1/* Catch segmentation faults and print backtrace.
2 Copyright (C) 1998-2020 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <https://www.gnu.org/licenses/>. */
19
20#include <alloca.h>
21#include <ctype.h>
22#include <errno.h>
23#include <execinfo.h>
24#include <fcntl.h>
25#include <signal.h>
26#include <stdint.h>
27#include <stdio.h>
28#include <stdlib.h>
29#include <string.h>
30#include <unistd.h>
31#include <_itoa.h>
32#include <ldsodefs.h>
33
34/* This file defines macros to access the content of the sigcontext element
35 passed up by the signal handler. */
36#include <sigcontextinfo.h>
37
38#ifdef SA_SIGINFO
39# define SIGCONTEXT siginfo_t *info, void *
40#endif
41
42/* Get code to possibly dump the content of all registers. */
43#include <register-dump.h>
44
45/* We'll use this a lot. */
46#define WRITE_STRING(s) write (fd, s, strlen (s))
47
48/* Name of the output file. */
49static const char *fname;
50
51
52/* We better should not use `strerror' since it can call far too many
53 other functions which might fail. Do it here ourselves. */
54static void
55write_strsignal (int fd, int signal)
56{
57 if (signal < 0 || signal >= _NSIG || _sys_siglist[signal] == NULL)
58 {
59 char buf[30];
60 char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
61 WRITE_STRING ("signal ");
62 write (fd, buf, &buf[sizeof (buf)] - ptr);
63 }
64 else
65 WRITE_STRING (_sys_siglist[signal]);
66}
67
68
69/* This function is called when a segmentation fault is caught. The system
70 is in an unstable state now. This means especially that malloc() might
71 not work anymore. */
72static void
73catch_segfault (int signal, SIGCONTEXT ctx)
74{
75 int fd, cnt, i;
76 void **arr;
77 struct sigaction sa;
78 uintptr_t pc;
79
80 /* This is the name of the file we are writing to. If none is given
81 or we cannot write to this file write to stderr. */
82 fd = 2;
83 if (fname != NULL)
84 {
85 fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT, 0666);
86 if (fd == -1)
87 fd = 2;
88 }
89
90 WRITE_STRING ("*** ");
91 write_strsignal (fd, signal);
92 WRITE_STRING ("\n");
93
94#ifdef REGISTER_DUMP
95 REGISTER_DUMP;
96#endif
97
98 WRITE_STRING ("\nBacktrace:\n");
99
100 /* Get the backtrace. */
101 arr = alloca (256 * sizeof (void *));
102 cnt = backtrace (arr, 256);
103
104 /* Now try to locate the PC from signal context in the backtrace.
105 Normally it will be found at arr[2], but it might appear later
106 if there were some signal handler wrappers. Allow a few bytes
107 difference to cope with as many arches as possible. */
108 pc = sigcontext_get_pc (ctx);
109 for (i = 0; i < cnt; ++i)
110 if ((uintptr_t) arr[i] >= pc - 16 && (uintptr_t) arr[i] <= pc + 16)
111 break;
112
113 /* If we haven't found it, better dump full backtrace even including
114 the signal handler frames instead of not dumping anything. */
115 if (i == cnt)
116 i = 0;
117
118 /* Now generate nicely formatted output. */
119 __backtrace_symbols_fd (arr + i, cnt - i, fd);
120
121#ifdef HAVE_PROC_SELF
122 /* Now the link map. */
123 int mapfd = open ("/proc/self/maps", O_RDONLY);
124 if (mapfd != -1)
125 {
126 write (fd, "\nMemory map:\n\n", 14);
127
128 char buf[256];
129 ssize_t n;
130
131 while ((n = TEMP_FAILURE_RETRY (read (mapfd, buf, sizeof (buf)))) > 0)
132 TEMP_FAILURE_RETRY (write (fd, buf, n));
133
134 close (mapfd);
135 }
136#endif
137
138 /* Pass on the signal (so that a core file is produced). */
139 sa.sa_handler = SIG_DFL;
140 sigemptyset (&sa.sa_mask);
141 sa.sa_flags = 0;
142 sigaction (signal, &sa, NULL);
143 raise (signal);
144}
145
146
147static void
148__attribute__ ((constructor))
149install_handler (void)
150{
151 struct sigaction sa;
152 const char *sigs = getenv ("SEGFAULT_SIGNALS");
153 const char *name;
154
155#ifdef SA_SIGINFO
156 sa.sa_sigaction = catch_segfault;
157 sa.sa_flags = SA_SIGINFO;
158#else
159 sa.sa_handler = (void*) catch_segfault;
160 sa.sa_flags = 0;
161#endif
162 sigemptyset (&sa.sa_mask);
163 sa.sa_flags |= SA_RESTART;
164
165 /* Maybe we are expected to use an alternative stack. */
166 if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
167 {
168 void *stack_mem = malloc (2 * SIGSTKSZ);
169 stack_t ss;
170
171 if (stack_mem != NULL)
172 {
173 ss.ss_sp = stack_mem;
174 ss.ss_flags = 0;
175 ss.ss_size = 2 * SIGSTKSZ;
176
177 if (sigaltstack (&ss, NULL) == 0)
178 sa.sa_flags |= SA_ONSTACK;
179 }
180 }
181
182 if (sigs == NULL)
183 sigaction (SIGSEGV, &sa, NULL);
184 else if (sigs[0] == '\0')
185 /* Do not do anything. */
186 return;
187 else
188 {
189 const char *where;
190 int all = __strcasecmp (sigs, "all") == 0;
191
192#define INSTALL_FOR_SIG(sig, name) \
193 where = __strcasestr (sigs, name); \
194 if (all || (where != NULL \
195 && (where == sigs || !isalnum (where[-1])) \
196 && !isalnum (where[sizeof (name) - 1]))) \
197 sigaction (sig, &sa, NULL);
198
199 INSTALL_FOR_SIG (SIGSEGV, "segv");
200 INSTALL_FOR_SIG (SIGILL, "ill");
201#ifdef SIGBUS
202 INSTALL_FOR_SIG (SIGBUS, "bus");
203#endif
204#ifdef SIGSTKFLT
205 INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
206#endif
207 INSTALL_FOR_SIG (SIGABRT, "abrt");
208 INSTALL_FOR_SIG (SIGFPE, "fpe");
209 }
210
211 /* Preserve the output file name if there is any given. */
212 name = getenv ("SEGFAULT_OUTPUT_NAME");
213 if (name != NULL && name[0] != '\0')
214 {
215 int ret = access (name, R_OK | W_OK);
216
217 if (ret == 0 || (ret == -1 && errno == ENOENT))
218 fname = __strdup (name);
219 }
220}
221