1 | /* Emergency actions in case of a fatal signal. |
2 | Copyright (C) 2003-2004, 2006-2019 Free Software Foundation, Inc. |
3 | Written by Bruno Haible <bruno@clisp.org>, 2003. |
4 | |
5 | This program is free software: you can redistribute it and/or modify |
6 | it under the terms of the GNU General Public License as published by |
7 | the Free Software Foundation; either version 3 of the License, or |
8 | (at your option) any later version. |
9 | |
10 | This program is distributed in the hope that it will be useful, |
11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
13 | GNU General Public License for more details. |
14 | |
15 | You should have received a copy of the GNU General Public License |
16 | along with this program. If not, see <https://www.gnu.org/licenses/>. */ |
17 | |
18 | |
19 | #include <config.h> |
20 | |
21 | /* Specification. */ |
22 | #include "fatal-signal.h" |
23 | |
24 | #include <stdbool.h> |
25 | #include <stdlib.h> |
26 | #include <signal.h> |
27 | #include <unistd.h> |
28 | |
29 | #include "sig-handler.h" |
30 | #include "xalloc.h" |
31 | |
32 | #define SIZEOF(a) (sizeof(a) / sizeof(a[0])) |
33 | |
34 | /* ========================================================================= */ |
35 | |
36 | |
37 | /* The list of fatal signals. |
38 | These are those signals whose default action is to terminate the process |
39 | without a core dump, except |
40 | SIGKILL - because it cannot be caught, |
41 | SIGALRM SIGUSR1 SIGUSR2 SIGPOLL SIGIO SIGLOST - because applications |
42 | often use them for their own purpose, |
43 | SIGPROF SIGVTALRM - because they are used for profiling, |
44 | SIGSTKFLT - because it is more similar to SIGFPE, SIGSEGV, SIGBUS, |
45 | SIGSYS - because it is more similar to SIGABRT, SIGSEGV, |
46 | SIGPWR - because it of too special use, |
47 | SIGRTMIN...SIGRTMAX - because they are reserved for application use. |
48 | plus |
49 | SIGXCPU, SIGXFSZ - because they are quite similar to SIGTERM. */ |
50 | |
51 | static int fatal_signals[] = |
52 | { |
53 | /* ISO C 99 signals. */ |
54 | #ifdef SIGINT |
55 | SIGINT, |
56 | #endif |
57 | #ifdef SIGTERM |
58 | SIGTERM, |
59 | #endif |
60 | /* POSIX:2001 signals. */ |
61 | #ifdef SIGHUP |
62 | SIGHUP, |
63 | #endif |
64 | #ifdef SIGPIPE |
65 | SIGPIPE, |
66 | #endif |
67 | /* BSD signals. */ |
68 | #ifdef SIGXCPU |
69 | SIGXCPU, |
70 | #endif |
71 | #ifdef SIGXFSZ |
72 | SIGXFSZ, |
73 | #endif |
74 | /* Native Windows signals. */ |
75 | #ifdef SIGBREAK |
76 | SIGBREAK, |
77 | #endif |
78 | 0 |
79 | }; |
80 | |
81 | #define num_fatal_signals (SIZEOF (fatal_signals) - 1) |
82 | |
83 | /* Eliminate signals whose signal handler is SIG_IGN. */ |
84 | |
85 | static void |
86 | init_fatal_signals (void) |
87 | { |
88 | static bool fatal_signals_initialized = false; |
89 | if (!fatal_signals_initialized) |
90 | { |
91 | size_t i; |
92 | |
93 | for (i = 0; i < num_fatal_signals; i++) |
94 | { |
95 | struct sigaction action; |
96 | |
97 | if (sigaction (fatal_signals[i], NULL, &action) >= 0 |
98 | && get_handler (&action) == SIG_IGN) |
99 | fatal_signals[i] = -1; |
100 | } |
101 | |
102 | fatal_signals_initialized = true; |
103 | } |
104 | } |
105 | |
106 | |
107 | /* ========================================================================= */ |
108 | |
109 | |
110 | typedef _GL_ASYNC_SAFE void (*action_t) (int sig); |
111 | |
112 | /* Type of an entry in the actions array. |
113 | The 'action' field is accessed from within the fatal_signal_handler(), |
114 | therefore we mark it as 'volatile'. */ |
115 | typedef struct |
116 | { |
117 | volatile action_t action; |
118 | } |
119 | actions_entry_t; |
120 | |
121 | /* The registered cleanup actions. */ |
122 | static actions_entry_t static_actions[32]; |
123 | static actions_entry_t * volatile actions = static_actions; |
124 | static sig_atomic_t volatile actions_count = 0; |
125 | static size_t actions_allocated = SIZEOF (static_actions); |
126 | |
127 | |
128 | /* The saved signal handlers. |
129 | Size 32 would not be sufficient: On HP-UX, SIGXCPU = 33, SIGXFSZ = 34. */ |
130 | static struct sigaction saved_sigactions[64]; |
131 | |
132 | |
133 | /* Uninstall the handlers. */ |
134 | static _GL_ASYNC_SAFE void |
135 | uninstall_handlers (void) |
136 | { |
137 | size_t i; |
138 | |
139 | for (i = 0; i < num_fatal_signals; i++) |
140 | if (fatal_signals[i] >= 0) |
141 | { |
142 | int sig = fatal_signals[i]; |
143 | if (saved_sigactions[sig].sa_handler == SIG_IGN) |
144 | saved_sigactions[sig].sa_handler = SIG_DFL; |
145 | sigaction (sig, &saved_sigactions[sig], NULL); |
146 | } |
147 | } |
148 | |
149 | |
150 | /* The signal handler. It gets called asynchronously. */ |
151 | static _GL_ASYNC_SAFE void |
152 | fatal_signal_handler (int sig) |
153 | { |
154 | for (;;) |
155 | { |
156 | /* Get the last registered cleanup action, in a reentrant way. */ |
157 | action_t action; |
158 | size_t n = actions_count; |
159 | if (n == 0) |
160 | break; |
161 | n--; |
162 | actions_count = n; |
163 | action = actions[n].action; |
164 | /* Execute the action. */ |
165 | action (sig); |
166 | } |
167 | |
168 | /* Now execute the signal's default action. |
169 | If the signal being delivered was blocked, the re-raised signal would be |
170 | delivered when this handler returns. But the way we install this handler, |
171 | no signal is blocked, and the re-raised signal is delivered already |
172 | during raise(). */ |
173 | uninstall_handlers (); |
174 | raise (sig); |
175 | } |
176 | |
177 | |
178 | /* Install the handlers. */ |
179 | static void |
180 | install_handlers (void) |
181 | { |
182 | size_t i; |
183 | struct sigaction action; |
184 | |
185 | action.sa_handler = &fatal_signal_handler; |
186 | /* If we get a fatal signal while executing fatal_signal_handler, enter |
187 | fatal_signal_handler recursively, since it is reentrant. Hence no |
188 | SA_RESETHAND. */ |
189 | action.sa_flags = SA_NODEFER; |
190 | sigemptyset (&action.sa_mask); |
191 | for (i = 0; i < num_fatal_signals; i++) |
192 | if (fatal_signals[i] >= 0) |
193 | { |
194 | int sig = fatal_signals[i]; |
195 | |
196 | if (!(sig < sizeof (saved_sigactions) / sizeof (saved_sigactions[0]))) |
197 | abort (); |
198 | sigaction (sig, &action, &saved_sigactions[sig]); |
199 | } |
200 | } |
201 | |
202 | |
203 | /* Register a cleanup function to be executed when a catchable fatal signal |
204 | occurs. */ |
205 | void |
206 | at_fatal_signal (action_t action) |
207 | { |
208 | static bool cleanup_initialized = false; |
209 | if (!cleanup_initialized) |
210 | { |
211 | init_fatal_signals (); |
212 | install_handlers (); |
213 | cleanup_initialized = true; |
214 | } |
215 | |
216 | if (actions_count == actions_allocated) |
217 | { |
218 | /* Extend the actions array. Note that we cannot use xrealloc(), |
219 | because then the cleanup() function could access an already |
220 | deallocated array. */ |
221 | actions_entry_t *old_actions = actions; |
222 | size_t old_actions_allocated = actions_allocated; |
223 | size_t new_actions_allocated = 2 * actions_allocated; |
224 | actions_entry_t *new_actions = |
225 | XNMALLOC (new_actions_allocated, actions_entry_t); |
226 | size_t k; |
227 | |
228 | /* Don't use memcpy() here, because memcpy takes non-volatile arguments |
229 | and is therefore not guaranteed to complete all memory stores before |
230 | the next statement. */ |
231 | for (k = 0; k < old_actions_allocated; k++) |
232 | new_actions[k] = old_actions[k]; |
233 | actions = new_actions; |
234 | actions_allocated = new_actions_allocated; |
235 | /* Now we can free the old actions array. */ |
236 | if (old_actions != static_actions) |
237 | free (old_actions); |
238 | } |
239 | /* The two uses of 'volatile' in the types above (and ISO C 99 section |
240 | 5.1.2.3.(5)) ensure that we increment the actions_count only after |
241 | the new action has been written to the memory location |
242 | actions[actions_count]. */ |
243 | actions[actions_count].action = action; |
244 | actions_count++; |
245 | } |
246 | |
247 | |
248 | /* ========================================================================= */ |
249 | |
250 | |
251 | static sigset_t fatal_signal_set; |
252 | |
253 | static void |
254 | init_fatal_signal_set (void) |
255 | { |
256 | static bool fatal_signal_set_initialized = false; |
257 | if (!fatal_signal_set_initialized) |
258 | { |
259 | size_t i; |
260 | |
261 | init_fatal_signals (); |
262 | |
263 | sigemptyset (&fatal_signal_set); |
264 | for (i = 0; i < num_fatal_signals; i++) |
265 | if (fatal_signals[i] >= 0) |
266 | sigaddset (&fatal_signal_set, fatal_signals[i]); |
267 | |
268 | fatal_signal_set_initialized = true; |
269 | } |
270 | } |
271 | |
272 | /* Temporarily delay the catchable fatal signals. */ |
273 | void |
274 | block_fatal_signals (void) |
275 | { |
276 | init_fatal_signal_set (); |
277 | sigprocmask (SIG_BLOCK, &fatal_signal_set, NULL); |
278 | } |
279 | |
280 | /* Stop delaying the catchable fatal signals. */ |
281 | void |
282 | unblock_fatal_signals (void) |
283 | { |
284 | init_fatal_signal_set (); |
285 | sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL); |
286 | } |
287 | |
288 | |
289 | unsigned int |
290 | get_fatal_signals (int signals[64]) |
291 | { |
292 | init_fatal_signal_set (); |
293 | |
294 | { |
295 | int *p = signals; |
296 | size_t i; |
297 | |
298 | for (i = 0; i < num_fatal_signals; i++) |
299 | if (fatal_signals[i] >= 0) |
300 | *p++ = fatal_signals[i]; |
301 | return p - signals; |
302 | } |
303 | } |
304 | |