1/* Catch segmentation faults and print backtrace.
2 Copyright (C) 1998-2016 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 <http://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/* Get code to possibly dump the content of all registers. */
39#include <register-dump.h>
40
41/* We'll use this a lot. */
42#define WRITE_STRING(s) write (fd, s, strlen (s))
43
44/* Name of the output file. */
45static const char *fname;
46
47
48/* We better should not use `strerror' since it can call far too many
49 other functions which might fail. Do it here ourselves. */
50static void
51write_strsignal (int fd, int signal)
52{
53 if (signal < 0 || signal >= _NSIG || _sys_siglist[signal] == NULL)
54 {
55 char buf[30];
56 char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
57 WRITE_STRING ("signal ");
58 write (fd, buf, &buf[sizeof (buf)] - ptr);
59 }
60 else
61 WRITE_STRING (_sys_siglist[signal]);
62}
63
64
65/* This function is called when a segmentation fault is caught. The system
66 is in an unstable state now. This means especially that malloc() might
67 not work anymore. */
68static void
69catch_segfault (int signal, SIGCONTEXT ctx)
70{
71 int fd, cnt, i;
72 void **arr;
73 struct sigaction sa;
74 uintptr_t pc;
75
76 /* This is the name of the file we are writing to. If none is given
77 or we cannot write to this file write to stderr. */
78 fd = 2;
79 if (fname != NULL)
80 {
81 fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT, 0666);
82 if (fd == -1)
83 fd = 2;
84 }
85
86 WRITE_STRING ("*** ");
87 write_strsignal (fd, signal);
88 WRITE_STRING ("\n");
89
90#ifdef REGISTER_DUMP
91 REGISTER_DUMP;
92#endif
93
94 WRITE_STRING ("\nBacktrace:\n");
95
96 /* Get the backtrace. */
97 arr = alloca (256 * sizeof (void *));
98 cnt = backtrace (arr, 256);
99
100 /* Now try to locate the PC from signal context in the backtrace.
101 Normally it will be found at arr[2], but it might appear later
102 if there were some signal handler wrappers. Allow a few bytes
103 difference to cope with as many arches as possible. */
104 pc = (uintptr_t) GET_PC (ctx);
105 for (i = 0; i < cnt; ++i)
106 if ((uintptr_t) arr[i] >= pc - 16 && (uintptr_t) arr[i] <= pc + 16)
107 break;
108
109 /* If we haven't found it, better dump full backtrace even including
110 the signal handler frames instead of not dumping anything. */
111 if (i == cnt)
112 i = 0;
113
114 /* Now generate nicely formatted output. */
115 __backtrace_symbols_fd (arr + i, cnt - i, fd);
116
117#ifdef HAVE_PROC_SELF
118 /* Now the link map. */
119 int mapfd = open ("/proc/self/maps", O_RDONLY);
120 if (mapfd != -1)
121 {
122 write (fd, "\nMemory map:\n\n", 14);
123
124 char buf[256];
125 ssize_t n;
126
127 while ((n = TEMP_FAILURE_RETRY (read (mapfd, buf, sizeof (buf)))) > 0)
128 TEMP_FAILURE_RETRY (write (fd, buf, n));
129
130 close (mapfd);
131 }
132#endif
133
134 /* Pass on the signal (so that a core file is produced). */
135 sa.sa_handler = SIG_DFL;
136 sigemptyset (&sa.sa_mask);
137 sa.sa_flags = 0;
138 sigaction (signal, &sa, NULL);
139 raise (signal);
140}
141
142
143static void
144__attribute__ ((constructor))
145install_handler (void)
146{
147 struct sigaction sa;
148 const char *sigs = getenv ("SEGFAULT_SIGNALS");
149 const char *name;
150
151 sa.sa_handler = (void *) catch_segfault;
152 sigemptyset (&sa.sa_mask);
153 sa.sa_flags = SA_RESTART;
154
155 /* Maybe we are expected to use an alternative stack. */
156 if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
157 {
158 void *stack_mem = malloc (2 * SIGSTKSZ);
159 struct sigaltstack ss;
160
161 if (stack_mem != NULL)
162 {
163 ss.ss_sp = stack_mem;
164 ss.ss_flags = 0;
165 ss.ss_size = 2 * SIGSTKSZ;
166
167 if (sigaltstack (&ss, NULL) == 0)
168 sa.sa_flags |= SA_ONSTACK;
169 }
170 }
171
172 if (sigs == NULL)
173 sigaction (SIGSEGV, &sa, NULL);
174 else if (sigs[0] == '\0')
175 /* Do not do anything. */
176 return;
177 else
178 {
179 const char *where;
180 int all = __strcasecmp (sigs, "all") == 0;
181
182#define INSTALL_FOR_SIG(sig, name) \
183 where = __strcasestr (sigs, name); \
184 if (all || (where != NULL \
185 && (where == sigs || !isalnum (where[-1])) \
186 && !isalnum (where[sizeof (name) - 1]))) \
187 sigaction (sig, &sa, NULL);
188
189 INSTALL_FOR_SIG (SIGSEGV, "segv");
190 INSTALL_FOR_SIG (SIGILL, "ill");
191#ifdef SIGBUS
192 INSTALL_FOR_SIG (SIGBUS, "bus");
193#endif
194#ifdef SIGSTKFLT
195 INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
196#endif
197 INSTALL_FOR_SIG (SIGABRT, "abrt");
198 INSTALL_FOR_SIG (SIGFPE, "fpe");
199 }
200
201 /* Preserve the output file name if there is any given. */
202 name = getenv ("SEGFAULT_OUTPUT_NAME");
203 if (name != NULL && name[0] != '\0')
204 {
205 int ret = access (name, R_OK | W_OK);
206
207 if (ret == 0 || (ret == -1 && errno == ENOENT))
208 fname = __strdup (name);
209 }
210}
211