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
51static 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
85static void
86init_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
110typedef _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'. */
115typedef struct
116{
117 volatile action_t action;
118}
119actions_entry_t;
120
121/* The registered cleanup actions. */
122static actions_entry_t static_actions[32];
123static actions_entry_t * volatile actions = static_actions;
124static sig_atomic_t volatile actions_count = 0;
125static 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. */
130static struct sigaction saved_sigactions[64];
131
132
133/* Uninstall the handlers. */
134static _GL_ASYNC_SAFE void
135uninstall_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. */
151static _GL_ASYNC_SAFE void
152fatal_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. */
179static void
180install_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. */
205void
206at_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
251static sigset_t fatal_signal_set;
252
253static void
254init_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. */
273void
274block_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. */
281void
282unblock_fatal_signals (void)
283{
284 init_fatal_signal_set ();
285 sigprocmask (SIG_UNBLOCK, &fatal_signal_set, NULL);
286}
287
288
289unsigned int
290get_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