1 /*
2  * Signal handling for Plan 9 programs. 
3  * We stubbornly use the strings from Plan 9 instead 
4  * of the enumerated Unix constants.  
5  * There are some weird translations.  In particular,
6  * a "kill" note is the same as SIGTERM in Unix.
7  * There is no equivalent note to Unix's SIGKILL, since
8  * it's not a deliverable signal anyway.
9  *
10  * We do not handle SIGABRT or SIGSEGV, mainly so that
11  * stack traces show the original source of the signal instead
12  * of notifysigf.
13  *
14  * We have to add some extra entry points to provide the
15  * ability to tweak which signals are deliverable and which
16  * are acted upon.  Notifydisable and notifyenable play with
17  * the process signal mask.  Notifyignore enables the signal
18  * but will not call notifyf when it comes in.  This is occasionally
19  * useful.
20  */
21 
22 #include <u.h>
23 #include <signal.h>
24 #define NOPLAN9DEFINES
25 #include <libc.h>
26 
27 extern char *_p9sigstr(int, char*);
28 extern int _p9strsig(char*);
29 
30 typedef struct Sig Sig;
31 struct Sig
32 {
33 	int sig;			/* signal number */
34 	int restart;			/* do we restart the system call after this signal is handled? */
35 	int enabled;		/* is this signal enabled (not masked)? */
36 	int notified;		/* do we call the notify function for this signal? */
37 };
38 
39 /* initial settings; for current status, ask the kernel */
40 static Sig sigs[] = {
41 	SIGHUP, 0, 1, 1,
42 	SIGINT, 0, 1, 1,
43 	SIGQUIT, 0, 1, 1,
44 	SIGILL, 0, 1, 1,
45 	SIGTRAP, 0, 1, 1,
46 /*	SIGABRT, 0, 1, 1,	*/
47 #ifdef SIGEMT
48 	SIGEMT, 0, 1, 1,
49 #endif
50 	SIGFPE, 0, 1, 1,
51 	SIGBUS, 0, 1, 1,
52 /*	SIGSEGV, 0, 1, 1,	*/
53 	SIGCHLD, 1, 0, 1,
54 	SIGSYS, 0, 1, 1,
55 	SIGPIPE, 0, 0, 1,
56 	SIGALRM, 0, 1, 1,
57 	SIGTERM, 0, 1, 1,
58 	SIGTSTP, 1, 0, 1,
59 	SIGTTIN, 1, 0, 1,
60 	SIGTTOU, 1, 0, 1,
61 	SIGXCPU, 0, 1, 1,
62 	SIGXFSZ, 0, 1, 1,
63 	SIGVTALRM, 0, 1, 1,
64 	SIGUSR1, 0, 1, 1,
65 	SIGUSR2, 0, 1, 1,
66 	SIGWINCH, 1, 0, 1,
67 #ifdef SIGINFO
68 	SIGINFO, 1, 1, 1,
69 #endif
70 };
71 
72 static Sig*
73 findsig(int s)
74 {
75 	int i;
76 
77 	for(i=0; i<nelem(sigs); i++)
78 		if(sigs[i].sig == s)
79 			return &sigs[i];
80 	return nil;
81 }
82 
83 /*
84  * The thread library initializes _notejmpbuf to its own
85  * routine which provides a per-pthread jump buffer.
86  * If we're not using the thread library, we assume we are
87  * single-threaded.
88  */
89 typedef struct Jmp Jmp;
90 struct Jmp
91 {
92 	p9jmp_buf b;
93 };
94 
95 static Jmp onejmp;
96 
97 static Jmp*
98 getonejmp(void)
99 {
100 	return &onejmp;
101 }
102 
103 Jmp *(*_notejmpbuf)(void) = getonejmp;
104 static void noteinit(void);
105 
106 /*
107  * Actual signal handler. 
108  */
109 
110 static void (*notifyf)(void*, char*);	/* Plan 9 handler */
111 
112 static void
113 signotify(int sig)
114 {
115 	int v;
116 	char tmp[64];
117 	Jmp *j;
118 
119 	j = (*_notejmpbuf)();
120 	switch(p9setjmp(j->b)){
121 	case 0:
122 		if(notifyf)
123 			(*notifyf)(nil, _p9sigstr(sig, tmp));
124 		/* fall through */
125 	case 1:	/* noted(NDFLT) */
126 		if(0)print("DEFAULT %d\n", sig);
127 		signal(sig, SIG_DFL);
128 		raise(sig);
129 		_exit(1);
130 	case 2:	/* noted(NCONT) */
131 		if(0)print("HANDLED %d\n", sig);
132 		return;
133 	}
134 }
135 
136 static void
137 signonotify(int sig)
138 {
139 	USED(sig);
140 }
141 
142 int
143 noted(int v)
144 {
145 	p9longjmp((*_notejmpbuf)()->b, v==NCONT ? 2 : 1);
146 	abort();
147 	return 0;
148 }
149 
150 int
151 notify(void (*f)(void*, char*))
152 {
153 	int i;
154 	static int init;
155 
156 	notifyf = f;
157 	if(!init){
158 		init = 1;
159 		noteinit();
160 	}
161 	return 0;
162 }
163 
164 /*
165  * Nonsense about enabling and disabling signals.
166  */
167 static void(*)(int)
168 handler(int s)
169 {
170 	struct sigaction sa;
171 
172 	sigaction(s, nil, &sa);
173 	return sa.sa_handler;
174 }
175 
176 static void
177 notifysetenable(int sig, int enabled)
178 {
179 	sigset_t mask;
180 
181 	if(sig == 0)
182 		return;
183 
184 	sigemptyset(&mask);
185 	sigaddset(&mask, sig);
186 	sigprocmask(enabled ? SIG_UNBLOCK : SIG_BLOCK, &mask, nil);
187 }
188 
189 void
190 notifyenable(char *msg)
191 {
192 	notifyenablex(_p9strsig(msg), 1);
193 }
194 
195 void
196 notifydisable(char *msg)
197 {
198 	notifyenablex(_p9strsig(msg), 0);
199 }
200 
201 static void
202 notifyseton(int s, int on)
203 {
204 	Sig *sig;
205 	struct sigaction sa;
206 
207 	sig = findsig(s);
208 	if(sig == nil)
209 		return;
210 	notifyenable(msg);
211 	memset(&sa, 0, sizeof sa);
212 	sa.sa_handler = on ? signotify : signonotify;
213 	if(sig->restart)
214 		sa.sa_flags |= SA_RESTART;
215 
216 	/*
217 	 * We can't allow signals within signals because there's
218 	 * only one jump buffer.
219 	 */
220 	sigfillset(&sa.sa_mask);
221 
222 	/*
223 	 * Install handler.
224 	 */
225 	sigaction(sig->sig, &sa, nil);
226 }
227 
228 void
229 notifyon(char *msg)
230 {
231 	notifyseton(_p9strsig(msg), 1);
232 }
233 
234 void
235 notifyoff(char *msg)
236 {
237 	notifysetoff(_p9strsig(msg), 0);
238 }
239 
240 /*
241  * Initialization follows sigs table.
242  */
243 static void
244 noteinit(void)
245 {
246 	int i;
247 	Sig *sig;
248 
249 	for(i=0; i<nelem(sigs); i++){
250 		sig = &sigs[i];
251 		/*
252 		 * If someone has already installed a handler,
253 		 * It's probably some ld preload nonsense,
254 		 * like pct (a SIGVTALRM-based profiler).
255 		 * Leave it alone.
256 		 */
257 		if(handler(sig->sig) != SIG_DFL)
258 			continue;
259 		/*
260 		 * Should we only disable and not enable signals?
261 		 * (I.e. if parent has disabled for us, should we still enable?)
262 		 * Right now we always initialize to the state we want.
263 		 */
264 		notifysetenable(sig->sig, sig->enabled);
265 		notifyseton(sig->sig, sig->notified);
266 	}
267 }
268