debug/segfault.c

   1 /* Catch segmentation faults and print backtrace.
   2    Copyright (C) 1998, 1999, 2000, 2001, 2002, 2004, 2007
   3    Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1998.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <http://www.gnu.org/licenses/>.  */
  20
  21 #include <alloca.h>
  22 #include <ctype.h>
  23 #include <errno.h>
  24 #include <execinfo.h>
  25 #include <fcntl.h>
  26 #include <signal.h>
  27 #include <stdint.h>
  28 #include <stdio.h>
  29 #include <stdlib.h>
  30 #include <string.h>
  31 #include <unistd.h>
  32 #include <_itoa.h>
  33 #include <ldsodefs.h>
  34
  35 #include <bp-checks.h>
  36
  37 /* This file defines macros to access the content of the sigcontext element
  38    passed up by the signal handler.  */
  39 #include <sigcontextinfo.h>
  40
  41 /* Get code to possibly dump the content of all registers.  */
  42 #include <register-dump.h>
  43
  44 /* We'll use this a lot.  */
  45 #define WRITE_STRING(s) write (fd, s, strlen (s))
  46
  47 /* Name of the output file.  */
  48 static const char *fname;
  49
  50
  51 /* We better should not use `strerror' since it can call far too many
  52    other functions which might fail.  Do it here ourselves.  */
  53 static void
  54 write_strsignal (int fd, int signal)
  55 {
  56   if (signal < 0 || signal >= _NSIG || _sys_siglist[signal] == NULL)
  57     {
  58       char buf[30];
  59       char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
  60       WRITE_STRING ("signal ");
  61       write (fd, buf, &buf[sizeof (buf)] - ptr);
  62     }
  63   else
  64     WRITE_STRING (_sys_siglist[signal]);
  65 }
  66
  67
  68 /* This function is called when a segmentation fault is caught.  The system
  69    is in an unstable state now.  This means especially that malloc() might
  70    not work anymore.  */
  71 static void
  72 catch_segfault (int signal, SIGCONTEXT ctx)
  73 {
  74   int fd, cnt, i;
  75   void **arr;
  76   struct sigaction sa;
  77   uintptr_t pc;
  78
  79   /* This is the name of the file we are writing to.  If none is given
  80      or we cannot write to this file write to stderr.  */
  81   fd = 2;
  82   if (fname != NULL)
  83     {
  84       fd = open (fname, O_TRUNC | O_WRONLY | O_CREAT, 0666);
  85       if (fd == -1)
  86         fd = 2;
  87     }
  88
  89   WRITE_STRING ("*** ");
  90   write_strsignal (fd, signal);
  91   WRITE_STRING ("\n");
  92
  93 #ifdef REGISTER_DUMP
  94   REGISTER_DUMP;
  95 #endif
  96
  97   WRITE_STRING ("\nBacktrace:\n");
  98
  99   /* Get the backtrace.  */
 100   arr = alloca (256 * sizeof (void *));
 101   cnt = backtrace (arr, 256);
 102
 103   /* Now try to locate the PC from signal context in the backtrace.
 104      Normally it will be found at arr[2], but it might appear later
 105      if there were some signal handler wrappers.  Allow a few bytes
 106      difference to cope with as many arches as possible.  */
 107   pc = (uintptr_t) GET_PC (ctx);
 108   for (i = 0; i < cnt; ++i)
 109     if ((uintptr_t) arr[i] >= pc - 16 && (uintptr_t) arr[i] <= pc + 16)
 110       break;
 111
 112   /* If we haven't found it, better dump full backtrace even including
 113      the signal handler frames instead of not dumping anything.  */
 114   if (i == cnt)
 115     i = 0;
 116
 117   /* Now generate nicely formatted output.  */
 118   __backtrace_symbols_fd (arr + i, cnt - i, fd);
 119
 120 #ifdef HAVE_PROC_SELF
 121   /* Now the link map.  */
 122   int mapfd = open ("/proc/self/maps", O_RDONLY);
 123   if (mapfd != -1)
 124     {
 125       write (fd, "\nMemory map:\n\n", 14);
 126
 127       char buf[256];
 128       ssize_t n;
 129
 130       while ((n = TEMP_FAILURE_RETRY (read (mapfd, buf, sizeof (buf)))) > 0)
 131         TEMP_FAILURE_RETRY (write (fd, buf, n));
 132
 133       close (mapfd);
 134     }
 135 #endif
 136
 137   /* Pass on the signal (so that a core file is produced).  */
 138   sa.sa_handler = SIG_DFL;
 139   sigemptyset (&sa.sa_mask);
 140   sa.sa_flags = 0;
 141   sigaction (signal, &sa, NULL);
 142   raise (signal);
 143 }
 144
 145
 146 static void
 147 __attribute__ ((constructor))
 148 install_handler (void)
 149 {
 150   struct sigaction sa;
 151   const char *sigs = getenv ("SEGFAULT_SIGNALS");
 152   const char *name;
 153
 154   sa.sa_handler = (void *) catch_segfault;
 155   sigemptyset (&sa.sa_mask);
 156   sa.sa_flags = SA_RESTART;
 157
 158   /* Maybe we are expected to use an alternative stack.  */
 159   if (getenv ("SEGFAULT_USE_ALTSTACK") != 0)
 160     {
 161       void *stack_mem = malloc (2 * SIGSTKSZ);
 162       struct sigaltstack ss;
 163
 164       if (stack_mem != NULL)
 165         {
 166           ss.ss_sp = stack_mem;
 167           ss.ss_flags = 0;
 168           ss.ss_size = 2 * SIGSTKSZ;
 169
 170           if (sigaltstack (&ss, NULL) == 0)
 171             sa.sa_flags |= SA_ONSTACK;
 172         }
 173     }
 174
 175   if (sigs == NULL)
 176     sigaction (SIGSEGV, &sa, NULL);
 177   else if (sigs[0] == '\0')
 178     /* Do not do anything.  */
 179     return;
 180   else
 181     {
 182       const char *where;
 183       int all = __strcasecmp (sigs, "all") == 0;
 184
 185 #define INSTALL_FOR_SIG(sig, name) \
 186       where = __strcasestr (sigs, name);                                      \
 187       if (all || (where != NULL                                               \
 188                   && (where == sigs || !isalnum (where[-1]))                  \
 189                   && !isalnum (where[sizeof (name) - 1])))                    \
 190         sigaction (sig, &sa, NULL);
 191
 192       INSTALL_FOR_SIG (SIGSEGV, "segv");
 193       INSTALL_FOR_SIG (SIGILL, "ill");
 194 #ifdef SIGBUS
 195       INSTALL_FOR_SIG (SIGBUS, "bus");
 196 #endif
 197 #ifdef SIGSTKFLT
 198       INSTALL_FOR_SIG (SIGSTKFLT, "stkflt");
 199 #endif
 200       INSTALL_FOR_SIG (SIGABRT, "abrt");
 201       INSTALL_FOR_SIG (SIGFPE, "fpe");
 202     }
 203
 204   /* Preserve the output file name if there is any given.  */
 205   name = getenv ("SEGFAULT_OUTPUT_NAME");
 206   if (name != NULL && name[0] != '\0')
 207     {
 208       int ret = access (name, R_OK | W_OK);
 209
 210       if (ret == 0 || (ret == -1 && errno == ENOENT))
 211         fname = __strdup (name);
 212     }
 213 }