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1.1 root 1: .TH SIGSYS 2J
2: .UC 4
3: .ie t .ds d \(dg
4: .el .ds d \z'|+'
5: .ie t .ds b \(bu
6: .el .ds b @
7: .SH NAME
8: sigsys \- catch or ignore signals
9: .SH SYNOPSIS
10: .nf
11: .B #include <signal.h>
12: .PP
13: .B (*sigsys(sig, func))()
14: .B void (*func)();
15: .PP
16: .B cc ... \-ljobs
17: .fi
18: .SH DESCRIPTION
19: .IR N.B. :
20: The system currently supports two signal implementations.
21: The one described in
22: .IR signal (2)
23: is standard in version 7 UNIX systems,
24: and retained for backward compatibility
25: as it is different
26: in a number of ways.
27: The one described here (with the interface in
28: .IR sigset (3))
29: provides for the needs of the job control mechanisms (see
30: .IR jobs (3))
31: used by
32: .IR csh (1),
33: and corrects the bugs in the standard implementation of signals,
34: allowing programs which process interrupts to be written reliably.
35: .PP
36: The routine
37: .I sigsys
38: is not normally called directly; rather the routines of
39: .IR sigset (3)
40: should be used.
41: These routines are kept in the ``jobs'' library, accessible by
42: giving the loader option
43: .B \-ljobs.
44: The features described here are less portable then those of
45: .IR signal (2)
46: and should not be used in programs which are
47: to be moved to other versions of UNIX.
48: .PP
49: A signal
50: is generated by some abnormal event,
51: initiated by a user at a terminal (quit, interrupt, stop),
52: by a program error (bus error, etc.),
53: by request of another program (kill),
54: or when a process is stopped because it wishes to access
55: its control terminal while in the background (see
56: .IR tty (4)).
57: Signals are optionally generated
58: when a process resumes after being stopped,
59: when the status of child processes changes,
60: or when input is ready at the control terminal.
61: Most signals cause termination of the receiving process if no action
62: is taken; some signals instead cause the process receiving them
63: to be stopped, or are simply discarded if the process has not
64: requested otherwise.
65: Except for the SIGKILL and SIGSTOP
66: signals which cannot be blocked, the
67: .I sigsys
68: call allows signals either to be ignored,
69: held until a later time (protecting critical sections in the process),
70: or to cause an interrupt to a specified location.
71: Here is the list of all signals with names as in the include file.
72: .LP
73: .nf
74: .ta \w'SIGMMMM 'u +\w'15* 'u
75: SIGHUP 1 hangup
76: SIGINT 2 interrupt
77: SIGQUIT 3* quit
78: SIGILL 4* illegal instruction (not reset when caught)
79: SIGTRAP 5* trace trap (not reset when caught)
80: SIGIOT 6* IOT instruction
81: SIGEMT 7* EMT instruction
82: SIGFPE 8* floating point exception
83: SIGKILL 9 kill (cannot be caught, held or ignored)
84: SIGBUS 10* bus error
85: SIGSEGV 11* segmentation violation
86: SIGSYS 12* bad argument to system call
87: SIGPIPE 13 write on a pipe with no one to read it
88: SIGALRM 14 alarm clock
89: SIGTERM 15 software termination signal
90: 16 unassigned
91: SIGSTOP 17\*d stop (cannot be caught, held or ignored)
92: SIGTSTP 18\*d stop signal generated from keyboard
93: SIGCONT 19\*b continue after stop
94: SIGCHLD 20\*b child status has changed
95: SIGTTIN 21\*d background read attempted from control terminal
96: SIGTTOU 22\*d background write attempted to control terminal
97: SIGTINT 23\*b input record is available at control terminal
98: SIGXCPU 24 cpu time limit exceeded (see \fIvlimit\fR(2))
99: SIGXFSZ 25 file size limit exceeded (see \fIvlimit\fR(2))
100: .fi
101: .PP
102: The starred signals in the list above cause a core image
103: if not caught, held or ignored.
104: .PP
105: If
106: .I func
107: is SIG_DFL, the default action
108: for signal
109: .I sig
110: is reinstated; this default is termination
111: (with a core image for starred signals)
112: except for signals marked with \*b or \*d.
113: Signals marked with \*b are discarded if the action is SIG_DFL; signals marked
114: with \*d cause the process to stop.
115: If
116: .I func
117: is SIG_HOLD
118: the signal is remembered if it occurs, but not presented to the process;
119: it may be presented later if the process changes the action for the signal.
120: If
121: .I func
122: is SIG_IGN the signal is subsequently ignored,
123: and pending instances of the signal are discarded (i.e. if the
124: action was previously SIG_HOLD.)
125: Otherwise
126: when the signal occurs
127: .I func
128: will be called.
129: .PP
130: A return from the function will
131: continue the process at the point it was interrupted.
132: Except as indicated,
133: a signal, set with
134: .I sigsys,
135: is reset to SIG_DFL after being caught. However by
136: specifying DEFERSIG(func) as the last argument to
137: .I sigsys,
138: one causes the action to be set to
139: SIG_HOLD before the interrupt is taken, so that recursive instances
140: of the signal cannot occur during handling of the signal.
141: .PP
142: When a caught signal occurs
143: during certain system calls, the call terminates prematurely.
144: In particular this can occur
145: during a
146: .I read
147: or
148: .IR write (2)
149: on a slow device (like a terminal; but not a file)
150: and during a
151: .I pause
152: or
153: .IR wait (2).
154: When a signal occurs
155: during one of these calls,
156: the saved user status
157: is arranged in such a way that,
158: when return from the
159: signal-catching takes place, it will appear that the
160: system call returned an error status.
161: The user's program may then, if it wishes,
162: re-execute the call.
163: .I Read
164: and
165: .I write
166: calls which have done no I/O,
167: .IR ioctl s
168: blocked with SIGTTOU,
169: and
170: .I wait3
171: calls are restarted.
172: .PP
173: The value of
174: .I sigsys
175: is the previous (or initial)
176: value of
177: .I func
178: for the particular signal.
179: .PP
180: The system provides two other functions by oring bits into the
181: signal number:
182: SIGDOPAUSE causes the process to
183: .I pause
184: after changing the signal action. It can be used to atomically
185: re-enable a held signal which was being processed and wait for
186: another instance of the signal.
187: SIGDORTI causes the system to simulate an
188: .I rei
189: instruction
190: clearing the mark the system placed on the stack at the point of
191: interrupt before checking for further signals to be presented due
192: to the specified change in signal actions. This allows a
193: signal package such as
194: .IR sigset (3)
195: to dismiss from interrupts cleanly removing the old state from
196: the stack before another instance of the interrupt is presented.
197: .PP
198: After a
199: .IR fork (2)
200: or
201: .IR vfork (2)
202: the child inherits
203: all signals.
204: .IR Exec (2)
205: resets all
206: caught signals to default action; held signals remain held
207: and ignored signals remain ignored.
208: .SH "SEE ALSO"
209: kill(1),
210: ptrace(2), kill(2),
211: jobs(3), sigset(3), setjmp(3),
212: tty(4)
213: .SH DIAGNOSTICS
214: The value BADSIG is returned if the
215: given signal is out of range.
216: .SH BUGS
217: The job control facilities are not available in standard version 7 UNIX.
218: These facilities are still under development and may change in future
219: releases of the system as better inter-process communication facilities
220: and support for virtual terminals become available. The options and
221: specifications of this facility and the system calls supporting it
222: are thus subject to change.
223: .PP
224: Since only one signal action can be changed at a time, it is not
225: possible to get the effect of SIGDOPAUSE for more than one signal
226: at a time.
227: .PP
228: The traps (listed below) should be distinguishable by extra arguments
229: to the signal handler, and all hardware supplied parameters should
230: be made available to the signal routine.
231: .SH "ASSEMBLER (PDP-11)"
232: (signal = 48.)
233: .br
234: .B sys signal; sig; label
235: .br
236: (old label in r0)
237: .PP
238: If
239: .I label
240: is 0,
241: default action is reinstated.
242: If
243: .I label
244: is 1, the signal is ignored.
245: If
246: .I label
247: is 3, the signal is held.
248: Any other even
249: .I label
250: specifies an address in the process
251: where an interrupt is simulated.
252: If label is otherwise odd, the signal is sent to the function
253: whose address is the label with the low bit cleared
254: with the action set to SIG_HOLD.
255: (Thus DEFERSIG is indicated by the low bit of a signal catch address.
256: An RTI or RTT instruction will return from the
257: interrupt.)
258: .SH "NOTES (VAX-11)"
259: The following defines the mapping of hardware traps to signals:
260: .LP
261: .ta \w' Floating/decimal divide by zero 'u +\w'15* 'u +8n
262: .nf
263: Arithmetic traps:
264: Integer overflow SIGFPE
265: Integer division by zero SIGFPE
266: Floating overflow SIGFPE
267: Floating underflow SIGFPE
268: Floating/decimal division by zero SIGFPE
269: Decimal overflow SIGFPE
270: Subscript-range SIGFPE
271: Length access control SIGSEGV
272: Protection violation SIGBUS
273: Reserved instruction SIGILL
274: Customer-reserved instr. SIGEMT
275: Reserved operand SIGILL
276: Reserved addressing SIGILL
277: Trace pending SIGTRAP
278: Bpt instruction SIGTRAP
279: Compatibility-mode SIGEMT
280: Chme SIGILL
281: Chms SIGILL
282: Chmu SIGILL
283: .fi
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