debug/segfault.c

   1 /* Catch segmentation faults and print backtrace.
   2    Copyright (C) 1998-2013 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 #include <bp-checks.h>
  35
  36 /* This file defines macros to access the content of the sigcontext element
  37    passed up by the signal handler.  */
  38 #include <sigcontextinfo.h>
  39
  40 /* Get code to possibly dump the content of all registers.  */
  41 #include <register-dump.h>
  42
  43 /* We'll use this a lot.  */
  44 #define WRITE_STRING(s) write (fd, s, strlen (s))
  45
  46 /* Name of the output file.  */
  47 static const char *fname;
  48
  49
  50 /* We better should not use `strerror' since it can call far too many
  51    other functions which might fail.  Do it here ourselves.  */
  52 static void
  53 write_strsignal (int fd, int signal)
  54 {
  55   if (signal < 0 || signal >= _NSIG || _sys_siglist[signal] == NULL)
  56     {
  57       char buf[30];
  58       char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
  59       WRITE_STRING ("signal ");
  60       write (fd, buf, &buf[sizeof (buf)] - ptr);
  61     }
  62   else
  63     WRITE_STRING (_sys_siglist[signal]);
  64 }
  65
  66
  67 /* This function is called when a segmentation fault is caught.  The system
  68    is in an unstable state now.  This means especially that malloc() might
  69    not work anymore.  */
  70 static void
  71 catch_segfault (int signal, SIGCONTEXT ctx)
  72 {
  73   int fd, cnt, i;
  74   void **arr;
  75   struct sigaction sa;
  76   uintptr_t pc;
  77
  78   /* This is the name of the file we are writing to.  If none is given
  79      or we cannot write to this file write to stderr.  */
  80   fd = 2;
  81   if (fname != NULL)
  82     {
  83       fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT, 0666);
  84       if (fd == -1)
  85         fd = 2;
  86     }
  87
  88   WRITE_STRING ("*** ");
  89   write_strsignal (fd, signal);
  90   WRITE_STRING ("\n");
  91
  92 #ifdef REGISTER_DUMP
  93   REGISTER_DUMP;
  94 #endif
  95
  96   WRITE_STRING ("\nBacktrace:\n");
  97
  98   /* Get the backtrace.  */
  99   arr = alloca (256 * sizeof (void *));
 100   cnt = backtrace (arr, 256);
 101
 102   /* Now try to locate the PC from signal context in the backtrace.
 103      Normally it will be found at arr[2], but it might appear later
 104      if there were some signal handler wrappers.  Allow a few bytes
 105      difference to cope with as many arches as possible.  */
 106   pc = (uintptr_t) GET_PC (ctx);
 107   for (i = 0; i < cnt; ++i)
 108     if ((uintptr_t) arr[i] >= pc - 16 && (uintptr_t) arr[i] <= pc + 16)
 109       break;
 110
 111   /* If we haven't found it, better dump full backtrace even including
 112      the signal handler frames instead of not dumping anything.  */
 113   if (i == cnt)
 114     i = 0;
 115
 116   /* Now generate nicely formatted output.  */
 117   __backtrace_symbols_fd (arr + i, cnt - i, fd);
 118
 119 #ifdef HAVE_PROC_SELF
 120   /* Now the link map.  */
 121   int mapfd = open ("/proc/self/maps", O_RDONLY);
 122   if (mapfd != -1)
 123     {
 124       write (fd, "\nMemory map:\n\n", 14);
 125
 126       char buf[256];
 127       ssize_t n;
 128
 129       while ((n = TEMP_FAILURE_RETRY (read (mapfd, buf, sizeof (buf)))) > 0)
 130         TEMP_FAILURE_RETRY (write (fd, buf, n));
 131
 132       close (mapfd);
 133     }
 134 #endif
 135
 136   /* Pass on the signal (so that a core file is produced).  */
 137   sa.sa_handler = SIG_DFL;
 138   sigemptyset (&sa.sa_mask);
 139   sa.sa_flags = 0;
 140   sigaction (signal, &sa, NULL);
 141   raise (signal);
 142 }
 143
 144
 145 static void
 146 __attribute__ ((constructor))
 147 install_handler (void)
 148 {
 149   struct sigaction sa;
 150   const char *sigs = getenv ("SEGFAULT_SIGNALS");
 151   const char *name;
 152
 153   sa.sa_handler = (void *) catch_segfault;
 154   sigemptyset (&sa.sa_mask);
 155   sa.sa_flags = SA_RESTART;
 156
 157   /* Maybe we are expected to use an alternative stack.  */
 158   if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
 159     {
 160       void *stack_mem = malloc (2 * SIGSTKSZ);
 161       struct sigaltstack ss;
 162
 163       if (stack_mem != NULL)
 164         {
 165           ss.ss_sp = stack_mem;
 166           ss.ss_flags = 0;
 167           ss.ss_size = 2 * SIGSTKSZ;
 168
 169           if (sigaltstack (&ss, NULL) == 0)
 170             sa.sa_flags |= SA_ONSTACK;
 171         }
 172     }
 173
 174   if (sigs == NULL)
 175     sigaction (SIGSEGV, &sa, NULL);
 176   else if (sigs[0] == '\0')
 177     /* Do not do anything.  */
 178     return;
 179   else
 180     {
 181       const char *where;
 182       int all = __strcasecmp (sigs, "all") == 0;
 183
 184 #define INSTALL_FOR_SIG(sig, name) \
 185       where = __strcasestr (sigs, name);                                      \
 186       if (all || (where != NULL                                               \
 187                   && (where == sigs || !isalnum (where[-1]))                  \
 188                   && !isalnum (where[sizeof (name) - 1])))                    \
 189         sigaction (sig, &sa, NULL);
 190
 191       INSTALL_FOR_SIG (SIGSEGV, "segv");
 192       INSTALL_FOR_SIG (SIGILL, "ill");
 193 #ifdef SIGBUS
 194       INSTALL_FOR_SIG (SIGBUS, "bus");
 195 #endif
 196 #ifdef SIGSTKFLT
 197       INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
 198 #endif
 199       INSTALL_FOR_SIG (SIGABRT, "abrt");
 200       INSTALL_FOR_SIG (SIGFPE, "fpe");
 201     }
 202
 203   /* Preserve the output file name if there is any given.  */
 204   name = getenv ("SEGFAULT_OUTPUT_NAME");
 205   if (name != NULL && name[0] != '\0')
 206     {
 207       int ret = access (name, R_OK | W_OK);
 208
 209       if (ret == 0 || (ret == -1 && errno == ENOENT))
 210         fname = __strdup (name);
 211     }
 212 }