Used to dynamically probe for flag bit support.
-.IP
-If an attempt to register a handler succeeds with this flag set in
-.I act\->sa_flags
-alongside other flags that are potentially unsupported by the kernel,
-and an immediately subsequent
-.BR sigaction ()
-call specifying the same signal number and with a non-NULL
-.I oldact
-argument yields
-.B SA_UNSUPPORTED
-.I clear
-in
-.IR oldact\->sa_flags ,
-then
-.I oldact\->sa_flags
-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.
-.TP
-.BR SA_EXPOSE_TAGBITS " (since Linux 5.11)"
-Normally, when delivering a signal,
-an architecture-specific set of tag bits are cleared from the
-.I si_addr
-field of
-.IR siginfo_t .
-If this flag is set,
-an architecture-specific subset of the tag bits will be preserved in
-.IR si_addr .
-.IP
-Programs that need to be compatible with Linux versions older than 5.11
-must use
-.B SA_UNSUPPORTED
-to probe for support.
-.SS The siginfo_t argument to a SA_SIGINFO handler
-When the
-.B SA_SIGINFO
-flag is specified in
-.IR act.sa_flags ,
-the signal handler address is passed via the
-.I act.sa_sigaction
-field.
-This handler takes three arguments, as follows:
-.P
-.in +4n
-.EX
-void
-handler(int sig, siginfo_t *info, void *ucontext)
-{
-    ...
-}
-.EE
-.in
-.P
-These three arguments are as follows
-.TP
-.I sig
-The number of the signal that caused invocation of the handler.
-.TP
-.I info
-A pointer to a
-.IR siginfo_t ,
-which is a structure containing further information about the signal,
-as described below.
-.TP
-.I ucontext
-This is a pointer to a
-.I ucontext_t
-structure, cast to \fIvoid\ *\fP.
-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
-.BR sigreturn (2).
-Further information about the
-.I ucontext_t
-structure can be found in
-.BR getcontext (3)
-and
-.BR signal (7).
-Commonly, the handler function doesn't make any use of the third argument.
-.P
-The
-.I siginfo_t
-data type is a structure with the following fields:
-.P
-.in +4n
-.EX
-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) */
-.\" FIXME
-.\" The siginfo_t 'si_trapno' field seems to be used
-.\" only on SPARC and Alpha; this page could use
-.\" a little more detail on its purpose there.
-    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 */
-.\" In the kernel: si_tid
-    void    *si_addr;      /* Memory location which caused fault */
-    long     si_band;      /* Band event (was \fIint\fP 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) */
-}
-.EE
-.in
-.P
-.IR si_signo ", " si_errno " and " si_code
-are defined for all signals.
-.RI ( si_errno
-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:
-.IP \[bu] 3
-Signals sent with
-.BR kill (2)
-and
-.BR sigqueue (3)
-fill in
-.IR si_pid " and " si_uid .
-In addition, signals sent with
-.BR sigqueue (3)
-fill in
-.IR si_int " and " si_ptr
-with the values specified by the sender of the signal;
-see
-.BR sigqueue (3)
-for more details.
-.IP \[bu]
-Signals sent by POSIX.1b timers (since Linux 2.6) fill in
-.I si_overrun
-and
-.IR si_timerid .
-The
-.I si_timerid
-field is an internal ID used by the kernel to identify
-the timer; it is not the same as the timer ID returned by
-.BR timer_create (2).
-The
-.I si_overrun
-field is the timer overrun count;
-this is the same information as is obtained by a call to
-.BR timer_getoverrun (2).
-These fields are nonstandard Linux extensions.
-.IP \[bu]
-Signals sent for message queue notification (see the description of
-.B SIGEV_SIGNAL
-in
-.BR mq_notify (3))
-fill in
-.IR si_int / si_ptr ,
-with the
-.I sigev_value
-supplied to
-.BR mq_notify (3);
-.IR si_pid ,
-with the process ID of the message sender; and
-.IR si_uid ,
-with the real user ID of the message sender.
-.IP \[bu]
-.B SIGCHLD
-fills in
-.IR si_pid ", " si_uid ", " si_status ", " si_utime ", and " si_stime ,
-providing information about the child.
-The
-.I si_pid
-field is the process ID of the child;
-.I si_uid
-is the child's real user ID.
-The
-.I si_status
-field contains the exit status of the child (if
-.I si_code
-is
-.BR CLD_EXITED ),
-or the signal number that caused the process to change state.
-The
-.I si_utime
-and
-.I si_stime
-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
-.BR getrusage (2)
-and
-.BR times (2)).
-Up to Linux 2.6, and since Linux 2.6.27, these fields report
-CPU time in units of
-.IR sysconf(_SC_CLK_TCK) .
-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
-.BR time (7)).
-.\" FIXME .
-.\" When si_utime and si_stime where originally implemented, the
-.\" measurement unit was HZ, which was the same as clock ticks
-.\" (sysconf(_SC_CLK_TCK)).  In Linux 2.6, HZ became configurable, and
-.\" was *still* used as the unit to return the info these fields,
-.\" with the result that the field values depended on the
-.\" configured HZ.  Of course, the should have been measured in
-.\" USER_HZ instead, so that sysconf(_SC_CLK_TCK) could be used to
-.\" convert to seconds.  I have a queued patch to fix this:
-.\" http://thread.gmane.org/gmane.linux.kernel/698061/ .
-.\" This patch made it into Linux 2.6.27.
-.\" But note that these fields still don't return the times of
-.\" waited-for children (as is done by getrusage() and times()
-.\" and wait4()).  Solaris 8 does include child times.
-.IP \[bu]
-.BR SIGILL ,
-.BR SIGFPE ,
-.BR SIGSEGV ,
-.BR SIGBUS ,
-and
-.B SIGTRAP
-fill in
-.I si_addr
-with the address of the fault.
-On some architectures,
-these signals also fill in the
-.I si_trapno
-field.
-.IP
-Some suberrors of
-.BR SIGBUS ,
-in particular
-.B BUS_MCEERR_AO
-and
-.BR BUS_MCEERR_AR ,
-also fill in
-.IR si_addr_lsb .
-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,
-.I si_addr_lsb
-contains
-.IR log2(sysconf(_SC_PAGESIZE)) .
-When
-.B SIGTRAP
-is delivered in response to a
-.BR ptrace (2)
-event (PTRACE_EVENT_foo),
-.I si_addr
-is not populated, but
-.I si_pid
-and
-.I si_uid
-are populated with the respective process ID and user ID responsible for
-delivering the trap.
-In the case of
-.BR seccomp (2),
-the tracee will be shown as delivering the event.
-.B BUS_MCEERR_*
-and
-.I si_addr_lsb
-are Linux-specific extensions.
-.IP
-The
-.B SEGV_BNDERR
-suberror of
-.B SIGSEGV
-populates
-.I si_lower
-and
-.IR si_upper .
-.IP
-The
-.B SEGV_PKUERR
-suberror of
-.B SIGSEGV
-populates
-.IR si_pkey .
-.IP \[bu]
-.BR SIGIO / SIGPOLL
-(the two names are synonyms on Linux)
-fills in
-.I si_band
-and
-.IR si_fd .
-The
-.I si_band
-event is a bit mask containing the same values as are filled in the
-.I revents
-field by
-.BR poll (2).
-The
-.I si_fd
-field indicates the file descriptor for which the I/O event occurred;
-for further details, see the description of
-.B F_SETSIG
-in
-.BR fcntl (2).
-.IP \[bu]
-.BR SIGSYS ,
-generated (since Linux 3.5)
-.\" commit a0727e8ce513fe6890416da960181ceb10fbfae6
-when a seccomp filter returns
-.BR SECCOMP_RET_TRAP ,
-fills in
-.IR si_call_addr ,
-.IR si_syscall ,
-.IR si_arch ,
-.IR si_errno ,
-and other fields as described in
-.BR seccomp (2).
-.\"
-.SS
-The si_code field
-The
-.I si_code
-field inside the
-.I siginfo_t
-argument that is passed to a
-.B SA_SIGINFO
-signal handler is a value (not a bit mask)
-indicating why this signal was sent.
-For a
-.BR ptrace (2)
-event,
-.I si_code
-will contain
-.B SIGTRAP
-and have the ptrace event in the high byte:
-.P
-.in +4n
-.EX
-(SIGTRAP | PTRACE_EVENT_foo << 8).
-.EE
-.in
-.P
-For a
-.RB non- ptrace (2)
-event, the values that can appear in
-.I si_code
-are described in the remainder of this section.
-Since glibc 2.20,
-the definitions of most of these symbols are obtained from
-.I <signal.h>
-by defining feature test macros (before including
-.I any
-header file) as follows:
-.IP \[bu] 3
-.B _XOPEN_SOURCE
-with the value 500 or greater;
-.IP \[bu]
-.B _XOPEN_SOURCE
-and
-.BR _XOPEN_SOURCE_EXTENDED ;
-or
-.IP \[bu]
-.B _POSIX_C_SOURCE
-with the value 200809L or greater.
-.P
-For the
-.B 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.
-.P
-For a regular signal, the following list shows the values which can be
-placed in
-.I si_code
-for any signal, along with the reason that the signal was generated.
-.RS 4
-.TP
-.B SI_USER
-.BR kill (2).
-.TP
-.B SI_KERNEL
-Sent by the kernel.
-.TP
-.B SI_QUEUE
-.BR sigqueue (3).
-.TP
-.B SI_TIMER
-POSIX timer expired.
-.TP
-.BR SI_MESGQ " (since Linux 2.6.6)"
-POSIX message queue state changed; see
-.BR mq_notify (3).
-.TP
-.B SI_ASYNCIO
-AIO completed.
-.TP
-.B SI_SIGIO
-Queued
-.B SIGIO
-(only up to Linux 2.2; from Linux 2.4 onward
-.BR SIGIO / SIGPOLL
-fills in
-.I si_code
-as described below).
-.TP
-.BR SI_TKILL " (since Linux 2.4.19)"
-.BR tkill (2)
-or
-.BR tgkill (2).
-.\" SI_DETHREAD is defined in Linux 2.6.9 sources, but isn't implemented
-.\" It appears to have been an idea that was tried during 2.5.6
-.\" through to Linux 2.5.24 and then was backed out.
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.B SIGILL
-signal:
-.RS 4
-.TP
-.B ILL_ILLOPC
-Illegal opcode.
-.TP
-.B ILL_ILLOPN
-Illegal operand.
-.TP
-.B ILL_ILLADR
-Illegal addressing mode.
-.TP
-.B ILL_ILLTRP
-Illegal trap.
-.TP
-.B ILL_PRVOPC
-Privileged opcode.
-.TP
-.B ILL_PRVREG
-Privileged register.
-.TP
-.B ILL_COPROC
-Coprocessor error.
-.TP
-.B ILL_BADSTK
-Internal stack error.
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.B SIGFPE
-signal:
-.RS 4
-.TP
-.B FPE_INTDIV
-Integer divide by zero.
-.TP
-.B FPE_INTOVF
-Integer overflow.
-.TP
-.B FPE_FLTDIV
-Floating-point divide by zero.
-.TP
-.B FPE_FLTOVF
-Floating-point overflow.
-.TP
-.B FPE_FLTUND
-Floating-point underflow.
-.TP
-.B FPE_FLTRES
-Floating-point inexact result.
-.TP
-.B FPE_FLTINV
-Floating-point invalid operation.
-.TP
-.B FPE_FLTSUB
-Subscript out of range.
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.B SIGSEGV
-signal:
-.RS 4
-.TP
-.B SEGV_MAPERR
-Address not mapped to object.
-.TP
-.B SEGV_ACCERR
-Invalid permissions for mapped object.
-.TP
-.BR SEGV_BNDERR " (since Linux 3.19)"
-.\" commit ee1b58d36aa1b5a79eaba11f5c3633c88231da83
-Failed address bound checks.
-.TP
-.BR SEGV_PKUERR " (since Linux 4.6)"
-.\" commit cd0ea35ff5511cde299a61c21a95889b4a71464e
-Access was denied by memory protection keys.
-See
-.BR pkeys (7).
-The protection key which applied to this access is available via
-.IR si_pkey .
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.B SIGBUS
-signal:
-.RS 4
-.TP
-.B BUS_ADRALN
-Invalid address alignment.
-.TP
-.B BUS_ADRERR
-Nonexistent physical address.
-.TP
-.B BUS_OBJERR
-Object-specific hardware error.
-.TP
-.BR BUS_MCEERR_AR " (since Linux 2.6.32)"
-Hardware memory error consumed on a machine check; action required.
-.TP
-.BR BUS_MCEERR_AO " (since Linux 2.6.32)"
-Hardware memory error detected in process but not consumed; action optional.
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.B SIGTRAP
-signal:
-.RS 4
-.TP
-.B TRAP_BRKPT
-Process breakpoint.
-.TP
-.B TRAP_TRACE
-Process trace trap.
-.TP
-.BR TRAP_BRANCH " (since Linux 2.4, IA64 only)"
-Process taken branch trap.
-.TP
-.BR TRAP_HWBKPT " (since Linux 2.4, IA64 only)"
-Hardware breakpoint/watchpoint.
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.B SIGCHLD
-signal:
-.RS 4
-.TP
-.B CLD_EXITED
-Child has exited.
-.TP
-.B CLD_KILLED
-Child was killed.
-.TP
-.B CLD_DUMPED
-Child terminated abnormally.
-.TP
-.B CLD_TRAPPED
-Traced child has trapped.
-.TP
-.B CLD_STOPPED
-Child has stopped.
-.TP
-.BR CLD_CONTINUED " (since Linux 2.6.9)"
-Stopped child has continued.
-.RE
-.P
-The following values can be placed in
-.I si_code
-for a
-.BR SIGIO / SIGPOLL
-signal:
-.RS 4
-.TP
-.B POLL_IN
-Data input available.
-.TP
-.B POLL_OUT
-Output buffers available.
-.TP
-.B POLL_MSG
-Input message available.
-.TP
-.B POLL_ERR
-I/O error.
-.TP
-.B POLL_PRI
-High priority input available.
-.TP
-.B POLL_HUP
-Device disconnected.
-.RE
-.P
-The following value can be placed in
-.I si_code
-for a
-.B SIGSYS
-signal:
-.RS 4
-.TP
-.BR SYS_SECCOMP " (since Linux 3.5)"
-Triggered by a
-.BR seccomp (2)
-filter rule.
-.RE
-.SS Dynamically probing for flag bit support
-The
-.BR sigaction ()
-call on Linux accepts unknown bits set in
-.I act\->sa_flags
-without error.
-The behavior of the kernel starting with Linux 5.11 is that a second
-.BR sigaction ()
-will clear unknown bits from
-.IR oldact\->sa_flags .
-However, historically, a second
-.BR sigaction ()
-call would typically leave those bits set in
-.IR oldact\->sa_flags .
-.P
-This means that support for new flags cannot be detected
-simply by testing for a flag in
-.IR sa_flags ,
-and a program must test that
-.B SA_UNSUPPORTED
-has been cleared before relying on the contents of
-.IR sa_flags .
-.P
-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
-.BR sigaction ()
-in the signal handler itself.
-.P
-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
-.IR act\->sa_flags .
-.P
-The flags
-.BR SA_NOCLDSTOP ,
-.BR SA_NOCLDWAIT ,
-.BR SA_SIGINFO ,
-.BR SA_ONSTACK ,
-.BR SA_RESTART ,
-.BR SA_NODEFER ,
-.BR SA_RESETHAND ,
-and, if defined by the architecture,
-.B 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.
-.P
-See EXAMPLES below for a demonstration of the use of
-.BR SA_UNSUPPORTED .
-.SH RETURN VALUE
-.BR sigaction ()
-returns 0 on success; on error, \-1 is returned, and
-.I errno
-is set to indicate the error.
-.SH ERRORS
-.TP
-.B EFAULT
-.IR act " or " oldact
-points to memory which is not a valid part of the process address space.
-.TP
-.B EINVAL
-An invalid signal was specified.
-This will also be generated if an attempt
-is made to change the action for
-.BR SIGKILL " or " SIGSTOP ,
-which cannot be caught or ignored.
-.SH VERSIONS
-.SS C library/kernel differences
-The glibc wrapper function for
-.BR sigaction ()
-gives an error
-.RB ( EINVAL )
-on attempts to change the disposition of the two real-time signals
-used internally by the NPTL threading implementation.
-See
-.BR nptl (7)
-for details.
-.P
-On architectures where the signal trampoline resides in the C library,
-the glibc wrapper function for
-.BR sigaction ()
-places the address of the trampoline code in the
-.I act.sa_restorer
-field and sets the
-.B SA_RESTORER
-flag in the
-.I act.sa_flags
-field.
-See
-.BR sigreturn (2).
-.P
-The original Linux system call was named
-.BR sigaction ().
-However, with the addition of real-time signals in Linux 2.2,
-the fixed-size, 32-bit
-.I sigset_t
-type supported by that system call was no longer fit for purpose.
-Consequently, a new system call,
-.BR rt_sigaction (),
-was added to support an enlarged
-.I sigset_t
-type.
-The new system call takes a fourth argument,
-.IR "size_t sigsetsize" ,
-which specifies the size in bytes of the signal sets in
-.I act.sa_mask
-and
-.IR oldact.sa_mask .
-This argument is currently required to have the value
-.I sizeof(sigset_t)
-(or the error
-.B EINVAL
-results).
-The glibc
-.BR sigaction ()
-wrapper function hides these details from us, transparently calling
-.BR rt_sigaction ()
-when the kernel provides it.
-.SH STANDARDS
-POSIX.1-2008.
-.SH HISTORY
-POSIX.1-2001, SVr4.
-.\" SVr4 does not document the EINTR condition.
-.P
-POSIX.1-1990 disallowed setting the action for
-.B SIGCHLD
-to
-.BR SIG_IGN .
-POSIX.1-2001 and later allow this possibility, so that ignoring
-.B SIGCHLD
-can be used to prevent the creation of zombies (see
-.BR wait (2)).
-Nevertheless, the historical BSD and System\ V behaviors for ignoring
-.B SIGCHLD
-differ, so that the only completely portable method of ensuring that
-terminated children do not become zombies is to catch the
-.B SIGCHLD
-signal and perform a
-.BR wait (2)
-or similar.
-.P
-POSIX.1-1990 specified only
-.BR SA_NOCLDSTOP .
-POSIX.1-2001 added
-.BR SA_NOCLDWAIT ,
-.BR SA_NODEFER ,
-.BR SA_ONSTACK ,
-.BR SA_RESETHAND ,
-.BR SA_RESTART ,
-and
-.B SA_SIGINFO
-as XSI extensions.
-POSIX.1-2008 moved
-.BR SA_NODEFER ,
-.BR SA_RESETHAND ,
-.BR SA_RESTART ,
-and
-.B SA_SIGINFO
-to the base specifications.
-Use of these latter values in
-.I sa_flags
-may be less portable in applications intended for older
-UNIX implementations.
-.P
-The
-.B SA_RESETHAND
-flag is compatible with the SVr4 flag of the same name.
-.P
-The
-.B 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
-.I sa_mask
-settings).
-.SH NOTES
-A child created via
-.BR fork (2)
-inherits a copy of its parent's signal dispositions.
-During an
-.BR execve (2),
-the dispositions of handled signals are reset to the default;
-the dispositions of ignored signals are left unchanged.
-.P
-According to POSIX, the behavior of a process is undefined after it
-ignores a
-.BR SIGFPE ,
-.BR SIGILL ,
-or
-.B SIGSEGV
-signal that was not generated by
-.BR kill (2)
-or
-.BR raise (3).
-Integer division by zero has undefined result.
-On some architectures it will generate a
-.B SIGFPE
-signal.
-(Also dividing the most negative integer by \-1 may generate
-.BR SIGFPE .)
-Ignoring this signal might lead to an endless loop.
-.P
-.BR 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.
-.P
-It is not possible to block
-.BR SIGKILL " or " SIGSTOP
-(by specifying them in
-.IR sa_mask ).
-Attempts to do so are silently ignored.
-.P
-See
-.BR sigsetops (3)
-for details on manipulating signal sets.
-.P
-See
-.BR signal\-safety (7)
-for a list of the async-signal-safe functions that can be
-safely called inside from inside a signal handler.
-.\"
-.SS Undocumented
-Before the introduction of
-.BR SA_SIGINFO ,
-it was also possible to get some additional information about the signal.
-This was done by providing an
-.I sa_handler
-signal handler with a second argument of type
-.IR "struct sigcontext" ,
-which is the same structure as the one that is passed in the
-.I uc_mcontext
-field of the
-.I ucontext
-structure that is passed (via a pointer) in the third argument of the
-.I sa_sigaction
-handler.
-See the relevant Linux kernel sources for details.
-This use is obsolete now.
-.SH BUGS
-When delivering a signal with a
-.B SA_SIGINFO
-handler,
-the kernel does not always provide meaningful values
-for all of the fields of the
-.I siginfo_t
-that are relevant for that signal.
-.P
-Up to and including Linux 2.6.13, specifying
-.B SA_NODEFER
-in
-.I sa_flags
-prevents not only the delivered signal from being masked during
-execution of the handler, but also the signals specified in
-.IR sa_mask .
-This bug was fixed in Linux 2.6.14.
-.\" commit 69be8f189653cd81aae5a74e26615b12871bb72e
-.SH EXAMPLES
-See
-.BR mprotect (2).
-.SS Probing for flag support
-The following example program exits with status
-.B EXIT_SUCCESS
-if
-.B SA_EXPOSE_TAGBITS
-is determined to be supported, and
-.B EXIT_FAILURE
-otherwise.
-.P
-.\" SRC BEGIN (sigaction.c)
-.EX
-#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);
-}
-.EE
-.\" SRC END
-.SH SEE ALSO
-.BR kill (1),
-.BR kill (2),
-.BR pause (2),
-.BR pidfd_send_signal (2),
-.BR restart_syscall (2),
-.BR seccomp (2),
-.BR sigaltstack (2),
-.BR signal (2),
-.BR signalfd (2),
-.BR sigpending (2),
-.BR sigprocmask (2),
-.BR sigreturn (2),
-.BR sigsuspend (2),
-.BR wait (2),
-.BR killpg (3),
-.BR raise (3),
-.BR siginterrupt (3),
-.BR sigqueue (3),
-.BR sigsetops (3),
-.BR sigvec (3),
-.BR core (5),
-.BR signal (7)