trap.c revision 287750 
1/*-
2 * Copyright (c) 1991, 1993
3 *	The Regents of the University of California.  All rights reserved.
4 *
5 * This code is derived from software contributed to Berkeley by
6 * Kenneth Almquist.
7 *
8 * Redistribution and use in source and binary forms, with or without
9 * modification, are permitted provided that the following conditions
10 * are met:
11 * 1. Redistributions of source code must retain the above copyright
12 *    notice, this list of conditions and the following disclaimer.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 *    notice, this list of conditions and the following disclaimer in the
15 *    documentation and/or other materials provided with the distribution.
16 * 4. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#ifndef lint
34#if 0
35static char sccsid[] = "@(#)trap.c	8.5 (Berkeley) 6/5/95";
36#endif
37#endif /* not lint */
38#include <sys/cdefs.h>
39__FBSDID("$FreeBSD: stable/10/bin/sh/trap.c 287750 2015-09-13 13:43:08Z jilles $");
40
41#include <signal.h>
42#include <unistd.h>
43#include <stdlib.h>
44
45#include "shell.h"
46#include "main.h"
47#include "nodes.h"	/* for other headers */
48#include "eval.h"
49#include "jobs.h"
50#include "show.h"
51#include "options.h"
52#include "syntax.h"
53#include "output.h"
54#include "memalloc.h"
55#include "error.h"
56#include "trap.h"
57#include "mystring.h"
58#include "builtins.h"
59#include "myhistedit.h"
60
61
62/*
63 * Sigmode records the current value of the signal handlers for the various
64 * modes.  A value of zero means that the current handler is not known.
65 * S_HARD_IGN indicates that the signal was ignored on entry to the shell,
66 */
67
68#define S_DFL 1			/* default signal handling (SIG_DFL) */
69#define S_CATCH 2		/* signal is caught */
70#define S_IGN 3			/* signal is ignored (SIG_IGN) */
71#define S_HARD_IGN 4		/* signal is ignored permanently */
72#define S_RESET 5		/* temporary - to reset a hard ignored sig */
73
74
75static char sigmode[NSIG];	/* current value of signal */
76volatile sig_atomic_t pendingsig;	/* indicates some signal received */
77volatile sig_atomic_t pendingsig_waitcmd;	/* indicates SIGINT/SIGQUIT received */
78int in_dotrap;			/* do we execute in a trap handler? */
79static char *volatile trap[NSIG];	/* trap handler commands */
80static volatile sig_atomic_t gotsig[NSIG];
81				/* indicates specified signal received */
82static int ignore_sigchld;	/* Used while handling SIGCHLD traps. */
83static int last_trapsig;
84
85static int exiting;		/* exitshell() has been called */
86static int exiting_exitstatus;	/* value passed to exitshell() */
87
88static int getsigaction(int, sig_t *);
89
90
91/*
92 * Map a string to a signal number.
93 *
94 * Note: the signal number may exceed NSIG.
95 */
96static int
97sigstring_to_signum(char *sig)
98{
99
100	if (is_number(sig)) {
101		int signo;
102
103		signo = atoi(sig);
104		return ((signo >= 0 && signo < NSIG) ? signo : (-1));
105	} else if (strcasecmp(sig, "EXIT") == 0) {
106		return (0);
107	} else {
108		int n;
109
110		if (strncasecmp(sig, "SIG", 3) == 0)
111			sig += 3;
112		for (n = 1; n < sys_nsig; n++)
113			if (sys_signame[n] &&
114			    strcasecmp(sys_signame[n], sig) == 0)
115				return (n);
116	}
117	return (-1);
118}
119
120
121/*
122 * Print a list of valid signal names.
123 */
124static void
125printsignals(void)
126{
127	int n, outlen;
128
129	outlen = 0;
130	for (n = 1; n < sys_nsig; n++) {
131		if (sys_signame[n]) {
132			out1fmt("%s", sys_signame[n]);
133			outlen += strlen(sys_signame[n]);
134		} else {
135			out1fmt("%d", n);
136			outlen += 3;	/* good enough */
137		}
138		++outlen;
139		if (outlen > 71 || n == sys_nsig - 1) {
140			out1str("\n");
141			outlen = 0;
142		} else {
143			out1c(' ');
144		}
145	}
146}
147
148
149/*
150 * The trap builtin.
151 */
152int
153trapcmd(int argc __unused, char **argv)
154{
155	char *action;
156	int signo;
157	int errors = 0;
158	int i;
159
160	while ((i = nextopt("l")) != '\0') {
161		switch (i) {
162		case 'l':
163			printsignals();
164			return (0);
165		}
166	}
167	argv = argptr;
168
169	if (*argv == NULL) {
170		for (signo = 0 ; signo < sys_nsig ; signo++) {
171			if (signo < NSIG && trap[signo] != NULL) {
172				out1str("trap -- ");
173				out1qstr(trap[signo]);
174				if (signo == 0) {
175					out1str(" EXIT\n");
176				} else if (sys_signame[signo]) {
177					out1fmt(" %s\n", sys_signame[signo]);
178				} else {
179					out1fmt(" %d\n", signo);
180				}
181			}
182		}
183		return 0;
184	}
185	action = NULL;
186	if (*argv && sigstring_to_signum(*argv) == -1) {
187		if (strcmp(*argv, "-") == 0)
188			argv++;
189		else {
190			action = *argv;
191			argv++;
192		}
193	}
194	for (; *argv; argv++) {
195		if ((signo = sigstring_to_signum(*argv)) == -1) {
196			warning("bad signal %s", *argv);
197			errors = 1;
198			continue;
199		}
200		INTOFF;
201		if (action)
202			action = savestr(action);
203		if (trap[signo])
204			ckfree(trap[signo]);
205		trap[signo] = action;
206		if (signo != 0)
207			setsignal(signo);
208		INTON;
209	}
210	return errors;
211}
212
213
214/*
215 * Clear traps on a fork.
216 */
217void
218clear_traps(void)
219{
220	char *volatile *tp;
221
222	for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
223		if (*tp && **tp) {	/* trap not NULL or SIG_IGN */
224			INTOFF;
225			ckfree(*tp);
226			*tp = NULL;
227			if (tp != &trap[0])
228				setsignal(tp - trap);
229			INTON;
230		}
231	}
232}
233
234
235/*
236 * Check if we have any traps enabled.
237 */
238int
239have_traps(void)
240{
241	char *volatile *tp;
242
243	for (tp = trap ; tp <= &trap[NSIG - 1] ; tp++) {
244		if (*tp && **tp)	/* trap not NULL or SIG_IGN */
245			return 1;
246	}
247	return 0;
248}
249
250/*
251 * Set the signal handler for the specified signal.  The routine figures
252 * out what it should be set to.
253 */
254void
255setsignal(int signo)
256{
257	int action;
258	sig_t sigact = SIG_DFL;
259	struct sigaction sa;
260	char *t;
261
262	if ((t = trap[signo]) == NULL)
263		action = S_DFL;
264	else if (*t != '\0')
265		action = S_CATCH;
266	else
267		action = S_IGN;
268	if (action == S_DFL) {
269		switch (signo) {
270		case SIGINT:
271			action = S_CATCH;
272			break;
273		case SIGQUIT:
274#ifdef DEBUG
275			{
276			extern int debug;
277
278			if (debug)
279				break;
280			}
281#endif
282			action = S_CATCH;
283			break;
284		case SIGTERM:
285			if (rootshell && iflag)
286				action = S_IGN;
287			break;
288#if JOBS
289		case SIGTSTP:
290		case SIGTTOU:
291			if (rootshell && mflag)
292				action = S_IGN;
293			break;
294#endif
295		}
296	}
297
298	t = &sigmode[signo];
299	if (*t == 0) {
300		/*
301		 * current setting unknown
302		 */
303		if (!getsigaction(signo, &sigact)) {
304			/*
305			 * Pretend it worked; maybe we should give a warning
306			 * here, but other shells don't. We don't alter
307			 * sigmode, so that we retry every time.
308			 */
309			return;
310		}
311		if (sigact == SIG_IGN) {
312			if (mflag && (signo == SIGTSTP ||
313			     signo == SIGTTIN || signo == SIGTTOU)) {
314				*t = S_IGN;	/* don't hard ignore these */
315			} else
316				*t = S_HARD_IGN;
317		} else {
318			*t = S_RESET;	/* force to be set */
319		}
320	}
321	if (*t == S_HARD_IGN || *t == action)
322		return;
323	switch (action) {
324		case S_DFL:	sigact = SIG_DFL;	break;
325		case S_CATCH:  	sigact = onsig;		break;
326		case S_IGN:	sigact = SIG_IGN;	break;
327	}
328	*t = action;
329	sa.sa_handler = sigact;
330	sa.sa_flags = 0;
331	sigemptyset(&sa.sa_mask);
332	sigaction(signo, &sa, NULL);
333}
334
335
336/*
337 * Return the current setting for sig w/o changing it.
338 */
339static int
340getsigaction(int signo, sig_t *sigact)
341{
342	struct sigaction sa;
343
344	if (sigaction(signo, (struct sigaction *)0, &sa) == -1)
345		return 0;
346	*sigact = (sig_t) sa.sa_handler;
347	return 1;
348}
349
350
351/*
352 * Ignore a signal.
353 */
354void
355ignoresig(int signo)
356{
357
358	if (sigmode[signo] == 0)
359		setsignal(signo);
360	if (sigmode[signo] != S_IGN && sigmode[signo] != S_HARD_IGN) {
361		signal(signo, SIG_IGN);
362		sigmode[signo] = S_IGN;
363	}
364}
365
366
367int
368issigchldtrapped(void)
369{
370
371	return (trap[SIGCHLD] != NULL && *trap[SIGCHLD] != '\0');
372}
373
374
375/*
376 * Signal handler.
377 */
378void
379onsig(int signo)
380{
381
382	if (signo == SIGINT && trap[SIGINT] == NULL) {
383		onint();
384		return;
385	}
386
387	/* If we are currently in a wait builtin, prepare to break it */
388	if (signo == SIGINT || signo == SIGQUIT)
389		pendingsig_waitcmd = signo;
390
391	if (trap[signo] != NULL && trap[signo][0] != '\0' &&
392	    (signo != SIGCHLD || !ignore_sigchld)) {
393		gotsig[signo] = 1;
394		pendingsig = signo;
395	}
396}
397
398
399/*
400 * Called to execute a trap.  Perhaps we should avoid entering new trap
401 * handlers while we are executing a trap handler.
402 */
403void
404dotrap(void)
405{
406	int i;
407	int savestatus, prev_evalskip, prev_skipcount;
408
409	in_dotrap++;
410	for (;;) {
411		pendingsig = 0;
412		pendingsig_waitcmd = 0;
413		for (i = 1; i < NSIG; i++) {
414			if (gotsig[i]) {
415				gotsig[i] = 0;
416				if (trap[i]) {
417					/*
418					 * Ignore SIGCHLD to avoid infinite
419					 * recursion if the trap action does
420					 * a fork.
421					 */
422					if (i == SIGCHLD)
423						ignore_sigchld++;
424
425					/*
426					 * Backup current evalskip
427					 * state and reset it before
428					 * executing a trap, so that the
429					 * trap is not disturbed by an
430					 * ongoing break/continue/return
431					 * statement.
432					 */
433					prev_evalskip  = evalskip;
434					prev_skipcount = skipcount;
435					evalskip = 0;
436
437					last_trapsig = i;
438					savestatus = exitstatus;
439					evalstring(trap[i], 0);
440
441					/*
442					 * If such a command was not
443					 * already in progress, allow a
444					 * break/continue/return in the
445					 * trap action to have an effect
446					 * outside of it.
447					 */
448					if (evalskip == 0 ||
449					    prev_evalskip != 0) {
450						evalskip  = prev_evalskip;
451						skipcount = prev_skipcount;
452						exitstatus = savestatus;
453					}
454
455					if (i == SIGCHLD)
456						ignore_sigchld--;
457				}
458				break;
459			}
460		}
461		if (i >= NSIG)
462			break;
463	}
464	in_dotrap--;
465}
466
467
468/*
469 * Controls whether the shell is interactive or not.
470 */
471void
472setinteractive(int on)
473{
474	static int is_interactive = -1;
475
476	if (on == is_interactive)
477		return;
478	setsignal(SIGINT);
479	setsignal(SIGQUIT);
480	setsignal(SIGTERM);
481	is_interactive = on;
482}
483
484
485/*
486 * Called to exit the shell.
487 */
488void
489exitshell(int status)
490{
491	TRACE(("exitshell(%d) pid=%d\n", status, getpid()));
492	exiting = 1;
493	exiting_exitstatus = status;
494	exitshell_savedstatus();
495}
496
497void
498exitshell_savedstatus(void)
499{
500	struct jmploc loc1, loc2;
501	char *p;
502	int sig = 0;
503	sigset_t sigs;
504
505	if (!exiting) {
506		if (in_dotrap && last_trapsig) {
507			sig = last_trapsig;
508			exiting_exitstatus = sig + 128;
509		} else
510			exiting_exitstatus = oexitstatus;
511	}
512	exitstatus = oexitstatus = exiting_exitstatus;
513	if (!setjmp(loc1.loc)) {
514		handler = &loc1;
515		if ((p = trap[0]) != NULL && *p != '\0') {
516			/*
517			 * Reset evalskip, or the trap on EXIT could be
518			 * interrupted if the last command was a "return".
519			 */
520			evalskip = 0;
521			trap[0] = NULL;
522			evalstring(p, 0);
523		}
524	}
525	if (!setjmp(loc2.loc)) {
526		handler = &loc2;		/* probably unnecessary */
527		flushall();
528#if JOBS
529		setjobctl(0);
530#endif
531	}
532	if (sig != 0 && sig != SIGSTOP && sig != SIGTSTP && sig != SIGTTIN &&
533	    sig != SIGTTOU) {
534		signal(sig, SIG_DFL);
535		sigemptyset(&sigs);
536		sigaddset(&sigs, sig);
537		sigprocmask(SIG_UNBLOCK, &sigs, NULL);
538		kill(getpid(), sig);
539		/* If the default action is to ignore, fall back to _exit(). */
540	}
541	_exit(exiting_exitstatus);
542}
543