debug/segfault.c

   1 /* Catch segmentation faults and print backtrace.
   2    Copyright (C) 1998-2018 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.  */
  45 static 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.  */
  50 static void
  51 write_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.  */
  68 static void
  69 catch_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
 143 static void
 144 __attribute__ ((constructor))
 145 install_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       stack_t 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 }